Abstract
In order to analyze the crack closure of a fatigue crack, nonlinear ultrasound is applied. In introduction of fatigue crack we develop the crack opening monitoring procedures using TOFD method to obtain the reliable result about the relation between crack opening displacement and nonlinear ultrasound. Longitudinal ultrasonic wave of 6.4MHz in frequency with large amplitude incident to three point bending aluminum alloy specimen. Normal probe and angle probe are fabricated for nonlinear ultrasound measurement. As the results, in addition to secondary superharmonics of 12.8 MHz in frequency, especially in angle probe measurement, remarkable subharmonics of 3.2MHz in frequency was observed. Mechanism of subharmonics was also investigated.
