Wei Song, Qizhe Tang, Chang Su, Xiang Chen, Yonggang Liu
We present a modification to the combined transmission-reflection method, which is frequently used to measure the elastic wave velocities in rocks and minerals at high pressure and high temperature in multi-anvil apparatus. The modification mainly focuses on the adoption of dual-mode ultrasonic transducer and new backing reflector (a molybdenum foil), the former was used to simultaneously measure the travel times of compressional wave and shear wave in the sample, and the latter was used to intensify the reflection signals of the buffer rod. The correction time of the molybdenum foils was determined using the equation of state and highpressure velocities of molybdenum. In addition, the length change of sample under high pressure was also taken into account. Using this method, we simultaneously measured the compressional wave and shear wave velocities in Z-cut a-quartz single crystal to 2 GPa at room temperature, and natural mafic granulite sample to 1.4 GPa and 500�C in a multianvil apparatus. The results of this work agree well with those of previous measurements and demonstrate the feasibility of this new method. We believe that by using this method, more accurate elastic properties of rocks and minerals under high pressure and high temperature can be obtained, especially Poisson�s ratio.
{"title":"A method for simultaneous measurements of compressional wave and shear wave velocities in rocks and minerals at high pressure and high temperature: A modification to the combined transmission-reflection method","authors":"Wei Song, Qizhe Tang, Chang Su, Xiang Chen, Yonggang Liu","doi":"10.32908/hthp.v51.1249","DOIUrl":"https://doi.org/10.32908/hthp.v51.1249","url":null,"abstract":"We present a modification to the combined transmission-reflection method, which is frequently used to measure the elastic wave velocities in rocks and minerals at high pressure and high temperature in multi-anvil apparatus. The modification mainly focuses on the adoption of dual-mode ultrasonic transducer and new backing reflector (a molybdenum foil), the former was used to simultaneously measure the travel times of compressional wave and shear wave in the sample, and the latter was used to intensify the reflection signals of the buffer rod. The correction time of the molybdenum foils was determined using the equation of state and highpressure velocities of molybdenum. In addition, the length change of sample under high pressure was also taken into account. Using this method, we simultaneously measured the compressional wave and shear wave velocities in Z-cut a-quartz single crystal to 2 GPa at room temperature, and natural mafic granulite sample to 1.4 GPa and 500�C in a multianvil apparatus. The results of this work agree well with those of previous measurements and demonstrate the feasibility of this new method. We believe that by using this method, more accurate elastic properties of rocks and minerals under high pressure and high temperature can be obtained, especially Poisson�s ratio.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69443476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nanofluids containing vanadium dioxide (VO2) are used in applications such as actuators, smart windows, and gastrointestinal tracts. Therefore, measuring the thermal conductivity of nanofluids with VO2 characteristics is important in various environmental industries. In this study, the bidirectional 3 omega (3ω) method was used to measure the thermal conductivity of nanofluids. Experimental equipment for measuring VO2 nanofluids in various environments was designed and fabricated. The effectiveness of the bidirectional 3ω equipment was verified by measuring the thermal conductivity of ethylene glycol, which has been extensively reported in the literature. The effects of elapsed time, specimen thickness, and operation temperature on the thermal conductivity are discussed in this paper. In addition, the measuring error was investigated with regard to the precipitation of particles in the suspension.
