Role of Stacking Fault Energy on Symmetric and Asymmetric Cyclic Deformation Behavior of FCC Metals

The present investigation is aimed towards an understanding on cyclic deformation behavior of two FCC metals having different stacking fault energy (SFE); annealed copper and annealed aluminium. Symmetric cyclic loading tests under strain-control mode have been conducted over strain amplitude from 0.2 to 1.0 pct until complete failure of the specimens. Asymmetric cyclic loading tests under stress-control mode, i.e. ratcheting tests, have also been conducted with various combinations of mean stress and stress amplitude till complete failure of the specimen. During symmetric cyclic loading, cyclic hardening response is followed by a stress saturation stage for both FCC metals. Whereas in case of copper, this saturation stage continues till failure, a secondary hardening stage appears at the end of stress saturation stage and continues till complete failure in case of aluminium. Such difference in cyclic hardening phenomenon of two different FCC metals is linked with the different values of SFEs. Asymmetric cyclic loading under stress-control mode results in continuous elongation of specimen in the direction of mean stress for both FCC metals. However, in case of aluminium such accumulation of inelastic strain ceases due to plastic shakedown after certain amount of ratcheting strain during asymmetric cyclic loading with stress combinations having maximum stress of 80 MPa or lower.