Chapter 18 Large Deformation of Particle-Filled Rubber Composites Toshio Nakamura and Marc Leonard Abstract Soft materials such as rubber may be stiffened by mixing with high modulus particles. In order to investigate their large behaviors at large deformation, particle-filled silicone rubber (RTV) specimens are fabricated. Although there have been numerous experiments for composites, a limited number of tests exists for finite deformation investigation of composites filled with uniformly shaped particles. In the tests, two types of particles are used. One is uniform glass beads with about 55μm diameter and the other is spherical zirconia powder with diameters ranging from 30 to 80μm. The former composites showed initial stiffening but the effects were limited as debonding of particles from matrix rubber occurs at large stresses. The latter composites showed better bonding as their surfaces are rough. Specimens are loaded multiple times in tension and compression. Their nonlinear behaviors as well as the Mullins effects are analyzed. The observed experimental results were compared with 3D finite element calculations as well as various nonlinear constitutive models and the rule of mixture. Keywords RTV silicone • Finite strain • Incompressible materials • Rule-of-mixture • Soft materials 18.1 Introduction Rubber has typically been used to make various products such as gloves, toys, boots, raincoats and tires. Due to its corrosion resistance properties, the chemical process industry found use for rubber in protecting storage tanks and process vessels [1]. As an engineering material rubber offers several benefits due to its corrosion, seal, damping, insulation and ablation properties. In engineering the term rubber refers to a specific class of materials called elastomer. Elastomers are amorphous polymers with their molecules in random motion. Polymers in turn are a high molecular compound formed by the addition of a small repeating unit, the monomer [1]. Usually in the form of a viscous liquid, rubber becomes usable through a process called vulcanization. The addition of curing agents creates cross-linking of the polymer chains and the material becomes a solid. Rubber is a soft material which is capable of very large deformation without failure. However, the deformation of rubber is highly non-linear although the material essentially remains elastic. The material also exhibits viscoelastic properties. As a result several material models have been proposed to characterize the behavior of rubber. The Ogden and Mooney-Rivlin are ones among widely utilized models because they can be well-fitted to experimental data. Recent advances in technology have created a need for high performance rubber with specific properties tailored to their end use. With advance manufacturing techniques, it is common to reinforce rubber with fillers made from elastic materials of high modulus. Most common fillers are carbon black and silica in fiber and particulate forms. The effect of particle volume concentration in rubber was first studied by Einstein on the effective viscosity for a dilute suspension of spheres. While it is well known that adding filler to the elastomer will increase its stiffness, the mechanics of such transformation still needs to be investigated. Often research is limited to small strain range for low filler concentration. Recently, Lopez-Pamies et al. [2, 3]. studied the effect of rigid particulate dilute inclusions in rubber. T. Nakamura (*) • M. Leonard Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY 11794-2300, USA e-mail: toshio.nakamura@stonybrook.edu #The Society for Experimental Mechanics, Inc. 2016 C. Ralph et al. (eds.), Mechanics of Composite and Multi-functional Materials, Volume 7, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-21762-8_18 149
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