{"title":"Thermal conductivity measurement of VO2 nanofluid using bidirectional 3ω method","authors":"Duk Hyung Lee, D. Oh, Sok-Won Kim, Yeon Suk Choi","doi":"10.32908/hthp.v50.1071","DOIUrl":"https://doi.org/10.32908/hthp.v50.1071","url":null,"abstract":"Nanofluids containing vanadium dioxide (VO2) are used in applications such as actuators, smart windows, and gastrointestinal tracts. Therefore, measuring the thermal conductivity of nanofluids with VO2 characteristics is important in various environmental industries. In this study, the bidirectional 3 omega (3ω) method was used to measure the thermal conductivity of nanofluids. Experimental equipment for measuring VO2 nanofluids in various environments was designed and fabricated. The effectiveness of the bidirectional 3ω equipment was verified by measuring the thermal conductivity of ethylene glycol, which has been extensively reported in the literature. The effects of elapsed time, specimen thickness, and operation temperature on the thermal conductivity are discussed in this paper. In addition, the measuring error was investigated with regard to the precipitation of particles in the suspension.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Altay, G. S. Tantug, H. Cekin, Y. Seki, M. Sarıkanat
Thermoplastics when they become thermally conductive, have a great potential to be used in thermal management applications due to their low cost, lightweight, and flexibility. Here, synthetic graphite and graphene are used as thermally conductive fillers to fabricate Polyphenylene Sulfide- (PPS) based composite materials with high thermal conductivity. Graphene and graphite added PPS composites were manufactured by using a twinscrew extruder and injection molding machine. Physical, thermal, mechanical, and morphological properties of the composites were investigated by several characterization methods including thermogravimetric analysis, differential scanning calorimetry, thermomechanical analysis, scanning electron microscopy, thermal diffusivity measurement, and tensile and flexural tests, The in-plane and through-plane thermal conductivity coefficient of graphene (5 wt. %) loaded synthetic graphite (40 wt. %)/PPS composites are greatly improved to 26.45 and 5.02 W/mK, respectively compared to that of neat PPS. The outstanding in-plane thermal conductivity of graphene loaded graphite/PPS composites is attributed to the formation of an effective thermal conductive pathway due to the alignment of the layered structure of graphene and graphite fillers in the flow direction.
{"title":"Thermal and mechanical behavior of graphene loaded synthetic graphite/polyphenylene sulfide (PPS) composites","authors":"L. Altay, G. S. Tantug, H. Cekin, Y. Seki, M. Sarıkanat","doi":"10.32908/hthp.v50.1089","DOIUrl":"https://doi.org/10.32908/hthp.v50.1089","url":null,"abstract":"Thermoplastics when they become thermally conductive, have a great potential to be used in thermal management applications due to their low cost, lightweight, and flexibility. Here, synthetic graphite and graphene are used as thermally conductive fillers to fabricate Polyphenylene Sulfide- (PPS) based composite materials with high thermal conductivity. Graphene and graphite added PPS composites were manufactured by using a twinscrew extruder and injection molding machine. Physical, thermal, mechanical, and morphological properties of the composites were investigated by several characterization methods including thermogravimetric analysis, differential scanning calorimetry, thermomechanical analysis, scanning electron microscopy, thermal diffusivity measurement, and tensile and flexural tests, The in-plane and through-plane thermal conductivity coefficient of graphene (5 wt. %) loaded synthetic graphite (40 wt. %)/PPS composites are greatly improved to 26.45 and 5.02 W/mK, respectively compared to that of neat PPS. The outstanding in-plane thermal conductivity of graphene loaded graphite/PPS composites is attributed to the formation of an effective thermal conductive pathway due to the alignment of the layered structure of graphene and graphite fillers in the flow direction.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The change in refractive index with respect to temperature (dn/dT) is defined as the thermo-optic coefficient. It varies according to the light wavelength and temperature, so it is a very important physical quantity that influences light propagation. In this study, we observed the metal-insulator transition (MIT) effect of VO2 on the optical properties of VO2 nanofluid and the thermo-optic coefficient of pure ethylene glycol (EG). We prepared two concentrations (1 × 10–3 mol% and 1 × 10–2 mol%) of EG + VO2 nanofluids by dispersing 50-nm VO2 nano-spheres and injecting them into a cubic glass cell (1 × 1 × 4 cm3). The thermo-optic coefficient was measured by counting the number of interference fringe movements with a Michelson interferometer. The thermo-optic coefficient obtained for pure EG agreed with the literature value within 13.3%. Below 60˚C, the thermo-optic coefficients of EG + VO2 were smaller than that of pure EG, but they increased rapidly as the temperature increased. Above 60˚C, the thermo-optic coefficients of both EG + VO2 nanofluids rapidly changed and showed a peak and valley near 62˚C and 67˚C, respectively. We used the maximum value of the derivative of the thermo-optic coefficient (d2n/dT2) to obtain the phase transition temperatures of the VO2 nanofluids, which were 64.6˚C and 65.0˚C in the samples with 1 × 10–3 mol% and 1 × 10–2 mol%, respectively.
