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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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The Kennedy Space Center Robotics Group recently completed development and testing on a novel approach to measure the mass properties of a rigid body. This unique design can measure the payload's weight, mass center location, and moments of inertia about three orthogonal axes. Furthermore, these measurements only require a single torque sensor and a single angular position sensor.
A series of creep tests were conducted on Cu-8 Cr-4 Nb (Cu-8 at.% Cr-4 at.% Nb), Cu-4 Cr-2 Nb (Cu-4 at.% Cr-2 at% Nb), and NARloy-Z (Cu-3 wt.% Ag-0.5 wt.% Zr) samples to determine their creep properties. In addition, a limited number of low cycle fatigue and thermal conductivity tests were conducted. The Cu-Cr-Nb alloys showed a clear advantage in creep life and sustainable load over the currently used NARloy-Z. Increases in life at a given stress were between 100% and 250% greater for the Cu-Cr-Nb alloys depending on the stress and temperature. For a given life, the Cu-Cr-Nb alloys could support a stress between 60% and 160% greater than NARloy-Z. Low cycle fatigue lives of the Cu-8 Cr-4 Nb alloy were equivalent to NARloy-Z at room temperature. At elevated temperatures (538 C and 650 C), the fatigue lives were 50% to 200% longer than NARloy-Z samples tested at 538 C. The thermal conductivities of the Cu-Cr-Nb alloys remained high, but were lower than NARloy-Z and pure Cu. The Cu-Cr-Nb thermal conductivities were between 72% and 96% that of pure Cu with the Cu-4 Cr-2 Nb alloy having a significant advantage in thermal conductivity over Cu-8 Cr4 Nb. In comparison, stainless steels with equivalent strengths would have thermal conductivities less than 25% the thermal conductivity of pure Cu. The combined results indicate that the Cu-Cr-Nb alloys offer an attractive alternative to current high temperature Cu-based alloys such as NARloy-Z.
In the development of advanced aircraft-engine fan cases and containment systems, composite materials are beginning to be used due to their low weight and high strength. The design of these structures must include the capability of withstanding impact loads from a released fan blade. Relatively complex triaxially braided fiber architectures have been found to yield the best performance for the fan cases. To properly work with and design these structures, robust analytical tools are required that can be used in the design process. A new analytical approach models triaxially braided carbon fiber composite materials within the environment of a transient dynamic finite-element code, specifically the commercially available transient dynamic finite-element code LS-DYNA. The geometry of the braided composites is approximated by a series of parallel laminated composites. The composite is modeled by using shell finite elements. The material property data are computed by examining test data from static tests on braided composites, where optical strain measurement techniques are used to examine the local strain variations within the material. These local strain data from the braided composite tests are used along with a judicious application of composite micromechanics- based methods to compute the stiffness properties of an equivalent unidirectional laminated composite required for the shell elements. The local strain data from the braided composite tests are also applied to back out strength and failure properties of the equivalent unidirectional composite. The properties utilized are geared towards the application of a continuum damage mechanics-based composite constitutive model available within LS-DYNA. The developed model can be applied to conduct impact simulations of structures composed of triaxially braided composites. The advantage of this technology is that it facilitates the analysis of the deformation and damage response of a triaxially braided polymer matrix composite within the environment of a transient dynamic finite-element code such as LS-DYNA in a manner which accounts for the local physical mechanisms but is still computationally efficient. This methodology is tightly coupled to experimental tests on the braided composite, which ensures that the material properties have physical significance. Aerospace or automotive companies interested in using triaxially braided composites in their structures, particularly for impact or crash applications, would find the technology useful. By the development of improved design tools, the amount of very expensive impact testing that will need to be performed can be significantly reduced.
