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

• Published in: Ultrasonics 2022-02, Vol.119, p.106629-106629, Article 106629
• Main Authors: Ohara, Yoshikazu, Oshiumi, Taro, Wu, Xiaoyang, Uchimoto, Tetsuya, Takagi, Toshiyuki, Tsuji, Toshihiro, Mihara, Tsuyoshi
• Format: Article
• Language: English
• Subjects: Crack closure; Fatigue crack; Phased array; Surface acoustic waves; Thermal environment; Thermal stress
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2021.106629

•Surface-acoustic-wave phased-array imaging of the closed fatigue crack due to thermal environment.•Fatigue-crack closure induced by high-temperature exposure.•Phased-array imaging combined with a crack opening method of using cooling sprays.•High-selectivity imaging of closed cracks in the vicinity of surfaces. 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.