Delamination growth in composite laminates is essentially two-dimensional (2D), indicating a multidirectional spreading of interlaminar damage. However, the evaluation and prediction of delamination growth mainly relies on the quantification of one-dimensional (1D) growth using unidirectional specimens. In this study, the discrepancies and similarities between 1D and 2D delamination behaviours of composite laminates are investigated, both experimentally and numerically. The fracture toughness of mode II delamination, measured experimentally through 1D tests, is compared with the numerically fitted critical Energy Release Rate (ERR) in 2D delamination using Cohesive Zone Modelling (CZM) method. The fracture mechanisms involved in 1D and 2D delamination growth are investigated through fractography at the delamination interfaces. Although similar damage mechanisms are present in 1D and 2D tests, using the fracture toughness measured from 1D tests to predict 2D growth is proven to be insufficient due to distinct extrinsic toughening effects. Variations in local stress states significantly influence delamination growth, necessitating different cohesive constitutive models to accurately describe 1D and 2D delamination processes.

Dynamic vibration is believed to be a basic property of the impacted composite laminates; however, its effect on delamination formation requires further investigation. This study proposes a numerical model in collaborating with ABAQUS, which was calibrated using experimental results, to investigate the effect of plate vibration on delamination formation in composite laminates subjected to two consecutive identical ice or steel projectile impacts with a fixed loading distance. The only variable parameter for the different simulations was the time interval between the two impacts. The loading condition considered in this study is an extreme case where the composite laminate was still vibrating after the first impact when the second impact occurred. The results showed that the delaminations that formed later were significantly affected by the time intervals of the two identical successive ice or steel projectiles. As the vibrated impact points travel from the minimum peak to the adjacent maximum peak during the first vibration period, the newly formed delamination areas monotonically increase with time and vice versa. The change in the maximum contact forces of two identical impacts induced by dynamic vibration is suggested to be a major reason for the discrepancy between the newly formed delamination and previous ones.

Multidirectional (MD) composite laminates are extensively employed in structural applications owing to their superior mechanical characteristics. Nevertheless, the evaluation of the fracture toughness of composite laminates primarily relies on tests using unidirectional (UD) specimens. This study evaluates the reliability of characterizing mode II delamination behaviour in MD laminates by using UD specimens. The quantification of delamination area through Digital Image Correlation (DIC) analysis is integrated with a physical Energy Release Rate (ERR) method to ascertain the fracture resistance, which is compared with the ERR derived via a modified J-integral method and the standardized compliance methods. Fractographic analysis reveals similar fracture mechanisms in specimens with identical interfaces. The physical ERR increases notably due to large-scale fibre bridging induced by fibre nesting at 0^∘//0^∘ interfaces. Conversely, in 0^∘//90^∘ interfaces, large-area matrix cracking enhances the intrinsic fracture resistance, excluding the extrinsic toughening provided by fibre bridging.

In this study, a novel experimental approach was devised to investigate shear dominant and combined opening-shear planar delamination behaviours in composite laminates subjected to quasi-static out-of-plane loading. The patterns of planar delamination growth were depicted through different inspection techniques, including digital image correlation (DIC), C-scan, and microscopic observation. The artificially embedded delamination propagated in the direction parallel to the fibre orientation of the layer above the mid interface, but migrated to an upper interface in the direction transverse to the directing ply. A continuous stiffening process was recognized with increasing delamination area. Furthermore, a numerical analysis based on virtual crack closure technique (VCCT) indicated that the local mode II was dominant for delamination growth, while the local mode III triggered delamination migration.