Reducing embodied carbon emissions in buildings and striving for carbon neutrality through sustainable design has become a primary goal in the construction industry. The industry is expanding its use of wood-engineered products, such as cross-laminated timber (CLT) to achieve those sustainability goals. Furthermore, replacing steel fasteners with lower embodied carbon alternatives is gaining increased attention in timber engineering. This paper aims to quantify the mechanical behavior of single shear-plane CLT-to-CLT joints using hardwood dowels. The study includes 154 single shear-plane experimental tests with four different CLT species, two hardwood dowel species, and two dowel diameters. Further, the test specimens were subjected to cyclic and monotonic loading until failure, and mechanical properties such as yielding and ultimate strength, serviceability and yielding stiffness, and ductility were quantified. The hardwood dowel CLT-to-CLT joints demonstrated high strength with up to 10.3 kN (2.3 kips) capacity per dowel and lateral stiffness of up to 5.2 kN/mm (30.8 k/in) per dowel. This strength and stiffness are roughly equivalent to or exceed values for mass timber wood screws, making hardwood dowels a good alternative. In addition, the observed mean ductility of joints ranged from 2.4 to 4.5. Finally, analytical equations for the joints' yielding strength, lateral serviceability stiffness, and yielding stiffness were derived with non-linear regression analysis and validated using the experimental test results.
Tristructural isotropic (TRISO) coated particle fuel was initially developed for high temperature gas cooled reactors (HTGR) and has been proposed for several other advanced reactor concepts. The design of TRISO particles focuses on preventing the release of fission products in normal and off-normal reactor conditions. The particle design features an actinide bearing fuel kernel that is surrounded by three pyrolytic carbon (PyC) layers and a silicon carbide layer (SiC). The mechanical stability of the particle and fission product retention for both metallic and gaseous fission products depend on the SiC layer. Post irradiation examination (PIE) of TRISO fuel from the first two US DOE Advanced Gas Reactor Fuel Development and Qualification Program irradiation campaigns, AGR-1 and AGR-2, had identified a low rate of particles exhibiting cracking in the SiC layer that did not propagate across the SiC layer. While cracking in the SiC is rare for test conditions and particles associated with the AGR program, understanding the stress state and mechanical properties of the SiC and PyC layers related to particle architecture can aid predicting thermomechanical response of TRISO fuel under the prescribed operation envelope and beyond as well as aiding in the development of similar fuel concepts for other advanced reactors. The presented investigation shows the relationship of the mechanical properties and mechanical response (e.g., understanding crack propagation) of the SiC and PyC layers relative to position within the particle. Testing was conducted on the inner and outer PyC layers of TRISO particles to quantify differences in mechanical behavior.
The effects of heat treatment and resulting microstructure variations on high temperature mechanical properties were assessed for a powder metallurgy disk superalloy LSHR. Blanks were consistently supersolvus solution heat treated and quenched at two cooling rates, than aged at varying temperatures and times. Tensile, creep, and dwell fatigue crack growth tests were then performed at 704 C. Gamma' precipitate microstructures were quantified. Relationships between heat treatment-microstructure, heat treatment-mechanical properties, and microstructure-mechanical properties were assessed.
Advanced turbine engine configurations using higher temperature combustor and airfoil concepts require compressor and turbine disks that can withstand temperatures higher than the 650 C typical of current engines. This requires disk alloy and processing improvements. A versatile disk alloy was needed that could be given either fine grain heat treatments for high strength and fatigue and creep resistance up to 704 C or given coarse grain heat treatments for high strength and creep and dwell crack-growth resistance at higher temperatures. This alloy could produce disks with uniform microstructures and properties, as well as with varied, optimized microstructures at disk bore and rim sections. A series of experimental disk alloys were designed and processed to give subscale disks about 13 cm in diameter and 4 cm thick. These alloys had varying levels of key elements to affect mechanical properties and change the "solvus" solution heat-treatment temperature necessary to produce coarse grain microstructures. Disks were given coarse grain heat treatments followed