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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Solar panel thermal cycling testing by solar simulation and infrared radiation methods

For the solar panels of the European Space Agency (ESA) satellites OTS/MAROTS and ECS/MARECS the thermal cycling tests were performed by using solar simulation methods. The performance data of two different solar simulators used and the thermal test results are described. The solar simulation thermal cycling tests for the ECS/MARECS solar panels were carried out with the aid of a rotatable multipanel test rig by which simultaneous testing of three solar panels was possible. As an alternative thermal test method, the capability of an infrared radiation method was studied and infrared simulation tests for the ultralight panel and the INTELSAT 5 solar panels were performed. The setup and the characteristics of the infrared radiation unit using a quartz lamp array of approx. 15 sq and LN2-cooled shutter and the thermal test results are presented. The irradiation uniformity, the solar panel temperature distribution, temperature changing rates for both test methods are compared. Results indicate the infrared simulation is an effective solar panel thermal testing method.

Nuss, H. E.↗
NASA NTRS1979

A higher order panel method for linearized supersonic flow

The basic integral equations of linearized supersonic theory for an advanced supersonic panel method are derived. Methods using only linear varying source strength over each panel or only quadratic doublet strength over each panel gave good agreement with analytic solutions over cones and zero thickness cambered wings. For three dimensional bodies and wings of general shape, combined source and doublet panels with interior boundary conditions to eliminate the internal perturbations lead to a stable method providing good agreement experiment. A panel system with all edges contiguous resulted from dividing the basic four point non-planar panel into eight triangular subpanels, and the doublet strength was made continuous at all edges by a quadratic distribution over each subpanel. Superinclined panels were developed and tested on s simple nacelle and on an airplane model having engine inlets, with excellent results.

Ehlers, F. E.↗
NASA NTRS1982

Flightweight radiantly and actively cooled panel: Thermal and structural performance

A 2- by 4-ft flightweight panel was subjected to thermal/structural tests representative of design flight conditions for a Mach 6.7 transport and to off-design conditions simulating flight maneuvers and cooling system failures. The panel utilized Rene 41 heat shields backed by a thin layer of insulation to radiate away most of the 12 Btu/ft2-sec incident heating. A solution of ethylene glycol in water circulating through tubes in an aluminum-honeycomb-sandwich panel absorbed the remainder of the incident heating (0.8 Btu/sq ft-sec). The panel successfully withstood (1) 46.7 hr of radiant heating which included 53 thermal cycles and 5000 cycles of uniaxial inplane loading of + or - 1200 lfb/in; (2) simulated 2g-maneuver heating conditions and simulated cooling system failures without excessive temperatures on the structural panel; and (3) the extensive thermal/structural tests and the aerothermal tests reported in NASA TP-1595 without significant damage to the structural panel, coolant leaks, or hot-gas ingress to the structural panel.

Shore, C. P.↗
NASA NTRS1980

Compression panel studies for supersonic cruise vehicles

Results of analytical and experimental studies are summarized for titanium, boron fiber reinforced aluminum matrix composite, Borsic fiber reinforced aluminum matrix composite, and titanium sheathed Borsic fiber reinforced aluminum matrix composite stiffened panels. The results indicate that stiffened panels with continuous joints (i.e., brazed, diffusion bonded or adhesive bonded joints) are more structurally efficient than geometrically similar panels with discrete joints (i.e., spotwelded or bolted joints). In addition, results for various types of fiber reinforced aluminum matrix stiffened panels indicate that titanium sheathed Borsic fiber reinforced aluminum matrix composite panels are the most structurally efficient. Analytical results are also presented for graphite fiber reinforced polyimide matrix composite stiffened panels and superplastically formed and diffusion bonded titanium sandwich panels.

Mcwithey, R. R.↗
NASA NTRS1983

Fabrication and evaluation of cold/formed/weldbrazed beta-titanium skin-stiffened compression panels

The room temperature and elevated temperature buckling behavior of cold formed beta titanium hat shaped stiffeners joined by weld brazing to alpha-beta titanium skins was determined. A preliminary set of single stiffener compression panels were used to develop a data base for material and panel properties. These panels were tested at room temperature and 316 C (600 F). A final set of multistiffener compression panels were fabricated for room temperature tests by the process developed in making the single stiffener panels. The overall geometrical dimensions for the multistiffener panels were determined by the structural sizing computer code PASCO. The data presented from the panel tests include load shortening curves, local buckling strengths, and failure loads. Experimental buckling loads are compared with the buckling loads predicted by the PASCO code. Material property data obtained from tests of ASTM standard dogbone specimens are also presented.

