Hygrothermal aging effects on the mechanical behaviors of twill-woven carbon fiber composite laminates with flame-retardant epoxy resin

Abstract

Composite structures are frequently exposed to varying hygrothermal environments, which can lead to the deterioration of their mechanical properties. This study explores the effects of hygrothermal aging on the mechanical behaviors of twill-woven carbon fiber composite laminates, with a particular focus on laminates with flame-retardant epoxy resin (CF_FR)—a relatively underexplored area. The findings reveal several key insights: (1) CF_FR exhibit more pronounced aging damage compared to those with general epoxy resin (CF_G), primarily due to higher moisture absorption, which results in increased surface swelling and internal delamination. (2) Hygrothermal aging enhances the impact resistance of both types of laminates by increasing peak force, particularly at higher temperatures, thereby reducing impact-induced damage. (3) CF_FR suffers greater reductions in compressive and compression after impact (CAI) strength following aging, with CAI strength decreasing by 36.3% for flame-retardant laminates and 14.8% for CF_G after immersion at 70°C. (4) Significant local buckling is observed in the swollen regions of CF_FR under compressive loading, indicating an heightened vulnerability to structural instability after aging. These findings offer valuable insights into the performance of composite materials under prolonged moisture exposure, particularly in safety-critical applications where both flame retardancy and mechanical integrity are crucial.