SEARCH · Search NASA

Results for “Thermomechanical Properties”

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.

SourceResearch connectionFrom yearThrough year

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

At least 109 records · Page 6

All sources NASA NTRS DOE OSTI

NASA NTRS2006

Development and Characterization of Improved NiTiPd High-Temperature Shape-Memory Alloys by Solid-Solution Strengthening and Thermomechanical Processing

The need for compact, solid-state actuation systems for use in the aerospace, automotive, and other transportation industries is currently motivating research in high-temperature shape-memory alloys (HTSMA) with transformation temperatures greater than 100 C. One of the basic high-temperature alloys investigated to fill this need is Ni(19.5)Ti(50.5)Pd30. Initial testing has indicated that this alloy, while having acceptable work characteristics, suffers from significant permanent deformation (or ratcheting) during thermal cycling under load. In an effort to overcome this deficiency, various solid-solution alloying and thermomechanical processing schemes were investigated. Solid-solution strengthening was achieved by substituting 5at% gold or platinum for palladium in Ni(19.5)Ti(50.5)Pd30, the so-called baseline alloy, to strengthen the martensite and austenite phases against slip processes and improve thermomechanical behavior. Tensile properties, work behavior, and dimensional stability during repeated thermal cycling under load for the ternary and quaternary alloys were compared. The relative difference in yield strength between the martensite and austenite phases and the dimensional stability of the alloy were improved by the quaternary additions, while work output was only minimally impacted. The three alloys were also thermomechanically processed by cycling repeatedly through the transformation range under a constant stress. This so-called training process dramatically improved the dimensional stability in these samples and also recovered the slight decrease in work output caused by quaternary alloying. An added benefit of the solid-solution strengthening was maintenance of enhanced dimensional stability of the trained material to higher temperatures compared to the baseline alloy, providing a greater measure of over-temperature capability.

Bigelow, Glen↗

NASA NTRSDate not supplied

Thermo-Poro-Mechanical Modeling of RTV Intumescence

Room temperature vulcanizing (RTV) silicone is a high-temperature adhesive used as a gap-filler between heatshield tiles in numerous entry missions. Its propensity to intumesce, or swell upon exposure to heat, is a well-known effect that needs to be carefully quantified during design. At tile interfaces of charring ablators, intumescence, combined with differential recession, could cause the gap filler to protrude past the ablator outer mold line, forming a “fence”. Fencing can in turn cause transition to turbulence of the flow wetting the heat shield, leading to augmented surface heating. Recent experiments conducted at the Plasmatron X facility, the high enthalpy wind tunnel of the Center for Hypersonics and Entry Systems Studies, have shown prominent fencing of RTV gap fillers in PICA, under both nitrogen and air plasmas. Similar observations are well known in the arcjet literature. Further experiments under controlled environment, performed using in situ X-ray micro-computed tomography (micro-CT) at the Advanced Light Source (ALS), have shown heating rate-dependent swelling and shrinkage of RTV during pyrolysis. To simulate RTV intumescence, a novel model was introduced in the Porous Materials Analysis Toolbox based on OpenFOAM, PATO, to account for pore-pressure buildup within both closed- and open-pores. The governing equation for the thermo-poro-mechanical response were developed, assuming linear elasticity for the charring silicone. A new multi-pyrolysis model that tracks non-monotonic advancement of material properties with pyrolysis was proposed. This model addresses the limitations of state-of-the-art ablator models to capture the different stages of thermal degradation and coupled thermomechanics. Swelling of RTV was simulated using the new thermo-poro-mechanical model and compared against in situ micro-CT data. Results showed good agreement in intumescence height and temperature profiles at all heating rates, indicating that the key factor contributing to RTV swelling is the internal pressure build-up within closed- and open-pores. As RTV is cured into a soft (rubbery) compound with low-porosity and permeability, initial temperature increase and pyrolysis gas production cause a significant increase of internal pressure, causing a pronounced volume growth. As thermal degradation progresses, rigidization of the silicone occurs due to char hardening which counteract volume shrinkage after gas pressure relief. Overall, our model shows that accounting for changes in properties such porosity, permeability and key thermomechanical coefficients is crucial for capturing the RTV volume change during ablation and enable a predictive capability for heatshield tile interface response. A plan for future calibration of thermomechanical properties evolution during degradation is discussed, as a key next step to close the new model.

