Instrumented impact testing of a glass swirl mat‐reinforced reaction injection‐molded polyamide block copolymer (NBC)

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Abstract
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°C, fracture mechanical parameters (fracture toughness, fracture energy) andE‐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 whenW> 12 mm andL0/L> 1.7 for the specimens. The fracture toughness andE‐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.