Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting

: Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ratcheting, they often fail when validated with experimental data collected under a wide array of loading conditions. In this study, an experimental setup was developed and an autonomous testing procedure was used to experimentally analyze the evolution of the yield surface shape due to cyclic biaxial loading. Thin-walled tubular test specimens were made of 304L steel with a diameter of 40 mm and underwent axial-torsional testing using the Instron 8852 system. The total axial strain was increased from 0 to 1% while the total shear strain underwent 5 cycles with the strain amplitude of 0.5% and the mean strain of 0.5%. Three yield surfaces were measured after the straining sequence was completed. Results showed strong directional distortional hardening and good agreement between the flow vectors and the normals to the yield surface, lending support to the associative flow rule.