In-plane compression of constrained preforms

Preforms constructed from a plain-weave, glass fabric were compressed in-pl ane within a fixture that mimicked the constraints of a closed mold. Typica lly, a gap was left between the bottom of the preform and the floor of the fixture; upon initial compression, the preform slid within the fixture, whi ch allowed the friction between the preform and the fixture wall to be meas ured. The preform began to compress as it contacted the floor of the fixtur e. The deformation was proportional to the applied stress until a critical stress was reached. Above this stress, the preform sustained damage in the form of localized buckling and a corresponding decrease in mechanical integ rity. The in-plane compressive behavior varied with system parameters, such as preform geometry, fabric orientation, and clamping stress and was shown to be strongly dependent on friction of the preform against the fixture wa ll. A model was developed to describe the contribution of preform friction with the fixture wall to the in-plane compressive behavior of constrained p reforms.