Nonlinear Material Modeling and Experimental Characterization of

ABSTRACT: 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. 1