1.
Aluminium alloy
–
Aluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, there are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for products, for example rolled plate, foils. Cast aluminium alloys yield cost-effective products due to the low melting point, the most important cast aluminium alloy system is Al–Si, where the high levels of silicon contribute to give good casting characteristics. Aluminium alloys are used in engineering structures and components where light weight or corrosion resistance is required. Alloys composed mostly of aluminium have been important in aerospace manufacturing since the introduction of metal-skinned aircraft. Aluminium-magnesium alloys are both lighter than aluminium alloys and much less flammable than alloys that contain a very high percentage of magnesium. Aluminium alloy surfaces will develop a white, protective layer of aluminium oxide if left unprotected by anodizing and/or correct painting procedures, referred to as dissimilar-metal corrosion, this process can occur as exfoliation or as intergranular corrosion. Aluminium alloys can be heat treated. This causes internal element separation, and the metal then corrodes from the inside out, Aluminium alloy compositions are registered with The Aluminum Association. Aluminium alloys with a range of properties are used in engineering structures. Alloy systems are classified by a system or by names indicating their main alloying constituents. Selecting the right alloy for a given application entails considerations of its strength, density, ductility, formability, workability, weldability. A brief historical overview of alloys and manufacturing technologies is given in Ref. Aluminium alloys are used extensively in aircraft due to their high strength-to-weight ratio. On the other hand, pure aluminium metal is too soft for such uses. Aluminium alloys typically have an elastic modulus of about 70 GPa, therefore, for a given load, a component or unit made of an aluminium alloy will experience a greater deformation in the elastic regime than a steel part of identical size and shape. Though there are aluminium alloys with somewhat-higher tensile strengths than the commonly used kinds of steel, with completely new metal products, the design choices are often governed by the choice of manufacturing technology. Extrusions are particularly important in regard, owing to the ease with which aluminium alloys, particularly the Al–Mg–Si series
2.
Ductile iron
–
While most varieties of cast iron are brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions. On October 25,1949, Keith Dwight Millis, Albert Paul Gagnebin, Ductile iron is not a single material but part of a group of materials which can be produced with a wide range of properties through control of their microstructure. The common defining characteristic of this group of materials is the shape of the graphite, in ductile irons, graphite is in the form of nodules rather than flakes as in grey iron. Nodule formation is achieved by adding nodulizing elements, most commonly magnesium and, less often now, yttrium, often a component of mischmetal, has also been studied as a possible nodulizer. Austempered Ductile Iron was discovered in the 1950s but was commercialized and achieved only some years later. In ADI, the structure is manipulated through a sophisticated heat treating process. The aus portion of the name refers to austenite, improved corrosion resistance can be achieved by replacing 15% to 30% of the iron in the alloy with varying amounts of nickel, copper, or chromium. Much of the production of ductile iron is in the form of ductile iron pipe. Ductile iron is specifically useful in automotive components, where strength needs surpass that of aluminum. Other major industrial applications include off-highway diesel trucks, Class 8 trucks, agricultural tractors, in wind power industry nodular cast iron is used for hubs and structural parts like machine frames. Nodular cast iron is suitable for large and complex shapes and high loads, SG iron is used in many grand piano harps. Malleable iron Smith, William F. Hashemi, Javad, Foundations of Materials Science and Engineering, McGraw-Hill, media related to Ductile iron at Wikimedia Commons Ductile Iron Society Ductile Iron Pipe Research Association
3.
Yield (engineering)
–
A yield strength or yield point is the material property defined as the stress at which a material begins to deform plastically. Prior to the point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent, in the three-dimensional principal stresses, an infinite number of yield points form together a yield surface. The yield point determines the limits of performance for mechanical components, in structural engineering, this is a soft failure mode which does not normally cause catastrophic failure or ultimate failure unless it accelerates buckling. It is often difficult to define yielding due to the wide variety of stress–strain curves exhibited by real materials. In addition, there are possible ways to define yielding. This definition is used, since dislocations move at very low stresses. Elastic limit Beyond the elastic limit, permanent deformation will occur, the elastic limit is therefore the lowest stress at which permanent deformation can be measured. This requires a manual procedure, and the accuracy is critically dependent on the equipment used. For elastomers, such as rubber, the limit is much larger than the proportionality limit. Also, precise measurements have shown that plastic strain begins at low stresses. Yield point The point in the curve at which the curve levels off. Offset yield point When a yield point is not easily defined based on the shape of the curve an offset yield point is arbitrarily defined. The value for this is set at 0.1 or 0. 2% plastic strain. The offset value is given as a subscript, e. g. Rp0. 2=310 MPa, high strength steel and aluminum alloys do not exhibit a yield point, so this offset yield point is used on these materials. Upper and lower yield points Some metals, such as mild steel, the material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value. If a metal is only stressed to the yield point. A yield criterion, often expressed as yield surface, or yield locus, is a hypothesis concerning the limit of elasticity under any combination of stresses
4.
Ductility
–
In materials science, ductility is a solid materials ability to deform under tensile stress, this is often characterized by the materials ability to be stretched into a wire. Malleability, a property, is a materials ability to deform under compressive stress. Both of these properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these properties are dependent on temperature and pressure. Ductility and malleability are not always coextensive – for instance, while gold has high ductility and malleability, lead has low ductility, the word ductility is sometimes used to encompass both types of plasticity. Ductility is especially important in metalworking, as materials that crack, break or shatter under stress cannot be manipulated using metal-forming processes such as hammering, rolling, malleable materials can be formed cold using stamping or pressing, whereas brittle materials may be cast or thermoformed. High degrees of ductility occur due to bonds, which are found predominantly in metals. In metallic bonds valence shell electrons are delocalized and shared between many atoms, the delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter. Ductility can be quantified by the fracture strain ε f, which is the strain at which a test specimen fractures during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture q, the ductility of steel varies depending on the alloying constituents. Increasing levels of carbon decrease ductility, many plastics and amorphous solids, such as Play-Doh, are also malleable. The most ductile metal is platinum and the most malleable metal is gold, DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. For example, zamak 3 exhibits good ductility at room temperature, DBTT is a very important consideration in selecting materials that are subjected to mechanical stresses. A similar phenomenon, the transition temperature, occurs with glasses and polymers. In some materials the transition is sharper than others and typically requires a temperature-sensitive deformation mechanism and this can be problematic for steels with a high ferrite content. This famously resulted in serious hull cracking in Liberty ships in colder waters during World War II, DBTT can also be influenced by external factors such as neutron radiation, which leads to an increase in internal lattice defects and a corresponding decrease in ductility and increase in DBTT. The most accurate method of measuring the DBTT of a material is by fracture testing, typically four point bend testing at a range of temperatures is performed on pre-cracked bars of polished material. For experiments conducted at higher temperatures, dislocation activity increases, the temperature at which this occurs is the ductile–brittle transition temperature
5.
Compression (physics)
–
It is contrasted with tension or traction, the application of balanced outward forces, and with shearing forces, directed so as to displace layers of the material parallel to each other. The compressive strength of materials and structures is an important engineering consideration, in uniaxial compression the forces are directed along one direction only, so that they act towards decreasing the objects length along that direction. If the stress vector itself is opposite to x, the material is said to be under compression or pure compressive stress along x. In a solid, the amount of compression depends on the direction x. If the stress vector is purely compressive and has the same magnitude for all directions and this is the only type of static compression that liquids and gases can bear. In a mechanical longitudinal wave, or compression wave, the medium is displaced in the waves direction, when put under compression, every material will suffer some deformation, even if imperceptible, that causes the average relative positions of its atoms and molecules to change. The deformation may be permanent, or may be reversed when the compression forces disappear, in the latter case, the deformation gives rise to reaction forces that oppose the compression forces, and may eventually balance them. Liquids and gases cannot bear steady uniaxial or biaxial compression, they will deform promptly and permanently, however they can bear isotropic compression, and may be compressed in other ways momentarily, for instance in a sound wave. The deformation may not be uniform and may not be aligned with the compression forces, what happens in the directions where there is no compression depends on the material. Most materials will expand in those directions, but some special materials will remain unchanged or even contract, by inducing compression, mechanical properties such as compressive strength or modulus of elasticity, can be measured. Compression machines range from small table top systems to ones with over 53 MN capacity. Gases are often stored and shipped in highly compressed form, to save space, slightly compressed air or other gases are also used to fill balloons, rubber boats, and other inflatable structures. Compressed liquids are used in equipment and in fracking. In internal combustion engines the explosive mixture gets compressed before it is ignited, in the Otto cycle, for instance, the second stroke of the piston effects the compression of the charge which has been drawn into the cylinder by the first forward stroke. This compression, moreover, obviates the shock which would otherwise be caused by the admission of the steam for the return stroke. Buckling Container compression test Compression member Compressive strength Longitudinal wave P-wave Rarefaction Strength of materials
6.
