PREDICTION OF SHRINKAGE AND WARPAGE OF FIBER-REINFORCED THERMOSET COMPOSITE PARTS

One of the most challenging tasks in designing plastic parts, especial ly those that are fiber reinforced, is to predict shrinkage and warpag e of the molded parts. Shrinkage and warpage result from material inho mogeneities caused by flow induced fiber orientation, curing, poor the rmal mold lay-out, and processing conditions. Shrinkage and warpage ar e directly related to residual stresses which result from locally vary ing 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 beh avior of compression molded fiber reinforced composite parts. The theo ry behind shrinkage and warpage of fiber reinforced composite parts is described first, followed by a description of finite element/finite d ifference simulation of the thermomechanical behavior of fiber reinfor ced composites during a part's manufacturing process. A coupled temper ature and stress simulation program with a three-noded shell element f ormulation was developed to calculate the residual stress build-up dur ing 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 mol ded parts are also investigated.