Toughening mechanisms in a multi-phase alloy of nylon 6,6/polyphenylene oxide

Toughening mechanisms in a nylon 6,6/polyphenylene oxide (PA/PPO) alloy are studied. This alloy consists of well dispersed PPO particles (containing an elastomeric phase) in a PA matrix. Both crazing and shear yielding mechanisms are found to be sequentially operative in this alloy. When a crack propagates in the material, a crazed zone forms ahead of the crack tip. This crazed zone then transforms into a shear yielded zone as the crack propagates through it. The crazes inside the original crazed zone are closed or distorted by the shear yielding process. In the transformed region, the shear yielded material is oriented at different angles as the crack propagates. These findings are consistent with the notion that hydrostatic tension has to be dissipated in order for the remaining deviatoric stress to reach the critical value for yielding. It is possible to partially attribute the increase in toughness to both crack blunting and zone shielding mechanisms.