Model development for the formation of resin-rich zones in composites processing

Resin-rich zones are a common phenomenon in liquid composite molding processes causing unwanted residual stress and deformation. They are normally caused by the gaps between the fiber preform and the internal mold surface due to mold closure. Because resin-rich zones are difficult to control, they cause part-to-part variations. Thus, resin-rich zones need to be studied in the design of composite structures. A model for predicting the formation of resin-rich zones in angled composite parts is presented in this paper. The functional relationship between gap thickness and radius, enclosed angle and fiber preform stiffness is derived by simple mechanics. The data from the experiments conducted using two open-channel molds were fit to two regression models for 0° unidirectional and cross-ply preforms, respectively. These models were validated against experimental data which shown in most cases, the relative difference of the model and the experimental data is within 20%. However, large difference is noticed in some cases.