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Thornton, Earl A.

Publications and source records attributed to Thornton, Earl A..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Thermally-Induced Structural Disturbances of Rigid Panel Solar Arrays

The performance of a significant number of spacecraft has been impacted negatively by attitude disturbances resulting from thermally-induced motions of flexible structures. Recent examples of spacecraft affected by these disturbances include the Hubble Space Telescope (HST) and the Upper Atmosphere Research Satellite (UARS). Thermally-induced structural disturbances occur as the result of rapid changes in thermal loading typically initiated as a satellite exits or enters the Earth's shadow. Temperature differences in flexible appendages give rise to structural deformations, which in turn result in disturbance torques reacting back on the spacecraft. Structures which have proven susceptible to these disturbances include deployable booms and solar arrays. This paper investigates disturbances resulting from thermally-induced deformations of rigid panel solar arrays. An analytical model for the thermal-structural response of the solar array and the corresponding disturbance torque are presented. The effect of these disturbances on the attitude dynamics of a simple spacecraft is then investigated using a coupled system of governing equations which includes the effects of thermally-induced deformations. Numerical results demonstrate the effect of varying solar array geometry on the dynamic response of the system.

Johnston, John D.↗
NASA NTRS1994

Analysis of high speed flow, thermal and structural interactions

Research for this grant focused on the following tasks: (1) the prediction of severe, localized aerodynamic heating for complex, high speed flows; (2) finite element adaptive refinement methodology for multi-disciplinary analyses; (3) the prediction of thermoviscoplastic structural response with rate-dependent effects and large deformations; (4) thermoviscoplastic constitutive models for metals; and (5) coolant flow/structural heat transfer analyses.

Thornton, Earl A.↗
NASA NTRS1994

NASA-UVA light aerospace alloy and structures technology program (LA2ST)

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA2ST) Program was initiated in 1986, and continues a high level of activity, with projects being conducted by graduate students and faculty advisors in the Departments of Materials Science and Engineering, and Mechanical and Aerospace Engineering at the University of Virginia. This work is funded by the NASA-Langley Research Center under Grant NAG-1-745. Here, we report on progress achieved between July 1 and December 31, 1993. The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys, composites and thermal gradient structures in collaboration with NASA-Langley researchers. Specific technical objectives are presented for each research project. We generally aim to produce relevant data and basic understanding of material mechanical response, environmental/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and critically, a pool of educated graduate students for aerospace technologies.

Gangloff, Richard P.↗
NASA NTRS1994

Viscoplastic response of structures for intense local heating

A thermoviscoplastic finite element method employing the Bodner-Partom constitutve model is used to investigate the response of simplified thermal-structural models to intense local heating. The computational method formulates the problem in rate and advances the solution in time by numerical integration. The thermoviscoplastic response of simplified structures with prescribed temperatures is investigated. 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 NTRS1993

NASA-UVA Light Aerospace Alloy and Structures Technology Program (LA2ST)

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA2ST) Program continues a high level of activity. Progress achieved between 1 Jan. and 30 Jun. 1993 is reported. The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys, composites, and thermal gradient structures in collaboration with NASA-Langley researchers. The following projects are addressed: environmental fatigue of Al-Li-Cu alloys; mechanisms of localized corrosion and environmental fracture in Al-Cu-Li-Mg-Ag alloy X2095 and compositional variations; the effect of zinc additions on the precipitation and stress corrosion cracking behavior of alloy 8090; hydrogen interactions with Al-Li-Cu alloy 2090 and model alloys; metastable pitting of aluminum alloys; cryogenic fracture toughness of Al-Cu-Li + In alloys; the fracture toughness of Weldalite (TM); elevated temperature cracking of advanced I/M aluminum alloys; response of Ti-1100/SCS-6 composites to thermal exposure; superplastic forming of Weldalite (TM); research to incorporate environmental effects into fracture mechanics fatigue life prediction codes such as NASA FLAGRO; and thermoviscoplastic behavior.

Gangloff, Richard P.↗
NASA NTRS1993

NASA-UVA Light Aerospace Alloy and Structures Technology Program: LA(2)ST

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA(2)ST) Program continues a high level of activity, with projects being conducted by graduate students and faculty advisors in the Departments of Materials Science and Engineering, Civil Engineering and Applied Mechanics, and Mechanical and Aerospace Engineering at the University of Virginia. This work is funded by the NASA-Langley Research Center under Grant NAG-1-745. We report on progress achieved between July 1 and December 31, 1992. The objective of the LA(2)ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys, composites and thermal gradient structures in collaboration with NASA-Langley researchers. Specific technical objectives are presented for each research project. We generally aim to produce relevant data and basic understanding of material mechanical response, corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement advances; and critically, a pool of educated graduate students for aerospace technologies.

Gangloff, Richard P.↗
NASA NTRS1993

Finite element study of plate buckling induced by spatial temperature gradients

Finite element analyses of thermal buckling of thin metallic plates with prescribed spatial temperature distributions are described. Thermally induced compressive membrane stresses and transverse plate displacement imperfections initiate plates buckling. A finite element formulation based on von Karman plate theory is presented. The resulting nonlinear equations are solved for incremental temperature increases by Newton-Raphson iteration. The computational method is used to investigate the buckling response of rectangular plates with steady and unsteady spatially varying temperature distributions. The role of initial plate imperfections and temperature distributions on the nonlinear response of plate displacements and stresses is described. The relatively high levels of stress induced by spatial temperature gradients should be considered carefully in the postbuckling design of panels for aerospace vehicles subjected to combined mechanical and thermal loads.

