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67 Cards in this Set
- Front
- Back
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Anelastic (viscoelastic) material |
A material in which the total strain developed has elastic and viscous components. Part of the total strain recovers similar to elastic strain. Some part, though, recovers over a period of time. Examples of viscoelastic materials include polymer melts and many polymers including Silly Putty®. Typically, the term anelastic is used for metallic materials. |
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Apparent viscosity
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Viscosity obtained by dividing shear stress by the corresponding value of the shear-strain rate for that stress.
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Bend test
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Application of a force to a bar that is supported on each end to determine the resistance of the material to a static or slowly applied load. Typically used for brittle materials.
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Dilatant (shear thickening)
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Materials in which the apparent viscosity increases with increasing rate of shear.
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Ductile to brittle transition temperature (DBTT)
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The temperature below which a material behaves in a brittle manner in an impact test; it also depends on the strain rate.
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Ductility
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The ability of a material to be permanently deformed without breaking when a force is applied.
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Elastic deformation |
Deformation of the material that is recovered instantaneously when the applied load is removed.
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Elastic limit
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The magnitude of stress at which plastic deformation commences.
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Elastic strain
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Fully and instantaneously recoverable strain in a material.
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Elastomers
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Natural or synthetic plastics that are composed of molecules with spring-like coils that lead to large elastic deformations (e.g., natural rubber, silicones).
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Engineering strain
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Elongation per unit length calculated using the original dimensions.
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Engineering stress
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The applied load, or force, divided by the original area over which the load acts.
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Extensometer
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An instrument to measure change in length of a tensile specimen, thus allowing calculation of strain. An extensometer is often a clip that attaches to a sample and elastically deforms to measure the length change. |
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Flexural modulus
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The modulus of elasticity calculated from the results of a bend test; it is proportional to the slope of the stress-deflection curve.
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Flexural strength (modulus of rupture)
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The stress required to fracture a specimen in a bend test.
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Fracture toughness
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The resistance of a material to failure in the presence of a flaw.
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Glass-transition temperature (Tg)
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A temperature below which an otherwise ductile material behaves as if it is brittle. Usually, this temperature is not fixed and is affected by processing of the material.
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Hardness test
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Measures the resistance of a material to penetration by a sharp object. Common hardness tests include the Brinell test, Rockwell test, Knoop test, and Vickers test.
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Hooke’s law
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The linear-relationship between stress and strain in the elastic portion of the stress-strain curve.
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Impact energy
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The energy required to fracture a standard specimen when the load is applied suddenly.
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Impact loading
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Application of stress at a very high strain rate (~ >100 s^-1).
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Impact test
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Measures the ability of a material to absorb the sudden application of a load without breaking. The Charpy and Izod tests are commonly used impact tests.
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Impact toughness
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Energy absorbed by a material, usually notched, during fracture, under the conditions of the impact test.
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Kinematic viscosity
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Ratio of viscosity and density, often expressed in centiStokes. Load The force applied to a material during testing.
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Macrohardness
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Bulk hardness of materials measured using loads > 2 N.
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Materials processing
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Manufacturing or fabrication methods used for shaping of materials (e.g., extrusion, forging).
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Microhardness
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Hardness of materials typically measured using loads less than 2 N with a test such as the Knoop (HK).
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Modulus of elasticity (E)
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Young’s modulus, or the slope of the linear part of the stress–strain curve in the elastic region. It is a measure of the stiffness of the bonds of a material and is not strongly dependent upon microstructure.
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Modulus of resilience (Er)
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The maximum elastic energy absorbed by a material when a load is applied.
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Nanoindentation
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Hardness testing performed at the nanometer length scale. The imposed load and displacement are measured with micro-Newton and sub-nanometer resolution, respectively.
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Necking
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Local deformation causing a reduction in the cross-sectional area of a tensile specimen. Many ductile materials show this behavior. The engineering stress begins to decrease at the onset of necking.
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Newtonian
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Materials in which the shear stress and shear strain rate are linearly related (e.g., light oil or water).
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Non-Newtonian
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Materials in which the shear stress and shear strain rate are not linearly related; these materials are shear thinning or shear thickening (e.g., polymer melts, slurries, paints, etc.).
