The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform
Gregory N. Morscher - One of the best experts on this subject based on the ideXlab platform.
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comparison of Bend Stress relaxation and tensile creep of cvd sic fibers
Journal of the American Ceramic Society, 1995Co-Authors: Gregory N. Morscher, Charles A Lewinsohn, Charles E Bakis, R E Tressler, Timothy WagnerAbstract:Three different CVD SiC fibers were tested for Bend Stress relaxation (BSR) and tensile creep over a wide range of temperatures, times, and Stresses. Primary creep was always observed, even for creep strains on the order of 2%. The BSR and tensile creep results were compared using simple linear viscoelastic principles. It was found that BSR results could predict the same time and temperature dependence as tensile creep; however, BSR-predicted creep strains usually overestimated the magnitude of tensile creep strain. The time, temperature, and Stress dependence were determined for all the fibers for the experimental conditions of this study. Some of the primary creep behavior can be explained by load-sharing effects between the core and the CVD SiC substrate and some microstructural changes; however, the extent of primary creep cannot fully be accounted for from this work.
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Bend Stress relaxation and tensile primary creep of a polycrystalline α sic fiber
1995Co-Authors: Gregory N. Morscher, Hee Man Yun, Jon C GoldsbyAbstract:Understanding the thermomechanical behavior (creep and Stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. Some uses of structural ceramic matrix composites require that the continuous ceramic fibers display creep strain tolerances of less than 1% and sometimes as low as 0.1% for long time service (Dicarlo, 1994). For this reason it is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the Stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance controlling for example, the distribution of residual Stress.
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Creep and Stress relaxation modeling of polycrystalline ceramic fibers
1994Co-Authors: James A. Dicarlo, Gregory N. MorscherAbstract:A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading about 800 C, these fibers display creep related instabilities which can result in detrimental changes in composite dimensions, strength, and internal Stress distributions. As a first step toward understanding these effects, this study examines the validity of a mechanism-based empirical model which describes primary stage tensile creep and Stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied Stress or strain. To verify these functional dependencies, a simple Bend test is used to measure Stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the Bend Stress Relaxation (BSR) test not only confirm the Stress, time, and temperature dependencies predicted by the model, but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model tensile creep predictions based on the BSR test results with the literature data show good agreement, supporting both the predictive capability of the model and the use of themore » BSR text as a simple method for parameter determination for other fibers.« less
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Simple Creep Test For Ceramic Fibers
1994Co-Authors: James A. Dicarlo, Gregory N. MorscherAbstract:Simple Bend-Stress-relaxation test yields information on creep-related properties of polycrystalline ceramic fibers. Determination of these properties important part of efforts to develop ceramic composite materials that retain mechanical strength and resistance to creep at high temperatures. Present test measures effects of time, temperature, and applied strain on creep-related relaxation of Bend Stress in ceramic fiber of almost any diameter in almost any environment, without need for contact sensors. Degree of relaxation of Bend Stress determined from radii of curvature.
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Proceedings of the 15th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings - Fiber Creep Evaluation by Stress Relaxation Measurements
Proceedings of the 15th Annual Conference on Composites and Advanced Ceramic Materials Part 1 of 2: Ceramic Engineering and Science Proceedings Volume, 1Co-Authors: Gregory N. Morscher, James A. Dicarlo, Timothy WagnerAbstract:A simple Bend Stress relaxation (BSR) test has been used to measure the creep related properties of a chemically vapor-deposited SiC fiber. Time, temperature, and strain dependent BSR data were analyzed to ascertain the ability of the Stress relaxation results to predict tensile creep as a function of the same parameters. The predictions compared very well to actual creep data obtained by axial measurements, indicating that the BSR test could be used for determining both creep and Stress relaxation of polycrystalline ceramic fibers under tensile loading. 10 refs.
Timothy Wagner - One of the best experts on this subject based on the ideXlab platform.
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comparison of Bend Stress relaxation and tensile creep of cvd sic fibers
Journal of the American Ceramic Society, 1995Co-Authors: Gregory N. Morscher, Charles A Lewinsohn, Charles E Bakis, R E Tressler, Timothy WagnerAbstract:Three different CVD SiC fibers were tested for Bend Stress relaxation (BSR) and tensile creep over a wide range of temperatures, times, and Stresses. Primary creep was always observed, even for creep strains on the order of 2%. The BSR and tensile creep results were compared using simple linear viscoelastic principles. It was found that BSR results could predict the same time and temperature dependence as tensile creep; however, BSR-predicted creep strains usually overestimated the magnitude of tensile creep strain. The time, temperature, and Stress dependence were determined for all the fibers for the experimental conditions of this study. Some of the primary creep behavior can be explained by load-sharing effects between the core and the CVD SiC substrate and some microstructural changes; however, the extent of primary creep cannot fully be accounted for from this work.
