Statistical distribution of strength of fiber‐reinforced composite materials

The Weibull distribution is presented as a physically consistent description of strength distribution in brittle composites. Methods are developed for obtaining point and one‐sided interval estimates for the parameters of the Weibull distribution. Strength data are obtained for 25 replicates of nine different sheet molded and injection molded composites, and the developed statistical methods are applied to these data. Details of the materials and processing are given. Strength results indicate that the reliability calculations using the one‐sided interval estimates are uniformly conservative for all materials. In addition, it is shown that composites produced with a less automated production process show more strength variability. Machining of an injection molded composite surface appears to lower strength and increase strength variability by introducing flaws which act as fracture initiation sites.