钢结构焊缝疲劳强度分析技术的最新进展

Latest Development of Fatigue Strength Analysis Technology for Welds in Steel Structures

在平板焊接钢结构焊缝疲劳强度分析中,近年来国外主要发展起了等效结构应力法和表面外推热点应力法2种新方法。等效结构应力法考虑焊趾部位的结构应力集中效应,应用改进线性化法或节点力法分析结构应力,确保计算结果对有限单元类型、网格形状及尺寸的不敏感,从而有效区分不同焊接接头类型的焊趾结构应力集中情形;以结构应力为控制参数计算应力强度因子,在主要考虑焊趾缺口、结构板厚、载荷模式等因素影响基础上,基于断裂力学分析确定与焊缝疲劳寿命直接相关的应力参数,导出等效结构应力转化方程;基于上述应力计算和转化方法对焊缝疲劳试验结果数据进行处理,建立焊缝疲劳强度设计单一主S—N曲线,实现对钢结构焊缝的疲劳强度评定和寿命预测。通过比较分析可知,表面外推热点应力法适用于钢结构焊缝设计阶段的方案比较及方案优化;等效结构应力法较适合对钢结构焊缝最终设计方案进行更为精确的焊缝疲劳强度评定和寿命预测以及不能用表面外推热点应力法进行钢结构焊缝疲劳强度分析时。

Aiming at the fatigue strength analysis of welds in welded steel structures, two new methods were mainly developed recently in overseas countries, including equivalent structural stress method and surface extrapolation hot spot stress method. For the equivalent structural stress method, the structural stress was analyzed by modified linearization or nodal forces approach by considering the welded toe structural stress concentration effect. In that the stress calculation results were insensitive to the finite element type, mesh shape and dimensions, so the welded toe structural stress concentration conditions for different welded joints could be distinguished effectively. Subsequently the stress intensity factor was calculated by using the structural stress as the control parameter. Based on mainly considering the effects of the welded toe notch, plate thickness and loading mode, the stress parameter relevant to the fatigue lives of welds directly were defined by using the fracture mechanics and the formula for equivalent structural stress transformation was determined. Based on the above method of stress calculation and transformation, the fatigue testing results data were analyzed. Then the single fatigue design master S-N curve, which is necessarily important in the fatigue strength assessment and life prediction, was established. It is known from the comparisons and analyses that the surface extrapolation hot spot stress method is suit for comparing and optimizing the scheme in welded structures fatigue design step, and the equivalent structural stress method is suit for assessing the fatigue strength and predicting lives more accurately for final structural scheme, or applied in the conditions that the surface extrapolation hot spot stress method can not be used.