Research on thermal degradation and tensile properties of carbon fiber reinforced epoxy resin composites at elevated temperatures

Carbon fiber reinforced epoxy resin composites (CFRCs) are widely used in the manufacture of high-pressure hydrogen storage cylinders. However, under accidental fire, these composite cylinders have a high failure risk since the elevated temperatures significantly degrade their structural integrity. In this work, thermal degradation behavior and tensile properties of CFRCs were systematically studied at temperatures ranging from 20 °C to 450 °C, with emphasis on the combined effects of ply orientation and temperature on mechanical performance and failure mechanisms. Three stacking laminates, including [0°] (CF0), [90°] (CF90), and [±45°] (CF45) , were examined through thermogravimetry analysis (TGA), high-temperature tensile testing, and scanning electron microscopy observation (SEM). Results indicated a sharp decline in tensile strength with increasing temperature and revealed distinct degradation mechanisms tied to ply orientation. For CF0 specimens, the loss of tensile strength was predominantly governed by matrix decomposition and fiber-matrix debonding (250 °C–400 °C). In contrast, the softening of the epoxy resin near the glass transition temperature (about 120 °C) had a more pronounced effect on the mechanical degradation of CF90 and CF45. Distinct failure modes were observed: interfacial debonding and fiber softening in CF0 at 450 °C, resin bonding strength degradation in CF90 from 150 °C, and extensive delamination between plies in CF45 above 125 °C. These findings provide guidance for structural integrity assessment and fire-resistance design of composite cylinders.