FRACTURE-BEHAVIOR OF GLASS-FIBER-REINFORCED POLYAMIDE MOLDINGS

Various grades of commercially available glass fibre reinforced and un filled Polyamide 66 compounds were injection moulded into a complex mo uld geometry. Mode I fracture toughness was determined using compact t ension specimens cut from the mouldings. Rapid photographic procedures were used to identify positively crack initiation. Fracture toughness was higher in the filled systems than in the unfilled compounds; K(Q) for the latter was approximately 4 MN m-3/2. However, there was only a slight variation between the short glass fibre (50%, w/w) and long g lass fibre (50%, w/w) containing grades with K(Q) values (calculated u sing load (P5%) in ASTM E399) of 7.0 and 6.4 M N m-3/2, respectively. Using photography, it was found that P5% coincides with the force at c rack initiation for unfilled PA66, while for the filled materials P5% and P(crack initiation) did not coincide. Crack-initiation force value s of 17 to 27% greater than P5% for the short fibre material and 29 to 67% larger than P5% for the long fibre material were identified. Howe ver, these higher values of load to crack initiation were at variance with the LEFM theory and are therefore questionable.