The full field three-dimensional finite element computation was performed for Compact Tension Shear（or CTS） specimens of an aeronautical structure aluminum alloy under Ⅰ/Ⅱ mixed mode-loading conditions.The characteristics of out-of-plane constraint Tz and in-plane constraint T-tress were analyzed.The effects of thickness and loading conditions on stresses,stress triaxiality Rσ and strain energy density U0 were examined.In particular the characteristics of these parameters on the observed crack initiation angle are discussed.It is shown：（1） in-plane constraint T-stress vanishes for the CTS specimen with a/W=0.5.（2） The size of the three-dimensional region scales with thickness B（0.4~0.5B） and is no relative with mode mixity.However,the thickness effect weakens with decreasing loading angle and almost disappears under pure II loading condition.（3） The out-of-plane constraint Tz decreases as polar radial r and thickness size z increase,and is independent of the polar angle θ.（4） The direction of U0min indeed represents the crack initiation direction of three-dimensional mixed mode fracture.The results make a theoretic basis to establish a three-dimensional mixed mode fracture criterion.%进行了Ⅰ/Ⅱ复合型载荷作用下航空结构铝合金CTS试样线弹性的全场三维有限元计算,分析了复合型离面应力约束因子Tz和面内约束T应力的分布特性,研究了厚度和载荷条件对应力各分量及应力三轴性水平Rσ、应变能密度U0的影响以及这些量在实验中观察到的裂纹起裂方向上的特点。结果表明：（1）平面内约束T应力在此种试样形式下为零;（2）复合型裂纹的三维效应区与厚度成正比,为0.4-0.5B,与载荷条件基本无关,但是厚度效应随着载荷角的减小逐渐变小,到II型载荷时基本消失;（3）离面约束因子Tz随着径向和厚度尺寸的增加逐渐
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