Abstract
Nonlinear ultrasound in the solid is expected as the promising tool for evaluating a crack which is difficult to evaluate with the linear ultrasound. We developed a procedure to introduce closed fatigue crack and controlled a crack closure accurately using tensile load during nonlinear ultrasonic testing. Transmitted echoes through the crack were analyzed with FFT varying the applied tensile load and the amplitude of incident ultrasound. As the results, especially in the case of oblique incidence, the strong subharmonic wave found to be appeared in addition to the superharmonics. Details of the subharmonic wave behaviors due to a crack closure were investigated and the mechanism of the subharmonic wave also discussed. Amplitude of the peak frequency of the subharmonic wave found to be a tool for monitoring the crack closure.
