The performance of soft devices is limited by the fracture resistance of elastomers. Thus, understanding how fracture resistance changes with material and sample geometry is an important challenge. A key observation is that thicker elastomers can be significantly tougher than thinner ones. We show that this surprising toughness enhancement in thick samples emerges from the 3D geometry of the fracture process. In contrast to the classical picture of a 2D crack, failure is driven by the growth of two separate “edge” cracks that nucleate early on at a sample’s sides. As loading is increased, these cracks propagate in towards the sample midplane. When they merge, samples reach their ultimate failure strength. In thicker samples, edge cracks need to propagate farther before meeting, resulting in increased sample toughness. We demonstrate that edge-crack growth is controlled by the elastomer’s strain-stiffening properties. Our results have direct implications for how to effectively toughen elastomers by controlling their geometry and large-strain mechanical properties.

中文翻译：

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弹性体从边缘失效

软装置的性能受到弹性体的抗断裂性的限制。因此，了解断裂阻力如何随材料和样品几何形状变化是一个重要的挑战。一个关键的观察结果是，较厚的弹性体比较薄的弹性体更坚韧。我们证明，厚样品中这种令人惊讶的韧性增强源于断裂过程的 3D 几何形状。与二维裂纹的经典图像相反，失效是由两个单独的“边缘”裂纹的生长驱动的，这些裂纹早期在样品侧面成核。随着载荷的增加，这些裂纹会向样品中面扩展。当它们合并时，样品达到最终的失效强度。在较厚的样品中，边缘裂纹在相遇之前需要传播得更远，从而提高样品的韧性。我们证明边缘裂纹的扩展是由弹性体的应变硬化特性控制的。我们的结果对于如何通过控制弹性体的几何形状和大应变机械性能来有效增韧弹性体具有直接影响。