RTV↗

NASA NTRSDate not supplied

Thermo-Poro-Mechanical Modeling of RTV Intumescence

silicone intumescence↗

NASA NTRS1998

Sintering and Creep Behavior of Plasma-Sprayed Zirconia and Hafnia Based Thermal Barrier Coatings

The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2-8wt%y2O3, ZrO2-25wt%CeO2-2.5wt%Y2O3, ZrO2-6w%NiO- 9wt%Y2O3, ZrO2-6wt%Sc2O3-2wt%y2O3 and HfO2-27wt%y2O3 coating materials were investigated using dilatometry. It was found that the HfO2-Y2O3 and baseline ZrO2-Y2O3 exhibited the best sintering resistance, while the NiO-doped ZrO2-Y2O3 showed the highest shrinkage strain rates during the tests. Higher shrinkage strain rates of the coating materials were also observed when the specimens were tested in Ar+5%H2 as compared to in air. This phenomenon was attributed to an enhanced metal cation interstitial diffusion mechanism under the reducing conditions. It is proposed that increased chemical stability of coating materials will improve the material sintering resistance.

Zhu, Dongming↗

NASA NTRS1999

Thermal Barrier Coatings for Advanced Gas Turbine and Diesel Engines

Ceramic thermal barrier coatings (TBCS) have been developed for advanced gas turbine and diesel engine applications to improve engine reliability and fuel efficiency. However, durability issues of these thermal barrier coatings under high temperature cyclic conditions are still of major concern. The coating failure depends not only on the coating, but also on the ceramic sintering/creep and bond coat oxidation under the operating conditions. Novel test approaches have been established to obtain critical thermomechanical and thermophysical properties of the coating systems under near-realistic transient and steady state temperature and stress gradients encountered in advanced engine systems. This paper presents detailed experimental and modeling results describing processes occurring in the ZrO2-Y2O3 thermal barrier coating systems, thus providing a framework for developing strategies to manage ceramic coating architecture, microstructure and properties.

Zhu, Dongming↗

NASA NTRS2007

Silicon Carbide Sensors and Electronics for Harsh Environment Applications

Silicon carbide (SiC) semiconductor has been studied for electronic and sensing applications in extreme environment (high temperature, extreme vibration, harsh chemical media, and high radiation) that is beyond the capability of conventional semiconductors such as silicon. This is due to its near inert chemistry, superior thermomechanical and electronic properties that include high breakdown voltage and wide bandgap. An overview of SiC sensors and electronics work ongoing at NASA Glenn Research Center (NASA GRC) will be presented. The main focus will be two technologies currently being investigated: 1) harsh environment SiC pressure transducers and 2) high temperature SiC electronics. Work highlighted will include the design, fabrication, and application of SiC sensors and electronics, with recent advancements in state-of-the-art discussed as well. These combined technologies are studied for the goal of developing advanced capabilities for measurement and control of aeropropulsion systems, as well as enhancing tools for exploration systems.

Evans, Laura J.↗

NASA NTRS2005

Improved Method of Manufacturing SiC Devices

The phrase, "common-layered architecture for semiconductor silicon carbide" ("CLASSiC") denotes a method of batch fabrication of microelectromechanical and semiconductor devices from bulk silicon carbide. CLASSiC is the latest in a series of related methods developed in recent years in continuing efforts to standardize SiC-fabrication processes. CLASSiC encompasses both institutional and technological innovations that can be exploited separately or in combination to make the manufacture of SiC devices more economical. Examples of such devices are piezoresistive pressure sensors, strain gauges, vibration sensors, and turbulence-intensity sensors for use in harsh environments (e.g., high-temperature, high-pressure, corrosive atmospheres). The institutional innovation is to manufacture devices for different customers (individuals, companies, and/or other entities) simultaneously in the same batch. This innovation is based on utilization of the capability for fabrication, on the same substrate, of multiple SiC devices having different functionalities (see figure). Multiple customers can purchase shares of the area on the same substrate, each customer s share being apportioned according to the customer s production-volume requirement. This makes it possible for multiple customers to share costs in a common foundry, so that the capital equipment cost per customer in the inherently low-volume SiC-product market can be reduced significantly. One of the technological innovations is a five-mask process that is based on an established set of process design rules. The rules provide for standardization of the fabrication process, yet are flexible enough to enable multiple customers to lay out masks for their portions of the SiC substrate to provide for simultaneous batch fabrication of their various devices. In a related prior method, denoted multi-user fabrication in silicon carbide (MUSiC), the fabrication process is based largely on surface micromachining of poly SiC. However, in MUSiC one cannot exploit the superior sensing, thermomechanical, and electrical properties of single-crystal 6H-SiC or 4H-SiC. As a complement to MUSiC, the CLASSiC five-mask process can be utilized to fabricate multiple devices in bulk single-crystal SiC of any polytype. The five-mask process makes fabrication less complex because it eliminates the need for large-area deposition and removal of sacrificial material. Other innovations in CLASSiC pertain to selective etching of indium tin oxide and aluminum in connection with multilayer metallization. One major characteristic of bulk micromachined microelectromechanical devices is the presence of three-dimensional (3D) structures. Any 3D recesses that already exist at a given step in a fabrication process usually make it difficult to apply a planar coat of photoresist for metallization and other subsequent process steps. To overcome this difficulty, the CLASSiC process includes a reversal of part of the conventional flow: Metallization is performed before the recesses are etched.

