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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 NTRS2009

Prediction of Material Properties of Nanostructured Polymer Composites Using Atomistic Simulations

Atomistic models of epoxy polymers were built in order to assess the effect of structure at the nanometer scale on the resulting bulk properties such as elastic modulus and thermal conductivity. Atomistic models of both bulk polymer and carbon nanotube polymer composites were built. For the bulk models, the effect of moisture content and temperature on the resulting elastic constants was calculated. A relatively consistent decrease in modulus was seen with increasing temperature. The dependence of modulus on moisture content was less consistent. This behavior was seen for two different epoxy systems, one containing a difunctional epoxy molecule and the other a tetrafunctional epoxy molecule. Both epoxy structures were crosslinked with diamine curing agents. Multifunctional properties were calculated with the nanocomposite models. Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between the carbon nanotube and the surrounding epoxy matrix. These estimated values were used in a multiscale model in order to predict the thermal conductivity of a nanocomposite as a function of the nanometer scaled molecular structure.

Hinkley, J.A.↗
NASA NTRS2017

The Impact of Ocular Pressures, Material Properties and Geometry on Optic Nerve Head Deformation

Alteration in intracranial pressure (ICP) has been associated with various diseases that cause visual impairment, including glaucoma, idiopathic intracranial hypertension and Visual Impairment and Intracranial Pressure (VIIP) syndrome. However, how changes in ICP lead to vision loss is unclear, although it is hypothesized to involve deformations of the tissues in the optic nerve head (ONH). Recently, understanding the effect of ICP alterations on ocular tissues has become a major concern for NASA, where 42 of astronauts that partake in long duration space missions suffer from VIIP syndrome. Astronauts with VIIP syndrome suffer from visual impairment and changes in ocular anatomy that persist after returning to earth (1). It is hypothesized that the cephalad fluid shift that occurs upon entering microgravity increases ICP, which leads to an altered biomechanical environment in the posterior globe and optic nerve sheath, and subsequently VIIP syndrome. Our goal was to develop a finite element (FE) model to simulate the acute effects of elevated ICP on the posterior eye. Here, we simulated how inter-individual differences affect the deformation of ONH tissues. Further, we examined how several different geometries influenced deformations when exposed to elevated ICP.

mathematical models↗
NASA NTRS2018

SiAl Alloy Feedhorn Arrays: Material Properties, Feedhorn Design, and Astrophysical Applications

We present here a study of the use of the SiAl alloy CE7 for the packaging of silicon devices at cryogenic temperatures. We report on the development of baseplates and feedhorn arrays for millimeter wave bolometric detectors for astrophysics. Existing interfaces to such detectors are typically made either of metals, which are easy to machine but mismatched to the thermal contraction profile of Si devices, or of silicon, which avoids the mismatch but is difficult to directly machine. CE7 exhibits properties of both Si and Al, which makes it uniquely well suited for this application. We measure CE7 to a) superconduct below a critical transition temperature, T (sub c), 1.2 K, b) have a thermal contraction profile much closer to Si than metals, which enables simple mating, and c) have a low thermal conductivity which can be improved by Au-plating. Our investigations also demonstrate that CE7 can be machined well enough to fabricate small structures, such as #0-80 threaded holes, to tight tolerances (approximately 25 microns) in contrast with pure silicon and similar substrates. We have fabricated CE7 baseplates being deployed in the 93 gigahertz polarimetric focal planes used in the Cosmology Large Angular Scale Surveyor (CLASS). We also report on the development of smooth-walled feedhorn arrays made of CE7 that will be used in a focal plane of dichroic 150/220 gigahertz detectors for the CLASS High-Frequency camera.

Ali, Aamir M.↗
NASA NTRS2021

Hypervelocity Impact Study for Migration from Kevlar® KM2® 705 to KM2® Plus 775: Material Property Measurement and Evaluation as a Ballistic Enhancement in Whipple Shields

