【摘要】 传统成形极限图(FLD)由第一主应变与第二主应变的比值构成。但FLD依赖于成形历史和应变路径。因此,本文采用成形极限应力图(FLSD)来预测铝合金5052-O1(AA5052-O1)的成形极限。将修订的Gurson-Tvergaard-Needleman(GTN)塑性势模型用来模拟Nakazima凸模胀形实验。采用带扫描电镜(SEM)的原位拉伸试验观察记录损伤演化过程以确定GTN模型中的材料参数。通过计算AA5052-O1三个损伤阶段的孔洞分数获得GTN模型参数。根据实验结果,原生孔洞体积分数、最大形核孔洞体积分数、临界孔洞体积分数,最终断裂孔洞体积分数分别为0.002918,0.0249,0.030103,0.04854。在断裂前最后一个载荷步获得的应力应变值用来绘制AA5052-O1的FLSD和FLD。与Nakazima凸模胀形试验和单轴拉伸试验结果相比较,预测结果与试验结果较为吻合。由原位拉伸试验确定的模型参数可用于研究韧性金属的成形极限。更多还原

【Abstract】 The conventional forming limit diagram (FLD) is described as a plot of major strain versus minor strain.However,FLD is dependent on forming history and strain path.In the present study,a forming limit stress-based diagram (FLSD) has been adopted to predict the fracture limit of aluminum alloy (AA) 5052-O1 sheet.Nakazima test is simulated by plastic constitutive formula derived from the modified Gurson-Tvergaard-Needleman (GTN) model.An in situ tensile test with scanning electron microscope (SEM) is proposed to determine the parameters in GTN model.The damage evolution is observed and recorded,and the parameters of GTN model are identified through counting void fraction at three damage stages of AA5052-O1.According to the experimental results,the original void volume fraction,the volume fraction of potential nucleated voids,the critical void volume fraction,the void volume fraction at the final failure of material are assigned as 0.002 918,0.024 9,0.030 103,0.048 54,respectively.The stress and strain are obtained at the last loading step before crack.FLSD and FLD of AA5052-O1 are plotted.Compared with the experimental Nakazima test and uniaxial tensile test,the predicted results show a good agreement.The parameters determined by in situ tensile test can be applied to the research of the forming limit for ductile metals.更多还原