On the essential work of fracture of neat and rubber toughened polyamide-66

Essential work of fracture (EWF) tests have been conducted on neat and rubber toughened polyamide-66 in order to measure the essential specific work of fracture ( w e) and the non-essential specific work of fracture ( βw p) parameters. Further, the w e value has been partitioned into two terms, one related to the specific energy contribution for yielding up to the onset of fracture ( w e,init), and another one representing the subsequent crack propagation process ( w e,prop), respectively. EWF tests performed on neat polyamide-66 specimens conditioned up to various equilibrium moisture contents clearly indicate that w e markedly increases as the material moisture content rises, and that this trend is mainly associated with the increase of its crack propagation component ( w e,prop), the initiation related term ( w e,init) being practically independent of the humidity level. The inclusion of various amounts (7, 16, and 25 wt%) of rubber particles (a random ethylene–acrylic ester–maleic anhydride terpolymer) into the polyamide-66 matrix induces a large increase of the w e parameter. It is interesting to observe that the w e,init and w e,prop terms display different trends with the rubber content. Most of the toughening effect of the rubber particles can be attributed to a large increase of the propagation-related term, the fracture initiation term decreasing with the rubber content. Finally, the loading rate effects on the fracture behaviour have been investigated for polyamide-66 toughened with 25 wt% rubber. An increase of the loading rate causes an increase of the crack-initiation related term w e,init, while the crack-propagation related parameter w e,prop decreases. As a consequence, the specific term w e shows a non-monotonic trend with the loading rate.