Shape change of composite corners due to tooling pressure distribution effects

Abstract

This study combined pressure mapping and shape sensors to track and correlate dynamic consolidation events during curing of composite prepreg corners made using external, internal, and matched tooling. Even though parts should nominally be equivalent, a clear influence of tool configuration was captured on pressure distributions and laminate shape. External tooling was found to create excess pressure in the corner region, leading to laminate thinning in the corner apex, while internal tooling showed reduced pressure due to bridging, resulting in local corner thickening in the final cured shape. The matched tooling showed a reduced corner pressure, indicative of lack of contact due to bulk factor in the flange regions that prevented proper seating the tooling, again leading to a final corner shape that showed relative thickening. Across all cases, shape change occurred due to material movement from higher to lower pressure regions and occurred within the low viscosity, pre-gelation time window which correlated roughly with the first dwell in the cure cycle. The shape of the corners changed from one with a constant curvature to one with a variable curvature, meaning the corner ovalized and was no longer equivalent to a quarter circle. Understanding pressure-driven shape change during consolidation enables better design and manufacturing optimization needed to produce high-quality composite parts.