Study on the multi‐scale online fatigue crack deformation and growth behaviors under overload in Q&P steel

Abstract

AbstractThe multi‐scale online fatigue crack deformation and growth behaviors under single overload (SOL) and periodic overload (POL) case in Quenching and Partitioning (Q&P) steel were studied using two micro cameras and sub‐image stitching and matching digital image correlation (DIC) method. Firstly, the microscopic crack tip speckle images and crack images on both sides of the compact tension (CT) specimen during the fatigue crack growth (FCG) process were collected under different overload parameters. Then, the FCG overload retardation, crack tip closing and blunting behaviors, and the crack tip strain distribution and evolution, overload retardation mechanism were analyzed. In addition, the corresponding multi‐scale FCG morphological characteristics and material microstructure under overload case were observed. The results indicate that the overload ratio and interval affect the overload retardation effect of Q&P steel seriously; the overload crack tip blunting and plastic zone are the major factors inducing the overload retardation effect in Q&P steel.