새로운 하한계응력확대계수 식에 의한 피로 거동 평가

Abstract

Crack is the cause of impairing the safety of the structure. Since long ago, many researchers have studied to solve the crack problem. In other words, crack propagation rates such as brittle fracture, fatigue fracture, and stress corrosion cracking were analyzed. In addition, there have been many studies on the threshold stress intensity factor (), which is the limit stress of crack initiation, but the micro-crack problem that can be applied uniformly to various failure modes has not been solved. This study was evaluated threshold stress intensity factor and fatigue limit of short cracks. Two equations used. That is, the crack length dependence equation of suggested by Tange et al with modification of Haddad et al's equation, and the crack length dependence equation of suggested by Ando et al considering the plastic zone dimensions. The two equations showed similar tendencies despite the different basic viewpoints. In addition, the equation of Ando et al was able to quantitatively evaluate the threshold stress intensity factor and fatigue limit despite of the difference in the specimen size, crack aspect ratio, and stress ratio. Therefore, this study proved that the structures safety for various materials and failure modes can be evaluated by Ando et al's equation.