Plasticity (physics)
–
In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is called yield, plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, foams, bone and skin. However, the mechanisms that cause plastic deformation can vary widely. At a crystalline scale, plasticity in metals is usually a consequence of dislocations, such defects are relatively rare in most crystalline materials, but are numerous in some and part of their crystal structure, in such cases, plastic crystallinity can result. In brittle materials such as rock, concrete and bone, plasticity is caused predominantly by slip at microcracks, for many ductile metals, tensile loading applied to a sample will cause it to behave in an elastic manner. Each increment of load is accompanied by an increment in extension. When the load is removed, the returns to its original size. However, once the load exceeds a threshold – the yield strength – the extension increases more rapidly than in the region, now when the load is removed. Elastic deformation, however, is an approximation and its quality depends on the time frame considered, if, as indicated in the graph opposite, the deformation includes elastic deformation, it is also often referred to as elasto-plastic deformation or elastic-plastic deformation. Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads, plastic materials with hardening necessitate increasingly higher stresses to result in further plastic deformation. Generally, plastic deformation is dependent on the deformation speed. Such materials are said to deform visco-plastically, the plasticity of a material is directly proportional to the ductility and malleability of the material. Plasticity in a crystal of pure metal is primarily caused by two modes of deformation in the lattice, slip and twinning. Slip is a deformation which moves the atoms through many interatomic distances relative to their initial positions. Twinning is the plastic deformation takes place along two planes due to a set of forces applied to a given metal piece. Most metals show more plasticity when hot than when cold, lead shows sufficient plasticity at room temperature, while cast iron does not possess sufficient plasticity for any forging operation even when hot. This property is of importance in forming, shaping and extruding operations on metals, most metals are rendered plastic by heating and hence shaped hot
7.
Fracture
–
A fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid, fracture strength or breaking strength is the stress when a specimen fails or fractures. The word fracture is often applied to bones of living creatures, or to crystalline materials, sometimes, individual crystals fracture without the structure actually separating into two or more pieces. Depending on the substance, a fracture reduces strength or inhibits transmission of waves, a detailed understanding of how fracture occurs in materials may be assisted by the study of fracture mechanics. Fracture strength, also known as breaking strength, is the stress at which a specimen fails via fracture and this is usually determined for a given specimen by a tensile test, which charts the stress-strain curve. The final recorded point is the fracture strength, ductile materials have a fracture strength lower than the ultimate tensile strength, whereas in brittle materials the fracture strength is equivalent to the UTS. If a ductile material reaches its ultimate strength in a load-controlled situation, it will continue to deform, with no additional load application. However, if the loading is displacement-controlled, the deformation of the material may relieve the load, in brittle fracture, no apparent plastic deformation takes place before fracture. In brittle crystalline materials, fracture can occur by cleavage as the result of tensile stress acting normal to crystallographic planes with low bonding. In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, the sinking of RMS Titanic in 1912 from an iceberg collision is widely reported to have been due to brittle fracture of the hulls steel plates. Putting these two together, we get σ f r a c t u r e = E γ ρ4 a r o. Looking closely, we can see that sharp cracks and large defects both lower the strength of the material. Recently, scientists have discovered supersonic fracture, the phenomenon of crack propagation faster than the speed of sound in a material and this phenomenon was recently also verified by experiment of fracture in rubber-like materials. Brittle fracture may be avoided by limiting pressure and temperature within limits, each system has a brittle fracture prevention limit curve defined by the weakest components at given temperatures and pressures allowing for the largest undetected preexisting flaw in each component. In ductile fracture, extensive plastic deformation takes place before fracture, the terms rupture or ductile rupture describe the ultimate failure of ductile materials loaded in tension. Rather than cracking, the material pulls apart, generally leaving a rough surface, in this case there is slow propagation and an absorption of a large amount energy before fracture. The ductility of a material is referred to as toughness. Many ductile metals, especially materials with high purity, can sustain very large deformation of 50–100% or more strain before fracture under favorable loading condition, the strain at which the fracture happens is controlled by the purity of the materials
8.
Percy Williams Bridgman
–
Percy Williams Bridgman was an American physicist who won the 1946 Nobel Prize in Physics for his work on the physics of high pressures. He also wrote extensively on the method and on other aspects of the philosophy of science. Known to family and friends as Peter, Bridgman was born in Cambridge, Massachusetts, Bridgmans parents were both born in New England. His father, Raymond Landon Bridgman, was religious and idealistic. His mother, Mary Ann Maria Williams, was described as more conventional, sprightly, Bridgman attended both elementary and high school in Auburndale, where he excelled at competitions in the classroom, on the playground, and while playing chess. Described as both shy and proud, his life consisted of family music, card games, and domestic. The family was religious, reading the Bible each morning and attending a Congregational Church. Bridgman entered Harvard University in 1900, and studied physics through to his Ph. D, from 1910 until his retirement, he taught at Harvard, becoming a full professor in 1919. In 1905, he began investigating the properties of matter under high pressure, a machinery malfunction led him to modify his pressure apparatus, the result was a new device enabling him to create pressures eventually exceeding 100,000 kgf/cm2. This was an improvement over previous machinery, which could achieve pressures of only 3,000 kgf/cm2. Bridgman is also known for his studies of electrical conduction in metals and he developed the Bridgman seal and is the eponym for Bridgmans thermodynamic equations. Bridgman made many improvements to his pressure apparatus over the years. His philosophy of science book The Logic of Modern Physics advocated operationalism, in 1938 he participated in the International Committee composed to organise the International Congresses for the Unity of Science. He was also one of the 11 signatories to the Russell–Einstein Manifesto, Bridgman married Olive Ware, of Hartford, Connecticut, in 1912. Wares father, Edmund Asa Ware, was the founder and first president of Atlanta University, the couple had two children and were married for 50 years, living most of that time in Cambridge. The family also had a home in Randolph, New Hampshire. Bridgman was a penetrating analytical thinker with a fertile mechanical imagination and he was a skilled plumber and carpenter, known to shun the assistance of professionals in these matters. He was also fond of music and played the piano, and took pride in his flower, Bridgman committed suicide by gunshot after suffering from metastatic cancer for some time
9.
Gold
–
Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly yellow, dense, soft, malleable. Chemically, gold is a metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions, Gold often occurs in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the element silver and also naturally alloyed with copper. Less commonly, it occurs in minerals as gold compounds, often with tellurium, golds atomic number of 79 makes it one of the higher numbered, naturally occurring elements. It is thought to have produced in supernova nucleosynthesis, from the collision of neutron stars. Because the Earth was molten when it was formed, almost all of the present in the early Earth probably sank into the planetary core. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of acid and hydrochloric acid. Gold also dissolves in solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction, as a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. A total of 186,700 tonnes of gold is in existence above ground, the world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold is also used in infrared shielding, colored-glass production, gold leafing, certain gold salts are still used as anti-inflammatories in medicine. As of 2014, the worlds largest gold producer by far was China with 450 tonnes, Gold is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃-. The symbol Au is from the Latin, aurum, the Latin word for gold, the Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning glow. This word is derived from the root as *h₂éu̯sōs, the ancestor of the Latin word Aurora. This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn, Gold is the most malleable of all metals, a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be thin enough to become semi-transparent
10.
Lead
–
Lead is a chemical element with atomic number 82 and symbol Pb. When freshly cut, it is bluish-white, it tarnishes to a dull gray upon exposure to air and it is a soft, malleable, and heavy metal with a density exceeding that of most common materials. Lead has the second-highest atomic number of the stable elements. Lead is a relatively unreactive post-transition metal and its weak metallic character is illustrated by its amphoteric nature and tendency to form covalent bonds. Compounds of lead are found in the +2 oxidation state. Exceptions are mostly limited to organolead compounds, like the lighter members of the group, lead exhibits a tendency to bond to itself, it can form chains, rings, and polyhedral structures. Lead is easily extracted from its ores and was known to people in Western Asia. A principal ore of lead, galena, often bears silver, Lead production declined after the fall of Rome and did not reach comparable levels again until the Industrial Revolution. Nowadays, global production of lead is about ten million tonnes annually, Lead has several properties that make it useful, high density, low melting point, ductility, and relative inertness to oxidation. In the late 19th century, lead was recognized as poisonous, Lead is a neurotoxin that accumulates in soft tissues and bones, damaging the nervous system and causing brain disorders and, in mammals, blood disorders. A lead atom has 82 electrons, arranged in a configuration of 4f145d106s26p2. The combined first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, leads upper neighbor in group 14. This is unusual since ionization energies generally fall going down a group as an elements outer electrons become more distant from the nucleus, the similarity is caused by the lanthanide contraction—the decrease in element radii from lanthanum to lutetium, and the relatively small radii of the elements after hafnium. The contraction is due to shielding of the nucleus by the lanthanide 4f electrons. The combined first four ionization energies of lead exceed those of tin, for this reason lead, unlike tin, mostly forms compounds in which it has an oxidation state of +2, rather than +4. Relativistic effects, which become particularly prominent at the bottom of the periodic table, as a result, the 6s electrons of lead become reluctant to participate in bonding, a phenomenon called the inert pair effect. A related outcome is that the distance between nearest atoms in crystalline lead is unusually long, the lighter group 14 elements form stable or metastable allotropes having the tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp3 orbitals
11.
