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In this paper, continuous carbon fiber reinforced alumina matrix (C/Al2O3) composites were fabricated through the “sol infiltration-drying-heat treatment” route. In the composites, nano aluminum sol with high solid content was elected as raw material. Similarly, carbon fiber cloth preform with a laminated-stitched structure was chosen for reinforcement. The preparation process and high-temperature failure behavior of the composites under an inert atmosphere were studied emphatically. The results showed that the porosity of C/Al2O3 composites prepared by 28 cycles was 16.6%, and the three-point bending strength was 208.5 MPa at room temperature. The fracture toughness of composites was 8.1 MPa · m1/2, which was 102.5% higher than that of alumina ceramic. After 1 h high-temperature test at 1400 °C and 1600 °C under Ar, the strength retention rate of C/Al2O3 composites was 84.4% and 73.0%, respectively. SEM indicated the thermal mismatch between matrix and fibers contributed to the reduction in mechanical properties of C/Al2O3 composites.

Mullite matrix composites with laminated and stitched carbon fiber cloth preform as reinforcement were fabricated via the route of “infiltration-drying-heat treatment” using Al2O3-SiO2 sol as raw materials. Thermal properties from room temperature to 1673K of the composites were investigated. The coefficient of thermal expansion (CTE) increases first and then decreases, and reaches a maximum of 4.83×10-6K-1 at 1273K. As a result of the further sintering of matrix, the CTE is negative at above 1300°C. The specific heat capacity increases to the maximum of 1.547J·g-1·K-1 at 1473K and remains stable at above 1473K, with a minimum of 0.756J·g-1·K-1 at room temperature. The thermal diffusivity decreases from 1.1mm2·s-1 at room temperature to 0.707 mm2·s-1 at 973K as the temperature was elevated, and remains stable at above 973K. On the contrary, the thermal conductivity is improved with increasing temperature on the whole and varies from 1.859W·m-1·K-1 at room temperature to 2.325W·m-1·K-1 at 1473K.

To protect carbon fiber-reinforced SiC (C/SiC) composites against oxidation,mullite coating was prepared on C/SiC composites by dip-coating method with high solid content Al2O3-SiO2 sol as raw materials. X-ray diffraction and scanning electron microscopy were employed to analyze the phase and microstructure of the coating. The results show that the as-prepared coating is SiO2-rich, monolithic and well bonded with substrate without penetrating crack, giving rise to good oxidation-resistance. After soaked at 1400°C for 30min under static air, the coated C/SiC composites possess 87% of original flexural strength. As a result of sealing and filling of cracks and pores by viscous SiO2 in coating, the coated C/SiC composites exhibit improved oxidation resistance at 1500°C and 1600°C. There is no change in flexural strength after oxidized at 1500°C and 1600°C for 30min, respectively. Nevertheless, the carbothermal reduction between viscous SiO2 and free carbon in C/SiC substrate would occur obviously when oxidation temperature was elevated or oxidation time was prolonged, leading to local foaming in coating and decreasing in oxidation resistance.

In order to efficiently fabricate dense three-dimensional carbon fiber reinforced mullite matrix composites (3D C/mullite), two kinds of Al2O3-SiO2sols with high solid content were used as raw materials. The ceramic yield and mullitization behavior of the sols and the densification process were investigated. It is indicated that the two sols have proper solid content and ceramic yield and can be completely transformed into mullite at 1573K, which make them be able to prepare composites. 3D C/mullite composites with a porosity of ∼25% were prepared by repeating less than 20 cycles of infiltration-drying-heating of sols, and the microstructures and mechanical properties were examined. The results suggest that the sol with smaller particle size derived composites exhibit well-sintered dense matrix and physically stronger interfacial bonding, which are beneficial to improve load-bearing and load-transferring capacity of matrix. As a result, this composites show much higher mechanical properties. The flexural strength and modulus are 2.4 times and 1.3 times as those of the sol with larger particle size derived composites, respectively.

Mesoporous and macroporous mullite ceramics were fabricated from pyrolysis of alumina nanopowders filled silicone resin. The effect of pore-forming agent (carbon nanopowders) on the pore structure and mechanical property of the porous mullite ceramics were investigated. By varying the carbon content, the porosity and flexural strength of the obtained ceramics could be easily tuned. Both of the open porosity and average pore size of the obtained samples increased at elevated carbon content, and reached the maximum value of 61.0%, 225.5 nm respectively when the carbon content got the highest point (40 Vol.%). The flexural strength of nanoporous mullite ceramics changed almost with an opposite trend of open porosity, with the biggest value of 36 MPa when 10 Vol.% carbon was adopted. The microstructure of porous mullite ceramics consists of dense region and loose region when the added carbon content was at relatively low level. However, the dense area gradually disappeared with the increasing of carbon content.

