Computational Characterization of Micro- to Macroscopic Mechanical Behavior and Damage of Polymers Containing Second-Phase Particles

To clarify the mechanical characteristics and damage of polymers containingsecond-phase particles, i.e., blended polymers, a homogenization method has been developed which can handle the large deformation problems, including onset and propagation of instability, and completely reproduce the periodic feature of the distribution of second-phase particles under any macroscopically homogeneous loading condition. The parametric study has clarified the characteristic features of polymers containingperiodically distributed soft cylindrical particles of different volume fractions and sizes subjected to macroscopically homogeneous stress in different directions. The results indicate that, dependingon the tensional direction with respect to the unit cell, different types of shear bands are observed, and that the shear band connectingthe particles that appeared in the early stages of deformation is responsible for the reduction of the macroscopic yield stress. Increasingthe volume fraction of particles causes a decrease of the macroscopic yield stress and of the directional dependence of the macroscopic stress–strain relation. The size difference of particles causes very complicated and different types of shear bands, however, due to the high stress concentration caused by the presence of small particles, the onset and propagation of shear bands are promoted, and the macroscopic deformation behaviors become essentially isotropic. The maximum mean stress appears in the small particle, which suggests that the blending of particles of different sizes promotes the onset of cavitation, which suppresses the maximum mean stress in the matrix and results in additional shear deformation and in preventing onset of damage in matrix caused by crazing. The location of maximum normal stress on the boundary surface between particles and matrix moves with the propagation of the shear band. The magnitude of maximum normal stress increases with the increase of the size difference between the particles and with the decrease of the volume fraction within the present simulation.