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MEE 312 Test 2 Cards
| Term | Definition |
|---|---|
| extensometer | a device used for measuring change in length of sample to determine strain |
| carburization | a heat treatment of steels to harden the surface using a gaseous source of carbon; the carbon diffusing into the surface makes the surface harder and more abrasion resistant |
| annealing | a heat treatment that typically involves heating a metallic material to a high temperature for an extended period of time conducted with a view to lower the dislocation density and hence impart ductility |
| sintering | a high temperature treatment used to join small particles, diffusion eventually fills in an remaining voids, the driving force is a reduction in the total surface area of the powder particles |
| stress relief anneal | a low temperature annealing heat treatment designed to eliminate residual stresses introduced during deformation without reducing the strength of a col worked material |
| anelastic/viscoelastic | a material in which the total strain developed has elastic and viscous components |
| Frank-Read Source | a pinned dislocation that, under an applied stress, produces additional dislocations. This mechanism is at least partly responsible for strain hardening |
| fibertexture | a preferred orientation of grains obtained during the wire drawing process (and other cold working processes); causes anisotropic behavior |
| shot peening | a process in which metal spheres are shot at the component which leads to residual compressive stresses at the surface of the component to help improve fatigue life |
| columnar zone | a region of elongated grains having a preferred orientation that forms as a result of competitive growth during solidification of a casting |
| equiaxed zone | A region of randomly orientated grains in the center of a casting produced as a result of widespread nucleation |
| polyganized subgrain structure | a subgrain structure produced in the early stages of annealing, a network of dislocations rearranged during heating |
| diffusion coefficient | a temperature dependent coefficient related to the rate at which atoms, ions or other species diffuse; depends on temperature, the composition and the microstructure of the host material and also the concentration of diffusing species |
| creep | a time dependent, permanent deformation at high temperatures, occurring at constant load or constant stress |
| bend test | application of a force to the center of a bar that is supported on each end to determine the resistance of the material to a static or slowly applied load, used a lot for brittle materials |
| hot working | deformation of a material above the recrystallization temperature; changes only shape, strength remains relatively unchanged |
| elastic deformation | deformation of a material that is recovered instantaneously when the applied load is removed |
| volume diffusion | diffusion of atoms through the interior of grains |
| interstitial diffusion | diffusion of small atoms from one interstitial position to another in the crystal structure |
| surface diffusion | diffusion of the atoms along surfaces such as cracks or particle surfaces |
| impact energy | energy absorbed by a material, usually notched during fracture under the conditions of an impact test |
| necking | local deformation causing a reduction in the cross sectional area of tensile specimen, many ductile materials show this behavior, the engineering stress begins to decrease at the onset of this |
| hardness test | measures the resistance of a material through penetration of a sharp object, includes Rockwell, Brinell, Vickers, and Knoop |
| climb | movement of dislocations perpendicular to slip plane by diffusion of atoms to or from the dislocation line |
| macrohardness | overall bulk hardness of materials measured using loads greater than 2 Newtons, leaves a visible indention on the material |
| striations | patterns seen on fractured surface of a fatigued sample, (very fine marks) |
| Young's modulus of elasticity | slope of the linear part of the stress-strain curve in the elastic region; measure of the stiffness of a material, depends upon strength of interatomic bonds and composition, not strongly dependent on microstructure |
| residual stresses | stresses introduced in a material during processing, can originate as a result of cold working |
| inoculation | the addition of hetergeneous nuclei in a controlled manner to increase the number of grains in a casting |
| activation energy | the energy required to cause a particular reaction to occur, in diffusion related to energy required to move an atom from one lattice site to another |
| Fick's First Law | the equation relating the flux of atoms by diffusion coefficient and the concentration gradient |
| latent heat of fusion | the heat evolved when a liquid solidifies, is related to the energy difference between the solid and the liquid |
| critical radius | the minimum size that must be formed by atoms clustering together in the liquid before the solid particle is stable and begins to grow |
| fatigue life | the number of cycles permitted at a particular stress before the material fails by fatigue |
| self diffusion | the random movement of atoms with an essentially pure material, no net change in composition results |
| fracture toughness | the resistance of a material to failure in the presence of a flaw |
| modulus of rupture | the stress required to fracture a specimen in a bend test |
| DBTT | the temperature below which a material behaves in a brittle manner in an impact test |
| percent elongation | the total percentage increase in the length of a specimen during a tensile test |