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Notch sensitivity
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Measures the effect of a notch, scratch, or other imperfection on a material’s properties such as toughness or fatigue life.
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Offset strain value
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A value of strain (e.g., 0.002) used to obtain the offset yield stress.
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Offset yield strength
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A stress value obtained graphically that describes the stress that gives no more than a specified amount of plastic deformation. Most useful for designing components. Also, simply stated as the yield strength.
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Percent elongation
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The total percentage permanent increase in the length of a specimen due to a tensile test.
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Percent reduction in area
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The total percentage permanent decrease in the cross-sectional area of a specimen due to a tensile test. |
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Plastic deformation or strain
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Permanent deformation of a material when a load is applied, then removed.
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Poisson’s ratio
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The negative of the ratio between the lateral and longitudinal strains in the elastic region.
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Proportional limit
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A level of stress above which the relationship between stress and strain is not linear.
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Pseudoplastics (shear thinning)
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Materials in which the apparent viscosity decreases with increasing rate of shear.
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Rheopectic behavior
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Materials that show shear thickening and also an apparent viscosity that at a constant rate of shear increases with time.
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Shear modulus (G)
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The slope of the linear part of the shear stress-shear strain curve.
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Shear-strain rate
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Time derivative of shear strain. See “Strain rate.”
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Shear thickening (dilatant)
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Materials in which the apparent viscosity increases with increasing rate of shear.
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Shear thinning (pseudoplastics)
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Materials in which the apparent viscosity decreases with increasing rate of shear.
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Stiffness
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A measure of a material’s resistance to elastic deformation. Stiffness is the slope of a load-displacement curve and is proportional to the elastic modulus. Stiffness depends on the geometry of the component under consideration, whereas the elastic or Young’s modulus is a materials property. The inverse of stiffness is known as compliance.
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Strain
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Elongation per unit length.
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Strain gage
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A device used for measuring strain. A strain gage typically consists of a fine wire embedded in a polymer matrix. The strain gage is bonded to the test specimen and deforms as the specimen deforms. As the wire in the strain gage deforms, its resistance changes. The resistance change is directly proportional to the strain.
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Strain rate
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The rate at which strain develops in or is applied to a material indicated; it is represented by or for tensile and shear-strain rates, respectively. Strain rate can have an effect on whether a material behaves in a ductile or brittle fashion.
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Stress
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Force per unit area over which the force is acting.
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Stress relaxation
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Decrease in stress for a material held under constant strain as a function of time, which is observed in viscoelastic materials. Stress relaxation is different from time dependent recovery of strain.
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Tensile strength
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The stress that corresponds to the maximum load in a tensile test.
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Tensile test
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Measures the response of a material to a slowly applied uniaxial force. The yield strength, tensile strength, modulus of elasticity, and ductility are obtained.
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Tensile toughness
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The area under the true stress–true strain tensile test curve. It is a measure of the energy required to cause fracture under tensile test conditions.
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Thixotropic behavior
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Materials that show shear thinning and also an apparent viscosity that at a constant rate of shear decreases with time.
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True strain
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Elongation per unit length calculated using the instantaneous dimensions.
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True stress
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The load divided by the instantaneous area over which the load acts.
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Ultimate tensile strength (UTS)
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See Tensile strength.
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Viscoelastic (or anelastic) material
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See Anelastic material.
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Viscosity ()
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Measure of the resistance to flow, defined as the ratio of shear stress to shear strain rate (units Poise or Pa-s).
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Viscous material
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A viscous material is one in which the strain develops over a period of time and the material does not return to its original shape after the stress is removed.
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Work of fracture
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Area under the stress–strain curve, considered as a measure of tensile toughness.
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Yield point phenomenon
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An abrupt transition, seen in some materials, from elastic deformation to plastic flow.
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Yield strength
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A stress value obtained graphically that describes no more than a specified amount of deformation (usually 0.002). Also known as the offset yield strength.
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Young’s modulus (E)
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The slope of the linear part of the stress–strain curve in the elastic region, same as modulus of elasticity. |
