Ductility
Ductility is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test. According to Shigley's Mechanical Engineering Design significant denotes about 5.0 percent elongation. See Eq. 2–12, p. 50 for definitions of percent elongation and percent area reduction. Ductility is characterized by a material's ability to be stretched into a wire. From examination of data in Tables A20, A21, A22, A23, A24 in Shigley's Mechanical Engineering Design, 10th Edition, for both ductile and brittle materials, it is possible to postulate a broader quantifiable definition of ductility that does not rely on percent elongation alone. In general, a ductile material must have a measurable yield strength, at which unrecoverable plastic deformation begins, must satisfy one of the following conditions: either have an elongation to failure of at least 5%, or area reduction to rupture at least 20%, or true strain to rupture at least 10%.
Malleability, a similar property, is a material's ability to deform under compressive stress. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture; these material 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 but high malleability; the word ductility is sometimes used to encompass both types of plasticity. Ductility is important in metalworking, as materials that crack, break or shatter under stress cannot be manipulated using metal-forming processes such as hammering, drawing or extruding. 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 metallic bonds, which are found predominantly in metals, leading to the common perception that metals are ductile in general.
In metallic bonds valence shell electrons are 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, the engineering strain at which a test specimen fractures during a uniaxial tensile test. Another used measure is the reduction of area at fracture q; the ductility of steel varies depending on the alloying constituents. Increasing the levels of carbon decreases ductility. Many plastics and amorphous solids, such as Play-Doh, are malleable; the most ductile metal is platinum and the most malleable metal is gold. When stretched, such metals distort via formation and migration of dislocations and crystal twins without noticeable hardening; the ductile–brittle transition temperature, nil ductility temperature, or nil ductility transition temperature of a metal is the temperature at which the fracture energy passes below a predetermined value.
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 but shatters when impacted at sub-zero temperatures. DBTT is a important consideration in selecting materials that are subjected to mechanical stresses. A similar phenomenon, the glass transition temperature, occurs with glasses and polymers, although the mechanism is different in these amorphous materials. In some materials, the transition is sharper than others and requires a temperature-sensitive deformation mechanism. For example, in materials with a body-centered cubic lattice the DBTT is apparent, as the motion of screw dislocations is temperature sensitive because the rearrangement of the dislocation core prior to slip requires thermal activation; 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, causing many sinkings.
DBTT can 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. 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. At a certain temperature, dislocations shield the crack tip to such an extent that the applied deformation rate is not sufficient for the stress intensity at the crack-tip to reach the critical value for fracture; the temperature at which this occurs is the ductile–brittle transition temperature. If experiments are performed at a higher strain rate, more dislocation shielding is required to prevent brittle fracture, the transition temperature is raised. Deformation Work hardening, which improves ductility in uniaxial tension by delaying the onset of instability Strength of materials Ductility definition at engineersedge.com DoITPoMS Teaching and Learning Package- "The Ductile-Brittle Transition
Salt
Salt is a mineral composed of sodium chloride, a chemical compound belonging to the larger class of salts. Salt is present in vast quantities in seawater; the open ocean has about 35 grams of solids per liter of sea water, a salinity of 3.5%. Salt is essential for life in general, saltiness is one of the basic human tastes. Salt is one of the oldest and most ubiquitous food seasonings, salting is an important method of food preservation; some of the earliest evidence of salt processing dates to around 6,000 BC, when people living in the area of present-day Romania boiled spring water to extract salts. Salt was prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and the Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, across the Sahara on camel caravans; the scarcity and universal need for salt have led nations to go to war over it and use it to raise tax revenues. Salt has other cultural and traditional significance.
Salt is processed from salt mines, by the evaporation of seawater and mineral-rich spring water in shallow pools. Its major industrial products are caustic chlorine. Of the annual global production of around two hundred million tonnes of salt, about 6% is used for human consumption. Other uses include water conditioning processes, de-icing highways, agricultural use. Edible salt is sold in forms such as sea salt and table salt which contains an anti-caking agent and may be iodised to prevent iodine deficiency; as well as its use in cooking and at the table, salt is present in many processed foods. Sodium is an essential nutrient for human health via its role as an osmotic solute. Excessive salt consumption may increase the risk of cardiovascular diseases, such as hypertension, in children and adults; such health effects of salt have long been studied. Accordingly, numerous world health associations and experts in developed countries recommend reducing consumption of popular salty foods; the World Health Organization recommends that adults should consume less than 2,000 mg of sodium, equivalent to 5 grams of salt per day.
