Elastic moduli of injection-molded short-glass-fiber-reinforced poly(ethylene terephthalate)

The nine independent elastic constants of injection-molded tensile bars of poly(ethylene terephthalate) reinforced with 30%, 45% and 55% by weight of glass fibers have been determined by ultrasonic techniques. The tensile and shear moduli increase with increasing fiber volume fraction, with the tensile modulus along the longitudinal direction showing the greatest change. For a composite containing 55 weight % of glass fibers, the longitudinal tensile and shear modulus exceed those of the matrix by factors of 5 and 3, respectively. By regarding the injection-molded bar as a multidirectional laminate comprising a large number of unidirectional plies, the elastic moduli have been calculated and found to agree closely with the experimental data.