ENGR 240 – October 3, 2007Stress, Strain, & ModulusoThree regions of deformationLinear elastic region (LER)•Will completely regain its form when the load is released•i.e. rubber band likeUniform 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•A1ℓ1= A2ℓ2Non-uniform plastic deformation (NUPD)•Localized deformation “necking”•Volume is not held constanto(Ultimate) Tensile Strengthmaximum stress that is achieved by a sample in the stress-strain curvematerial is useless at this pointnot as important as yield strengthoTrue Stress (σT)A true stress-true strain curve should not decrease in strength at a certain pointThe only reason it decreases on a engineering stress-strain curve is because you are calculating from original areaσT= F/A = (Force)/(actual cross-sectional area)
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