All through history, the availability of salt has been pivotal to civilization. What is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, a salt mine, providing the area now known as the Balkans with salt since 5400 BC; the name Solnitsata means "salt works". While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative for meat, for many thousands of years. A ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamț County, Romania. Evidence indicates that Neolithic people of the Precucuteni Culture were boiling the salt-laden spring water through the process of briquetage to extract the salt as far back as 6050 BC; the salt extracted from this operation may have had a direct correlation to the rapid growth of this society's population soon after its initial production began. The harvest of salt from the surface of Xiechi Lake near Yuncheng in Shanxi, dates back to at least 6000 BC, making it one of the oldest verifiable saltworks.
There is more salt in animal tissues, such as meat and milk, than in plant tissues. Nomads who subsist on their flocks and herds do not eat salt with their food, but agriculturalists, feeding on cereals and vegetable matter, need to supplement their diet with salt. With the spread of civilization, salt became one of the world's main trading commodities, it was of high value to the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and other peoples of antiquity. In the Middle East, salt was used to ceremonially seal an agreement, the ancient Hebrews made a "covenant of salt" with God and sprinkled salt on their offerings to show their trust in him. An ancient practice in time of war was salting the earth: scattering salt around in a defeated city to prevent plant growth; the Bible tells the story of King Abimelech, ordered by God to do this at Shechem, various texts claim that the Roman general Scipio Aemilianus Africanus ploughed over and sowed the city of Carthage with salt after it was defeated in the Third Punic War.
Salt may have been used for barter in connection with the obsidian trade in Anatolia in the Neolithic Era. Salt was included among funeral offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds, salt fish. From about 2800 BC, the Egyptians began exporting salt fish to the Phoenicians in return for Lebanon cedar and the dye Tyrian purple. Herodotus described salt trading routes across Libya back in the 5th century BC. In the early years of the Roman Empire, roads were built for the transportation of salt from the salt imported at Ostia to the capital. In Africa, salt was used as currency south of the Sahara, slabs of rock salt were used as coins in Abyssinia. Moorish merchants in the 6th century traded salt for weight for weight; the Tuareg have traditionally maintained routes across the Sahara for the transportation of salt by Azalai. The caravans
Bolt (firearms)
A bolt is the part of a repeating, breech-loading firearm that blocks the rear opening of the barrel chamber while the propellant burns, moves back and forward to facilitate loading/unloading of cartridges from the magazine. The extractor and firing pin are integral parts of the bolt. In gas-operated firearms, the bolt itself is housed within the larger bolt carrier group, which contains additional parts that receives rearward push from the gas piston; the slide of a semi-automatic pistol is a form of bolt, as it contains the same parts and serves the same functions. In manually operated firearms, such as bolt-action, lever-action, pump-action rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas forward, is manually withdrawn to chamber another round. In an automatic or semi-automatic firearm, the bolt cycles back and forward between each shot, propelled by recoil or expanding gas or the recoil spring; when it moves back, the extractor pulls the spent casing from the chamber.
When it moves forward, it pushes it into the chamber. Once the case is clear of the chamber, the ejector kicks the case out of the firearm. In a closed bolt firearm, the bolt is in its foremost position upon firing; this is opposed to an open bolt firearm where the bolt is held rearward and pulling the trigger releases it to slam forward and fire the cartridge. Rotating bolt Telescoping bolt Action Full Auto describes the function of the bolt in detail
Firing pin
A firing pin or striker is part of the firing mechanism used in a firearm or explosive device. Firing pins may take many forms, though the types used in fuzes for single-use devices have a sharpened point. In contrast, firing pins used in firearms have a small, rounded portion designed to strike the primer of a cartridge, detonating the priming compound, which ignites the propellant or fires the detonator and booster. Firing pins or strikers are made from steel, aluminum or titanium. However, for specialist applications such as zero metal mines, non-metallic materials are used such as glass ceramic. A firing pin is a lightweight part, which serves to transfer energy from a spring-loaded hammer to the primer, while a striker is heavier and is directly connected to the spring providing the energy to impact the primer. Striker mechanisms are simpler, since they combine the functions of hammer and firing pin in one; the firing pin or striker is located in the bolt of a repeating firearm. Firearms that do not have bolts, such as revolvers and many types of single-shot actions have a short firing pin in the frame, or else attached to the hammer itself.
