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  • 1
    Electronic Resource
    Electronic Resource
    On isoparametric vs linear strain triangular elements (1977)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 11 (1977), S. 1041-1043 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620110610
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A finite element solution method for contact problems with friction (1987)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 477-495 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new finite element solution method for the analysis of frictional contact problems is presented. The contact problem is solved by imposing geometric constraints on the pseudo equilibrium configuration, defined as a configuration at which the compatibility conditions are violated. The algorithm does not require any a priori knowledge of the pairs of contactor nodes or segments. The contact condition of sticking, slipping, rolling or tension release is determined from the relative magnitudes of the normal and tangential global nodal forces. Contact iterations are in general found to converge within one or two iterations. The analysis method is applied to selected problems to illustrate the applicability of the solution procedure.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620240302
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  • 3
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    An automated procedure for material parameter evaluation for viscoplastic constitutive models (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An automated procedure is presented for evaluating the material parameters in Walker's exponential viscoplastic constitutive model for metals at elevated temperature. Both physical and numerical approximations are utilized to compute the constants for Inconel 718 at 1100 F. When intermediate results are carefully scrutinized and engineering judgement applied, parameters may be computed which yield stress output histories that are in agreement with experimental results. A qualitative assessment of the theta-plot method for predicting the limiting value of stress is also presented. The procedure may also be used as a basis to develop evaluation schemes for other viscoplastic constitutive theories of this type.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center, Nonlinear Constitutive Relations for High Temperature Applications, 1986; p 317-352
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  • 4
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    An experimental comparison of several current viscoplastic constitutive models at elevated temperature (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Four current viscoplastic models are compared experimentally for Inconel 718 at 593 C. This material system responds with apparent negative strain rate sensitivity, undergoes cyclic work softening, and is susceptible to low cycle fatigue. A series of tests were performed to create a data base from which to evaluate material constants. A method to evaluate the constants is developed which draws on common assumptions for this type of material, recent advances by other researchers, and iterative techniques. A complex history test, not used in calculating the constants, is then used to compare the predictive capabilities of the models. The combination of exponentially based inelastic strain rate equations and dynamic recovery is shown to model this material system with the greatest success. The method of constant calculation developed was successfully applied to the complex material response encountered. Backstress measuring tests were found to be invaluable and to warrant further development.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center, Nonlinear Constitutive Relations for High Temperature Applications, 1986; p 253-289
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  • 5
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    Integrated research in constitutive modelling at elevated temperatures, part 2 (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Four current viscoplastic models are compared experimentally with Inconel 718 at 1100 F. A series of tests were performed to create a sufficient data base from which to evaluate material constants. The models used include Bodner's anisotropic model; Krieg, Swearengen, and Rhode's model; Schmidt and Miller's model; and Walker's exponential model.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-177233 , NAS 1.26:177233 , MM-4998-86-13-PT-2
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  • 6
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    Development of constitutive models for cyclic plasticity and creep behavior of super alloys at high temperature (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-176418 , NAS 1.26:176418
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  • 7
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    Integrated research in constitutive modelling at elevated temperatures, part 1 (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Topics covered include: numerical integration techniques; thermodynamics and internal state variables; experimental lab development; comparison of models at room temperature; comparison of models at elevated temperature; and integrated software development.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-177237 , NAS 1.26:177237 , MM-4998-86-13-PT-1
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  • 8
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    Application of an Uncoupled Elastic-plastic-creep Constitutive Model to Metals at High Temperature (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A uniaxial, uncoupled constitutive model to predict the response of thermal and rate dependent elastic-plastic material behavior is presented. The model is based on an incremental classicial plasticity theory extended to account for thermal, creep, and transient temperature conditions. Revisions to he combined hardening rule of the theory allow for better representation of cyclic phenomenon including the high rate of strain hardening upon cyclic reyield and cyclic saturation. An alternative approach is taken to model the rate dependent inelastic deformation which utilizes hysteresis loops and stress relaxation test data at various temperatures. The model is evaluated and compared to experiments which involve various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl.; p 185-190
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  • 9
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    On 3D inelastic analysis methods for hot section components (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Accomplishments are described for the 2-year program, to develop advanced 3-D inelastic structural stress analysis methods and solution strategies for more accurate and cost effective analysis of combustors, turbine blades and vanes. The approach was to develop a matrix of formulation elements and constitutive models. Three constitutive models were developed in conjunction with optimized iterating techniques, accelerators, and convergence criteria within a framework of dynamic time incrementing. Three formulations models were developed; an eight-noded mid-surface shell element, a nine-noded mid-surface shell element and a twenty-noded isoparametric solid element. A separate computer program was developed for each combination of constitutive model-formulation model. Each program provides a functional stand alone capability for performing cyclic nonlinear structural analysis. In addition, the analysis capabilities incorporated into each program can be abstracted in subroutine form for incorporation into other codes or to form new combinations.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology 1986; p 257-268
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  • 10
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    Numerical considerations in the development and implementation of constitutive models (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Several unified constitutive models were tested in uniaxial form by specifying input strain histories and comparing output stress histories. The purpose of the tests was to evaluate several time integration methods with regard to accuracy, stability, and computational economy. The sensitivity of the models to slight changes in input constants was also investigated. Results are presented for In100 at 1350 F and Hastelloy-X at 1800 F.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 169-185
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