Predictions of carbon fibre sheet moulding compound (CF-SMC) mechanical properties based on local fibre orientation

Carbon Fibre-Sheet Moulding Compound materials (CF-SMC) are an innovative class of intermediate materials made of chopped carbon fibre strands dispersed in uncured (or partially cured) thermoset resin. These sheets are then compression moulded into the final desired shape. Currently, the more commonly used models for SMC mechanical properties were initially developed for injection moulded composites, where the reinforcement is in the form of individual fibres, rather than tows or bundles. However, the presence of an additional intermediate scale of inclusions in the SMCs is not considered by those models. Their accuracy is thus questionable, and their adoption challenging: the user should generally choose whether to consider inclusions as tows or fibres, and thus have access to different material parameters, not always available (for example, the volume fraction of the tows in the composite). This work aims to validate two different formulations of a mixed Mori-Tanaka iso-strain model: one where inclusions are considered to be fibres, one where inclusions are tows; in addition, stiffness predictions are compared with the ones obtained a shear-lag multiscale model, that involves description of both tows and fibres. The models are compared with experimental evidence.