基于拉弯比的焊缝名义应力的提取

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In order to obtain nominal stress of weld under arbitrary combination of tension and bending load, stress and strain transformation coefficient of combined nominal stress of tension and bending was introduced, and fatigue data of weld based on pure tension nominal stress was transformed to that based on combined nominal stress of tension and bending with the same dam- age by means of stress concentration factor of tension and bending. Combined calculation stress of tension and bending was transformed to combined nominal stress by introducing element size effect factor to eliminate stress concentration in finite element model of weld. With the above transformations, transformation coefficient of combined calculation nominal stress of tension and bending was introduced, and combined calculation stress of tension and bending was transformed to the nominal stress based on pure tension load test so that the fatigue data of weld based on pure tension nominal stress could be used to evaluate welded structure directly. Calculation results show that transformation coefficient of combined calculation nominal stress of tension and bending is related to ratio of tension and bending, ratio of stress concentration factor of tension and bending, and element size effect factor of tension and bending caused by finite element modeling. Proper selection of element size will make the element size effect factor of tension equal to the ratio of stress concentration factor of tension and bending and the element size effect factor of bending equal to one, which makes the transformation coefficient of combined calculation nominal stress of tension and bending be identical to the element size effect factor of tension and independent to ratio of tension and bending.为了获得任意拉弯组合载荷下焊缝的名义应力，利用纯弯和纯拉压载荷下的应力集中系数，引入拉弯组合名义应力换算系数，将基于纯拉压名义应力的焊缝疲劳性能数据，转换为疲劳损伤一致的、基于拉弯组合名义应力的焊缝疲劳性能数据．为了消除有限元建模导致的计算误差，引入单元尺寸影响因子，将拉弯组合的计算应力转换为拉弯组合的名义应力．通过上面2个转换，引入拉弯组合计算名义应力换算系数，将有限元中的拉弯组合计算应力转换为基于拉压载荷疲劳试验的名义应力，从而在具体的焊缝结构疲劳强度评估时可以直接使用拉压载荷下的疲劳试验数据．计算结果表明：拉弯组合计算名义应力换算系数与拉弯比、拉弯应力集中因子比和有限元模型中拉弯单元尺寸影响因子有关．通过选择合适的单元尺寸，使得拉压单元尺寸影响因子等于拉弯应力集中因子比，且弯曲单元尺寸影响因子等于1，可使得拉弯组合计算名义应力换算系数恒等于拉压单元尺寸影响因子，而与拉弯比无关．