Metalworking
–
Metalworking is the process of working with metals to create individual parts, assemblies, or large-scale structures. The term covers a range of work from large ships and bridges to precise engine parts. It therefore includes a wide range of skills, processes. Metalworking is a science, art, hobby, industry and trade and its historical roots span cultures, civilizations, and millennia. Metalworking has evolved from the discovery of smelting various ores, producing malleable and ductile metal useful for tools, modern metalworking processes, though diverse and specialized, can be categorized as forming, cutting, or joining processes. Todays machine shop includes a number of machine tools capable of creating a precise, the oldest archaeological evidence of copper mining and working was the discovery of a copper pendant in northern Iraq from 8,700 BCE. The earliest substantiated and dated evidence of metalworking in the Americas was the processing of copper in Wisconsin, Copper was hammered until brittle then heated so it could be worked some more. This technology is dated to about 4000-5000 BCE, the oldest gold artifacts in the world come from the Bulgarian Varna Necropolis and date from 4450 BCE. Not all metal required fire to obtain it or work it, isaac Asimov speculated that gold was the first metal. His reasoning is that by its chemistry it is found in nature as nuggets of pure gold, in other words, gold, as rare as it is, is sometimes found in nature as the metal that it is. There are a few metals that sometimes occur natively. Almost all other metals are found in ores, a mineral-bearing rock, another feature of gold is that it is workable as it is found, meaning that no technology beyond a stone hammer and anvil to work the metal is needed. This is a result of properties of malleability and ductility. The earliest tools were stone, bone, wood, and sinew, at some unknown point the connection between heat and the liberation of metals from rock became clear, rocks rich in copper, tin, and lead came into demand. These ores were mined wherever they were recognized, remnants of such ancient mines have been found all over Southwestern Asia. Metalworking was being carried out by the South Asian inhabitants of Mehrgarh between 7000–3300 BCE, the end of the beginning of metalworking occurs sometime around 6000 BCE when copper smelting became common in Southwestern Asia. Ancient civilisations knew of seven metals. Here they are arranged in order of their potential, Iron +0.44 V
12.
Hammer
–
A hammer is a tool or device that delivers a blow to an object. Most hammers are hand tools used to drive nails, fit parts, forge metal, hammers vary in shape, size, and structure, depending on their purposes. Hammers are basic tools in many trades, the usual features are a head and a handle. Although most hammers are hand tools, powered versions exist, they are known as powered hammers, types of power hammer include steam hammers and trip hammers, often for heavier uses, such as forging. Some hammers have other names, such as sledgehammer, mallet, the term hammer also applies to devices that deliver blows, such as the hammer of a firearm or the hammer of a piano or the hammer ice scraper. The use of simple hammers dates to about 2,600,000 BCE when various shaped stones were used to strike wood, bone, or other stones to break them apart and shape them. Stones attached to sticks with strips of leather or animal sinew were being used as hammers with handles by about 30,000 BCE during the middle of the Paleolithic Stone Age. The hammers archeological record shows that it may be the oldest tool for which evidence exists of its early existence. A traditional hand-held hammer consists of a head and a handle, fastened together by means of a special wedge made for the purpose, or by glue. This two-piece design is used, to combine a dense metallic striking head with a non-metallic mechanical-shock-absorbing handle. If wood is used for the handle, it is often hickory or ash, rigid fiberglass resin may be used for the handle, this material does not absorb water or decay, but does not dissipate shock as well as wood. A loose hammer head is hazardous because it can fly off the handle when in use. Wooden handles can often be replaced when worn or damaged, specialized kits are available covering a range of sizes and designs. Some hammers are one-piece designs made primarily of a single material, a one-piece metallic hammer may optionally have its handle coated or wrapped in a resilient material such as rubber, for improved grip and reduced user fatigue. The hammer head may be surfaced with a variety of materials, including brass, bronze, wood, plastic, rubber, some hammers have interchangeable striking surfaces, which can be selected as needed or replaced when worn out. A large hammer-like tool is a maul, a wood- or rubber-headed hammer is a mallet, the essential part of a hammer is the head, a compact solid mass that is able to deliver a blow to the intended target without itself deforming. The impacting surface of the tool is usually flat or slightly rounded, some upholstery hammers have a magnetized face, to pick up tacks. In the hatchet, the hammer head may be secondary to the cutting edge of the tool
13.
Rolling (metalworking)
–
In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform. The concept is similar to the rolling of dough, Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, if the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other manufacturing process, Roll stands holding pairs of rolls are grouped together into rolling mills that can quickly process metal, typically steel, into products such as structural steel, bar stock, and rails. Most steel mills have rolling mill divisions that convert the semi-finished casting products into finished products, there are many types of rolling processes, including ring rolling, roll bending, roll forming, profile rolling, and controlled rolling. The invention of the mill in Europe may be attributed to Leonardo da Vinci in his drawings. The earliest rolling mills in crude form but the basic principles were found in Middle East. Earliest rolling mills were slitting mills, which were introduced from what is now Belgium to England in 1590 and these passed flat bars between rolls to form a plate of iron, which was then passed between grooved rolls to produce rods of iron. The first experiments at rolling iron for tinplate took place about 1670, in 1697, Major John Hanbury erected a mill at Pontypool to roll Pontypool plates—blackplate. Later this began to be rerolled and tinned to make tinplate, the earlier production of plate iron in Europe had been in forges, not rolling mills. The slitting mill was adapted to producing hoops and iron with a half-round or other sections by means that were the subject of two patents of c. Some of the earliest literature on rolling mills can be traced back to Christopher Polhem in 1761 in Patriotista Testamente and he also explains how rolling mills can save on time and labor because a rolling mill can produce 10 to 20 or more bars at the same time. A patent was granted to Thomas Blockley of England in 1759 for the polishing and rolling of metals, another patent was granted in 1766 to Richard Ford of England for the first tandem mill. A tandem mill is one in which the metal is rolled in successive stands, Fords tandem mill was for hot rolling of wire rods, Rolling mills for lead seem to have existed by the late 17th century. Copper and brass were also rolled by the late 18th century, modern rolling practice can be attributed to the pioneering efforts of Henry Cort of Funtley Iron Mills, near Fareham, England. In 1783 a patent was issued to Henry Cort for his use of grooved rolls for rolling iron bars, with this new design mills were able to produce 15 times more output per day than with a hammer. Although Cort was not the first to use grooved rolls, he was first to combine the use of many of the best features of various ironmaking and shaping processes known at the time, thus modern writers have called him father of modern rolling. The first rail rolling mill was established by John Birkenshaw in 1820, with the advancement of technology in rolling mills the size of rolling mills grew rapidly along with the size products being rolled
14.
Drawing (manufacturing)
–
Drawing is a metalworking process which uses tensile forces to stretch metal. As the metal is drawn, it stretches thinner, into a desired shape, Drawing is classified in two types, sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis, for wire, bar, and tube drawing the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing differs from rolling in that the pressure of drawing is not transmitted through the action of the mill. This means the amount of possible drawing force is limited by the strength of the material. The success of forming is in relation to two things, the flow and stretch of material, as a die forms a shape from a flat sheet of metal, there is a need for the material to move into the shape of the die. The flow of material is controlled through pressure applied to the blank, if the form moves too easily, wrinkles will occur in the part. To correct this, more pressure or less lubrication is applied to the blank to limit the flow of material, if too much pressure is applied, the part will become too thin and break. Drawing metal requires finding the balance between wrinkles and breaking to achieve a successful part. Sheet metal drawing becomes deep drawing when the workpiece is drawing longer than its diameter and it is common that the workpiece is also processed using other forming processes, such as piercing, ironing, necking, rolling, and beading. In shallow drawing, the depth of drawing is less than the smallest dimension of the hole, bar, tube, and wire drawing all work upon the same principle, the starting stock drawn through a die to reduce the diameter and increase the length. Usually the die is mounted on a draw bench, the end of the workpiece is reduced or pointed to get the end through the die. The end is placed in grips and the rest of the workpiece is pulled through the die. Steels, copper alloys, and aluminium alloys are common materials that are drawn, Drawing can also be used to produce a cold formed shaped cross-section. Cold drawn cross-sections are more precise and have a surface finish than hot extruded parts. Inexpensive materials can be used instead of expensive alloys for strength requirements, bars or rods that are drawn cannot be coiled therefore straight-pull draw benches are used. Chain drives are used to draw workpieces up to 30 m, hydraulic cylinders are used for shorter length workpieces. The reduction in area is restricted to between 20 and 50%, because greater reductions would exceed the tensile strength of the material
15.
