Comparative study of the fracture behavior of flow-molded GMT-PP with random and chopped-fiber mats

The fracture toughness, K_Q, of hot-flow compression-molded glass-mat-reinforced thermoplastic polypropylene (GMT-PP) with random (R) and chopped (C) fiber mats was determined on single-edge-notched specimens loaded in tension (SEN-T) at ambient temperature. The development of damage was assessed by location of the acoustic emission (AE) activity in specimens cut from the side and central parts of the molded plaques and loaded along (L) and transverse (T) to the flow direction. The molding-induced anisotropy was clearly reflected in the K_Q values, which were considerably higher in the L than in the T orientation, especially for specimens cut from the side of the plaque. The toughness response of GMT-PPs with R and C mats was similar however. It was found that the fracture toughness calculated by considering non-linearity in the force vs. displacement curve according to ASTM E 399 is the best estimate for the initiation value. The damage zone and its development was estimated by considering the located AE events. AE served also to trace the differences in the failure mode as a function of mat type and loading ranges.