SEARCH · Engineering Papers
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.
Polyurethane foamable mixture remains inert in storage unit activated to produce a rapid foaming reaction. The storage-stable foamable composition is spread as a paste on the surface of an expandable structure and, when heated, yields a rigid open-cell polyurethane foam that is self-bondable to the substrate.
An embodiment includes a system comprising: a monolithic shape memory polymer (SMP) foam having first and second states; wherein the SMP foam includes: (a) polyurethane, (b) an inner half portion having inner reticulated cells defined by inner struts, (c) an outer half portion, having outer reticulated cells defined by outer struts, surrounding the inner portion in a plane that provides a cross-section of the SMP foam, (d) hydroxyl groups chemically bound to outer surfaces of both the inner and outer struts. Other embodiments are discussed herein.
An embodiment includes a system comprising: a monolithic shape memory polymer (SMP) foam having first and second states; wherein the SMP foam includes: (a) polyurethane, (b) an inner half portion having inner reticulated cells defined by inner struts, (c) an outer half portion, having outer reticulated cells defined by outer struts, surrounding the inner portion in a plane that provides a cross-section of the SMP foam, (d) hydroxyl groups chemically bound to outer surfaces of both the inner and outer struts. Other embodiments are discussed herein.
Nondestructive test methods are used for evaluating bond integrity of low-density polyurethane spray-on foam used as cryogenic insulation on aluminum alloy surfaces.
The Aerospace industry has a long history of using low density polyurethane and polyurethane-modified isocyanurate foam systems as lightweight, low cost, easily processed cryogenic Thermal Protection Systems (TPS) for ascent vehicles. The Thermal Protection System of the Space Shuttle External Tank (ET) is required so that quality liquid cryogenic propellant can be supplied to the Orbiter main engines and to protect the metal structure of the tanks from becoming too hot from aerodynamic heating, hence preventing premature break-up of the tank. These foams are all blown with CFC-1 I blowing agent which has been identified by the Environmental Protection Agency (EPA) as an ozone depleting substance. CFCs will not be manufactured after 1995, Consequently, alternate blowing agent substances must be identified and implemented to assure continued ET manufacture and delivery. This paper describes the various testing performed to select and qualify HCFC-1 41 b as a near term drop-in replacement for CFC-11. Although originally intended to be a one for one substitution in the formulation, several technical issues were identified regarding material performance and processability which required both formulation changes and special processing considerations to overcome. In order to evaluate these material changes, each material was subjected to various tests to qualify them to meet the various loads imposed on them during long term storage, pre-launch operations, launch, separation and re-entry. Each material was tested for structural, thermal, aeroshear, and stress/strain loads for the various flight environments each encounters. Details of the development and qualification program and the resolution of specific problems are discussed in this paper.
In situ synchrotron X-ray microtomography was used to characterize the bulk deformation behavior by computing the Poisson's ratio of expanded thermoplastic polyurethane (eTPU) molded bead foams used in footwear midsole during compression. Quantitative data on morphological characteristics were obtained using an iterative image processing workflow. Image correlation on the 4D datasets using DVC was performed to calculate the volumetric and axial strain to estimate the Poisson ratio. Strain maps from DVC showed the influence of variability in ligament thickness distribution on the global mechanical behavior exhibited which dominated the response seen in these bead foams. Lastly, our results showed a strong correlation between Poisson ratio and distribution of ligament thickness in foams.
The selection and quantification of four foams using a more environmentally friendly HCFC-141b blowing agent replacing foams that used the CFC-11 blowing agent for the external tank (ET) LWT has been addressed along with problems and solutions that were encountered during verification. The effort on two lower density spray foams for the ET SLWT are presented, but predicted weight savings were not encouraging. Suggestions for possible problem solving are included along with a new approach for selecting foams for qualification as back-up foams for the foams used on the ET LWT. We investigated three resins for use as thermally sprayed coatings for corrosion prevention on metal. The best coating was obtained with a thermoplastic polyimide resin. This coating has a good chance of meeting ET requirements. Possible third generation blowing agents have been shown usable in polyurethane spray and pour foams, and solubility in isocyannate foam components are acceptable. We considered aerogels as insulation materials on space vehicles, and suggested a liner for a liquid oxygen (LOX) composite tank.