Royster, D. M.↗
NASA NTRS1984

Investigation of articulated panel dynamics

An articulated panel dynamics experiment to evaluate present analysis and ground test methods as well as damping effectiveness is proposed. The experiment uses an existing panel design which was extensively analyzed and tested. These data provide a firm basis for evaluating the adequacy of panel analysis and ground test methodology. The key issues for future large space structure panel designs are addressed: the critical launch transient and vibroacoustic loading; the deployment analysis adequacy including air and gravitational effects; and the orbital resonant frequencies and mode shapes of deployed panel assemblies. By using an existing mature design that was thoroughly tested, the effort can focus on correlation of actual flight results with existing predictions. A second panel assembly incorporating passive damping is proposed to provide a direct measure of damped panel benefits that can be obtained. These benefits include: reduced launch loads and responses; and highly damped deployed modes. Existing space-qualified viscoelastic epoxy, in combination with composite materials or an alternate more effective damping material, will be used.

Stahle, C. V., Jr.↗
NASA NTRS1987

Advanced radiator concepts utilizing honeycomb panel heat pipes

The feasibility of fabricating and processing moderate temperature range vapor chamber type heat pipes in a low mass honeycomb panel configuration for highly efficient radiator fins for potential use on the space station was investigated. A variety of honeycomb panel facesheet and core-ribbon wick concepts were evaluated within constraints dictated by existing manufacturing technology and equipment. Concepts evaluated include type of material, material and panel thickness, wick type and manufacturability, liquid and vapor communication among honeycomb cells, and liquid flow return from condenser to evaporator facesheet areas. A thin-wall all-welded stainless steel design with methanol as the working fluid was the initial prototype unit. It was found that an aluminum panel could not be fabricated in the same manner as a stainless steel panel due to diffusion bonding and resistance welding considerations. Therefore, a formed and welded design was developed. The prototype consists of ten panels welded together into a large panel 122 by 24 by 0.15 in., with a heat rejection capability of 1000 watts and a fin efficiency of essentially 1.0.

Fleischman, G. L.↗
NASA NTRS1988

Effects of moisture, elevated temperature, and fatigue loading on the behavior of graphite/epoxy buffer strip panels with center cracks

The effects of fatigue loading combined with moisture and heat on the behavior of graphite epoxy panels with either Kevlar-49 or S-glass buffer strips were studied. Buffer strip panels, that had a slit in the center to represent damage, were moisture conditioned or heated, fatigue loaded, and then tested in tension to measure their residual strength. The buffer strips were parallel to the loading direction and were made by replacing narrow strips of the 0 deg graphite plies with Kevlar-49 epoxy or S-glass epoxy on a 1-for-1 basis. The panels were subjected to a fatigue loading spectrum. One group of panels was preconditioned by soaking in 60 C water to produce a 1 percent weight gain then tested at room temperature. One group was heated to 82 C during the fatigue loading. Another group was moisture conditioned and then tested at 82 C. The residual strengths of the buffer panels were not highly affected by the fatigue loading, the number of repetitions of the loading spectrum, or the maximum strain level. The moisture conditioning reduced the residual strengths of the S-glass buffer strip panel by 10 to 15 percent below the ambient results. The moisture conditioning did not have a large effect on the Kevlar-49 panels.

Bigelow, C. A.↗
NASA NTRS1988

Two-Dimensional Sequential and Concurrent Finite Element Analysis of Unstiffened and Stiffened Aluminum and Composite Panels with Hole

The results of a detailed investigation of the distribution of stresses in aluminum and composite panels subjected to uniform end shortening are presented. The focus problem is a rectangular panel with two longitudinal stiffeners, and an inner stiffener discontinuous at a central hole in the panel. The influence of the stiffeners on the stresses is evaluated through a two-dimensional global finite element analysis in the absence or presence of the hole. Contrary to the physical feel, it is found that the maximum stresses from the glocal analysis for both stiffened aluminum and composite panels are greater than the corresponding stresses for the unstiffened panels. The inner discontinuous stiffener causes a greater increase in stresses than the reduction provided by the two outer stiffeners. A detailed layer-by-layer study of stresses around the hole is also presented for both unstiffened and stiffened composite panels. A parallel equation solver is used for the global system of equations since the computational time is far less than that using a sequential scheme. A parallel Choleski method with up to 16 processors is used on Flex/32 Multicomputer at NASA Langley Research Center. The parallel computing results are summarized and include the computational times, speedups, bandwidths, and their inter-relationships for the panel problems. It is found that the computational time for the Choleski method decreases with a decrease in bandwidth, and better speedups result as the bandwidth increases.

