Transient and Stable Deformation Behavior Under Cyclic Nonproportional Loading

Abstract

The transient hardening behavior of metals subjected to nonproportional cyclic loading, including the corresponding cyclically stable state, is dependent on plastic strain range in addition to the “degree” of nonproportionality. Experiments were performed on thin-walled tubular specimens of stainless steel 304 in combined tension-compression and torsion to investigate sequence effects, memory of prior loading, and rate changes of cyclic hardening under complex, nonproportional, strain-controlled cyclic loading. The material was observed to remember cyclic hardening achieved under the most severe nonproportional loading case. Effective stress states achieved by cycling at increasingly severe nonproportionality of loading increased correspondingly and tended to “wash out” the effects of less severe nonproportional paths. For several complex nonproportional paths, the actual intermediate cyclically stable (or near stable) effective stress states were correlated accurately using a path-dependent integral. Only uniaxial and 90° out-of-phase sinusoidal test results are required by this integral representation.