| dendrite | the treelike structure of the solid that grows when an undercooled liquid solidifies |
| undercooled | when a liquid is below the equilibrium freezing temperature |
| characteristics of a ductile fracture | a cup cone type failure with a dimpled surface and necking |
| hot working characteristic | has a relatively rough surface finish |
| homogeneous nucleation requires what during solidification | undercooling |
| impact loading | materials are subject to high strain rates |
| anisotropic properties | the properties resulting during plastic deformation in cold working grains. the grains rotate, causing certain crystallographic directions and planes to become aligned with the direction in which stress is applied |
| increase in the number of line defects | the microstructural mechanism for strain hardening metals |
| vacancy diffusion is strongly dependent on what? | temperature |
| electrical conductivity improves | not a characteristic of cold working |
| the microstructural mechanism for strain hardening polymers | stretching and aligning polymer chains |
| macrohardness (types of tests) | Rockwell and Brinell |
| fatigue testing measures the material's resistance to what? | cyclic loading |
| Why is understanding diffusion important? | anything that affects diffusion will also affect material processing |
| fastest mechanism of diffusion | vacancy |
| type of atom for which diffusion would occur fastest | BCC |
| fast type of diffusion | surface |
| mechanism most greatly affected by temperature | vacancy |
| factors that affect diffusion | temperature, mechanism and type of diffusion, crystal structure, bond type, and time |
| diffusion | net flux of atoms, ions, or other species caused by temp and concentration gradients |
| diffusion couple | combination of elements involved in diffusion studies |
| volume diffusion | diffusion of atoms through the interior of grains |
| vacancy diffusion | diffusion of atoms when an atoms leaves a regular lattice position to fill a vacancy in the crystal. |
| elastic strain | fully and instanteously recoverable strain in a material |
| engineering stress | applied load, or force, divided by the original cross section area of the material |
| engineering strain | amount that a material deforms per unit length in a tensile test |
| fracture toughness | the resistance of a material to failure in the presence of a flaw |
| impact toughness | energy absorbed during fracture under the conditions of an impact test |
| modulus of resilience | max elastic energy absorbed by a material when a load is applied |
| offset strain value | a value of strain (0.002) used to obtain the offset yield stress value |
| offset yield strenght | stress value that describes the stress that gives no more than a specified amount of plastic deformation |
| percent reduction in area | total percentage decrease in the cross section area of a specimen during the tensile test |
| stiffness | qualitative measure of the elastic deformation produced in a material |
| strain gage | device used for measuring change in length and therefore strain |
| tensile strength | stress that corresponds to the max load in a tensile test |
| endurance limit | defines a stress below which a material will not fail in a fatigue test |
| fracture toughness | the resistance of a material to failure in the presence of a flaw |
| toughness | qualitative measure of the energy required to cause fracture of a material |
| cold working | deformation of a material below the recrystallization temp. number of dislocations increase, causing the metal to be strengthened while changing its shape |
| drawing | material is PULLED through an opening in a die |
| extrusion | material is PUSHED through an opening in a die |
| recovery | low temp annealing, eliminates residual stresses introduced during deformation without reducing strength of the cold-worked material. also called stress-relief anneal |
| recrystallization | med-temp annealing heat treatment designed to eliminate all of the effects of strain hardening produced during cold working |
| strain hardening | strengthening of a material by increasing number of dislocations by deformation, or cold working. |
| embryo | tiny particle of solid that forms from the liquid as atoms cluster together |
| grain refinement | addition of heterogeneous nuclei in a controlled manner to increase the number of grains in a casting |
| heterogeneous | formation of a critically sized solid from the liquid on an impurity surface |
| homogeneous | formation of a critically sized solid form the liquid by the clustering together of a large number of atoms at high undercooling |
| lamellar | plate-like arrangement of crystals within a material |
| local solidification time | time required for a particular location in a casting to solidify once nucleation has begun |
| nucleation | the physical process by which a new phase is produced in a material |
| nuclei | tiny particles of solid that form from the liquid as atoms cluster together |
| planar growth | growth of a smooth solid-liquid inerface during solidification, no undercooling |
| recalescence | increase in temperature of an undercooled liquid metal as a result of the liberation of heat during solidification |
| superheat | pouring temp minus freezing temp |
| thermal arrest | plateau on the cooling curve. |
| total solidification time | time required for the casting to solidify completely after the casting has been poured |
| undercooling | temp to which liquid metal must cool below the equil freezing temp before nucleation occurs |
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