These types of firearms are never striker fired, as there is insufficient space to house a striker mechanism. Strikers are most found in semi-automatic pistols and bolt-action firearms; the typical firing pin is a small rod with a hardened, rounded end. The rounded end ensures the primer is indented rather than pierced, as would happen if the firing pin were pointed. Most firing pins have a spring to push them out of contact with the primer and will have an integrated passive safety mechanism, such as a block that prevents them from moving forward unless the trigger is depressed, or a transfer bar trigger actuated, that must be in place to allow the hammer to depress the firing pin; this safety is in addition to any manually operated safety or safeties that act to block the trigger or hammer. Firearms that use long firing pins, such as pistols, will use a firing pin, too short to project when depressed flush by the hammer; this type of firing pin, called an inertial firing pin, must be struck by a full fall of the hammer to provide the momentum to move forward and strike the primer.
If the hammer is down, resting on the firing pin, it is unlikely that a blow to the rear will provide enough energy to the firing pin to detonate the primer. Most variants of the M1911 pistol use this type of firing pin. Many firing pins are stamped from sheet steel, forming a rectangular cross-section rather than a round one; these will have a cylindrical section at the front rather than a hemispherical one and are common in rimfire firearms. Sturm, for example, uses sheet metal firing pins in its 10/22 carbine and Mark II pistol. High performance firing pins are made from lighter materials than steel, such as titanium; the lighter material increases the speed at which the firing pin travels and reduces the lock time, or the time from trigger pull to the bullet leaving the barrel. Strikers are spring-loaded firing pins of a one- or two-piece construction. In the one-piece striker, the striker is turned on a lathe out of a round bar of metal, much larger in diameter than a firing pin, to provide the mass required to detonate the primer.
Two-piece strikers consist of a firing pin attached to a heavier rear section—in essence a hammer attached to the base of a firing pin. Two-piece strikers are found in bolt-action rifles, while single-piece strikers are found in pistols, such as the Glock. Mechanisms involving firing pins can be used in other pyrotechnical systems, ranging from hand grenades to chemical oxygen generators
Molybdenum
Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered in 1778 by Carl Wilhelm Scheele; the metal was first isolated in 1781 by Peter Jacob Hjelm. Molybdenum does not occur as a free metal on Earth; the free element, a silvery metal with a gray cast, has the sixth-highest melting point of any element. It forms hard, stable carbides in alloys, for this reason most of world production of the element is used in steel alloys, including high-strength alloys and superalloys. Most molybdenum compounds have low solubility in water, but when molybdenum-bearing minerals contact oxygen and water, the resulting molybdate ion MoO2−4 is quite soluble. Industrially, molybdenum compounds are used in high-pressure and high-temperature applications as pigments and catalysts. Molybdenum-bearing enzymes are by far the most common bacterial catalysts for breaking the chemical bond in atmospheric molecular nitrogen in the process of biological nitrogen fixation.
At least 50 molybdenum enzymes are now known in bacteria and animals, although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation. These nitrogenases contain molybdenum in a form different from other molybdenum enzymes, which all contain oxidized molybdenum in a molybdenum cofactor; these various molybdenum cofactor enzymes are vital to the organisms, molybdenum is an essential element for life in all higher eukaryote organisms, though not in all bacteria. In its pure form, molybdenum is a silvery-grey metal with a Mohs hardness of 5.5, a standard atomic weight of 95.95 g/mol. It has a melting point of 2,623 °C, it has one of the lowest coefficients of thermal expansion among commercially used metals. The tensile strength of molybdenum wires increases about 3 times, from about 10 to 30 GPa, when their diameter decreases from ~50–100 nm to 10 nm. Molybdenum is a transition metal with an electronegativity of 2.16 on the Pauling scale. It does not visibly react with water at room temperature.
Weak oxidation of molybdenum starts at 300 °C. Like many heavier transition metals, molybdenum shows little inclination to form a cation in aqueous solution, although the Mo3+ cation is known under controlled conditions. There are 35 known isotopes of molybdenum, ranging in atomic mass from 83 to 117, as well as four metastable nuclear isomers. Seven isotopes occur with atomic masses of 92, 94, 95, 96, 97, 98, 100. Of these occurring isotopes, only molybdenum-100 is unstable. Molybdenum-98 is the most abundant isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a half-life of about 1019 y and undergoes double beta decay into ruthenium-100. Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of 150 ns. All unstable isotopes of molybdenum decay into isotopes of niobium and ruthenium; as noted below, the most common isotopic molybdenum application involves molybdenum-99, a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m, a nuclear isomer used in various imaging applications in medicine.
