Search NASA⌕ Search

SEARCH · Search NASA

Results for “graphite modeling”

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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Observational constraints on interstellar dust models

No single model has been able to account for all of the observed spectroscopic properties of interstellar or circumstellar dust. The reason for this is that, despite the agreement that the grains are composed of silicaceous/metal oxide and carbonaceous material, there is strong disagreement as to their exact structure and composition. This led Draine and Lee (1984) to use interstellar extinction data to define an interstellar graphitic material; new observational findings have made even that identification uncertain. But the great advantage of their approach is that they used observations at all of the wavelengths available to define the material. Here, the authors attempt a variation of that approach. They examine recent UV and IR data and attempt to put constraints on the possible types of interstellar grain composition, and to connect these constraints with grain models. A summary of some of the important constraints imposed by the observations is given.

Hecht, James H.↗
NASA NTRSDate not supplied

Towards Quantifying and Correlating RTV Intumescence to Entry-Relevant Conditions

Room Temperature Vulcanizing silicone (RTV) is a high-temperature adhesive used as a gap-filler between Thermal Protection System (TPS) tiles for heatshields on numerous missions. It is also adopted to bond instrumentation plugs of temperature and pressure sensors into heatshield’s tiles. While RTV has been traditionally assumed to be a non-porous and non-ablating material, numerous experiments have shown that RTV pyrolyzes and becomes highly porous as it is heated. Experimental data has also shown heating rate-dependent swelling (or intumescence) and shrinking of RTV, these volume changes may cause roughness-induced boundary layer transition. Outgassing and surface oxide formation of RTV upon decomposition also occur, which can be sources of contamination of heat shield sensors. This combination of detrimental effects motivates a critical need to develop a high-fidelity model for RTV ablation. As a first critical step in RTV modeling, a comprehensive material properties database for RTV was collected that account for the lack of data in properties such as pyrolysis char yield, shape change, virgin and char porosity. The next step is to quantify the volume change of RTV as a function of temperature. While this was done in previous campaigns, limited data was collected which showed a possible heating rate dependent intumescent behavior. To further understand the intumescence phenomenon of RTV, numerous dedicated experiments were performed at Beamline 8.3.2 of the Advanced Light Source, where RTV samples were heated while X-ray scans were taken in situ. Micro-Computed Tomography scans were taken in situ for low heating rates (≤ 60 °C/min), whereas continuous radiography scans were taken for higher heating rates (≤ 1500 ºC/min). Unconstrained samples and samples constrained in different holders (quartz, graphite, FiberForm and PICA) were tested to determine the change in intumescence due to confinement. Using deep learning techniques, the tomographies and radiographies are segmented to obtain volume change, porosity, pore size distributions and connectivity. From the results obtained, modifications to the previous RTV intumescence model are proposed, along with preliminary comparisons to testing RTV at high-enthalpy facilities.

RTV↗
NASA NTRS1990

Analytical and experimental study of the vibration of bonded beams with a lap joint

A theoretical model to study the flexural vibration of a bonded lap joint system is described in this paper. First, equations of motion at the joint region are derived using a differential element approach. The transverse displacements of the upper and lower beam are considered to be different. The adhesive is assumed to be linearly viscoelastic and the widely used Kelvin-Voight model is used to represent the viscoelastic behavior of the adhesive. The shear force at the interface between the adhesive and the beam is obtained from the simple bending motion equations of the two beams. The resulting equations of motion are combined with the equations of transverse vibration of the beams in the unjointed regions. These are later solved as a boundary value problem to obtain the eigenvalues and eigenvectors of the system. The model can be used to predict the natural frequencies, modal damping ratios, and mode shapes of the system for free vibration. Good agreement between numerical and experimental results was obtained for a system of graphite epoxy beams lap-jointed by an epoxy adhesive.

Rao, M. D.↗
NASA NTRS1992

Experimental and analytical study of the effects of floor location on response of composite fuselage frames

Experimental and analytical results are presented of the effects of floor placement on the structural response and strength of I-cross section, semi-circular fuselage frames constructed of graphite-epoxy composite material. The composite frame configuration is representative of current conventional aircraft design. Experimental strain distributions are presented from static loading tests of the composite frames and compared with finite element structural models and closed form solutions. An understanding of floor location effects can aid dynamists in predicting the crash behavior of these conventional structures, and may assist the designer in developing crashworthy structures for future aircraft.

