Effect of Microstructure of a Filled Rubber on its Overall Mechanical Properties

In order to answer the question of why the mechanical behavior of filled rubber is so different from the corresponding unfilled gum rubber, a multiscale material model of filled rubber, which combines molecular mechanics, statistical mechanics and micromechanics, has been developed. The model has been used to explore the effect of filler particles and bond strength at the filler-elastomer interface on the overall elastic properties of a filled rubber. The model confirmed the well-established phenomena such as non-uniform strain-amplification but now the model added much more detailed molecular information such as crosslinking density, bond strength at filler-elastomer interface, etc. to the whole phenomena. This capability enables us to investigate the influences of such factors on the overall mechanical properties of filled rubber. The results revealed that the degree of stretching is greatly amplified in elastomer chains located between the filler particles along the loading direction. The degree of nonuniform stretching increases with filler volume fraction. The fully-stretched elastomer chains contribute significantly greater force and stiffness than those that are stretched less. Both the Mullins effect and the Payne effect come from the non-uniform filler size and/or spatial distribution. Reducing non-uniformity of filler size and spatial distribution can decrease the degree of the Mullins effect and the Payne effect. Improving bond strength at filler-elastomer interface can delay happening of the Mullins effect and the Payne effect but cannot eliminate them.