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Definition
Ceramic (often)
Electron Transfer |
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Polymers
Electron Sharing |
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Metals
Non-Localized, Electron "cloud" |
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Dipoles
very weak compared to primary bonds |
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| Non-Zero stresses and strains remaining in a structure after loading is removed |
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| The method of impacting tiny glass or metal balls on the surface of a material to produce residual compressive stresses that impede crack propogation |
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| Time dependent deformation |
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| Time dependent deformation under constant loading conditions |
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| Caused by sliding of planes of atoms, also called slip |
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| Component has many individual crystals (grains) |
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| Repeating structure of atoms in three dimensions |
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| Simplest repeating structure in a crystalline material |
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| Positions in 3D space of locations of atoms in crystal |
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| Non-crystalline materials, atoms are in random locations |
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| Atoms are spheres, just in contact with nearest neighbors |
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| The number of nearest neighboring atoms to a single atom |
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| Plane on which slip occurs and Direction in which slip occurs |
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| Condition when an element can exist in more than one crystal structure |
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Definition
| When a material can exist in more than one crystal structure |
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Definition
| Point, Linear, Surface and Volume defects |
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Definition
Vacnacy- an atom missing from a normally occupied position
Interstitial- an atom of same element in a normally unoccupied lattice position
Substitutinal- an atom of a different element is in a regular occupying lattice position
Interstitial Impurity- an atom of different type in a normal in a normally unoccupied lattice position |
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| Point and Linear Defects-Linear are also called Dislocations |
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| Cracks, grain boundary, surface of component |
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| Particle/inclusion and void |
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| Mixture of more than one element that is homogenous in material properties |
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| Atoms of different sizes, bonding strength, etc., warp the slip plane, therefore require higher shear to cause slip |
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| Like Solid Solution hardening but on a larger scale. Particles can precipitate out of solid solution, interupts the slip plane |
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| Single Crystal vs. Polycrystalline material |
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Definition
| Polycrystalline is stronger because of the change of direction in the slip plane |
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| Grain size is reduced because smaller grains require higher shear to cause slip |
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| Induce plastic deformation and is stronger after because dislocations warp slip plane |
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When carbon or nitrogen atoms are precipitated into steel
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| Transfer of mass through a gas or liquid through random atomic motion |
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| Liquid to two distinct solids |
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| Solid to two distinct other solid phases |
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| Heat specimen up to eutectic temperature, then rapidly quench in water. Iron tries to go back to BCC but cannot due to carbon in intertstitial locations. Vary hard and brittle. Needle like particles. Diffusionless process gicing metastable |
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| Iron in alpha form, soft and ductile phase of steel |
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| Martensite that has been reheated to a modest temperature for some time. Diffusion breaks up the needle like particles into tiny Fe3C particles in alpha matrix. Good strength, OK ductility. |
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| Iron Carbide particles, hard particles, Fe3C |
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| Cracks on the outside of metals that have been rapidly quenched. Results from different rates of cooling on outer and inner parts-or Thermal Shock |
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| Lamellar microstructure formed from remaining gamma from just above horizontal line to just below horizontal line |
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| Time Temperature Transformation diagram shows non-equilibrium condition |
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| Fe3C is in the form of small needle like particles, harder and stronger than pearlite |
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| Fine Pearlite has smaller grains, therefore is stronger than Coarse Pearlite because smaller grains change the slip direction more, so a higher force is required to cause slip |
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Definition
| Put sample in water. Cools slowly at top and faster at the bottom, then perform multiple hardness tests. |
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| High electrical, thermal conductivity, very corrosion resistant, low melting temperature, easily machined and formed. |
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Definition
| Shaped by working (forging, bending, extruding, drawing) |
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| Pour into mold and cool (2xx, 3xx, etc. designations) |
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| Wrought Aluminum Alloy Designations |
