Stacking sequence effects on compressive failure using pin-ended buckling test

A pin-ended buckling test, inspired by the work of Wisnom (M. Wisnom, 1992), was developed to assess the influence of strain gradients on the compressive failure strain of composite laminates. Experiments were carried out on laminates manufactured with unidirectional (UD) carbon/epoxy AS4/8552 prepegs, with full-field strain measurements obtained via digital image correlation. The influence of stacking sequence on compressive failure—specifically the effects of 0° ply thickness and the adjacent ply interface—was investigated by testing a range of cross-ply and quasi-isotropic specimens. To prevent premature tensile failure, a 2024 aluminium ply was bonded to the tensile side of the 8-ply and 16-ply specimens, following the approach described in (Bianchi et al. 2025). Comparisons between the different stacking sequences were carried out by analysing the evolution of the maximum compressive strain as a function of the strain gradient. Additionally, a comparative analysis was performed between scaled specimens—32-ply, 16-ply, and 8-ply—in both cross-ply and quasi-isotropic configurations. The experimental results confirmed the nonlinear character of the strain-gradient effect on compressive failure. Furthermore, they indicated that neither the 0° ply thickness nor the adjacent ply interface exert a significant influence on the material investigated. These observations differ from earlier models that predicted such effects.