Search NASA⌕ Search

SEARCH · Search NASA

Results for “Panel method”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Effect of Thin-Film Adhesives on Mode I Interlaminar Fracture Toughness in Carbon Fiber Composites with Shape Memory Alloy Inserts

A single sheet of NiTi shape memory alloy (SMA) was introduced within a unidirectional HexPly® 8552/IM7 (Hexcel®) polymer matrix composite (PMC) panel in conjunction with multiple thin-film adhesives to promote the interfacial bond strength between the SMA and PMC. A double cantilever beam (DCB) test was performed in accordance with the ASTM D5528 method for evaluation of Mode I interlaminar fracture toughness of unidirectional fiber-reinforced PMCs. The modal acoustic emissions (MAEs) were monitored during testing with two acoustic sensors attached to the specimens. The composite panels were subjected to a C-scan before testing and examined using optical and scanning electron microscopy (SEM) techniques after part failure. The data were used in conjunction with modified beam theory (MBT), the compliance calibration (CC) method, and the modified compliance calibration (MCC) method. The Mode I interlaminar toughness (G(sub IC)) values for control specimens were higher than previously reported and are attributed to extensive fiber bridging during testing. The presence of adhesives with SMA inserts stabilized crack propagation during DCB testing. The results reveal a new phenomenon of SMA bridging, whereby crack propagation would switch from one side of the SMA insert to the other, thus increasing the load and G(sub IC) values of specimens containing SMA.

shape memory alloys↗
NASA NTRS1971

A Stability Analysis of Cylindrical Panels Using a Finite Element Formulation

A cylindrical finite element suitable for the linear stability analysis of cylindrical shells is developed. Energy principles and variational methods lead to a problem formulation which lends itself to physical interpretations of the governing matrices of the finite element. By properly grouping the terms which result from taking the second variation of the potential energy of the element, it is possible to identify three distinct types of matrices. The first matrix is the conventional stiffness matrix; the second is an initial stress stiffness matrix; and the third is an initial displacement stiffness matrix. With the assumption of linearity, the buckling problem is stated in terms of the classical linear real eigenvalue equation. This problem formulation was programmed on the CDC 6600 series computer. The computer program is used to analyze the buckling of a variety of structures. Columns, arches, flat plates and curved panels with and without cutouts are considered.

Snyder, R. E.↗
NASA NTRS1990

NDE of thermal protection system for space shuttle solid rocket booster

Potential nondestructive test (NDE) methods were evaluated for detecting debonds and weak bonds in the thermal protection system (TPS) for the space shuttle solid rocket boosters. The primary thermal protection material is a sprayable, thick epoxy coating that is filled with lightweight and thermal insulating materials. Test panels were fabricated with a wide variety of hidden realistic defects, including contact debonds and weak bonds. Nondestructive test results were obtained. Candidate NDE methods evaluated for booster production applications include laser interferometry (e.g., electronic shearography), infrared thermography, radiography (e.g., computed tomography), acousto-ultrasonics, mechanical/acoustic impedance, ultrasonics, acoustic emission, and the tap test. Capabilities, advantages, disadvantages, and relative performances in defect detection of each test method for TPS bonding applications are reported. Electronic shearography NDE was technically the superior method for detecting debonds.

Myers, R. S.↗
NASA NTRS1997

Thermostructural Behavior of a Hypersonic Aircraft Sandwich Panel Subjected to Heating on One Side

Thermostructural analysis was performed on a heated titanium honeycomb-core sandwich panel. The sandwich panel was supported at its four edges with spar-like substructures that acted as heat sinks, which are generally not considered in the classical analysis. One side of the panel was heated to high temperature to simulate aerodynamic heating during hypersonic flight. Two types of surface heating were considered: (1) flat-temperature profile, which ignores the effect of edge heat sinks, and (2) dome-shaped-temperature profile, which approximates the actual surface temperature distribution associated with the existence of edge heat sinks. The finite-element method was used to calculate the deformation field and thermal stress distributions in the face sheets and core of the sandwich panel. The detailed thermal stress distributions in the sandwich panel are presented, and critical stress regions are identified. The study shows how the magnitudes of those critical stresses and their locations change with different heating and edge conditions. This technical report presents comprehensive, three-dimensional graphical displays of thermal stress distributions in every part of a titanium honeycomb-core sandwich panel subjected to hypersonic heating on one side. The plots offer quick visualization of the structural response of the panel and are very useful for hot structures designers to identify the critical stress regions.

