Matrix and Fibre Stiffness Degradation of a Quasi-isotrope Graphite Epoxy Laminate Under Flexural Bending Test

Abstract

The permanent research of reliability and precision for failure criteria is a major concern for proper dimensioning of composite structures. Discrepancies are observed between theoretical results based on laminated theory or finite element analysis [Greif, R. and Chapon, E. (1993). Investigation of Successive Failure Modes in Graphite Epoxy Laminated Composites Beams, Journal of Reinforced Plastics and Composites, 29; Echaabi, J., Trochu, F., Pham, F. X. T. and Ouelette, M. (1996). Theroretical and Experimental Investigation of Failure and Damage Progression of Quasi-Isotropic Graphite Epoxy Composites in Flexural Bending Test, Journal of Reinforced Plastics and Composites, 15(7)] and experiments. In order to investigate these problems, numerical simulations were carried out to study the behavior of graphite-epoxy [[+45/-45/90/0]3] laminates subjected to three point bending tests. Two approaches were followed. The first one is based on laminate theory with transverse shear. The successive failures, failure modes, progression of failure and the effect of the geometrical characteristics of the specimens were analyzed during loading. Various failure criteria have been studied to predict the load when the weakest ply fails under flexural bending. Traditional failure criteria and new ones taking into account physical considerations were used. These criteria are tested with two models of stiffness reduction to account for ply failure. The second approach is based on a finite element analysis of laminate, in which three-dimensional failure criteria were implemented. Finally, the results obtained with these two approaches are compared with theoretical and experimental predictions of the scientific literature [Echaabi, J., Trochu, F., Pham, F. X. T. and Ouelette, M. (1996). Theroretical and Experimental Investigation of Failure and Damage Progression of Quasi-Isotropic Graphite Epoxy Composites in Flexural Bending Test, Journal of Reinforced Plastics and Composites, 15(7)].