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  • Other Sources  (139)
  • 1900-1903
  • ENERGY PRODUCTION AND CONVERSION
  • STRUCTURAL MECHANICS
  • 1995-1999  (135)
  • 1900-1904  (4)
  • 1
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    Numerical simulation of the nonlinear response of composite plates under combined thermal and acoustic loading (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: A time-domain study of the random response of a laminated plate subjected to combined acoustic and thermal loads is carried out. The features of this problem also include given uniform static inplane forces. The formulation takes into consideration a possible initial imperfection in the flatness of the plate. High decibel sound pressure levels along with high thermal gradients across thickness drive the plate response into nonlinear regimes. This calls for the analysis to use von Karman large deflection strain-displacement relationships. A finite element model that combines the von Karman strains with the first-order shear deformation plate theory is developed. The development of the analytical model can accommodate an anisotropic composite laminate built up of uniformly thick layers of orthotropic, linearly elastic laminae. The global system of finite element equations is then reduced to a modal system of equations. Numerical simulation using a single-step algorithm in the time-domain is then carried out to solve for the modal coordinates. Nonlinear algebraic equations within each time-step are solved by the Newton-Raphson method. The random gaussian filtered white noise load is generated using Monte Carlo simulation. The acoustic pressure distribution over the plate is capable of accounting for a grazing incidence wavefront. Numerical results are presented to study a variety of cases.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-197426 , NAS 1.26:197426
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  • 2
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    Investigation of the basic physics of high efficiency semiconductor hot carrier solar cell (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The main purpose of this research program is to investigate potential semiconductor materials and their multi-band-gap MQW (multiple quantum wells) structures for high efficiency solar cells for aerospace and commercial applications. The absorption and PL (photoluminescence) spectra, the carrier dynamics, and band structures have been investigated for semiconductors of InP, GaP, GaInP, and InGaAsP/InP MQW structures, and for semiconductors of GaAs and AlGaAs by previous measurements. The barrier potential design criteria for achieving maximum energy conversion efficiency, and the resonant tunneling time as a function of barrier width in high efficiency MQW solar cell structures have also been investigated in the first two years. Based on previous carrier dynamics measurements and the time-dependent short circuit current density calculations, an InAs/InGaAs - InGaAs/GaAs - GaAs/AlGaAs MQW solar cell structure with 15 bandgaps has been designed. The absorption and PL spectra in InGaAsP/InP bulk and MQW structures were measured at room temperature and 77 K with different pump wavelength and intensity, to search for resonant states that may affect the solar cell activities. Time-resolved IR absorption for InGaAsP/InP bulk and MQW structures has been measured by femtosecond visible-pump and IR-probe absorption spectroscopy. This, with the absorption and PL measurements, will be helpful to understand the basic physics and device performance in multi-bandgap InAs/InGaAs - InGaAs/InP - InP/InGaP MQW solar cells. In particular, the lifetime of the photoexcited hot electrons is an important parameter for the device operation of InGaAsP/InP MQW solar cells working in the resonant tunneling conditions. Lastly, time evolution of the hot electron relaxation in GaAs has been measured in the temperature range of 4 K through 288 K using femtosecond pump-IR-probe absorption technique. The temperature dependence of the hot electron relaxation time in the X valley has been measured.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-CR-198945 , NAS 1.26:198945
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  • 3
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    Space Electrochemical Research and Technology. Abstracts (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This document contains abstracts of the proceedings of NASA's fifth Space Electrochemical Research and Technology (SERT) Conference, held at the NASA Lewis Research Center on May 1-3, 1995. The objective of the conference was to assess the present status and general thrust of research and development in those areas of electrochemical technology required to enable NASA missions into the next century. The conference provided a forum for the exchange of ideas and opinions of those actively involved in the field, in order to define new opportunities for the application of electrochemical processes in future NASA missions. Papers were presented in three technical areas: (1) the electrochemical interface, (2) the next generation in aerospace batteries and fuel cells, and (3) electrochemistry for non-energy storage applications. This document contains the abstracts of the papers presented.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-CP-10172 , E-9609 , NAS 1.55:10172 , May 01, 1995 - May 03, 1995; Cleveland, OH; United States
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  • 4
