Nondestructive evaluation of spall damage evolution under cumulative impacts

Evolution of spall damage of pure iron under cumulative impacts was evaluated nondestructively with a low frequency scanning acoustic microscope as well as ultrasonic wave velocity, attenuation (amplitude ratio of B2 to B1 echo), backscattering intensity and amplitude spectrum of reflected wave. The spall damage distribution within the target plates were visualized by the C-scan images. When the impact stress is greater than the spall threshold stress, the spall damage increased with an increase in impact stress. In ultrasonic measurement, higher impact stress gives the lower sound velocity and amplitude ratio and the increased backscattering intensity, whereas the significant attenuation in the high frequency component of the reflected wave. These ultrasonic measurement on the spall damage under cumulative impacts shows that the minute cracks once generated have increased by the successive impact of which stress is higher or lower than the previous impact stress. Thus, these ultrasonic methods are useful to evaluate nondestructively the spall damage evolution under cumulative impact.