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| 1000-99% pure and up; 2000-copper; 3000-manganese; 4000- silicon; 5000-magnesium; 6000 magnesium and silicon; 7000-zinc. |
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| Density reduced by 10%, retained strength and fracture resistance |
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| O-annealed; F-as-fabricated; H-strain hardened (do not respond well to heat treatments), T-heat treatment (and also possibly strain hardnened |
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| Usind in aircraft since 1920s |
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| Developed in 1940s, greater tensile strength, but poorer mechanical fatigue resistance |
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| Developed in 1950s, imporved strength, but with good fatigue/fracture resistance |
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| Lightest of structural metals (low density), high temps can ignite (powder form) susceptible to corrosion in several environments, mostly cast, hot worked, not very ductile at RT |
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| Chromium is the primary alloying element in excess of 11wt.%; chromium oxide layer forms on exterior, makes corrosion resitant. |
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| High strenth, ductile, can be mahined 'readily', very corrosion resitant, Tm>3000F, but chemically reactive above 1000F and loses structural integrity, becomes brittle |
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| Bronze is an alloy of copper and tin, brass is copper and zinc. Beryllium coppers up to 200ksi tensile strength, ductile, soft, easy to work. Resistant to corrosion, high electrical and thermal conductivity |
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| Metals with highest melting point; noibium, malybdenum, tungsten, tantalum. High desity, high strength and stiffness at high temps |
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| Good combination of high strength, creep resistance at high temperatures for lonh durations of time, very good in highly oxidating environments at high temperatures, primarily made of nickel, iron and cobalt. Mainly used in turbine engine components |
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| Try to line grain boundaries up so they become more creep resistant |
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| Very high corrosion resitance, most are already oxidized, good compressive strength, poor tensile strength, high modulus E |
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| Why are ceramics so brittle? |
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Definition
| Majority of cermaics are ionically bonded, crystalline structure; dislocations cannot occure due to like charges lining up |
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| Crystalline and amorphous (referred to as glasses) |
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Start in powder form, compact powder, fire/sinter-particles joined by diffusion
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| Measure of pores in ceramics, = (volume of pores)/(volume of ceramic); directly affects mechanical properties, provides good insulation |
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| Act as stress concentrations, lead to low tensile strengths, since ceramics are brittle, any small cracks grow quickly to failure, compressive strength much higher since cracks do not grow in compression |
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| Crystal structures are named after a common example (or first to be identified); lack of close packed planes and many elements have low atomic number, so density tends to be lower than with metals |
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Definition
| Positively charged, loses electron, smaller "measured" radius than anion |
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Definition
| Positevly charged, gains electrons, larger "measured" radius than anion |
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| Silica glass wants to be in crystalline form, crystallizes slowly when melted, such that it won't fully become crystallized before hardening with cooling. Also, impurites interfere with crystallization |
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Definition
| "Flaws" in between layers that end up adding strength in the out-of-plane direction. |
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| Fabrication of Ceramics (typical) |
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Definition
| Compact powder in rough shape in mold; prior to sintering, called green ceramic, low strngth; sinter/fire powder, gains strength |
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| Aqueous form of ceramic powder |
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| Pour slip into slip mold, mold is porous which takes out moisture by capillary action; pour out slip, take out green ceramic, sinter |
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| Formed using float method |
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| Typically a chain of carbon atoms with other atoms connected to the sides, consists of repeating units; many mers attached in a long chain, referred to as macromolecule |
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| Repeating unit of polymer chain |
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| Short chain polymer; made up of a few mers |
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| Common properties of poymers |
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Definition
| Low density; typically low melting temperature, some degrade without melting; some ductile, some brittle, can change over small temperature; covalent bonding-primary bonding type, some secondary bonding; no free electrons-electrically nonconductive; generally low strength, stiffness, modulus of elasticity; typically corrosion resistant |
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Definition
| Start with ethylene molecule, break double bond with catalysts and combine with another ethylene molecule |
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| Stress-Strain for Polymers |
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Definition
| Diagrams nonlinear; certain polymers can stretch out chains-may have high strains |
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| Three basic types of polymers |
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Definition
| Thermosplastics, Thermosets, Elastomers |
