The cyclic ablation resistance of coated carbon/carbon (c/c) composites play crucial roles in their further engineering applications and development due to the cyclic ablation environment accompanied by rapid heating ...
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The cyclic ablation resistance of coated carbon/carbon (c/c) composites play crucial roles in their further engineering applications and development due to the cyclic ablation environment accompanied by rapid heating and cooling and high-speed heat flow scouring, which can reflect the performance stability of the coating. In this research, a (Sic/Hfc)4/Sic (SHS) multi-layer coating was prepared on c/ccomposites. compared with single layer (Sic and Hfccoating) coated sample, the mass and linear ablation rate of SHS coated sample after three ablation cycles (60 s x 3) were only 0.64 mg/s and 0.53 mu m/s, respectively. This is mainly because the introduction of many interfaces inhibits the propagation of cracks, the irregular cracks region only exists in the outer layer. Besides, the oxide layer with dense structure was formed near the c/c substrate, which could prevent oxygen from penetrating into the coating and continue to play a protective role.
A novel method to prepare a coating on the c/ccomposite is discussed. The precursor infiltration pyrolysis method is usually applied to prepare interior ceramic matrix, thus Sic nanowires that can absorb the surficia...
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A novel method to prepare a coating on the c/ccomposite is discussed. The precursor infiltration pyrolysis method is usually applied to prepare interior ceramic matrix, thus Sic nanowires that can absorb the surficial precursor are added to prepare surficial ceramics. The method accomplishes the integration of the coating and the matrix so that no coating peels off after ablation. Moreover, the material with a Zrc/Sic precursor ratio of 5:1 (Z5S1), whose mass and linear rates are 0.47 mg/s and 0.95 mu m/s, exhibits the highest overall resistance to ablation. The results demonstrate that higher Zrccontent and more uniform phase distribution are beneficial to keep ZrO2 in solid and form a denser and firmer oxide layer, which is more effective in improving the ablation resistance of the c/ccomposite.
B4c modified HfB2-Siccoating for c/c substrate was designed to expand the application of HfB2-Sic based coating in low-medium temperature environment. The oxidation protection behavior of HfB2-Sic based ceramiccoati...
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B4c modified HfB2-Siccoating for c/c substrate was designed to expand the application of HfB2-Sic based coating in low-medium temperature environment. The oxidation protection behavior of HfB2-Sic based ceramiccoatings with and without B4c at 1073, 1273 and 1473 K was tested and analyzed. The experimental results reveal that the oxidative damage of HfB2-Siccoated c/c reduces by over 20% after introducing B4c, which may be due to the protection of borosilicate glass with more suitable viscosity during oxidation. Meanwhile, B4ccan improve the oxidation protection ability of HfB2-Siccoating best at 1473 K. And the introduction of B4ccan reduce the mass loss of HfB2-Siccoated c/c sample by 77.6% after oxidation for 58 h at 1473 K. The fluidity of glass film becoming better with temperature-rising, and the fluid borosilicate glass layer makes the coated samples have the best anti-oxidation properties at 1473 K among these three temperatures.
Ba0.25Sr0.75Al2Si2O8 (BSAS), Yb2SiO5 and Y2SiO5 are widely deposited as the main phase of composite coatings or as the functional layer in multilayer coatings. The investigation of monolayer coating can not only broad...
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Ba0.25Sr0.75Al2Si2O8 (BSAS), Yb2SiO5 and Y2SiO5 are widely deposited as the main phase of composite coatings or as the functional layer in multilayer coatings. The investigation of monolayer coating can not only broaden the application of monolayer anti-oxidation coating, but also be an important basis for the design of multilayer and composite coatings. Monolayer BSAS, Yb2SiO5 and Y2SiO5 coatings were deposited on c/Siccomposite by atmospheric plasma spraying (APS). Thermal physics and chemical properties, microstructure, bond stability and oxidation protection of the monolayer coatings were investigated. The results showed that the monolayer coating effectively improved the oxidation resistance of c/Siccomposite. The microstructure and mechanical properties of the coatings play an important role in the bond stability and oxidation resistance of the coated sample. Among the tested coatings, the Y2SiO5 coating exhibited excellent mechanical properties and compact structure, which resulted in the highest bond stability and the best protection.
