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Results for “constitutive model”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Solid-state greenhouses and their implications for icy satellites

The 'solid-state greenhouse effect' model constituted by the subsurface solar heating of translucent, high-albedo materials is presently applied to the study of planetary surfaces, with attention to frost and ice surfaces of the solar system's outer satellites. Temperature is computed as a function of depth for an illustrative range of thermal variables, and it is discovered that the surfaces and interiors of such bodies can be warmer than otherwise suspected. Mechanisms are identified through which the modest alteration of surface properties can substantially change the solid-state greenhouse and force an interior temperature adjustment.

Matson, Dennis L.↗
NASA NTRS1989

Thermo-viscoplastic analysis of hypersonic structures subjected to severe aerodynamic heating

A thermoviscoplastic computational method for hypersonic structures is presented. The method employs a unified viscoplastic constitutive model implemented in a finite element approach for quasi-static thermal-structural analysis. Applications of the approach to convectively cooled hypersonic structures illustrate the effectiveness of the approach and provide insight into the transient inelastic structural behavior at elevated temperatures.

Thornton, Earl A.↗
NASA NTRS1988

Micromechanics of cyclic deformation in SSME turbopump blade materials

Current and candidate Space Shuttle Main Engine (SSME) turbopump blade materials are anisotropic, both in their elastic and plastic response. The major objective is to characterize the plastic deformation behavior of a typical single crystal nickel-base superalloy, PWA 1480, and to use this information to help guide the development of anisotropic constitutive models.

Milligan, Walter W.↗
NASA NTRS1989

Application of HOST technology to the SSME HPFTP blade

The development of turbine blade analysis tools as they moved from research contracts under the NASA HOST (Hot Section Technology) program to a PC-based system for preliminary design and to use in evaluating the SSME HPFTP (Space Shuttle Main Engine High Pressure Fuel Turbo Pump) blade is discussed. The heat transfer and structural analysis of the blade, the development of a data base for constitutive modeling of the blade materials, including coatings, and the use of advanced nonlinear finite element methods are addressed.

Mcknight, R. L.↗
NASA NTRS1990

Thermoviscoelastic characterization and prediction of Kevlar/epoxy composite laminates

The thermoviscoelastic characterization of Kevlar 49/Fiberite 7714A epoxy composite lamina and the development of a numerical procedure to predict the viscoelastic response of any general laminate constructed from the same material were studied. The four orthotropic material properties, S sub 11, S sub 12, S sub 22, and S sub 66, were characterized by 20 minute static creep tests on unidirectional (0) sub 8, (10) sub 8, and (90) sub 16 lamina specimens. The Time-Temperature Superposition-Principle (TTSP) was used successfully to accelerate the characterization process. A nonlinear constitutive model was developed to describe the stress dependent viscoelastic response for each of the material properties. A numerical procedure to predict long term laminate properties from lamina properties (obtained experimentally) was developed. Numerical instabilities and time constraints associated with viscoelastic numerical techniques were discussed and solved. The numerical procedure was incorporated into a user friendly microcomputer program called Viscoelastic Composite Analysis Program (VCAP), which is available for IBM PC type computers. The program was designed for ease of use. The final phase involved testing actual laminates constructed from the characterized material, Kevlar/epoxy, at various temperatures and load level for 4 to 5 weeks. These results were compared with the VCAP program predictions to verify the testing procedure and to check the numerical procedure used in the program. The actual tests and predictions agreed for all test cases which included 1, 2, 3, and 4 fiber direction laminates.

Gramoll, K. C.↗
NASA NTRS1991

Stirling engine: Available tools for long-life assessment

A review is presented for the durability approaches applicable to long-time life assessment of Stirling engine hot-section components. The crucial elements are experimental techniques for generating long-time materials property data (both monotonic and cyclic flow and failure properties); analytic representations of slow strain rate material stress-strain response characteristics (monotonic and cyclic constitutive relations) at high temperatures and low stresses and strains; analytic creep-fatigue-environmental interaction life prediction methods applicable to long lifetimes at high temperatures and small stresses and strains; and experimental verification of life predictions. Long-lifetime design criteria for materials of interest are woefully lacking. Designing against failures due to creep, creep-rupture, fatigue, environmental attack, and creep-fatigue-environmental interaction will require considerable extrapolation. Viscoplastic constitutive models and time-temperature parameters will have to be calibrated for the hot-section materials of interest. Analysis combined with limited verification testing in a short-time regime will be required to build confidence in long-lifetime durability models.

Halford, Gary R.↗
NASA NTRS1991

Rate dependent stress-strain behavior of advanced polymer matrix composites

The formulation of an elastic/viscoplastic constitutive model which was used to predict the measured behavior of graphite/thermoplastic and graphite/bismaleimide composite materials at elevated temperature is described. The model incorporates the concepts of overstress and effective strain/strain to provide a simple formulation which was able to account for material behavior under monotonic tension or compression loads over a temperature range of 23 to 200 C. Observed behavior such as stress relaxation and steady state creep, in off-axis tension and compression tests, were predicted by the model. Material constants required by the model were extracted from simple off-axis test data.

Gates, Thomas S.↗
NASA NTRS1991

Experimental study of the viscoplastic response of high temperature structures

Computational and experimental studies of the thermal structural behavior of thin panels subjected to localized heating are described. Three research tasks are described: (1) development of a finite element thermoviscoplastic computational approach; (2) experimental determination of material parameters for Bodner-Partom constitutive models of panel materials; and (3) experimental study of 'Heldenfels' panels subjected to intense local heating. Recent progress in each task is reviewed. Development of a new experimental set-up for the panel tests is described in detail and preliminary test results are presented.

