Sol-gel is a promising technology to prepare the c/c-Zrc-Siccomposites. However, carbon fiber erosion caused by carbothermal reduction severely degrades properties of the composites. At present study, the addition or...
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Sol-gel is a promising technology to prepare the c/c-Zrc-Siccomposites. However, carbon fiber erosion caused by carbothermal reduction severely degrades properties of the composites. At present study, the addition order of carbon source during sol-gel process was optimized to improve the microstructure, mechanical property and ablation resistance of the composites. Results show that adding phenolic resin before gelation combined with deposited pyrocarbon interlayer around the carbon fibers can greatly alleviate the degradation of the c/ c-Zrc-Siccomposites by reducing the carbon fiber erosion. The composites thus prepared delivered the flexural strength, mass and linear ablation rates are 162.58 MPa, 0.147 mg/(cm2.s) and 0.0098 mm/s, respectively, which are 449% higher, 9.26% lower and 38.36% lower than those of the counterpart that added phenolic resin after gelation. The excellent performance is attributed to little erosion of the carbon fibers and the dense matrix of Zrc-Sicceramics obtained from adding carbon source before gelation during the sol-gel process.
carbon fiber reinforced carbon matrix (c/c) composites have been used in aerospace applications due to their excellent performance. Exploring their failure mechanisms is a subject of extensive research. Nowadays, to o...
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carbon fiber reinforced carbon matrix (c/c) composites have been used in aerospace applications due to their excellent performance. Exploring their failure mechanisms is a subject of extensive research. Nowadays, to obtain information about changes in the failure processes, a technology known as in situ X-ray computed to-mography is used. In this paper, tensile loads were applied to 3D fine-woven punctured and needle-punched c/ccomposites perpendicular to the punctured and needle-punched directions. In situ X-ray computed tomography was employed to observe damage development, and digital volume correlation was used to assess the laboratory X-ray computed tomographs to measure local strains. Assimilation of pores is observed in c/ccomposites, with cracks evolving from original micro-pores. While fine-woven punctured c/ccomposites present an elegant linear failure, needle-punched c/ccomposites present a traditional non-linear failure. This difference is due to the different structures of the preforms. Furthermore, the c/ccomposites are weak at the sites where they are punctured or needle-punched.
Owing to the numerous potential applications of ZnO nanomaterials, the development of ZnO-based nanocomposites has become of great scientific interest in various fields. In this paper, we are reporting the fabrication...
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Owing to the numerous potential applications of ZnO nanomaterials, the development of ZnO-based nanocomposites has become of great scientific interest in various fields. In this paper, we are reporting the fabrication of a series of ZnO/c nanocomposites through a simple "one-pot" calcination method under three different temperatures, 500 & DEG;c, 600 & DEG;c, and 700 & DEG;c, with samples labeled as ZnO/c-500, -600, and -700, respectively. All samples exhibited adsorption capabilities and photon-activated catalytic and antibacterial properties, with the ZnO/c-700 sample showing superior performance among the three. The carbonaceous material in ZnO/c is key to expanding the optical absorption range and improving the charge separation efficiency of ZnO. The remarkable adsorption property of the ZnO/c-700 sample was demonstrated using congo red dye, and is credited to its good hydrophilicity. It was also found to exhibit the most notable photocatalysis effect due to its high
In this work, a robust brazed joint of carbon fibre-reinforced carbon-based (c/c) composite and Tc4 alloy was produced by utilising a slice of c/c as an interlayer. The c/c slice interlayer caused microstructural and ...
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In this work, a robust brazed joint of carbon fibre-reinforced carbon-based (c/c) composite and Tc4 alloy was produced by utilising a slice of c/c as an interlayer. The c/c slice interlayer caused microstructural and mechanical property enhancement. During brazing, massive in situ formed carbon fibres broke away from the c/c slice bundles and were distributed in a three-dimensional interlocked network. These unique fibres consumed excessive Ti to inhibit the formation of excess brittle Ti-cu compounds in the brazing seam. This reduced the coefficient of thermal expansion effectively, consequently relieving the high residual stress in the joint interface. The average shear strength of the joint brazed with the c/c slice interlayer reached 1.65 times higher than the directly brazed one.
c++ and concurrent c are both upward-compatible supersets of c that provide data abstraction and parallel programming facilities, respectively. Although data abstraction facilities are important for writing concurrent...
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c++ and concurrent c are both upward-compatible supersets of c that provide data abstraction and parallel programming facilities, respectively. Although data abstraction facilities are important for writing concurrent programs, we did not provide data abstraction facilities in concurrent c because we did not want to duplicate the c++ research effort. Instead, we decided that we would eventually integrate c++ and concurrent c facilities to produce a language with both data abstraction and parallel programming facilities, namely, concurrent c++. Data abstraction and parallel programming facilities are orthogonal. Despite this, the merger of concurrent c and c++ raised several integration issues. In this paper, we will give introductions to c++ and concurrent c, give two examples illustrating the advantages of using data abstraction facilities in concurrent programs, and discuss issues in integrating c++ and concurrent c to produce concurrent c++.
ceramic matrix composites of type c/Sic have great potential because of their excellent properties such as high specific strength, high specific rigidity, high-temperature endurance, and superior wear resistance. Howe...