Razzaq, Zia↗
NASA NTRS1990

An automatic gore panel mapping system

The Automatic Gore Mapping System is being developed to reduce the time and labor costs associated with manufacturing the External Tank. The present chem-milling processes and procedures are discussed. The down loading of the simulation of the system has to be performed to verify that the simulation package will translate the simulation code into robot code. Also a simulation of this system has to be programmed for a gantry robot instead of the articulating robot that is presently in the system. It was discovered using the simulation package that the articulation robot cannot reach all the point on some of the panels, therefore when the system is ready for production, a gantry robot will be used. Also a hydrosensor system is being developed to replace the point-to-point contact probe. The hydrosensor will allow the robot to perform a non-contact continuous scan of the panel. It will also provide a faster scan of the panel because it will eliminate the in-and-out movement required for the present end effector. The system software is currently being modified so that the hydrosensor will work with the system. The hydrosensor consists of a Krautkramer-Branson transducer encased in a plexiglass nozzle. The water stream pumped through the nozzle is the couplant for the probe. Also, software is being written so that the robot will have the ability to draw the contour lines on the panel displaying the out-of-tolerance regions. Presently the contour lines can only be displayed on the computer screens. Research is also being performed on improving and automating the method of scribing the panels. Presently the panels are manually scribed with a sharp knife. The use of a low power laser or water jet is being studied as a method of scribing the panels. The contour drawing pen will be replaced with scribing tool and the robot will then move along the contour lines. With these developments the Automatic Gore Mapping Systems will provide a reduction in time and labor costs associated with manufacturing the External Task. The system also has the potential of inspecting other manufactured parts.

Shiver, John D.↗
NASA NTRS1991

Combined-load buckling behavior of metal-matrix composite sandwich panels under different thermal environments

Combined compressive and shear buckling analysis was conducted on flat rectangular sandwich panels with the consideration of transverse shear effects of the core. The sandwich panel is fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that the square panel has the highest combined load buckling strength, and that the buckling strength decreases sharply with the increases of both temperature and panel aspect ratio. The effect of layup (fiber orientation) on the buckling strength of the panels was studied in detail. The metal matrix composite sandwich panel was much more efficient than the sandwich panel with nonreinforced face sheets and had the same specific weight.

Ko, William L.↗
NASA NTRS1991

Active control of sound radiation from a vibrating rectangular panel by sound sources and vibration inputs - An experimental comparison

Active control of sound radiation from a rectangular panel by two different methods has been experimentally studied and compared. In the first method a single control force applied directly to the structure is used with a single error microphone located in the radiated acoustic field. Global attenuation of radiated sound was observed to occur by two main mechanisms. For 'on-resonance' excitation, the control force had the effect of increasing the total panel input impedance presented to the nosie source, thus reducing all radiated sound. For 'off-resonance' excitation, the control force tends not significantly to modify the panel total response amplitude but rather to restructure the relative phases of the modes leading to a more complex vibration pattern and a decrease in radiation efficiency. For acoustic control, the second method, the number of acoustic sources required for global reduction was seen to increase with panel modal order. The mechanism in this case was that the acoustic sources tended to create an inverse pressure distribution at the panel surface and thus 'unload' the panel by reducing the panel radiation impedance. In general, control by structural inputs appears more effective than control by acoustic sources for structurally radiated noise.

Fuller, C. R.↗
NASA NTRS1992

Structural and thermal testing of lightweight reflector panels

The paper describes the test facility developed for testing large lightweight reflective panels with very accurate and stable surfaces, such as the mirror panels of composite construction developed for the NASA's Precision Segmented Reflector (PSR). Special attention is given to the panel construction and the special problems posed by the characteristics of these panels; the design of the Optical/Thermal Vacuum test facility for structural and thermal testing, developed at the U.S. AFPL; and the testing procedure. The results of the PSR panel test program to date are presented. The test data showed that the analytical approaches used for the panel design and for the prediction of the on-orbit panel behavior were adequate.

