INSTRUMENTED IMPACT TESTING OF A GLASS SWIRL MAT-REINFORCED REACTION INJECTION-MOLDED POLYAMIDE BLOCK COPOLYMER (NBC)

The fracture behavior of a reaction injection-molded (RIM) polyamide block copolymer (NBC) reinforced with a continuous glass strand mat (swirl mat) was studied in instrumented high-speed impact-bending tests. Investigations were carried out on Charpy and Izod specimens of different size and notching direction to elucidate specimens' size effects. From the tests performed at ambient temperature and -40-degrees-C, fracture mechanical parameters (fracture toughness, fracture energy) and E-modulus were derived. Changes observed in the above parameters of the matrix were attributed to a molding-induced skin-core morphology. Both fracture toughness and energy of the composites depended strongly on the type, i.e., on the ligament width (W) and length-to-span ratio (L0/L) of the specimens. Reliable fracture mechanics data can be determined in three-point bending when W > 12 mm and L0/L > 1.7 for the specimens. The fracture toughness and E-modulus increased monotonously, whereas the fracture energy reached a plateau as a function of fiber mat content. Their values were only slightly influenced by the temperature. It was also shown how molding- and machining-induced flaw size can be defined. The failure mode of the materials was studied by fractography and the failure events were summarized in a model and discussed.