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Proceedings of the 15th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings - Fiber Creep Evaluation by Stress Relaxation Measurements
Proceedings of the 15th Annual Conference on Composites and Advanced Ceramic Materials Part 1 of 2: Ceramic Engineering and Science Proceedings Volume, 1Co-Authors: Gregory N. Morscher, James A. Dicarlo, Timothy WagnerAbstract:A simple Bend Stress relaxation (BSR) test has been used to measure the creep related properties of a chemically vapor-deposited SiC fiber. Time, temperature, and strain dependent BSR data were analyzed to ascertain the ability of the Stress relaxation results to predict tensile creep as a function of the same parameters. The predictions compared very well to actual creep data obtained by axial measurements, indicating that the BSR test could be used for determining both creep and Stress relaxation of polycrystalline ceramic fibers under tensile loading. 10 refs.
L L Snead - One of the best experts on this subject based on the ideXlab platform.
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neutron irradiation creep of silicon carbide materials beyond the initial transient
Journal of Nuclear Materials, 2016Co-Authors: Takaaki Koyanagi, Kazumi Ozawa, Yutai Katoh, Kazuya Shimoda, Tatsuya Hinoki, L L SneadAbstract:Abstract Irradiation creep beyond the transient regime was investigated for various silicon carbide (SiC) materials. The materials examined included polycrystalline or monocrystalline high-purity SiC, nanopowder sintered SiC, highly crystalline and near-stoichiometric SiC fibers (including Hi-Nicalon Type S, Tyranno SA3, isotopically-controlled Sylramic and Sylramic-iBN fibers), and a Tyranno SA3 fiber–reinforced SiC matrix composite fabricated through a nano-infiltration transient eutectic phase process. Neutron irradiation experiments for Bend Stress relaxation tests were conducted at irradiation temperatures ranging from 430 to 1180 °C up to 30 dpa with initial Bend Stresses of up to ∼1 GPa for the fibers and ∼300 MPa for the other materials. Initial Bend Stress in the specimens continued to decrease from 1 to 30 dpa. Analysis revealed that (1) the Stress exponent of irradiation creep above 1 dpa is approximately unity, (2) the Stress normalized creep rate is ∼1 × 10 −7 [dpa −1 MPa −1 ] at 430–750 °C for the range of 1–30 dpa for most polycrystalline SiC materials, and (3) the effects on irradiation creep of initial microstructures—such as grain boundary, crystal orientation, and secondary phases—increase with increasing irradiation temperature.
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Bend Stress relaxation creep of cvd silicon carbide
Ceramic engineering and science proceedings, 2008Co-Authors: Yutai Katoh, L L SneadAbstract:Bend Stress relaxation (BSR) creep of two forms of chemically vapor-deposited beta phase silicon carbide, namely polycrystalline and single-crystalline, was studied. The experiment was primarily oriented to demonstrate the applicability of BSR technique to irradiation-induced / enhanced creep behavior of silicon carbide in nuclear environments. It was demonstrated that thin strip samples with sufficient strength for BSR experiment could be machined and the small creep strains occurred in those samples could be measured to sufficient accuracy. The thermal creep experiment was conducted at 1573-1773K in argon to maximum hold time of 10 hours. Both materials exhibited similar primary creep deformation at the initial Stresses of 65 - 100 MPa. The relative Stress relaxation determined in the present experiment appeared significantly smaller than those reported for a commercial CVD SiC fiber at given temperature, implying a significant effect of the initial material conditions on the relaxation behavior. The analysis based on the relaxation time - temperature relationship gave an activation energy of ∼850 kJ/mol for the primary responsible process in CVD SiC.
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irradiation creep of high purity cvd silicon carbide as estimated by the Bend Stress relaxation method
Journal of Nuclear Materials, 2007Co-Authors: Yutai Katoh, Tatsuya Hinoki, L L Snead, Sosuke Kondo, Akira KohyamaAbstract:Abstract The Bend Stress relaxation technique was applied for an irradiation creep study of high purity, chemically vapor-deposited beta-phase silicon carbide (CVD SiC) ceramic. A constant Bend strain was applied to thin strip samples during neutron irradiation to fluences 0.2–4.2 dpa at various temperatures in the range ∼400 to ∼1080 °C. Irradiation creep strain at 0.7 dpa were estimated to be 2.7(±2.6) × 10 −7 and 1.5(±0.8) × 10 −6 (MPa dpa) −1 at ∼600 to ∼950 °C and ∼1080 °C, respectively, whereas linear-averaged creep compliances of 1–2 × 10 −6 (MPa dpa) −1 were obtained for doses of 0.6–0.7 dpa at all temperatures. Monocrystalline 3C SiC samples exhibited significantly smaller transient creep strain and greater subsequent deformation when loaded along 〈0 1 1〉 direction.