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    Load transfer in the stiffener-to-skin joints of a pressurized fuselage (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Structural analyses are developed to determine the linear elastic and the geometrically nonlinear elastic response of an internally pressurized, orthogonally stiffened, composite material cylindrical shell. The configuration is a long circular cylindrical shell stiffened on the inside by a regular arrangement of identical stringers and identical rings. Periodicity permits the analysis of a unit cell model consisting of a portion of the shell wall centered over one stringer-ring joint. The stringer-ring-shell joint is modeled in an idealized manner; the stiffeners are mathematically permitted to pass through one another without contact, but do interact indirectly through their mutual contact with the shell at the joint. Discrete beams models of the stiffeners include a stringer with a symmetrical cross section and a ring with either a symmetrical or an asymmetrical open section. Mathematical formulations presented for the linear response include the effect of transverse shear deformations and the effect of warping of the ring's cross section due to torsion. These effects are important when the ring has an asymmetrical cross section because the loss of symmetry in the problem results in torsion and out-of-plane bending of the ring, and a concomitant rotation of the joint at the stiffener intersection about the circumferential axis. Data from a composite material crown panel typical of a large transport fuselage structure are used for two numerical examples. Although the inclusion of geometric nonlinearity reduces the 'pillowing' of the shell, it is found that bending is localized to a narrow region near the stiffener. Including warping deformation of the ring into the analysis changes the sense of the joint rotation. Transverse shear deformation models result in increased joint flexibility.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-198610 , NAS 1.26:198610 , CCMS-95-04 , VPI-E-95-01
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  • 5
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    Probabilistic simulation of long term behavior in polymer matrix composites (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A methodology to compute cumulative probability distribution functions (CDF) of fatigue life for different ratios, r of applied stress to the laminate strength based on first ply failure criteria has been developed and demonstrated. Degradation effects due to long term environmental exposure and mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation/aging of material properties due to cyclic loads. Fast probability integration method is used to perform probabilistic simulation of uncertainties. Sensitivity of fatigue life reliability to uncertainties in the primitive random variables are computed and their significance in the reliability based design for maximum life is discussed. The results show that the graphite/epoxy (0/+45/90) deg laminate with ply thickness 0.125 in. has 500,000 cycles life for applied stress to laminate strength ratio of 0.6 and a reliability of 0.999. Also, the fatigue life reliability has been found to be most sensitive to the ply thickness and matrix tensile strength. Tighter quality controls must therefore be enforced on ply thickness and matrix strength in order to achieve high reliability of the structure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-106893 , E-9537 , NAS 1.15:106893 , AIAA PAPER 94-1445 , Structures, Structural Dynamics and Materials Conference; Apr 18, 1994 - Apr 21, 1994; Hilton Head, SC; United States
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  • 6
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    The 1994 27th Annual NASA Aerospace Battery Workshop (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The proceedings of the 27th Annual NASA Aerospace Battery Workshop, hosted by the Marshall Space Flight Center on November 15-17, 1994 are presented. The workshop was attended by representatives from various government agencies, as well as contractors and manufacturers, both U.S. and abroad. The subjects covered included: (1) nickel-cadium; (2) nickel-hydrogen, (3) nickel-metal hydride, and (4) lithium based technologies, as well as flight and ground test data.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-CP-3292 , M-772 , NAS 1.55:3292 , Nov 15, 1994 - Nov 17, 1994; Huntsville, AL; United States
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  • 7
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    A fully associative, nonisothermal, nonlinear kinematic, unified viscoplastic model for titanium alloys (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Specific forms for both the Gibb's and complementary dissipation potentials are chosen such that a complete (i.e., fully associative) potential base multiaxial, nonisothermal unified viscoplastic model is obtained. This model possesses one tensorial internal state variable (that is, associated with dislocation substructure) and an evolutionary law that has nonlinear kinematic hardening and both thermal and strain induced recovery mechanisms. A unique aspect of the present model is the inclusion of nonlinear hardening through the use of a compliance operator, derived from the Gibb's potential, in the evolution law for the back stress. This nonlinear tensorial operator is significant in that it allows both the flow and evolutionary laws to be fully associative (and therefore easily integrated), greatly influences the multiaxial response under non-proportional loading paths, and in the case of nonisothermal histories, introduces an instantaneous thermal softening mechanism proportional to the rate of change in temperature. In addition to this nonlinear compliance operator, a new consistent, potential preserving, internal strain unloading criterion has been introduced to prevent abnormalities in the predicted stress-strain curves, which are present with nonlinear hardening formulations, during unloading and reversed loading of the external variables. The specific model proposed is characterized for a representative titanium alloy commonly used as the matrix material in SiC fiber reinforced composites, i.e., TIMETAL 21S. Verification of the proposed model is shown using 'specialized' non-standard isothermal and thermomechanical deformation tests.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-106926 , E-9644 , NAS 1.15:106926 , Symposium on Thermomechanical Fatigue Behavior of Materials; Nov 13, 1994 - Nov 18, 1994; Phoenix, AZ; United States
