| Abstract Scope |
From Hooke’s law in the 1660s to the 1930s work of Flory on polymer chains, the understanding of rubber elasticity was formalised 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. The presentation will end with a broad overview of laboratory X-ray techniques including high-speed tomography and energy dispersive diffraction that might open new understandings for a range of materials. |