Mesoscale Numerical Modelling and Failure Prediction of Automated Fibre Placement Composites

Automated fibre placement (AFP) is an advanced and fully automated composites manufacturing technique and offers a huge design space for lightweight composite structures through flexible fibre distribution and orientation. Advanced placed ply (AP-Ply) and variable stiffness laminate (VSL) are typical examples and are called Advanced AFP Laminates in this thesis. However, due to the machine tolerance and novel tow path manipulation, a great variety of intrinsic mesoscale geometric features (gaps, overlaps, tow drops, tow crimping, etc.) can be produced, which may have a great impact on the laminate strength depending on specific applications. Despite the increasing awareness of the significance of these features, understanding the corresponding effect on part performance is still challenging due to the huge parameter space, particularly for advanced AFP laminates. This research has developed a finite element (FE) method to predict the mechanical properties of AFP composites at coupon or part scale while retaining the intrinsic geometric features. The AP-Ply is an example used to validate this technique due to the sophisticated fibre architecture. Thus, several experimental programs including short beam shear, low-velocity impact, and compression-after-impact were conducted to facilitate understanding the effect of these geometric features on the structural performance of AP-Ply. The finite element method provided in this thesis was developed at mesoscale, specifically at a length scale of tows rather than plies or laminates in conventional methods. This method significantly improves the geometric fidelity of the model with the potential of depicting each tow and geometric feature individually. To improve the efficiency of model generation, an automated tow-wise modelling (TWM) algorithm was developed, aiming to build the part virtually following the robotic kinematics. The downstream use of TWM in the prediction of different failures is achieved with the implementation of a novel cohesive network approach, which greatly eases the pre-processing effort of explicitly allocating cohesive elements or developing complex fracture criteria. This method allows greater mesh size to be used in the crack front compared to conventional methods. The feasibility and accuracy of TWM in the prediction of mechanical properties of AFP composites were validated with AP-Ply experiments, specifically the short beam shear and low-velocity impact tests