Extrusion
–
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section and it also forms parts with an excellent surface finish. Drawing is a process, which uses the tensile strength of the material to pull it through the die. This limits the amount of change which can be performed in one step, so it is limited to simpler shapes, Drawing is the main way to produce wire. Metal bars and tubes are often drawn. Extrusion may be continuous or semi-continuous, the extrusion process can be done with the material hot or cold. Commonly extruded materials include metals, polymers, ceramics, concrete, play dough, the products of extrusion are generally called extrudates. Hollow cavities within extruded material cannot be produced using a simple flat extrusion die, instead, the die assumes the shape of a block with depth, beginning first with a shape profile that supports the center section. The die shape then internally changes along its length into the final shape, the material flows around the supports and fuses together to create the desired closed shape. The extrusion process in metals may increase the strength of the material. In 1797, Joseph Bramah patented the first extrusion process for making out of soft metals. It involved preheating the metal and then forcing it through a die via a hand-driven plunger, in 1820 Thomas Burr implemented that process for lead pipe, with a hydraulic press. At that time the process was called squirting, in 1894, Alexander Dick expanded the extrusion process to copper and brass alloys. The process begins by heating the stock material and it is then loaded into the container in the press. A dummy block is placed behind it where the ram then presses on the material to push it out of the die, afterward the extrusion is stretched in order to straighten it. If better properties are required then it may be treated or cold worked. The extrusion ratio is defined as the starting cross-sectional area divided by the area of the final extrusion. One of the advantages of the extrusion process is that this ratio can be very large while still producing quality parts
16.
Machine press
–
A forming press, commonly shortened to press, is a machine tool that changes the shape of a workpiece by the application of pressure. Good for general-purpose work in the mechanic shop, machine shop, garage or basement shops. Typically 1 to 30 tons of pressure, depending on size, classed with engine hoists and engine stands in many tool catalogs. A press brake is a type of machine press that bends sheet metal into shape. A good example of the type of work a press brake can do is the backplate of a computer case, other examples include brackets, frame pieces and electronic enclosures. Some press brakes have CNC controls and can form parts with accuracy to a fraction of a millimetre, bending forces can range up to 3,000 tons. A punch press is used to form holes, a screw press is also known as a fly press. A stamping press is a press used to shape or cut metal by deforming it with a die. It generally consists of a frame, a bolster plate. Capping presses form caps from rolls of foil at up to 660 per minute. A servomechanism press, also known as a press or a electro press, is a press driven by an AC servo motor. The torque produced is converted to a linear force via a ball screw, pressure and position are controlled through a load cell and an encoder. The main advantage of a press is its low energy consumption. When stamping, its really about maximizing energy as opposed to how the machine can deliver tonnage, up until recently, the way to increase tonnage between the die and workpiece on a mechanical press was through bigger machines with bigger motors. The press style used is in correlation to the end product. Press types are straightside, BG, geared, gap, OBI, hydraulic and mechanical presses are classified by the frame the moving elements are mounted on. The most common are the gap-frame, also known as C-frame, a straightside press has vertical columns on either side of the machine and eliminates angular deflection. A C-frame allows easy access to the die area on three sides and require less floor space, a type of gap-frame, the OBI pivots the frame for easier scrap or part discharge
17.
Casting
–
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more together, examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods. The oldest surviving casting is a frog from 3200 BC. In metalworking, metal is heated until it becomes liquid and is poured into a mold. The mold is a cavity that includes the desired shape. The mold and the metal are then cooled until the metal solidifies, the solidified part is then recovered from the mold. Subsequent operations remove excess material caused by the casting process, when casting plaster or concrete, the material surface is flat and lacks transparency. Often topical treatments are applied to the surface, for example, painting and etching can be used in a way that give the appearance of metal or stone. Alternatively, the material is altered in its initial casting process, by casting concrete, rather than plaster, it is possible to create sculptures, fountains, or seating for outdoor use. A simulation of high-quality marble may be made using certain chemically-set plastic resins with powdered stone added for coloration, raw castings often contain irregularities caused by seams and imperfections in the molds, as well as access ports for pouring material into the molds. The process of cutting, grinding, shaving or sanding away these unwanted bits is called fettling, simulation accurately describes a cast component’s quality up-front before production starts. The casting rigging can be designed with respect to the component properties. This has benefits beyond a reduction in sampling, as the precise layout of the complete casting system also leads to energy, material. The software supports the user in component design, the determination of melting practice and casting methoding through to pattern and mold making, heat treatment and this saves costs along the entire casting manufacturing route. Since the late 80s, commercial programs are available which make it possible for foundries to gain new insight into what is happening inside the mold or die during the casting process
18.
Thermoforming
–
Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. Its simplified version is vacuum forming, in its simplest form, a small tabletop or lab size machine can be used to heat small cut sections of plastic sheet and stretch it over a mold using vacuum. This method is used for sample and prototype parts. Thermoforming differs from injection molding, blow molding, rotational molding, thin-gauge thermoforming is primarily the manufacture of disposable cups, containers, lids, trays, blisters, clamshells, and other products for the food, medical, and general retail industries. Thick-gauge thermoforming includes parts as diverse as vehicle door and dash panels, refrigerator liners, utility vehicle beds, a stripper plate may also be utilized on the mold as it opens for ejection of more detailed parts or those with negative-draft, undercut areas. The sheet web remaining after the parts are trimmed is typically wound onto a take-up reel or fed into an inline granulator for recycling. Frequently, scrap and waste plastic from the process is converted back into extruded sheet for forming again. There are two general thermoforming process categories, sheet thickness less than 1.5 mm is usually delivered to the thermoforming machine from rolls or from a sheet extruder. Thin-gauge roll-fed or inline extruded thermoforming applications are dominated by rigid or semi-rigid disposable packaging, sheet thicknesses greater than 3 mm are usually delivered to the forming machine by hand or an auto-feed method already cut to final dimensions. Heavy, or thick-gauge, cut sheet thermoforming applications are used as permanent structural components. There is a small but growing medium-gauge market that forms sheet 1.5 mm to 3 mm in thickness, heavy-gauge forming utilizes the same basic process as continuous thin-gauge sheet forming, typically draping the heated plastic sheet over a mold. Many heavy-gauge forming applications use only in the form process. Aircraft windscreens and machine gun turret windows spurred the advance of heavy-gauge forming technology during World War II, Thermoforming has benefited from applications of engineering technology, although the basic forming process is very similar to what was invented many years ago. Quartz and radiant-panel oven heaters generally provide more precise and thorough sheet heating over older cal-rod type heaters, a new technology, ToolVu, has been developed to provide real-time feedback on thermoformer machines. The system sends out multiple warnings and alerts whenever pre-set production parameters are compromised during a run and this reduces machine down time, lowers startup time and decreases startup scrap. An integral part of the process is the tooling which is specific to each part that is to be produced. Typically thick-gauge parts must be trimmed on CNC routers or hand trimmed using saws or hand routers, even the most sophisticated thermoforming machine is limited to the quality of the tooling. Some large thermoforming manufacturers choose to have design and tool making facilities in house while others rely on outside tool-making shops to build the tooling
19.
Electron shell
–
In chemistry and atomic physics, an electron shell, or a principal energy level, may be thought of as an orbit followed by electrons around an atoms nucleus. The closest shell to the nucleus is called the 1 shell, followed by the 2 shell, then the 3 shell, the shells correspond with the principal quantum numbers or are labeled alphabetically with letters used in the X-ray notation. Each shell can contain only a number of electrons, The first shell can hold up to two electrons, the second shell can hold up to eight electrons, the third shell can hold up to 18. The general formula is that the nth shell can in principle hold up to 2 electrons, since electrons are electrically attracted to the nucleus, an atoms electrons will generally occupy outer shells only if the more inner shells have already been completely filled by other electrons. However, this is not a requirement, atoms may have two or even three incomplete outer shells. For an explanation of why electrons exist in these shells see electron configuration, the electrons in the outermost occupied shell determine the chemical properties of the atom, it is called the valence shell. Each shell consists of one or more subshells, and each consists of one or more atomic orbitals. The shell terminology comes from Arnold Sommerfelds modification of the Bohr model, sommerfeld retained Bohrs planetary model, but added mildly elliptical orbits to explain the fine spectroscopic structure of some elements. The multiple electrons with the principal quantum number had close orbits that formed a shell of positive thickness instead of the infinitely thin circular orbit of Bohrs model. The existence of electron shells was first observed experimentally in Charles Barklas, barkla labeled them with the letters K, L, M, N, O, P, and Q. The origin of this terminology was alphabetic, a J series was also suspected, though later experiments indicated that the K absorption lines are produced by the innermost electrons. These letters were found to correspond to the n values 1,2,3. They are used in the spectroscopic Siegbahn notation, the physical chemist Gilbert Lewis was responsible for much of the early development of the theory of the participation of valence shell electrons in chemical bonding. Linus Pauling later generalized and extended the theory while applying insights from quantum mechanics. The electron shells are labeled K, L, M, N, O, P, and Q, or 1,2,3,4,5,6, and 7, going from innermost shell outwards. Electrons in outer shells have higher energy and travel farther from the nucleus than those in inner shells. This makes them important in determining how the atom reacts chemically and behaves as a conductor, because the pull of the atoms nucleus upon them is weaker. In this way, a given elements reactivity is highly dependent upon its electronic configuration, each shell is composed of one or more subshells, which are themselves composed of atomic orbitals
20.
