The Effect of Stress Ratio on Fatigue Crack Propagation Rate and Arrest Behavior in 7075-T735 Al Alloy

J. Ocean Eng. Technol. 1992;6(1):131-139.

7075-T735 Al 합금의 피로균열 진전속도와 정류거동에 미치는 응력비의 영향

오세욱,강상훈,허정원,김태형

동아대학교 기계공학과,창원기계공업고등학교 기계과,동아대학교 공과대학 재료실험실,동아대학교대학원

Keywords: Single tension peak overload, Crack arrest, Effective stress intensity factor, Threshold overload shut of ratio, Fictitious effective stress intensity factor ratio

핵심용어: 단일인장 과대하중, 정유구렬, 유교응력확대계수, 임계 정유과대하중화, 가상유교응력확대계수화

Abstract

The understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading is very important for life prediction of the air travel structures. Particularly, the retardation and arrest behavior of fatigue crack propagation by single tension overloading is essential to the understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading. Numerous studies of the retardation behavior have been performed, however investigations of the arrest behavior have not been enough yet. As for the arrest behavior, Willenborg had reported that the overload shut-off ratio $[R_{so}=(K_{OL})/K_{max})_{crack arrest}]$ had been the material constant, but recently several investigators have reported that the overload shut-off ratio depends upon the stress ratio. In this study, authors have investigated the effect of stress ratio on the threshold overload shut-off ratio to generate arrest of fatigue crack growth in high tensile aluminum alloy 7075-T735 which have used in material for air travel structures, It has been $-0.4leqqRleqq0.4$ till/nnow, the region of stress ratio investigated. The threshold overload shut-off ratio has decreased as stress ratio has increased in overall region of -$-0.4leqqRleqq0.4$ and the linearity has been seen in this material. Moreover, the experimental equation between $R_{so}$ and R has been made; The relation has been $R_{so}=-R+2.6$.