Impact damage to composite structures results in multiple, complex failure modes, often requiring the replacement of entire components and thereby escalating aircraft maintenance costs. To address this issue, the present study investigates the damage propagation behaviour with particular emphasis on intra- and interlaminar failure modes. Carbon fibre/epoxy composites were subjected to tensile after impact (TAI) fatigue tests at different energy levels to induce different damage modes and extents within the specimens. A non-destructive testing technique (C-scan) was used to assess the interlaminar damage propagation, while the intralaminar fracture toughness of the post-impact specimens was characterised using a finite fracture mechanics model. The results show that the crack propagation behaviour is strongly influenced by the initial impact damage characteristics, in particular the impact energy level. Lower impact energies tend to promote interlaminar failure modes leading to fatigue crack propagation by delamination. Conversely, higher impact energy levels induce fibre fracture, resulting in a self-similar relationship between intra- and interlaminar propagation.

The demand to capture translaminar crack growth under fatigue loading scenarios led this work contribution to carry out the Finite Fracture Mechanics (FFM) method in fatigue damage growth and the application of the Paris model to generate the translaminar damage propagation prediction. The purpose of this study is to analyse the effect of fibre orientation on translaminar crack propagation rate using the FFM model, which includes cycle damage increment estimation and fractographic analysis. The results confirm the feasibility of FFM in predicting crack growth and estimating life under cyclic loading. However, C-scan analysis and the revised crack propagation direction are critical in determining the realistic crack length, considering adhesive failure along the fibre direction. Additionally, this work contribution is also related to the application of the Paris model (based on dL/dN vs ΔK) to generate the translaminar damage propagation prediction model. The most dominant damage mechanism was the splitting pattern, which changed the aspect of failure for each laminate architecture as a function of fibre orientation. The laminate with multidirectional fibre orientation exhibited higher resistance to translaminar crack propagation due to the growth of splitting and delamination in multiple directions. The fibre orientation changed the propagation path, which influenced the fracture toughness and crack propagation rate behaviour.