Aluminium alloys contain various types of intermetallic particles with different sizes, such as constituent particles and dispersoids. The main mechanism of ductile fracture in these materials is assumed to be nucleation of voids around the constituent particles, which grow during plastic deformation and eventually coalesce, resulting in material failure. The role of the dispersoids is less certain, but they are assumed to contribute in the last stages of the ductile fracture process. While the constituent particles are in the range of a couple of microns, the size of dispersoids is normally one order of magnitude smaller. To disclose the possible effects of the dispersoids on the ductile fracture process in aluminium alloys, this paper presents a numerical study of a finite-element based unit cell, which consists of a single spherical void embedded in a matrix material represented by a porous plasticity model with void size effects. Accordingly, the single, primary void of the unit cell is assumed to have nucleated on a constituent particle, whereas the matrix porosity is assumed to account for secondary, smaller voids nucleated on dispersoids. The effects of the intrinsic length scale of the matrix material on the void growth and coalescence are studied for a range of stress states, while the initial primary and secondary void volume fractions are kept constant. The secondary voids have a substantial effect on the behaviour of the unit cell when their size is large compared to the intrinsic material length scale, but they were not found to influence the growth of the primary void. Instead, the growth of the secondary voids promotes strain softening and influences the coalescence process of the primary voids, which gradually changes mode from internal necking to loss of load-carrying capacity of the inter-void ligament.

铝合金含有各种不同尺寸的金属间化合物颗粒，如组成颗粒和弥散体。假定这些材料的韧性断裂的主要机制是组成颗粒周围空隙的成核，这些空隙在塑性变形过程中增长并最终聚结，导致材料失效。弥散体的作用不太确定，但假定它们在韧性断裂过程的最后阶段起作用。虽然组成颗粒在几微米的范围内，但分散体的尺寸通常要小一个数量级。为了揭示弥散体对铝合金韧性断裂过程的可能影响，本文提出了基于有限元的晶胞的数值研究，它由嵌入基质材料中的单个球形空隙组成，由具有空隙尺寸效应的多孔塑性模型表示。因此，假定晶胞的单个初级空隙已在组成颗粒上成核，而基体孔隙率则假定为在弥散体上成核的次级较小空隙。针对一系列应力状态研究了基体材料的固有长度尺度对空隙增长和聚结的影响，同时初始主要和次要空隙体积分数保持恒定。当二次空隙与固有材料长度尺度相比较大时，二次空隙对晶胞的行为有重大影响，但未发现它们影响一次空隙的生长。反而，