by rapid oil quenching and slower fan air quenching. These heat treatments were intended to simulate the cooling paths of rapidly cooled full-scale disks at the outermost rim and interior bore locations, respectively. Preliminary quench tests of tensile specimens and coin-size minidisks had indicated that alloys having high solvus temperatures were more prone to cracking during rapid quenching from coarse grain heat treatments. These findings were confirmed in the subscale disks, where such alloys did form undesirable quench cracks. Mechanical tests were performed on specimens from subscale disks given these coarse grain heat treatments, as well as on specimens given a fine grain heat treatment. Tensile, creep, and crack growth tests were performed at 704 C and higher temperatures. A versatile alloy was identified that had a low solvus temperature for resistance to quench cracking as well as an optimal combination of high levels of strengthening refractory elements that produced balanced high mechanical properties for both fine grain and coarse grain microstructures. This low-solvus, high-refractory (LSHR) alloy has been scaled-up to produce prototype full-scale turbine disks typical of regional jet turbofan engines. Disks were successfully heat treated to give uniform coarse grain and uniform fine grain microstructures. Additional disks were given a NASA dual microstructure heat treatment (DMHT) that intentionally varied the solution heat-treatment temperatures between the disk rim and bore (re f. 1). The disk rim was heated to a high enough temperature to produce a coarse grain microstructure, while the bore was maintained at a lower temperature to produce a fine grain microstructure (see the figure). This DMHT can produce optimal high strength, fatigue, and creep resistance up to 704 C in the cooler running disk bore, and high strength, creep resistance, and dwell crack growth resistance at higher temperatures for the hotter disk rim. Extensive mechanical testing is being initiated to compare the mechanical properties of the uniform and DMHT disks.
The objective of this project was to conduct additive manufacturing to produce aircraft engine components by Fused Deposition Modeling (FDM), using commercially available polyetherimides - Ultem 9085 and experimental Ultem 1000 mixed with 10 percent chopped carbon fiber. A property comparison between FDM-printed and injection-molded coupons for Ultem 9085, Ultem 1000 resin and the fiber-filled composite Ultem 1000 was carried out. Furthermore, an acoustic liner was printed from Ultem 9085 simulating conventional honeycomb structured liners and tested in a wind tunnel. Composite compressor inlet guide vanes were also printed using fiber-filled Ultem 1000 filaments and tested in a cascade rig. The fiber-filled Ultem 1000 filaments and composite vanes were characterized by scanning electron microscope (SEM) and acid digestion to determine the porosity of FDM-printed articles which ranged from 25-31 percent. Coupons of Ultem 9085 and experimental Ultem 1000 composites were tested at room temperature and 400 degrees Fahrenheit to evaluate their corresponding mechanical properties.
This article presents a comprehensive study concerning size and geometry effect on the ambient and high-temperature mechanical behavior of additively manufactured laser powder bed fusion Ti-6Al-4V alloy. Key mechanical property metrics are presented, including strain hardening rate, yield strength, and Young’s modulus as a function of thickness and testing temperature (ambient, 250 °C, and 450 °C). Here, the effect of specimen size on manufacturing-induced microstructural feature formation is demonstrated and discussed. A detailed analysis regarding Young’s modulus, yield strength, and strain hardening rate variation at elevated temperatures is also presented. Size effect and temperature-sensitive deformation mechanisms are linked to the underlying microstructural deformation mechanisms activated at respective temperatures. Counter-intuitively, this study determined that irrespective of the geometry, strain hardening rates increased as temperature increased. An in-depth microstructural examination is presented to explain the stated observation. The texture of Interrupted tensile test samples examined for ambient, 250 °C, and 450 °C post-yield was observed to be unchanged, indicating the strain hardening behavior was not texture dependent. Schmid factor analysis, coupled with experimental findings from previous work, was implemented to generate a hypothesis. This hypothesis suggests that the drop in critical resolved shear stress for basal and pyramidal slip systems, as temperature increases, paired with the high dislocation density of laser powder bed fusion Ti-6Al-4V, leads to dislocation entanglement and results in increased strain hardening at elevated temperatures.
