Modelling the tensile behaviour of aligned discontinuous carbon fibre thermoplastic matrix composites under processing conditions

This study aims to develop a predictive tool for simulating the forming process of aligned discontinuous fibre reinforced composites (ADFRCs). Poly(L-lactic acid) (PLA) reinforced with discontinuous carbon fibres is used to form HiPerDiF tapes. An analytical micromechanical model is developed to predict the tensile stress of the tape as a function of tensile strain rate, incorporating the viscoelastic properties of the PLA matrix and the microstructural characteristics of the tape. The model uses a Maxwell approach for the viscoelastic behaviour of PLA and assumes tensile load transfer between fibres via matrix shearing. Additionally, a degree of crystallisation is integrated to account for a small amount of crystallisation that develops in the PLA whilst brought to temperature. This parameter is determined by fitting experimental data prior to validation. Hence, the model's predictions at temperatures at which the tape was not originally characterised and for non-monotonic deformation speeds fell within the 95% confidence interval of a new set of experimental data. This work offers a pragmatic approach for optimising the forming of ADFRCs from the knowledge of known microstructural characteristics of the tape (i.e., fibre length, radius and volume fraction and resin viscosity and storage modulus).