弯曲载荷作用下含切口T型节点表面裂纹应力强度因子计算

含裂纹修理切口T型节点的切口底部易于产生疲劳损伤,因而需要对该处新萌生的表面裂纹的疲劳寿命进行估算,以评判下次检修的时间.本文采用基于线弹性断裂力学的有限元方法,对弯曲载荷作用下于修理切口底部产生的表面裂纹最深处的应力强度因子进行了计算.计算结果表明,对于同一类型节点,在相同裂纹深度下,裂纹底部的应力强度因子随着a/c的减小而增大.进而,根据修理切口的不同形状,给出了一组具有一定工程适用范围的回归公式.根据基于线弹性有限元计算结果得出的经验公式,对含修理切口T型节点切口底部萌生的表面裂纹扩展规律进行分析,得出了不同裂纹深长比下,裂纹深长增量比随裂纹深度的变化曲线.在数值计算的基础上,采用船用普通钢制备的试件,对切口底部萌生的表面裂纹进行试验研究,描述了在交变弯曲载荷作用下裂纹形貌的变化规律.试验结果表明,试验数据点与计算曲线相比,具有较高的一致性,验证了根据有限元计算结果提出的拟合公式的精度.

Calculation of Stress Intensity Factors of surface cracks initiated from repaired welded details under bending load

It has been observed that fatigue cracks are prone to initiating from the stress concentration ar-eas such as the bottom of weld repaired profiles.When the surface crack has been found,the fatigue life should be evaluated in order to schedule the inspection period.In this paper,the stress intensity factors(SIFs) at the deepest point of the surface crack initiated from the bottom of the repaired profiles were cal-culated by finite element method based on linear elastic fracture mechanics(LEFM).To the repaired de-tails,the results show that SIFs will increase as the ratio of a/c decreases when the depth of the surface cracks was fixed.According to different weld repaired profiles,a group of empirical formulas were obtained by regressive method.It can be verified by the calculated results that the empirical formulas can be appli-cable to a certain range of details.According to empirical formulas based on LEFM,crack aspect ratio vari-ation of surface crack initiated from bottom of repaired profiles was investigated.With different aspect ratio from 1/2~1/5,the variation of increment ratio of minor and major half axis of semielliptical surface crack was obtained.Using specimens made of mild steel,experiments were carried out to study the crack aspect ratio variation under bending fatigue loading.The results indicate that the experimental points are consistent with calculated points from empirical formulas.The applicability of the empirical formulas was validated by comparison between experiments and finite element analyses.