In this study, nineteen unmodified lignins from various sources (hardwood, softwood, wheat straw, and corn stover) and isolation processes (kraft, soda, organosolv, sulfite, and enzymatic hydrolysis) were used to replace 30 wt.% of petroleum-based polyol in rigid polyurethane/polyisocyanurate (PUR/PIR) foam formulations. Lignin samples were characterized by measuring their ash content, hydroxyl content (Phosphorus Nuclear Magnetic Resonance Spectroscopy), impurities (Inductively Coupled Plasma), and pH. After foam formulation, properties of lignin-based foams were evaluated and compared with a control foam (with no lignin) via cell morphology, closed-cell content, compression strength, apparent density, thermal conductivity, and color analysis. Lignin-based foams passed all measured standard specifications required by ASTM International C1029-15 for type 1 rigid insulation foams, except for three foams. These three foams had poor compressive strengths, significantly larger cell sizes, darker color, lower closed-cell contents, and slower foaming times. The foam made with corn stover enzymatic hydrolysis lignin showed no significant difference from the control foam in terms of compressive strength and outperformed all other lignin-based foams due to its higher aliphatic and p-hydroxyphenyl hydroxyl contents. Lignin-based foams that passed all required performance testing were made with lignins having higher pH, potassium, sodium, calcium, magnesium, and aliphatic/p-hydroxyphenyl hydroxyl group contents than those that failed.
The paper considers the selection of cushioning foam and upholstery fabric materials for aircraft passenger seats. Polyurethane, polychloroprene, polyimide, and polyphosphazene are the foam materials considered; and a variety of commercial and developmental fabrics (including wool, cotton, synthetics, and blends) are examined. Viable approaches to the design of fire-resistant seat assemblies are indicated. Results of an experimental laboratory study of fabrics and fabric/foam assemblies exposed to external point-source radiative heat flux are discussed.
Suitable reference materials need to be selected in order to standardize any test method. The evaluation of cotton, polyethylene, polyether sulfone, polycarbonate, polystyrene, and polyurethane flexible and rigid foams as possible reference materials for the University of San Francisco/NASA toxicity screening test method is discussed.
A simple laboratory method for determining flash fire propensity of materials is described. The apparatus consists of a tube furnace and a combustion tube. The ignition source can be a wooded match but the hot pyrolysis tube itself may be the most suitable ignition source. Test results are presented for various materials including polyethylene, polystyrene, polycarbonate, and polyurethane and polychloroprene flexible foams.
A sprayable aerogel insulation has been developed that has good mechanical integrity and lower thermal conductivity than incumbent polyurethane spray-on foam insulation, at similar or lower areal densities, to prevent insulation cracking and debonding in an effort to eliminate the generation of inflight debris. This new, lightweight aerogel under bead form can be used as insulation in various thermal management systems that require low mass and volume, such as cryogenic storage tanks, pipelines, space platforms, and launch vehicles.
