Numerical analysis and optimal design of composite thermoforming process

In this paper, we present a numerical methodology to simulate and design the composite thermoforming process. First, in the process simulation, the FEM modeling including flow, heat transfer and residual stress is developed to analyze the thermoforming process of composite laminates with woven fabric microstructures. The governing equations and material properties of thermoplastic composites at the forming temperature are obtained by the homogenization method based on the assumption of instantaneously rigid solid fibers suspended in a viscous non-Newtonian polymer melt. The processing rheology of the composites is characterized by a power-law constitutive model for this non-isothermal and shear thinning fluid. To simulate the shaping and cooling stages of the entire forming process, the three-dimensional finite element method incorporating a fiber orientation model of woven-fabric microstructures is developed. Based on kinematic considerations, the fiber orientation model is used to keep track of the microstructure change due to large deformation. This global-local numerical methodology is capable of predicting macroscopic and microscopic deformation mechanics during processing. Second, in the process optimization, the design objective is to achieve a uniform final thickness distribution by designing the preheated composite temperature field. The finite difference approximation is utilized to evaluate the design sensitivities. Using the FEM developed in the first part as the analysis tool, the optimization scheme can allow process designers to optimally design this process. A number of numerical examples and experimental results are presented to demonstrate this combined analysis and optimization algorithm. (C) 1999 Elsevier Science S.A. All rights reserved.