Dupont™, the manufacturer of Kevlar®, has begun migrating from KM2® to KM2® Plus for ballistic textiles. Kevlar® KM2® has become an essential element of numerous meteoroid and orbital debris (MMOD) shield systems primarily as a multi-layer insulation (MLI) enhancement, and as such, the migration has implications for numerous system level risk assessments for future vehicles that will need to use the newer KM2® Plus fiber system. While the chemical makeup of the two fabrics are identical, differences in processing have yielded higher tenacities and toughness for the KM2® Plus system. To address this migration, the Hypervelocity Impact Technology (HVIT) group in NASA Exploration Sciences at Johnson Space Center (JSC) has worked with the NASA Engineering and Safety Center (NESC), the Multi-Purpose Crew Vehicle (MPCV) and the MPCV European Service Module (MPCV-ESM) group of the European Space Agency (ESA) with its contractors Airbus and Thales Alenia Space-Italy (TAS-I) to study how KM2® Plus in the woven form of 850 denier 775 compares with KM2® in the woven form of 850 denier 705. The two forms of Kevlar® fabrics have been compared by direct-impact with a known mass and as the rear wall in Whipple shields using the two-stage, light-gas-gun at the Remote Hypervelocity Test Laboratory (RHTL) of NASA JSC White Sands Test Facility (WSTF). From these examinations, it has been found that KM2® Plus does in fact improve the ballistic performance as a ballistic enhancement of MLI with an estimated improvement of 9.5±6.1% between the two fabrics, and on a mass basis, the estimated mass of KM2® Plus 775 is 3.6±0.7% lighter than KM2 705, which means the mass performance improvement is even higher.

Joshua E Miller↗
NASA NTRS2022

SiAl Composite Feedhorn Arrays for Astrophysical Applications: Cryogenic Material Properties

A study investigating the physical properties and use of the SiAl composite Controlled Expansion 7 (CE7) for the packaging of silicon bolometric detectors for millimeter-wave astrophysical applications at cryogenic temperatures is presented. The existing interfaces to such detectors are typically made of either ductile metals or micro-machined silicon. As a composite of Si and Al, we find that CE7 exhibits properties of both in ways that may be advantageous for this application. This exploration of the physical properties of CE7 reveals: (a) superconductivity below a critical transition temperature, T_c ∼ 1.2 K; (b) a thermal contraction profile much closer to Si than metal substrates; (c) the relatively low thermal conductivity anticipated for a superconductor, which can be improved by Au-plating; and (d) the feasibility of machining mechanical features with tolerances of ∼25 µm. We further discuss the use of CE7 in the cosmology large angular scale surveyor telescope array, which deployed CE7 in several of its detector focal planes.

Aamir M. Ali↗
NASA NTRS1976

Review of world experience and properties of materials for encapsulation of terrestrial photovoltaic arrays

Published and unpublished information relating to encapsulation systems and materials properties was collected by searching the literature and appropriate data bases (over 1,300 documents were selected and reviewed) and by personal contacts including site and company visits. A data tabulation summarizing world experience with terrestrial photovoltaic arrays (50 installations) is presented in the report. Based on criteria of properties, processability, availability, and cost, candidate materials were identified which have potential for use in encapsulation systems for arrays with a lifetime of over 20 years high reliability, an efficiency greater than 10 percent, a total price less than $500/kW, and a production capacity of 500,000 kW/yr. The recommended materials (all commercially available) include, depending upon the device design, various borosilicate and soda-lime glasses and numerous polymerics suitable for specific encapsulation system functions.

Carmichael, D. C.↗
NASA NTRS2014

Using SpaceClaimTD Direct for Modeling Components with Complex Geometries for the Thermal Desktop-Based Advanced Stirling Radioisotope Generator Model

SpaceClaim/TD Direct has been used extensively in the development of the Advanced Stirling Radioisotope Generator (ASRG) thermal model. This paper outlines the workflow for that aspect of the task and includes proposed best practices and lessons learned. The ASRG thermal model was developed to predict component temperatures and power output and to provide insight into the prime contractor's thermal modeling efforts. The insulation blocks, heat collectors, and cold side adapter flanges (CSAFs) were modeled with this approach. The model was constructed using mostly TD finite difference (FD) surfaces/solids. However, some complex geometry could not be reproduced with TD primitives while maintaining the desired degree of geometric fidelity. Using SpaceClaim permitted the import of original CAD files and enabled the defeaturing/repair of those geometries. TD Direct (a SpaceClaim add-on from CRTech) adds features that allowed the "mark-up" of that geometry. These so-called "mark-ups" control how finite element (FE) meshes are to be generated through the "tagging" of features (e.g. edges, solids, surfaces). These tags represent parameters that include: submodels, material properties, material orienters, optical properties, and radiation analysis groups. TD aliases were used for most tags to allow analysis to be performed with a variety of parameter values. "Domain-tags" were also attached to individual and groups of surfaces and solids to allow them to be used later within TD to populate objects like, for example, heaters and contactors. These tools allow the user to make changes to the geometry in SpaceClaim and then easily synchronize the mesh in TD without having to redefine the objects each time as one would if using TDMesher. The use of SpaceClaim/TD Direct helps simplify the process for importing existing geometries and in the creation of high fidelity FE meshes to represent complex parts. It also saves time and effort in the subsequent analysis.

