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29 Cards in this Set
- Front
- Back
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What is stress?
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-resistance of material to deformation
-generally a reaction force created within a structure in response to an applied load |
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What is strain?
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-deformation that occurs in a material in response to load
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What is load?
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-application of a force, moment or combination to test a material
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What is compression?
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-occurs with equal and opposite loads applied toward a structure causing shortening and widening
-causes compression stresses to occur within the tissue |
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What is tension?
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-equal and opposite loads applied away from a structure causing narrowing and lengthening
-causes tensile stress within |
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What is shearing?
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-opposing loads are applied parallel to the surface of a structure, resulting in internal angular deformation
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What is torsion?
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-opposing loads are applied causing a structure to twist about an internal axis
-causes a combination of compression, torsion and shear stresses |
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Describe bending.
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-combination of 3 or more loads are applied causing bending about an external axis
-compression occurs with concavity -tension occurs with convexity |
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What are the typical characteristics of the Stress-Strain Curve?
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-toe region
-elastic region -elastic limit (yield) -plastic region -ultimate stress -necking -failure point |
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What is the toe region?
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-represents settling of the structure being tested
-taking up the slack |
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What is the elastic region?
(Also Hooke's Law) |
-stress in a material is directly proportional to the strain
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What is the modulus of elasticity? (Young's modulus)
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-the slope of the elastic region
-measure of the stiffness of a material |
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What is the elastic limit?
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-the end of the elastic region marking a critical juncture for the structure
-begins to undergo damage -also known as YIELD POINT |
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What is the plastic region?
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-elastic limit exceeded, tissue begins to lengthen at a rate disproportionate to the stress
-usually permanent deformation of the tissue |
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What is biological memory?
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-permits biological tissues to slowly contract back to original length
-signifies importance of home stretching program |
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What is the ultimate stress?
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-stress-strain curve peak
-maximum load a tissue can tolerate before failure |
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What is necking?
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-rapid narrowing of tissues under tension
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Describe the process of necking.
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-immediately following ultimate stress, tissue begins to fail
-initial microfailure occurs as strain increases, which causes narrowing of tissue under tension |
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What is the failure point?
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-sudden decrease in stress while strain continues to rise
-substance of the material has begun to fail -bundles may fail 1 at a time |
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What is pre-yield testing?
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-stressing a tissue below the elastic limit
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What is hysteresis?
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-difference in stress between loading and unloading
-the area under the curve -represents energy lost, usually in the form of heat |
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What is pre-failure testing? What is its significance?
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-test is taken beyond the elastic limit, short of failure
-results in permanent elongation of the structure |
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What is fatigue testing?
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-cyclic loading of a structure at pre-yield level
-may produce plastic deformation |
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What are the determinants of fatigue?
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-magnitude of applied loads
-number of repetitions |
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What is the significance of rate of loading in a biological structure?
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-because bio structures can adapt and heal they can counteract cumulative effects of repeated loading
-LOW RATE = possible repair and strengthen -HIGH RATE = less time for adaptation and fatigue failure may occur |
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What is the effect of speed of loading?
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-stiffness increases with loading rate, failure occurs at higher stresses and lower strains
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What is the effect of temperature on tissues?
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-less stiff at higher temperatures, resulting in failure at higher strain and lower stress
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What is creep?
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-progressive deformation of a structure under a constant load
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What is stress relaxation?
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-decrease in stress of a structure in presence of a constant strain
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