Characterization of cyclic plastic bending of austenitic AISI 304 stainless steel

Abstract

Steels used in chemical, nuclear and power industries are usually subjected to repeated loads that may induce significant inelastic deformations. Successful assessment of a component life places a great demand on understanding of material behaviour under strain histories involving cyclic plasticity under bending conditions.This work is concerned with an experimental study of low-cycle fatigue behaviour under both load and deflection controlled conditions. The tests were conducted on AISI 304 stainless steels with the objective of determining strain cycling properties under cyclic plastic bending. These properties are characterized by the cyclic stress-strain hysteresis responses obtained.The cyclic bending plasticity behaviour is investigated for beams with circular cross-section at two conditions of the material, under constant strain and under constant stress. Hysteresis loops for five different strain ranges of ±0.4%, ±0.82%, ±1.1%, ±1.33% and ±1.55% were obtained and also for different stress ranges of 730, 800, 870 and 940 MPa. The material exhibits cyclic hardening in its virgin state, the rate of hardening is very rapid at first but diminishes quickly as the stabilized condition is approached. The cyclic hardening for the constant strain condition is higher than the constant load condition.The results also confirm the applicability of the reference stress method for predicting the cyclic moment-curvature curve for beams with circular cross-sections. The observed strain values are higher in the lower strain range and lower in the higher strain. However, the correlation obtained is considered quite satisfactory in view of the nonlinearity of the problem.