Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances.
Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others.
Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
Roller burnishing is a method of cold working metal surfaces to induce compressive residual stresses and enhance surface roughness qualities. The tooling typically consists of a sphere or cylindrical roller. These tools are pressed onto/across the part being processed, another application is thrust bearing surfaces of some production crankshafts. A dual roller tool is moved into the thrust bearing journal of a crankshaft, so the diameters of each roller added together equals the finish dimension of the thrust bearing. In deep hole machining, a burnishing tool is often combined with skiving knives on the same tool. The skiving knives pass first, scraping the inside layer of metal, followed by the burnishing rollers, skive-burnishing is often used in hydraulic cylinder applications. This process can happen on a deep hole drilling machine or a dedicated skiving machine
The Online Computer Library Center is a US-based nonprofit cooperative organization dedicated to the public purposes of furthering access to the worlds information and reducing information costs. It was founded in 1967 as the Ohio College Library Center, OCLC and its member libraries cooperatively produce and maintain WorldCat, the largest online public access catalog in the world. OCLC is funded mainly by the fees that libraries have to pay for its services, the group first met on July 5,1967 on the campus of the Ohio State University to sign the articles of incorporation for the nonprofit organization. The group hired Frederick G. Kilgour, a former Yale University medical school librarian, Kilgour wished to merge the latest information storage and retrieval system of the time, the computer, with the oldest, the library. The goal of network and database was to bring libraries together to cooperatively keep track of the worlds information in order to best serve researchers and scholars. The first library to do online cataloging through OCLC was the Alden Library at Ohio University on August 26,1971 and this was the first occurrence of online cataloging by any library worldwide.
Membership in OCLC is based on use of services and contribution of data, between 1967 and 1977, OCLC membership was limited to institutions in Ohio, but in 1978, a new governance structure was established that allowed institutions from other states to join. In 2002, the structure was again modified to accommodate participation from outside the United States. As OCLC expanded services in the United States outside of Ohio, it relied on establishing strategic partnerships with networks, organizations that provided training, support, by 2008, there were 15 independent United States regional service providers. OCLC networks played a key role in OCLC governance, with networks electing delegates to serve on OCLC Members Council, in early 2009, OCLC negotiated new contracts with the former networks and opened a centralized support center. OCLC provides bibliographic and full-text information to anyone, OCLC and its member libraries cooperatively produce and maintain WorldCat—the OCLC Online Union Catalog, the largest online public access catalog in the world.
WorldCat has holding records from public and private libraries worldwide. org, in October 2005, the OCLC technical staff began a wiki project, WikiD, allowing readers to add commentary and structured-field information associated with any WorldCat record. The Online Computer Library Center acquired the trademark and copyrights associated with the Dewey Decimal Classification System when it bought Forest Press in 1988, a browser for books with their Dewey Decimal Classifications was available until July 2013, it was replaced by the Classify Service. S. The reference management service QuestionPoint provides libraries with tools to communicate with users and this around-the-clock reference service is provided by a cooperative of participating global libraries. OCLC has produced cards for members since 1971 with its shared online catalog. OCLC commercially sells software, e. g. CONTENTdm for managing digital collections, OCLC has been conducting research for the library community for more than 30 years.
In accordance with its mission, OCLC makes its research outcomes known through various publications and these publications, including journal articles, reports and presentations, are available through the organizations website. The most recent publications are displayed first, and all archived resources, membership Reports – A number of significant reports on topics ranging from virtual reference in libraries to perceptions about library funding
Residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable or undesirable, unintended residual stress in a designed structure may cause it to fail prematurely. Residual stresses can occur through a variety of mechanisms including inelastic deformations, heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some cool and contract more than others. The stress variation through a stack of thin film materials can be very complex, while uncontrolled residual stresses are undesirable, some designs rely on them. In particular, brittle materials can be toughened by including compressive residual stress, as in the case for toughened glass, the predominant mechanism for failure in brittle materials is brittle fracture, which begins with initial crack formation. This causes the initial crack to enlarge quickly as the material is overwhelmed by the stress concentration. A material having compressive residual stress helps to prevent brittle fracture because the crack is formed under compressive stress.
The manufacture of some swords utilises a gradient in martensite formation to produce particularly hard edges, the difference in residual stress between the harder cutting edge and the softer back of the sword gives such swords their characteristic curve. In toughened glass, compressive stresses are induced on the surface of the glass, due to the residual compressive stress on the surface, toughened glass is more resistant to cracks, but shatter into small shards when the outer surface is broken. As a result, the solid globule is extremely tough, able to be hit with a hammer, but if its long tail is broken, the balance of forces is upset, causing the entire piece to shatter violently. In certain types of gun barrels made with two tubes forced together, the tube is compressed while the outer tube stretches, preventing cracks from opening in the rifling when the gun is fired. Castings may have large residual stresses due to uneven cooling, residual stress is often a cause of premature failure of critical components, and was probably a factor in the collapse of the Silver Bridge in West Virginia, United States in December 1967.
