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给出一个用来计算对接和角接焊接接头焊趾半椭圆表面裂纹在复杂应力场中，例如在残余应力场中，裂纹前缘应力强度因子（ＳＩＦ）分布的工程实用计算法——基本模式法。本文先通过高自由度的三维有限元分析，给出接头和裂纹几何参数Ｔ１／Ｔ、ａ／Ｔ、ａ／ｃ一系列组合的基本几何模型（文中给出２７种）在选定的基本应力模式（本文给出８种）作用下，沿裂纹前缘的ＳＩＦ分布，并形成一个数据库。利用这些基本模式解的插值和组合，可以非常迅速地求得一般几何参数情况下焊趾半随圆表面裂纹在复杂应力场中沿裂纹前缘的ＳＩＦ分布。在本方法中，可以考虑角接接头板厚比Ｔ１／Ｔ对ＳＩＦ分布的影响。计算过程极简单而迅速，因此特别适用于疲劳裂纹扩展行为及寿命计算问题。
A practical engineering method for calculating the SIF distribution of cracks in the weld toe semi-elliptical surface cracks of butt-and-toe welded joints in complex stress fields, such as residual stress fields, is given - Basic Mode law. In this paper, three dimensional finite element analysis of high degree of freedom is used to give the basic geometrical model (27 kinds) of series combination of joint and crack geometrical parameters T1 / T, a / T and a / c in the selected basic stress Mode (8 given in this paper), the SIF distribution along the leading edge of the crack and the formation of a database. Using the interpolation and combination of these basic model solutions, the SIF distribution along the crack front in the complex stress field of toe-and-semicircle with general togeometric parameters can be very quickly obtained. In this method, the influence of the fillet thickness ratio T1 / T on the SIF distribution can be considered. The calculation process is very simple and fast, so it is particularly suitable for fatigue crack growth behavior and life calculation problems.