Hardness and flexural performance of 3D orthogonal carbon/glass fibers hybrid composites under thermal-oxidative aging

This study reports the hardness and flexural performance of the three-dimensional (3 D) orthogonal carbon/glass hybrid fiber/bismaleimide composites subjected to the accelerated aging conditions for 10, 30, 90, 120, and 180 days at 250 °C in an air environment. The rate of reduction in the flexural performance and failure modes were observed, in general, to be related to the aging time. The experimental findings revealed that the significant decline in the flexural performance of the samples aged for less than 30 days was predominantly attributed to the matrix degradation, while for the longer aging durations, the cracks in the composites and decomposition of the residual matrix were responsible for the gradual reduction in the flexural performance. The unaged and 30 days aged samples suffered a brittle failure represented by the macro-cracks and fiber breakage, while the cracked fiber/matrix interface and loosened fiber bundles were the main failure modes for the samples aged for longer times. The changes in the flexural failure modes resulted due to the severe degradation of the matrix under an extreme thermo-oxidative environment. Subsequently, a nonlinear relationship relating the flexural modulus to hardness was proposed.