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| N=# of mers in polymer chain (average volume) =(molecular weight of polymer chain)/(molecular weight of mer) |
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Definition
| Can be reheated and reshaped, often ductile, high strains to failure |
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Definition
| Cure with first heat cycle, cannot be reheated (burns/chars); brittle |
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Definition
| long-chained polymers with light cross-linkin that have larger elastic strains to failure>200% |
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| Secondary Bonding in Polymers |
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Definition
| Approximately 108 degrees between carbon atoms, bonding between dipoles; covalent (primary) bonding most likely failure location between carbon atoms |
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| Glass (Brittle) Transition Temperatue |
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Definition
| Somewhat similar to ductile to brittle transition; heat overcomes weak secondary bonds, allowing molecules to slide past each other; results in permanent deformation; significant cross-linking stops this behavior; lower temperatures results in higher stresses, lower strains |
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Definition
| Has more than one type of mer in chain (typically two); four types: alternating, random, block, grafted |
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| Glass Transition Temperature, results in necking of molecules, not slip; molecules are elongated |
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| Combination of two or more materials, each of which retains its own identity and properties |
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| Fiber-reinforced, particle-reinforced, structural/laminated; particle and fiber are dispersed phase |
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Definition
| Strengthen, increase hardness |
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Definition
| Provides come strength (especially tranverse to fiber orientation), transfers load between reinforcements, holds reinforcement together, leads impact resistance |
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| Particle Strengthening in Composites |
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Definition
| Resist slip, similar to precipitation hardening; particulate composites are also for hardening surfaces, creates wear resistance |
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| Four Stuctural types in polymers |
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Definition
| Single chain/linear, branched, cross linking and networked |
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Definition
| Continous or discontinous; discontinous leads to increased load tranfer in matrix |
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| Fiber information, why fibers? |
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Definition
| Larger defects cannot occur in fibers (too thin); Kl, Kcrit: Kl depends on on crack length, but with the small diameters of fibers, the crack length cannot become very large, meaning Kl will not grow; it is imposisble to have large flaws in the fibers, large flaws lead to low strength, so the composite will not have low strength |
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| Same as above, but also strong covalent bonds are aligned along axial direction to increase strength |
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Describe amount of force in either fibers or matrix
Vfib=(volume of fibers)/(volume of composite)
Vm=(volume of matrix)/(volume of composite)
Vfib+Vm=1 |
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| Short (non-continous) Fibers |
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Definition
| Fiber will never fail if too short since shear transfer will not develop a high tensile load |
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Definition
Fiber is just long enough that it could fail if the force in the composite is high
Ic=(Tensile Strength of fibers*diameter)/(2*Tau matrix/fiber bond) |
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| Carbon Fiber Manufacturing |
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Definition
| High temperature: 3000C-2500C-graphitizing, high modulus fibers; 1500C-2000C- carbonizing, high strength fibers |
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| Uniform, Galvanizing or two metals, crevice, pitting, intergranular, selective leaching, erosion, stress corrosion |
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Definition
| Occuring entire part at a uniform rate; results in the largest tonnage of corroded material compared to the other 7 forms; typically measure rates and therefore predict corrosion |
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| Galvanic or two steels Corrosion |
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Definition
| Consists of anode (loses material) and cathode (does not lose material); creates a current between that corrodes more anodic (negatively charged) metal |
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Definition
| Corrosion occuring small, protected areas; not easy to predict, can occur at accelerated rates; rates are hard to predict; cause by oxygen starvation, causing those regions to become anodic and corrode relative to cathodic regions exposed to air |
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Definition
| Occurs with liquid flow (i.e. pipes) where a defect can lead to oxygen starvation and corrosion in the same manner as crevice |
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| Attack is along grain boundaries; grains can fall out over time; atoms are more energetic at grain boundaries causing anodic behavior; ex: weld decay: slow cooling leads to formation of chromium carbide which depletes steel of Cr making it susceptible to this type of corrosion |
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| Corrosive environment attacks only certain elements in an alloy; ex: in brass, dezincification |
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Definition
| Erosion breaks away protective oxide layer, it reforms, broken away again, etc. |
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| Certain materials, when loaded in tension, can have the surface attacked and become brittle which causes cracks to form and grow; the cracks become anodic which causes local corrosion and the crack to grow and failure of the metal; high strenth aluminums are susceptible in salt water |
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