Reliability analysis of tensile strengths using Weibull distribution in glass/epoxy and carbon/epoxy composites

In this study, experiments are carried out to determine the tensile strength of laminates, for three different orientations [(0/90/30/-60), (0/90/45/-45) and (30/-60/60/-30)] of glass/epoxy and carbon/epoxy composites, for the strain rate range of 0.0083–542 s−1. Using two-parameter Weibull distribution, the theoretical tensile strength values are determined for Glass Fiber Reinforced Polymer (GFRP) and Carbon Fiber Reinforced polymer (CFRP) composites for different strain rates by a linear curve fitting. The theoretical and experimental values match well. The deviation between the theoretical and experimental values is less than 12% for GFRP laminates and less than 13% for CFRP laminates. Normally the mean values of mechanical properties are sufficient to use theoretical models, whereas all tested specimen data are considered (including the mean values) in Weibull distribution. Therefore, Weibull distribution contains more information and it will be useful for designers and composite manufacturers to ensure the reliability of structures. Studies show that the (0/90/45/-45) laminates have exhibited the highest scale parameter increment of 80.5% for glass/epoxy and 53% for carbon/epoxy composites with the increase of strain rate, when compared to laminates of other orientations. Using scanning electron microscopy (SEM), the failure mechanisms such as matrix microcracking and fiber-matrix interface microcracking are observed in quasi-static testing whereas the fiber pull-out, matrix damage and fiber-matrix interface cracking are seen in the high strain rate tests, which ensure the increase in strength values at high strain rate.