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At least 181 records · Page 10

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NASA NTRS2015

High-Melt Carbon-Carbon Coating for Nozzle Extensions

Carbon-Carbon Advanced Technologies, Inc. (C-CAT), has developed a high-melt coating for use in nozzle extensions in next-generation spacecraft. The coating is composed primarily of carbon-carbon, a carbon-fiber and carbon-matrix composite material that has gained a spaceworthy reputation due to its ability to withstand ultrahigh temperatures. C-CAT's high-melt coating embeds hafnium carbide (HfC) and zirconium diboride (ZrB2) within the outer layers of a carbon-carbon structure. The coating demonstrated enhanced high-temperature durability and suffered no erosion during a test in NASA's Arc Jet Complex. (Test parameters: stagnation heat flux=198 BTD/sq ft-sec; pressure=.265 atm; temperature=3,100 F; four cycles totaling 28 minutes) In Phase I of the project, C-CAT successfully demonstrated large-scale manufacturability with a 40-inch cylinder representing the end of a nozzle extension and a 16-inch flanged cylinder representing the attach flange of a nozzle extension. These demonstrators were manufactured without spalling or delaminations. In Phase II, C-CAT worked with engine designers to develop a nozzle extension stub skirt interfaced with an Aerojet Rocketdyne RL10 engine. All objectives for Phase II were successfully met. Additional nonengine applications for the coating include thermal protection systems (TPS) for next-generation spacecraft and hypersonic aircraft.

Thompson, James↗

NASA NTRS1993

Analysis of matrix cracking and local delamination in (0/theta/-theta)s graphite epoxy laminates under tensile load

Three-dimensional element analyses of (0/theta/-theta)s graphite epoxy laminates, where theta = 15, 20, 25, 30, and 45 deg, subjected to axial tensile load, were performed. The interlaminar stresses in the theta/-theta interface were calculated with and without a matrix crack in the central -theta plies. The interlaminar normal stress changes from a small compressive stress when no matrix crack is present to a high tensile stress at the intersection of the matrix crack and the free edge. The analysis of local delamination from the -theta matrix crack indicates a high strain energy release rate and a localized Mode I component near the free edge, within one-ply distance from the matrix crack. To examine the stress state causing the matrix cracking, the maximum principal normal stress in a plane perpendicular to the fiber direction in the -theta ply was calculated in an uncracked laminate. The corresponding shear stress parallel to the fiber was also calculated. The principal normal stress at the laminate edge increased through the ply thickness and reached a very high tensile value at the theta/-theta interface indicating that the crack in the -theta ply may initiate at the theta/-theta interface.

Salpekar, S. A.↗

NASA NTRS1991

Analysis of matrix cracking and local delamination in (0/theta/-theta)sub s graphite epoxy laminates under tension load

Several 3D finite element analyses of (0/theta/-theta)sub s graphite epoxy laminates, where theta=15, 20, 25, 30, and 45 deg, subjected to axial tension load were performed. The interlaminar stresses in the theta/-theta interface were calculated with and without a matrix crack in the central -theta plies. The interlaminar normal stress changes from a small compressive stress when no matrix crack is present to a high tensile stress at the intersection of the matrix crack and free edge. The analysis of local delamination from the -theta matrix crack indicates a high strain energy release rate and a localized mode I component near the free edge, within one ply distance from the matrix crack. In order to examine the stress state causing the matrix cracking the maximum principal normal stress in a plane perpendicular to the fiber direction in the -theta ply was calculated in an uncracked laminate. The corresponding shear stress parallel to the fiber was also calculated. The principal normal stress at the laminate edge increases through the ply thickness and reached a very high tensile value at the theta/-theta interface indicating that the crack in the -theta ply may initiate at the theta/-theta interface. Crack profiles on the laminate edge in the -theta ply were constructed from the principal stress directions. The cracks were found to be more curved for layups with smaller theta angles, which is consistent with experimental observations in the literature.

