The Hardening and Rate-Dependent Behavior of Fully Annealed AISI Type 304 Stainless Steel Under Biaxial In-Phase and Out-of-Phase Strain Cycling at Room Temperature

Abstract

Thin-walled tubes were subjected to fully reversed strain-controlled axial (A), torsional (T), in-phase (I) and out-of-phase (O) loading. A computer controlled MTS axial-torsion servocontrolled testing machine and strain measurement on the uniform section of the specimen were used in all tests. Each of four specimens was subjected to combinations of A, T, and I segments, of two hundred cycles each, followed by an O-segment. In between every segment, axial, and torsional check-tests were performed to obtain information on hardening and rate dependence. During cycling the normalized stress amplitude was observed to increase nearly threefold. Even if cyclic saturation was reached during a segment, a change in loading direction caused further hardening followed by subsequent softening which rapidly subsided. Only the O-segment showed hardening exclusively. After the A, T, and I segments, a “cross-effect” was observed which disappeared after the final O-segment. Compared to the considerable hardening, rate dependence as measured by relaxation and strain-rate change tests varied little during cycling.