Abstract
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.
- Received 21 July 2023
- Revised 4 December 2023
- Accepted 25 January 2024
DOI:https://doi.org/10.1103/PhysRevX.14.011054
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Soft elastomers can undergo large and reversible deformations, making them useful in many fields ranging from soft robotics to stretchable electronics. In each of these applications, a key consideration is how the elastomers fail via fracture. Our current understanding of soft fracture is based on a classical picture of essentially 2D crack growth, augmented by an emerging consensus that the crack-tip fracture process is controlled by two material length scales. Here, we reveal that this 2D picture does not capture the behavior of strain-stiffening elastomers: Their fracture properties can be surprisingly dependent on thickness, with thicker elastomers being stronger than thinner ones.
In our experiments, we perform tension tests on samples of a commercial, highly stretchable silicone elastomer and image the fracture surface across the sample thickness as the sample is loaded. We find that cracks in such materials grow in an unusual way: Damage nucleates on the two faces of cracked samples and propagates inward toward their center line. Ultimately, samples fail when the two damaged zones meet. We further show how the elastomer stretch behavior controls this process.
Our results have implications for how to effectively toughen elastomer samples by controlling their geometry and material properties.