This work is part of the overall advanced main combustion chamber (AMCC) casting characterization program of the Materials and Processes Laboratory of the Marshall Space Flight Center. The influence of hydrogen on the tensile properties and ductility behavior of NASA-23 alloy were analyzed. NASA-23 and other referenced alloys in cast and hipped conditions were solution treated and aged under selected conditions and characterized using optical metallography, scanning electron microscopy, and electron microprobe analysis techniques. The yield strength of NASA-23 is not affected much by hydrogen under tensile tests carried at 5000 psig conditions; however, the ultimate strength and ductility properties are degraded. This implies that the physical mechanisms operating would be related to the plastic deformation process. The fracture surfaces characteristics of NASA-23 specimens tensile tested in hydrogen, helium, and air were also analyzed. These revealed surface cracks around specimen periphery with the fracture surface showing a combination of intergranular and transgranular modes of fracture. It is seen that the specimens charged in hydrogen seem to favor a more brittle fracture mode in comparison to air and helium charged specimens. The AMCC casting characterization program is to be analyzed for their hydrogen behavior. As a result of this program, the basic microstructural factors and fracture characteristics in some cases were analyzed.
Fiber-reinforced polymer composites have been extensively utilized in recent years as feedstock materials for material extrusion additive manufacturing (AM) processes to improve strength, stiffness, and functionality of printed parts over unfilled printed polymers. However, the widespread adoption of AM of fiber-reinforced polymer composites requires a deeper understanding of the process-structure-property relationships in printed components, and such relationships are not well understood yet. Fiber length is critically important to the mechanical performance of short fiber composites, but very few studies to-date have focused on how the fiber length distribution (FLD) evolves during processing of composite feedstocks and how this evolution affects printing behavior and mechanical properties in 3D-printed composites. Here, FLD is measured for carbon fiber reinforced epoxy composites over a wide range of ink compositions and shear mixing times, and the distributions are fit with a Weibull-type distribution function. The effects of FLD on the tradeoff between ink processability, ink rheology, printing behavior and mechanical properties are investigated. Furthermore, the effects of printing parameters (nozzle size and print speed) on mechanical anisotropy and fiber orientation distribution (FOD) in printed composites are explored. Mechanical properties of printed composites are characterized via 3 pt-flexural testing, and microstructure is investigated using optical and scanning electron microscopy (SEM), and x-ray computed tomography. Finally, the fitted Weibull parameters are fed into a composite model that incorporates FLD and FOD, and model predictions are found to be in excellent agreement with experimental observations.
In searching for new working fluids for power generation, supercritical CO 2 (sCO 2 ) offers some attractive features for efficient cycles. However, compatibility with structural alloys is a concern. NiCr-based alloys have excellent compatibility at 600°-800°C at 20-30 MPa sCO 2 . However, conventional steels have restrictions in temperature because of carburization and accelerated oxidation in sCO 2 , similar to observations in CO 2 . To assess the impact of carburization on steel mechanical properties, small (25mm long) dogbone tensile bars are being exposed and tested after exposure at 450°-650°C. Only highly alloyed advanced austenitic steels are resistant to carburization at 650°-750°C, suggesting that Crrich oxide scales are good barriers to C ingress. Above 800°C, it is only possible to conduct subcritical evaluations at this time, but initial results suggest most conventional high-temperature Fe- and Ni-based alloys are more rapidly degraded by CO 2 at higher temperatures. Coatings are a potential solution that require more study.