{"title":"Measurement of thermo-optic coefficient of vanadium dioxide nanofluids using an interferometer","authors":"Hyunki Kim, Taesung Kim, Sok-Won Kim","doi":"10.32908/hthp.v50.1045","DOIUrl":"https://doi.org/10.32908/hthp.v50.1045","url":null,"abstract":"The change in refractive index with respect to temperature (dn/dT) is defined as the thermo-optic coefficient. It varies according to the light wavelength and temperature, so it is a very important physical quantity that influences light propagation. In this study, we observed the metal-insulator transition (MIT) effect of VO2 on the optical properties of VO2 nanofluid and the thermo-optic coefficient of pure ethylene glycol (EG). We prepared two concentrations (1 × 10–3 mol% and 1 × 10–2 mol%) of EG + VO2 nanofluids by dispersing 50-nm VO2 nano-spheres and injecting them into a cubic glass cell (1 × 1 × 4 cm3). The thermo-optic coefficient was measured by counting the number of interference fringe movements with a Michelson interferometer. The thermo-optic coefficient obtained for pure EG agreed with the literature value within 13.3%. Below 60˚C, the thermo-optic coefficients of EG + VO2 were smaller than that of pure EG, but they increased rapidly as the temperature increased. Above 60˚C, the thermo-optic coefficients of both EG + VO2 nanofluids rapidly changed and showed a peak and valley near 62˚C and 67˚C, respectively. We used the maximum value of the derivative of the thermo-optic coefficient (d2n/dT2) to obtain the phase transition temperatures of the VO2 nanofluids, which were 64.6˚C and 65.0˚C in the samples with 1 × 10–3 mol% and 1 × 10–2 mol%, respectively.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"54 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442486","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, the characteristics of volumetric absorption for solar harvesting using a Fe3O4@polyacrylic acid (PAA) nanofluid (NF) are investigated experimentally. The concentration of the Fe3O4@PAA NF was varied from 0 to 0.2wt%, and its mass flow rate was set to 0.0025 and 0.005 kg/s. As a result, the average efficiency of the solar collector at the Fe3O4@PAA NF of 0.05wt% was the highest at the mass flow rates of 0.0025 kg/s and 0.005 kg/s and the improvement ratio of average efficiency was 1.15 and 1.19, respectively, compared to water. The collector performance of the solar thermal harvesting improved owing to the improvement in the solar absorption and heat transfer, as well as the uniform temperature at the receiver tube as the concentration of the Fe3O4@PAA NF increased to a concentration of 0.05wt%. However, the collector performance of the solar thermal harvesting decreased for the 0.05wt% Fe3O4@PAA NF because of the increase in heat loss by the non-uniform temperature at the receiver tube and heat transfer. The increase in mass flow rate can reduce the heat loss by the decrease in temperature in the receiver tube; consequently, the efficiency of the solar collector using NFs is improved.
{"title":"Thermal performance of solar collector based on volumetric absorption harvesting method using Fe3O4 nanofluid","authors":"J. Ham, Yunchan Shin, Honghyun Cho","doi":"10.32908/hthp.v50.1061","DOIUrl":"https://doi.org/10.32908/hthp.v50.1061","url":null,"abstract":"In this study, the characteristics of volumetric absorption for solar harvesting using a Fe3O4@polyacrylic acid (PAA) nanofluid (NF) are investigated experimentally. The concentration of the Fe3O4@PAA NF was varied from 0 to 0.2wt%, and its mass flow rate was set to 0.0025 and 0.005 kg/s. As a result, the average efficiency of the solar collector at the Fe3O4@PAA NF of 0.05wt% was the highest at the mass flow rates of 0.0025 kg/s and 0.005 kg/s and the improvement ratio of average efficiency was 1.15 and 1.19, respectively, compared to water. The collector performance of the solar thermal harvesting improved owing to the improvement in the solar absorption and heat transfer, as well as the uniform temperature at the receiver tube as the concentration of the Fe3O4@PAA NF increased to a concentration of 0.05wt%. However, the collector performance of the solar thermal harvesting decreased for the 0.05wt% Fe3O4@PAA NF because of the increase in heat loss by the non-uniform temperature at the receiver tube and heat transfer. The increase in mass flow rate can reduce the heat loss by the decrease in temperature in the receiver tube; consequently, the efficiency of the solar collector using NFs is improved.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Physical properties of molten oxides such as viscosity and surface tension are important in various fields. However, it is very difficult to measure the properties of molten oxides owing to their high melting points, high reactivity, and high vapor pressure. Hence, the physical properties of molten oxides are scarcely reported. Therefore, we developed a new method, termed the �impingement method,� for measuring the surface tension of molten oxides in a very short time, using the aerodynamic levitation technique. In this work, we developed an apparatus for measuring the surface tension of molten Al2O3 and compared the value with that of other methods, considered as reference values. Results showed that the surface tension of molten Al2O3 was approximately 0.72 N/m at around 2500 K, which is close to the reference value; moreover, the measurements could be obtained in a very short time (approximately 80 ms). Thus, it is expected that the surface tension of molten materials with high vapor pressures such as ZrO2 and UO2 can be measured using this method.
