Shearing of particles during crack growth in polymer blends

Microstructural investigations below the fracture surface have revealed tha t the rubber particles in a number of polymer-rubber blends were deformed i nto remarkable S-like shapes. These shapes seem to have been largely ignore d in previous microstructural studies of blends, but in fact cannot be expl ained from the known deformation states around a crack. We hypothesize in t his paper that these shape changes develop as a consequence of macroscopic shearing of the blend as the crack front sweeps through the material. Large strain, finite element models for simple shearing of a blend are reported which demonstrate the evolution of round particles into S-shape ones for a range of material parameters, and thus support our hypothesis. The 'microsc opic' localized deformation processes are identified, and the implications for the toughening mechanism in these blends is discussed. (C) 1999 Elsevie r Science Ltd. Ail rights reserved.