Electron
–
The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
21.
Delocalized electron
–
In chemistry, delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. The term is general and can have different meanings in different fields. In organic chemistry, this refers to resonance in conjugated systems, in solid-state physics, this refers to free electrons that facilitate electrical conduction. In quantum chemistry, this refers to molecular orbitals that extend over several adjacent atoms, in the simple aromatic ring of benzene the delocalization of six π electrons over the C6 ring is often graphically indicated by a circle. The fact that the six C-C bonds are equidistant is one indication of this delocalization, in valence bond theory, delocalization in benzene is represented by resonance structures. Delocalized electrons also exist in the structure of solid metals, metallic structure consists of aligned positive ions in a sea of delocalized electrons. This means that the electrons are free to move throughout the structure, in diamond all four outer electrons of each carbon atom are localized between the atoms in covalent bonding. The movement of electrons is restricted and diamond does not conduct an electric current, in graphite, each carbon atom uses only 3 of its 4 outer energy level electrons in covalently bonding to three other carbon atoms in a plane. Each carbon atom contributes one electron to a system of electrons that is also a part of the chemical bonding. The delocalized electrons are free to move throughout the plane, for this reason, graphite conducts electricity along the planes of carbon atoms, but does not conduct in a direction at right angles to the plane. Standard ab initio quantum chemistry methods lead to delocalized orbitals that, in general, localized orbitals may then be found as linear combinations of the delocalized orbitals, given by an appropriate unitary transformation. In the methane molecule for example, ab initio calculations show bonding character in four molecular orbitals, there are two orbital levels, a bonding molecular orbital formed from the 2s orbital on carbon and triply degenerate bonding molecular orbitals from each of the 2p orbitals on carbon. The localized sp3 orbitals corresponding to each individual bond in valence bond theory can be obtained from a combination of the four molecular orbitals
22.
Deformation (mechanics)
–
Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body, a deformation may be caused by external loads, body forces, or changes in temperature, moisture content, or chemical reactions, etc. Strain is a description of deformation in terms of displacement of particles in the body that excludes rigid-body motions. In a continuous body, a deformation field results from a field induced by applied forces or is due to changes in the temperature field inside the body. The relation between stresses and induced strains is expressed by constitutive equations, e. g. Hookes law for linear elastic materials, deformations which are recovered after the stress field has been removed are called elastic deformations. In this case, the continuum completely recovers its original configuration, on the other hand, irreversible deformations remain even after stresses have been removed. Another type of deformation is viscous deformation, which is the irreversible part of viscoelastic deformation. In the case of elastic deformations, the response function linking strain to the stress is the compliance tensor of the material. Strain is a measure of deformation representing the displacement between particles in the relative to a reference length. A general deformation of a body can be expressed in the form x = F where X is the position of material points in the body. Such a measure does not distinguish between rigid body motions and changes in shape of the body, a deformation has units of length. We could, for example, define strain to be ε ≐ ∂ ∂ X = F ′ − I, hence strains are dimensionless and are usually expressed as a decimal fraction, a percentage or in parts-per notation. Strains measure how much a given deformation differs locally from a rigid-body deformation, a strain is in general a tensor quantity. Physical insight into strains can be gained by observing that a given strain can be decomposed into normal and this could be applied by elongation, shortening, or volume changes, or angular distortion. However, it is sufficient to know the normal and shear components of strain on a set of three perpendicular directions. In this case, the undeformed and deformed configurations of the continuum are significantly different and this is commonly the case with elastomers, plastically-deforming materials and other fluids and biological soft tissue. Infinitesimal strain theory, also called small strain theory, small deformation theory, small displacement theory, in this case, the undeformed and deformed configurations of the body can be assumed identical. Large-displacement or large-rotation theory, which assumes small strains but large rotations, in each of these theories the strain is then defined differently
23.
Tensile testing
–
Tensile testing, is also known as tension testing, is a fundamental materials science test in which a sample is subjected to a controlled tension until failure. The results from the test are used to select a material for an application, for quality control. Properties that are measured via a tensile test are ultimate tensile strength. From these measurements the following properties can also be determined, Youngs modulus, Poissons ratio, yield strength, uniaxial tensile testing is the most commonly used for obtaining the mechanical characteristics of isotropic materials. For anisotropic materials, such as materials and textiles, biaxial tensile testing is required. A tensile specimen is a standardized sample cross-section and it has two shoulders and a gage in between. The shoulders are large so they can be gripped, whereas the gauge section has a smaller cross-section so that the deformation. The shoulders of the test specimen can be manufactured in various ways to mate to various grips in the testing machine, on the other hand, a pinned grip assures good alignment. In large castings and forgings it is common to add extra material and these specimens may not be exact representation of the whole workpiece because the grain structure may be different throughout. In smaller workpieces or when critical parts of the casting must be tested, for workpieces that are machined from bar stock, the test specimen can be made from the same piece as the bar stock. The repeatability of a machine can be found by using special test specimens meticulously made to be as similar as possible. A standard specimen is prepared in a round or a section along the gauge length. Both ends of the specimens should have sufficient length and a condition such that they are firmly gripped during testing. The most common testing machine used in testing is the universal testing machine. This type of machine has two crossheads, one is adjusted for the length of the specimen and the other is driven to apply tension to the test specimen, there are two types, hydraulic powered and electromagnetically powered machines. The machine must have the capabilities for the test specimen being tested. There are four parameters, force capacity, speed, precision. Force capacity refers to the fact that the machine must be able to generate enough force to fracture the specimen, the machine must be able to apply the force quickly or slowly enough to properly mimic the actual application
24.
Steel
–
Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties
25.
Carbon
–
Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically resistant and require high temperature to react even with oxygen, the most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond. It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature. Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies,1086.5,2352.6,4620.5 and 6222.7 kJ/mol, are higher than those of the heavier group 14 elements. Carbons covalent radii are normally taken as 77.2 pm,66.7 pm and 60.3 pm, although these may vary depending on coordination number, in general, covalent radius decreases with lower coordination number and higher bond order. Carbon compounds form the basis of all life on Earth
26.
Amorphous solid
–
In condensed matter physics and materials science, an amorphous or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal. In some older books, the term has been used synonymously with glass, nowadays, glassy solid or amorphous solid is considered to be the overarching concept, and glass the more special case, A glass is an amorphous solid that exhibits a glass transition. Other types of solids include gels, thin films. Amorphous materials have a structure made of interconnected structural blocks. Even amorphous materials have some shortrange order at the length scale due to the nature of chemical bonding. Furthermore, in small crystals a large fraction of the atoms are the crystal, relaxation of the surface and interfacial effects distort the atomic positions. Amorphous phases are important constituents of thin films, which are layers of a few nm to some tens of µm thickness deposited upon a substrate. For higher values, the diffusion of deposited atomic species would allow for the formation of crystallites with long range atomic order. Regarding their applications, amorphous metallic layers played an important role in the discussion of a suspected superconductivity in amorphous metals, today, optical coatings made from TiO2, SiO2, Ta2O5 etc. and combinations of them in most cases consist of amorphous phases of these compounds. Much research is carried out into thin films as a gas separating membrane layer. Also, hydrogenated amorphous silicon, a-Si, H in short, is of significance for thin film solar cells. In case of a-Si, H the missing long-range order between silicon atoms is partly induced by the presence by hydrogen in the percent range, the occurrence of amorphous phases turned out as a phenomenon of particular interest for studying thin film growth. Remarkably, the growth of polycrystalline films is used and preceded by an initial amorphous layer. The most investigated example is represented by thin multicrystalline silicon films, an initial amorphous layer was observed in many studies. The phenomenon has been interpreted in the framework of Ostwalds rule of stages that predicts the formation of phases to proceed with increasing condensation time towards increasing stability. Experimental studies of the phenomenon require a clearly defined state of the substrate surface, the Physics of Structurally Disordered Matter, An Introduction. Amorphous Solids and the Liquid State
27.
