A Fatigue Life Prediction by Growth Characteristics of a Small Surface Crack

J. Ocean Eng. Technol. 1989;3(2):108-117.

Suh Chang-Min,Lim Chang-Soon,Gang Yong-Gu

작은 표면균열의 성장특성에 의한 수명예측

서창민,임창순,강용구

경북대학교 기계공학과,한국조폐공사대구지사,금오공과대학 기계공학과

Keywords: Surface Crack, Fatigue Life Prediction, Stress Intensity Factor, Crack Growth Rate, Fracture Mechanics, Cycle Ratio, Total Strain Intensity Factor

핵심용어: 표면균열, 피로수명예측, 응력확대계수, 균열성장율, 파괴역학, 수명비, 전스트레인 확대계수

Abstract

This paper deals with a fatigue life prediction of a surface crack based on the experimentally obtained relationship between surface crack length ratio $a/a_{f}$ and cycle ratio $N/N_{f}$ using micro computer. Firstly $a/a_{f}$-$N/N_{f}$ curves obtained from experimental tests, were assumed as three curves UC(the upper limit curve), LC(the lower limit curve) and MC(the middle curve), and these were utilized to predict the fatigue life. Comparing the calculated values which represent the characteristics of crack growth behaviors from the three assumed curves with the experimental ones, it has been found that in the stable crack growth region, they coincide reasonably well each other. And the differences between the fatigue lives obtained from the assumed curves and the experimental fatigue life did not exceed 20%. Using the characteristics of $a/a_{f}$-$N/N_{f}$ curves, it is possible to predict the da/dN-Kmax curves and the S-$N_{f}$ curves.