疲劳拉伸载荷作用下的表面裂纹扩展分析

Analysis of Surface Crack Propagation under Fatigue Tensile Load

贮箱在长时间工作状态下会衍生出很多疲劳裂纹,这些裂纹的存在不仅影响容器的结构强度与使用寿命,还威胁到工作人员的人身安全,因此开展贮箱材料疲劳裂纹的动态扩展以及寿命机理的分析研究。通过Franc3D裂纹分析软件,预制不同长深比的半椭圆裂纹试样,研究裂纹动态应力强度因子在疲劳拉伸载荷作用下的变化规律,同时开展裂纹扩展路径、速率和寿命的探究。结果表明:不同长深比的半椭圆裂纹在扩展过程中尖端动态应力强度因子分布规律基本一致,且近表面处强度因子数值大小最高,仿真结果的裂纹形貌仍为半椭圆形;裂纹刚开始扩展时扩展速率近乎相等,随着载荷循环次数的增加,扩展距离呈指数型增长,近表面处的扩展速率最高,长深比小于等于1的裂纹在近表面的扩展速率基本相同。

Many fatigue cracks can be derived from tank under long-term working conditions.These cracks not only affect the structural strength and service life of tank,but also threaten the personal safety of operators.Therefore,the analysis and research on the dynamic expansion of fatigue cracks in tank materials and the life mechanism were carried out.The semi-elliptical crack specimens with different length-to-depth ratios were prefabricated by Franc3D crack analysis software to study the change of dynamic stress intensity factor of cracks under fatigue tensile loading,and to investigate the crack expansion path,rate and life time.The results show that the distribution law of the dynamic stress intensity factor at the tip of the semi-elliptic cracks with different length-depth ratios is basically the same,and the magnitude of the intensity factor at the near surface is the highest.The final crack morphology is still semi-oval in final.At the beginning of crack growth,crack propagation rate is almost equal,the growth distance increases exponentially with the increase of the number of load cycles,and the propagation rate at the near surface is the highest,but the crack propagation rate at the near surface of the crack with length-depth ratio less than or equal to 1 is basically the same.