Abstract: Early stage of plasticity and fatigue damage are difficult to detect by using conventional ultrasonic techniques. Nonlinear ultrasonic technique based on harmonic generation has been shown to have the ability to solve the question. A nonlinear ultrasonic high power transmission testing system is developed to detect early-stage plasticity and fatigue damage of Aluminum 2024-T4 alloy. During the test, the nonlinear parameter of the material based on the amplitude of second harmonic is monotonically correlated with the plasticity and fatigue damage of the samples. The experimental nonlinearities are successfully reduced by using the natural filter effect of piezo-electric discs, which makes the experimental method more robust. The experimental results show that the nonlinear ultrasonic technique based on harmonic generation can be used to detect early-stage plasticity and fatigue damage of aluminum alloy.

Key words: Fatigue damage, Nondestructive evaluation, Nonlinear ultrasonic, Plasticity