Bio-inspired heterogeneous soft materials are under rapid development due to their superior fracture and fatigue resistance. In the last few years, several kinds of fibrous soft composites in different length scales have been fabricated. However, the fracture behavior and toughening mechanism of this class of materials are still elusive. Here we develop a theoretical model for the crack tip field of fiber reinforced soft composites. The distribution of deformation around the crack tip and released elastic energy during crack propagation are obtained. The fracture process zone and fracture energy are quantified. There is a critical sample height, below which the fracture process zone size and fracture energy are size-dependent, above which they approach material-specific constants: steady-state fracture process zone size and steady-state fracture energy. A formula is derived to relate the steady-state fracture process zone size and parameters of the composite. It is found that both the steady-state fracture process zone size and the critical sample height scale with the fractocohesive length of the composite. The steady-state fracture energy of the composite can be enhanced either by enlarging the fracture process zone size through tuning fiber geometry or by increasing the work to rupture of the fiber through chemical treatment. This work reveals the toughening mechanism of heterogeneous soft materials and paves the way to design soft materials of high fracture energy, high fatigue threshold, and low hysteresis. It also provides a practical guideline for determining the sample size to measure the steady-state fracture energy of heterogeneous soft materials.

中文翻译：

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非均质软材料的断裂过程区和断裂能量


仿生异质软材料因其卓越的抗断裂性和抗疲劳性而正在迅速发展。在过去的几年中，已经制造了几种不同长度尺度的纤维软复合材料。然而，这类材料的断裂行为和增韧机制仍然难以捉摸。在这里，我们开发了纤维增强软复合材料裂纹尖端场的理论模型。得到了裂纹尖端周围的变形分布和裂纹扩展过程中释放的弹性能。对断裂过程区和断裂能量进行了量化。有一个临界样品高度，低于该高度的裂缝过程区大小和裂缝能量与尺寸有关，高于该高度，它们接近特定于材料的常数：稳态裂缝过程区尺寸和稳态裂隙能量。推导了一个公式来关联复合材料的稳态断裂过程区大小和参数。研究发现，稳态断裂过程区大小和临界试样高度都随复合材料的分裂内聚长度而变化。复合材料的稳态断裂能可以通过调整纤维几何形状来扩大断裂过程区的大小，或者通过化学处理增加纤维断裂功来提高。这项工作揭示了非均相软材料的增韧机理，为设计高断裂能、高疲劳阈值和低滞后的软材料铺平了道路。它还为确定样本量以测量非均相软材料的稳态断裂能量提供了实用指南。