Okojie, Robert S.↗

NASA NTRS2024

Filament Wound Composite Analysis Using the NASA Multiscale Analysis Tool (NASMAT) and Finite Element Analysis

Fiber reinforced composite materials, owing to their tailorable thermomechanical and functional properties, allow one to produce a structure that is stronger, stiffer, and lighter than its metal counterpart while performing the same function, yielding a more efficient structure. This not only allows for the improvement of current technologies like aircraft structures, but also enables new technologies like gaseous hydrogen storage for mobility applications, which are otherwise impractical when manufactured using traditional metals due to weight and space restrictions or material embrittlement. However, the use of composites imposes greater design and manufacturing challenges on an engineer, since they are heterogenous, having a distinct structure across multiple length scale, behave generally anisotropically at the structural level and require complex manufacturing and processing methods. Capturing this complex behavior requires detailed numerical simulations, including the modeling of microstructural features like undulations, voids, and fiber alignment. In this paper, multiple repeating unit cells (RUCs), representing filament wound composites, are developed (via a script provided in the Appendix) and analyzed. The refinement of these RUCs is varied, and the analyses are performed using both the Abaqus finite element software and the NASA Multiscale Analysis Tool (NASMAT). A study is undertaken to compare the predicted effective elastic properties of the wound RUC to a laminate representation of the wound RUC, which neglects the undulations. Additionally, two different sets of periodic boundary conditions (PBCs) have been examined. One approximates the real boundary conditions using a standard approach and the other represents the PBCs exactly through the use of an offset. Lastly, a comparison of the local elastic stress fields is made among the models and approaches. Since wound structures are often approximated as laminated structures, it is important to understand the degree to which this assumption is valid, namely by first comparing the elastic constants and local elastic fields. This will provide, on the one hand, information concerning the bulk mechanical behavior and, on the other hand, insights concerning local load distributions and likely damage initiation sites.

Composites↗

NASA NTRS1983

Influence of thermomechanical processing on elevated temperature slow plastic flow properties of B2 aluminide Fe-39.8at.% Al

A study of the elevated temperature slow plastic flow properties of the B2 aluminide Fe-39.8at.% Al was undertaken. Polycrystalline materials possessing several different microstructures were produced by the hot extrusion of prealloyed powder and, in some cases, postextrusion heat treatments. Compression tests were conducted in air at 1200, 1300 and 1400 K. Such testing revealed that the extrusion temperature affected the active deformation mechanisms where material extruded at 1505 K had a stress exponent about twice that of the intermetallic extruded at 1200 K. Grain size refinement to about 10 microns was found to strengthen the Fe-39.8at.% Al material; unfortunately, the effectiveness of such strengthening is limited to a homologous temperature of about 0.75 for strain rates of commercial interest (less than 10 to the -7th/sec).

Whittenberger, J. D.↗

NASA NTRSDate not supplied

A Machine Learning-Derived Atomistic Potential for Y2Si2O7

Incorporation of SiC/SiC ceramic matrix composite (CMC) hot section components into aircraft engines promises to increase efficiency and safety. However, SiC/SiC CMCs are subject to water vapor-induced oxidation and recession at the high temperatures of engine operation, and thus environmental barrier coatings (EBCs) are required to reduce this degradation and enable their widespread adoption. An understanding of EBCs failure mechanisms, including thermochemical and thermomechanical mechanisms, is essential as coating degradation leads to reduced CMC component service life. Computational modeling approaches can provide insight into EBC material properties important for coating design. However, density functional theory (DFT) is computationally expensive and atomistic potentials are lacking for materials of interest. In this work, we utilize a machine learning approach and DFT training data to parameterize atomistic potentials for two candidate EBC materials, Y2Si2O7 and Yb2Si2O7. These potentials enable near DFT-accurate calculations of thermodynamic and thermomechanical properties essential to EBC design.

