On the applicability of a damage mechanics based model for stress controlled very low cycle fatigue

Study of the Very Low Cycle Fatigue (VLCF) behavior of materials assumes importance in the context of design of structures that are subjected to extreme loading conditions such as rocket components, earthquakes and accidents. During VLCF, large plastic strains are encountered and the number of cycles to failure is in the range of less than 100. In general, models based on damage mechanics approaches mimic closely the physical phenomena that occur during VLCF and, therefore, are very good candidates suitable for life prediction under such circumstances. In the present study, a simple damage mechanics model based on an earlier proposed model, is considered for the description of stress controlled VLCF. In this model, the life of a material undergoing VLCF is expressed in terms of the maximum stress and the plastic strain. At present, the capability is limited to uniaxial loading but can be extended to multiaxial loading with due modifications. For the numerical validation of the model, uniaxial stress controlled very low cycle fatigue tests have been carried out on commercial steel and mild steel at different stress levels. It is shown that the life predicted by the present model is in close agreement with the experimental results.