Modeling the dynamic fracture of polymer blends processed under shear

Using computational models, we examine how shearing a binary polymer melt affects the dynamic fracture mechanics of the final solid material. The phase separation of the immiscible blend under an imposed shear is simulated through the Cahn-Hilliard method, where an advection term is added to introduce the flow field. Using this model, we simulate the structural evolution of the blend and obtain the late-stage morphology of the sheared mixture. As expected, the domains are elongated in the direction of the imposed shear. We couple these morphological results with micromechanical studies. The dynamic Lattice spring model (LSM) is utilized to simulate crack propagation through the solid blend structure. The dynamic LSM consists of a network of springs that connect regularly spaced mass points; the behavior of these points is dictated by Newtonian dynamics. The model allows us to simulate crack propagation through these heterogeneous structures and determine the strength, toughness, fracture toughness, and critical J integral of the material. Consequently, we can correlate the relative orientation of the interfacial regions to the overall mechanical behavior of the system. We also contrast these results with findings from simulations on the unsheared samples and thereby probe the effect of processing on the performance of polymer blends.