Nonlinear Material Modeling and Experimental Characterization of Graphite/PPS and Glass/PPS Thermoplastic Matrix Composites

This paper summarizes results of a theoretical and experimental study on the nonlinear deformation behavior of thermoplastic matrix composites. The experimental work focuses on the processing and characterization of laminates of AS4 graphite/poly phenylene sulfide (PPS), E glass/PPS, and graphite/PPS-glass/PPS hybrids. The theoreti cal study develops a generic material constitutive model applicable for all thermoplastic matrix composites that exhibit nonlinear stress-strain response. On the lamina level, a stress-based nonlinear stress-strain model for a unidirectionally reinforced ply is transformed into a mixed stress/strain-based model. Then, a model for the nonlinear material response of a multi-directional laminate is developed. The laminate model pre dicts the nonlinear compliances based on the current effective laminate stresses and strains, and does so without need for iteration. In these models, the full three-dimensional stress and strain states have been retained so the models are applicable for both thin and thick section composites. While the three-dimensional nature of the models is discussed in detail elsewhere [1], the emphasis of the present paper is on the nonlinear deformation response. There is good agreement between the theoretical predictions and experimental results for laminates of graphite/PPS, glass/PPS, and their hybrids. The paper also pre sents scanning electron micrographs to portray microscopic failure modes that may cause additional, damage-induced, nonlinear response in these laminates.