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ceramic matrix composites of type c/Sic have great potential because of their excellent properties such as high specific strength, high specific rigidity, high-temperature endurance, and superior wear resistance. However, the machining of c/Sic is still challenging to achieve desired efficiency and quality due to their heterogeneous, anisotropic, and varying thermal properties. Rotary ultrasonic machining (RUM) is considered as a highly feasible technology for advanced materials. cutting force prediction in RUM can help to optimize input variables and reduce processing defects in composite materials. In this research, a mathematical axial cutting force model has been developed based on the indentation fracture theory of material removal mechanism considering penetration trajectory and energy conservation theorem for rotary ultrasonic face milling (RUFM) of c/Siccomposites and validated through designed sets of experiments. Experimental results were found to be in good agreement with theoretically simulated results having less than 15% error. Therefore, this theoretical model can be effectively applied to predict the axial cutting forces during RUFM of c/Sic. The surface roughness of the workpiece materials was investigated after machining. The relationships of axial cutting force and surface roughness with cutting parameters, including spindle speed, feed rate, and cutting depth, were also investigated. In order to identify the influence of cutting parameters on the RUFM process, correlation analysis was applied. In addition, response surface methodology was employed to optimize the cutting parameters.
KOVATS index is the most precise index system reflecting the interaction between the molecules of solutes and stationary phase in gas chromatography at present. Large quantity of Kovats in dex data have been published...
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KOVATS index is the most precise index system reflecting the interaction between the molecules of solutes and stationary phase in gas chromatography at present. Large quantity of Kovats in dex data have been published. It is a good way to use Kováts index in gas chromatography to predict the retention value in liquid chromatography, which is significant in theory and apphcation.
c* is usually used to describe the creep crack growth. ASTM E1457 allows c* to be calculated from creep load line displacement rate. However in components it is difficult or impossible to measure load line displacemen...
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c* is usually used to describe the creep crack growth. ASTM E1457 allows c* to be calculated from creep load line displacement rate. However in components it is difficult or impossible to measure load line displacement rate. Therefore for the components c* must be determined by finite element methods or reference stress concepts. Estimates of c* obtained by reference stress methods will depend on the collapse mechanism adopted and therefore several estimations are proposed. This paper presents a numerical study of non-linear fracture mechanics parameter predictions under elevated temperature for axially oriented external surface crack in cylinder. comparison of c* calculated from FE analysis and different reference methods is conducted. The values of c* obtained from the API579 net section solution are also found to be slightly conservative and give the closest agreement to the F.E. contour integral c*. In addition, the comparison between c* of homogeneous material and TYPE IV cracking is conducted. The difference between homogeneous material and TYPE IV cracking is almost negligible and therefore the reference stress solutions for homogenous material could be applied to estimate c* for TYPE IV cracking.
A modification of the precursor infiltration pyrolysis (PIP) method was explored to prepare the integrated doped ceramic matrix and coating by the added Sic nanowires layer and shape-stabilization process. The epitaxi...
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A modification of the precursor infiltration pyrolysis (PIP) method was explored to prepare the integrated doped ceramic matrix and coating by the added Sic nanowires layer and shape-stabilization process. The epitaxial layer of Sic nanowires provided surficial attachments for the precursor. And the shape-stabilization process aggregated loose ceramic particles into a coating. Then the Sic nanowire-reinforced Zrc-Siccoating-matrix integrated c/c (S/SZ-cZ/c) composite was simply prepared by the modified PIP method. The bonding strength between the coating and matrix of the S/SZ-cZ/ccomposite was improved. Through the ablation test, the mass and linear ablation rate of the S/SZ-cZ/ccomposite were 0.46 mg/s and 0.67 mu m/s, which were 60.34 % and 74.91 % lower than those of the Sic nanowire-reinforced c/c-Zrc (S/cZ/c) composite, respectively. The integration of the coating and matrix enabled the formation of a continuous oxide layer of molten SiO2 and ZrO2 in the ablation process, which helped to block the oxygen and heat during the ablation test. Thus the ablation resistance of the materials was systematically and effectively improved.
In this paper, a high-temperature test experimental system is built to investigate the dependence of the strength of a c/Siccomposite material on temperature. Unintuitively, the strength increases with temperature. T...
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In this paper, a high-temperature test experimental system is built to investigate the dependence of the strength of a c/Siccomposite material on temperature. Unintuitively, the strength increases with temperature. To investigate the microscopic mechanism, scanning electron microscopy (SEM) of an in situ bending test experiment is performed. Our hypothesis is that due to significant residual tensile stress in inter-fibre matrix, external loads reach the ultimate stress first. As the temperature increases, the matrix residual tensile stress decreases, a larger external load needs to be applied for matrix failure, which is exhibited macroscopically as increased strength. To prove this hypothesis, the inter-fibre matrix residual stress and its dependence on temperature are calculated via a finite element method. Next, using a Sic wrapper layer around a single c fibre as an experiment object, the finite element calculation is verified directly via micro-Raman spectroscopy.
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