Jones, Lisa E.↗
NASA NTRS2003

Transmission measurement based on STM observation to detect the penetration depth of low-energy heavy ions in botanic samples

The penetration depth of low-energy heavy ions in botanic samples was detected with a new transmission measurement. In the measurement, highly oriented pyrolytic graphite (HOPG) pieces were placed behind the botanic samples with certain thickness. During the irradiation of heavy ions with energy of tens of keV, the energetic particles transmitted from those samples were received by the HOPG pieces. After irradiation, scanning tunneling microscope (STM) was applied to observe protrusion-like damage induced by these transmitted ions on the surface of the HOPG. The statistical average number density of protrusions and the minimum transmission rate of the low-energy heavy ions can be obtained. The detection efficiency of the new method for low-energy heavy ions was about 0.1-1 and the background in the measurement can be reduced to as low as 1.0 x 10(8) protrusions/cm2. With this method, the penetration depth of the energetic particles was detected to be no less than 60 micrometers in kidney bean slices when the slices were irradiated by 100 keVAr+ ion at the fluence of 5 x 10(16) ions/cm2. c2002 Elsevier Science Ltd. All rights reserved.

DNA Damage↗
NASA NTRS1990

Free vibrations of thin-walled semicircular graphite-epoxy composite frames

A detailed study is made of the effects of variations in lamination and material parameters of thin walled composite frames on their vibrational characteristics. The structures considered are semicircular thin walled frames with I and J sections. The flanges and webs of the frames are modeled by using 2-D shell and plate finite elements. A mixed formulation is used with the fundamental unknowns consisting of both the generalized displacements and stress resultants in the frame. The frequencies and modes predicted by the 2-D finite element model are compared with those obtained from experiments, as well as with the predictions of a non-dimensional thin walled beam finite element model. A detailed study is made of the sensitivity of the vibrational response to variations in the fiber orientation, material properties of the individual layers, and boundary conditions.

Carden, Huey D.↗
NASA NTRS1990

Free vibrations of thin-walled semicircular graphite-epoxy composite frames

A detailed study is made of the effects of variations in lamination and material parameters of thin walled composite frames on their vibrational characteristics. The structures considered are semicircular thin walled frames with I and J sections. The flanges and webs of the frames are modelled by using 2-D shell and plate finite elements. A mixed formulation is used with the fundamental unknowns consisting of both the generalized displacements and stress resultants in the frames. The frequencies and modes predicted by the 2-D finite element model are compared with those obtained from experiments, as well as with the predictions of a 1-D thin walled beam finite element model. A detailed study is made of the sensitivity of the vibrational response to variations in the fiber orientation, material properties of the individual layers, and boundary conditions.

Noor, Ahmed K.↗
NASA NTRS1990

Free vibrations of thin-walled semicircular graphite-epoxy composite frames

A detailed study is made of the effects of variations in lamination and material parameters of thin walled composite frames on their vibrational characteristics. The structures considered are semicircular thin walled frames with I and J sections. The flanges and webs of the frames are modeled by using 2-D shell and plate finite elements. A mixed formulation is used with the fundamental unknowns consisting of both the generalized displacements and stress resultants in the frame. The frequencies and modes predicted by the 2-D finite element model are compared with those obtained from experiments, as well as with the predictions of a non-dimensional thin walled beam finite element model. A detailed study is made of the sensitivity of the vibrational response to variations in the fiber orientation, material properties of the individual layers, and boundary conditions.

Carden, Huey D.↗
DOE OSTI2025

The HTR-Proteus Benchmark: Analysis and Use as a Verification and Validation Case

This presentation outlines the evaluation and application of the HTR-Proteus benchmark as a verification and validation (V&V) case for advanced reactor modeling tools. The work supports the U.S. Department of Energy’s HALEU Availability Program (HAP) and the joint DOE/NRC DNCSH project, which aims to reduce criticality safety uncertainties in commercial-scale HALEU fuel cycle and transportation systems. The HTR-Proteus experiments, conducted at the Paul Scherrer Institute, provide high-fidelity data for TRISO-fueled, graphite-moderated pebble bed reactors with high neutron leakage—conditions relevant to HALEU transport scenarios. This study focuses on Cores 4.2 and 4.3 of the HTR-Proteus benchmark, analyzing key sources of uncertainty including pebble packing, TRISO particle positioning, and core height. Using Project Chrono for realistic pebble geometries and Serpent, SHIFT, and MCNP for neutronics simulations, the study quantifies the impact of these uncertainties on the effective multiplication factor (keff). Results show that a sample size of 110 pebble configurations is sufficient to converge keff, with ±30 pcm uncertainty due to packing randomness. TRISO positioning and core height variations also significantly influence keff, highlighting the importance of detailed modeling in V&V efforts. The benchmark serves as a valuable test case for validating the Griffin reactor physics code and improving confidence in HALEU system simulations.

