A model for the autoclave consolidation of prepregs during manufacturing of complex curvature parts
Date
2021
Authors
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Publisher
University of Delaware
Abstract
Autoclave consolidation is used to manufacture composites in applications that have very strict part porosity requirements. The high applied pressure capable in this process is attractive for the best possible reduction in part porosity, which is a typical measure of part quality. However, some part geometries can cause porosity issues even under high applied pressure. The simplest example of this is concave corner seen in an L-bracket geometry. Higher porosity is typically seen in areas of high curvature such as this, hindering part quality. Since the autoclave process takes several hours and prepreg material is expensive, trial-and-error methods of resolving these issues are not practical. ☐ The goal of this research project is to predict the final porosity distribution in composite parts with complex curvatures, particularly the L-bracket corner, by modeling the material behavior of uncured prepreg during autoclave processing. This type of modeling framework will allow the autoclave process to be optimized for specific applications at a significantly reduced time and cost compared to traditional trial-and-error troubleshooting methods. Multiple factors such as the part geometry, layup pattern, prepreg fiber and resin type, and autoclave conditions contribute to the quality of the final part and can cause significant variability. ☐ In this work, a unique physics-based viscoelastic model is proposed to describe the mechanical behavior of uncured prepreg undergoing consolidation in an autoclave. This model directly takes into account stress due to compaction of the fiber network, stress due to compression of voids in the resin, and stress due to moving resin relative to the fibers. These are combined additively to represent the prepreg’s total response to applied pressure loading. The constitutive expressions for these are coupled to other important mechanisms present in autoclave consolidation, including the dissolution of volatiles into the resin and the resin cure kinetics. ☐ The viscoelastic model is incorporated into the commercial finite element analysis software ABAQUS/Standard using a UMAT subroutine, which allows user defined material behavior to be implemented. Throughout the consolidation process, the model calculates and tracks important parameters such as the porosity in the prepreg plies, the fiber volume fraction, the resin viscosity, and the resin degree of cure. The numerical model results are validated by both analytic solutions and experimental comparison for flat and L-bracket corner geometries. A parametric study is conducted to identify important process and material parameters that influence the final quality of the manufactured composite component.
Description
Keywords
Autoclave, Composites, Finite element, Modeling