Cameron J Bodenschatz↗

NASA NTRS1994

Effects of thermomechanical processing on tensile and long-time creep behavior of Nb-1 percent Zr-0.1 percent C sheet

Effects of thermomechanical processing on the mechanical properties of Nb-1 wt. percent Zr-0.1 wt. percent C, a candidate alloy for use in advanced space power systems, were investigated. Sheet bars were cold rolled into 1-mm thick sheets following single, double, or triple extrusion operations at 1900 K. All the creep and tensile specimens were given a two-step heat treatment 1 hr at 1755 K + 2 hr 1475 K prior to testing. Tensile properties were determined at 300 as well as at 1350 K. Microhardness measurements were made on cold rolled, heat treated, and crept samples. Creep tests were carried out at 1350 K and 34.5 MPa for times of about 10,000 to 19,000 hr. The results show that the number of extrusions had some effects on both the microhardness and tensile properties. However, the long-time creep behavior of the samples were comparable, and all were found to have adequate properties to meet the design requirements of advanced power systems regardless of thermomechanical history. The results are discussed in correlation with processing and microstructure, and further compared to the results obtained from the testing of Nb-1 wt. percent Zr and Nb-1 wt. percent Zr-0.06 wt. percent C alloys.

Titran, Robert H.↗

NASA NTRS2018

Polyurethane Microparticles for Stimuli Response and Reduced Oxidative Degradation in Highly Porous Shape Memory Polymers

Shape memory polymers (SMPs) have been found to be promising biomaterials for a variety of medical applications; however, the clinical translation of such technology is dependent on tailorable properties such as gravimetric changes in degradation environments. For SMPs synthesized from amino-alcohols, oxidation resulting in rapid mass loss may be problematic in terms of loss of material functionality as well as toxicity and cytocompatibility concerns. Control of gravimetric changes was achieved through the incorporation of small molecule antioxidants, either directly into the polymer matrix or included in microparticles to form a SMP composite material. Direct incorporation of small molecule antioxidants, such as phenolic alcohols, was found to alter shape memory attributes and increase elastic modulus at the expense of the strain to failure. Such changes could not ensure retention of the antioxidants and therefore did not increase oxidative stability. However, the inclusion of antioxidants in microparticles was found to produce materials with similar thermomechanical and shape memory properties while increasing oxidative resistance compared to controls. The microparticle composite SMPs also act as a platform for environmental sensing, such as pH-dependent fluorescence shifts and payload release, as demonstrated by fluorescent dyes and the release of antioxidants. The use of polyurethane-urea microparticles in porous SMPs is demonstrated to increase biostability of the materials, by approximately 25%, and ultimately extend their lifespan for use in aneurysm occlusion as determined through calculated in vivo degradation rates corresponding to a porcine aneurysm environment.

Weems, A. C.↗

NASA NTRS2008

Effects of Palladium Content, Quaternary Alloying, and Thermomechanical Processing on the Behavior of Ni-Ti-Pd Shape Memory Alloys for Actuator Applications

The need for compact, solid-state actuation systems for use in the aerospace, automotive, and other transportation industries is currently driving research in high-temperature shape memory alloys (HTSMA) having transformation temperatures above 100 C. One of the basic high temperature systems under investigation to fill this need is NiTiPd. Prior work on this alloy system has focused on phase transformations and respective temperatures, no-load shape memory behavior (strain recovery), and tensile behavior for selected alloys. In addition, a few tests have been done to determine the effect of boron additions and thermomechanical treatment on the aforementioned properties. The main properties that affect the performance of a solid state actuator, namely work output, transformation strain, and permanent deformation during thermal cycling under load have mainly been neglected. There is also no consistent data representing the mechanical behavior of this alloy system over a broad range of compositions. For this thesis, ternary NiTiPd alloys containing 15 to 46 at.% palladium were processed and the transformation temperatures, basic tensile properties, and work characteristics determined. However, testing reveals that at higher levels of alloying addition, the benefit of increased transformation temperature begins to be offset by lowered work output and permanent deformation or "walking" of the alloy during thermal cycling under load. In response to this dilemma, NiTiPd alloys have been further alloyed with gold, platinum, and hafnium additions to solid solution strengthen the martensite and parent austenite phases in order to improve the thermomechanical behavior of these materials. The tensile properties, work behavior, and dimensional stability during repeated thermal cycling under load for the ternary and quaternary alloys were compared and discussed. In addition, the benefits of more advanced thermomechanical processing or training on the dimensional stability of these alloys during repeated actuation were investigated. Finally, the effect of quaternary alloying on the thermal stability of NiTiPdX alloys is determined via thermal cycling of the materials to increasing temperatures under load. It was found that solid solution additions of platinum and gold resulted in about a 30 C increase in upper use temperature compared to the baseline NiTiPd alloy, providing an added measure of over-temperature protection.

