Ultrasonic back reflection evaluation of crack growth from PSBs in low-cycle fatigue of stainless steel under constant load amplitude

The objective of this study is to develop a method for evaluating crack growth from persistent slip bands (PSBs) in low-cycle fatigue of stainless steel, using an ultrasonic back reflection wave during the early stages of its fatigue life. Changes in the back reflection intensity from surface of the material under cyclic loading are measured. Back reflection intensity decreased due to the evolution of PSBs before the start of fatigue crack growth from the crack initiated along PSBs with increase in the number of cyclic loads. The average dislocation density in a grain including PSBs corresponds to the attenuation change measured during the fatigue test, from the initial state to the nucleation and growth of the fatigue crack. The attenuation is caused by the movement of dislocation due to ultrasonic waves, whose mechanism was considered quantitatively. In this study, micromechanical modeling was conducted as a prediction method for remaining fatigue life to start crack growth from PSBs based on the changes in ultrasonic back reflection intensity.