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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Crosslink Density and Molecular Weight Effects on the Viscoelastic Response of a Glassy High-Performance Polyimide

Durability and long-term performance are among the primary concerns for the use of advanced polymer matrix composites (PMCs) in modern aerospace structural applications. For a PMC subJected to long-term exposure at elevated temperatures. the viscoelastic nature of the polymer matrix will contribute to macroscopic changes in composite stiffness, strength and fatigue life. Over time. changes in the polymer due to physical aging will have profound effects on tile viscoelastic compliance of the material, hence affecting its long-term durability. Thus, the ability to predict material performance using intrinsic properties, such as crosslink density and molecular weight, would greatly enhance the efficiency of design and development of PMCs. The objective of this paper is to discuss and present the results of an experimental study that considers the effects of crosslink density, molecular weight and temperature on the viscoelastic behavior including physical aging of an advanced polymer. Five distinct variations in crosslink density were used to evaluate the differences in mechanical performance of an advanced polyimide. The physical aging behavior was isolated by conducting sequenced, short-term isothermal creep compliance tests in tension. These tests were performed over a range of sub-glass transition temperatures. The material constants, material master curves and physical aging-related parameters were evaluated as a function of temperature crosslink density and molecular weight using time-temperature and time-aging time superposition techniques.

Nicholson, Lee M.↗
NASA NTRS2001

High Temperature Polyimide Materials in Extreme Temperature Environments

At the end of the NASA High Speed Research (HSR) Program, NASA Langley Research Center (LaRC) began a program to screen the high-temperature Polymeric Composite Materials (PMCs) characterized by the HSR Durability Program for possible use in Reusable Launch Vehicles (RLVs) operating under extreme temperature conditions. The HSR Program focused on developing material-related technologies to enable a High Speed Civil Transport (HSCT) capable of operating temperatures ranging from 54 C (-65 F) to 177 C (350 F). A high-temperature polymeric resin, PETI-5 was used in the HSR Program to satisfy the requirements for performance and durability for a PMC. For RLVs, it was anticipated that this high temperature material would contribute to reducing the overall weight of a vehicle by eliminating or reducing the thermal protection required to protect the internal structural elements of the vehicle and increasing the structural strain limits. The tests were performed to determine temperature-dependent mechanical and physical proper-ties of IM7/PETI-5 composite over a temperature range from cryogenic temperature -253 C (-423F) to the material's maximum use temperature of 230 C (450 F). This paper presents results from the test program for the temperature-dependent mechanical and physical properties of IM7/PETI-5 composite in the temperature range from -253 C (-423 F) to 27 C (80 F).

Johnson, Theodore F.↗
NASA NTRS2001

Progressive Fracture of Composite Structures

This report includes the results of a research in which the COmposite Durability STRuctural ANalysis (CODSTRAN) computational simulation capabilities were augmented and applied to various structures for demonstration of the new features and verification. The first chapter of this report provides an introduction to the computational simulation or virtual laboratory approach for the assessment of damage and fracture progression characteristics in composite structures. The second chapter outlines the details of the overall methodology used, including the failure criteria and the incremental/iterative loading procedure with the definitions of damage, fracture, and equilibrium states. The subsequent chapters each contain an augmented feature of the code and/or demonstration examples. All but one of the presented examples contains laminated composite structures with various fiber/matrix constituents. For each structure simulated, damage initiation and progression mechanisms are identified and the structural damage tolerance is quantified at various degradation stages. Many chapters contain the simulation of defective and defect free structures to evaluate the effects of existing defects on structural durability.

