面向低应力三轴度的金属板料压剪试验及其断裂表征研究

发布时间：2018-05-13 06:27

本文选题：应力三轴度 + 压剪试验　；参考：《上海交通大学》2015年硕士论文

【摘要】：在板料成形领域,精冲成形工艺已成为一种重要的成形手段。精冲成形过程中,材料处于三向压应力状态,塑性变形能力得到了极大改善。但是,精冲成形过程中也常常伴随着复杂的损伤断裂等问题,其适用的韧性断裂准则需借助剪切试验进行试验验证和参数标定。因此,有必要对金属板料在低应力三轴度状态下的韧性断裂行为进行研究。本文通过构建一种新型的压剪试验装置作为切入点,运用数值模拟和物理实验相结合的方法对处于低/负应力三轴度的压剪试验进行研究。结合数值模拟结果和压剪试验结果分析了不同材料的压剪试验试样在不同应力状态下的塑性变形行为和断裂失效特征。通过宏微观断口的定性和定量分析,研究了压剪试验的断裂机制和试样断口表征响应。主要研究成果如下:1)围绕现有板料剪切试验方法的特点和不足,构建了一种新的板料压剪试验。通过预加载,实现了特定应变路径下的剪切成形,通过调整试样几何结构实现了低/负应力三轴度范围的剪切成形。2)压剪试样较拉剪试样的塑性变形能力有所改善,相同条件下压剪试样较晚发生断裂失效。材料的抗拉强度越高,压剪试验所需的成形载荷越大,最终断裂位移量越小。压剪试样的裂纹起源于靠近变形区切槽边缘的内侧位置,裂纹扩展角和主加载方向的夹角值随着β角增大而呈现逐渐减小的趋势。3)试样宏观断口大致可分为光滑平整、剪切平面密集的I区和韧窝密集存在的II区。β角增大,I区所占比例增加。断面两侧I区是明显的剪切断裂特征,剪切平面台阶状分布,孔洞极少且几乎没有扩展。断面中心II区为典型的抛物线型韧窝断裂,韧窝密集且沿着剪切方向拉长,韧窝底部存在形核粒子。β角增大,II区的韧窝取向性更加明显,其等效平均韧窝直径d略有增加。4)相同条件下,同种材料(不同β角)获得的平均韧窝直径d和长短轴径比相差不大。β角增大,平均韧窝直径d略微增大,约在0.4~0.5μm左右,而韧窝密度ρ则呈现明显减小的趋势。材料抗拉强度增加,平均韧窝直径d减小,而韧窝密度ρ则出现抛物线形状。
[Abstract]:In the field of sheet metal forming, precision stamping has become an important forming method. In the process of precision stamping, the material is in the state of three dimensional compressive stress, and the plastic deformation ability is greatly improved. However, in the process of precision stamping, there are some complicated problems such as damage and fracture. The applicable ductile fracture criterion needs to be verified by shear test and calibrated by parameters. Therefore, it is necessary to study the ductile fracture behavior of sheet metal under low stress triaxiality. In this paper, a new type of compression shear test device is constructed as a starting point, and the compression shear test with low / negative stress triaxiality is studied by means of numerical simulation and physical experiment. The plastic deformation behavior and fracture failure characteristics of different materials under different stress states are analyzed by combining the numerical simulation results and the compression shear test results. The fracture mechanism of compression shear test and the response of specimen fracture were studied by qualitative and quantitative analysis of macro and micro fracture. The main research results are as follows: (1) A new compression shear test of sheet metal is constructed around the characteristics and shortcomings of the existing shearing test methods. By preloading, shear forming under specific strain path is realized. By adjusting the geometric structure of the specimen, the plastic deformation ability of the compression shear specimen is improved compared with that of the tensile shear specimen, and the shear forming of low / negative stress triaxiality range is realized. Under the same conditions, the fracture failure of the compressive shear specimen occurred later. The higher the tensile strength of the material is, the greater the forming load is and the smaller the final fracture displacement is. The crack of compression shear specimen originates from the inner position near the edge of the notch in the deformation zone, and the angle between the crack propagation angle and the main loading direction decreases gradually with the increase of 尾 angle. 3) the macroscopic fracture surface of the specimen can be roughly divided into smooth and smooth. The ratio of 尾 -angle increasing in I region and II region in dimple densification increased with the increase of shear plane density and dimple density. The I region on both sides of the section is an obvious shear fracture feature. The shear plane is a step like distribution with very few holes and almost no expansion. Section II is a typical parabolic dimple fracture, the dimple is dense and elongated along the shear direction, and nucleation particles exist at the bottom of the dimple. Under the same condition, the average dimple diameter d and the long axis diameter ratio obtained by the same material (different 尾 angle) were not different. The 尾 angle increased, the average dimple diameter d increased slightly, and the average dimple diameter was about 0.4 ~ 0.5 渭 m. However, the dimple density 蟻 decreased obviously. With the increase of tensile strength, the average dimple diameter d decreases, while the dimple density 蟻 appears parabola shape.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG115

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