Activities

TYC Highlight Seminar: A reassessment of rubber elasticity via full-field X-ray measurements - Vikram Deshpande, Cambridge University - THOMAS YOUNG CENTRE

Abstract

Engineering polymers, including rubbers, find extensive applications across diverse industries, from aerospace to medicine. From Hooke’s law in the 1660s to the 1930s and 1940s work of Flory on polymer chains (1974 Nobel prize), the understanding of rubber elasticity was formalised in the 1940s via the Neo-Hookean model. This established the idea that, under isothermal conditions, stress is (non)linearly related to strain and no other state variable. Here, we suggest that this fundamental concept might need to be revisited.  Using innovative X-ray measurements capturing the three-dimensional spatial volumetric strain fields, we demonstrate that rubbers and indeed many common engineering polymers, undergo significant local volume changes. But remarkably the overall specimen volume remains constant regardless of the imposed loading. This strange behaviour which also leads to apparent negative local bulk moduli is due to the presence of a mobile phase within these materials. Using a combination of X-ray tomographic observations and high-speed radiography to track the motion of the mobile phase we have revised classical thermodynamic frameworks of rubber elasticity.

Z. Wang, S. Das. A. Joshi, A.J.D. Shaikeea and V.S. Deshpande (2024), 3D observations provide striking findings in rubber elasticity, Proceedings of the National Academy of Sciences, 121 (24), e2404205121.

Commentary: C. Hartquist, S. Wang and X. Zhao (2024), Local volume changes in deformed elastomers with mobile chains, Proceedings of the National Academy of Sciences, 121 (30), e2410811121.