Testing was completed on the Structural Heat Intercept, Insulation, and Vibration Evaluation Rig (SHIIVER) between August 2019 and January 2020. SHIIVER was designed to be a test bed for the scaling of cryogenic fluid management technologies as applied to large upper stages and long duration in-space stages. The baseline SHIIVER design consists of uninsulated structural skirts attached to a propellant tank insulated with polyurethane Spray-On Foam Insulation (SOFI). The initial testing of the SHIIVER hardware was with liquid hydrogen and sought to demonstrate the use of boil-off vapor to intercept heat on a structural skirt, multilayer insulation (MLI) on the tank domes, and the radio frequency mass gauge (RFMG). Testing was completed in four stages: a baseline thermal vacuum test prior to installation of the MLI on the tank domes, a thermal vacuum test after the MLI installation, a reverberant acoustic test, and a subsequent thermal vacuum test to verify that no damage occurred during the reverberant acoustic testing. Each thermal vacuum test with chamber wall at ambient temperature and vacuum level in the 10-6 torr range was conducted continuously between approximately 90% full and 25% full. Test results showed that the vapor cooling reduced the heat load to the tank by approximately 10%, but the boil-off by less than 3% at 50% full, with and without MLI installed on the domes. The MLI installed on the domes reduced the heat load to the tank by approximately 40% at all fill levels, but the boil-off by approximately 25% at 90% full and 45% below 65% full. The RFMG performed well over all fill ranges, and several RF tank modes were used to gauge the mass of fluid in the tank. SHIIVER was then exposed to an acoustic environment of 147 dB OASPL (overall sound pressure level) in a reverberant chamber. The acoustic environment envelopes the upper stage internal acoustic level of several different modern launch vehicles. No structural or thermal performance changes were observed after exposure to the acoustic environment. Final thermal vacuum testing after the acoustic testing showed no degradation to the MLI due to the acoustic environment as measured via system heat loads
Application of Polyurethane Science and Engineering to reduce ALARA conditions while securing Low Level Waste (LLW) loads for shipment within and between locations within the DOE complex. Potential reduction in cost as well. Interdepartmental collaborative efforts between new hires was established.
Lightweight polyurethane insulation for liquid hydrogen tanks of space vehicles
Fillers and pore formers are used in many materials at Kansas City National Security Campus (KCNSC) to fine tune density and stiffness. Current off-the-shelf options such as urea and Expancel do not always provide the desired properties. This project investigated several methods for introducing porosity in rigid polymers such as epoxy and polyurethane. This work was done at partnering universities to identify a variety of methods to create porous polymeric materials. The University of Oklahoma (OU) investigated emulsion templating of epoxy, where the epoxy is mixed with a surfactant and water to form an emulsion. The emulsion is then molded and cured. During the cure process, water droplets evaporate to form porous structures. Total porosity can be tuned by changing the concentration of water added to the polymer. The University of Kansas (KU) investigated the synthesis of phenolic microballoons by spray drying, as well as methods of incorporating removable porogens into epoxy and polyurethane materials to create polymeric foams.
Foamable materials which can be readily decomposed to yield inert gas in a precise and moderate temperature range are desirable for applications in nuclear waste storage and securement during transportation. In the proposed work, promising lead candidates for such foams were identified from extant peer-reviewed literature, and initial samples synthesized and characterized.
The overall objective of this project is to measure the fire signatures of typical spacecraft materials in 1-g and determine how these signatures may be altered in a microgravity environment. During this project, we will also develop a test technique to obtain representative low-gravity signatures. The specific tasks that will be accomplished to achieve these objectives are to: (1) measure the time history of various fire signatures of typical spacecraft materials in 1-g at varying heating rates, temperatures, convective velocities, and oxygen concentrations, (2) conduct tests in the Zero-Gravity Facility at NASA John H. Glenn Research Center to investigate the manner that a microgravity environment alters the fire signature,(3) compare 0-g and 1-g time histories and determine if 0-g data exhibits the same dependence on the test parameters as experienced in 1-g (4) develop a 1-g test technique by which 0-g fire signatures can be measured. The proposed study seeks to investigate the differences in the identities and relative concentrations of the volatiles produced by pyrolyzing and/or smoldering materials between normal gravity and microgravity environments. Test materials will be representative of typical spacecraft materials and, where possible, will be tested in appropriate geometries. Wire insulation materials of Teflon, polyimide, silicone, and PVC will be evaluated using either cylindrical samples or actual wire insulation. Other materials such as polyurethane, polyimide, melamine, and silicone-based foams will be tested using cylindrical samples, in addition to fabric materials, such as Nomex. Electrical components, such as resistors, capacitors, circuit board will also be tested.