A novel approach to the analysis of distributed shear banding in polymer blends

The toughness of glassy polymers can be enhanced by blending with rubber particles. The consensus is that this toughening is due to massive plastic deformation of the matrix that takes place once the particles have cavitated. Micromechanical studies of regular stackings of particles in a polymer matrix have provided much insight into the localized plastic flow in blends at the microscale of individual particles (or voids, once cavitated). Even some steps towards macroscopic constitutive models have been made. However, at intermediate length scales (i.e. larger than several particles, but smaller than the scale at which the material may be regarded as homogeneous) the situation is unclear. It is this length scale that becomes important around crack tips, for example, where a thorough understanding of the toughening effect has to be derived from. In this paper, we therefore present a novel approach to the analysis of distributed shear banding in polymer–rubber blends. A coarse-grain description, in which much of the morphology is retained but the local shear banding is idealized into ‘shear surfaces’, will enable us to analyse ensembles with large numbers of particles. The parameters of this model will be validated with results from detailed cell analyses.