Multi-scale characterization and modelling of the transverse compression response of unidirectional carbon fiber reinforced epoxy

Thick unidirectional fiber reinforced RTM6 epoxy resin specimens were processed by resin transfer molding and tested in transverse compression. Homogenized response from micromechanical analyses on representative volume elements, using a constitutive model for the matrix identified and validated on bulk RTM6 specimens, were assessed towards the experimental results. Large discrepancies were observed in terms of failure initiation and non-linearity in the stress-strain response. Regarding the interfaces, the use of frictional cohesive elements greatly enhanced the damage tolerance of the RVEs to interface damage. Regarding the matrix behavior, in situ tests on UD specimens and microscale digital image correlation highlighted significant gaps between the numerical and experimental strain fields. Excessive strain localization in the simulations is believed to be the main reason for these differences. This study raises fundamental questions on the degree of confidence that can be granted to constitutive models validated at the macroscale to predict strain field at the microscale.