Power Systems↗
NASA NTRS2014

Using SpaceClaim/TD Direct for Modeling Components with Complex Geometries for the Thermal Desktop-Based Advanced Stirling Radioisotope Generator Model

SpaceClaim/TD Direct has been used extensively in the development of the Advanced Stirling Radioisotope Generator (ASRG) thermal model. This paper outlines the workflow for that aspect of the task and includes proposed best practices and lessons learned. The ASRG thermal model was developed to predict component temperatures and power output and to provide insight into the prime contractors thermal modeling efforts. The insulation blocks, heat collectors, and cold side adapter flanges (CSAFs) were modeled with this approach. The model was constructed using mostly TD finite difference (FD) surfaces solids. However, some complex geometry could not be reproduced with TD primitives while maintaining the desired degree of geometric fidelity. Using SpaceClaim permitted the import of original CAD files and enabled the defeaturing repair of those geometries. TD Direct (a SpaceClaim add-on from CRTech) adds features that allowed the mark-up of that geometry. These so-called mark-ups control how finite element (FE) meshes were generated and allowed the tagging of features (e.g. edges, solids, surfaces). These tags represent parameters that include: submodels, material properties, material orienters, optical properties, and radiation analysis groups. TD aliases were used for most tags to allow analysis to be performed with a variety of parameter values. Domain-tags were also attached to individual and groups of surfaces and solids to allow them to be used later within TD to populate objects like, for example, heaters and contactors. These tools allow the user to make changes to the geometry in SpaceClaim and then easily synchronize the mesh in TD without having to redefine these objects each time as one would if using TD Mesher.The use of SpaceClaim/TD Direct has helped simplify the process for importing existing geometries and in the creation of high fidelity FE meshes to represent complex parts. It has also saved time and effort in the subsequent analysis.

Power Systems↗
NASA NTRS2006

Numerical Evaluation of Mode 1 Stress Intensity Factor as a Function of Material Orientation For BX-265 Foam Insulation Material

Foam; a cellular material, is found all around us. Bone and cork are examples of biological cell materials. Many forms of man-made foam have found practical applications as insulating materials. NASA uses the BX-265 foam insulation material on the external tank (ET) for the Space Shuttle. This is a type of Spray-on Foam Insulation (SOFI), similar to the material used to insulate attics in residential construction. This foam material is a good insulator and is very lightweight, making it suitable for space applications. Breakup of segments of this foam insulation on the shuttle ET impacting the shuttle thermal protection tiles during liftoff is believed to have caused the space shuttle Columbia failure during re-entry. NASA engineers are very interested in understanding the processes that govern the breakup/fracture of this complex material from the shuttle ET. The foam is anisotropic in nature and the required stress and fracture mechanics analysis must include the effects of the direction dependence on material properties. Material testing at NASA MSFC has indicated that the foam can be modeled as a transversely isotropic material. As a first step toward understanding the fracture mechanics of this material, we present a general theoretical and numerical framework for computing stress intensity factors (SIFs), under mixed-mode loading conditions, taking into account the material anisotropy. We present mode I SIFs for middle tension - M(T) - test specimens, using 3D finite element stress analysis (ANSYS) and FRANC3D fracture analysis software, developed by the Cornel1 Fracture Group. Mode I SIF values are presented for a range of foam material orientations. Also, NASA has recorded the failure load for various M(T) specimens. For a linear analysis, the mode I SIF will scale with the far-field load. This allows us to numerically estimate the mode I fracture toughness for this material. The results represent a quantitative basis for evaluating the strength and fracture properties of anisotropic foam insulation material.

Knudsen, Erik↗