Thin plates of epoxy resin matrix composites reinforced with glass, carbon and aramid fibers, as well as a plate from a hybrid glass-aramid composite, were submitted to flexure tests. The specimens were fixed in order to conduct the testes under restricted conditions of deflection. The experimental results of the maximum deflection agreed qualitatively with the Ritz method of energy balance. Carbon fiber reinforced composites showed the highest values for the initiation energy and for the maximum force. Both results were attributed to the high intrinsic properties of carbon fibers. The specific properties of the hybrid composite were higher than the properties of the glass or aramid reinforced composites. This synergistic effect is indicative of a properly designed hybrid composite. The macroscopic failure mode of all composites was similar. At the front face the interaction between the composite and the indenter followed the behavior of Hertz Law. At the rear face, delamination occurred preferentially.
Epoxy matrix composites; bending of plates; stiffness matrix