{"title":"Development of a new method to measure surface tension of molten oxides","authors":"Toshiki Kondo, H. Muta, Y. Ohishi","doi":"10.32908/hthp.v50.857","DOIUrl":"https://doi.org/10.32908/hthp.v50.857","url":null,"abstract":"Physical properties of molten oxides such as viscosity and surface tension are important in various fields. However, it is very difficult to measure the properties of molten oxides owing to their high melting points, high reactivity, and high vapor pressure. Hence, the physical properties of molten oxides are scarcely reported. Therefore, we developed a new method, termed the �impingement method,� for measuring the surface tension of molten oxides in a very short time, using the aerodynamic levitation technique. In this work, we developed an apparatus for measuring the surface tension of molten Al2O3 and compared the value with that of other methods, considered as reference values. Results showed that the surface tension of molten Al2O3 was approximately 0.72 N/m at around 2500 K, which is close to the reference value; moreover, the measurements could be obtained in a very short time (approximately 80 ms). Thus, it is expected that the surface tension of molten materials with high vapor pressures such as ZrO2 and UO2 can be measured using this method.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The elastic and thermodynamic properties of TbAl and DyAl under high pressure and temperature are investigated using the density-functional theory (DFT) and the density-functional perturbation theory (DFPT) within the quasi-harmonic approximation (QHA). The calculated lattice and elastic constants at ground state (0 GPa and 0 K) are in agreement with the experimental data and previous theoretical results. Finally, when the pressure is given, all the thermodynamic quantities except for the bulk modulus increase with temperature, but the increase of the thermal expansion coefficient and the heat capacity with temperature becomes smaller. Besides, the effects of pressure on the elastic constants and the thermodynamic quantities are opposite with those of the temperature on them for TbAl and DyAl.
{"title":"The elastic and thermodynamic properties of TbAl and DyAl under high pressure","authors":"Lili Liu, Cai Chen, Liwan Chen, Y. Wen","doi":"10.32908/hthp.v50.903","DOIUrl":"https://doi.org/10.32908/hthp.v50.903","url":null,"abstract":"The elastic and thermodynamic properties of TbAl and DyAl under high pressure and temperature are investigated using the density-functional theory (DFT) and the density-functional perturbation theory (DFPT) within the quasi-harmonic approximation (QHA). The calculated lattice and elastic constants at ground state (0 GPa and 0 K) are in agreement with the experimental data and previous theoretical results. Finally, when the pressure is given, all the thermodynamic quantities except for the bulk modulus increase with temperature, but the increase of the thermal expansion coefficient and the heat capacity with temperature becomes smaller. Besides, the effects of pressure on the elastic constants and the thermodynamic quantities are opposite with those of the temperature on them for TbAl and DyAl.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The 3ω method is widely used for measuring the thermal properties of a substrate or thin film on which a microheater is deposited. Recently, samples with non-formal shapes and has a thermal conductivity of 1 W/mK or below have been analyzed using the bidirectional 3ω method. In measuring the thermal conductivity of such samples, the measurement sensitivity and accuracy can be increased using a 3ω sensor fabricated on a low thermal conductivity substrate such as glass or polyimide. In this study, thermal characterization is conducted on a microheater deposited on glass and polyimide substrates for a 3ω sensor. The effects of the microheater thickness and the interfacial thermal resistance between the substrate and microheater, on the temperature amplitude and phase lag are analyzed. Results from analytic solutions considering the microheater thickness and the interfacial thermal resistance are compared with results from numerical analysis of two-dimensional conduction heat transfer and experiment.
