EBSD analysis of cyclic load effect on final misorientation distribution of post-mortem low alloy steel: A new method for fatigue crack tip driving force prediction

Abstract The effect of applied cyclic load, including the maximum plastic strain e max p and the plastic strain amplitude e a p on final misorientation level of post-mortem low alloy steel after low cycle fatigue (LCF) test, was analyzed by Electron Back-Scattered Diffraction (EBSD) in this research at first. Two misorientation parameters widely used in EBSD analysis, Kernel Average Misorientation ( KAM ) and Grain Reference Orientation Deviation ( GROD ), are compared in terms of accumulated plasticity characterization after LCF failure, where a bilinear function is found between final KAM and applied cyclic load e max p & e a p . Then the cyclic load effect on final misorientation distribution of post-mortem low alloy steel after fatigue crack propagation (FCP) test was further analyzed by EBSD based on the above bilinear function between final KAM and e max p & e a p , as well as the equivalent e ¯ max p & Δ e ¯ p distribution functions given by HRR field. −1/2 power law is established to describe final KAM distribution near crack path. The area S KAM between final KAM distribution curve and undeformed KAM 0 base line within a certain range, rather than S GROD , is proposed as a better measurement of fatigue crack tip driving force Δ K in constant load ratio R condition. Meanwhile, the influence of load ratio R on final misorientation distribution is also discussed.