Unveiling Carbon Fiber Reinforced Polyurea Composites Engineered through Vacuum Assisted Resin Transfer Molding: An In-depth Analysis of Mechanical, Thermal, and Degradation Performance

Abstract

Carbon fiber reinforced polymer (CFRP) composites have attracted increasing attention in recent years as they exhibit excellent mechanical strength and are substituting metals in marine, automotive, aerospace, and construction industries. However, the brittleness of CFRP leads to low toughness, limiting its structural performance. In this work, for the first time, the utilization of super elastomeric polyurea as the matrix with carbon fiber via vacuum-assisted resin transfer molding is featured. This study revealed a direct correlation between the number of carbon fabric layers and the enhancement of the flexural load, stiffness, and resistance to mechanical indentation. The 8-layer laminate with a thickness of 2.5 mm showed flexural strength of 237 MPa at 5% flexural strain, flexural modulus of 93.4 GPa and hardness of 80 HD. Polyurea matrix demonstrated exceptional stress absorption and redistribution capabilities, preventing complete breakage up to 5% flexural strain, ultimately restoring the laminates' position upon unloading. Field emission scanning electron microscopy analysis showed strong matrix-fiber interfacial adhesion that could be attributed to the interphase mechanical locking resulting in high storage modulus of 2441 MPa. An in-depth analysis of the laminates' fracture morphology unveiled delamination predominantly within the compression zone, except for the 2-layer laminate, where fractures manifested simultaneously in both compression and tension zones due to the slender thickness. Furthermore, the degradation behavior of the polyurea composite laminates under exposure to 5% NaCl solution at a temperature of 60 °C highlighted an initial increase in flexural strength within the initial 28-day period, attributed to the plasticizing effect induced by moisture. However, at 63 days, a decline in flexural strength is observed, signaling the degradation and debonding of the matrix from the reinforcing fibers. This work opens the door for viscoelastic CFRP as an excellent absorbing composite material with high toughness that is suitable for marine environments.