Play-Doh
–
Play-Doh is a modeling compound used by young children for art and craft projects at home and in school. Composed of flour, water, salt, boric acid, and mineral oil, the product was reworked and marketed to Cincinnati schools in the mid-1950s. Play-Doh was demonstrated at a convention in 1956 and prominent department stores opened retail accounts. Advertisements promoting Play-Doh on influential childrens television shows in 1957 furthered the products sales, since its launch on the toy market in the mid-1950s, Play-Doh has generated a considerable amount of ancillary merchandise such as The Fun Factory. In 2003, the Toy Industry Association named Play-Doh in its Century of Toys List and it was devised at the request of Kroger Grocery, which wanted a product that could clean coal residue from wallpaper. McVickers nephew, Joe McVicker, joined Kutol with the remit to save the company from bankruptcy, Joe McVicker was the brother-in-law of nursery school teacher Kay Zufall, and Zufall had seen a newspaper article about making art projects with the wallpaper cleaning putty. Her students enjoyed it, and she persuaded Bill Rhodenbaugh and Joe McVicker to manufacture it as a child’s toy, Zufall and her husband came up with the name Play-Doh, Joe McVicker and Rhodenbaugh had wanted to call it Rainbow Modeling Compound. Joe McVicker took Play-Doh to a convention for manufacturers of school supplies, and Woodward & Lothrop. In 1956, the McVickers formed the Rainbow Crafts Company to make, also in 1956, a three-pack of 7-ounce cans was added to the product line, and, after in-store demonstrations, Macys of New York and Marshall Fields of Chicago opened retail accounts. In 1957, chemist Dr. Tien Liu reduced Play Dohs salt content, and Play-Doh ads were telecast on Captain Kangaroo, Ding Dong School, in 1958, Play-Dohs sales reached nearly $3 million. In 1964, Play-Doh was exported to Britain, France, in the 1980s, its cardboard can was scuttled for a more cost effective plastic container. By 1965, Rainbow Crafts was issued a patent for Play-Doh, also in 1965, General Mills purchased Rainbow Crafts and all rights to Play-Doh for $3 million, placing the compound with its Kenner Products subsidiary. In 1971, Rainbow Crafts and Kenner Products merged, and, in 1987, in 1991, Hasbro became Play-Dohs owner, and continues to manufacture the product today through its preschool division. In 1996, gold and silver were added to Play-Dohs palette to celebrate its 40th anniversary, Play-Doh packaging was briefly illustrated with children in the mid-1950s, but replaced by an elf mascot which, in 1960, was superseded by Play-Doh Pete, a smock and beret-wearing cartoonish boy. In 2002, Play-Doh Petes beret was replaced with a baseball cap, since 2011, living Play-Doh cans named the Doh-Dohs have been seen in adverts. A petroleum additive gives the compound a smooth feel, and borax prevents mold from developing, many home-made recipes will include salt, flour or corn starch, a vegetable oil and cream of tartar. In 1960, the Play-Doh Fun Factory was invented by Bob Boggild, the Play-Doh Fuzzy Pumper Barber & Beauty Shop of 1977 featured a figurine whose extruded hair could be styled. Making its debut in 1996 for computer-savvy young modelers was an educational software CD-ROM game, Play-Doh Creations, and, in 2003, in 2012, Play-Doh Plus was created
28.
Platinum
–
Platinum is a chemical element with symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious and its name is derived from the Spanish term platina, translated into little silver. Platinum is a member of the group of elements and group 10 of the periodic table of elements. It has six naturally occurring isotopes and it is one of the rarer elements in Earths crust with an average abundance of approximately 5 μg/kg. It occurs in some nickel and copper ores along with some deposits, mostly in South Africa. Because of its scarcity in Earths crust, only a few hundred tonnes are produced annually, Platinum is one of the least reactive metals. It has remarkable resistance to corrosion, even at high temperatures, consequently, platinum is often found chemically uncombined as native platinum. Because it occurs naturally in the sands of various rivers. Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Being a heavy metal, it leads to health issues upon exposure to its salts, compounds containing platinum, such as cisplatin, oxaliplatin and carboplatin, are applied in chemotherapy against certain types of cancer. Pure platinum is a lustrous, ductile, and malleable, silver-white metal, Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals, but it is less malleable than gold. The metal has excellent resistance to corrosion, is stable at temperatures and has stable electrical properties. Platinum reacts with oxygen slowly at high temperatures. It reacts vigorously with fluorine at 500 °C to form platinum tetrafluoride and it is also attacked by chlorine, bromine, iodine, and sulfur. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia to form chloroplatinic acid and its physical characteristics and chemical stability make it useful for industrial applications. Its resistance to wear and tarnish is well suited to use in fine jewelry, the most common oxidation states of platinum are +2 and +4. The +1 and +3 oxidation states are common, and are often stabilized by metal bonding in bimetallic species. As is expected, tetracoordinate platinum compounds tend to adopt 16-electron square planar geometries, Platinum has six naturally occurring isotopes, 190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt
29.
Charpy impact test
–
The Charpy impact test, also known as the Charpy V-notch test, is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given materials notch toughness and it is widely applied in industry, since it is easy to prepare and conduct and results can be obtained quickly and cheaply. A disadvantage is that results are only comparative. The test was developed around 1900 by S. B, the test became known as the Charpy test in the early 1900s due to the technical contributions and standardization efforts by Charpy. The test was pivotal in understanding the problems of ships during World War II. Today it is utilized in many industries for testing materials, for example the construction of pressure vessels, in 1896 S. B. Russell introduced the idea of residual fracture energy and devised a pendulum fracture test. Russells initial tests measured un-notched samples, in 1897 Frémont introduced a test trying to measure the same phenomenon using a spring-loaded machine. In 1901 Georges Charpy proposed a standardized method improving Russells by introducing a redesigned pendulum, notched sample, the apparatus consists of a pendulum of known mass and length that is dropped from a known height to impact a notched specimen of material. The energy transferred to the material can be inferred by comparing the difference in the height of the hammer before, the notch in the sample affects the results of the impact test, thus it is necessary for the notch to be of regular dimensions and geometry. The size of the sample can also affect results, since the dimensions determine whether or not the material is in plane strain and this difference can greatly affect conclusions made. The quantitative result of the tests the energy needed to fracture a material. There is a connection to the yield strength but it cannot be expressed by a standard formula, also, the strain rate may be studied and analyzed for its effect on fracture. The ductile-brittle transition temperature may be derived from the temperature where the energy needed to fracture the material drastically changes, however, in practice there is no sharp transition and it is difficult to obtain a precise transition temperature. An exact DBTT may be derived in many ways, a specific absorbed energy, change in aspect of fracture. The qualitative results of the impact test can be used to determine the ductility of a material, if the material breaks on a flat plane, the fracture was brittle, and if the material breaks with jagged edges or shear lips, then the fracture was ductile. According to ASTM A370, the standard size for Charpy impact testing is 10 mm × 10mm × 55mm. Details of specimens as per ASTM A370, according to EN 10045-1, standard specimen sizes are 10 mm ×10 mm ×55 mm. Subsize specimens are,10 mm ×7.5 mm ×55 mm and 10 mm ×5 mm ×55 mm
30.
Zamak
–
Zamak is a family of alloys with a base metal of zinc and alloying elements of aluminium, magnesium, and copper. Zamak alloys are part of the aluminium alloy family, they are distinguished from the other ZA alloys because of their constant 5% aluminium composition. The name zamak is an acronym of the German names for the metals of which the alloys are composed, Zink, Aluminium, Magnesium, the New Jersey Zinc Company developed zamak alloys in 1929. Zinc alloys are referred to as pot metal or white metal. While zamak is held to higher standards, it is still considered a pot metal. The most common zamak alloy is zamak 3, besides that, zamak 2, zamak 5 and zamak 7 are also commercially used. These alloys are most commonly die cast, zamak alloys are frequently used in the spin casting industry. A large problem with early zinc die casting materials was zinc pest, zamak avoided this by the use of 99. 99% pure zinc metal, produced by New Jersey Zincs use of a refluxer as part of the smelting process. Zamak can be electroplated, wet painted, and chromate conversion coated well, in the early 1930s Morris Ashby in Britain had licensed the New Jersey zamak alloy. The high-purity refluxer zinc was not available in Britain and so acquired the right to manufacture the alloy using a locally available electrolytically refined zinc of 99. 95% purity. This was given the name Mazak, partly to distinguish it from zamak, in 1933, National Smelting licensed the refluxer patent with the intent of using it to produce 99. 99% zinc in their plant at Avonmouth. Zamak 2 has the greatest strength out of all the zamak alloys, over time it retains its strength and hardness better than the other alloys, however, it becomes more brittle, shrinks, and less elastic. Zamak 2 is also known as Kirksite when gravity cast for use as a die and it was originally designed for low volume sheet metal dies. It later gained popularity for making short run injection molding dies and it is also less commonly used for non-sparking tools and mandrels for metal spinning. The KS alloy was developed for spin casting decorative parts and it has the same composition as zamak 2, except with more magnesium in order to produce finer grains and reduce the orange peel effect. Zamak 3 is the de facto standard for the series of zinc alloys. Zamak 3 has the composition for the zamak alloys. It has excellent castability and long term dimensional stability, more than 70% of all North American zinc die castings are made from zamak 3
31.