In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of molybdenum-99. Molybdenum forms chemical compounds in oxidation states from -II to +VI. Higher oxidation states are more relevant to its terrestrial occurrence and its biological roles, mid-level oxidation states are associated with metal clusters, low oxidation states are associated with organomolybdenum compounds. Mo and W chemistry shows strong similarities; the relative rarity of molybdenum, for example, contrasts with the pervasiveness of the chromium compounds. The highest oxidation state is seen in molybdenum oxide, whereas the normal sulfur compound is molybdenum disulfide MoS2. From the perspective of commerce, the most important compounds are molybdenum disulfide and molybdenum trioxide; the black disulfide is the main mineral. It is roasted in air to give the trioxide: 2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2The trioxide, volatile at high temperatures, is the precursor to all other Mo compounds as well as alloys.
Molybdenum has several oxidation states, the most stable being +4 and +6. Molybdenum oxide is soluble in strong alkaline water, forming molybdates. Molybdates are weaker oxidants than chromates, they tend to form structurally complex oxyanions by condensation at lower pH values, such as 6− and 4−. Polymolybdates can incorporate other ions; the dark-blue phosphorus-containing heteropolymolybdate P3− is used for the spectroscopic detection of phosphorus. The broad range of oxidation states of molybdenum is reflected in various molybdenum chlorides: Molybdenum chloride MoCl2, which exists as the hexamer Mo6Cl12 and the related dianion 2-. Molybdenum chloride MoCl3, a dark red solid, which converts to the anion trianionic complex 3-. Molybdenum chloride MoCl4, a black solid, which adopts a polymeric structure. Molybdenum chloride MoCl5 dark green solid that
Boron
Boron is a chemical element with symbol B and atomic number 5. Produced by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar system and in the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common occurring compounds, the borate minerals; these are mined industrially as evaporites, such as kernite. The largest known boron deposits are in the largest producer of boron minerals. Elemental boron is a metalloid, found in small amounts in meteoroids but chemically uncombined boron is not otherwise found on Earth. Industrially pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder; the primary use of elemental boron is as boron filaments with applications similar to carbon fibers in some high-strength materials. Boron is used in chemical compounds. About half of all boron consumed globally is an additive in fiberglass for insulation and structural materials.
The next leading use is in polymers and ceramics in high-strength, lightweight structural and refractory materials. Borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron as sodium perborate is used as a bleach. A small amount of boron is used as a dopant in semiconductors, reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are in study. Natural boron is composed of two stable isotopes, one of which has a number of uses as a neutron-capturing agent. In biology, borates have low toxicity in mammals, but are more toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, several natural boron-containing organic antibiotics are known. Boron is an essential plant nutrient and boron compounds such as borax and boric acid are used as fertilizers in agriculture, although it's only required in small amounts, with excess being toxic. Boron compounds play a strengthening role in the cell walls of all plants.
There is no consensus on whether boron is an essential nutrient for mammals, including humans, although there is some evidence it supports bone health. The word boron was coined from borax, the mineral from which it was isolated, by analogy with carbon, which boron resembles chemically. Borax, its mineral form known as tincal, glazes were used in China from AD 300, some crude borax reached the West, where the Perso-Arab alchemist Jābir ibn Hayyān mentioned it in AD 700. Marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy. In 1777, boric acid was recognized in the hot springs near Florence and became known as sal sedativum, with medical uses; the rare mineral is called sassolite, found at Sasso, Italy. Sasso was the main source of European borax from 1827 to 1872. Boron compounds were rarely used until the late 1800s when Francis Marion Smith's Pacific Coast Borax Company first popularized and produced them in volume at low cost.
Boron was not recognized as an element until it was isolated by Sir Humphry Davy and by Joseph Louis Gay-Lussac and Louis Jacques Thénard. In 1808 Davy observed that electric current sent through a solution of borates produced a brown precipitate on one of the electrodes. In his subsequent experiments, he used potassium to reduce boric acid instead of electrolysis, he named the element boracium. Gay-Lussac and Thénard used iron to reduce boric acid at high temperatures. By oxidizing boron with air, they showed. Jöns Jakob Berzelius identified boron as an element in 1824. Pure boron was arguably first produced by the American chemist Ezekiel Weintraub in 1909; the earliest routes to elemental boron involved the reduction of boric oxide with metals such as magnesium or aluminium. However, the product is always contaminated with borides of those metals. Pure boron can be prepared by reducing volatile boron halides with hydrogen at high temperatures. Ultrapure boron for use in the semiconductor industry is produced by the decomposition of diborane at high temperatures and further purified by the zone melting or Czochralski processes.