Minnetyan, Levon↗
NASA NTRS2002

Flexible Wing Base Micro Aerial Vehicles: Composite Materials for Micro Air Vehicles

This paper will discuss the development of the University of Florida's Micro Air Vehicle concept. A series of flexible wing based aircraft that possess highly desirable flight characteristics were developed. Since computational methods to accurately model flight at the low Reynolds numbers associated with this scale are still under development, our effort has relied heavily on trial and error. Hence a time efficient method was developed to rapidly produce prototype designs. The airframe and wings are fabricated using a unique process that incorporates carbon fiber composite construction. Prototypes can be fabricated in around five man-hours, allowing many design revisions to be tested in a short period of time. The resulting aircraft are far more durable, yet lighter, than their conventional counterparts. This process allows for thorough testing of each design in order to determine what changes were required on the next prototype. The use of carbon fiber allows for wing flexibility without sacrificing durability. The construction methods developed for this project were the enabling technology that allowed us to implement our designs. The resulting aircraft were the winning entries in the International Micro Air Vehicle Competition for the past two years. Details of the construction method are provided in this paper along with a background on our flexible wing concept.

Ifju, Peter G.↗
NASA NTRS2002

Atomic Oxygen Protection of Materials in Low Earth Orbit

Spacecraft polymeric materials as well as polymer-matrix carbon-fiber composites can be significantly eroded as a result of exposure to atomic oxygen in low Earth orbit (LEO). Several new materials now exist, as well as modifications to conventionally used materials, that provide much more resistance to atomic oxygen attack than conventional hydrocarbon polymers. Protective coatings have also been developed which are resistant to atomic oxygen attack and provide protection of underlying materials. However, in actual spacecraft applications, the configuration, choice of materials, surface characteristics and functional requirements of quasi-durable materials or protective coatings can have great impact on the resulting performance and durability. Atomic oxygen degradation phenomena occurring on past and existing spacecraft will be presented. Issues and considerations involved in providing atomic oxygen protection for materials used on spacecraft in low Earth orbit will be addressed. Analysis of in-space results to determine the causes of successes and failures of atomic oxygen protective coatings is presented.

Banks, Bruce A.↗
NASA NTRS2002

Upper Temperature Limit of Environmental Barrier Coatings Based on Mullite and BSAS

Current state-of-the-art environmental barrier coatings (EBCs) for Si-based ceramics consist of three layers: a silicon bond coat, an intermediate mullite (3Al2O3-2SiO2) or mullite + BSAS (1-xBaO-xSrO-Al2O3-2SiO2) layer, and a BSAS top coat. Areas of concern for long-term durability are environmental durability, chemical compatibility, silica volatility, phase stability, and thermal conductivity. Variants of this family of EBCs were applied to monolithic SiC and melt infiltrated SiC/SiC composites. Reaction between BSAS and silica results in low melting (approx. 1300 C) glasses at T > 1400 C, which can cause the spallation of the EBC. At temperatures greater than 1400 C, the BSAS top coat also degrades by formation of a porous structure, and it suffers significant recession via silica volatilization in water vapor-containing atmospheres. All of these degradation mechanisms can be EBC life-limiting factors. BSAS undergoes a very sluggish phase transformation (hexagonal celsian to monoclinic celsian), the implications of which are not fully understood at this point. There was evidence of rapid sintering at temperatures as low as 1300 C, as inferred from the sharp increase in thermal conductivity.

Lee, Kang N.↗
NASA NTRS1995

Effect of Cyclic Aeroconvective Heating on Flexible Thermal Insulations

This paper describes the effect of cyclic aeroconvective heating on the thermal performance of ceramic flexible insulations considered for potential use as thermal protection systems or thermal insulations for future hypersonic vehicles such as the Reusable Launch Vehicles (RLV's) and other applications where structures require thermal protection from severe heating. The thermal response of these materials after exposure to cyclic aeroconvective heating from a plasma arc is described. The thermal insulations evaluated were Composite Flexible Blanket Insulations composed of an outer layer of aluminoborosilicate fabric and alumina insulation. The insulations were evaluated with and without a high emissivity coating. These insulations were exposed to the plasma arc stream for nine minutes reaching surface temperatures of 1150 C and a heat flux of 10.5 W/sq cm. Insulations were exposed three, six, or nine times in order to demonstrate reusability and to determine the effect oi coatings on the surface durability of these insulations. Test results demonstrated the capability of these insulations to protect either composite or metallic structures from high heating environments. It is shown that high emittance coatings reduce backface temperatures. The durability of these insulations when impacted at low velocities was also demonstrated. The interaction of the coatings with the ceramic fibers was characterized. An analytical thermal model was utilized to correlate experimental thermal test results with calculated values.

