The ductile fracture process in porous metals due to growth and coalescence of micron scale voids is not only affected by the imposed stress state but also by the distribution of the voids and the material size effect. The objective of this work is to understand the interaction of the inter-void spacing (or ligaments) and the resultant gradient induced material size effect on void coalescence for a range of imposed stress states. To this end, three dimensional finite element calculations of unit cell models with a discrete void embedded in a strain gradient enhanced material matrix are performed. The calculations are carried out for a range of initial inter-void ligament sizes and imposed stress states characterised by fixed values of the stress triaxiality and the Lode parameter. Our results show that in the absence of strain gradient effects on the material response, decreasing the inter-void ligament size results in an increase in the propensity for void coalescence. However, in a strain gradient enhanced material matrix, the strain gradients harden the material in the inter-void ligament and decrease the effect of inter-void ligament size on the propensity for void coalescence.

中文翻译：

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空隙间距和材料尺寸的相互作用对空隙间流动定位的影响

由于微米级空隙的生长和聚结，多孔金属的韧性断裂过程不仅受外加应力状态的影响，还受空隙分布和材料尺寸效应的影响。这项工作的目的是了解空隙间距（或韧带）的相互作用以及由此产生的梯度诱导材料尺寸对一系列施加应力状态下空隙聚结的影响。为此，执行具有嵌入应变梯度增强材料矩阵的离散空隙的晶胞模型的三维有限元计算。计算是针对一系列初始空隙间韧带尺寸和施加的应力状态进行的，其特征是应力三轴性和 Lode 参数的固定值。我们的结果表明，在没有应变梯度对材料响应的影响的情况下，减小空隙间韧带尺寸会导致空隙聚结倾向增加。然而，在应变梯度增强的材料基质中，应变梯度使空隙间韧带中的材料硬化并降低空隙间韧带尺寸对空隙聚结倾向的影响。