Investigation of subsequent viscoplastic deformation of austenitic stainless steel subjected to cyclic preloading

Abstract

This paper investigates the effects of cyclic preloading on the subsequent viscoplastic deformation. A series of experiments such as the subsequent creep, subsequent stress relaxation, and cyclic loading with strain rate changes after cyclic preloading were conducted with Type 304 stainless steel at room temperature. The cyclic proportional and non-proportional loadings were conducted as cyclic preloadings.Tension-compression loading was chosen as the cyclic proportional loading, and circular and cruciform loading as the cyclic non-proportional loading. The experimental results showed that the subsequent deformation changes with the number of cycles of cyclic preloading. The differences in the subsequent deformation were examined by transmission electron microscopy (TEM). The observations suggest that changes in the dislocation structure depending on the number of cycles of cyclic preloading affect the subsequent viscoplastic deformation.

A constitutive model of cyclic viscoplasticity considering changes in subsequent viscoplastic deformation due to the evolution of dislocation structures

“…These results are similar to the results for Type 304 stainless steel in a previous paper (Mayama and Sasaki 2006). Both Type 304 and Type 304 stainless steels show qualitatively similar cyclic hardening and softening, the subsequent creep, the subsequent stress relaxation, and dislocation structural changes.…”

“…In other words, hardening and softening could depend on the loading conditions. A similar conclusion has been suggested elsewhere (El-Danaf et al 2001, Mayama andSasaki 2006). Thielen et al (1976) have conducted the strain controlled low cycle fatigue of a 4140 steel at room temperature.…”

“…Figs.10 (a) and (b) show the dislocation structures after 10 and 50 cycles of tension-compression cyclic loading. The dislocation structure after 10 cycles shows scattered dislocations and after 50 cycles there are dislocation cell structures similar to those in the previous paper (Mayama and Sasaki 2006). The subsequent creep and stress relaxation cannot be predicted from conventional phenomenological models because these macroscopic models assume that the amount of viscoplastic deformation depends on only the strain (or stress) rate.…”

“…From the TEM observations of dislocation structures in Fig.10 and the previous paper (Mayama and Sasaki 2006), it can be assumed that the flow stress is related to the density of a randomly increased number of scattered dislocations, which leads to the cyclic hardening and larger time-dependent deformations, and the viscous stress is related to the organization of dislocation structures, which leads to the cyclic softening and the decrease in time dependent deformation. The cyclic hardening and larger time-dependent deformation would appear to be contradictory phenomena.…”

“…Similarly, Mayama and Sasaki (2006) showed that dislocation structures are strikingly different during cyclic hardening and cyclic softening even when subjected to the similar stress-strain curves. Further, even when the stress-strain curves before the subsequent tests are very similar, the subsequent viscoplastic deformation such as creep and stress relaxation is different for different numbers of cycles of cyclic preloading.…”