铝合金在两种应力状态下损伤机理研究

The Study of Damage Mechanism of Aluminum Alloy under Two Kinds of Stress State

铝合金汽车构件在撞击的过程中,构件的应力状态各点均不相同,而且在撞击的过程中各点的应力状态随着时间变化而变化。为了研究铝合金构件在不同应力状态下损伤机理,采取了两种代表性的三轴应力状态,即缺口拉伸与纯剪切所产生的应力状态。研究结果表明:缺口拉伸试验中,缺口根部产生相对较高的三轴应力,而且缺口根部明显产生微孔洞,随着应力的不断升高,微孔洞的体积分数不断增大。当达到材料的临界孔洞体积分数时,试样断裂:纯剪切试验中,三轴应力几乎等于0,在材料内部几乎没有产生微孔洞而产生了剪切带。剪切带在切应力的作用下变形不断增大,当到达材料的等效塑性断裂应变时,试样发生断裂;用Gurson损伤模型和剪切失效分别模拟缺口拉伸和翦切试验,试验的工程应力-应变曲线与模拟的工程应力-应变曲线拟合的很好。

During the impacting process of the automobile component of aluminum alloy, the stress state of each point is different, and the stress state in the impacting process, changes with the time. In order to study the damage mechanism under different stress states of aluminum alloy component, two kinds of representative triaxial stress states have been adopted, namely notch tensile and pure shear. The results of the study show that during the tensile experiment, a relatively high triaxial stress state appears at the notch root. With the increasing of the stress, the volume of the micro-void at notch root is increasing constantly. When the volume of the micro-void reaches the critical micro-void volume fraction, the specimen fractures; during the pure shear experiment, the triaxial stress almost equals to zero, there is almost no micro-void but shear band within the specimen. The shear band deforms constantly under the shear stress and when the stress reaches the equivalent plastic fracture strain, the specimen fractures. With the Gurson damage model and the shear failure model to simulate the notch tensile and shear experiment, simulation engineering stress-strain curve and experiment engineering stress-strain curve fit very well.