Metals which are widely used in many types of industries are usually subjected to fatigue and surface corrosion. There is a demand to detect the surface damage caused by fatigue and corrosion at an early stage to ensure the structural integrity. In this paper. a novel nonlinear ultrasonic technique based on the measure of third-order combined harmonic generation. https://www.roneverhart.com/10mm-Male-GRAV-Angled-Quartz-Banger-45/