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  • 1
    Electronic Resource
    Electronic Resource
    A new uniformly valid asymptotic integration algorithm for elasto-plastic creep and unified viscoplastic theories including continuum damage (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 32 (1991), S. 385-418 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new scheme to integrate a system of stiff differential equations for both the elasto-plastic-creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code, through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620320210
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals (2014)
    Springer Nature
    Details
    Publication Date: 2014-10-25
    Description: Nature Materials 13, 1033 (2014). doi:10.1038/nmat4093 Authors: Maxim Tabachnyk, Bruno Ehrler, Simon Gélinas, Marcus L. Böhm, Brian J. Walker, Kevin P. Musselman, Neil C. Greenham, Richard H. Friend & Akshay Rao
    Print ISSN: 1476-1122
    Electronic ISSN: 1476-4660
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 3
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    Thermoviscoplastic analysis of fibrous periodic composites by the use of triangular subvolumes (1994)
    Elsevier
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0266-3538
    Electronic ISSN: 1879-1050
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Elsevier
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  • 4
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    A new uniformly valid asymptotic integration algorithm for elasto-plastic creep and unified viscoplastic theories including continuum damage (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.
    Keywords: METALLIC MATERIALS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 32; 385-418
    Format: text
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  • 5
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    Nonlinear Asymptotic Integration Algorithms for One-dimensional Autonomous Dissipative First-order Odes (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Nonlinear asymptotic integrators are applied to one-dimensional, nonlinear, autonomous, dissipative, ordinary differential equations. These integrators, including a one-step explicit, a one-step implicit, and a one- and two-step midpoint algorithm, are designed to follow the asymptotic behavior of a system approaching a steady state. The methods require that the differential equation be written in a particular asymptotic form. This is always possible for a one-dimensional equation with a globally asymptotic steady state. In this case, conditions are obtained to guarantee that the implicit algorithms are well defined. Further conditions are determined for the implicit methods to be contractive. These methods are all first order accurate, while under certain conditions the midpoint algorithms may also become second order accurate. The stability of each method is investigated and an estimate of the local error is provided.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-TM-106780 , E-9233 , NAS 1.15:106780
    Format: application/pdf
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  • 6
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    Critical experiments of the self-consistent model for polycrystalline Hastelloy-X (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A viscoplastic constitutive model is presented for the estimation of the overall mechanical response of Hastelloy-X polycrystalline metals from a knowledge of single crystal behavior. The behavior of polycrystal is derived from that of single crystals using a self-consistent formulation. The single crystal behavior which has been used was developed by summing postulated slip on crystallographic slip systems. The plasticity and creep are treated coupledly using unified viscoplastic model which includes the interaction effects between rapid and slow deformation at elevated temperature. The validity of the model is directly tested by experiments on Hastelloy-X in both single crystal and polycrystalline versions.
    Keywords: METALLIC MATERIALS
    Type: In: Modeling the deformation of crystalline solids; Proceedings of the Symposium, Annual Meeting of the Minerals, Metals & Materials Society, New Orleans, LA, Feb. 17-21, 1991 (A93-21951 07-26); p. 601-612.
    Format: text
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  • 7
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    Thermoviscoplastic analysis of fibrous periodic composites using triangular subvolumes (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The nonlinear viscoplastic behavior of fibrous periodic composites is analyzed by discretizing the unit cell into triangular subvolumes. A set of these subvolumes can be configured by the analyst to construct a representation for the unit cell of a periodic composite. In each step of the loading history, the total strain increment at any point is governed by an integral equation which applies to the entire composite. A Fourier series approximation allows the incremental stresses and strains to be determined within a unit cell of the periodic lattice. The nonlinearity arising from the viscoplastic behavior of the constituent materials comprising the composite is treated as fictitious body force in the governing integral equation. Specific numerical examples showing the stress distributions in the unit cell of a fibrous tungsten/copper metal matrix composite under viscoplastic loading conditions are given. The stress distribution resulting in the unit cell when the composite material is subjected to an overall transverse stress loading history perpendicular to the fibers is found to be highly heterogeneous, and typical homogenization techniques based on treating the stress and strain distributions within the constituent phases as homogeneous result in large errors under inelastic loading conditions.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-106076 , E-7686 , NAS 1.15:106076
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  • 8
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    Nonlinear mesomechanics of composites with periodic microstructure (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This work is concerned with modeling the mechanical deformation or constitutive behavior of composites comprised of a periodic microstructure under small displacement conditions at elevated temperature. A mesomechanics approach is adopted which relates the microimechanical behavior of the heterogeneous composite with its in-service macroscopic behavior. Two different methods, one based on a Fourier series approach and the other on a Green's function approach, are used in modeling the micromechanical behavior of the composite material. Although the constitutive formulations are based on a micromechanical approach, it should be stressed that the resulting equations are volume averaged to produce overall effective constitutive relations which relate the bulk, volume averaged, stress increment to the bulk, volume averaged, strain increment. As such, they are macromodels which can be used directly in nonlinear finite element programs such as MARC, ANSYS and ABAQUS or in boundary element programs such as BEST3D. In developing the volume averaged or efective macromodels from the micromechanical models, both approaches will require the evaluation of volume integrals containing the spatially varying strain distributions throughout the composite material. By assuming that the strain distributions are spatially constant within each constituent phase-or within a given subvolume within each constituent phase-of the composite material, the volume integrals can be obtained in closed form. This simplified micromodel can then be volume averaged to obtain an effective macromodel suitable for use in the MARC, ANSYS and ABAQUS nonlinear finite element programs via user constitutive subroutines such as HYPELA and CMUSER. This effective macromodel can be used in a nonlinear finite element structural analysis to obtain the strain-temperature history at those points in the structure where thermomechanical cracking and damage are expected to occur, the so called damage critical points of the structure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102051 , E-4670 , NAS 1.15:102051
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  • 9
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    From differential to difference equations for first order ODEs (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: When constructing an algorithm for the numerical integration of a differential equation, one should first convert the known ordinary differential equation (ODE) into an ordinary difference equation. Given this difference equation, one can develop an appropriate numerical algorithm. This technical note describes the derivation of two such ordinary difference equations applicable to a first order ODE. The implicit ordinary difference equation has the same asymptotic expansion as the ODE itself, whereas the explicit ordinary difference equation has an asymptotic that is similar in structure but different in value when compared with that of the ODE.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-TM-104530 , E-6406 , NAS 1.15:104530
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  • 10
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    Constitutive modeling of superalloy single crystals with verification testing (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The goal is the development of constitutive equations to describe the elevated temperature stress-strain behavior of single crystal turbine blade alloys. The program includes both the development of a suitable model and verification of the model through elevated temperature-torsion testing. A constitutive model is derived from postulated constitutive behavior on individual crystallographic slip systems. The behavior of the entire single crystal is then arrived at by summing up the slip on all the operative crystallographic slip systems. This type of formulation has a number of important advantages, including the prediction orientation dependence and the ability to directly represent the constitutive behavior in terms which metallurgists use in describing the micromechanisms. Here, the model is briefly described, followed by the experimental set-up and some experimental findings to date.
    Keywords: METALLIC MATERIALS
    Type: NASA. Lewis Research Center, Turbine Engine Hot Section Technology, 1985; p 277-286
    Format: application/pdf
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