Kohser , Jt. Black , E. Askeland and Pradeep P. Fulay, Cengage Learning, deformation usually by several orders of magnitude , thereby enhancing the probability of interaction. The effects of strain hardening become attractive when one considers that mechanical deformation metal-forming is frequently used in the shaping of metal products. As the product shape is b Kohser , J. Black , J. Temple Black , Roland A. Heat Treating. Finishing, and Coating, Vol. Powder Metallurgy, Vol. Mechanical Testing, Vol. Materials Characteristics.
Failure Analysis and Prevention. Corrosion, 2. Metals Handbook. Desk Edition. Topics covered include: process quality control; casting and forming; and machining processes. Still need help? Feel free to contact us. With our dedicated customer support team, day no-questions-asked return policy, and our price match guarantee, you can rest easy knowing that we're doing everything we can to save you time, money, and stress.
The spine may show signs of wear. Pages include considerable notes in pen or highlighter, but the text is not obscured. Choose between standard or expedited shipping to make sure that your textbooks arrive in time for class. When your books are due, just pack them up and ship them back. And don't worry about shipping - it's absolutely free! Paul DeGarmo , J T. Black , Ronald A. For example, the performance of a manufacturingprocess depends on the friction acting, any lubricants and coolants used, the constraintsimposed on the deformation such as by die shape in forging, etc.
Further, materialproperties change with temperature and rate of deformation. In addition to heatingmaterials to change there temperature before processing temperature changes during theprocess due to cooling and heating due to deformation. Materials are often processed inhigh speed operations in which strain rates are very high. Comparing material behaviors in processing is very difficult, and dubious, since thebehavior depends so critically on the processing conditions.
The basic premise of the fracture mechanics approach to testing and design is that allmaterials contain flaws or defects of some given size. Fracture mechanics then attemptsto distinguish between the conditions where these defects will remain dormant and thoseconditions for which the defects might grow and propagate to failure. The three principal quantities that fracture mechanics tries to relate are: 1 the size ofthe largest or most critical flaw, 2 the applied stress, and 3 the fracture toughness ofthe material a material property.
Fracture toughness is resistance to crack growth, K. Crack growth rate is shown as itdepends on K in Figure The three primary thermal properties of a material are: 1 heat capacity or specific heat - a measure of the amount of energy that must beimparted or extracted to produce a one degree change in temperature; 2 thermalconductivity - a measure of the rate at which heat can be transported or conductedthrough a material; and 3 thermal expansion - a measure of the degree of expansion orcontraction that will occur upon heating or cooling of the material.
Since density is directly related to weight any engineering application in whichweight is important will be one in which density is an important material property. Anexample of light weight, low density, being important is an airplane. An example ofheavy weigh, high density, being important is a boat anchor. Often the minimum weight structure needed to support a loading is desired and strength-to-weight ratio is relevant.
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Products in which performance does not depend on resistance to mechanical loadingare probably examples where performance does depend on physical properties. An example is electrical wire. The intent is to conduct electricity, not to withstandappreciable loads. Another example is a camera lens. Electrical conductivity and optical properties determine the major part of theperformance of wires and lenses. For wires the material should be ductile so it can be routed and should be a low strainhardening material so working it in installation will not cause large loads and fracture.
Bookshelves are subjected to static loading over long time. In addition to static strength, bookshelf materials should be stiff and should not creep,i. Material secondary characteristics might include light weight low density , easy towork and easy to finish in various ways. The material should have a high fatigue strength large number of cycles to failureunder the expected loading situation. A desirable secondary characteristics is being easy to work so as not to produce arough surface containing sites of fatigue failure initiation.
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For discussion of ductile-to-brittle transition using the data for steel presented inSection2. Typical transport and short time storage containers for liquid nitrogen are composed ofDewar flasks usually made of annealed borosilicate glass held in an aluminum, stainlesssteel, plastic or steel casing. The Dewar may be surrounded by netting to contain theglass in case of breakage. Since the liquid nitrogen does not come into contact with thecasing steel casings are used.
In the event of Dewar fracture the liquid nitrogen is not contained on the surface soboiling and the formation of gas at the liquid nitrogen-casing interface probably meansthat a steel casing would not be subjected to stress and temperature conditions to makeductile-to-brittle transition considerations important. Stainless steel Dewars are available. A different deformationpattern, rolling texture, results and this leads to different microstructure and properties indifferent directions.
