A Study on Fatigue Damage Modelling in Cold Rolled Steel using X-ray Residual Stress

J. Ocean Eng. Technol. 1999;13(4):55-62.

Cho, Seok-Swoo;Joo, Won-Sik;

X선 잔류응력을 이용한 냉간압연강의 피로손상 모델링에 관한 연구

조석수;주원식;

삼척대학교 자동차공학과;동아대학교 기계공학과;

Keywords: X-ray Diffraction, Fatigue Load, Compressive Residual Stress, Cycle Ratio, $N_f$ Line, SPCC Steel

핵심용어: X선 회절, 피로하중, 압축잔류응력, 피로수명비, $N_f$ 선, SPCC 강

Abstract

Cold rolled steel has much plastic strain in the material surface produced by manufacturing process. The strain causes the variation of surface residual stress, in which influences the fatigue behavior under repeated loading. As experimental results, it was confirmed that the behavior of residual stress ${sigma}_r$, with cycle N consisted of three stages except stress amplitude near fatigue limit in SPCC steel. On the first stage compressive residual stress decreased rapidly, on the second stage gradually, and on the last stage slightly. The relation between ${sigma}_r$, and log N appeared linear behavior except the early part of cycle ratio $N/N_f$. The average gradient of ${sigma}_r$, with respect to log N seemed to take a constant value without initial cycle ratio. On the other hand, the $N_f$ line was regressed by the first-order polynomial equation on ${sigma}_r-log;N_f$ diagram. Therefore, this study showed that both the gradient of ${sigma}_r$, with respect to log N and the $N_f$ line was useful in predicting the cycle ratio $N/N_f$.