Micromechanical modeling of particle-toughening of polymers by locally induced anisotropy

The impact strength of several semi-crystalline polymers can be improved by the dispersion ofsecond-phase rubber particles. A criterion for the effect of this practice is based on the averageinterparticle matrix ligament thickness. The critical interparticle distance, below which a substantialtoughness increase can be observed, is considered to be an intrinsic material propertyof the matrix. A toughening mechanism has recently been suggested which considers a layerof transcrystallized material around well-dispersed particles, having a reduced yield strengthin certain preferentially oriented directions. In this work, the potential of local anisotropy forthe toughening of semi-crystalline polymeric material is investigated. The matrix material ismodeled within the framework of anisotropic Hill plasticity with a rate dependent and hardeningyield stress. The applicability of different two-dimensional micromechanical models is assessedby comparison to fully three-dimensional simulations with irregularly dispersed particles. Areduced plastic shear resistance of percolating transcrystallized material is found to be very effectivein inducing extensive delocalized shear deformations and alters the location of the peaktensile hydrostatic stresses.