James A. Dicarlo - One of the best experts on this subject based on the ideXlab platform.
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Creep and Stress relaxation modeling of polycrystalline ceramic fibers
1994Co-Authors: James A. Dicarlo, Gregory N. MorscherAbstract:A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading about 800 C, these fibers display creep related instabilities which can result in detrimental changes in composite dimensions, strength, and internal Stress distributions. As a first step toward understanding these effects, this study examines the validity of a mechanism-based empirical model which describes primary stage tensile creep and Stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied Stress or strain. To verify these functional dependencies, a simple Bend test is used to measure Stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the Bend Stress Relaxation (BSR) test not only confirm the Stress, time, and temperature dependencies predicted by the model, but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model tensile creep predictions based on the BSR test results with the literature data show good agreement, supporting both the predictive capability of the model and the use of themore » BSR text as a simple method for parameter determination for other fibers.« less
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Simple Creep Test For Ceramic Fibers
1994Co-Authors: James A. Dicarlo, Gregory N. MorscherAbstract:Simple Bend-Stress-relaxation test yields information on creep-related properties of polycrystalline ceramic fibers. Determination of these properties important part of efforts to develop ceramic composite materials that retain mechanical strength and resistance to creep at high temperatures. Present test measures effects of time, temperature, and applied strain on creep-related relaxation of Bend Stress in ceramic fiber of almost any diameter in almost any environment, without need for contact sensors. Degree of relaxation of Bend Stress determined from radii of curvature.
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creep limitations of current polycrystalline ceramic fibers
Composites Science and Technology, 1994Co-Authors: James A. DicarloAbstract:Abstract The objective of this paper is to present an overview of the issues, property status, and potential for use of creep-prone polycrystalline ceramic fibers in thermostructural ceramic composites. Issues arise because the fine-grained microstructures of high-strength fibers can result in creep-related property changes, often at temperatures as low as 800°C. The underlying mechanism is grain boundary sliding controlled by grain size and grain boundary character, and thus by the fiber processing method. With the assumption of upper and lower limit creep requirements, the creep properties of a variety of current SiC and Al2O3 polycrystalline fibers are reviewed and discussed. Property evaluation is based on the results of a simple Bend Stress relaxation test which allows predictive creep equations to be developed for each fiber type describing the effects of time, temperature, and applied Stress. It is shown that sintered SiC fibers with grain sizes below 1000 nm appear to offer the best performance in terms of strength and creep resistance. However, even these fibers may not be capable of long-term service above 1400°C.
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Proceedings of the 15th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings - Fiber Creep Evaluation by Stress Relaxation Measurements
Proceedings of the 15th Annual Conference on Composites and Advanced Ceramic Materials Part 1 of 2: Ceramic Engineering and Science Proceedings Volume, 1Co-Authors: Gregory N. Morscher, James A. Dicarlo, Timothy WagnerAbstract:A simple Bend Stress relaxation (BSR) test has been used to measure the creep related properties of a chemically vapor-deposited SiC fiber. Time, temperature, and strain dependent BSR data were analyzed to ascertain the ability of the Stress relaxation results to predict tensile creep as a function of the same parameters. The predictions compared very well to actual creep data obtained by axial measurements, indicating that the BSR test could be used for determining both creep and Stress relaxation of polycrystalline ceramic fibers under tensile loading. 10 refs.
Yutai Katoh - One of the best experts on this subject based on the ideXlab platform.
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Neutron-irradiation creep of silicon carbide materials beyond the initial transient ☆
Journal of Nuclear Materials, 2016Co-Authors: Takaaki Koyanagi, Kazumi Ozawa, Yutai Katoh, Kazuya Shimoda, Tatsuya Hinoki, Lance Lewis SneadAbstract:Abstract Irradiation creep beyond the transient regime was investigated for various silicon carbide (SiC) materials. The materials examined included polycrystalline or monocrystalline high-purity SiC, nanopowder sintered SiC, highly crystalline and near-stoichiometric SiC fibers (including Hi-Nicalon Type S, Tyranno SA3, isotopically-controlled Sylramic and Sylramic-iBN fibers), and a Tyranno SA3 fiber–reinforced SiC matrix composite fabricated through a nano-infiltration transient eutectic phase process. Neutron irradiation experiments for Bend Stress relaxation tests were conducted at irradiation temperatures ranging from 430 to 1180 °C up to 30 dpa with initial Bend Stresses of up to ∼1 GPa for the fibers and ∼300 MPa for the other materials. Initial Bend Stress in the specimens continued to decrease from 1 to 30 dpa. Analysis revealed that (1) the Stress exponent of irradiation creep above 1 dpa is approximately unity, (2) the Stress normalized creep rate is ∼1 × 10 −7 [dpa −1 MPa −1 ] at 430–750 °C for the range of 1–30 dpa for most polycrystalline SiC materials, and (3) the effects on irradiation creep of initial microstructures—such as grain boundary, crystal orientation, and secondary phases—increase with increasing irradiation temperature.
