Temperature, strain rate and weldine effects on strength and micromechanical parameters of short glass fibre reinforced polybutylene terephthalate (PBT)

The effect of fibre concentration, strain rate, temperature and the type of loading on strength of single and double-gate injection moulded polybutylene terephthalate (PBT) reinforced with 0, 10, 20 and 30% by weight short glass fibre was studied. It was found that tensile strength of single-gate mouldings increased nonlinearly with increasing fibre volume fraction, increased linearly with increasing natural logarithm of strain rate and decreased linearly with increasing temperature. It was noted that for fibre concentrations of up to 12% v/v, tensile strength of single-gate mouldings can be modelled by a simple additive rule-of-mixtures. The overall efficiency parameter as obtained from the slope of linear regression lines increased linearly with increasing strain rate but decreased linearly with increasing temperature. Tensile strength of double-gate mouldings increased initially with increasing fibre volume fraction but decreased as fibre concentration exceeded 10%v/v, or thereabouts. Results indicated that tensile strength of double-gate mouldings, like their single-gate counterparts, increased linearly with increasing strain rate and decreased linearly with increasing temperature. The strength of single and double-gate mouldings in flexure was higher than in tension by a factor of 1.60. The presence of weld lines in double-gate mouldings led to a considerable reduction in tensile and flexural strength of reinforced PBT mouldings, but had no significant effect on strength of unreinforced PBT mouldings. Weld line integrity factor strength decreased with increasing fibre volume fraction but showed no significant variation with respect to temperature, strain rate or the type of loading. A linear dependence was obtained between the natural logarithm of weld line integrity factor and (fibre volume fraction) 2/3 for both tensile and flexural strength.