The eyebar links were castings which showed high levels of residual stress, when the crack reached a critical size, it grew catastrophically, and from that moment, the whole structure started to fail in a chain reaction. Because the structure failed in less than a minute,46 drivers and passengers in cars on the bridge at the time were killed as the roadway fell into the river below. Common methods to induce residual stress are shot peening for surfaces. Depth of compressive residual stress varies depending of the method, both methods can increase lifetime of constructions significiantly. There are some techniques which are used to create uniform residual stress in a beam, for example, the four point bend allows inserting residual stress by applying a load on a beam using two cylinders
Rake angle is a parameter used in various cutting and machining processes, describing the angle of the cutting face relative to the work. There are two angles, namely the back rake angle and side rake angle, both of which help to guide chip flow. There are three types of angles, positive and zero. Generally, positive rake angles, Make the tool more sharp and this reduces the strength of the tool, as the small included angle in the tip may cause it to chip away. Reduce cutting forces and power requirements, helps in the formation of continuous chips in ductile materials. Can help avoid the formation of a built-up edge, negative rake angles, by contrast, Make the tool more blunt, increasing the strength of the cutting edge. Can increase friction, resulting in higher temperatures, a zero rake angle is the easiest to manufacture, but has a larger crater wear when compared to positive rake angle as the chip slides over the rake face. Recommended rake angles can vary depending on the material being cut, tool material, depth of cut, cutting speed and this table summarizes recommended rake angles for single-point turning on a lathe, rake angles for drilling, milling, or sawing are often different
Asperity (materials science)
In materials science, defined as unevenness of surface, ruggedness, has implications in physics and seismology. Smooth surfaces, even those polished to a finish, are not truly smooth on an atomic scale. They are rough, with sharp, rough or rugged projections, surface asperities exist across multiple scales, often in a self affine or fractal geometry. The fractal dimension of these structures has been correlated with the contact mechanics, when two macroscopically smooth surfaces come into contact, initially they only touch at a few of these asperity points. These cover only a small portion of the surface area. Friction and wear originate at these points, and thus understanding their behavior becomes important when studying materials in contact, the relationship between frictional interactions and asperity geometry is complex and poorly understood. The Archard equation provides a model of asperity deformation when materials in contact are subject to a force. Due to the presence of deformable asperities in self affine hierarchical structures
A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. Most bearings facilitate the desired motion by minimizing friction, Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads applied to the parts. Rotary bearings hold rotating components such as shafts or axles within mechanical systems, the simplest form of bearing, the plain bearing, consists of a shaft rotating in a hole. Lubrication is often used to reduce friction, a wide variety of bearing designs exists to allow the demands of the application to be correctly met for maximum efficiency, reliability and performance. The term bearing is derived from the verb to bear, a bearing being an element that allows one part to bear another. The simplest bearings are bearing surfaces, cut or formed into a part, with varying degrees of control over the form, roughness, other bearings are separate devices installed into a machine or machine part.
The most sophisticated bearings for the most demanding applications are very precise devices, the invention of the rolling bearing, in the form of wooden rollers supporting, or bearing, an object being moved is of great antiquity, and may predate the invention of the wheel. Though it is claimed that the Egyptians used roller bearings in the form of tree trunks under sleds. They are depicted in their own drawings in the tomb of Djehutihotep as moving massive stone blocks on sledges with liquid-lubricated runners which would constitute a plain bearing, there are Egyptian drawings of bearings used with hand drills. The earliest recovered example of a rolling element bearing is a ball bearing supporting a rotating table from the remains of the Roman Nemi ships in Lake Nemi. The wrecks were dated to 40 BC, leonardo da Vinci incorporated drawings of ball bearings in his design for a helicopter around the year 1500. This is the first recorded use of bearings in an aerospace design, Agostino Ramelli is the first to have published sketches of roller and thrust bearings.
An issue with ball and roller bearings is that the balls or rollers rub against each other causing additional friction which can be reduced by enclosing the balls or rollers within a cage, the captured, or caged, ball bearing was originally described by Galileo in the 17th century. The first practical caged-roller bearing was invented in the mid-1740s by horologist John Harrison for his H3 marine timekeeper and this uses the bearing for a very limited oscillating motion but Harrison used a similar bearing in a truly rotary application in a contemporaneous regulator clock. The first modern recorded patent on ball bearings was awarded to Philip Vaughan and his was the first modern ball-bearing design, with the ball running along a groove in the axle assembly. Bearings played a role in the nascent Industrial Revolution, allowing the new industrial machinery to operate efficiently. For example, they saw use for holding wheel and axle to greatly reduce friction over that of dragging an object by making the act over a shorter distance as the wheel turned.
