Numerical Modelling of Damage Initiation and Failure of Long Fibre-Reinforced Thermoplastics

Characterising the mechanical properties of long fibre-reinforced thermoplastic (LFT) composites including failure is a challenging task. The macroscopic behaviour is generally associated with parameters like fibre orientation, volume fraction and length. A thorough understanding of the micromechanical mechanisms gets more and more important for describing macroscopic behaviour. Large aspect ratios (fibre length divided by fibre diameter) make it difficult to create numerical models of the random LFT microstructure since representative volume elements (RVE) that consider the microstructure in a cross section over the entire thickness lead to a large computational effort. Numerical explorations of selectively predetermined fibre constellations can reduce the model size. In addition, complex interface behaviour can be considered. Therefore a numerical study is performed to identify relevant parameters in micromechanical finite element models of a long fibre-reinforced thermoplastic composite. Different unit cell models of discontinuous fibres embedded in a polypropylene matrix are analysed numerically to identify major mechanisms related to damage and failure in relevant loading directions.