Ko, William L.↗
NASA NTRS2006

Overview of High-Resolution Nondestructive Inspection of the Space Shuttle External Tank (ET) Spray-on-Foam Insulation (SOFI) and Acreage Heat tiles using Focused, Synthetic and Holographical Millimeter Wave Techniques

Space Shuttle Columbia's catastrophic failure has been attributed to a piece of spray-on-foam insulation (SOFI) that was dislodged from the external tank (ET) and struck the leading edge of the left wing. A piece of SOFI was also dislodged in the recent Space Shuttle Discovery's flight. From immediately after the Columbia accident, microwave and millimeter wave nondestructive testing methods were considered as potential effective inspection tools for evaluating the integrity of the SOFI. To this end and as a result of these efforts, both real-focused, synthetic focusing and holographical techniques, at a wide range of frequencies covering 24 GHz to 150 GHz, have been developed for this purpose. Images of various complex SOFI panels with a wide range of embedded anomalies (representing real potential defects) have been produced using these techniques, including relatively small anomalies located near complex structural features representative of the external tank. These real-focused and 3D holographical images have effectively demonstrated the utility of these methods for SOFI inspection as being viable, robust, repeatable, simple, portable and relatively inexpensive (tens of $K as opposed to hundreds of $K). In addition, the potential viability of these methods for inspecting acreage heat tiles have has been demonstrated. This paper presents an overview of these activities, representative images of these panels using all of the imaging techniques used and a discussion of the practical attributes of these inspection methods.

Kharkovsky, S.↗
NASA NTRS2021

Confronting Future Models with Future Satellite Observations of Clouds and Aerosols

The NASA Aerosol, Clouds, Convection and Precipitation (ACCP) Study convened a workshop in November 2020 to understand the future of modeling aerosols, clouds, convection and precipitation, and how satellite data can contribute to that future. ACCP is a project to define a satellite mission to be launched late in the 2020’s to advance cloud and aerosol science, following the recommendations of the latest NASA Decadal Survey. The ACCP modeling workshop goal was to answer the following questions: 1. What will be the critical science questions for clouds and aerosols in 10 years? 2. Where will simulations of clouds and aerosols across scales of space (process models to global) and time (nowcasting to climate prediction) be in 10 years? 3. What data will be available from space? What data would provide the most benefit? 4. What are the state of the art methods for confronting models with cloud and aerosol observations, including assimilation and climatological analysis techniques? The virtual workshop was anchored by a series of pre-recorded talks. Two days of synchronous sessions focused on discussion of the talks, along with small group breakout exercises. After an introduction to the ACCP concept came a panel discussing the future of modeling clouds and aerosols across scales. Participants were then asked to contribute their ideas. On the second day, there were two panel discussions. First came a discussion of the future of satellite observing systems. Second was a discussion of model-data synthesis methods. Finally, participants were asked to develop their own model-data synthesis proposal. The meeting began with an overview of the ACCP mission concept by Graeme Stephens (NASA-JPL). ACCP is a satellite mission for clouds and aerosols, likely anchored by advanced active lidar and radar systems in space, designed to observe detailed aerosol profile and type information, as well as cloud microphysics and dynamics. ACCP will integrate across sensors and observational types to get multi-spectral views of the same scenes, with better resolution than is available today. Launch is scheduled for 2027 or 2029. ACCP is being thought of as a comprehensive mission that may comprise more than one platform and more than one orbit plane (i.e., inclined and polar), with multiple combinations of sensors.

Future Models↗
NASA NTRS1971

Thermoelastic damping and its effect on flutter of stressed panels situated in a supersonic airflow

The effects of material damping on flutter of stressed rectangular panels are studied within the context of linear thermoelasticity theory. The closed-form expression for the thermoelastic (material) damping coefficient is obtained as a function of frequency, panel temperature and dimensions, and material properties. The solution of the stability boundary value problem is obtained by use of a generalized Galerkin method in the cross stream direction which reduces the governing partial differential equations to a system of ordinary differential equations in the streamwise direction. These equations are then solved exactly. Numerical results are given for the thermoelastic damping coefficients and for the flutter speeds of partially and fully clamped panels subjected to midplane stress.

