RESIDUAL STRENGHT OF LAMINATED GRAPHITE-EPOXY COMPOSITE CIRCULAR PLATES DAMAGED BY TRANSVERSAL LOAD

Fibre-reinforced composite materials are increasingly used in airframes and the tendency is to built the main fuselage in Carbon Fibre Reinforced Polymer (CFRP).In general CFRP has a wide application in light-weight structural members, because it is characterized by a high strength-to-weight and stiffness-to-weight ratio, but it is vulnerable to damage caused by transverse loads, such as those arising from indentation and impact loading. One of the main reasons that inhibits more widespread applications of composite materials is their lack of resistance to low velocity and low energy impact damage[1-3], particularly in the case of thermoset matrix like epoxy, while the probability of such loadings occurring during the manufacture, service or maintenance of composite structures is very high. The research dealt with the correlation between damage and tensile residual strength in quasi-isotropic carbon fibre reinforced epoxy resin laminate loaded at the centre. Load was applied by means of a servo hydraulic machine and it was supposed to simulate a low velocity impact. The Acoustic Emission (AE) technique was used to detect damage progression. Tensile resistance after indentation was investigated and correlated with acoustic emissions parameters. This was been done for different lamination sequences on specimens cut from the damaged plates and for two different damage levels, one corresponding to the first load drop in the loaddisplacement curve and to the complete perforation of the plate.