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Compression Molding of Hybrid Continuous and Discontinuous Fiber Reinforced Thermoplastics for Enhancing Strength Characteristics

Compression molding with long discontinuous fiber-reinforced thermoplastics enables replacing traditionally machined metallic components with geometrical complexity and with reductions in weight and potential enhancements in structural characteristics like durability, fatigue, and serviceability. Fiber length is critical in fiber-reinforced composites. While long continuous fibers limit the geometrical complexity that can be fabricated but provide exceptional mechanical properties, discontinuous fibers provide manufacturing flexibility but with a penalty in strength. This work demonstrates enhancement in strength and reduction in strength variability achieved by compression molding of long discontinuous fiber platelets and continuous fiber preforms. This approach was demonstrated for an overhead bin pin bracket geometry. Continuous fiber preforms were manufactured with 60% by volume of carbon fiber-reinforced Poly Ether Ketone Ketone (PEKK) using the 9T Labs continuous fiber Additive Fusion Technology (AFT). Similarly, fiber platelets with 60% by volume of carbon fiber reinforced PEKK were utilized. Continuous fiber preforms were designed considering both the concurrent flow of continuous and discontinuous fibers with the desired mesostructure of continuous and discontinuous fibers. The results presented in this work showed an increase of 99.6% in the load at the onset of damage by reinforcing the pin bracket with about 17% by weight of continuous fiber preforms. Similarly, the coefficient of variance of the load at the onset of failure decreased by 46%. Finally, reinforcing the pin bracket with continuous fiber preforms not only enhanced the strength characteristics but also decreased the variability in strength characteristics.