Shallow surface microcracks in metals can directly affect the performance and service life of metals,and nonlinear ultrasonic detection methods have shown excellent results for detecting shallow surface defects.This paper studies the nonlinear ultrasonic laws of crack d...MORE Shallow surface microcracks in metals can directly affect the performance and service life of metals,and nonlinear ultrasonic detection methods have shown excellent results for detecting shallow surface defects.This paper studies the nonlinear ultrasonic laws of crack det...