A model for the autoclave consolidation of prepregs during manufacturing of complex curvature parts

Autoclave consolidation is used to manufacture continuous fiber composites in applications that have strict part porosity requirements. The applied positive pressure in this process is attractive for reduction in part porosity. However, some part geometries can cause porosity issues even under positive pressure. One is the concave corner seen in an L-bracket geometry. Higher porosity is seen in areas of high curvature, hindering part quality. Since the autoclave process takes several hours and prepreg material is expensive, trial-and-error methods of resolving issues are not practical. In this work, a unique physics-based viscoelastic model is proposed to describe the mechanical behavior of uncured continuous fiber thermoset prepreg undergoing consolidation under hydrostatic pressure. This model considers stress due to compaction of the fiber network, compression of voids in the resin, and viscous stress from resin flow relative to fibers. The constitutive expressions for these are coupled to important mechanisms that occur during autoclave consolidation. The viscoelastic model is incorporated into the finite element analysis software ABAQUS/Standard using a UMAT subroutine. Numerical results are validated by analytic solutions and experimental comparison for flat and L-bracket geometries. A parametric study identifies important process and material parameters that influence the quality of the manufactured part.