Warpage of rubber pressed composites

The rubber pressing process is applied for the rapid production of thermoplastic composite products. However, rubber pressed products show geometrical distortions, such as warpage, due to process-induced residual stresses. It is believed that these stresses build up as a result of the large thermal gradients that are present during consolidation. An experimental study is performed to measure the curvature after rubber pressing of initially flat woven fabric glass/PPS composite panels. A material model is proposed that incorporates the solidification of the composite in order to predict the residual stresses and the warpage due to inhomogenous cooling. The model is employed in Finite Element simulations of the rubber pressing process. The simulations are compared to the experimentally obtained curvatures. It shows that inhomogeneous cooling has a minor effect on the warpage in this case, and that another mechanism is present.