Flow-control and hybridization strategies for thermoplastic stiffened panels of long discontinuous fibers

Abstract

The current research aims at mitigating the flow-induced manufacturing issues (strand waviness and swirling of strands) encountered in complex parts of randomly oriented strands, through the hybridization of randomly oriented strands with continuous fibers, while emphasizing the ease of manufacturing and repeatability. Three hybridization strategies are proposed for T-stiffeners that represent the generalized intersecting junctions of stiffened panels. The strategies include: flow-control element, flange reinforcements, and rib reinforcements. A quantitative assessment of pull-out strengths of five T-stiffener configurations is made. Flow-control element improves the strand flow at the junction, reduces variability, and enhances the pull-out b-basis design allowable by about 24%. A quasi-isotropic laminate as flange reinforcement with a flow-control element produces 12.5% pull-out strength improvement. Rib reinforcement causes reinforcement delamination from the randomly oriented strands part, dropping pull-out strength by about 6%. A transient heat transfer analysis of the tooling set-up was simulated using finite elements to devise a preferential cooling strategy that minimizes porosity in randomly oriented strands panels with T-stiffeners.