The difference in absorbed energy with rolling direction shown in Figure 2P-1 indicatesthat the rolling texture has an effect on energy absorbed, i. If impact properties have been improved in steel making the causes must be in the areasof- development of alloys that are less temperature dependent, i. The general explanation is that material properties and deformation behavior aredetermined by composition, structure and surrounding conditions. For fixed deformationconditions, improvement in deformation behavior is the result of improvements instructure, probably due to changing steel composition.
The materials are to be distinguished based on the tests described in Chapter 2, the useof readily available household items and the ability to machine the materials. The use ofhousehold items and a machine shop indicates that mechanical and physical propertieslisted in Chapter 2 may be qualitatively measured comparisons rather that quantitativemeasurements in addition to the tests described in Chapter 2. One way to organize a material separation plan is to consider the applicability to materialseparation of each test described.
The tests may be obviously useful for identifyingdistinguishable properties, perhaps useful or not useful depending on if the measuredquantity is sufficiently different for the two materials. The materials used in this problemare described in detail further on in the text as listed in the table. Distinguishing between materials based on the characteristics and properties mentionedin Chapter 2 and using readily available items can be discussed by considering theproperties mentioned.
The same general conclusion can be reached — when materials are of similar typedistinguishing between them is difficult. However there are particular differences inproperties that are qualitatively different and make for easy material identification, e. Differences in deformationbehavior can lead to identifiable differences in material use and processing, such asdifferences in ductility leading to differences in formability. There are two reasonable causes of failure worth investigating, given that the hookshave sufficient load carrying capacity to support pounds under typical conditions.
First a simple experiment or analytical stress analysis to determine expected loadcapacity. With assurance that the hooks are capable of holding the anticipated load, theproblem is use of a material that is adversely affected by the in-use environment. Arecommended solution is to use stainless steel for the material. It is corrosion resistantand does not behave in a brittle manner at the use temperature. It seems that in a meatpacking plant stainless steel would be the first choice for health, cleanliness andmechanical reasons. Underlying materials engineering is the close relationship between structure andmechanical behavior.
So, at the level of determining mechanical properties, allmicrostructural characteristics are important. With respect to the behavior in the usesituation described and possible accelerated failure mechanisms, grain boundaries areimportant in stress corrosion since they are active chemical-mechanical process initiationsites. Material structure determines material properties. So if material structure can bedesigned and produced, desirable properties can be obtained.
For example, the strength ofsteel can be controlled by changing not only composition but also by producing usefulmicrostructures in heat treating processes. Microstructure is the structure in a polycrystalline material that is determined by thesize, shape and arrangement of the grains making up the material. This is in contrast tothe atomic level structure of the material. An ion is an atom that has a different number of electrons than the number of electronsneeded for stability. That is, a different number of electrons and protons. Negative ions have more electrons than protons and so have a net negative charge.
Positive ions have missing electrons and so contain more neutrons than electrons and sohave a net positive charge.
M.P Black Kohser DeGarmo's Materials Processes Manufacturing 10th
Valence electrons play a large part in an atoms interactions with other atoms and inatomic level processes. The determine the kind of interatomic bonding, chemicalproperties, electrical properties and optical properties. The three types of primary bonds arei. In contrast atoms that assume a lower energy state by sharingelectrons form covalent bonds. Metallic bonds form between atoms that readily give upelectrons to a shared electron gas. Position in the table of elements is a starting place forpredicting what kind of boning will occur between atoms.
Ionic bonds are strong primary bonds between ions. The result is that ionically bondedmaterial are hard, brittle, have high melting point and low electrical conductivity. Theyare strong but not as strong as typical covalently boned materials. Covalent bonds are strong and so materials are strong, hard and brittle. Depending onthe number of electrons participating in the bond, covalently bonded materials show wideranges of electrical, chemical and optical properties.
In metallically bonded materials there is a mobile electron cloud that producesbonding. Properties that depend on electron mobility are extreme compared to other typesof materials. For example, metals have high electrical and thermal conductivities. Electron-photon interactions account for the opacity of metals. Asymmetric molecules that have nonsymmetrical charge distribution form van derWaal bonds. The bonding is due to the attraction between the differently charged regionsof the molecules. The atomic radius is the distance between centers of atoms in a grouping of atoms,i.
The distance between a particularpair of atoms is determined by the balance of attractive and repulsive forces betweenatoms and between the particular atoms and all their surrounding atomic neighbors. Indifferent crystal structures the ordering of atoms is different, so interatomic forceinteractions are different, the compliant response of individual atoms to theirsurroundings is different and hence the distance between atom centers, atomic radius, isdifferent.
