Flexural response of additively manufactured continuous fiber-reinforced composites under quasi-static and dynamic loading

The flexural behavior of additively manufactured continuous fiber-reinforced composites remains insufficiently understood, particularly under dynamic loading, limiting their reliable application in functional structures. This study presents a systematic experimental investigation of the flexural performance of dual-extrusion fused deposition modeling composites, focusing on maximum force, deformation patterns, and failure modes. Carbon, Kevlar, and glass fiber filaments with varying volume fractions were tested under quasi-static and dynamic loading using a custom split Hopkinson pressure bar system. The results show that fiber type governs the maximum force, with carbon fiber-reinforced Onyx exhibiting the highest values, followed by glass and Kevlar fibers. Dynamic loading consistently produces higher maximum forces than quasi-static loading, indicating a pronounced rate effect. Fiber type also determines distinct deformation patterns under quasi-static conditions. Loading velocity significantly influences failure modes: carbon fiber specimens tend to rupture quasi-statically but may exhibit suppressed failure dynamically, whereas Kevlar and glass fiber specimens show no quasi-static failure but undergo interlayer delamination under dynamic loading. These findings provide quantitative guidance for material selection and structural design in additive manufacturing.