High-Selectivity imaging of the closed fatigue crack due to thermal environment using surface-acoustic-wave phased array (SAW PA)

Crack closure can cause the underestimation or misdetection of fatigue cracks in ultrasonic testing (UT). Fatigue crack closure due to an environmental factor, i.e., high temperature, was found in eddy current testing (ECT), which is used to inspect the vicinity of surfaces. However, its effect and countermeasures have yet to be examined in UT. In this study, we examined the fatigue-crack closure induced by heat processing using a surface-acoustic wave phased array (SAW PA). SAW PA is a phased-array imaging method using Rayleigh waves, which can sensitively visualize defects in the vicinity of surfaces. As a result, the intensity of crack responses visualized by SAW PA markedly decreased after the heat processing of a fatigue-crack specimen. Furthermore, we demonstrated that the combination of SAW PA with a crack opening method, global preheating and local cooling (GPLC), and a load difference phased array (LDPA) is useful for the high-selectivity imaging of closed fatigue cracks. We also discussed a possible mechanism of the fatigue-crack closure induced by heat processing.

Automated summary

The study found that environmental factors such as high temperature can cause fatigue crack closure, affecting the results of ultrasonic or eddy current testing; By using surface-acoustic wave phased array (SAW PA) in combination with other methods, closed fatigue cracks can be effectively imaged.