热疲劳裂纹网的屏蔽规律及主裂纹应力强度因子的计算方法

热疲劳裂纹网中主裂纹的应力强度因子可反映构件的损伤程度，然而由于裂纹间的屏蔽效应，直接计算裂纹网中主裂纹的应力强度因子是困难的。根据热疲劳试验提出假设：① 主裂纹不会位于裂纹网的边缘；② 裂纹网中的裂纹互相平行，且垂直于约束方向。定义主裂纹的屏蔽剩余百分数s，裂纹的比间距n，裂纹长度比f。分别研究两条长度相等裂纹、两任意长度裂纹、三条裂纹和多条裂纹屏蔽效应的规律。发现s-f-n有确定的关系，这一关系由裂纹网的结构确定，而与边界条件、裂纹尺寸等因素无关。利用屏蔽效应的规律可由单条裂纹时的应力强度因子推算裂纹网中屏蔽效应发生时主裂纹的应力强度因子。算例表明此方法精确、简便、快捷。

Shielding Effect Rule of Thermal Fatigue Crack Net and Calculating Method of Stress Intensity Factor of Main Crack

The stress intensity factor of the main crack in crack net can reflect the damage degree of components. However, it is difficult to calculate the stress intensity factor directly due to the shielding effect between cracks. It is supposed that the main crack cannot locate in the edge of the crack net, and the cracks in the net parallel to each other and perpendicular to constraint direction. The shielding residual percent s of main crack, the cracks' space ratio n and the crack length radio/are defined. The rule of shielding effect between two same length cracks, two random cracks, three cracks and multi -cracks is studied. The relation of s-f-n is definitive, and it is independent of the boundary conditions, size of cracks and other factors. The stress intensity factor of main crack can be calculated by the factor of single crack by using this rule when shielding effect happens. The example shows that this method is accurate, simple, convenient and fast.