The growth and coalescence of ellipsoidal voids in plane strain under combined shear and tension
The growth and coalescence of ellipsoidal voids in plane strain under combined shear and tension
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DOI：
10.1016/j.jmps.2010.10.003
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发表时间：
2011-02
影响因子：
5.3
通讯作者：
Florence Scheyvaerts;P. Onck;C. Tekoğlu;T. Pardoen
中科院分区：
文献类型：
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作者：
Florence Scheyvaerts;P. Onck;C. Tekoğlu;T. Pardoen
提出了基于Gurson形式的椭球体孔洞生长和合并模型的新扩展，以处理在平面应变加载条件下涉及剪切和/或孔洞轴不一定与主加载方向对齐的问题。这些扩展是通过三维有限元空洞单元计算来激发和验证的，整个平面应变在一个方向上强制执行。本文的出发点是处理球面空洞形状的Gologanu模型。将基于均匀化理论的空洞旋转规律耦合到该损伤模型中。模型预测结果与三维单元计算结果吻合较好，反映了初始孔洞形状和方向对孔洞旋转速率的影响。本文还引入了一种经验校正方法，用于计算孔洞轴线横向平面上孔洞宽高比偏离其初始圆形的变化。为了准确地预测聚结的开始，需要这种修正。其次，提出了一种新的方法，在内部颈缩的Thomason准则中考虑应变硬化，避免使用应变硬化相关的拟合参数。将聚结准则推广到聚结面和空洞方向的任何可能方向。最后，对模型进行了补充，给出了聚并过程中应力承载能力最终下降的数学描述。整个模型是针对平面应变条件开发的，将路径设置为3D扩展。在验证模型后，参数化研究了在不同应力状态下，剪切对金属合金微观组织和流动参数的延性影响。总的来说，剪切的存在，对于相同的应力三轴性，降低了延性，部分解释了最近在低应力三轴性下获得的实验结果。
New extensions of a model for the growth and coalescence of ellipsoidal voids based on the Gurson formalism are proposed in order to treat problems involving shear and/or voids axis not necessarily aligned with the main loading direction, under plane strain loading conditions. These extensions are motivated and validated using 3D finite element void cell calculations with overall plane strain enforced in one direction. The starting point is the Gologanu model dealing with spheroidal void shape. A void rotation law based on homogenization theory is coupled to this damage model. The predictions of the model closely agree with the 3D cell calculations, capturing the effect of the initial void shape and orientation on the void rotation rate. An empirical correction is also introduced for the change of the void aspect ratio in the plane transverse to the main axis of the void departing from its initially circular shape. This correction is needed for an accurate prediction of the onset of coalescence. Next, a new approach is proposed to take strain hardening into account within the Thomason criterion for internal necking, avoiding the use of strain hardening-dependent fitting parameters. The coalescence criterion is generalized to any possible direction of the coalescence plane and void orientation. Finally, the model is supplemented by a mathematical description of the final drop of the stress carrying capacity during coalescence. The entire model is developed for plane strain conditions, setting the path to a 3D extension. After validation of the model, a parametric study addresses the effect of shear on the ductility of metallic alloys for a range of microstructural and flow parameters, under different stress states. In general, the presence of shear, for identical stress triaxiality, decreases the ductility, partly explaining recent experimental results obtained in the low stress triaxiality regime.