Nanoporous carbonaceous materials derived from polysiloxane were first prepared by pyrolysis at 1300°C followed with hydrofluoric acid (HF) etching treatment. Their thermal stability of pore structure in inert condition was investigated in this paper by nitrogen adsorption technique in detail. The specific surface area (SSA) and pore volume (total pore volume, micropore volume, mesopore volume) decreased continually in the heat-treatment temperature range of 1000~1400°C. The average pore size almost kept the same with the raw sample. However, when the temperature exceeded 1400°C, the micropore interconnection began transforming to mesopore structure, which led to the decline of SSA and the increase of average pore size. Furthermore, the pore size distributions (PSDs) curves showed that heat-treatment had an advantage on the transition process of pore structure from disorder to regularity to some extent when heat-treated in the range 1000~1400°C for the most possible reason of relief of residue strain in the carbonaceous materials.

Carbon fiber reinforced silicon carbide composites (Cf/SiC) were derived through precursor infiltration pyrolysis route (PIP) at 1600°C in vacuum atmosphere using polysiloxane as precursor. The matrix of Cf/SiC was characterized by X-ray diffraction and elemental analysis. The results show that crystalline β-SiC can be derived at 1600°C in vacuum from polysiloxane. The flexural strength and fracture toughness of polysiloxane derived from Cf/SiC can reach up to 70 MPa and 2.3MPa·m respectively1/2.

A damage constitutive model was established to evaluate the stability of jointed rock masses around the underground caverns of Shuangjiangkou Hydropower Station. In this model, a second-order damage tensor was formulated to describe the initial geometric imperfection of jointed rock masses. A failure criterion for crack coalescence and a damage evolution equation were proposed by considering the secondary cracks induced by excavations according to the fracture mechanics principles. A subprogram under the framework of FLAC-3D was developed for the damage constitutive model and the damage evolution equation. The model and program were then applied in the stability assessment for the Shuangjiangkou underground cavern group.

Two-dimensional carbon fiber cloth reinforced silicon oxycarbide (2D-Cf/Si-O-C) composites were fabricated with silicone resin (SR) as precursors, ethanol as solvent and SiC as inert fillers by precursor infiltration pyrolysis (PIP). Effects of the pyrolysis temperatures in the first cycle and the last but third cycle on the microstructure and mechanical properties of 2D-Cf/Si-O-C composites were investigated. The results showed that, when the pyrolysis temperature of the first cycle was 1200°C, 2D-Cf/Si-O-C composites exhibited good mechanical properties, which can be attributed to the better fiber/matrix interfacial bonding. When the pyrolysis temperature of the last but third cycle was 1400°C, the mechanical properties of 2D Cf/Si-O-C composites were further enhanced. The flexural strength and fracture toughness of the composites reached 263.9MPa and 12.8 MPa·m1/2, respectively.

Carbon fiber cloth reinforced silicon carbide (2D-Cf/SiC) composites were prepared through polycarbosilane(PCS) /divinylbenzene(DVB) pyrolysis with SiC as inactive filler. Effects of the molding pressure on the microstructure and mechanical properties of 2D-Cf/SiC composites were investigated. With increasing molding pressure from 0MPa to 3MPa, the fiber volume fraction of the composites was increased. As a result, the strengths of the composites were enhanced. But when the molding pressure exceeded 3MPa, SiC particles would damage the carbon fibers seriously. Therefore, although the fiber fraction of the composites was increased further, the flexural strengths of the composites were decreased. It was found that the composites fabricated with the molding pressure of 3 MPa exhibited highest flexural strength, reached 319.4 MPa.

Continuous SiC fiber reinforced SiC composites were fabricated by PIP route and their microstructures and mechanical properties were characterized. The density, flexural strength and fracture toughness of the composites were 1.88 g/cm3, 307 MPa and 8.24 MPa⋅m1/2, respectively. The low mechanical properties were ascribed to low density and strong interfacial bonding. The composites exhibited poor oxidation and thermal shock resistance; however, they showed desirable thermal stability.

SR-249, a kind of polysiloxane (PSO), was used as the precursor for the first time to fabricate carbon fiber cloth reinforced silicon oxycarbide (2D Cf/Si-O-C) composites. The cure and pyrolysis of the SR-249 as well as the mechanical properties, oxidation and thermal shock behavior of the composites were investigated in the paper. The flexural strength and fracture toughness of the composites reached 217.6 MPa and 12.5 MPa·m1/2, respectively. After soaked at 1300°C under the static air for 10 min, the composites retained 58.5% flexural strength and 64.5% fracture toughness. The thermal shock behavior of the composites was studied by water quenched method. The composites retained 49.3% flexural strength and 47.4% fracture toughness after 10 times of quenching from 1200 to 20°C.

In this paper, 3D Cf/Si-Ti-C-O composites were prepared with a polytitanocarbosilane (PTC) via polymer infiltration and pyrolysis (PIP) process, and accordingly the mechanical, oxidation resisting and thermal shock resisting properties were investigated. The composites with density of 1.93g·cm-3 show rather high flexural strength (485.3MPa) and fracture toughness (19.95MPa⋅m1/2), and typical non-brittle fracture failure mode. After oxidation treatment at 1300°C for 10 minutes in air, the flexural strength of the samples is 306.2MPa, with 63% strength retention. After 5 times of thermal shock tests from room temperature to 1300°C, the flexural strength of the samples is 408.9MPa, about 85% strength retention. SEM observation also testifies non-brittle failure because many fibers are pulled out on the fracture surface. After oxidation treatment, the matrix shows no changes from XRD measurement.