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238 Part II Ultimate Strength
where Ho ' and H' can be expressed as follow,
EH; . EH'
H=- Ho=-
E-H, I , E+H'
As shown in Figure A.3, when the stress is beyond the yield point of material, plastic strain
occurs; if the load is released after point B, and a compressive load is applied, the relationship
between stress and strain will follow curve BCD, and the material yields at a compressive
stress (point C) that is lower than its initial yield stress. This phenomenon is called
Bauschinger's effect.
&
do
H O X
Yield position
B'
E
Figure A.1 Stress and Strain Diagram
Figure A.2 Curve of Strain Hardening
Although there is a one-to-one correspondence between stress and strain in the elastic region
as described by Hook's law, this correlation does not exist in the plastic region. This means