Bigelow, Glen↗

NASA NTRS1975

Compositional effects on mechanical properties of hafnium-carbide-strengthened molybdenum alloys

The mechanical properties of swaged rod thermomechanically processed from arc melted Mo-2Re-Hf-C alloys containing as much as 0.9-mol% HfC were evaluated. The low-temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2- to 0.3-at.% excess Hf. At 0.3- to 0.5-mol% HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2-at.% Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

Witzke, W. R.↗

NASA NTRS1976

Composition effects on mechanical properties of HfC-strengthened molybdenum alloys

The mechanical properties of swaged rod thermomechanically processed from arc-melted Mo-2Re-Hf-C alloys containing as much as 0.9 mol pct HfC have been evaluated. The low temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2 to 0.3 at. pct excess Hf. At 0.3 to 0.5 mol pct HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2 at. pct Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

Witzke, W. R.↗

NASA NTRS1998

Noncontact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites

High-temperature materials are of increasing importance in the development of more efficient engines and components for the aeronautics industry. In particular, ceramic matrix composite (CMC) and metal matrix composite (MMC) structures are under active development for these applications. The acousto-ultrasonic (AU) method has been shown to be useful for assessing mechanical properties in composite structures. In particular, plate wave analysis can characterize composites in terms of their stiffness moduli. It is desirable to monitor changes in mechanical properties that occur during thermomechanical testing and to monitor the health of components whose geometry or position make them hard to reach with conventional ultrasonic probes. In such applications, it would be useful to apply AU without coupling directly to the test surface. For a number of years, lasers have been under investigation as remote ultrasonic input sources and ultrasound detectors. The use of an ultrasonic transducer coupled through an air gap has also been under study. So far at the NASA Lewis Research Center, we have been more successful in using lasers as ultrasonic sources than as output devices. On the other hand, we have been more successful in using an air-coupled piezoelectric transducer as an output device than as an input device. For this reason, we studied the laser in/air-coupled-transducer out combination-using a pulsed NdYAG laser as the ultrasonic source and an air-coupled-transducer as the detector. The present work is focused on one of the AU parameters of interest, the ultrasonic velocity of the antisymmetric plate-wave mode. This easily identified antisymmetric pulse can be used to determine shear and flexure modulus. It was chosen for this initial work because the pulse arrival times are likely to be the most precise. The following schematic illustrates our experimental arrangement for using laser in/air-transducer out on SiC/SiC composite tensile specimens. The NdYAG pulse was directed downward by a 90 infrared prism to the top of the specimen, but at the edge of one end. An energy sensor measured a single pulse at 13 millijoules (mJ) before it passed through the prism, which attenuated 15 percent of its energy. It also provided an output trigger for the waveform time-delay synthesizer.

Kautz, Harold E.↗

NASA NTRS1980

Effect of TMP variables upon structure and properties in ODS alloy HDA 8077 sheet

The effects of oxide content level and variations in thermomechanical processing upon the final structure and properties of HDA 8077 sheet have been systematically examined. It was found that creep strength and formability are substantially influenced by both oxide content and TMP schedule. Variations in creep properties obtained appear to correlate with observed microstructures.

Rothman, M. F.↗

NASA NTRS1974

Mechanical properties and structural characteristics of Unitemp C-300

A direct comparison of vacuum-melted, argon-atomized, hot-pressed, and extruded Unitemp C-300, an experimental, nickel-base superalloy, is made with as-cast and extruded material, with respect to mechanical properties and structural characteristics, utilizing the optimum thermomechanical processing variables previously established. Comparisons are also made with published mechanical properties of existing high temperature alloys in their temperature range of operation. These studies have established the exceptional versatility of this alloy for both high and low temperature applications and have shown that its strength characteristics significantly exceed those of the best currently available alloys on the market today.

Schwertz, J. H.↗