Modeling of porosity and grain size effects on mechanical behavior of additively manufactured structures
Modeling of porosity and grain size effects on mechanical behavior of additively manufactured structures
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DOI：
10.1016/j.addma.2020.101833
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发表时间：
2021-02
影响因子：
11
通讯作者：
M. Hamid;M. S. Saleh;Ali Afrouzian;R. Panat;H. Zbib
中科院分区：
文献类型：
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作者：
M. Hamid;M. S. Saleh;Ali Afrouzian;R. Panat;H. Zbib
气溶胶喷射（AJ）打印等增材制造（AM）方法允许通过烧结微纳米颗粒和/或纳米颗粒来制造结构，从而产生由各种孔隙和粒度组合组成的微结构。据报道，AJ印刷和烧结银微柱在高孔隙率结构中表现出高刚度和高应变破坏的不寻常行为，反之亦然（Saleh et al. 2018[1]）。然而，伴随着这种行为的是具有较小晶粒尺寸的刚性结构和具有较大晶粒尺寸的柔性结构。为了解释这种由尺寸效应（晶粒细化和梯度）引起的硬化和由孔隙率引起的软化之间的权衡将发挥关键作用的物理行为，本文提出了一种多尺度建模方法。该模型由连续位错动力学（CDD）框架、连续塑性和有限元分析相结合组成。将位错动力学公式引入到用户材料子程序中，并与商业有限元求解器（在本例中为LS-DYNA）相结合，在与AM微柱尺寸相同的三维尺度上求解模型。该模型的结果反映了AM微柱压缩试验中观察到的一般趋势。特别是，与孔隙率相比，晶粒尺寸和位错密度对金属组织的机械变形有不成比例的更高的影响。这些结果表明，AM结构在塑性状态下的行为受晶粒尺寸的影响而不是孔隙率的影响。讨论了该模型的一些局限性和未来可能的改进。本文提供了一个重要的分析框架来模拟具有内部孔隙率的AM结构在塑性状态下的力学行为。
Additive manufacturing (AM) methods such as Aerosol Jet (AJ) printing allow the fabrication of structures via sintering of micro and/or nanoparticles, leading to microstructures that consist of various combinations of pore and grain sizes. It has been reported that AJ printed and sintered silver micropillars show an unusual behavior of high stiffness and high strain-to-failure for structures with high porosity and vice versa (Saleh et al. 2018 [1]). This behavior, however, is accompanied by the stiffer structures having smaller grain sizes and softer structures having larger grain sizes. To explain the physics of this behavior where a trade-off between hardening caused by size effects (grain refinement and gradients) and softening caused by porosity is expected to play a critical role, a multi-scale modeling approach is proposed in this paper. The model formulation consists of a continuum dislocation dynamics (CDD) framework, coupled with continuum plasticity and finite element analysis. The dislocation dynamics formulation is introduced into a user material subroutine and coupled with a finite element commercial solver, in this case, LS-DYNA, to solve the model in three-dimensional scale with the same size as the AM micropillars. The results from the model capture the general trends observed in compression tests of AM micropillars. In particular, it is shown that the grain size and dislocation density have a disproportionately higher influence over the mechanical deformation of metallic structures when compared to the porosity. These results show that the behavior of AM structures in the plastic regime is dominated by grain size effects rather than porosity. Some limitations of the model and possible future refinements are discussed. The paper provides an important analytical framework to model the mechanical behavior of AM structures with internal porosity in the plastic regime.