Study of the damage behavior of T800 carbon fiber/epoxy resin composites after low-velocity impact under thermo-oxidative aging

Here, the effect of thermo-oxidative aging on domestic T800 carbon fiber/epoxy resin composites was studied using mass loss rate curves, interface morphology, infrared spectroscopy, and dynamic mechanical property analysis. The composites were subjected to thermo-oxidative aging tests after low-velocity impact. Then, the effect of environmental factors on the damage area of the composites and the compression performance after impact were investigated. The results showed that the composites underwent physical and chemical aging at 185°C. Due to the short aging time, the mass loss rate slowly increased. After aging, thermo-oxidative aging caused the matrix to crack, and the sample cracks that formed after impact expanded, and the damage area also slightly increased. The residual compressive strength of the material fluctuated due to the competing reinforcing and destructive effects of the composite during thermo-oxidative aging; however, aging had little effect on the impact damage morphology and compression failure mode. Upon extending the aging time, thermo-oxidative aging caused the tanδ peak to gradually shift to a higher temperature, and the glass transition temperature ( Tg) increased.

Effects of aging process and testing temperature on the open-hole compressive properties of a carbon fiber composite

The properties of T800 carbon fiber–epoxy composite specimens with a hole were studied in terms of mass change, scanning electron microscopy, glass transition temperature ( T g), heat-resistant temperature, Fourier-transform infrared (FTIR) spectroscopy, open-hole compressive strength at different temperatures, and stereomicroscopic observations after being subjected to hygrothermal aging and thermal-oxidative aging processes. FTIR spectra indicated that after hygrothermal aging at 70°C and 85% relative humidity (RH), chemical aging did not occur, whereas after thermal-oxidative aging at 190°C, the specimens exhibited chemical aging. The unaged specimens had a T g of 229°C and an extreme heat-resistant temperature T gmod of 184°C; after hygrothermal aging, the specimens had a T g and T gmod of 207°C and 143°C, respectively; and after thermal-oxidative aging, the specimens had a T g and T gmod of 252°C and 215°C, respectively. The effects of temperature on open-hole compressive strength were evaluated at room temperature of 23°C, 50°C, 100°C, 150°C, and 200°C. The compressive strengths of the specimens decreased after aging and with the increasing test temperature. At the highest test temperature, the unaged specimens, hygrothermal-aged, and thermal-oxidative-aged specimens retained over 73.7%, 65.5%, and 67.9%, respectively, of their compressive strength. Thus, the T800 carbon fiber–epoxy composite evaluated in this study exhibited good resistance to the effects of aging and high temperature. These results should be beneficial to the understanding of the long-term performance of composites.

Effects of thermal–oxidative aging on the mechanical properties of open-hole T800 carbon fiber/high-temperature epoxy composites

T800 carbon fiber/high-temperature epoxy resin composites with holes were subjected to thermal–oxidative aging, and the effects of different aging temperatures and times on the composite properties were investigated. The mass loss, surface topography, open-hole tensile performance, fracture morphologies, dynamic mechanical properties, and infrared spectra were analyzed. The results showed that chemical aging did not occur with thermal–oxidative aging at 70°C and 130°C. However, chemical aging occurred at 190°C. At 70°C, 130°C, and 190°C, all samples showed a slight increase followed by a slight decrease and stabilization in the open-hole tensile strength. The open-hole tensile strength was maximized after 240 h aging at different temperatures; the open-hole tensile strength after 1920 h aging exceeded that of the unaged samples. All composites experienced through-hole failure. With aging, the glass transition temperature ( T g) was gradually increased and then decreased. After 960 h aging at different temperatures, T g was maximized.