The analysis of fracture stress using reflection coefficient of surface acoustic wave

탄성표면파의 반사계수를 이용한 파괴응력의 해석

In this study, the analysis technique of fracture stress using the reflection coefficient of SAW reflected from a brittle solid with surface crack has been studied. Fracture stress of brittle solid with surface crack has been obtained by the function of the critical stress intensity factor and the maximum normalized stress intensity factor of the crack in the body. And the maximum normalized stress intensity factor of a surface crack can be inferred from a measurement of reflection coefficient of SAW. In experiment, the surface cracks ranging from 0.5mm to 0.9mm in crack depth has been made at the center of each Pyrex disc, and the SAW wedge transducer has been set up for the pitch-catch mode. It has been compared the theoretical values of the fracture stress calculated from the reflection coefficient of SAW with the values of the fracture stress measured from UTM.

본 연구에서는 취약한 고체의 표면에 존재하는 crack에 탄성표면파를 입사 시켰을 때 발생하는 반사계수를 측정하여 파괴응력을 해석하는 방법을 연구 분석하였다. Crack이 존재하는 취약한 고체에서의 파괴응력은 임계응력확대계수와 정규화된 최대응력확대계수의 함수로써 나타나며, 이 때 정규화된 최대응력확대계수는 탄성표면파의 반사계수를 측정하여 구할 수 있었다. 실험을 위하여 Pyrex glass원판 중앙에 깊이가 0.5mm~0.9mm인 crack을 제작하였고, SAW wedge transducer를 피치캐치(pitch-catch) 모드로 구성하여 반사계수를 측정하고 파괴응력값을 산출하였으며 UTM(Universal Testing Machine)으로 측정한 값과 비교 분석하였다.