Low cycle fatigue performance of DP600 steel under various pre-straining paths

Abstract

The present work concerns the assessment of low cycle fatigue performance of dual phase steel subjected to change in uniaxial pre-strain path. An uniaxial pre-strain of 12.5% in the rolling or transverse direction were imposed on the dual phase steel blanks, thereafter fully reversed strain controlled fatigue tests were conducted parallel or orthogonal to the initial pre-straining direction. As received specimens depict mild cyclic hardening in the initial cycles followed by gradual cyclic softening until failure. However, all pre-strained materials exhibit continuous cyclic softening with higher magnitude and rate throughout the life as compared to the as received specimen. Relaxation of mean stresses were observed for the fatigue tests with pre-straining. Rotation of principal axis due to orthogonal reloading (i.e. low cycle fatigue) after initial pre-straining introduces non-proportionality, thereby leading to significant reduction of fatigue lives. In-grain misorientation and lattice rotation analyses are noticed during electron backscattered diffraction investigation, and which is due to the non-proportional loading effect.