应力三轴度和罗德参数对铝合金材料韧性断裂的影响

大量研究表明应力三轴度对韧性断裂有重要影响。然而,最新研究表明,与应力偏张量第三不变量相关的罗德参数也是影响韧性断裂的重要因素。采用7075铝合金制成的缺口圆棒和凹槽平板试样分析了应力三轴度和罗德参数对韧性断裂的影响及相应的微观机理。通过准静态拉伸试验和数值模拟得到应力三轴度、罗德参数及失效轨迹,同时利用扫描电镜分析了试样不同应力状态下的空穴演化规律。结果表明,应力三轴度和罗德参数对破坏应变有重要影响,并且罗德参数的影响随应力三轴度的增加而降低。断口分析表明,孔洞的尺寸随着应力三轴度的增大而减小,不同罗德参数的空穴形态明显不同。二级孔洞的成核速率和生长程度也受罗德参数的影响。

Effects of Stress Triaxiality and Lode Parameter on Ductile Fracture in Aluminum Alloy

Many theoretical and experimental studies showed that stress triaxiality has an important influence on ductile fracture. However, recent studies showed that Lode parameter, which can be linked to normalized third stress invariant, is also an essential factor. In the present study, round notched bar and flat grooved plate specimens made of 7075 aluminum alloy were used to assess the effect of stress triaxiality and Lode parameter on ductile fracture and on theScorresponding microscopicSmechanism. Quasi-static tensile experiments and parallel numerical simulations were conducted to obtain stress triaxiality, Lode parameter and failure locus. A fractographical analysis was performed to determine the rules of void evolution under different stress states. Stress triaxiality and Lode parameter have an important influence on failure strain. The effect of Lode parameter decreased with the increases in stress triaxiality. The fractographs showed that the size of the void decreased with the increase of stress triaxiality, and the morphologies of the voids of different Lode parameters were obviously different. TheSnucleation rate and growth degree of secondary voids were also affected by Lode parameter.