It is generally accepted that the superimposed hydrostatic pressure increases fracture strain in sheet metal and mode of fracture changes with applying pressure. Void growth is delayed or completely eliminated under pressure and the shear damage mechanism becomes the dominant mode of fracture. In this study, the effect of superimposed hydrostatic pressure on the ductility of sheet metal under tension is investigated using the finite element (FE) method employing the modified Gurson–Tvergaard–Needleman (GTN) model. The shear damage mechanism is considered as an increment in the total void volume fraction and the model is implemented using the VUMAT subroutine in the ABAQUS/Explicit. It is shown that ductility and fracture strain increase significantly by imposing hydrostatic pressure as it suppresses the damage mechanisms of microvoid growth and shear damage. When hydrostatic pressure is applied, it is observed that although the shear damage mechanism is delayed, the shear damage mechanism is dominant over the growth of microvoids. These numerical findings are consistent with those experimental results published in the previous studies about the effect of superimposed hydrostatic pressure on fracture strain. The numerical results clearly show that the dominant mode of failure changes from microvoid growth to shear damage under pressure. Numerical studies in the literature explain the effect of pressure on fracture strain using the conventional GTN model available in the ABAQUS material behavior library when the mode of fracture does not change. However, in this study, the shear modified GTN model is used to understand the effect of pressure on the shear damage mechanism as one of the individual void volume fraction increments and change in mode of fracture is explained numerically.

中文翻译：

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叠加静水压力对钣金剪切损伤机理影响的数值研究

人们普遍认为，叠加的静水压力会增加金属板的断裂应变，并且断裂模式会随着施加压力而变化。在压力作用下空隙生长被延迟或完全消除，剪切破坏机制成为断裂的主要模式。在这项研究中，使用改进的 Gurson-Tvergaard-Needleman (GTN) 模型的有限元 (FE) 方法研究了叠加静水压力对受拉金属板延展性的影响。剪切损伤机制被认为是总空隙体积分数的增量，该模型使用 ABAQUS/Explicit 中的 VUMAT 子程序实现。结果表明，通过施加静水压力，延展性和断裂应变显着增加，因为它抑制了微孔生长和剪切损伤的损伤机制。当施加静水压力时，观察到虽然剪切损伤机制被延迟，但剪切损伤机制在微孔洞的生长中占主导地位。这些数值结果与先前发表的关于叠加静水压力对断裂应变影响的研究中发表的实验结果一致。数值结果清楚地表明，主要的破坏模式从微孔增长转变为压力下的剪切破坏。文献中的数值研究使用 ABAQUS 材料行为库中提供的常规 GTN 模型在断裂模式不变时解释了压力对断裂应变的影响。然而，在本研究中，剪切修正 GTN 模型用于将压力对剪切损伤机制的影响理解为单个空隙体积分数增量之一，并以数值方式解释断裂模式的变化。