Explore the vast range of titles available.

Currently, hypersonic vehicles are confronted with severe aerodynamic heating challenges, imposing strict demands on the thermal insulation and other characteristics of vehicle thermal protection materials. C/SiC composites have emerged as one of the favored materials for aircraft thermal protection, owing to their outstanding ablation resistance, oxidation resistance, and other properties. In this paper, a thermochemical ablation model was developed to elucidate the ablation mechanism of C/SiC composites. The dimensionless ablation rates of C/SiC under different pressures and material ratios were comparatively examined, and the total and linear ablation rates of C/SiC composites over 50 seconds were determined. The simulation results were contrasted with existing experimental data, and the error was within 10%.

Resorcinol–formaldehyde/silica composite (RF/SiO 2 ) aerogels were synthesized using sol–gel process followed by supercritical CO 2 drying. Monolithic carbon/silicon carbide composite (C/SiC) aerogels were formed from RF/SiO 2 aerogels after carbothermal reduction. X-ray diffraction and transmission electron microscopy demonstrate that β-SiC was obtained after carbothermal reduction. Scanning electron microscopy and nitrogen adsorption/desorption reveal that the as-prepared C/SiC aerogels are typical mesoporous materials. The pore structural properties were measured by nitrogen adsorption/desorption analysis. The resulting C/SiC aerogels possess a BET surface area of 564 m 2 /g, a porosity of 95.1 % and a pore volume of 2.59 cm 3 /g. The mass fraction of SiC in C/SiC aerogels is 31 %.

Continuous carbon fiber reinforced silicon carbide ceramic matrix composites (C/SiC) are promising materials in aerospace and space optical fields due to their excellent properties. However, poor machining quality resulted from surface/subsurface breakage is hard to meet precision requirements of some components. With an objective to study surface/subsurface breakage formation mechanism and improve machining quality of C/SiC composites, ultrasonic assisted grinding (UAG) and conventional grinding (CG) tests with a defined diamond grain distribution brazed grinding wheel were conducted. The surface/subsurface breakage types and formation mechanism were studied by comparative analysis of grinding force, micro-morphology of grinding surface/subsurface, and ground surface roughness. The results showed that main breakage types of different angle fibers in ground surface were lamellar brittle fracture and pit group originating from fracture and pullout of fibers, while breakage types of different angles fibers in ground surface were brittle fracture. Compared to CG, these breakages were reduced by UAG in varying degrees because it can reduce grinding force that determined fiber breakage. Consequently, because of the lower fiber breakages, the ground surface roughness S a obtained by UAG was lower than CG and the maximum reduction was 12%.

Carbon-fiber reinforced silicon carbide matrix (C/SiC) composites are typical difficult-to-cut materials due to high hardness and brittleness. Aiming at the problem of the serious tool wear in conventional milling (CM) C/SiC composite process, ultrasonic vibration–assisted milling (UVAM) and conventional milling tests with a diamond-coated milling cutter were conducted. Theoretical and experimental research on the cutting force during the ultrasonic vibration milling process of C/SiC composites is carried out. Based on the kinematics analysis of tool path during ultrasonic vibration milling process, the cutting force model of ultrasonic vibration milling is established, and the influence mechanism of ultrasonic vibration on the cutting force is revealed. Based on the analysis of the evolution law of tool wear profile and wear curve during the traditional milling and ultrasonic vibration milling of C/SiC, the tool wear forms and mechanism of diamond-coated milling cutters in two processing modes and the influence mechanism of ultrasonic vibration on tool wear are revealed. It is found that the main wear mechanism of the diamond-coated milling cutter is abrasive wear, and the main wear form is the coating peeling. Compared with the traditional milling, the tool wear can be reduced by the ultrasonic vibration milling in machining process. In the range of test parameters, the tool wear decreases first and then increases with the increase of ultrasonic amplitude.

In order to improve the micro-grinding quality of 2.5D carbon fiber-reinforced silicon carbide ceramic matrix (2.5D C f /SiC) composite materials, their characteristics under different grinding parameters were investigated in this study. Firstly, theoretical models for the undeformed chip thickness and micro-grinding force were established. Then, orthogonal and single-factor experiments were conducted using 0.9-mm-diameter micro-grinding tools electroplated with 500# diamond abrasive particles. Through the range and variance analysis of the orthogonal experimental results, the order in which grinding parameters affect the grinding performance of 2.5D C f /SiC composites was obtained. Single-factor experimental results indicate that the theoretical model of the micro-grinding force shows consistent trends with the experimental results. As the grinding depth a p and the feed speed v w increase, the grinding force, the surface roughness Ra , and surface defects after micro-grinding also increase, indicating that the grinding performance of 2.5D C f /SiC composites gradually deteriorates. On the contrary, increasing the grinding speed v s can improve their grinding performance. Based on the established theoretical model, the reasons for the variation of grinding force, surface morphology, and surface roughness with grinding parameters were elaborated. This research would supply a basis for understanding the micro-grinding performance and provide guidance for improving the micro-grinding quality of 2.5D C f /SiC composites.

