Enhancing Mode-I and Mode-II fracture toughness of carbon fiber/epoxy laminated composites using 3D-printed polyamide interlayers

Delamination is a critical concern in laminated composites, affecting their structural integrity and overall performance. This study investigates the enhancement of Mode-I and Mode-II fracture toughness in carbon fiber/epoxy (CF/EP) composites through the incorporation of 3D-printed polyamide (PA) interlayers. Vacuum-assisted resin transfer molding was utilized to fabricate composite laminates with and without 3D-printed PA interlayers. Comprehensive testing was conducted to assess the effect of 3D-printed PA interlayers on the Mode-I and Mode-II fracture toughness, interlaminar shear strength, and flexural properties, as well as thermomechanical response using dynamic mechanical analysis. The results revealed a significant improvement in critical energy release rates for both Mode-I and Mode-II (G Ic and G IIc ), increasing by 43.5% and 81.2% respectively, compared to the reference composites. This enhancement was primarily attributed to crack bridging and plastic deformation of PA filaments in the interlaminar region. Additionally, interlaminar shear strength increased by 17.4%. While the reference composites had a glass transition temperature of 117.3 °C, the PA-reinforced composites showed a slightly higher value at 119.6 °C, with no significant change in the glass transition temperature. tanδ max values increased from 0.321 to 0.576, suggesting better energy dissipation in PA-reinforced composites. However, flexural properties were adversely affected by the increased thickness and reduced fiber volume fraction due to the introduction of 3D-printed PA interlayers, with the flexural modulus decreasing by approximately 28% and the flexural strength by around 50%. These findings offer promising opportunities to enhance the performance of CF/EP composites under specific loading scenarios, thus expanding their potential applications across diverse industries.