Micro-mechanical analysis of the effect of ply thickness on curing micro-residual stresses in a carbon/epoxy composite laminate

During the manufacturing of thermoset-based carbon fiber reinforced polymers (CFRPs), micro-residual stresses are developed in the material, due a mismatch of the chemical-thermal-mechanical properties of the fibers and the polymer matrix. This ultimately leads to a reduction in the mechanical performance of the composite material. In this work, a representative volume element (RVE) of a composite sub-laminate with a 90 degrees ply discretized at micro-scale level, stacked within homogenized plies, is proposed to study the micro-residual stresses and the ply mechanical response considering the in-situ effect caused by the constraining adjacent layers. A model framework is developed using finite elements in Abaqus & REG;/Standard with user-subroutines. The retrieved micro-residual stresses in the 90 degrees layer are generated by the dissimilar chemical shrinkage and thermal expansions, plus the additional residual meso-scale stresses caused by the constraining effect of adjacent plies. The residual stresses in the constrained condition can achieve almost 80 % of the ply failure load for the 0/90/0 sublaminate, meaning lower sub-laminate strain to failure. Thick laminates retrieve more residual stresses in the transverse 90 degrees layer and exhibit lower constrained strength and more unstable post-failure response, demonstrating that thin-ply laminates exhibit beneficial constraining effects during the curing process.