Shieh, R. C.↗
NASA NTRS1973

Advanced beaded and tubular structural panels.

A review is presented of an NASA program to develop light-weight beaded and tubular structural panels which can be applied where beaded external surfaces are acceptable aerodynamically or where primary structure is protected by heat shields. The design shapes were obtained with an optimization computer code which iterates geometric parameters to satisfy strength, stability and weight constraints. Methods of fabricating these new configurations are discussed. Nondestructive testing produced extensive combined compression, shear and bending test data on local buckling specimens and large panels. The optimized design concepts offer 25 to 40% weight savings compared to conventional stiffened sheet construction.

Musgrove, M. D.↗
NASA NTRS1995

Production of aluminum-lithium near net shape extruded cylinders

In the late 1980's, under funding from the Advanced Launch System Program, numerous near net shape technologies were investigated as a means for producing high quality, low cost Aluminum-Lithium (Al-Li) hardware. Once such option was to extrude near net shape barrel panels instead of producing panels by machining thick plate into a final tee-stiffened configuration (which produced up to 90% scrap). This method offers a reduction in the volume of scrap and consequently reduces the buy-to-fly cost. Investigation into this technology continued under Shuttle-C funding where four Al alloys 2219, 2195, 2096, and RX 818 were extruded. Presented herein are the results of that program. Each alloy was successfully extruded at Wyman Gordon, opened and flattened at Ticorm, and solution heat treated and stretched at Reynolds Metals Company. The first two processes were quite successful while the stretching process did offer some challenges. Due to the configuration of the panels and the stretch press set-up, it was difficult to induce a consistent percentage of cold work throughout the length and width of each panel. The effects of this variation will be assessed in the test program to be conducted at a future date.

Hartley, Paula J.↗
NASA NTRS2000

Electromagnetic Field Penetration Studies

A numerical method is presented to determine electromagnetic shielding effectiveness of rectangular enclosure with apertures on its wall used for input and output connections, control panels, visual-access windows, ventilation panels, etc. Expressing EM fields in terms of cavity Green's function inside the enclosure and the free space Green's function outside the enclosure, integral equations with aperture tangential electric fields as unknown variables are obtained by enforcing the continuity of tangential electric and magnetic fields across the apertures. Using the Method of Moments, the integral equations are solved for unknown aperture fields. From these aperture fields, the EM field inside a rectangular enclosure due to external electromagnetic sources are determined. Numerical results on electric field shielding of a rectangular cavity with a thin rectangular slot obtained using the present method are compared with the results obtained using simple transmission line technique for code validation. The present technique is applied to determine field penetration inside a Boeing-757 by approximating its passenger cabin as a rectangular cavity filled with a homogeneous medium and its passenger windows by rectangular apertures. Preliminary results for, two windows, one on each side of fuselage were considered. Numerical results for Boeing-757 at frequencies 26 MHz, 171-175 MHz, and 428-432 MHz are presented.

Deshpande, M.D.↗
NASA NTRS1972

Field repair of coated columbium Thermal Protection System (TPS)

The requirements for field repair of coated columbian panels were studied, and the probable cause of damage were identified. The following types of repair methods were developed, and are ready for use on an operational system: replacement of fused slurrey silicide coating by a short processing cycle using a focused radiant spot heater; repair of the coating by a glassy matrix ceramic composition which is painted or sprayed over the defective area; and repair of the protective coating by plasma spraying molybdenum disilicide over the damaged area employing portable equipment.

