Picture-frame intraply shearing test for sheet-forming of composite materials

Sheet forming shapes of double curvature from continuous fiber reinforced polymer composites involves, among other deformation modes, significant shearing in the plane of the material along the reinforcement directions. The purpose of this paper is to describe an experiment which investigates the nature of this mechanism, called intra-ply shear, and to present a method for interpreting the results of such a test in terms of some appropriate constitutive models. An experiment is designed in which a square composite specimen, reinforced with either unidirectional fibers or fabric, is subjected to a shearing deformation by a linkage of four rigid bars, known as the picture-frame apparatus. Models are proposed to analyze the test which assume the materials to behave as anisotropic fluids, subject to the kinematic constraints of material incompressibility and inextensibility in either one (unidirectional) or two (fabric) directions. Preliminary experiments at various displacement rates are carried out on a glass-fabric reinforced thermoplastic and the force response is then compared to the model predictions.