This paper focuses on the effects of specimen type and thickness on the fracture parameters for I-II and I-III mixed mode cracks. Results show that mode III and mode II components emerge simultaneously near free surfaces of specimens under I-II and I-III mixed mode loadings, which is called coupling effect. For specimen under I-II mixed mode loading, the level of coupling effect is independent of specimen geometry. While for specimen under I-III mixed mode loading, the coupling effect is much affected by specimen geometry. Thicker middle cracked specimen has smaller coupling effect than thinner single edge notched specimen. Due to the non-negligible coupling effect on crack tip field and fracture behavior, a new mixity parameter taking the coupling effect into consideration is proposed to describe the mixed mode crack. Furthermore, mode I component is the main reason that constraint of I-II or I-III mixed mode crack exists, which is related with loading mode like tensile opening loading and bending opening loading. Specimen under tensile opening loading like middle cracked specimen is in a lower constraint than that under bending opening loading like single edge cracked specimen. Results also shows that the effect of specimen type on constraint is greater than that of thickness.

本文重点研究试样类型和厚度对 I-II 和 I-III 混合模式裂纹断裂参数的影响。结果表明，在 I-II 和 I-III 混合模式载荷下，模式 III 和模式 II 分量在试样的自由表面附近同时出现，这称为耦合效应。对于在 I-II 混合模式加载下的试件，耦合效应的水平与试件几何形状无关。而对于在 I-III 混合模式加载下的试件，耦合效应受试件几何形状的影响很大。较厚的中间裂纹试样比较薄的单边缺口试样具有更小的耦合效应。由于裂纹尖端场和断裂行为的耦合效应不可忽略，因此提出了一种新的混合参数来描述混合模式裂纹。此外，模态I分量是I-II或I-III混合模态裂纹约束存在的主要原因，这与拉伸张开加载和弯曲张开加载等加载方式有关。拉伸开口载荷下的试样如中裂纹试样比弯曲开口载荷下的单边裂纹试样约束更低。结果还表明，试样类型对约束的影响大于厚度。