73 - NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1990

Gravimetric measurements of materials outgassing applied to graphite-epoxy laminates

The outgassing rates of two graphite-epoxy laminates, American Cyanamide 985B-626 and HST-7B-112, were obtained using a gravimetric method. The rates as a function of time and temperature were derived from the measurements of their mass losses at temperatures varying from 25 to 150 C and for a time span of up to 400 hours in a vacuum. The data from those measurements were reduced to obtain the outgassing activation energies, the mass losses per unit mass or area, and the corresponding outgassing rates. The rates are expressed in closed-form equations and are directly usable for modeling computations. The procedures to obtain these parameters are shown and may be used for the evaluation of other materials. The results of the tests show that the activation energies of the two materials are: 4630 cal/mole for the 985B-626 materials and 4791 cal/mole for the HST-7B-112 sample no. 10 Graphite Epoxy. The outgassing rates of these materials are in the 1OE-5 g sq cm/hr range and they decay according to a power of time of 0.60 at 25 C, indicating that the outgassing process is mainly a diffusion at that temperature. The normalized mass losses versus time obtained from these tests were compared to the discrete results obtained from the ASTM-E595 tests. The comparison provides general indications on the effects of temperature and time in relation to the ASTM test values obtained at 125 C for a 24-hour test duration.

Scialdone, John J.↗
NASA NTRS1991

Analysis of delamination in cross ply laminates initiating from impact induced matrix cracking

Several two dimensional finite element analyses of (0 sub 2/90 sub 8/0 sub 2) glass/epoxy and graphite-epoxy composite laminates were performed to study some of the characteristics of damage development due to an impact load. A cross section through the thickness of the laminate with fixed ends, and carrying a transverse load in the center was analyzed. Inclined matrix cracks such as those produced by low velocity impact were modeled in the 90 deg ply group. The introduction of the matrix cracks caused large interlaminar tension and shear stresses in the vicinity of both crack tips in the 0/90 and 90/0 interfaces. The large interlaminar stresses at the ends of the matrix cracks indicate that matrix cracking may give rise to delamination. The ratio of mode I to total strain energy release rate at the beginning of delamination calculated at the two matrix crack tips was 60 and 28 pct., respectively, in the glass/epoxy laminate. The corresponding ratio was 97 and 77 pct. in the graphite-epoxy laminate. Thus, a significant mode I component of strain energy release rate may be present at the delamination initiation due to an impact load.

Salpekar, S. A.↗
NASA NTRS1996

Graphite Fiber Textile Preform/Copper Matrix Composites

Graphite fiber reinforced/copper matrix composites are candidate materials for critical heat transmitting and rejection components because of their high thermal conduction. The use of textile (braid) preforms allows near-net shapes which confers additional advantages, both for enhanced thermal conduction and increased robustness of the preform against infiltration and handling damage. Issues addressed in the past year center on the determination of the braid structure following infiltration, and the braidability vs. the conductivity of the fibers. Highly conductive fibers eventuate from increased graphitization, which increases the elastic modulus, but lowers the braidability; a balance between these factors must be achieved. Good quality braided preform bars have been fabricated and infiltrated, and their thermal expansion characterized; their analytic modeling is underway. The braided preform of an integral finned tube has been fabricated and is being prepared for infiltration.

Filatovs, G. J.↗
NASA NTRS1991

Free vibrations of thin-walled semicircular graphite-epoxy composite frames

A detailed study is made of the effects of variations in lamination and material parameters of thin-walled composite frames on their vibrational characteristics. The structures considered are semicircular thin-walled frames with I and J sections. The flanges and webs of the frames are modeled by using two-dimensional shell and plate finite elements. A mixed formulation is used with the fundamental unknowns consisting of both the generalized displacements and stress resultants in the frame. The frequencies and modes predicted by the two-dimensional finite-element model are compared with those obtained from experiments, as well as with the predictions of a one-dimensional, thin-walled-beam, finite-element model. A detailed study is made of the sensitivity of the vibrational response to variations in the fiber orientation, material properties of the individual layers, and boundary conditions.

