Experimental study on ratcheting and softening behavior of stainless steel 304L thin-walled shells under cyclic pure bending load

In this research, softening and ratcheting behavior of SS304L thin-walled shells under cyclic pure bending load were investigated. Experimental tests were carried out by a servo-hydraulic INSTRON 8802 machine under force-control and displacement-control conditions and the effect of different parameters such as mean force, force amplitude, length of the shells existence and position of cutout were examined. Under displacement-control loading, softening behavior was observed and under force-control loading with non-zero mean force, accumulation of plastic deformation or ratcheting phenomena was occurred. Based on experimental results, linear relation was observed between plastic energy and rate of plastic deformation, which shows the rigidity of fixtures used in the experimental tests. It was observed that increase of the force amplitude accompanied with an increase in maximum force and plastic deformation, finally. Also, analyzing the existence of cutout, ratcheting displacement of cylindrical shells with cutout in the middle of shell is higher than that of the shell without cutout and crack propagation occurred in this area. Under displacement-control loading, reaction of thin-walled shells under cyclic pure bending load is divided into four areas, incubation, transition, steady-state and crack propagation.