Culp, J. D.↗
NASA NTRS1980

Fiber release characteristics of graphite hybrid composites

The paper considers different material concepts that can be fabricated of hybridized composites which demonstrate improved graphite fiber retention capability in a severe fire without significant reduction to the composite properties. More than 30 panels were fabricated for mechanical and fire tests, the details and results of which are presented. Methods of composite hybridization investigated included the addition of oxidation resistant fillers to the resin, mechanically interlocking the graphite fibers by the use of woven fabrics, and the addition of glass fibers and glass additives designed to melt and fuse the graphite fibers together. It is concluded that a woven fabric with a serving of glass around each graphite tow is by far the superior of those evaluated: not only is there a coalescing effect in each graphite layer, but there is also a definite adhesion of each layer to its neighbor.

Henshaw, J.↗
NASA NTRS1986

Evaluation of 3 numerical methods for propulsion integration studies on transonic transport configurations

An effort has been undertaken at the NASA Langley Research Center to assess the capabilities of available computational methods for use in propulsion integration design studies of transonic transport aircraft, particularly of pylon/nacelle combinations which exhibit essentially no interference drag. The three computer codes selected represent state-of-the-art computational methods for analyzing complex configurations at subsonic and transonic flight conditions. These are: EULER, a finitie volume solution of the Euler equation; VSAERO, a panel solution of the Laplace equation; and PPW, a finite difference solution of the small disturbance transonic equations. In general, all three codes have certain capabilities that allow them to be of some value in predicting the flows about transport configurations, but all have limitations. Until more accurate methods are available, careful application and interpretation of the results of these codes are needed.

Yaros, S. F.↗
NASA NTRS1986

Model-size reduction for the buckling and vibration analyses of anisotropic panels

A computational procedure is presented for reducing the size of the model used in the buckling and vibration analyses of symmetric anisotropic panels to that of the corresponding orthotropic model. The key elements of the procedure are the application of an operator splitting technique through the decomposition of the material stiffness matrix of the panel into the sum of orthotropic and nonorthotropic (anisotropic) parts and the use of a reduction method through successive application of the finite element method and the classical Rayleigh-Ritz technique. The effectiveness of the procedure is demonstrated by numerical examples.

Noor, A. K.↗
NASA NTRS1986

Evaluation of three numerical methods for propulsion integration studies on transonic transport configurations

An effort has been undertaken at the NASA Langley Research Center to assess the capabilities of available computational methods for use in propulsion integration design studies of transonic transport aircraft, particularly of pylon/nacelle combinations which exhibit essentially no interference drag. The three computer codes selected represent state-of-the-art computational methods for analyzing complex configurations at subsonic and transonic flight conditions. These are: EULER, a finite volume solution of the Euler equation; VSAERO, a panel solution of the Laplace equation; and PPW, a finite difference solution of the small disturbance transonic equations. In general, all three codes have certain capabilities that allow them to be of some value in predicting the flows about transport configurations, but all have limitations. Until more accurate methods are available, careful application and interpretation of the results of these codes are needed.

Yaros, Steven F.↗
NASA NTRS1987

Vibration analysis of quasi-symmetric structures

A computational technique is developed to reduce the size of the dynamical model of a large complex quasi-symmetric structure prior to free vibration analysis. The structure is discretized using a two-field mixed FEM model; the response vectors are decomposed into symmetric and antisymmetric components; the eigenvectors of the quasi-symmetric structure are approximated by a linear combination of a few preselected sets of symmetric and antisymmetric modes generated by the reduced-size model; global approximation vectors are selected and generated; and the resulting eigenvalue problem is significantly reduced via a classical Bubnov-Galerkin procedure. Numerical results for a shallow laminated anisotropic panel of quadrilateral planform are presented in extensive tables and graphs, demonstrating the effectiveness of the method.

Noor, Ahmed K.↗
NASA NTRS2001

Fuzzy Structures Analysis of Aircraft Panels in NASTRAN

This paper concerns an application of the fuzzy structures analysis (FSA) procedures of Soize to prototypical aerospace panels in MSC/NASTRAN, a large commercial finite element program. A brief introduction to the FSA procedures is first provided. The implementation of the FSA methods is then disclosed, and the method is validated by comparison to published results for the forced vibrations of a fuzzy beam. The results of the new implementation show excellent agreement to the benchmark results. The ongoing effort at NASA Langley and Penn State to apply these fuzzy structures analysis procedures to real aircraft panels is then described.

Sparrow, Victor W.↗