Effect of fibre concentration and strain rate on mechanical properties of single-gated and double-gated injection-moulded short glass fibre-reinforced polypropylene copolymer composites

The effect of fibre concentration, strain rate and weldline on tensile strength, tensile modulus and fracture toughness of injection-moulded polypropylene copolymer (PPC) reinforced with 10, 20, 30 and 40% by weight short glass fibre was studied. It was found that tensile modulus of single- and double-gated mouldings increased with increasing volume fraction of fibres, phi f, according to additive rule-of-mixtures, and increased linearly with natural logarithm of strain rate (ln (e) over dot). The presence of weldlines in double-gated mouldings led to reduction in tensile modulus which for composite containing 40% by weight short fibres was as much as 30%. A linear dependence was obtained between fibre efficiency parameter for composite modulus and ln (e) over dot for both single- and double-gated moulding. Tensile strength of single- gated mouldings, sigma(c), increased with increasing phi f in a nonlinear manner. However, for phi f in the range 0-12% a simple additive rule-of-mixtures adequately described the variation of sigma(c) with phi f. A linear dependence was obtained between fibre efficiency parameter for tensile strength and ln (e) over dot. The presence of weldlines in double-gated mouldings reduced tensile strength by as much as 70%. Tensile strength of both single- and double-gated mouldings increased linearly with ln (e) over dot. Fracture toughness of single- gated mouldings increased linearly with increasing phi f. The presence of weldlines in double-gated mouldings reduced fracture toughness by as much as 60% for composite containing 40% by weight short glass fibres.