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neutron irradiation creep of silicon carbide materials beyond the initial transient
Journal of Nuclear Materials, 2016Co-Authors: Takaaki Koyanagi, Kazumi Ozawa, Yutai Katoh, Kazuya Shimoda, Tatsuya Hinoki, L L SneadAbstract:Abstract Irradiation creep beyond the transient regime was investigated for various silicon carbide (SiC) materials. The materials examined included polycrystalline or monocrystalline high-purity SiC, nanopowder sintered SiC, highly crystalline and near-stoichiometric SiC fibers (including Hi-Nicalon Type S, Tyranno SA3, isotopically-controlled Sylramic and Sylramic-iBN fibers), and a Tyranno SA3 fiber–reinforced SiC matrix composite fabricated through a nano-infiltration transient eutectic phase process. Neutron irradiation experiments for Bend Stress relaxation tests were conducted at irradiation temperatures ranging from 430 to 1180 °C up to 30 dpa with initial Bend Stresses of up to ∼1 GPa for the fibers and ∼300 MPa for the other materials. Initial Bend Stress in the specimens continued to decrease from 1 to 30 dpa. Analysis revealed that (1) the Stress exponent of irradiation creep above 1 dpa is approximately unity, (2) the Stress normalized creep rate is ∼1 × 10 −7 [dpa −1 MPa −1 ] at 430–750 °C for the range of 1–30 dpa for most polycrystalline SiC materials, and (3) the effects on irradiation creep of initial microstructures—such as grain boundary, crystal orientation, and secondary phases—increase with increasing irradiation temperature.
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Bend Stress relaxation creep of cvd silicon carbide
Ceramic engineering and science proceedings, 2008Co-Authors: Yutai Katoh, L L SneadAbstract:Bend Stress relaxation (BSR) creep of two forms of chemically vapor-deposited beta phase silicon carbide, namely polycrystalline and single-crystalline, was studied. The experiment was primarily oriented to demonstrate the applicability of BSR technique to irradiation-induced / enhanced creep behavior of silicon carbide in nuclear environments. It was demonstrated that thin strip samples with sufficient strength for BSR experiment could be machined and the small creep strains occurred in those samples could be measured to sufficient accuracy. The thermal creep experiment was conducted at 1573-1773K in argon to maximum hold time of 10 hours. Both materials exhibited similar primary creep deformation at the initial Stresses of 65 - 100 MPa. The relative Stress relaxation determined in the present experiment appeared significantly smaller than those reported for a commercial CVD SiC fiber at given temperature, implying a significant effect of the initial material conditions on the relaxation behavior. The analysis based on the relaxation time - temperature relationship gave an activation energy of ∼850 kJ/mol for the primary responsible process in CVD SiC.
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irradiation creep of high purity cvd silicon carbide as estimated by the Bend Stress relaxation method
Journal of Nuclear Materials, 2007Co-Authors: Yutai Katoh, Tatsuya Hinoki, L L Snead, Sosuke Kondo, Akira KohyamaAbstract:Abstract The Bend Stress relaxation technique was applied for an irradiation creep study of high purity, chemically vapor-deposited beta-phase silicon carbide (CVD SiC) ceramic. A constant Bend strain was applied to thin strip samples during neutron irradiation to fluences 0.2–4.2 dpa at various temperatures in the range ∼400 to ∼1080 °C. Irradiation creep strain at 0.7 dpa were estimated to be 2.7(±2.6) × 10 −7 and 1.5(±0.8) × 10 −6 (MPa dpa) −1 at ∼600 to ∼950 °C and ∼1080 °C, respectively, whereas linear-averaged creep compliances of 1–2 × 10 −6 (MPa dpa) −1 were obtained for doses of 0.6–0.7 dpa at all temperatures. Monocrystalline 3C SiC samples exhibited significantly smaller transient creep strain and greater subsequent deformation when loaded along 〈0 1 1〉 direction.