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.kaliboat.com/product-category/freezers-refrigeratorsundercounter-refrigerators-food-servicerefrigeration-equipmentcommercial-freezers/