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A 336 degrees of freedom slave finite element processing capability to analyze engine structures under severe thermomechanical loading is presented. Description of the theoretical development and demonstration of that element is presented in this volume.
This report deals with the development of a general mathematical model and solution methodology for analyzing the structural response of thin, metallic shell-like structures under dynamic and/or static thermomechanical loads. In the mathematical model, geometric as well as the material-type of nonlinearities are considered. Traditional as well as novel approaches are reported and detailed applications are presented in the appendices. The emphasis for the mathematical model, the related solution schemes, and the applications, is on thermal viscoelastic and viscoplastic phenomena, which can predict creep and ratchetting.
The object of the research reported herein was to develop a general mathematical model and solution methodologies for analyzing the structural response of thin, metallic shell structures under large transient, cyclic, or static thermomechanical loads. Among the system responses associated with these loads and conditions are thermal buckling, creep buckling, and ratcheting. Thus geometric and material nonlinearities (of high order) can be anticipated and must be considered in developing the mathematical model. The methodology is demonstrated through different problems of extension, shear, and of planar curved beams. Moreover, importance of the inclusion of large strain is clearly demonstrated, through the chosen applications.
NASA sponsored the Turbine Engine Hot Section (HOST) project to address the need for improved durability in advanced aircraft engine combustors and turbines. Analytical and experimental activities aimed at more accurate prediction of the aerothermal environment, the thermomechanical loads, the material behavior and structural responses to loads, and life predictions for cyclic high temperature operation were conducted from 1980 to 1987. The project involved representatives from six engineering disciplines who are spread across three work disciplines - industry, academia, and NASA. The HOST project not only initiated and sponsored 70 major activities, but also was the keystone in joining the multiple disciplines and work sectors to focus on critical research needs. A broad overview of the project is given along with initial indications of the project's impact.
One of the trays aboard LDEF was an experiment having the objective of assessing the effects of long term exposure of candidate balloon films, tapes, and lines to the hostile environment of space. The fortuitous location of these materials on LDEF minimized direct impact by atomic oxygen thus providing an opportunity to study the effects of low earth orbit environments on polymeric materials without the worry of atomic oxygen abrasion. The resulting chemical, morphological, and thermomechanical changes for polyethylene specimens are reviewed. In addition, preliminary data for fluorinated ethylene/propylene copolymers used for thermal blankets is presented. Polyethylene is observed to crosslink and branch from exposure to atomic oxygen and/or ultraviolet with a decrease in crystallinity.
Cross ply laminate behavior of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced with continuous silicon carbide fibers (SCS-6) subjected to a generic hypersonic flight profile was evaluated experimentally and analytically. Thermomechanical fatigue test techniques were developed to conduct a simulation of a generic hypersonic flight profile. A micromechanical analysis was used. The analysis predicts the stress-strain response of the laminate and of the constituents in each ply during thermal and mechanical cycling by using only constituent properties as input. The fiber was modeled using a thermo-viscoplastic constitutive relation. The fiber transverse modulus was reduced in the analysis to simulate the fiber matrix interface failure. Excellent correlation was found between measured and predicted laminate stress-strain response due to generic hypersonic flight profile when fiber debonding was modeled.
This report presents the results from a 35 month period of a program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program is composed of a base program and an optional program. The base program addresses the high temperature coated single crystal regime above the airfoil root platform. The optional program investigates the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involve experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material form the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: (001), (011), (111), and (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal material were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were selected for TMF crack initiation of coated PWA 1480. An initial life model used to correlate smooth and notched fatigue data obtained in the option program shows promise. Computer software incorporating the overlay coating and PWA 1480 constitutive models was developed.
This report presents a summary of results from a 7 year program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program was composed of a base program and an optional program. The base program addressed the high temperature coated single crystal regime above the airfoil root platform. The optional program investigated the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involved experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material formed the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: group of zone axes (001), group of zone axes (011), group of zone axes (111), and group of zone axes (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal materials were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were developed for TMF crack initiation of coated PWA 1480. A life model was developed for smooth and notched fatigue in the option program. Finally, computer software incorporating the overlay coating and PWA 1480 constitutive and life models was developed.
The study addresses the effect of systematically varying gamma-gamma-prime eutectic content and porosity level on the fatigue life of a hydrogen-charged single crystal PWA 1480 superalloy. Four microstructural variants are produced, and differences in gamma-gamma-prime eutectic morphology among the four processing variants are analyzed. Single valued tensile test data indicate that the tensile and yield strength of the PWA 1480 are degraded by hydrogen charging, with the exception of the material given a eutectic solution treatment. It is shown that the reduction of the fatigue life can be minimized by a duplex thermomechanical treatment consisting of a eutectic solution followed by hot isostatic pressing.