Crystalline materials have a regular, repeating structure, a repeating elementaryarrangement of atoms. Amorphous material does have a repeating, predicablearrangement of the atoms or molecules that make up the material. The metallic bonding of the atoms making up a metal results in a material that isstrong, ductile, has high density, high electrical and thermal conductivities and opticalluster. Allotropic materials are those that can exist in two or more atomic lattice structuresdepending on temperature and pressure conditions.
Compared to the simple cubic structure, the closer packing arrangement of atoms inface center cubic and body center crystal structure results in a higher packing density ofatoms and so more effective electron sharing. In contract to the existence of particular metallic structures, a more general definition ofengineering metals is metals that are used in engineering applications.
Simple cubicstructure materials are, would be, brittle and so difficult to mechanically work into usefulshapes. The common metal crystal structures are body-centered cubic, face-centered cubicand hexagonal close-packed. Efficiency is the amount of space in the lattice that is occupied by the atoms modeledas solid spheres. Body-centered cubic 68 Face-centered cubic 74 Hexagonal close-packed When close-packed planes form in the face-centered cubic arrangement there aremany possible direction of atomic plane motion resulting in higher ductility than for thehexagonal close-packed arrangement with its smaller number of easy deformationdirections.
Deformation or slip systems are determined by the possible planes on whichdeformation can occur easily and the possible directions of slip. Face-centered cubicarrangements have more active slip systems than hexagonal close-packed arrangements. A grain boundary is the relatively disordered region between crystals or grains inwhich atomic arrangement is relatively well defined and well ordered. The American Society for Testing and Materials grain size number is commonly usedto specify grain size.
Standards are specified for specimen preparation and measurement procedures. Metallic crystals respond to low applied loads by simply stretching or compressingthe distance between atoms. All atoms retain their basic positions, with the load servingonly to disrupt the force balance of the atomic bonds in such a way as to produce elasticdeformations.
Plastic deformation is a permanent shift of atoms resulting in a permanent change insize or shape.
A slip system for the plastic deformation of a metal is the specific combination of apreferred plane and a preferred direction within that plane. In general, the preferredplanes are those with the highest atomic density and greatest parallel separation - theclose-packed planes. The preferred directions are the close-packed directions. The dominant mechanical property of the bcc crystal structure metals is high strength. The fcc metals have high ductility. The hcp metals tend to be brittle. A dislocation is a line-type defect within a crystalline solid. Edge dislocations are theterminal edges of extra half-planes of atoms, and screw dislocations are the ends ofpartial "tears" through the crystal.
Since the movement of dislocations provides theplasticity of a material, the force required to move dislocations determines the resistanceto plastic deformation, or the strength of the material. Other crystal imperfections can provide effective barriers to dislocation movementand be used to strengthen the metal. These include: point-type defects such as vacancies,interstitials, or substitutional atoms , additional line-type dislocations, and surface-type 22 The three major types of point defects in crystalline materials are: vacancies missingatoms , interstitials extra atoms forced between regular atom sites , and substitutionalatoms atoms of a different variety occupying lattice sites.
The strain hardening of a metal is the result of the multiplication of the number ofdislocations and the interaction between the various dislocations to pin or block themovements of one another. Since dislocations cannot cross grain boundaries a discontinuity to crystal structure ,these boundaries serve to impede dislocation movement and make the material stronger. A material with a finer grain structure more grain boundaries will, therefore, tend to bestronger than one with larger grains.
An anisotropic property is a property that has different values in different directions. Possible causes of anisotropy are;- material creation as in the growth of trees and the casting of metals in which small scalestructures wood fibers, dendritic metallic microstructure have anisotropic structures andcombine in an oriented way to produce large scale anisotropic structure grain in wood,large grains near the surface of castings ,- material processing in which symmetric microstructures are deformed into structureswith distinctive shapes.
For example, rolling of a metal that has ideally spherical grainsproduces elongated grains along the rolling direction. The resulting product hasanisotropic mechanical properties, such as different strength and ductility along therolling direction and perpendicular to the rolling direction.. Brittle fractures occur without the prior warning of plastic deformation and propagaterapidly through the metal with little energy absorption. Ductile fractures generally occurafter the available plastic deformation has been exceeded.
Plastic deformation increases the internal energy of a material through both thecreation of numerous additional dislocations and the increased surface area of thedistorted grain boundaries. Given the opportunity, the metal will seek to reduce itsenergy through the creation of a new crystal structure, i. Recrystallization is often used to restore ductility to a metal and enable furtherdeformation to be performed. Without recrystallization, further deformation would resultin fracture. NOTE: If the deformation is performed at temperatures above the recrystallizationtemperature, deformation and recrystallization can take place simultaneously and largedeformations are possible.
