Notch sensitivity of polycarbonate and toughened polycarbonate

Notch sensitivity, the effect of a notch radius on the impact behavior of polycarbonate and rubber-toughened polycarbonate, is investigated by using a model based on the slip-lines field theory. Impact strength, determined by the Charpy impact test, was found to increase drastically with an increasing notch radius for pure polycarbonate, whereas the increase of impact strength with increased notch radius was not as extreme for rubber-toughened polycarbonate. These results indicate that the inclusion of rubber particles reduces notch sensitivity. An examination of fracture surfaces reveals that cracks were initiated by internal crazing at some distance from the notch tip for specimens with blunt notches. For pure polycarbonate, the impact strength is found to have a linear relationship with the square of the notch radius, which is in good agreement with that predicted by the proposed model. However, for rubber-toughened polycarbonate, the linear relationship broke down as the notch radius increased due to the enhanced toughening effect. The proposed model can be applied to clearly explain the notch sensitivity of ductile polymers which exhibit large plastic yielding around the notch tip. (C) 2003 Wiley Periodicals, Inc.