Mechanical Properties of Carbon Fiber and Polyimide Fiber Hybrid Reinforced Polyimide Resin Matrix Composites at Room and High Temperatures

High-strength, high-modulus polyimide (PI) fibers are a type of high-performance organic fiber known for their exceptional high-temperature resistance. When blended with carbon fibers to prepare hybrid composite materials, they have the potential to strike a balance between rigidity and toughness, thereby offering a composite structure with high modulus, strength and high toughness. In this study, a series of hybrid fiber-reinforced composites were fabricated using high-strength, high-modulus PI fibers together with carbon fibers as reinforcements and a PI resin matrix. The effects of the hybrid ratio on the tensile, compressive and flexural properties, as well as the failure modes, were systematically investigated. Experimental results showed that, compared to pure PI fiber composites, the hybrid fiber composites exhibited significant improvements in the compressive and flexural properties, in accordance with the hybrid law. Specifically, the hybrid composites demonstrated a negative hybrid effect in terms of tensile properties, whereas they exhibited a positive hybrid effect in terms of compressive and flexural properties. In high-temperature flexural tests, the addition of carbon fibers significantly enhanced the retention of the properties at 300 °C and 370 °C; for instance, the incorporation of carbon fibers at a volume fraction of 24% enhanced the flexural strength retention rate of the composite laminate at 300 °C from 37% to 66%, and remarkably increased the modulus retention rate from 50% to 94%, showing great advantages of the hybrid composite in a load-bearing structure at elevated temperatures.