Two-scale porosity effects on cohesive crack growth in a ductile media
Two-scale porosity effects on cohesive crack growth in a ductile media
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DOI：
10.1016/j.ijsolstr.2020.04.035
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发表时间：
2020-09-01
影响因子：
3.6
通讯作者：
Chew, H. B.
中科院分区：
文献类型：
--
作者：
Cui, Y.;Gao, Y. F.;Chew, H. B.
具有两种不同尺寸的孔洞的微结构在增材制造金属中很常见。较小的孔洞是由金属内部的夹杂物形成的，而较大的孔洞是由未烧结的粉末颗粒形成的。在这项工作中，我们研究了裂纹前这两种尺寸的空洞之间的相互作用，以及对韧性断裂过程的影响。采用小尺度屈服条件下的中心线裂纹有限元模型。裂纹前方的扩散过程区是由由Gurson多孔材料关系控制的几排含空隙的胞元来模拟的。结果表明：初始裂纹尖端附近存在较大的孔洞，有利于孔洞与裂纹尖端结合形成单一的连续损伤区，从而降低了断裂韧性；然而，在裂纹尖端的活性塑性区域内战略性地放置这些较大的空隙可以促进裂纹尖端的屏蔽，从而导致以多个不连接的损伤区域的形式扩散损伤，最终使韧性提高几倍。我们通过非线性场投影重建弹塑性介质中的等效裂纹尖端内聚区规律，将断裂行为量化为扩散过程区中较大尺度空洞的相对尺寸和比例的函数。结果表明，黏结强度、黏结能以及黏结带律的功能形式与双空隙尺寸尺度密切相关，从而在均质化的牵引-分离关系中引入了尺寸效应。(C) 2020 Elsevier Ltd.版权所有。
Microstructures with two distinct size-scales of voids are commonplace in additively-manufactured metals. The smaller-scale voids nucleate from inclusions within the metal, while the larger-scale voids originate from unsintered powder particles. In this work, we study the interaction between these two sizescales of voids ahead of a crack, and the influence on the ductile fracture process. We adopt a finite element model of a centerline crack subjected to small-scale yielding conditions. The diffuse process zone ahead of the crack is modeled by several rows of void-containing cell elements governed by a Gurson porous material relation. Results show that the larger-scale voids near the initial crack tip generally reduces the fracture toughness by facilitating void coalescence with the crack-tip to form a single contiguous damage zone. However, strategic placements of these larger-scale voids within the active plastic zone of the crack-tip can promote crack-tip shielding, leading to diffused damage in the form of multiple unconnected damage zones, and ultimately, a several-fold improvement in toughness. We quantify the fracture behavior, as a function of the relative size and proportion of larger-scale voids in the diffuse process zone, by reconstructing the equivalent crack-tip cohesive zone laws in an elasto-plastic medium via nonlinear field projection. We demonstrate that the cohesive strength, cohesive energy, as well as the functional form of the cohesive zone law, are strongly dependent on the dual void size-scales, which introduces a size-effect into the homogenized traction-separation relationship. (C) 2020 Elsevier Ltd. All rights reserved.