Salpekar, S. A.↗

NASA NTRS1991

Analysis of matrix cracking and local delamination in (O/theta/-theta)sub s graphite epoxy laminates under tension load

Several 3D finite element analyses of (O/theta/-theta)sub s graphite epoxy laminates, where theta = 15, 20, 25, 30, and 45 deg, subjected to axial tension load were performed. The interlaminar stresses in the theta/-theta interface were calculated with and without a matrix crack in the central -theta plies. The interlaminar normal stress changes from a small compressive stress when no matrix crack is present to a high tensile stress at the intersection of the matrix crack and free edge. The analysis of local delamination from the -theta matrix crack indicates a high strain energy release rate and a localized mode I component near the free edge, within one ply distance from the matrix crack. In order to examine the stress state causing the matrix cracking the maximum principal normal stress in a plane perpendicular to the fiber direction in the -theta ply was calculated in an uncracked laminate. The corresponding shear stress parallel to the fiber was also calculated. The principal normal stress at the laminate edge increases through the ply thickness and reached a very high tensile value at the theta/-theta interface indicating that the crack in the -theta ply may initiate at the theta/-theta interface. Crack profiles on the laminate edge in the -theta ply were constructed from the principal stress directions. The cracks were found to be more curved for layups with smaller theta angles, which is consistent with experimental observations in the literature.

Salpekar, S. A.↗

DOE OSTI2022

On the efficacy of post-build thermomechanical treatments to improve properties of Zirconium fabricated using ultrasonic additive manufacturing

Here, hot-isostatic pressing has been applied to Zirconium plate fabricated using the ultrasonic additive manufacturing (UAM) technique to enhance interfacial bond quality. Specimens heated to 800 C for 1 h at 100 MPa pressure showed grain growth across many prior foil-to-foil interfaces, thereby increasing foil adhesion. In addition to the material softening induced by a loss of Hall-Petch strengthening, premature failure of specimens loaded parallel to the build direction was observed. Premature specimen failure was attributed to the local delamination at prior foil-to-foil boundaries where grain growth was pinned by Ti impurities introduced during the UAM process via the interaction between a Ti-alloy buffer foil and the welded Zr-foils underneath. In addition, the presence of Ti along select foil interfaces resulted in the nucleation and growth of secondary (Zr,Ti)(Fe,Cr) laves phases during higher-temperature thermomechanical processing. Using a combination of micro-scale X-ray computed tomography, fractography, and in-situ digital image correlation, the effect of defects along prior foil-to-foil boundaries was revealed as delamination-assisted plasticity accelerated specimen failure in preferred tensile orientations. These findings underscore the importance of impurity control when optimizing weld quality of higher-strength material systems using ultrasonic welding.

36 MATERIALS SCIENCE↗

NASA NTRS1991

Chemical compatibility issues related to use of copper as an interfacial layer for SiC fiber reinforced Ti3Ai+Nb composite

The reaction of Cu, a potential interfacial compliant layer for the Ti3Al plus Nb/SiC composite, with SiC, SCS-6 fiber, and the Ti3Al plus Nb matrix was examined at two temperatures: 1223 and 1273 K. Reaction of Cu with SiC resulted in the formation of a CuSi solution and free carbon, the reaction product being molten at 1273 K. Hot pressing the SCS-6 fiber in a Cu matrix at 1273 K resulted in cracking and delamination of the outer carbon-rich coating, thus allowing the Cu to penetrate to the SiC-carbon coating interface and react with SiC. In contrast, no such damage to the outer coating was observed at 1223 K. There was excessive reaction between Cu and the Ti3Al plus Nb matrix, the reaction product being molten both at 1223 and 1273 K. An interlayer of Nb between Cu and Ti3Al plus Nb matrix prevented the reaction between the two.

Misra, Ajay K.↗

NASA NTRSDate not supplied

TPSAS-NF1676L-32227-DND

The ability of a recently proposed cohesive fatigue model to predict the initiation and propagation of skin/stiffener separation was evaluated using a three-point bend (3PB) configuration. The 3PB specimen consists of a quasi-isotropic laminate representing the skin of a fuselage. A shorter doubler representing the flange of a stiffener is co-cured at the center of the specimen. A simplified modeling technique was applied, in which the complex damage mechanisms involved in the separation, such as delamination migration, matrix cracking, bridging, and crack delving are represented by a mixed-mode trilinear cohesive law at the interface between the skin and the doubler. The quasi-static properties of the trilinear law were characterized. The main advantage of the proposed fatigue model is that it relies on quasi-static properties as well as engineering assumptions to compose the shape of the S-N diagram. The model does not require Paris law data, and it is capable of predicting the initiation of separation, the rate of propagation, as well as the effects of crack resistance curves and the stress ratio.

