Experimental study on ratchetting-fatigue interaction of SS304 stainless steel in uniaxial cyclic stressing

Abstract

The ratchetting behaviour and fatigue failure, as well as their interaction were investigated by uniaxial cyclic stressing tests for SS304 stainless steel at room temperature. The ratchetting strain and fatigue life of the material were measured in different loading levels. The effects of mean stress, stress amplitude and stress ratio on the ratchetting strain and final failure life were discussed. Simultaneously, the variations of responded strain amplitude with the number of cycles were illustrated to discuss the interaction of ratchetting behaviour and fatigue failure. The experimental results show that the ratchetting strain and fatigue life of the material depend greatly on mean stress, stress amplitude and stress ratio of uniaxial cyclic stressing, and two kinds of failure modes (i.e., ratchetting failure with obvious necking due to large ratchetting strain and fatigue failure due to low-cycle fatigue with nearly constant responded strain amplitude) take place respectively, depending on the stress level prescribed in the tests.

Introduction

Ratchetting, a cyclic accumulation of inelastic deformation, takes place in the components subjected to asymmetrical cyclic stressing if the applied stress is high enough (e.g., larger than the yield strength of the structure material). It is one of the important factors should be considered in design of such structure components. In the last two decades, uniaxial and multiaxial ratchetting behaviours were studied experimentally and theoretically by some researchers, as reviewed by Ohno [1], Bari and Hassan [2] and Abdel-Karim [3] and recently done by Chen et al. [4], [5], Kang [6], [7] and Kang et al. [8], [9], [10], [11], [12], [13], Feaugas and Gaudin [14], Mayama et al. [15], Vincent et al. [16], Abdel-Karim [17], Gupta et al. [18], Johansson et al. [19], Khoei and Jamali [20], Yaguchi and Takahashi [21], [22] and so on. The existing results showed that the ratchetting varies depending on the material type. Based on the Armstrong–Frederick non-linear kinematic hardening rule [23], many constitutive models have been constructed to simulate the uniaxial and multiaxial ratchetting. Examples of these models have been created by Chaboche and Nouailhas [24], Ohno and Wang [25], [26], Chaboche [27], Delobelle et al. [28], Jiang and Sehitoglu [29], Abdel-Karim and Ohno [30], Kang et al. [8], [9], [31], [32], Gao et al. [33], Vincent et al. [16], Yaguchi and Takahashi [22], Chen et al. [4], [5] and so on. However, the above-referred works were only focused on the ratchetting behaviour and its constitutive model. The effect of the ratchetting strain produced in cyclic stressing on the fatigue life, i.e., ratchetting-fatigue interaction was not involved. Since the ratchetting-fatigue interaction is very important in the design and assessment of structure components, it has been investigated by Rider et al. [34] and Xia et al. [35] for a low carbon steel En3, low alloy steel En19 and ASTM A-516 Gr. 70 steel, respectively, and some useful conclusions have been obtained. However, the existing experimental observations have shown that the ratchetting behaviour differs from various materials. It is necessary to examine the ratchetting-fatigue interaction of many other materials.

Therefore, in this work, the ratchetting behaviour and fatigue failure of SS304 stainless steel are tested under asymmetrical uniaxial cyclic stressing. First, the dependence of the ratchetting on mean stress, stress amplitude and stress ratio are observed, and then the fatigue lives of the material are investigated in various loading cases. Finally, the interaction between ratchetting and fatigue is discussed in detail. Some significant conclusions are obtained, which are useful to construct a failure model to predict the cyclic failure life of the material with the ratchetting concerned.