The effects of laser parameters and the ablation mechanism in laser ablation of a carbon fiber reinforced silicon carbide (C/SiC) composite are investigated in the present study. Six different power densities are provided, as well as six levels of pulse numbers, and then ablation experiments are conducted for the C/SiC composite, induced by a pulsed laser. Based on the experimental results, the characteristics of surface morphology and ablation behavior are discussed. It is revealed that the surface morphology of the C/SiC composite under laser irradiation usually includes three regions: the center region, the transition region, and the border region. With the increase of laser power density, the ablation of the center region becomes severe, surface cracks occur, and more spherical SiC particles are found in the transition region. As for scenarios involving multiple pulses, the damage occurs in the center region at low power density limits, within the first two layers below the surface. However, if the power density is relatively high, an ablation pit occurs in the center region when the pulse number is larger than 50. Meanwhile, the transition region and the border region diminish with increase of the pulse number. It is noted that both the power density and pulse number have noticeable effects on surface morphology and ablation behavior during laser ablation, which is helpful for material design and performance evaluation of C/SiC composites.

Due to the anisotropic characteristic of carbon fiber-reinforced silicon carbide ceramics, the fiber orientation angle significantly affects the grinding force. Therefore, it is important to study the influence rule of different fiber orientations on the grinding force of 2.5D-C f /SiC composites. To study the comprehensive influence of machine tool parameters and the anisotropy of carbon fiber-reinforced ceramic matrix composites on the grinding force, two-dimensional ultrasonic plane grinding was studied by orthogonal test and single-factor experiment. Based on the multi-exponential fitting analysis method of multiple linear regression equation, the empirical equations of power exponential grinding force prediction model of 2D ultrasonic-assisted grinding and conventional grinding 2.5D-C f /SiC composites at 0°, 45°, and 90° fiber orientation and considering fiber orientation and ultrasonic amplitude were established, respectively. To verify the empirical formula model in predicting the grinding force of 2.5D-C f /SiC composites under various fiber orientation angles, the regression equation and regression coefficient of the model were examined. The influence of 2.5D-C f /SiC grinding parameters on the grinding force was analyzed. The parameters of the grinding force model were optimized based on range analysis and variance analysis, and the optimal process parameter combination was obtained. The results show that the grinding force is negatively correlated with the linear speed and positively correlated with the feed speed and grinding depth within the range of experimental parameters. The maximum reduction of the normal grinding force is 29.78% when the line speed is 10.48 m/s, the feed speed is 100 mm/min, the grinding depth is 50 μm, and along the 45° fiber direction. The optimal grinding parameter combination is a line speed of 23.60 m/s, feed speed of 5 mm/min, and grinding depth of 10 μm along the 0° fiber orientation.

In this paper, water jet-guided laser (WJGL) drilling of Cf/SiC composites was employed and the effects of the processing parameters on the depth and quality of the micro-holes were systematically investigated. Firstly, the depth measurement showed that the increase in processing time and power density led to a significant improvement in micro-hole drilling depth. However, the enhancement of the water jet speed resulted in a pronounced decrease in the depth due to the phenomenon of water splashing. In contrast, the scanning speed, path overlap ratio, pulse frequency, and helium pressure exhibited less effect on the micro-hole depth. Secondly, the microstructural analysis revealed that the increase in power density resulted in the deformation and fracture of the carbon fibers, while the augmentation in water jet speed reduced the thermal defects. Finally, based on the optimization of the processing parameters, a micro-hole of exceptional quality was achieved, with a depth-to-diameter ratio of 8.03 and a sidewall taper of 0.72°. This study can provide valuable guidance for WJGL micro-hole drilling of Cf/SiC composites.

Ultrasonic-assisted machining of silicon carbide (SiC) ceramic matrix composites (CMCs) has the ability to decrease grinding force and improve processing quality. The machining process often produces large cutting forces which cause defects, such as delamination and burrs, due to the brittleness and high hardness of the material. Therefore, it is significant to precisely predict the grinding force. In published literature, the modelling of cutting force has been investigated based on brittle removal assumption. However, a ductile flow phenomenon exists simultaneously during the micro-grinding of CMCs. Hence, in this paper, we present an analytical model of grinding force with the consideration of ductile–brittle transition. Additionally, the critical cutting depth for removal mode transition can be applied to distinguish the ductile and brittle fracture removal processes. The establishment of the analytical model was on the basis of the research of single abrasive grain, including motion trajectory, micromechanical analysis, cutting time, and removal volume in ductile and brittle fracture processes during one cutting cycle. Thereafter, the final model was proposed with respect to the quantity of active abrasive grains in the cutting area. The trend of the experiment results was in good agreement with the predicted values of the analytical model.

Carbon fiber-reinforced silicon carbide matrix (C/SiC) composites are typical difficult-to-cut materials due to high hardness and brittleness. Aiming at the problem of the serious high cutting force and poor surface quality in conventional milling (CM) C/SiC composite process, ultrasonic vibration-assisted milling (UVAM) and conventional milling tests with a diamond-coated milling cutter were conducted. The results showed that reducing the feed per tooth, cutting depth, or increasing the cutting speed can reduce the average cutting force, and increasing the ultrasonic amplitude, the average cutting force decreases first and then increases. With the assistance of ultrasonic vibration, the maximum reduction rates of average cutting forces Fx , Fy , and Fz were 43.7%, 29.16%, and 68.09%.The ultrasonic vibration assisting effect does not significantly improve the damage of materials such as fiber breakage during processing. The ultrasonic vibration assisting effect improves the quality of processing edges. It is found that reducing feed per tooth, cutting depth, or increasing cutting speed can reduce surface roughness and increasing the ultrasonic amplitude reduces the surface roughness first and then increases. On the whole, the surface roughness of C/SiC ultrasonic vibration milling is slightly smaller than that of conventional machining.