Analysis of tensile and flexural strengths of single and double gated injection moulded short glass fibre reinforced PBT/PC composites

Tensile and flexural strengths of single and double gated polybutylene terephthalate and polycarbonate (PBT/PC) reinforced with 0-30 wt-% short glass fibres were investigated. Results showed that tensile and flexural strengths of single gated mouldings conform to modified rule of mixtures with overall fibre efficiency parameter eta(sigma) of 0? 128 for tensile strengths and 0.132 for flexural strengths. The presence of weldlines in double gated mouldings significantly reduced strength of PBT/PC composites but had a minor effect on the strength of the unreinforced PBT/PC matrix. Results indicated that the flexural strengths of both single and double gated mouldings were always greater than tensile strengths. The weldline integrity factor for both strengths decreased with increasing fibre concentration in a linear manner and was independent of the test method. The strength data for both specimen types and test methods were found to fit a two parameter Weibull distribution reasonably well. The Weibull modulus m for single gated composites was found to be independent of the test method and fibre concentration (m approximate to 48) and was higher than the value for the unreinforced matrix (m approximate to 30). The presence of weldline in double gated composites reduced the value of m quite significantly. The m value for double gated mouldings decreased with increasing fibre concentration. Analysis showed that the variation in strength values with test method cannot be explained solely by the two parameter Weibull distribution model.