The theory of the fountain effect, also known as the thermomechanical effect, exhibited by superfluid helium is presented, and the application of this effect in space projects is described. Future uses of superfluid He in space are also discussed. These include the use of the fountain effect for liquid-vapor phase separation; for pumping superfluid helium from a storage vessel to a payload (as in the Superfluid Helium On-Orbit Transfer Flight Demonstration and the Superfluid Helium Tanker); for actuating a low-temperature refrigerator; and for circulating liquid helium within a cryostat (as in the Astromag dewar).
The thermomechanical structure is investigated in strongly chaotic non-Newtonian thermal convection for both base-heated and internally-heated systems. Temperature can build up in stagnant regions and a non-Newtonian mantle can tolerate less internal heating. Viscosity fields of the strongly chaotic regime show a granular structure. The horizontal spectra of viscosity fluctuations obey a power-law and yield a fractal dimension of 1.6 to 1.8 for the isoviscosity lines, providing evidence for 2D turbulence. Long-wavelength viscosity variations are smoothed out by the turbulent non-Newtonian flows.
A viscoplastic constitutive model is described in which deformation behavior is postulated on representative slip systems and the behavior of the entire crystal is determined by summing the slip on the active slip systems. By building in the slip geometry known from the metallurgical literature, it is possible to predict the anisotropic deformation behavior and to model in a straightforward manner other phenomena which have been described by metallurgists in crystallographic terms. Elevated temperature tension-torsion tests were run and used to verify the model's predictive abilities. Ratchetting behavior under thermomechanical loading conditions is specifically addressed.
The governing differential equations are developed to model the thermomechanical behavior of chemically decomposing, polymeric materials. These equations account for thermal and gaseous diffusion through a poroelastic, transversely isotropic solid. The Bubnov-Galerkin finite element method is applied to the governing equations to cast the coupled set into a single matrix equation. A method for solving these equations simultaneously at each time step is discussed.
A practical computer code has been developed which uses the accepted two-fluid model to simulate He II flow in complicated systems. The full set of equations are used, retaining the coupling between the pressure, temperature and velocity fields. This permits modeling He II flow over the full range of conditions, from strongly or weakly driven flow through large pipes, narrow channels and porous media. The system may include most of the components used in modern superfluid flow systems: non-ideal thermomechanical pumps, tapered sections, constrictions, lines with heated side walls and heat exchangers. The model is validated by comparison with published experimental data. It is applied to a complex system to show some of the non-intuitive feedback effects that can occur. This code is ready to be used as a design tool for practical applications of He II. It can also be used for the design of He II experiments and as a tool for comparison of experimental data with the standard two-fluid model.
A new family of addition curing polyimides were prepared that contained 4-amino (2.2)-paracyclophane as the endcap. An improved synthesis of the endcap 4-amino-(2.2) cyclophane was accomplished increasing the yield to 60 percent and simplifying the procedure. DSC and rheological analysis of endcapped polyimide oligomers confirmed that the onset for polymerization of the ethylene bridge was 250 C. C-13 CP/MAS NMR was used to determine the structural changes of the oligomers after thermal treatment. The cyclophane capped polyimides were successfully compression molded to form void free neat resin specimens. Tg's as high as 353 C were obtained by thermomechanical analysis for postcured samples. Preliminary thermal stability studies suggest that these resins have a high onset of decomposition ranging from 549 to 567 C.
A variationally consistent theory is developed in order to derive the governing equations of anisotropic thin-walled beams with closed sections subjected to axial load, torsion, bending and hygrothermal loads. The theory is based on an asymptotical analysis of two-dimensional shell theory. Closed-form expressions for the beam stiffness coefficients, equivalent hygrothermal loads, stress and displacement fields are provided. The influence of material anisotropy and hygrothermal coefficients on the displacement field is identified. The analysis is applied to predict the response of composite beams under thermomechanical loading.
A computational simulation procedure is described for multidisciplinary analysis and tailoring of multilayered multimaterial hot composite engine structural components subjected to simultaneous multiple discipline-specific thermal, structural, vibration, and acoustic loadings including the effect of aggressive environments. The simulation is based on a 3D finite element analysis technique in conjunction with structural mechanics codes, thermal/acoustic analysis methods, and tailoring procedures. The integrated multidisciplinary simulation procedure is general-purpose including the coupled effects of nonlinearities in structure geometry, material, loading, and environmental complexities. The composite material behavior is assessed at all composite scales, i.e., the laminate/ply/constituents (fiber/matrix), via a nonlinear material characterization hygro-thermomechanical model. Sample tailoring cases exhibiting nonlinear material/loading/environmental behavior of aircraft engine fan blades, are presented. The various multidisciplinary loadings lead to different tailored designs, even those opposite of each other, as in the case of minimum material cost versus minimum structure weight and in the case of minimum vibration frequency versus minimum acoustic noise.
A computer code, high temperature composite analyzer (HITCAN), was developed to analyze/design hot metal matrix composite structures. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structural level, including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters, including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model, i.e., the material properties are expressed in terms of a product of several factors that affect the properties. HITCAN structural analysis capabilities (static, load stepping - a multistep static analysis with material properties updated at each step, modal, and buckling) for cooled hot structures are demonstrated through a specific example problem.