Mcgregor, J.↗
NASA NTRS1993

Effect of bow-type initial imperfection on reliability of minimum-weight, stiffened structural panels

Computations were performed to determine the effect of an overall bow-type imperfection on the reliability of structural panels under combined compression and shear loadings. A panel's reliability is the probability that it will perform the intended function - in this case, carry a given load without buckling or exceeding in-plane strain allowables. For a panel loaded in compression, a small initial bow can cause large bending stresses that reduce both the buckling load and the load at which strain allowables are exceeded; hence, the bow reduces the reliability of the panel. In this report, analytical studies on two stiffened panels quantified that effect. The bow is in the shape of a half-sine wave along the length of the panel. The size e of the bow at panel midlength is taken to be the single random variable. Several probability density distributions for e are examined to determine the sensitivity of the reliability to details of the bow statistics. In addition, the effects of quality control are explored with truncated distributions.

Stroud, W. Jefferson↗
NASA NTRS1957

Some Experimental Studies of Panel Flutter at Mach Number 1.3

Experimental studies of panel flutter using thin metal plates were conducted at a Mach number of 1.3 to verify its existence and to study the effects of some structural parameters on the flutter characteristics. The effects of tensile forces and buckling were studied on panels clamped front and rear, in addition to initially buckled panels clamped on all four edges. Panel flutter was obtained under controlled laboratory conditions and it was found that tensile forces, shortening the panels, and increasing the bending stiffness were effective means for eliminating flutter. Buckled panels were more susceptible to flutter than unbuckled panels. No apparent systematic trends in the flutter modes or frequencies could be observed.

VIBRATION AND FLUTTER↗
NASA NTRS1994

Test and analysis of a stitched RFI graphite-epoxy panel with a fuel access door

A stitched RFI graphite-epoxy panel with a fuel access door was analyzed using a finite element analysis and loaded to failure in compression. The panel was initially 56-inches long and 36.75-inches wide and the oval access door was 18-inches long and 15-inches wide. The panel was impact damaged with impact energy of 100 ft-lb prior to compressive loading; however, no impact damage was detectable visually or by A-scan. The panel carried a failure load of 695,000 Ib and global failure strain of .00494 in/in. Analysis indicated the panel would fail due to collapse at a load of 688,100 Ib. The test data indicate that the maximum strain in a region near the access door was .0096 in/in and analysis indicates a local surface strain of .010 in/in at the panel's failure load. The panel did not fail through the impact damage, but instead failed through bolt holes for attachment of the access door in a region of high strain.

Jegley, Dawn C.↗
NASA NTRS1995

Buckling and postbuckling of composite panels with cutouts subjected to combined edge shear and temperature change

The results of a detailed study of the buckling and postbuckling responses of composite panels with central circular cutouts are presented. The panels are subjected to combined edge shear and temperature change. The panels are discretized by using a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the panel. The fundamental unknowns consist of the average mechanical strains through the thickness and the displacement components. The effects of geometric nonlinearities and laminated anisotropic material behavior are included. The stability boundary, postbuckling response and the hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the panel stiffnesses, and the material properties of both the individual layers and the constituents (fibers and matrix). Numerical results are presented for composite panels with central circular cutouts subjected to combined edge shear and temperature change, showing the effects of variations in the hole diameter, laminate stacking sequence and fiber orientation, on the stability boundary and postbuckling response and their sensitivity to changes in the various panel parameters.

Noor, Ahmed K.↗
NASA NTRS1995

Fracture analysis of stiffened panels under biaxial loading with widespread cracking

An elastic-plastic finite-element analysis with a critical crack-tip opening angle (CTOA) fracture criterion was used to model stable crack growth and fracture of 2024-T3 aluminum alloy (bare and clad) panels for several thicknesses. The panels had either single or multiple-site damage (MSD) cracks subjected to uniaxial or biaxial loading. Analyses were also conducted on cracked stiffened panels with single or MSD cracks. The critical CTOA value for each thickness was determined by matching the failure load on a middle-crack tension specimen. Comparisons were made between the critical angles determined from the finite-element analyses and those measured with photographic methods. Predicted load-against-crack extension and failure loads for panels under biaxial loading, panels with MSD cracks, and panels with various numbers of stiffeners were compared with test data whenever possible. The predicted results agreed well with the test data even for large-scale plastic deformations. The analyses were also able to predict stable tearing behavior of a large lead crack in the presence of MSD cracks. The analyses were then used to study the influence of stiffeners on residual strength in the presence of widespread fatigue cracking. Small MSD cracks were found to greatly reduce the residual strength for large lead cracks even for stiffened panels.

Newman, J. C., Jr.↗