Glass transition
–
An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the state, is called vitrification. The glass-transition temperature Tg of a material characterizes the range of temperatures over which this transition occurs. It is always lower than the temperature, Tm, of the crystalline state of the material. Hard plastics like polystyrene and poly are used well below their glass transition temperatures, such conventions include a constant cooling rate and a viscosity threshold of 1012 Pa·s, among others. The question of whether some phase transition underlies the glass transition is a matter of continuing research, the glass transition of a liquid to a solid-like state may occur with either cooling or compression. The transition comprises a smooth increase in the viscosity of a material by as much as 17 orders of magnitude without any pronounced change in material structure, the consequence of this dramatic increase is a glass exhibiting solid-like mechanical properties on the timescale of practical observation. In many materials that undergo a freezing transition, rapid cooling will avoid this phase transition. Other materials, such as polymers, lack a well defined crystalline state and easily form glasses. The tendency for a material to form a glass while quenched is called glass forming ability and this ability depends on the composition of the material and can be predicted by the rigidity theory. Below the transition temperature range, the structure does not relax in accordance with the cooling rate used. The expansion coefficient for the state is roughly equivalent to that of the crystalline solid. If slower cooling rates are used, the time for structural relaxation to occur may result in a higher density glass product. Similarly, by annealing the glass structure in time approaches an equilibrium density corresponding to the liquid at this same temperature. Tg is located at the intersection between the curve for the glassy state and the supercooled liquid. The configuration of the glass in this range changes slowly with time towards the equilibrium structure. The principle of the minimization of the Gibbs free energy provides the driving force necessary for the eventual change. It should be noted here that at higher temperatures than Tg
32.
Body-centered cubic
–
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals, there are three main varieties of these crystals, Primitive cubic Body-centered cubic, Face-centered cubic Each is subdivided into other variants listed below. Note that although the cell in these crystals is conventionally taken to be a cube. This is related to the fact that in most cubic crystal systems, a classic isometric crystal has square or pentagonal faces. The three Bravais lattices in the crystal system are, The primitive cubic system consists of one lattice point on each corner of the cube. Each atom at a point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom. The body-centered cubic system has one point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell, Each sphere in a cF lattice has coordination number 12. The face-centered cubic system is related to the hexagonal close packed system. The plane of a cubic system is a hexagonal grid. Attempting to create a C-centered cubic crystal system would result in a simple tetragonal Bravais lattice, there are a total 36 cubic space groups. Other terms for hexoctahedral are, normal class, holohedral, ditesseral central class, a simple cubic unit cell has a single cubic void in the center. Additionally, there are 24 tetrahedral voids located in a square spacing around each octahedral void and these tetrahedral voids are not local maxima and are not technically voids, but they do occasionally appear in multi-atom unit cells. A face-centered cubic unit cell has eight tetrahedral voids located midway between each corner and the center of the cell, for a total of eight net tetrahedral voids. One important characteristic of a structure is its atomic packing factor. This is calculated by assuming all the atoms are identical spheres. The atomic packing factor is the proportion of space filled by these spheres, assuming one atom per lattice point, in a primitive cubic lattice with cube side length a, the sphere radius would be a⁄2 and the atomic packing factor turns out to be about 0.524. Similarly, in a bcc lattice, the atomic packing factor is 0.680, as a rule, since atoms in a solid attract each other, the more tightly packed arrangements of atoms tend to be more common
33.
Dislocation
–
In materials science, a dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations strongly influences many of the properties of materials, some types of dislocations can be visualized as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the planes are not straight. The two primary types of dislocations are edge dislocations and screw dislocations, mixed dislocations are intermediate between these. Mathematically, dislocations are a type of defect, sometimes called a soliton. Dislocations behave as stable particles, they can move around, two dislocations of opposite orientation can cancel when brought together, but a single dislocation typically cannot disappear on its own. Two main types of dislocations exist, edge and screw, dislocations found in real materials are typically mixed, meaning that they have characteristics of both. A crystalline material consists of an array of atoms, arranged into lattice planes. One approach is to begin by considering a 3D representation of a crystal lattice. The viewer may then start to simplify the representation by visualising planes of atoms instead of the atoms themselves, an edge dislocation is a defect where an extra half-plane of atoms is introduced mid way through the crystal, distorting nearby planes of atoms. When enough force is applied from one side of the crystal structure, a simple schematic diagram of such atomic planes can be used to illustrate lattice defects such as dislocations. In an edge dislocation, the Burgers vector is perpendicular to the line direction, the stresses caused by an edge dislocation are complex due to its inherent asymmetry. A screw dislocation is much harder to visualize, imagine cutting a crystal along a plane and slipping one half across the other by a lattice vector, the halves fitting back together without leaving a defect. This is similar to the Riemann surface of the complex logarithm, if the cut only goes part way through the crystal, and then slipped, the boundary of the cut is a screw dislocation. It comprises a structure in which a path is traced around the linear defect by the atomic planes in the crystal lattice. Perhaps the closest analogy is a spiral-sliced ham, in pure screw dislocations, the Burgers vector is parallel to the line direction. Despite the difficulty in visualization, the caused by a screw dislocation are less complex than those of an edge dislocation. This equation suggests a long cylinder of stress radiating outward from the cylinder, please note, this simple model results in an infinite value for the core of the dislocation at r=0 and so it is only valid for stresses outside of the core of the dislocation
34.
Liberty ship
–
The Liberty ship was a class of cargo ship built in the United States during World War II. Though British in conception, the design was adapted by the United States for its simple, mass-produced on an unprecedented scale, the now iconic Liberty ship came to symbolize U. S. wartime industrial output. The class was developed to meet British orders for transports to replace those torpedoed by German U-boats, the vessels were purchased both for the U. S. fleet and lend-lease deliveries of war materiel to Britain and the Soviet Union. Eighteen American shipyards built 2,710 Liberty ships between 1941 and 1945, easily the largest number of ships produced to a single design and their production mirrored on a much larger scale the manufacture of the Hog Islander and similar standardized ship types during World War I. Only three Liberty Ships are preserved, two as operational museum ships. S, the number was doubled in 1939 and again in 1940 to 200 ships a year. Ship types included two tankers and three types of merchant vessel, all to be powered by steam turbines, limited industrial capacity, especially for reduction gears, meant that relatively few of these ships were built. In 1940 the British government ordered 60 Ocean-class freighters from American yards to replace war losses and these were simple but fairly large with a single 2,500 horsepower compound steam engine of obsolete but reliable design. Britain specified coal-fired plants, because it then had extensive coal mines, the order specified an 18-inch increase in draft to boost displacement by 800 long tons to 10,100 long tons. The accommodation, bridge, and main engine were located amidships, the first Ocean-class ship, SS Ocean Vanguard, was launched on 16 August 1941. The design was modified by the United States Maritime Commission, in part to increase conformity to American construction practices, but more importantly to make it even quicker and cheaper to build. The US version was designated EC2-S-C1, EC for Emergency Cargo,2 for a ship between 400 and 450 feet long, S for steam engines, and C1 for design C1. The new design replaced much riveting, which accounted for one-third of the costs, with welding. It was adopted as a Merchant Marine Act design, and production awarded to a conglomerate of West Coast engineering and construction companies headed by Henry J. Kaiser known as the Six Companies. Liberty ships were designed to carry 10,000 long tons of cargo, usually one type per ship, but, during wartime, generally carried loads far exceeding this. On 27 March 1941, the number of ships was increased to 200 by the Defense Aid Supplemental Appropriations Act and increased again in April to 306. By 1941, the turbine was the preferred marine steam engine because of its greater efficiency compared to earlier reciprocating compound steam engines. Eighteen different companies built the engine. It had the advantage of ruggedness and simplicity
35.
World War II
–
World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945, although related conflicts began earlier. It involved the vast majority of the worlds countries—including all of the great powers—eventually forming two opposing alliances, the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people from over 30 countries. Marked by mass deaths of civilians, including the Holocaust and the bombing of industrial and population centres. These made World War II the deadliest conflict in human history, from late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, and formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Poland, Finland, Romania and the Baltic states. In December 1941, Japan attacked the United States and European colonies in the Pacific Ocean, and quickly conquered much of the Western Pacific. The Axis advance halted in 1942 when Japan lost the critical Battle of Midway, near Hawaii, in 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained all of its territorial losses and invaded Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in South Central China and Burma, while the Allies crippled the Japanese Navy, thus ended the war in Asia, cementing the total victory of the Allies. World War II altered the political alignment and social structure of the world, the United Nations was established to foster international co-operation and prevent future conflicts. The victorious great powers—the United States, the Soviet Union, China, the United Kingdom, the Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the influence of European great powers waned, while the decolonisation of Asia, most countries whose industries had been damaged moved towards economic recovery. Political integration, especially in Europe, emerged as an effort to end pre-war enmities, the start of the war in Europe is generally held to be 1 September 1939, beginning with the German invasion of Poland, Britain and France declared war on Germany two days later. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or even the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously and this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935. The British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the forces of Mongolia and the Soviet Union from May to September 1939, the exact date of the wars end is also not universally agreed upon. It was generally accepted at the time that the war ended with the armistice of 14 August 1945, rather than the formal surrender of Japan
36.
