ANALYSIS OF THE WEDGE-SHAPED DAMAGE ZONE IN EDGE-NOTCHED POLYPROPYLENE

The irreversible deformation behaviour of polypropylene during sharp single-edge-notched tension testing has been studied as a function of temperature. Specimens were tested at room temperature, -20, -40, and -60-degrees-C with photographs taken of the notch tip area during testing. Below T(g), a narrow wedge-shaped damage zone grew from the notch tip with increased stress. The damage zone length correlated with the ratio of applied stress to yield stress in agreement with the Dugdale model. The crack tip opening displacement (CTOD) was found to follow the predicted Dugdale CTOD when modified by using the secant modulus to account for viscoelasticity. The shape of the damage zone did not agree with the Dugdale model near the notch tip, but instead was found to follow a path of the minor principal stress trajectory. About T(g), the damage zone had a lower length-to-width ratio which no longer resembled the Dugdale model.