Dimensional accuracy of thermoset polymer composites: Process simulation and optimization.

摘要

The warpage of thermoset composite structures during the manufacturing process is a direct consequence of residual stress development. The capability to predict residual stresses is crucial to the manufacture of dimensionally accurate composite structures. The first part of this work is focused on understanding the fundamental issues leading to residual stresses in thermoset polymer composites and their effect on the dimensional accuracy of the manufactured components. A three-dimensional coupled thermo-chemo-viscoelastic model is developed to simulate the heat transfer, curing, residual stresses and deformation of a composite part during the entire cure cycle. The predicted curvature for graphite-epoxy laminates and springforward for L-shaped composite parts agree well with experimental observations. The numerical results indicate that the residual stresses developed before cooldown can be, in some cases, quite significant.; The second part of our work is focused on a design sensitivity analysis, which supports the shape optimization of the tool and component in thermoset composite manufacturing. The method provides a systematic way to predict the optimal tool and component geometry that leads to the minimum difference between desired and final shapes of the manufactured part. The design process is formalized by integrating process modeling, design sensitivity analysis, and numerical optimization into a single framework. Design sensitivity information is extracted efficiently from the primal analysis using an analytical, direct differentiation method. The sensitivities are then provided to a numerical optimization program to improve the tool and component design. Optimization results are presented for three specific applications involving mold design for cross-ply laminates, mold design for L-shaped composite parts, and hat stiffener design for an exterior body panel.; Finally, the three-dimensional finite element code is utilized to predict the viscoelastic response of a woven composite substrate for multilayer circuit board applications. Comparisons between numerical predictions and experimental data clearly indicate that the creep compliance of the composite depends not only on the relaxation of the matrix, but also on flexural deformations of the woven fabric bundles.