Study of Strain Ratio effects on Low Cycle Fatigue (LCF) Behavior of Dual Phase (DP) Steel

This paper aims at investigating the effect of strain ratio on LCF behavior of dual phase (DP) steel at room temperature. LCF tests are generally performed at strain ratio of -1. In real life scenarios, cyclic loading does not usually correspond to fully reversed condition due to operational circumstances such as preload, duty cycle, vibrations or the environmental effects. Therefore, it becomes necessary to investigate the fatigue properties and LCF behavior for un-symmetric loading conditions as well. Dual Phase (DP) steels are extensively used in automotive industries owing to its large energy absorption capacity in the event of crash. Hence, evaluation of their LCF behavior becomes crucial. In this study, tests are carried out under strain-controlled conditions at two different strain ratios (-1 and 0.1) to investigate the LCF and mean stress relaxation behavior of a DP steel. Fractured surfaces of failed specimens are investigated under SEM to investigate its crack nucleation and propagation sites and to determine its failure mechanism. A correlation is established between fatigue properties at two strain ratios which can be extended for other grades of dual phase steels.