Prediction of Shrinkage and Warpage of Fiber Reinforced Thermoset Composite Parts

Abstract

One of the most challenging tasks in designing plastic parts, especially those that are fiber reinforced, is to predict shrinkage and warpage of the molded parts. Shrinkage and warpage result from material inhomogeneities caused by flow induced fiber orientation, curing, poor thermal mold lay-out, and processing conditions. Shrinkage and warpage are directly related to residual stresses which result from locally varying strain fields that occur during the curing or solidification stage of a manufacturing process. This paper presents research conducted in modeling, analysis and process simulation of the thermomechanical behavior of compression molded fiber reinforced composite parts. The theory behind shrinkage and warpage of fiber reinforced composite parts is described first, followed by a description of finite element/finite difference simulation of the thermo mechanical behavior of fiber reinforced composites during a part's manufacturing process. A coupled temperature and stress simulation program with a three-noded shell element formulation was developed to calculate the residual stress build-up during curing and solidification stages of a compression molding process. The effects of fiber content, part thickness, unsymmetric curing and flow-induced fiber orientation on the shrinkage and warpage of the molded parts are also investigated.