复合载荷作用下大晶粒铝裂纹尖端延性损伤行为的研究

应用电镜原位拉伸方法研究了复合载荷（Ⅰ＋Ⅱ型）作用下大晶粒铝裂纹尖端的塑性变形行为和延性损伤过程，用有限元结果对复合型损伤进行了力学分析。结果表明：在复合载荷作用下，裂纹尖端受相反塑性变形作用，裂尖变形符合锐化－钝化模型，异于纯Ｉ型载荷下的钝化模型，是多系滑移的结果。延性材料裂尖的损伤发生在钝化区域（裂尖的均匀滑移区）而非锐化区（裂尖的集中滑移区）。裂尖的启裂是沿应力三轴性水平最大方向进行，此方向

THE RESEARCH OF DUCTILE DAMAGE IN LARGE CRYSTAL PURE ALUMINIUM AT CRACK TIP UNDER MIXED MODE LOADING

In this Paper, an in situ temsile experiment with SEM was carried out to investigate theplastic deformation,and the behavior of ductile damage in the immediate vicinity of crack tipin commercial large crystal pure aluminium under mixed mode loading,and the mechanicsanalysis of mixed damage was made by using the result of finite element calculation. It isshown that the model of a mixed crack tip deformation is a sharpening-blunting because anopposite kind of deformation carried out at the upper and the down side of the crack tip,andit occurred by successive activation of a number of slip systems,The ductile damage has de-veloped in the blunting region(which is the uniform slip zone)but not in the sharpening re-gion(which is the concentration slip zone ).The crack initiates at the place where the effec-tive strain is maximum and propagates along the direction of maximum gradient of effectivestrain, which agrees well with that of maximum stress triaxiality in the blunting region undermixed mode loading.The deformation of a mixed crack tip investigated by SEM was alsoproved by FEM.