Neutron radiation
–
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. Free neutrons are unstable, decaying into a proton, an electron, neutrons may be emitted from nuclear fusion or nuclear fission, or from any number of different nuclear reactions such as from radioactive decay or reactions from particle interactions. Large neutron sources are rare, and are limited to large-sized devices like nuclear reactors or particle accelerators. Neutron radiation was discovered as a result of observing a beryllium nucleus reacting with an alpha particle thus transforming into a nucleus and emitting a neutron. The combination of a particle emitter and an isotope with a large nuclear reaction probability is still a common neutron source. The neutrons in nuclear reactors are generally categorized as slow neutrons or fast neutrons depending on their energy, in order to achieve an effective fission chain reaction, the neutrons produced during fission must be captured by fissionable nuclei, which then split, releasing more neutrons. Common neutron moderators include graphite, ordinary water and heavy water, a few reactors and all nuclear weapons rely on fast neutrons. This requires certain changes in the design and in the nuclear fuel. The element beryllium is particularly due to its ability to act as a neutron reflector or lens. This allows smaller quantities of material to be used and is a primary technical development that led to the creation of neutron bombs. Most of them activate a nucleus before reaching the ground, a few react with nuclei in the air, the reactions with nitrogen-14 lead to the formation of carbon-14, widely used in radiocarbon dating. Neutron radiation is used in select facilities to treat cancerous tumors due to its highly penetrating and damaging nature to cellular structure. Neutron imaging is used in the nuclear industry, the space and aerospace industry. Neutron radiation is often called indirectly ionizing radiation and it does not ionize atoms in the same way that charged particles such as protons and electrons do, because neutrons have no charge. Because neutrons are uncharged, they are more penetrating than alpha radiation or beta radiation, in some cases they are more penetrating than gamma radiation, which is impeded in materials of high atomic number. In materials of low atomic number such as hydrogen, a low energy gamma ray may be more penetrating than a high energy neutron, in health physics neutron radiation is a type of radiation hazard. This occurs through the capture of neutrons by nuclei, which are transformed to another nuclide. This process accounts for much of the material released by the detonation of a nuclear weapon
37.
Crystallographic defect
–
Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, however, the arrangement of atoms or molecules in most crystalline materials is not perfect. The regular patterns are interrupted by crystallographic defects, point defects are defects that occur only at or around a single lattice point. They are not extended in space in any dimension, strict limits for how small a point defect is are generally not defined explicitly. However, these defects typically involve at most a few extra or missing atoms, larger defects in an ordered structure are usually considered dislocation loops. For historical reasons, many point defects, especially in ionic crystals, are called centers, for example a vacancy in many ionic solids is called a luminescence center and these dislocations permit ionic transport through crystals leading to electrochemical reactions. These are frequently specified using Kröger–Vink Notation, vacancy defects are lattice sites which would be occupied in a perfect crystal, but are vacant. If a neighboring atom moves to occupy the vacant site, the moves in the opposite direction to the site which used to be occupied by the moving atom. The stability of the crystal structure guarantees that the neighboring atoms will not simply collapse around the vacancy. In some materials, neighboring atoms actually move away from a vacancy, a vacancy is sometimes called a Schottky defect. Interstitial defects are atoms that occupy a site in the structure at which there is usually not an atom. They are generally high energy configurations, small atoms in some crystals can occupy interstices without high energy, such as hydrogen in palladium. A nearby pair of a vacancy and an interstitial is often called a Frenkel defect or Frenkel pair and this is caused when an ion moves into an interstitial site and creates a vacancy. Due to fundamental limitations of material purification methods, materials are never 100% pure, in the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site, the atom is not supposed to be anywhere in the crystal, and is thus an impurity. In some cases where the radius of the atom is substantially smaller than that of the atom it is replacing. These types of defects are often referred to as off-center ions. There are two different types of defects, Isovalent substitution and aliovalent substitution
38.
Deformation (engineering)
–
In materials science, deformation refers to any changes in the shape or size of an object due to- an applied force or a change in temperature. The first case can be a result of forces, compressive forces, shear. The movement or displacement of such mobile defects is thermally activated, deformation is often described as strain. As deformation occurs, internal inter-molecular forces arise that oppose the applied force, a larger applied force may lead to a permanent deformation of the object or even to its structural failure. In the figure it can be seen that the compressive loading has caused deformation in the cylinder so that the shape has changed into one with bulging sides. The sides bulge because the material, although enough to not crack or otherwise fail, is not strong enough to support the load without change. Internal forces resist the applied load, the concept of a rigid body can be applied if the deformation is negligible. Depending on the type of material, size and geometry of the object, the image to the right shows the engineering stress vs. strain diagram for a typical ductile material such as steel. Different deformation modes may occur under different conditions, as can be depicted using a deformation mechanism map and this type of deformation is reversible. Once the forces are no longer applied, the returns to its original shape. Elastomers and shape memory metals such as Nitinol exhibit large elastic deformation ranges, however elasticity is nonlinear in these materials. Normal metals, ceramics and most crystals show linear elasticity and an elastic range. This relationship only applies in the range and indicates that the slope of the stress vs. strain curve can be used to find Youngs modulus. Engineers often use this calculation in tensile tests, the elastic range ends when the material reaches its yield strength. At this point plastic deformation begins, note that not all elastic materials undergo linear elastic deformation, some, such as concrete, gray cast iron, and many polymers, respond in a nonlinear fashion. For these materials Hookes law is inapplicable and this type of deformation is irreversible. However, an object in the plastic deformation range will first have undergone elastic deformation, soft thermoplastics have a rather large plastic deformation range as do ductile metals such as copper, silver, and gold. Steel does, too, but not cast iron, hard thermosetting plastics, rubber, crystals, and ceramics have minimal plastic deformation ranges
39.
Work hardening
–
Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the structure of the material. Many non-brittle metals with a high melting point as well as several polymers can be strengthened in this fashion. Alloys not amenable to treatment, including low-carbon steel, are often work-hardened. Some materials cannot be work-hardened at low temperatures, such as indium, however others can only be strengthened via work hardening, such as pure copper, Work hardening may be desirable or undesirable depending on the context. An example of work hardening is during machining when early passes of a cutter inadvertently work-harden the workpiece surface. Certain alloys are prone to this than others, superalloys such as Inconel require machining strategies that take it into account. An example of work hardening is that which occurs in metalworking processes that intentionally induce plastic deformation to exact a shape change. These processes are known as working or cold forming processes. They are characterized by shaping the workpiece at a temperature below its recrystallization temperature, cold forming techniques are usually classified into four major groups, squeezing, bending, drawing, and shearing. Applications include the heading of bolts and cap screws and the finishing of cold rolled steel, in cold forming, metal is formed at high speed and high pressure using tool steel or carbide dies. The cold working of the increasing the hardness, yield strength. Copper was the first metal in use for tools and containers since it is one of the few metals available in non-oxidized form. Copper is easily softened by heating and then cooling, in this annealed state it may then be hammered, stretched and otherwise formed, progressing toward the desired final shape, but becoming harder and less ductile as work progresses. If work continues beyond a certain hardness the metal will tend to fracture when worked, annealing is stopped when the workpiece is near its final desired shape, and so the final product will have a desired stiffness and hardness. The technique of repoussé exploits these properties of copper, enabling the construction of durable jewelry articles and sculptures, for this reason modern aluminum aircraft will have an imposed working lifetime, after which the aircraft must be retired. Before work hardening, the lattice of the material exhibits a regular, the defect-free lattice can be created or restored at any time by annealing. As the material is work hardened it becomes saturated with new dislocations
40.
Strength of materials
–
Strength of materials, also called mechanics of materials, is a subject which deals with the behavior of solid objects subject to stresses and strains. An important founding pioneer in mechanics of materials was Stephen Timoshenko, the study of strength of materials often refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. In materials science, the strength of a material is its ability to withstand a load without failure or plastic deformation. The field of strength of materials deals with forces and deformations that result from their acting on a material, a load applied to a mechanical member will induce internal forces within the member called stresses when those forces are expressed on a unit basis. The stresses acting on the material cause deformation of the material in various manners, deformation of the material is called strain when those deformations too are placed on a unit basis. The applied loads may be axial, or rotational, the stresses and strains that develop within a mechanical member must be calculated in order to assess the load capacity of that member. This requires a description of the geometry of the member, its constraints, the loads applied to the member. With a complete description of the loading and the geometry of the member, once the state of stress and strain within the member is known, the strength of that member, its deformations, and its stability can be calculated. The calculated stresses may then be compared to some measure of the strength of the such as its material yield or ultimate strength. The calculated deflection of the member may be compared to a deflection criteria that is based on the members use, the calculated buckling load of the member may be compared to the applied load. The calculated stiffness and mass distribution of the member may be used to calculate the dynamic response. The ultimate strength refers to the point on the engineering stress–strain curve corresponding to the stress that produces fracture, transverse loading - Forces applied perpendicular to the longitudinal axis of a member. Transverse loading causes the member to bend and deflect from its position, with internal tensile. Transverse loading also induces shear forces that cause shear deformation of the material, axial loading - The applied forces are collinear with the longitudinal axis of the member. The forces cause the member to either stretch or shorten, uniaxial stress is expressed by σ = F A where F is the force acting on an area A. The area can be the area or the deformed area. A simple case of compression is the uniaxial compression induced by the action of opposite, compressive strength for materials is generally higher than their tensile strength. However, structures loaded in compression are subject to additional failure modes, such as buckling, that are dependent on the members geometry
41.
International Standard Book Number
–
The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