Coyle, Marshall F.↗
NASA NTRS1991

Viscoplastic analysis of an experimental cylindrical thrust chamber liner

A viscoplastic stress-strain analysis of an experimental cylindrical thrust chamber is presented. A viscoelastic constitutive model incorporating a single internal state variable that represents kinematic hardening was employed to investigate whether such a viscoplastic model could predict the experimentally observed behavior of the thrust chamber. Two types of loading cycles were considered: a short cycle of 3.5 sec. duration that corresponded to the experiments, and an extended loading cycle of 485.1 sec. duration that is typical of the Space Shuttle Main Engine (SSME) operating cycle. The analysis qualitatively replicated the deformation behavior of the component as observed in experiments designed to simulate SSME operating conditions. The analysis also showed that the mode and location in the component may depend on the loading cycle. The results indicate that using viscoplastic models for structural analysis can lead to a more realistic life assessment of thrust chambers.

Arya, Vinod K.↗
NASA NTRS1990

Dynamic effects in thermoviscoplastic structures

An algorithm for three-dimensional thermoviscoplasticity with inertial effects is presented. The algorithm utilizes a unified thermoviscoplastic constitutive model with directional hardening (Bodner-Partom). An example problem is shown in which thermally induced vibrations lead to material yielding at elevated temperatures. Significant dampening caused by inelastic strain is shown to take place in the structure.

Byrom, Ted G.↗
NASA NTRS1991

Viscoplastic response of structures for intense local heating

A thermoviscoplastic finite element method employing the Bodner-Partom constitutive model is used to investigate the response of simplified thermal-structural models to intense local heating. With rapid rises of temperature, the nickel alloy structures display initially higher yield stresses due to strain rate effects. As temperatures approach elevated values, yield stress and stiffness degrade rapidly and pronounced plastic deformation occurs.

Thornton, Earl A.↗
NASA NTRS1991

On the symbolic manipulation and code generation for elasto-plastic material matrices

A computerized procedure for symbolic manipulations and FORTRAN code generation of an elasto-plastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples.

Chang, T. Y.↗
NASA NTRS1991

Development of BEM for ceramic composites

It is evident that for proper micromechanical analysis of ceramic composites, one needs to use a numerical method that is capable of idealizing the individual fibers or individual bundles of fibers embedded within a three-dimensional ceramic matrix. The analysis must be able to account for high stress or temperature gradients from diffusion of stress or temperature from the fiber to the ceramic matrix and allow for interaction between the fibers through the ceramic matrix. The analysis must be sophisticated enough to deal with the failure of fibers described by a series of increasingly sophisticated constitutive models. Finally, the analysis must deal with micromechanical modeling of the composite under nonlinear thermal and dynamic loading. This report details progress made towards the development of a boundary element code designed for the micromechanical studies of an advanced ceramic composite. Additional effort has been made in generalizing the implementation to allow the program to be applicable to real problems in the aerospace industry.

Henry, D. P.↗
NASA NTRS1990

Integrated analysis and applications

An overview is presented of current research activities which, in a broad context, are focused on the development and verification of integrated structural analysis and optimal design capabilities for advanced aerospace propulsion and power systems. The overview encompasses a variety of subject areas including: (1) composite materials; (2) advanced structural analysis; (3) constitutive modeling; (4) computational simulation; (5) probabilistic analysis; and (6) multidisciplinary optimization. Typical results are presented which illustrate the benefit and utility of the emerging technologies as applied to propulsion and power system structures.

Hopkins, Dale A.↗
NASA NTRS1992

Matrix dominated stress/strain behavior in polymeric composites: Effects of hold time, nonlinearity and rate dependency

In order to understand matrix dominated behavior in laminated polymer matrix composites, an elastic/viscoplastic constitutive model was developed and used to predict stress strain behavior of off-axis and angle-ply symmetric laminates under in-plane, tensile axial loading. The model was validated for short duration tests at elevated temperatures. Short term stress relaxation and short term creep, strain rate sensitivity, and material nonlinearity were accounted for. The testing times were extended for longer durations, and periods of creep and stress relaxation were used to investigate the ability of the model to account for long term behavior. The model generally underestimated the total change in strain and stress for both long term creep and long term relaxation respectively.

Gates, Thomas S.↗
NASA NTRS1992

Structural mechanics simulations

Sandia National Laboratory has a very broad structural capability. Work has been performed in support of reentry vehicles, nuclear reactor safety, weapons systems and components, nuclear waste transport, strategic petroleum reserve, nuclear waste storage, wind and solar energy, drilling technology, and submarine programs. The analysis environment contains both commercial and internally developed software. Included are mesh generation capabilities, structural simulation codes, and visual codes for examining simulation results. To effectively simulate a wide variety of physical phenomena, a large number of constitutive models have been developed.

Biffle, Johnny H.↗
NASA NTRS1992

Viscoplastic analysis of an experimental cylindrical thrust chamber liner

A viscoplastic stress-strain analysis of an experimental cylindrical thrust chamber is presented. A viscoelastic constitutive model incorporating a single internal state variable that represents kinematic hardening was employed to investigate whether such a viscoplastic model could predict the experimentally observed behavior of the thrust chamber. Two types of loading cycles were considered: a short cycle of 3.5-s duration that corresponded to the experiments, and an extended loading cycle of 485.1 s duration that is typical of the Space Shuttle Main Engine (SSME) operating cycle. The analysis qualitatively replicated the deformation behavior of the component as observed in experiments designed to simulate SSME operating conditions. The analysis also showed that the mode and location of failure in the component may depend on the loading cycle. The results indicate that using viscoplastic models for structural analysis can lead to a more realistic life assessment of thrust chambers.

Arya, Vinod K.↗