Process-induced deformation in U-shaped honeycomb aerospace composite structures

This study presents the findings of a combined experimental and numerical investigation to study process-induced deformation in sandwich structures manufactured using autoclave molding techniques. U-shaped sandwich structure based on woven carbon prepregs and an over-expanded Nomex honeycomb core were man-ufactured. For purposes of comparison, a U-shaped composite laminate, i.e. without the inclusion of a core, was also manufactured and modeled. Process-induced spring-in at different locations within the U-shaped parts were measured, both optically and using a feeler gauge. Thermo-chemical and stress-deformation finite ele-ment models were employed to predict the degree of spring-in for both the sandwich structures and the plain laminates using the ABAQUS/COMPRO. The predicted spring-in values were shown to be in good agreement with those measured experimentally. Parametric studies to investigate the effect of changing both the tooling material and the sandwich core have shown that employing an aluminum tool and an aluminum core reduced the degree of spring-in and warpage in the structures. However, spring-in phenomena is dominated by the core structure and geometry of the part. Finally, it has been shown that the process-induced deformation is less in the curved sandwich structures than in their laminated counterparts, with both structures deforming due to the combined effects of spring-in and warpage of the flat regions.