桥式起重机桥架疲劳裂纹扩展的数值分析

Numerical analysis of fatigue crack growth on bridge crane frame

采用有限元方法,计算某桥式起重机桥架的最大主应力分布,通过应力状态判断桥架某处裂纹的主要断裂类型,并利用扩展有限元方法(XFEM),计算桥架在最大载荷和最小载荷两种状态下不同裂纹长度时裂纹的尖端应力强度因子(SIF),由此根据Paris疲劳裂纹扩展公式的基本理论,描述该处疲劳裂纹扩展的基本规律,建立裂纹长度与交变应力循环周期数的函数关系,对起重机桥架裂纹短期内快速扩展的原因给出量化分析。结果表明,低应力的循环作用是该处裂纹形成和快速扩展的原因。

Finite element method was used to calculate the maximum principal stress distribution on a certain bridge crane frame.Through the stress state,the crack fracture type on the frame was determined,and extended finite element method（XFEM） was employed to calculate the stress intensity factor（SIF） at the tip of the cracks of different lengths under maximum load and minimum load.According to the Paris fatigue crack propagation formula,basic patterns of the fatigue crack propagation was described accurately and the function between crack length and the numbers of alternating stress cycle was established.With these,a reasonable explanation for the short-term rapidly expanding crack can be given for the bridge crane frame,which provides theoretical basis for the bridge crane life assessment and management.The results show that low stress cycle effect is the main reason of crack formation and rapid expansion.