In order to evaluate the viability of ShAPE processed Mg alloys as a feedstock for fabricating lightweight sheet material, tubes consisting of ShAPE-extruded Mg alloy ZK60 were flattened into plates and hot rolled at 450 °C to reductions of 37%, 68%, and 93%. The mechanical properties and microstructure of the rolled material were characterized through tensile testing and electron backscattered diffraction (EBSD). ZK60 specimens rolled to 68% reduction had tensile properties similar to published properties of rolled ZK60 sheets fabricated using conventional processes, and exhibited negligible tensile anisotropy referenced to the rolling direction. Additional rolling from 68% to 93% reduced the ultimate tensile stress in the rolling direction from 341.74±5.96 MPa to 260.76±22.4MPa. The yield stress and elongation to failure of the material also decreased from 292.16±1.11 MPa to 256.93±18.4 MPa and 6.95±1.94% to 3.38±0.51%, respectively, but negligible little anisotropy was observed with respect to loading direction. EBSD mapping indicated that the as-extruded ZK60 had texture rotated away from the basal direction which developed into a strong basal texture over numerous hot rolling steps. This evolution in texture has been observed after rolling for hot-rolled ZK60 fabricated through conventional extrusion processes. The initial grain structure was found to have experienced noticeable twinning from flattening the tube into plate. After hot rolling, the grain structure became more equiaxed, but the average grain diameter did not change appreciably from 5.15 ± 3.39 µm in the ShAPE extruded material, to 5.27 ± 12.44 µm in the 93% hot rolled sheet. This response to hot rolling is similar to the response of ZK60 fabricated using other methods such as Equal Channel Angular Processing (ECAP). Therefore, this work demonstrates ShAPE has the potential as an alternative method to producing feedstock for Mg alloy sheets. Modifications to the experimental procedure which could lead to improvements in observed properties are briefly discussed.
This work aims to fabricate a small-scale battery module with the baseline RBD-CFRC and conduct mechanical crush test to develop an initial thermal runaway model. Test the adhesive properties of the RBD-CFRCs using their resin constituent, ultrasonic welding, and other resins employed today. Recommend a future direction for resin development to enable the welding of RBDCFRCs to dissimilar materials. Time and Cost Permitting. Iterate on resin development for flame resistance and adhesive properties, demonstrating how thermal runaway can be reduced or joining properties can be improved.
Aerospace applications of elastomers are considered, including: propellant binders, bladder materials for liquid propellant expulsion systems, and fuel tank sealants for high-speed aircraft. A comprehensive molecular theory for mechanical properties of these materials has been developed but has only been tested experimentally in cases where chemical degradation processes are excluded. Hence, a study is being conducted to ascertain the nature, extent, and rate of chemical changes that take place in some elastomers of interest. Chemical changes that may take place in the fluorosilicone elastomer, LS 420, which is regarded as a fuel and high-temperature-resistant rubber are investigated. The kinetic analysis of the chemical stress relaxation and gel permeation chromatography studies comprise the major portion of the report.
Two Pyrrone materials, pure Pyrrone foam with a density of 481 kg/cu m and hollow glass microsphere-Pyrrone composite with a density of 962 kg/cu m, were tested in the Langley 20-inch hypersonic arc heated tunnel at pressure levels from 0.06 to 0.27 atm and heating rates from 1.14 to 11.4 MW/sq m. The 481-kg/cu m Pyrrone foam was also flight tested as an experiment aboard a Pacemaker test vehicle. The results of the ground tests indicated that the thermal effectiveness of the 481-kg/cu m Pyrrone foam was superior to the 962-kg/cu m glass sphere-Pyrrone composite. The 481-kg/cu m Pyrrone foam had approximately one-half the thermal effectiveness of low density phenolic nylon. The 481-kg/cu m Pyrrone foam experienced random mechanical char removal over the entire range of test conditions. Char thermal property inputs for an ablation computer program were developed from the ground test data of the 481-kg/cu m Pyrrone foam. The computer program using these developed char thermal properties, as well as the measured uncharred material properties, adequately predicted the in-depth temperature histories measured during the Pacemaker flight.
The mechanical behavior of a filled elastomer was studied with emphasis on understanding the vacuum-material interactions occurring, and to develop analytical techniques for predicting the vacuum behavior. The test results indicate that two separate mechanisms are involved in the observed property changes: the first controls the time response to applied stress; the second determines the initial internal state of the materials as the result of stresses. It is concluded that the mechanical property changes are attributable to changes in the relaxation processes occurring in the material. These changes are brought about by outgassing of water. Recommendations for future investigations are included.
The use of high strength and modulus of advanced filamentary composites to reduce the structural weight of aerospace vehicles was investigated. Application of the technology to space shuttle components was the primary consideration. The mechanical properties for the boron/epoxy, graphite/epoxy, and polyimide data are presented. Structural testing of two compression panel components was conducted in a simulated space shuttle thermal environment. Results of the tests are analyzed.