The production of boron compounds does not involve the formation of elemental boron, but exploits the convenient availability of borates. Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. Nominally disordered boron contains regular boron icosahedra which are, bonded randomly to each other without long-range order. Crystalline boron is a hard, black material with a melting point of above 2000 °C, it forms four major polymorphs: β-rhombohedral, γ and β-tetragonal. Most of the phases are based on B12 icosahedra, but the γ-phase can be described as a rocksalt-type arrangement of the icosahedra and B2 atomic pairs, it can be produced by compressing other boron phases to 12–20 GPa and heating to 1500–1800 °C. The T phase is produced at similar pressures, but higher temperatures of 1800–2200 °C; as to the α and β phases, they might both coexist at ambient conditions with the β phase being more stable
Wear
Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical or chemical; the study of wear and related processes is referred to as tribology. Wear in machine elements, together with other processes such as fatigue and creep, causes functional surfaces to degrade leading to material failure or loss of functionality. Thus, wear has large economic relevance as first outlined in the Jost Report. Wear of metals occurs by plastic displacement of surface and near-surface material and by detachment of particles that form wear debris; the particle size may vary from millimeters to nanometers. This process may occur by contact with other metals, nonmetallic solids, flowing liquids, solid particles or liquid droplets entrained in flowing gasses; the wear rate is affected by factors such as type of loading, type of motion, temperature. Depending on the tribosystem, different wear types and wear mechanisms can be observed. Wear is classified according to so-called wear types, which occur in isolation or complex interaction.
Common types of wear include: Adhesive wear Abrasive wear Surface fatigue Fretting wear Erosive wear Corrosion and oxidation wearOther, less common types of wear are impact-, cavitation- and diffusive wear. Each wear type is caused by one or more wear mechanisms. For example, the primary wear mechanism of adhesive wear is adhesion. Wear mechanisms and/or sub-mechanisms overlap and occur in a synergistic manner, producing a greater rate of wear than the sum of the individual wear mechanisms. Adhesive wear can be found between surfaces during frictional contact and refers to unwanted displacement and attachment of wear debris and material compounds from one surface to another. Two adhesive wear types can be distinguished: Adhesive wear is caused by relative motion, "direct contact" and plastic deformation which create wear debris and material transfer from one surface to another. Cohesive adhesive forces, holds two surfaces together though they are separated by a measurable distance, with or without any actual transfer of material.
Adhesive wear occurs when two bodies slide over or are pressed into each other, which promote material transfer. This can be described as plastic deformation of small fragments within the surface layers; the asperities or microscopic high points found on each surface affect the severity of how fragments of oxides are pulled off and added to the other surface due to strong adhesive forces between atoms, but due to accumulation of energy in the plastic zone between the asperities during relative motion. The type of mechanism and the amplitude of surface attraction varies between different materials but are amplified by an increase in the density of "surface energy". Most solids will adhere on contact to some extent. However, oxidation films and contaminants occurring suppress adhesion, spontaneous exothermic chemical reactions between surfaces produce a substance with low energy status in the absorbed species. Adhesive wear can lead to an increase in roughness and the creation of protrusions above the original surface.
In industrial manufacturing, this is referred to as galling, which breaches the oxidized surface layer and connects to the underlying bulk material, enhancing the possibility for a stronger adhesion and plastic flow around the lump. Abrasive wear occurs. ASTM International defines it as the loss of material due to hard particles or hard protuberances that are forced against and move along a solid surface. Abrasive wear is classified according to the type of contact and the contact environment; the type of contact determines the mode of abrasive wear. The two modes of abrasive wear are known as three-body abrasive wear. Two-body wear occurs when hard particles remove material from the opposite surface; the common analogy is that of material being displaced by a cutting or plowing operation. Three-body wear occurs when the particles are not constrained, are free to roll and slide down a surface; the contact environment determines whether the wear is classified as closed. An open contact environment occurs when the surfaces are sufficiently displaced to be independent of one another There are a number of factors which influence abrasive wear and hence the manner of material removal.
Several different mechanisms have been proposed to describe the manner in which the material is removed. Three identified mechanisms of abrasive wear are: Plowing Cutting FragmentationPlowing occurs when material is displaced to the side, away from the wear particles, resulting in the formation of grooves that do not involve direct material removal; the displaced material forms ridges adjacent to grooves, which may be removed by subsequent passage of abrasive particles. Cutting occurs when material is separated from the surface in the form of primary debris, or microchips, with little or no material displaced to the sides of the grooves; this mechanism resembles conventional machining. Fragmentation occurs when material is separated from a surface by a cutting process and the indenting abrasive causes localized fracture of the wear material; these cracks freely propagate locally around the wear groove, resulting in additional material removal by spalling. Abrasive wear can be measured as loss of mass by the Taber Abrasion Test according to ISO 9352 or ASTM D 4060.
Surface fatigue is a process by which the surface of a material is weakened by cyclic loading, one type of general material fatigue. Fatigue wear is produ
