Size effect on tensile strength of unidirectional CFRP composites— experiment and simulation

The present paper studies the size effect on the strength of unidirectional carbon fiber reinforced plastic (CFRP) composites both experimentally and numerically. The main aim of the present study is to validate the recent micro-mechanical model for internal damage occurring in composites. The relationship between the composite size and strength was experimentally evaluated, and the composite strength decreased as the composite size increased. Microscopic damage observation showed the existence of localized damage (i.e. a cluster of fiber breakage). Based on a 3D shear-lag model considering the matrix-yielding properties, we conducted a Monte Carlo simulation of the damage process using the measured fiber strength distribution for several gage lengths. The simulation shows that Weibull of Weibull (WOW) statistics considering the fiber-to-fiber strength variation is appropriate for predicting the present composite failure, rather than a traditional Weibull model. The simulated result showed a good agreement with the upper bounds of the experimental data. It was found that the size-dependent strength of composite could be predicted based on the microscopic models.