Visualization of Ultrasound Propagation in the Glass with a Crack Possessing Residual Inner Stress

Abstract

The detection of cracks in a solid is an important issue of ultrasonic nondestructive testing. Cracks can be broadly categorized as an opened crack or a closed crack. Although an opened crack is detectable using the conventional pulse-echo method, a closed crack with a width of several nanometers may not be detected because the ultrasound transmits through the crack [1-2]. Higher harmonic detection techniques such as Contact Acoustic Nonlinearity (CAN) [3-5] have been developed to locate closed cracks or local plastic deformations in the material [6], but these methods cannot fully identify the behavior of the ultrasonic wave around the defects. Photoelastic method is the representative method to visualize the stress or ultrasonic wave propagation in the transparent material. Many previous studies [7-11], however, have not detailed with the wave propagation around the closed crack, especially tip of crack in the sample. In this paper, the visualization of ultrasonic wave around a crack which changes from opening condition to the closed one in a glass sample is carried out by the strobo-photoelastic method to explore the propagation properties of ultrasonic wave. The effect of the residual stress in the sample around the closed crack and their tip is also described. Possibility of pilot tool as the quantitative measurement system is also explored.