The major distinguishing factor between hot and cold working is whether thedeformation is produced at a temperature that is above or below the recrystallization 23 In cold working, no recrystallization occurs and the metalretains its strain hardened condition. When hot working is performed, recrystallizationproduces a new grain structure and no strain hardening is possible. When an alloy addition is made to a base metal, several possibilities can occur.
Thetwo materials can be insoluble and refuse to combine or interact. If there is solubility, thealloy can dissolve in the base metal to produce a solid solution of either the substitutionalor interstitial variety. A final possibility is that the two can react to produce anintermetallic compound - a combination with definite atomic proportions and definitegeometric relationships. Intermetallic compounds tend to be hard, brittle, high-strength materials. The charge carriers in metals are the valence electrons.
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The general concept becomesslightly cloudy since in metals the electron sea or electron cloud is composed of electronsthat are in essence shared by all the atoms. In a sense the valence electrons belong to allthe atoms and are not valence electrons in the sense of the valence electron of an atom. Electrical resistance in a metal depends largely on two factors - the number of latticeimperfections and the temperature. Vacancies, interstitials, substitutional atoms,dislocations, and grain boundaries all act as disruptions to the regularity of a crystallinelattice.taylor.evolt.org/camih-ller-citas-gratis.php
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Thermal energy causes the atoms to vibrate about their equilibrium positions andinterferes with electron transport. Intrinsic semiconductors are ones that occur naturally. Extrinsic semiconductors havechemistries that have been modified by "doping" to enhance or alter their conductivity. Problems: NoneCase Study: Window Frame Materials and DesignWood such as kiln-dried Ponderosa pine is easily shaped, can be painted or finished in awide spectrum of finishes, and has low thermal conductivity keeping the winter cold andsummer heat out.
Unfortunately, the material has a definite grain structure, which maylead to cracking or splintering. The material requires special impregnation and coating toimprove its ability to resist degradation. Wood requires regular surface maintenance such as painting or sealing to minimize moisture absorption and rot. While itsdimensions are relatively insensitive to changes in temperature, they can changesignificantly with changes in humidity or moisture content, leading to possible warpingor twisting.
The shrinking, swelling and cracking tendencies make it extremely difficult 24 Finally, wood is a combustible material. Aluminum can be extruded into the complex channels used for window frames, isdurable, non-corrosive, and can be color anodized or finished into a variety of surfaces. The properties are consistent and predictable and do not change over time, or withvariations in temperature over the range where windows would operate. The materialdoes not absorb moisture, swell, shrink, split, crack or rust. Maintenance is extremelylow, but the material has a high thermal conductivity.
If the same piece is exposed to acold exterior and warm, moist interior as in winter weather , the material will try toachieve thermal uniformity.
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The inside surfaces will "sweat" with condensation, andthermal efficiency of the window will be poor. Compared with alternatives, however,aluminum is stronger and more rigid 23 times stiffer than vinyl. From a safetyperspective, aluminum is noncombustible and does not emit any toxic fumes when heatedto high temperature. Vinyl windows offer a range of color, and the color is integral to the material. There isno need for any surface finishing and the appearance requires no periodic maintenance. Inaddition, the thermal conductivity is low, giving the window good thermal efficiency.
Unfortunately, polymers have poor dimensional stability, generally shrinking over time,and often deteriorate with prolonged exposure to ultraviolet light becoming brittle.
Since windows will see prolonged exposure to sunlight, the long term durability andstability may come into question. The thermal expansion of vinyl is considerably greaterthan either aluminum or wood, and the resulting dimensional changes may causedistortion of the windows. In addition, the properties of vinyl will vary over thetemperature range that the product will see. When heated, vinyl loses strength, and whencold, it becomes more brittle and less impact resistant. The material is combustible andmay emit toxic fumes when exposed to high temperatures.
It would appear that aluminum is a superior structural material, whose primary detrimentis its high thermal conductivity. If a design could be developed to insert some form ofconductivity barrier between the outside and inside surfaces, the resulting window wouldoffer the best of all worlds. Several companies currently offer such a design, linking theinside and outside extrusions with a high-strength polymeric link. Being totally internal,this polymer is not subject to sunlight deterioration, and does not significantly impair thestructural performance of the window.
