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  • 1
    Publication Date: 2015-07-30
    Description: Author(s): W. Y. So, K. S. Kim, K. S. Choi, and Myung-Ki Cheoun We investigate the effects of the long-range dynamic polarization (LRDP) potential, which consists of the Coulomb dipole excitation (CDE) potential and the long-range nuclear (LRN) potential, for the Be 11 projectile on Zn 64 . To study these effects, we perform a χ 2 analysis of an optical model includ… [Phys. Rev. C 92, 014627] Published Wed Jul 29, 2015
    Keywords: Nuclear Reactions
    Print ISSN: 0556-2813
    Electronic ISSN: 1089-490X
    Topics: Physics
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  • 2
    Publication Date: 2014-11-21
    Description: Author(s): W. Y. So, K. S. Kim, K. S. Choi, and Myung-Ki Cheoun We investigate the effects of long-range dynamic polarization on elastic cross sections for heavy-ion collisions which comprise the Coulomb dipole excitation (CDE) potential and the long-range nuclear (LRN) potential. To study these effects, we perform a χ2 analysis for the elastic cross sections of... [Phys. Rev. C 90, 054615] Published Thu Nov 20, 2014
    Keywords: Nuclear Reactions
    Print ISSN: 0556-2813
    Electronic ISSN: 1089-490X
    Topics: Physics
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  • 3
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    In:  CASI
    Publication Date: 2013-08-31
    Description: Alloy 718 crack growth experiments were conducted to assess the ability of the selected path-independent (P-I) integrals to describe the elevated temperature crack growth behavior. These tests were performed on single edge notch (SEN) specimens under displacement control with multiple extensometers to monitor the specimen and crack mouth opening displacement (CMOD). The displacements in these tests were sufficiently high to induce bulk cyclic inelastic deformation of the specimen. Under these conditions, the linear elastic fracture mechanics (LEFM) parameter K does not correlate the crack growth data. The experimentally measured displacement gradients at the end of specimen gage length were used as the boundary conditions in elastic-plastic finite element method (FEM) analyses. These analyses were performed with a node release approach using CYANIDE, a GEAE FEM code, which included a gap element which is capable of efficiently simulating crack closure. Excellent correlation was obtained between the experimentally measured and predicted variation of stress and CMOD with crack length and the stress-CMOD loops for Alloy 718 tests conducted at 538 C. This confirmed the accuracy of the FEM crack growth simulation approach. The experimentally measured crack growth rate data correlated well the selected P-I integrals. These investigations have produced significant progress in developing P-I integrals as non-linear fracture mechanics parameters. The results suggest that this methodology has the potential of accurately describing elevated temperature crack growth behavior under the combined influence of thermal cycling and bulk elastic-inelastic deformation states.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center, Structural Integrity and Durability of Reusable Space Propulsion Systems; p 45-52
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  • 4
    Publication Date: 2013-08-31
    Description: The applicability of a classical constitutive model for stress-strain analysis of a nickel base superalloy, Rene' 80, in the gas turbine thermomechanical fatigue (TMF) environment is examined. A variety of tests were conducted to generate basic material data and to investigate the material response under cyclic thermomechanical loading. Isothermal stress-strain data were acquired at a variety of strain rates over the TMF temperature range. Creep curves were examined at 2 temperature ranges, 871 to 982 C and 760 to 871 C. The results provide optimism on the ability of the classical constitutive model for high temperature applications.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center, Nonlinear Constitutive Relations for High Temperature Applications, 1986; p 395-418
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  • 5
    Publication Date: 2016-06-07
    Description: Critical gas turbine engine hot section components such as blades, vanes, and combustor liners tend to develop minute cracks during early stages of operations. The ability of currently available path-independent (P-I) integrals to correlate fatigue crack propagation under conditions that simulate the turbojet engine combustor liner environment was determined. To date, an appropriate specimen design and a crack displacement measurement method were determined. Alloy 718 was selected as the analog material based on its ability to simulate high temperature behavior at lower temperatures in order to facilitate experimental measurements. Available P-I integrals were reviewed and the best approaches are being programmed into a finite element post processor for eventual comparison with experimental data. The experimental data will include cyclic crack growth tests under thermomechanical conditions, and, additionally, thermal gradients.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Turbine Engine Hot Section Technology, 1984; 10 p
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  • 6
    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
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  • 7
    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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  • 8
    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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  • 9
    Publication Date: 2019-06-28
    Description: Damage tolerance design and analysis is widely used in fracture critical military aircraft engine components. Linear elastic fracture mechanics techniques have been developed and verified. These are used to predict the crack propagation lives of complex geometries under mission cycling conditions. Research on methods necessary for the prediction of elevated temperature crack growth in advanced structures is reviewed. These include environmentally assisted time-dependent crack growth, non-linear fracture mechanics parameters for thermal mechanical fatigue crack growth, and finite element modeling of crack growth in composites.
    Keywords: STRUCTURAL MECHANICS
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  • 10
    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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