On the Relationship Between Threshold and Mean Stress Intensity Factor
The threshold of fatigue crack propagation is strongly dependent on stress ratio or mean SIF.Determining thresholds systemically by experiments would take too much time and cost,so a formula to estimate thresholds under various mean SIFs is surely the effective alternative way.Many empirical relationships between threshold and stress ratio can be found in literature already.However,all these empirical formulas are basically limited to the tested materials and stress ratio ranges,besides,different types of empirical formula should be adopted for different metals or stress ratios.More inconveniently,they can provide only very rough estimations if a simple fitting function is used.Considering the fatigue limit condition of crack front,a threshold formula has been derived.Examinations with experimental results show that this formula can express threshold quantitatively and uniformly.It is found that threshold varies with mean stress intensity factor just as that fatigue limit with mean stress if the mean stress intensity is smaller than the critical value,while plastic deformation at crack front would affect threshold greatly if the mean stress intensity factor is larger than the critical value.Why there would be such a critical mean stress intensity factor can be explained as the boundary whether damages induced by plastic deformation at crack front could be neglected or not.A formula to estimate the critical mean stress intensity factor has also been derived.
J.Q.Xu
State Key Laboratory of Ocean Engineering,Shanghai Jiao Tong University,Shanghai,China
国际会议
海口
英文
19-20
2018-01-12（万方平台首次上网日期，不代表论文的发表时间）