Thornton, Earl A.↗
NASA NTRS1992

Light thermal structures and materials for high speed flight

Over the last twenty years, unified viscoplastic constitutive models have evolved to meet this need. These constitutive models provide a means for representing a material's response from the elastic through the plastic range including strain-rate dependent plastic flow, creep, and stress relaxation. Rate-dependent plasticity effects are known to be important at elevated temperatures. The purpose of this paper is to describe computational and experimental research programs underway at the Light Thermal Structures Center focused on the investigation of the response of structures and materials to local heating. In the first part of the paper, finite element thermoviscoplastic analysis is highlighted. In the second part of the paper, the thermal-structures experimental program is outlined.

Thornton, Earl A.↗
NASA NTRS1992

NASA-UVA light aerospace alloy and structures technology program (LA(sup 2)ST)

The general objective of the Light Aerospace Alloy and Structures Technology (LA(sup 2)ST) Program is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys, composites, and thermal gradient structures in collaboration with Langley researchers. Specific technical objectives are established for each research project. We aim to produce relevant data and basic understanding of material behavior and microstructure, new monolithic and composite alloys, advanced processing methods, new solid and fluid mechanics analyses, measurement advances, and critically, a pool of educated graduate students for aerospace technologies. Four research areas are being actively investigated, including: (1) Mechanical and Environmental Degradation Mechanisms in Advanced Light Metals and Composites; (2) Aerospace Materials Science; (3) Mechanics of Materials and Composites for Aerospace Structures; and (4) Thermal Gradient Structures.

Gangloff, Richard P.↗
NASA NTRS1992

Thermoviscoplastic response of thin plates subjected to intense local heating

A finite element method is employed to investigate the thermoviscoplastic response of a half-cylinder to intense localized transient heating. Thermoviscoplastic material behavior is characterized by the Bodner-Partom constitutive model. Structure geometry is modeled with a three-dimensional assembly of CST-DKT plate elements incorporating the large deflection von Karman assumptions. The paper compares the results of a dynamic analysis with a quasi-static analysis for the half-cylinder structure with a step-function transient temperature loading similar to that which may be encountered with shock wave interference on a hypersonic leading edge.

Byrom, Ted G.↗
NASA NTRS1992

Experimental study of plate buckling induced by spatial temperature gradients

An experimental study of plate buckling induced by spatial temperature gradients is described. A rectangular Hastelloy-X panel is subjected to local line heating by a focused quartz heat lamp. Two parallel panel edges are maintained at constant temperature by coolant flow. Point supports provide well-defined thermal-structural boundary conditions. Test results from transient elastic and inelastic tests demonstrate that substantial panel bending occurs due to initial panel warpage and thermally induced membrane compressive stresses.

Thornton, Earl A.↗
NASA NTRS1991

Materials and light thermal structures research for advanced space exploration

The Light Thermal Structures Center at the University of Virginia sponsors educational and research programs focused on the development of reliable, lightweight structures to function in hostile thermal environments. Technology advances in materials and design methodology for light thermal structures will contribute to improved space vehicle design concepts with attendant weight savings. This paper highlights current research activities in three areas relevant to space exploration: low density, high temperature aluminum alloys, composite materials, and structures with thermal gradients. Advances in the development of new aluminum-lithium alloys and mechanically alloyed aluminum alloys are described. Material properties and design features of advanced composites are highlighted. Research studies in thermal structures with temperature gradients include inelastic panel buckling and thermally induced unstable oscillations. Current and future research is focused on the integration of new materials with applications to structural components with thermal gradients.

Thornton, Earl A.↗
NASA NTRS1991

NASA-UVa light aerospace alloy and structures technology program

The general objective of the NASA-UVa Light Aerospace Alloy and Structures Technology Program was to conduct research on the performance of next generation, light weight aerospace alloys, composites, and associated thermal gradient structures. The following research areas were actively investigated: (1) mechanical and environmental degradation mechanisms in advanced light metals and composites; (2) aerospace materials science; (3) mechanics of materials and composites for aerospace structures; and (4) thermal gradient structures.

Gangloff, Richard P.↗
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 NTRS1990

Finite element thermo-viscoplastic analysis of aerospace structures

The time-dependent thermo-viscoplastic response of aerospace structures subjected to intense aerothermal loads is predicted using the finite-element method. The finite-element analysis uses the Bodner-Partom unified viscoplastic constitutive relations to determine rate-dependent nonlinear material behavior. The methodology is verified by comparison with experimental data and other numerical results for a uniaxially-loaded bar. The method is then used (1) to predict the structural response of a rectangular plate subjected to line heating along a centerline, and (2) to predict the thermal-structural response of a convectively-cooled engine cowl leading edge subjected to aerodynamic shock-shock interference heating. Compared to linear elastic analysis, the viscoplastic analysis results in lower peak stresses and regions of plastic deformations.

Pandey, Ajay K.↗
NASA NTRS1990

Thermal structures: Four decades of progress

Since the first supersonic flight in October 1947, the United States has designed, developed and flown flight vehicles within increasingly severe aerothermal environments. Over this period, major advances in engineering capabilities have occurred that will enable the design of thermal structures for high speed flight vehicles in the twenty-first century. Progress in thermal-structures is surveyed for the last four decades to provide a historical perspective for future efforts.

Thornton, Earl A.↗