{"title":"Analysis of thickness and interfacial thermal resistance of Au microheater on glass or polyimide substrate","authors":"H. Kim, Woong Ko, D. Oh","doi":"10.32908/hthp.v50.1073","DOIUrl":"https://doi.org/10.32908/hthp.v50.1073","url":null,"abstract":"The 3ω method is widely used for measuring the thermal properties of a substrate or thin film on which a microheater is deposited. Recently, samples with non-formal shapes and has a thermal conductivity of 1 W/mK or below have been analyzed using the bidirectional 3ω method. In measuring the thermal conductivity of such samples, the measurement sensitivity and accuracy can be increased using a 3ω sensor fabricated on a low thermal conductivity substrate such as glass or polyimide. In this study, thermal characterization is conducted on a microheater deposited on glass and polyimide substrates for a 3ω sensor. The effects of the microheater thickness and the interfacial thermal resistance between the substrate and microheater, on the temperature amplitude and phase lag are analyzed. Results from analytic solutions considering the microheater thickness and the interfacial thermal resistance are compared with results from numerical analysis of two-dimensional conduction heat transfer and experiment.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Kim, Kyoon Choi, Yoonsoo Han, S. Nahm, Sung-Min Lee
A cyclic fatigue test of SiCf/SiC ceramic matrix composites was conducted at 1400°C and compared to the monotonic tensile test. The specimens were prepared with an interface layer of pyrolytic carbon and densified through chemical vapor infiltration. In the monotonic tensile test, at 1400°C, the specimen fractured at a strain of 0.35% with a proportional limit stress of 175 MPa, showing a typical fiber pull-out. However, after a prolonged cyclic test with increasing stresses from 65 to 95 MPa, the specimen fractured brittlely with almost no fiber pull-out. The microstructure analysis of the fracture surface showed different oxidation levels with respect to fracture locations, indicating that the crack propagated during the cyclic fatigue test. Transmission electron microscopy analysis revealed that the interface layer of pyrolytic carbon was removed by oxidation and oxide layers were formed on both sides of the fiber and matrix at the later stage of the cyclic test, resulting in a strong interface between the fibers and matrix and brittle fracture during the cyclic test at 1400°C.
{"title":"High-temperature cyclic fatigue in air of SiCf/SiC ceramic matrix composite with a pyrolytic carbon interface","authors":"K. Kim, Kyoon Choi, Yoonsoo Han, S. Nahm, Sung-Min Lee","doi":"10.32908/HTHP.V50.1079","DOIUrl":"https://doi.org/10.32908/HTHP.V50.1079","url":null,"abstract":"A cyclic fatigue test of SiCf/SiC ceramic matrix composites was conducted at 1400°C and compared to the monotonic tensile test. The specimens were prepared with an interface layer of pyrolytic carbon and densified through chemical vapor infiltration. In the monotonic tensile test, at 1400°C, the specimen fractured at a strain of 0.35% with a proportional limit stress of 175 MPa, showing a typical fiber pull-out. However, after a prolonged cyclic test with increasing stresses from 65 to 95 MPa, the specimen fractured brittlely with almost no fiber pull-out. The microstructure analysis of the fracture surface showed different oxidation levels with respect to fracture locations, indicating that the crack propagated during the cyclic fatigue test. Transmission electron microscopy analysis revealed that the interface layer of pyrolytic carbon was removed by oxidation and oxide layers were formed on both sides of the fiber and matrix at the later stage of the cyclic test, resulting in a strong interface between the fibers and matrix and brittle fracture during the cyclic test at 1400°C.","PeriodicalId":12983,"journal":{"name":"High Temperatures-high Pressures","volume":"1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69442225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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