Cure gradient induced warpage: Bounding critical thickness

Residual deformations caused by processing, such as spring-in and warpage, pose a significant risk to the production of high-performance composite components, especially in aerospace applications given tight tolerances. Capturing stress gradients through thickness caused by differential thermal and cure shrinkage strains requires detailed process modeling, which is computationally demanding and extensive materials characterization needs to be performed. Thus, threshold values for considering a laminate as ‘thick’ are targeting. To determine the critical lower thickness limit at which cure gradient-induced warpage becomes significant, a finite differences-based process model was validated by comparing it with finite element process simulation results. A comprehensive parameter study, based on a full factorial design of virtual processing experiments, was conducted to evaluate estimated rigging loads across three different material systems, various tooling configurations and thermal boundary conditions. Manually applicable moment fluxes were estimated and compared to those calculated required to bend back the laminate after processing. While for standard aerospace processing conditions, the rule of thumb of 20 mm laminate thickness was confirmed, on particularly asymmetric tooling and thermal boundary conditions, the thickness criterion was observed to be as low as 10 mm.