A four directional carbon/ carbon (4D C/ C) composite was fabricated by first using liquid phase impregnation carbonization (LPIC), followed by hot isostatic pressure impregnation and carbonization (HIPIC) at 75MPa, and finally high temperature treatment. The flexural properties and fracture behavior of the composite were investigated in the through-thickness direction under static and fatigue loading. The critical fatigue limit of the composite was 80% of the static flexural strength for one million loading cycles at 10 Hz. The failure mechanism of the composite under static flexural loading was dependent on the orientation of the carbon fibers in the tested specimen. Cyclic fatigue loading decreased the interfacial bonding strength and released the inherent stresses in the composite, which increased fiber pull-out, enhanced pseu-doductility and increased the residual static flexural strength at the expense of a decrease in the flexural modulus. The fatigue loading increased the number of noncritical matrix cracks, increased interfacial debonding, and caused the fracture of filaments in the surviving fatigued C/ C composite. These features of the fatigued composite internally accommodated expansion in long direction as the temperature was increased, which resulted in a decrease in its residual thermal expansion.

Carbon fiber/ bismaleimide composites have received increasing interest, owing to their excellent properties, especially their toughness under extreme working conditions. We established a micromechanical model for a finite element simulation of the micro-droplet test, which involves pulling a carbon fiber out of a bead of matrix using two moving knives acting on the bead as scrapers to quantify the interfacial properties of carbon fiber reinforced bismaleimide composites. The interfacial shear strength of carbon fiber/ bismaleimide composites subjected to different hydrothermal environments was tested by micro-droplet method to illustrate the impact of moisture absorption on their interfacial properties. Hydrothermal aging caused a reduction of interfacial shear strength, which leveled off when the immersion time in water exceeded 7 days at 71°C . A numerical simulation of the debonding process was performed based on the interface cohesive element damage model to simulate the interfacial properties of the composite and to determine the correlation between experimental parameters and interfacial properties. The simulation successfully provided essential parameters for numerical analysis of the macroscopic mechanical properties of the composite. Finite element analysis of the micro-droplet test revealed that the factors that influence the interfacial shear stress distribution are the position of the knives on the bead, thermal residual stress and hydrothermal treatment conditions

A TiO₂ sol was prepared from tetrabutyltitanate using polyethylene glycol as a stabilizer, and this was homogeneously mixed with polyfurfuryl alcohol, dip-coated on a porous Al ₂O₃ substrate and carbonized at 700°C for 4h to produce TiO₂-doped carbon membranes. SEM, TEM, XRD and granulometry were used to characterize the membranes, and their permeation performance for CO₂ , N₂ and CH₄ were tested. It was found that polyethylene glycol is effective in controlling the hydroxylation of the tetrabu-tyltitanate. This not only favored the formation of spherical TiO₂ nanoparticles with a small size and narrow size distribution but also improved the homogeneity of the dispersion of the TiO₂ nanoparticles in polyfurfuryl alcohol. The doping of the membranes with TiO₂ nanoparticles greatly improved the CO₂ permeance and permselectivity. The TiO₂ doping helps to create diffusion paths, but it may also block the pores in the carbon matrix. Therefore, the CO₂ permeance reached a maximum of 7. 0×10 ^-8 mol·m ^-2·s ^-1·Pa ^-1 with a mass ratio of TiO₂ sol to polyfurfuryl alcohol of 2, where the CO₂ / N₂ and the CO₂ / CH4 selectivities were 34 and 64, respectively.