If a long metal rod is pulled in a testing machine, the normal stress in the direction of the applied load (σ) may be plotted against the normal strain in the direction of the elongation (ɛ) as shown in Fig. 9.1, in which OA * denotes the elastic range, AB the ideal plastic range, BD the nonlinear work-hardening range, and DE ‘necking’ range. There is a small unstable region A * A, but it will be ignored in this study, since no well accepted theories have been proposed as yet for unstable materials. In the ideal plastic range AB, the strain e increases while the stress c remains constant. There is a nonlinear rise of the curve beyond the point B until the ultimate load at the point D.
KeywordsYield Function Yield Surface Flow Rule Kinematic Hardening Plastic State
Unable to display preview. Download preview PDF.