Noor, Ahmed K.↗
NASA NTRS1986

A heater made from graphite composite material for potential deicing application

A surface heater was developed using a graphite fiber-epoxy composite as the heating element. This heater can be thin, highly electrically and thermally conductive, and can conform to an irregular surface. Therefore it may be used in an aircraft's thermal deicing system to quickly and uniformly heat the aircraft surface. One-ply of unidirectional graphite fiber-epoxy composite was laminated between two plies of fiber glass-epoxy composite, with nickel foil contacting the end portions of the composite and partly exposed beyond the composites for electrical contact. The model heater used brominated P-100 fibers from Amoco. The fiber's electrical resistivity, thermal conductivity and density were 50 micro ohms per centimeter, 270 W/m-K and 2.30 gm/cubic cm, respectively. The electricity was found to penetrate through the composite in the transverse direction to make an acceptably low foil-composite contact resistance. When conducting current, the heater temperature increase reached 50 percent of the steady state value within 20 sec. There was no overheating at the ends of the heater provided there was no water corrosion. If the foil-composite bonding failed during storage, liquid water exposure was found to oxidize the foil. Such bonding failure may be avoided if perforated nickel foil is used, so that the composite plies can bond to each other through the perforated holes and therefore lock the foil in place.

Hung, C. C.↗
NASA NTRS1987

A heater made from graphite composite material for potential deicing application

A surface heater was developed using a graphite fiber-epoxy composite as the heating element. This heater can be thin, highly electrically and thermally conductive, and can conform to an irregular surface. Therefore it may be used in an aircraft's thermal deicing system to quickly and uniformly heat the aircraft surface. One-ply of unidirectional graphite fiber-epoxy composite was laminated between two plies of fiber glass-epoxy composite, with nickel foil contacting the end portions of the composite and partly exposed beyond the composites for electrical contact. The model heater used brominated P-100 fibers from Amoco. The fiber's electrical resistivity, thermal conductivity and density were 50 micro ohms per centimenter, 270 W/m-K and 2.30 gm/cubic cm, respectively. The electricity was found to penetrate through the composite in the transverse direction to make an acceptably low foil-composite contact resistance. When conducting current, the heater temperature increase reached 50 percent of the steady state value within 20 sec. There was no overheating at the ends of the heater provided there was no water corrosion. If the foil-composite bonding failed during storage, liquid water exposure was found to oxidize the foil. Such bonding failure may be avoided if perforated nickel foil is used, so that the composite plies can bond to each other through the perforated holes and therefore lock the foil in place.

Hung, Ching-Cheh↗
NASA NTRS2001

Dynamic Finite Element Predictions for Mars Sample Return Cellular Impact Test #4

The nonlinear, transient dynamic finite element code, MSC.Dytran, was used to simulate an impact test of an energy absorbing Earth Entry Vehicle (EEV) that will impact without a parachute. EEVOs are designed to return materials from asteroids, comets, or planets for laboratory analysis on Earth. The EEV concept uses an energy absorbing cellular structure designed to contain and limit the acceleration of space exploration samples during Earth impact. The spherical shaped cellular structure is composed of solid hexagonal and pentagonal foam-filled cells with hybrid graphite-epoxy/Kevlar cell walls. Space samples fit inside a smaller sphere at the center of the EEVOs cellular structure. Pre-test analytical predictions were compared with the test results from a bungee accelerator. The model used to represent the foam and the proper failure criteria for the cell walls were critical in predicting the impact loads of the cellular structure. It was determined that a FOAM1 model for the foam and a 20% failure strain criteria for the cell walls gave an accurate prediction of the acceleration pulse for cellular impact.

Fasanella, Edwin L.↗
NASA NTRS2001

Thermal Analysis in Support of the Booster Separation Motor Crack Investigation

During a post-test inspection of a Booster Separation Motor (BSM) from a Lot Acceptance Test (LAT), a crack was noticed in the graphite throat. Since this was an out-of-family occurrence, an investigation team was formed to determine the cause of the crack. This paper will describe thermal analysis techniques used in support of this investigation. Models were generated to predict gradients in nominal motor conditions, as well as potentially anomalous conditions. Analysis was also performed on throats that were tested in the Laser Hardened Material Evaluation Laboratory (LHMEL). Some of these throats were pre-cracked, while others represented configurations designed to amplify effects of thermal stresses. Results from these analyses will be presented in this paper.

Davis, Darrell↗
NASA NTRS2002

Thermal Analysis in Support of the Booster Separation Motor Crack Investigation

During a post-test inspection of a Booster Separation Motor (BSM) from a Lot Acceptance Test (LAT), a crack was noticed in the graphite throat. Since this was an out-of-family occurrence, an investigation team was formed to determine the cause of the crack. This paper will describe thermal analysis techniques used in support of this investigation. Models were generated to predict gradients in nominal motor conditions, as well as potentially anomalous conditions. Analysis was also performed on throats that were tested in the Laser Hardened Material Evaluation Laboratory (LHMEL). Some of these throats were pre-cracked, while others represented configurations designed to amplify effects of thermal stresses. Results from these analyses will be presented in this paper.

Davis, Darrell↗