On the effect of geometrical fiber arrangement on damage initiation in CFRPs under transverse tension and compression

The mechanical performance of composite materials is strongly dependent on its microstructure. Efficient design of composites requires proper estimation of the effect of the microstructure on residual stresses that arising from cooling due to manufacturing temperature. The study of the stresses and damage in fibres interface and its relationship with geometrical distribution of the fibres can contribute to a better comprehension of the mechanical response of the composite. We use 2D numerical models to represent a composite material reinforced with longitudinal fibres. The mechanical behaviour is analysed taking into account the cooling effect and tension/compression transverse loading. We have generated a range of virtual microstructures, characterized by the microstructure randomness, to study the influence of the fiber randomness on the damage initiation. Damage initiation at fibres interfaces has been estimated from the stresses induced at the interface, both in the whole structure and for individual fibers. As expected, a strong effect of the randomness of the fiber arrangement on the damage initiation has been found. For all microstructures and loading modes, higher values of microstructure randomness results in earlier damage development. Normal and shear stresses at individual fibre interfaces have been analysed under tension and compression loading. In tension, normal stress at the fiber interface fully dominates the interfacial damage initiation. In compression, damage is almost completely dominated by the interfacial tangential stress. In compression, localized plasticity develops simultaneously with damage initiation whereas in tension, damage initiation occurs at a stress three times lower than the required for the onset of plasticity. The maximum shear and normal stresses around individual fibers are strongly affected by the local neighborhood.