The first plain and rolling-element bearings were wood closely followed by bronze, over their history bearings have been made of many materials including ceramic, glass, bronze, other metals and plastic which are all used today
Contact mechanics is the study of the deformation of solids that touch each other at one or more points. Central aspects in contact mechanics are the pressures and adhesion acting perpendicular to the bodies surfaces. This page focuses mainly on the direction, i. e. on frictionless contact mechanics. Frictional contact mechanics is discussed separately, current challenges faced in the field may include stress analysis of contact and coupling members and the influence of lubrication and material design on friction and wear. Applications of contact mechanics further extend into the micro- and nanotechnological realm, the original work in contact mechanics dates back to 1882 with the publication of the paper On the contact of elastic solids by Heinrich Hertz. Hertz was attempting to understand how the properties of multiple. Hertzian contact stress refers to the stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads. This amount of deformation is dependent on the modulus of elasticity of the material in contact and it gives the contact stress as a function of the normal contact force, the radii of curvature of both bodies and the modulus of elasticity of both bodies.
Hertzian contact stress forms the foundation for the equations for load bearing capabilities and fatigue life in bearings, classical contact mechanics is most notably associated with Heinrich Hertz. In 1882, Hertz solved the problem of two elastic bodies with curved surfaces. This still-relevant classical solution provides a foundation for modern problems in contact mechanics, for example, in mechanical engineering and tribology, Hertzian contact stress is a description of the stress within mating parts. The Hertzian contact stress refers to the stress close to the area of contact between two spheres of different radii. It was not until one hundred years that Johnson, Kendall. This theory was rejected by Boris Derjaguin and co-workers who proposed a different theory of adhesion in the 1970s, the Derjaguin model came to be known as the DMT model, and the Johnson et al. model came to be known as the JKR model for adhesive elastic contact. This rejection proved to be instrumental in the development of the Tabor, further advancement in the field of contact mechanics in the mid-twentieth century may be attributed to names such as Bowden and Tabor.
Bowden and Tabor were the first to emphasize the importance of surface roughness for bodies in contact, through investigation of the surface roughness, the true contact area between friction partners is found to be less than the apparent contact area. Such understanding drastically changed the direction of undertakings in tribology, the works of Bowden and Tabor yielded several theories in contact mechanics of rough surfaces. The contributions of Archard must be mentioned in discussion of pioneering works in this field, Archard concluded that, even for rough elastic surfaces, the contact area is approximately proportional to the normal force
Broaching is a machining process that uses a toothed tool, called a broach, to remove material. There are two types of broaching and rotary. In linear broaching, which is the common process, the broach is run linearly against a surface of the workpiece to effect the cut. Linear broaches are used in a machine, which is sometimes shortened to broach. In rotary broaching, the broach is rotated and pressed into the workpiece to cut an axis symmetric shape, a rotary broach is used in a lathe or screw machine. In both processes the cut is performed in one pass of the broach, which makes it very efficient, Broaching is used when precision machining is required, especially for odd shapes. Commonly machined surfaces include circular and non-circular holes, keyways, typical workpieces include small to medium-sized castings, screw machine parts, and stampings. Even though broaches can be expensive, broaching is usually favored over other processes used for high-quantity production runs. Broaches are shaped similar to a saw, except the height of the teeth increases over the length of the tool, the broach contains three distinct sections, one for roughing, another for semi-finishing, and the final one for finishing.
Broaching is a machining process because it has the feed built into the tool. The profile of the surface is always the inverse of the profile of the broach. The rise per tooth, known as the step or feed per tooth, determines the amount of material removed, the broach can be moved relative to the workpiece or vice versa. Because all of the features are built into the broach no complex motion or skilled labor is required to use it. A broach is effectively a collection of single-point cutting tools arrayed in sequence, cutting one after the other, the process depends on the type of broaching being performed. Surface broaching is very simple as either the workpiece is moved against a stationary surface broach, the process begins by clamping the workpiece into a special holding fixture, called a workholder, which mounts in the broaching machine. The broaching machine elevator, which is the part of the machine moves the broach above the workholder. Once through, the broaching machines puller, essentially a hook, the elevator releases the top of the pilot and the puller pulls the broach through the workpiece completely.
The workpiece is removed from the machine and the broach is raised back up to reengage with the elevator, the broach usually only moves linearly, but sometimes it is rotated to create a spiral spline or gun-barrel rifling
Work hardening, 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, bending 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 cooling, in this annealed state it may be hammered 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
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire.
Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest.
The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
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, 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 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