Fracture Toughness

Abstract

Studies on plain syntactic foams have revealed that the fracture toughness and specific fracture toughness are found to be maximum around 30 vol. % of hollow particles. At low hollow particle volume, fraction stiffening effect and crack bowing failure mechanism was observed whereas at high volume fraction, hollow filler particle-matrix debonding is found to the dominant failure mechanism. Fracture toughness studies on reinforced syntactic foams have been performed only at a constant hollow particle volume fraction of 30 vol. %. A study on phenolic hollow particle filled syntactic foams concluded that fracture toughness increased with increasing fibers content. A maximum increase of 95 % was observed with respect to plain syntactic foam for 10 mm length fiber at 3 wt%. Carbon fibers were found to have a significantly stronger effect on the fracture toughness than glass fibers. PEEKMOH toughened epoxy matrix syntactic foams were found to have up to a 46 % improvement in fracture toughness with the addition of 5 wt% nanoclay. An increase of 37 % in fracture toughness is observed for the addition of 1.5 vol. % of carbon nanofibers in comparison to plain syntactic foams. It was also observed that microscale reinforcement (short carbon fibers) was more effective than nanoscale reinforcement (nanoclay), at similar weight fractions.