ENGR 240 - 10.3.07

ENGR 240 - 10.3.07 - ENGR 240 October 3, 2007 Stress,...

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ENGR 240 – October 3, 2007 Stress, Strain, & Modulus o Three regions of deformation Linear elastic region (LER) Will completely regain its form when the load is released i.e. rubber band like Uniform Plastic Deformation (UPD) Permanent/not recoverable deformation Occurs because atoms break bonds and form new ones with other atoms Uniform deformation in reduced section of the specimen – no localized deformation A 1 1 = A 2 2 Non-uniform plastic deformation (NUPD) Localized deformation “necking” Volume is not held constant o (Ultimate) Tensile Strength maximum stress that is achieved by a sample in the stress-strain curve material is useless at this point not as important as yield strength o True Stress (σ T ) A true stress-true strain curve should not decrease in strength at a certain point The only reason it decreases on a engineering stress-strain curve is because you are calculating from original area σ T = F/A = (Force)/(actual cross-sectional area)
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