Mechanical Properties of Epoxy- and Dicyclopentadiene-Based Carbon-Fiber-Reinforced Plastics at Low and Room Temperatures

Abstract

In this study, the material properties of carbon-fiber-reinforced polymers (CFRPs) were investigated at room temperature (20 °C) and cryogenic temperature (–196 °C). Two types of CFRPs incorporating thermoset resins, namely epoxy (E) and dicyclopentadiene (D), were employed to evaluate their mechanical properties and failure behaviors. For low-temperature testing, an originally designed apparatus was utilized, in which mechanical properties were evaluated using a polystyrene container filled with liquid nitrogen (LN). The LN level was maintained automatically via a capacitance sensor-based monitoring system that regulated its replenishment as necessary. The results revealed that the bending and fatigue strengths of both CFRP types increased by approximately 30% at –196 °C compared to those at 20 °C. This enhancement may be attributed to various reasons, including increased internal strain induced by the disparity in thermal expansion coefficients between the carbon fiber and the resin. CFRP exhibited relatively higher creep resistance at –196 °C, compared to that at 20 °C. Under static bending load, E-CFRP displayed a sudden stress drop at approximately 2% bending strain, likely due to delamination between the epoxy resin and carbon fibers. In contrast, D-CFRP demonstrated enhanced strain tolerance, sustaining strains exceeding 5% without severe delamination, which can be attributed to the superior wettability of dicyclopentadiene with carbon. Details of the wettability and the above material properties of both CFRPs were analyzed in this paper.