Hexagonal boron nitride (h-BN) has excellent oxidation resistance, self-healing function, and self-lubricating properties, which can significantly improve the oxidation resistance of c/c-Siccomposites in low or mediu...
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Hexagonal boron nitride (h-BN) has excellent oxidation resistance, self-healing function, and self-lubricating properties, which can significantly improve the oxidation resistance of c/c-Siccomposites in low or medium temperature condition and affect their tribological properties and mechanisms. In this work, c/c-Sic and c/c-BN-Siccomposites were prepared by the same molding, carbonization and liquid silicon infiltration (LSI) processes and the influences of h-BN addition on their microstructure, tribological properties, and mechanisms were investigated. h-BN addition can promote the formation of friction film and reduce the oxidation wear of the composites. compared with c/c-Siccomposites, due to more lubricant components and different matrix structure, the c/c-BN-Siccomposite shows lower wear rate (reduced by 53%) and moderate rather than too high coefficient of friction (coF) and its coF is less influenced by braking velocity. Moreover, the friction process is more stable and does not appear clamping stagnation phenomenon in high braking speed condition.
Many critical codebases are written in c, and most of them use preprocessor directives to encode variability, effectively encoding software product lines. These preprocessor directives, however, challenge any staticc...
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Many critical codebases are written in c, and most of them use preprocessor directives to encode variability, effectively encoding software product lines. These preprocessor directives, however, challenge any staticcode analysis. SPLlift, a previously presented approach for analyzing software product lines, is limited to Java programs that use a rather simple feature encoding and to analysis problems with a finite and ideally small domain. Other approaches that allow the analysis of real-world c software product lines use special-purpose analyses, preventing the reuse of existing analysis infrastructures and ignoring the progress made by the static analysis community. This work presents VarAlyzer, a novel static analysis approach for software product lines. VarAlyzer first transforms preprocessor constructs to plain c while preserving their variability and semantics. It then solves any given distributive analysis problem on transformed product lines in a variability-aware manner. VarAlyzer 's analysis results are annotated with feature constraints that encode in which configurations each result holds. Our experiments with 95 compilation units of OpenSSL show that applying VarAlyzer enables one to conduct inter-procedural, flow-, field- and context-sensitive data-flow analyses on entire product lines for the first time, outperforming the product-based approach for highly-configurable systems.
Taking the advantages of porous ceramic (c/c-Siccomposite) and transpiration cooling (copper alloy), c/c-Sic-cu composite was fabricated to attain a novel anti-ablation material for high temperature structure applica...
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Taking the advantages of porous ceramic (c/c-Siccomposite) and transpiration cooling (copper alloy), c/c-Sic-cu composite was fabricated to attain a novel anti-ablation material for high temperature structure application of aerospace systems, via chemical vapor deposition and infiltration technologies. The effects of Siccontent on microstructure, thermal conductivity, mechanical and ablation properties of c/c-Sic-cu composite were investigated. As the Siccontent increases from 0 vol% to 25.12 vol%, thermal conductivity, flexural strength and ablation resistance are improved by 84.99%, 78.76% and 53.68%, respectively. Thermal conductivity and thermal diffusivity exhibit proportional linear correlation with Siccontent. The high Siccontent could shorten the yield stage and increase the breaking strength during the flexural fracture process. When the Siccontent is 25.12 vol%, the formation continuous and compact anti-ablation (SiO2) layer is formed by oxidizing and melting fluidity processes during oxyacetylene ablation test, and the protective layer covers the ablation surface and slows down the oxidative ablation, which combines with the transpiration cooling effect of copper alloy to further improve ablation resistance of c/c-Sic-cu composite.
