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  • 1
    Publication Date: 2012-06-21
    Description: Author(s): A. Steyerl, J. M. Pendlebury, C. Kaufman, S. S. Malik, and A. M. Desai We develop a theory of ultracold and very cold neutron scattering on viscoelastic surface waves up to second-order perturbation theory. The results are applied to reanalyze the 1989 neutron-lifetime experiment using ultracold neutron storage in a Fomblin-coated vessel by Mampe et al. [ Phys. Rev. L... [Phys. Rev. C 85, 065503] Published Wed Jun 20, 2012
    Keywords: Electroweak Interaction, Symmetries
    Print ISSN: 0556-2813
    Electronic ISSN: 1089-490X
    Topics: Physics
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  • 2
    Publication Date: 2012-12-14
    Description: Author(s): A. Steyerl, C. Kaufman, G. Müller, S. S. Malik, and A. M. Desai We analyze the depolarization of ultracold neutrons confined in a magnetic field configuration similar to those used in existing or proposed magnetogravitational storage experiments aiming at a precise measurement of the neutron lifetime. We use an extension of the semiclassical Majorana approach as... [Phys. Rev. C 86, 065501] Published Fri Dec 07, 2012
    Keywords: Electroweak Interaction, Symmetries
    Print ISSN: 0556-2813
    Electronic ISSN: 1089-490X
    Topics: Physics
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  • 3
    Publication Date: 2017-03-23
    Description: Author(s): A. Steyerl, K. K. H. Leung, C. Kaufman, G. Müller, and S. S. Malik We analyze the spin flip loss for ultracold neutrons in magnetic bottles of the type used in experiments aiming at a precise measurement of the neutron lifetime, extending the one-dimensional field model used previously by Steyerl et al. [ Phys. Rev. C 86 , 065501 (2012) ] to two dimensions for cylindr… [Phys. Rev. C 95, 035502] Published Wed Mar 22, 2017
    Keywords: Electroweak Interaction, Symmetries
    Print ISSN: 0556-2813
    Electronic ISSN: 1089-490X
    Topics: Physics
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  • 4
    Publication Date: 2019-06-28
    Description: The objective of the Elevated Temperature Crack Growth Program is to evaluate proposed nonlinear fracture mechanics methods for application to hot section components of aircraft gas turbine engines. Progress during the past year included linear-elastic fracture mechanics data reduction on nonlinear crack growth rate data on Alloy 718. The bulk of the analytical work centered on thermal gradient problems and proposed fracture mechanics parameters. Good correlation of thermal gradient experimental displacement data and finite element prediction was obtained.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-179601 , NAS 1.26:179601
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-28
    Description: It is necessary to relate the processes that control crack growth in the immediate vicinity of the crack tip to parameters that can be calculated from remote quantities, such as forces, stresses, or displacements. The most likely parameters appear to be certain path-independent (PI) integrals, several of which have already been proposed for application to high temperature inelastic problems. The ability of currently available PI-integrals to correlate fatigue crack propagation under conditions that simulate the engine combustor liner environment was determined. The utility of advanced fracture mechanics measurements will also be evaluated and determined during the course of the program.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology 1986; p 371-383
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  • 6
    Publication Date: 2019-06-28
    Description: The problem of crack growth in hot path components such as combustor liners is complicated by several practical and theoretical considerations. The loading environment of such components involves high temperature levels and gradients that lead to considerations such as thermal stresses, crack closure, hold time, inelastic strains (both time dependent and independent), and Thermal Mechanical Fatigue (TMF). In general, a good understanding of the influence of these factors on crack growth was not obtained. At the same time, several nonlinear fracture mechanics parameters were suggested for such applications; however, most of the proposed methods were not tested for broad applications such as required for hot section components. It was the purpose of this program to evaluate proposed nonlinear methods by performing a thorough experimental and analytical study. The results illustrated that much progress was made in developing nonlinear methods.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center, Lewis Structures Technology, 1988. Volume 3: Structural Integrity Fatigue and Fracture Wind Turbines HOST; p 187-198
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  • 7
    Publication Date: 2019-06-28
    Description: The objective of the Elevated Temperature Crack Growth Project is to evaluate proposed nonlinear fracture mechanics methods for application to combustor liners of aircraft gas turbine engines. During the first year of this program, proposed path-independent (P-I) integrals were reviewed for such applications. Several P-I integrals were implemented into a finite-element postprocessor which was developed and verified as part of the work. Alloy 718 was selected as the analog material for use in the forthcoming experimental work. A buttonhead, single-edge notch specimen was designed and verified for use in elevated-temperature strain control testing with significant inelastic strains. A crack mouth opening displacement measurement device was developed for further use.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-174957 , NAS 1.26:174957 , ASR-1
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  • 8
    Publication Date: 2019-06-28
    Description: The purpose is to determine the ability of currently available P-I integrals to correlate fatigue crack propagation under conditions that simulate the turbojet engine combustor liner environment. The utility of advanced fracture mechanics measurements will also be evaluated. Research showed that the experimentally measured displacements and loads can be accurately predicted by finite element analyses that consider the growth of the fatigue crack. These results are being used to evaluate nonlinear fracture mechanics parameters for correlating the observed fatigue crack growth rates for different strain ranges.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 413-422
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  • 9
    Publication Date: 2019-06-28
    Description: A study was performed to examine the applicability of path-independent (P-I) integrals to crack growth problems in hot section components of gas turbine aircraft engines. Alloy 718 was used and the experimental parameters included combined temperature and strain cycling, thermal gradients, elastic-plastic strain levels, and mean strains. A literature review was conducted of proposed P-I integrals, and those capable of analyzing hot section component problems were selected and programmed into the postprocessor of a finite element code. Detailed elastic-plastic finite element analyses were conducted to simulate crack growth and crack closure of the test specimen, and to evaluate the P-I integrals. It was shown that the selected P-I integrals are very effective for predicting crack growth for isothermal conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-182247 , NAS 1.26:182247 , R89AEB-325 , AD-B149073L
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  • 10
    Publication Date: 2019-06-28
    Description: The purpose is to determine the ability of currently available P-I integrals to correlate fatigue crack propagation under conditions that simulate the turbojet engine combustor liner environment. The utility of advanced fracture mechanics measurements will also be evaluated during the course of the program. To date, an appropriate specimen design, a crack displacement measurement method, and boundary condition simulation in the computational model of the specimen were achieved. Alloy 718 was selected as an analog material based on its ability to simulate high temperature behavior at lower temperatures. Tensile and cyclic tests were run at several strain rates so that an appropriate constitutive model could be developed. Suitable P-I integrals were programmed into a finite element post-processor for eventual comparison with experimental data.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center, Turbine Engine Hot Section Technology, 1985; p 329-340
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