Determination of the relationship between strength and test method for glass fibre epoxy composite coupons using Weibull analysis

Glass fibre epoxy composite test coupons exhibit variability in their tensile strength data dependent on the test method used. The three common test standards are for tensile, three-point flexure and four-point flexure and it is accepted that flexure tests yield higher strengths than tensile tests. Tests were carried out on coupons of a woven E-glass epoxy composite for each type of test. The data for each test was found to fit a two-parameter Weibull distribution. The Weibull moduli for each of the test methods were approximately the same. This Weibull modulus is used to relate the strengths for different test methods using an equivalent volume method. It was found that the strength variability is dependent only on the equivalent volumes of test coupons and thus, a method is proposed for the prediction of tensile strengths from flexural strength tests and vice versa.