A phase is a portion of a substance possessing a well-defined structure, uniformcomposition, and distinct boundaries or interfaces. In a glass of soda with ice, the soda is continuous and the ice is discontinuous. Heliumin a balloon is a gaseous phase, and coffee with cream is a single-phase solution. An equilibrium phase diagram is a graphical mapping of the natural tendencies of amaterial system assuming that equilibrium has been attained as a function of suchvariables as pressure, temperature, and composition.
The three primary variables considered in equilibrium phase diagrams are:temperature, pressure and composition. A pressure-temperature phase diagram is not that useful for many engineeringapplications because most processes are conducted at atmospheric pressure. Mostvariations occur in temperature and composition. A cooling curve is a temperature versus time plot of the cooling history when a fixed-composition material is heated and subsequently cooled by removing heat at a uniformlyslow rate.
Transitions in a materials structure are indicated by characteristic points on the coolingcurve. These characteristic points may take the form of an isothermal hold, abruptchange in slope, or localized aberration to the continuity of the curve. Solubility limits denote the conditions at which a solution becomes completelysaturated, i. Solubility limits aregenerally determined through use of inspection techniques such as X-ray analysis detectswhere a new crystal structure or lattice spacing appears or microscopy detects thepresence of the second phase , that can be used to identify the composition where thetransition from one to two-phase occurs.
In general, as the temperature of a system is increased, the maximum amount of asubstance that can be held in solution also increases. Complete solubility implies complete solubility in both liquid and solid states. Thetwo types of atoms have to be able to exist in the same crystalline structure. Partial solubility results when there is a saturation limit for one type of material inanother and this saturation limit depends on temperature.
So, as temperature is loweredand solubility decreases a two phase material forms from the initially one phase material. Insolubility means that the materials are so different in nature atomic size, valenceelectron structure, etc. Upon crossing the liquidus line during cooling, the first solid begins to form in thematerial.
Upon crossing the solidus line, solidification is complete, i. Upon crossing a solvus line, a single phase material begins toprecipitate a second phase, since the solubility limit is now being exceeded. The three pieces of information that can be obtained from each point in anequilibrium phase diagram are: the phases present, the composition or chemistry ofeach phase, and the amount of each phase present. A tie-line is an isothermal line drawn through any point in the two phase region of aphase diagram, terminating at the boundaries of the single phase regions on either side.
Itis used in the two-phase regions of an equilibrium phase diagram. The end points of the tie-line correspond to the compositions of the two phasespresent. The relative amounts of the component phases in a two-phase mixture can becomputed through use of the lever law. The tie-line is separated into two segments bydividing it at the chemistry of the alloy in question. The fraction of the total length of thetie-line that lies opposite to a given phase corresponds to the fractional amount of thatparticular phase.
Cored structures refer to materials that have microscopic level variations in chemicalcomposition. Cored structures form because as the metal solidifies through the freezing range thechemical composition constantly changes. If cooling rate is rapid, material diffusion rateis too slow to produce uniform chemistry. Different regions of the solid material havedifferent chemical characteristics determined by the temperature at which the regionssolidified.
Three-phase reactions appear as horizontal lines in binary two-component phasediagrams. The intersection of the V and the horizontal line denotes thethree-phase reaction, which is usually written in the form of cooling, i. In essence,a liquid solidifies to form two distinctly different solids of differing chemistries. Eutectic alloys are attractive for casting and as filler metals in soldering and brazingbecause they generally have the lowest melting point of all alloys in a given system andsolidify into a relatively high-strength structure. A stoichiometric intermetallic compound is a single-phase solid that forms when twoelements react to form a compound of fixed atomic ratio.
The compound cannot tolerateany deviation from that fixed ratio, so it appears as a single vertical line in a phasediagram, breaking the diagram into recognizable sub areas. Non-stoichiometricintermetallic compounds are single phases that appear in the central regions of a phasediagram, that can tolerate chemical variations, and thus have an observed width. Theyappear as a region and not a line. In general, intermetallic compounds tend to be hard, brittle materials. If an intermetallic compound can be uniformly distributed throughout a structure inthe form of small particles in a ductile matrix, the effect can be considerablestrengthening of the material.
If the intermetallic should become the continuous phase as in a grain boundary coating or be present in large quantities, the material will becharacteristically brittle. The four single phases in the iron-carbon equilibrium phase diagram are: ferrite alpha , which is the room-temperature body-centered cubic structure; austenite gamma ,the elevated temperature face-centered cubic phase; delta-ferrite delta , the high-temperature body-centered cubic phase; and cementite Fe3C , the iron-carbonintermetallic compound that occurs at 6.
The point of maximum carbon solubility in iron, 2. Cast irons contain greater than 2.