Micro-sphere model for strain-induced crystallization in rubber

Natural rubber is known to crystallize under strain so that samples subjected to loading-unloading cycles exhibit hysteresis. In the present paper, an anisotropic constitutive model for strain-induced crystallization rubber is proposed based on review of the numerous experiments conducted on this material. Detailed information on the semi-crystalline system is therefore available, particularly simultaneous measurements of stress and crystallinity versus elongation. Then, introducing an internal variable associated to crystallinity, a solution to the evolution of this variable can be found, that is thermodynamically consistent. This 1D model is then plugged into a micro-sphere approach. In this approach, each direction is free to have its own history, which allows us to obtain an evolving anisotropy. This model is assessed by uniaxial tensile tests under cyclic loadings and anisotropy measurements.