A simulation methodology for assessing the damage in thick fabric Carbon Fibre Reinforced Polymer (CFRP) composite laminates under low- and high-velocity impacts is presented. It encompasses steps for calibration, verification, and validation of the elastic and fracture material properties as well as determination of model parameters for the numerical simulations. Damage is modelled using a discrete fracture approach with cohesive interface elements that capture individual cracks occurring in and between plies. For computational efficiency, the method is implemented in a two-dimensional (2D) axi-symmetric model. Results from double-cantilever beam, end-notched flexure, and quasi-static indentation experiments align well with numerical simulations and serve to calibrate and verify the implementation of the discrete fracture approach. The methodology is extended to dynamic impact analysis to predict damage mechanisms, force–displacement histories, and is validated using test results. This methodology combines meaningful insight in the failure mechanisms with a manageable computational effort, achieving a factor 50 improvement compared to a benchmark. A parametric analysis summarised in failure maps relates damage mechanisms to impact energy, mass, and laminate thickness. The proposed methodology strikes a balance between computational efficiency and accuracy, making it a valuable tool for optimum design and certification of thick CFRP composite laminates under impact.

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength.

Despite the increased use of thick fabric Carbon Fibre Reinforced Polymer (CFRP) materials in highly loaded aerospace structures (e.g., 20-50mm thick CFRP structures), a comprehensive characterisation of damage due to impact events on these structures remains an elusive and challenging task. To address this issue, three methods with varying degrees of computational complexity are developed to simulate and predict a representative impact problem on a thick composite plate. These simulation methods range from a low-fidelity 1D semi-analytical impact response model to high-fidelity 2D and 3D numerical impact damage models. The accuracy, in terms of impact response and damage prediction, is assessed by comparison with experimental results. It was found that the higher fidelity does not directly translate to a higher accuracy due to challenging modelling strategies for the 2D and 3D numerical impact damage models. The 1D semi-analytical impact response model was found to be the most accurate in predicting the force and displacement histories of both large-mass and small-mass impact events. However, this model is not capable of predicting the extent of damage. Comparison of the resulting impact damage from the 2D and 3D numerical impact damage models with experiments showed that improvements are required to capture the correct damage mechanisms. These damage mechanisms are complex and increasing the model complexity requires an extensive evaluation of the modelling strategies and numerical variables. Improvements are suggested that should increase the accuracy of these models. Dynamics are important for thick laminates as there is almost no plate bending and most of the impact energy is absorbed in local damage and deformations. Thinner composites generally experience more bending and can therefore be evaluated quasi-statically.