Kourtides, Demetrius A.↗
NASA NTRS2002

Robust Low Cost Liquid Rocket Combustion Chamber by Advanced Vacuum Plasma Process

Next-generation, regeneratively cooled rocket engines require materials that can meet high temperatures while resisting the corrosive oxidation-reduction reaction of combustion known as blanching, the main cause of engine failure. A project was initiated at NASA-Marshal Space Flight Center (MSFC) to combine three existing technologies to build and demonstrate an advanced liquid rocket engine combustion chamber that would provide a 100 mission life. Technology developed in microgravity research to build cartridges for space furnaces was utilized to vacuum plasma spray (VPS) a functional gradient coating on the hot wall of the combustion liner as one continuous operation, eliminating any bondline between the coating and the liner. The coating was NiCrAlY, developed previously as durable protective coatings on space shuttle high pressure fuel turbopump (HPFTP) turbine blades. A thermal model showed that 0.03 in. NiCrAlY applied to the hot wall of the combustion liner would reduce the hot wall temperature 200 F, a 20% reduction, for longer life. Cu-8Cr-4Nb alloy, which was developed by NASA-Glenn Research Center (GRC), and which possesses excellent high temperature strength, creep resistance, and low cycle fatigue behavior combined with exceptional thermal stability, was utilized as the liner material in place of NARloy-Z. The Cu-8Cr-4Nb material exhibits better mechanical properties at 650 C (1200 F) than NARloy-Z does at 538 C (1000 F). VPS formed Cu-8Cr-4Nb combustion chamber liners with a protective NiCrAlY functional gradient coating have been hot fire tested, successfully demonstrating a durable coating for the first time. Hot fire tests along with tensile and low cycle fatigue properties of the VPS formed combustion chamber liners and witness panel specimens are discussed.

Holmes, Richard↗
NASA NTRS2002

Thermal Conductivity and Sintering Behavior of Advanced Thermal Barrier Coatings

Advanced thermal barrier coatings, having significantly reduced long-term thermal conductivities, are being developed using an approach that emphasizes real-time monitoring of thermal conductivity under conditions that are engine-like in terms of temperatures and heat fluxes. This is in contrast to the traditional approach where coatings are initially optimized in terms of furnace and burner rig durability with subsequent measurement in the as-processed or furnace-sintered condition. The present work establishes a laser high-heat-flux test as the basis for evaluating advanced plasma-sprayed and physical vapor-deposited thermal barrier coatings under the NASA Ultra Efficient Engine Technology (UEET) Program. The candidate coating materials for this program are novel thermal barrier coatings that are found to have significantly reduced thermal conductivities due to an oxide-defect-cluster design. Critical issues for designing advanced low conductivity coatings with improved coating durability are also discussed.

Zhu, Dongming↗
NASA NTRS2002

Issues and Consequences of Atomic Oxygen Undercutting of Protected Polymers in Low Earth Orbit

Hydrocarbon based polymers that are exposed to atomic oxygen in low Earth orbit are slowly oxidized which results in recession of their surface. Atomic oxygen protective coatings have been developed which are both durable to atomic oxygen and effective in protecting underlying polymers. However, scratches, pin window defects, polymer surface roughness and protective coating layer configuration can result in erosion and potential failure of protected thin polymer films even though the coatings are themselves atomic oxygen durable. This paper will present issues that cause protective coatings to become ineffective in some cases yet effective in others due to the details of their specific application. Observed in-space examples of failed and successfully protected materials using identical protective thin films will be discussed and analyzed. Proposed approaches to prevent the failures that have been observed will also be presented.

