Hybrid effects and interactive failure mechanisms of hybrid fiber composites under flexural loading: Carbon/Kevlar, carbon/glass, carbon/glass/Kevlar

Abstract

Regulatable and customized mechanical properties of aeronautical composites, e.g., stiffness, strength, elongation, energy-absorption (EA), etc., can be flexibly obtained with fiber hybridization, but the hybridization design is challenging due to complex hybrid effects. Hence, hybrid effects and interactive failure mechanisms of carbon-glass-Kevlar hybrid fiber reinforced polymer (HFRP) composites under flexural loading are revealed. Double-/multi-fiber HFRP (carbon/glass, carbon/Kevlar and carbon/glass/Kevlar) with different hybrid ratios and stacking sequences are proposed. Experimental specimens are fabricated and a series of flexural tests are conducted to assess flexural properties and cost-effectiveness. It is found that HFRP has 152.9% and 76.2% higher EA than CF9 and KF9 which benefits from the combination of ductile Kevlar-fiber and strong carbon-fiber. Different hybrid effects are also produced by different fiber-hybridizations, e.g., +0.866 (CF5/KF4), +0.72 (CF5/GF2/KF2) in EA. From microscopic characterization, the combined brittle/ductile breakage, buckling, fiber-splitting, crack suppression and underlying interactions are revealed to explain the improvements. It is also indicated that the interactive or coupling effects of hybrid ratio and dispersity on flexural properties are identified. Finally, numerical simulations using a validated finite element model are conducted to qualitatively study the mechanical behaviors of HFRP. It provides a useful guidance for the customized design of composites.