In situ study of matrix strain in carbon/resin composite materials

The mechanical behaviour of three polymeric resins (two thermosets and one thermoplastic) was studied. Mechanical rests were performed on the unreinforced resins and on the same resins as matrices in transversely loaded unidirectional composites. In the latter case the plastic strain was revealed from the distorsions of microgrids settled on the specimen surface. Despite differences between the plain resins, their behaviour inside composites is similar, the deformation being heterogeneously confined between the fibres near the rips of microcracks. The strain level and the interfacial strength nevertheless allow a distinction between the three systems. In all cases, strain extension is limited by the nearest fibres. The overall mechanical response under transverse loading is, therefore, macroscopically brittle. (C) 1996 Elsevier Science Limited