Banks, Bruce A.↗
NASA NTRS1998

Tough Like Metal

Under an SBIR (Small Business Innovative Research) with Lewis Research Center, Advanced Ceramics Corporation developed a family of high temperature and doped boron nitride coating that offer improvement in interface durability of SiC/SiC composites. The new materials are 1,000 times more durable and greatly extend composite lifetimes. The development of this was commercialized with assistance from Lewis and Advanced Ceramic's own money and is supplying several composites manufacturers with new interface coating from an expanded in-line tow coating facility.

Source record↗
NASA NTRS2002

Characterization of C/SiC Ceramic Matrix Composites (CMCs) with Novel Interface Fiber Coatings

Ceramic Matrix Composites (CMCs) are attractive candidate aerospace materials due to their high specific strength, low density and high temperature capabilities. The National Aeronautics and Space Administration (NASA) is pursuing the use of CMC components in advanced Reusable Launch Vehicle (RLV) propulsion applications. Carbon fiber-reinforced silicon carbide (C/SiC) is the primary material of interest for a variety of RLV propulsion applications. These composites consist of high-strength carbon fibers and a high modulus, oxidation resistant matrix. For RLV propulsion applications, environmental durability will be critical. Two types of carbon fibers were processed with both standard (pyrolytic carbon) and novel (multilayer and pseudoporous) types of interface coatings as part of a study investigating various combinations of constituents. The benefit of protecting the composites with a surface sealant was also investigated. The strengths, durability in oxidizing environments, and microstructures of these developmental composite materials are presented. The novel interface coatings and the surface sealant show promise for protecting the carbon fibers from the oxidizing environment.

Petko, Jeanne F.↗
NASA NTRS2002

Hypersonic Propulsion at Pratt and Whitney: Overview

Pratt & Whitney (P&W) is developing the technology for hypersonic components and engines. A supersonic combustion ramjet (scramjet) database was developed during the National Aero Space Plane (NASP) program using hydrogen fueled propulsion systems for space access vehicles and serves as a point of departure for the current emphasis on hydrocarbon scramjets. The Air Force Hypersonic Technology (HyTech) Office has put programs in place to develop the technologies necessary to demonstrate the operability, performance and structural durability of a liquid hydrocarbon fueled scramjet system that operates from Mach 4 to 8. Fuel-cooled superalloys and lightweight structures are being developed to improve thermal protection and durability and to reduce propulsion system weight. The application of scramjet engine technology as part of combined cycle propulsion systems is also being pursued under NASA and U.S. Air Force sponsorship. The combination of scramjet power and solid rocket booster acceleration is applicable to hypersonic cruise missiles. Scramjets that use gas turbines for low speed acceleration and scramjets using rocket power for low speed acceleration are being studied for application to reusable launch systems and hypersonic cruise vehicles. P&W's recent activities and future plans for hypersonic propulsion will be described.

Kazmar, Richard R.↗
NASA NTRS2004

Polyimide/Carbon Nanotube Composite Films for Electrostatic Charge Mitigation

Low color, space environmentally durable polymeric films with sufficient electrical conductivity to mitigate electrostatic charge build-up have been under investigation as part of a materials development activity. In the work described herein, single-walled carbon nanotubes (SWNT) solutions were dispersed in solutions of a novel ionomer in N,N-dimethylacetamide resulting in homogenous suspensions or quasi-solutions. The ionomer was used to aid in the dispersal of SWNTs in to a soluble, low color space environmentally durable polyimide. The use of the ionomer as a dispersant enabled the nanotubes to be dispersed at loading levels up to 3 weight % in a polyimide solution without visual agglomeration. The films were further characterized for their electrical and mechanical properties.

Delozier, D. M.↗
NASA NTRS2004

Novel Phenylethynyl Imide Silanes as Coupling Agents for Titanium Alloy

The durability of titanium (Ti) alloys bonded with high temperature adhesives such as polyimides has failed to attain the level of performance required for many applications. The problem to a large part is attributed to the instability of the surface treatment on the Ti substrate. Although Ti alloy adhesive specimens with surface treatments such as chromic acid anodization, Pasa-Jell, Turco, etc. have provided high initial mechanical properties, these properties have decreased as a function of aging at ambient temperature and faster, when aged at elevated temperatures or in a hot-wet environment. As part of the High Speed Civil Transport program where Ti honeycomb sandwich structure must perform for 60,000 hours at 177 C, work was directed to the development of environmentally safe, durable Ti alloy surface treatments.

