Effect of High–Low Temperature Treatment on Mechanical Properties and Crack Propagation Behavior of Carbon Fiber‐Reinforced Composites

ABSTRACT This study investigates the mechanical properties and crack propagation behavior of carbon fiber‐reinforced epoxy composites subjected to high–low temperature treatment. Experimental findings revealed that immersion in liquid nitrogen (36 h–720 h) initially enhanced and subsequently decreased tensile strength, flexural properties, and interlaminar shear strength (ILSS). Tensile strength and modulus peaked at 72 h. Flexural and ILSS properties reached optimal values at 168 h. Subsequent heat treatments at 90°C (below T g ) minimally affected mechanical properties, whereas treatments at 150°C (above T g ) significantly decreased tensile and flexural performance but enhanced ILSS and elongation at break, restoring them to their original state prior to processing. Microstructural observations indicated that cryogenic exposure led to crack refinement but increased crack density. Interestingly, high‐temperature treatment at 150°C promoted partial crack healing, resulting in material property rejuvenation, a phenomenon validated through simulation modeling. The study highlights that thermal treatment involving low and high temperatures does not merely impart detrimental effects but can also beneficially influence composite properties.