Abstract In a composite material a soft, ductile matrix can be confined by a hard, brittle phase, altering its deformation and fracture behavior. Increasing confinement leads to embrittlement of the matrix and, in turn, also the composite. From a materials design perspective, it is usually desired to avoid brittle fracture without compromising the hardness of the material. Understanding confined ductile fracture is therefore critical for modeling the mechanical response of composite materials with fine microstructure. The present work is focused on confined ductile fracture of a thin ductile film, with elasto-plastic power-law hardening behavior, sandwiched between ideal linear elastic substrates. Fracture of the ductile layer is modeled by growth and coalescence of prescribed voids in 2D. Influences of material properties, initial void volume fraction, geometric constraints and elastic mismatch are investigated. The results show a loss of ductility with decreasing film thickness that is accompanied by a severe decrease in fracture initiation toughness as well as an increased stress at the interface. The influence of materials properties is significant in all cases while the effect of initial void volume fraction is comparatively less critical for highly confined materials than for bulk materials. Increasing confinement also results in increasing normal stress at the phase interface, promoting interface decohesion prior to ductile fracture of the film. The present approach and results are a step towards more detailed prediction of composite fracture toughness and crack-growth resistance.

中文翻译：

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建模受限韧性断裂——一种空隙增长和聚结方法

摘要 在复合材料中，软的、可延展的基体可以被硬的、脆的相限制，从而改变其变形和断裂行为。增加约束导致基体脆化，进而导致复合材料脆化。从材料设计的角度来看，通常希望在不影响材料硬度的情况下避免脆性断裂。因此，了解受限韧性断裂对于模拟具有精细微观结构的复合材料的机械响应至关重要。目前的工作重点是夹在理想线弹性基材之间的具有弹塑性幂律硬化行为的薄延性薄膜的受限延性断裂。韧性层的断裂通过二维中指定空隙的生长和聚结来建模。材料特性的影响，研究了初始空隙体积分数、几何约束和弹性失配。结果表明延展性随着薄膜厚度的减小而损失，伴随着断裂起始韧性的严重降低以及界面处的应力增加。材料特性的影响在所有情况下都是显着的，而初始空隙体积分数的影响对于高度受限的材料比对散装材料的影响要小。增加约束还会导致相界面处的法向应力增加，从而在薄膜延展性断裂之前促进界面脱聚。目前的方法和结果是朝着更详细地预测复合材料断裂韧性和抗裂纹扩展性迈出的一步。结果表明延展性随着薄膜厚度的减小而损失，伴随着断裂起始韧性的严重降低以及界面处的应力增加。材料特性的影响在所有情况下都是显着的，而初始空隙体积分数的影响对于高度受限的材料比对散装材料的影响要小。增加约束还会导致相界面处的法向应力增加，从而在薄膜延展性断裂之前促进界面脱聚。目前的方法和结果是朝着更详细地预测复合材料断裂韧性和抗裂纹扩展性迈出的一步。结果表明延展性随着薄膜厚度的减小而损失，伴随着断裂起始韧性的严重降低以及界面处的应力增加。材料特性的影响在所有情况下都是显着的，而初始空隙体积分数的影响对于高度受限的材料比对散装材料的影响要小。增加约束还会导致相界面处的法向应力增加，从而在薄膜延展性断裂之前促进界面脱聚。目前的方法和结果是朝着更详细地预测复合材料断裂韧性和抗裂纹扩展性迈出的一步。