矩形管接头疲劳失效位置预测及应力因子分析

Fatigue Failure Location Prediction and Stress Factor Analysis of Rectangular Pipe Joints

为解决复杂焊接接头的抗疲劳设计,依据BS7608标准中的名义应力法和ASME标准中的结构应力法及BS EN15085-3标准中的焊接结构疲劳设计要求,研究矩形管接头的疲劳问题.首先,研究标准中的疲劳寿命预测方法以及涉及的名义应力与结构应力的区别与联系;接着,利用某矩形管接头的有限元分析模型,研究沿接头焊缝应力的分布规律及影响因素,结果表明:与最大主应力和Von.Mises应力分布规律不同,矩形管接头沿焊缝结构应力最大值发生在焊缝拐角焊趾处,与其疲劳试验中接头失效位置一致;位于焊趾表面的、具有高应力梯度变化的区域内名义应力对单元尺寸表现出强的敏感性,而在能够表示焊缝轮廓的模型中描述整个断裂截面的结构应力则对单元尺寸变化不敏感.最后,基于名义应力法和结构应力法对矩形管接头焊缝进行应力因子分析,结果表明:管接头失效位置的应力因子最大值大于0.90,应力等级为高.

In order to solve the fatigue resistance design of complex welded joints,the fatigue problems of rectangular pipe joints were studied in accordance with the nominal stress method in BS7608 standard,the structural stress method in ASME standard,and the fatigue design requirements for welded structures in BS EN15085-3 standard.The fatigue life prediction methods in the standard and the differences and connections between the nominal and structural stresses involved are studied,and finite element analysis model of a rectangular pipe joint is used to study the distribution of stress along the joint weld and its influencing factors.The results show that unlike the maximum principal stress and Von.Mises stress distribution rules,the maximum structural stress of the rectangular pipe joint along the weld structure occurs at the corner of the weld toe,which is consistent with the joint failure location in the fatigue test.The nominal stress in the region with a high stress gradient change on the surface of the weld toe shows a strong sensitivity to the element size,while in the model that can represent the contour of the weld,the structural stress describing the entire fracture cross section is not sensitive to the change of element size.Based on the nominal stress method and structural stress method,stress factor analysis is performed on the welds of rectangular pipe joints.The results show that the maximum stress factor of the joint failure location is greater than 0.90,and the stress state is high.