Park, C.↗
NASA NTRS2004

Development of Advanced Low Conductivity Thermal Barrier Coatings

Advanced multi-component, low conductivity oxide thermal barrier coatings have been developed using an approach that emphasizes real-time monitoring of thermal conductivity under conditions that are engine-like in terms of temperatures and heat fluxes. This is in contrast to the traditional approach where coatings are initially optimized in terms of furnace and burner rig durability with subsequent measurement in the as-processed or furnace-sintered condition. The present work establishes a laser high-heat-flux test as the basis for evaluating advanced plasma-sprayed and electron beam-physical vapor deposited (EB-PVD) thermal barrier coatings under the NASA Ultra-Efficient Engine Technology (UEET) Program. The candidate coating materials for this program are novel thermal barrier coatings that are found to have significantly reduced thermal conductivities and improved thermal stability due to an oxide-defect-cluster design. Critical issues for designing advanced low conductivity coatings with improved coating durability are also discussed.

Zhu, Dong-Ming↗
NASA NTRS2004

Furnace Cyclic Oxidation Behavior of Multi-Component Low Conductivity Thermal Barrier Coatings

Ceramic thermal barrier coatings will play an increasingly important role in advanced gas turbine engines because of their ability to further increase engine operating temperatures and reduce cooling, thus helping achieve future engine low emission, high efficiency and improved reliability goals. Advanced multi-component zirconia-based thermal barrier coatings are being developed using an oxide defect clustering design approach to achieve the required coating low thermal conductivity and high temperature stability. Although the new composition coatings were not yet optimized for cyclic durability, an initial durability screening of the candidate coating materials was conducted using conventional furnace cyclic oxidation tests. In this paper, furnace cyclic oxidation behavior of plasma-sprayed zirconia-based defect cluster thermal barrier coatings was investigated at 1163 C using 45 min hot cycles. The ceramic coating failure mechanisms were studied using scanning electron microscopy (SEM) combined with X-ray diffraction (XRD) phase analysis after the furnace tests. The coating cyclic lifetime is also discussed in relation to coating processing, phase structures, dopant concentration, and other thermo-physical properties.

Zhu, Dong-Ming↗
NASA NTRS2004

Design Analysis and Thermo-Mechanical Fatigue of a Polyimide Composite for Combustion Chamber Support

Polyimide composites are being evaluated for use in lightweight support structures designed to preserve the ideal flow geometry within thin shell combustion chambers of future space launch propulsion systems. Principles of lightweight design and innovative manufacturing techniques have yielded a sandwich structure with an outer face sheet of carbon fiber polyimide matrix composite. While the continuous carbon fiber enables laminated skin of high specific stiffness; the polyimide matrix materials ensure that the rigidity and durability is maintained at operation temperatures of 316 C. Significant weight savings over all metal support structures are expected. The protypical structure is the result of ongoing collaboration, between Boeing and NASA-GRC seeking to introduce polyimide composites to the harsh environmental and loads familiar to space launch propulsion systems. Design trade analyses were carried out using relevant closed form solutions, approximations for sandwich beams/panels and finite element analysis. Analyses confirm the significant thermal stresses exist when combining materials whose coefficients of thermal expansion (CTEs) differ by a factor of about 10 for materials such as a polymer composite and metallic structures. The ramifications on design and manufacturing alternatives are reviewed and discussed. Due to stringent durability and safety requirements, serious consideration is being given to the synergistic effects of temperature and mechanical loads. The candidate structure operates at 316 C, about 80% of the glass transition temperature T(sub g). Earlier thermomechanical fatigue (TMF) investigations of chopped fiber polyimide composites made this near to T(sub g), showed that cyclic temperature and stress promoted excessive creep damage and strain accumulation. Here it is important to verify that such response is limited in continuous fiber laminates.

Thesken, J. C.↗