Delamination of Thin Layers Promoted by Local Buckling

The detachment of a thin superficial layer from an underlying substrate due to the combined action of local buckling and fracture propagation is a damage mode common to many technological applications and natural objects. Delamination is one of the most critical issues for the integrity and the mechanical performance of fibre-reinforced composite laminates. The phenomenon occurs when the superficial layer is loaded under compression and the regions where bonding is weak or missing may undergo local buckling. As a consequence, high stresses arise at the crack tips, thus promoting the further expansion of the debonded region. Delamination cracks in composite laminates may originate from manufacturing defects, low-energy impacts, and many other causes. We have developed an analytical model to simulate and interpret four-point bending tests, where the specimens have a symmetrical, superficial through-the-width delamination, that could buckle because the thin layer is indirectly loaded under compression. Furthermore, we have conducted experimental test to validate the theoretical model, in particular using the Digital Image Correlation to track the deformation historyof tested specimens.