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  • 8
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    Use of Advanced Solar Cells for Commercial Communication Satellites (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The current generation of communications satellites are located primarily in geosynchronous Earth orbit (GEO). Over the next decade, however, a new generation of communications satellites will be built and launched, designed to provide a world-wide interconnection of portable telephones. For this mission, the satellites must be positioned in lower polar and near-polar orbits. To provide complete coverage, large numbers of satellites will be required. Because the required number of satellites decreases as the orbital altitude is increased, fewer satellites would be required if the orbit chosen were raised from low to intermediate orbit. However, in intermediate orbits, satellites encounter significant radiation due to trapped electrons and protons. Radiation tolerant solar cells may be necessary to make such satellites feasible. We analyze the amount of radiation encountered in low and intermediate polar orbits at altitudes of interest to next-generation communication satellites, calculate the expected degradation for silicon, GaAs, and InP solar cells, and show that the lifetimes can be significantly increased by use of advanced solar cells.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-106879 , E-9515 , NAS 1.15:106879 , First World Conference on Photovoltaic Energy Conversion; Dec 05, 1994 - Dec 09, 1994; Waikoloa, HI; United States
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  • 9
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    Solar Eagle 2 (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During a 22-month period from February 1991 to December 1993, a dedicated group of students, faculty, and staff at California State University, Los Angeles completed a project to design, build, and race their second world class solar-powered electric vehicle, the Solar Eagle 2. This is the final report of that project. As a continuation of the momentum created by the success of the GM-sponsored Sunrayce USA in 1990, the U.S. Department of Energy (DOE) picked up the banner from General Motors as sponsors of Sunrayce 93. In February 1991, the DOE sent a request for proposals to all universities in North America inviting them to submit a proposal outlining how they would design, build, and test a solar-powered electric vehicle for a seven-day race from Arlington, Texas to Minneapolis, Minnesota, to be held in June 1993. Some 70 universities responded. At the end of a proposal evaluation process, 36 universities including CSLA were chosen to compete. This report documents the Solar Eagle 2 project--the approaches take, what was learned, and how our experience from the first Solar Eagle was incorporated into Solar Eagle 2. The intent is to provide a document that would assist those who may wish to take up the challenge to build Solar Eagle 3.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-CR-198043 , NAS 1.26:198043
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  • 10
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    Closed-form Static Analysis with Inertia Relief and Displacement-Dependent Loads Using a MSC/NASTRAN DMAP Alter (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Solving for the displacements of free-free coupled systems acted upon by static loads is commonly performed throughout the aerospace industry. Many times, these problems are solved using static analysis with inertia relief. This solution technique allows for a free-free static analysis by balancing the applied loads with inertia loads generated by the applied loads. For some engineering applications, the displacements of the free-free coupled system induce additional static loads. Hence, the applied loads are equal to the original loads plus displacement-dependent loads. Solving for the final displacements of such systems is commonly performed using iterative solution techniques. Unfortunately, these techniques can be time-consuming and labor-intensive. Since the coupled system equations for free-free systems with displacement-dependent loads can be written in closed-form, it is advantageous to solve for the displacements in this manner. Implementing closed-form equations in static analysis with inertia relief is analogous to implementing transfer functions in dynamic analysis. Using a MSC/NASTRAN DMAP Alter, displacement-dependent loads have been included in static analysis with inertia relief. Such an Alter has been used successfully to solve efficiently a common aerospace problem typically solved using an iterative technique.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-106836 , E-9398 , NAS 1.15:106836 , 1995 World Users'' Conference; May 08, 1995 - May 12, 1995; Los Angeles, CA; United States
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