FRACTURE-TOUGHNESS AND IMPACT BEHAVIOR OF GLASS-FIBER-REINFORCED POLYAMIDE-6,6 INJECTION MOLDINGS

The fracture toughness of injection-moulded long-glass-fibre-reinforce d polyamide 6,6 (average fibre aspect ratio in mouldings, l/d approxim ate to 55) with fibre weight contents of 50 and 60% was studied and co mpared with that of short-glass-fibre-reinforced polyamide 6,6 (l/d ap proximate to 20). Toughness was measured by using Mode I compact-tensi on specimens cut from the mouldings and also by means of instrumented drop-weight impact tests. The addition of fibres to a polyamide 6,6 ma trix led to an improvement of fracture roughness. The improvement was marginally greater in the long-fibre grades. Fracture roughness values were dictated by the average in-plane fibre orientation angle ahead o f the crack front and fibre length, particularly for the long-fibre gr ades. Instrumented drop-weight impact tests indicated brittle fracture for unreinforced polyamide 6,6, causing possible catastrophic shatter ing into several pieces. Short-fibre and long-fibre materials both rem ained intact after impact, with smaller dimensions of the damaged area for the long-fibre materials. Crack initiation force and total energy values were increased by 25-37% and 300-600%, respectively, with the inclusion of glass fibres. Negligible differences in these values were observed between the long- and short-fibre grades and with the long-f ibre content increasing from 50 to 60% w/w.