In this paper, the time-dependent damage evolution in carbon fiber-reinforced silicon carbide ceramic-matrix composites (c/SiccMcs) under creep fatigue loading at elevated temperature was analyzed using a micromechan...
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In this paper, the time-dependent damage evolution in carbon fiber-reinforced silicon carbide ceramic-matrix composites (c/SiccMcs) under creep fatigue loading at elevated temperature was analyzed using a micromechanical approach. Synergistic effects of creep fatigue peak stress level and damage in the matrix and the interface on time-dependent damage evolution in c/Siccomposites were analyzed. Next, relationships of timedependent creep fatigue damage mechanisms, damage parameters, environmental temperature and duration were determined. Then, the effects of composite constituent properties, creep fatigue damage state, environmental temperature, and duration on time-dependent damage evolution in c/Siccomposites were analyzed. Furthermore, time-dependent composite strain response and interface debonding and oxidation state in c/Siccomposite under different creep fatigue peak stress levels were predicted. Under creep fatigue loading, the composite internal damage evolution contributed to the increased time/temperature-dependent composite peak strain. Hysteresis-based damage parameters were developed and utilized to monitor c/Siccomposite internal damage evolution. Under creep fatigue loading, the hysteresis area and width increased with oxidation duration to a peak value and remained constant, and the hysteresis modulus decreased with oxidation duration.
This paper offers a new way of testing the ablation property of material under an oxyacetylene torch using a thinblade specimen, which costs much less time to reach the maximum temperature and provides a harsh turbule...
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This paper offers a new way of testing the ablation property of material under an oxyacetylene torch using a thinblade specimen, which costs much less time to reach the maximum temperature and provides a harsh turbulence fluid field that's closer to reality. The thin-blade specimen experiences a higher turbulent intensity than the traditional disk-like specimen, leading to more efficient heat exchange. The fluid field simulation agrees with the testing results. In addition, we manage to synthesize the c/cx-Sicy composites with the co-deposition chemical vapor infiltration (cVI) method. The c/cx-Sicy composites exhibit a similar anti-ablation property as c/ccomposites and consist of enough Sic phase simultaneously, combining the advantages of both c/ccomposites and c/Siccomposites. The thin-blade c/cx-Sicy composites show a lower linear ablation rate (1.6 mu m/s) than c/ ccomposites (4.1 mu m/s) and c/Siccomposites (19.6 mu m/s) during the oxyacetylene test. The glass layer formed on the surface of c/cx-Sicy could cling to the bulk material instead of peeling off due to the high Pyccontent in the matrix could protect the SiO2 from blowing away.
In this paper, a micromechanical approach is developed to predict the fatigue life and fracture process in different c/Siccomposites subjected to different stochastic fatigue loading spectrums at elevated temperature...
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In this paper, a micromechanical approach is developed to predict the fatigue life and fracture process in different c/Siccomposites subjected to different stochastic fatigue loading spectrums at elevated temperatures. Three types of stochastic fatigue load spectrums are considered in the fatigue life prediction at elevated temperature, that is, constant, increasing, and decreasing stochastic stress with cycles. Stress distribution between intact and broken fibers and the broken fibers fraction under stochastic fatigue loading spectrum are determined using the Global Load Sharing criterion considering multiple fatigue damage mechanisms at elevated temperatures. A new damage parameter of fatigue life degradation rate is developed to characterize the effect of stochastic loading on fatigue damage and fracture in c/Siccomposites. Relationships between stochastic fatigue loading spectrum, broken fibers fraction, fatigue life, and fatigue life degradation rate in different c/Siccomposite are established. Effects of stochastic fatigue loading spectrum type, stress level, and testing temperature on fatigue life degradation rate are discussed. The fatigue life degradation rate is very sensitive to the fiber preform, loading sequence, and testing temperature.
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