Mechanical characterization of carbon-epoxy and glass-epoxy composites by indentation testing

The indentation technique has been developed to perform surface mechanical characterization of materials. This technique consists in monitoring the penetration of a diamond indenter in the material to be characterized while the displacement and the force are continuously measured. Modelling loading and unloading curves allows estimation of plastic and elastic properties of the material. Linking this technique with an optical sighting system permits the characterization of various phases of the composite materials with a displacement accuracy better than 0.1 mu m. The mechanical behaviour of carbon or glass fibre reinforced polymer under various solicitations is mainly related to the behaviour of its 'phases': the matrix, the fibres and the fibre-matrix interface. Several techniques have been developed giving information about mechanical properties of the composite, particularly for the interfacial strength. Modelling static and dynamic indentation curves on fibres allows computation of the interfacial strength and fibre mechanical properties. This paper presents our indentation technique and the model that we have developed to study glass fibre-epoxy matrix and carbon fibre-epoxy matrix composites with a fibre diameter of 5-20 mu m.