Experiments and analysis of laminates with artificial damage

Quasi-isotropic carbon/epoxy laminates with holes, polymer plugs and cut fibres are studied experimentally and analytically. Strain fields are measured using digital speckle photography. The results are used to validate an inverse method, where elastic properties of inclusions are determined by matching computed and measured displacements. Tensile and compressive strength is measured and the applicability of notch failure criteria to soft inclusions is examined. Available closed form solutions agree well with measured strains. The elastic properties predicted by the inverse method are in fairly good agreement with data from coupon tests although predictions are sensitive to measuring errors. The laminate toughness in compression was higher than in tension, as expected from the different failure mechanisms (fibre kinking versus fibre tearing). Laminates with inclusions were tougher than laminates with holes, which may indicate that inclusions restrain in-plane fibre kinking. Higher toughness was reflected in larger characteristic lengths.