Influence of overload on the fatigue crack growth retardation and the statistical variation

J. Ocean Eng. Technol. 1997;11(3):76-88.

강의 피로균열지연거동에 미치는 과대하중의 영향과 통계적 변동에 관한 연구

김선진,남기우,김종훈,이창용,박은희,서상하

부경대학교 공과대학 기계공학과,부경대학교 재료공학과,부경대학교 공과대학 기계공학과,부경대학교 공과대학 기계공학과,부경대학교 공과대학 기계공학과,부경대학교 공과대학 기계공학과

Keywords: Crack Retardation, Multiple Overload, Plastic Zone Size, Number of Overload Application, Probability Distribution Function, COV, Minimum Crack Growth Rate

핵심용어: 균열지연현상, 다중과대하중, 소성역크기, 과대하중 작용수, 확률분포, 변동계수, 최소균열전파율

Abstract

Constant .DELTA.K fatigue crack growth rate experiments were performed by applying an intermediate single and multiple overload for structural steel, SM45C. The purpose of the present study is to investigate the influence of multiple overloads at various stress intensity factor ranges and the effect of statistical variability of crack retardation behavior. The normalized delayed load cycle, delayed crack length and the minimum crack growth rate are increased with increasing baseline stress intensity factor range when the overload ratio and the number of overload application were constant. The crack retardation under low baseline stress intensity factor range increases by increasing the number of overload application, but the minimum crack growth rate decreases by increasing the number of overload application. A strong linear correlation exists between the minimum crack growth rate and the number of overload applications. And, it was observed that the variability in the crack growth retardation behavior are presented, the probability distribution functions of delayed load cycle, delayed crack length and crack growth life are 2-parameter Weibull. The coefficient of variation of delayed load cycle and delayed crack length for the number of 10 overload applications data are 14.8 and 9.2%, respectively.