Carlos G Davila↗

DOE OSTI2026

Geometrical effects on the measured neutron residual stress in additively manufactured cold spray AA6061

Aluminum cold spray additive builds were made with varying wall widths and geometries to explore the effects of build geometry on residual stress development in the additively sprayed material. Deposition rates of over 750 g/hr were achieved without any cracking or delamination of the additively manufactured components. Neutron residual stress measurements revealed a maximum tensile residual stress of 41 MPa at the interface of the substrate and a maximum compressive residual stress of −35 MPa in the cold sprayed material. While there was not found to be significant residual stress changes between the cold sprayed walls, the cold sprayed cylinder had varying residual stress throughout the diameter with the outer diameter having a higher tensile residual stress than the interior. The low residual stress and minimal geometrical dependency demonstrate further part size is possible without concerns for component failure in AA6061. The application of common coating residual stress models to full scale additive builds is evaluated and discussed. The lack of residual stress evolution was studied by in-situ coating property measurement that revealed that the deposition stress of the AA6061 sprays reduced with increased layer thickness. In conclusion, this study provides insight into the evolution of residual stress in cold spray additive components and how both the mechanics and material responses differ from coatings.

Additive manufacturing↗

DOE OSTI2023

Understanding and Mitigating the Dissolution and Delamination Issues Encountered with High-Voltage LiNi 0.5 Mn 1.5 O 4

In our initial study on the high-voltage 5 V cobalt-free spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode, we discovered a severe delamination issue in the laminates when cycled at a high upper cut-off voltage (UCV) of 4.95 V, especially when a large cell format was used. This delamination problem prompted us to investigate further by studying the transition metal (TM) dissolution mechanism of cobalt-free LNMO cathodes, and as a comparison, some cobalt-containing lithium nickel manganese cobalt oxides (NMC) cathodes, as the leachates from the soaking experiment might be the culprit for the delamination. Unlike other previous reports, we are interested in the intrinsic stability of the cathode in the presence of a baseline Gen2 electrolyte consisting of 1.2 M of LiPF 6 in ethylene carbonate/ethyl methyl carbonate (EC/EMC), similar to a storage condition. The electrode laminates (transition metal oxides, transition metal oxides, TMOs, coated on an Al current collector with a loading level of around 2.5 mAh/cm 2 ) or the TMO powders (pure commercial quality spinel LNMO, NMC, etc.) were stored in the baseline solution, and the transition metal dissolution was studied through nuclear magnetic resonance, such as 1 H NMR, 19 F NMR, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). Significant electrolyte decomposition was observed and could be the cause that leads to the TM dissolution of LNMO. To address this TM dissolution, additives were introduced into the baseline electrolyte, effectively alleviating the issue of TM dissolution. The results suggest that the observed delamination is caused by electrolyte decompositions that lead to etching, and additives such as lithium difluorooxalato borate and p-toluenesulfonyl isocyanate can alleviate this issue by forming a firm cathode electrolyte interface. This study provides a new perspective on cell degradation induced by electrode/electrolyte interactions under storage conditions.

25 ENERGY STORAGE↗

NASA NTRS1999

Mechanical Behavior of a Hi-Nicalon(tm)/SiC Composite Having a Polycarbosilane Derived Matrix

Polymer infiltration of a rigidized preform, followed by pyrolysis to convert the polymer to a ceramic, potentially offers a lower cost alternative to CVD. It also offers more moderate temperature requirements than melt infiltration approaches, which should minimize potential fiber damage during processing. However, polymer infiltration and pyrolysis results in a more microcracked matrix. Preliminary mechanical property characterization, including elevated temperature (1204 C) tensile, 500 h stress rupture behavior and low cycle fatigue, was conducted on Hi-Nicalon (TM)/Si-C-(O) composites having a dual layer BN/SiC interface and a matrix derived by impregnation and pyrolysis of allylhydridopolycarbosilane (AHPCS). Microstructural evaluation of failure surfaces and of polished transverse and longitudinal cross sections of the failed specimens was used to identify predominant failure mechanisms. In stress rupture testing at 1093 C, the failure was interface dominated, while at 1204 C in both stress rupture and two hour hold/fatigue tests failure was matrix dominated, resulting in specimen delamination.

Hurwitz, Frances I.↗

NASA NTRS2004

The Influence of Sizings on the Durability of High-Temperature Polymer Composites

To increase performance and durability of high-temperature composites for potential rocket engine components, it is necessary to optimize wetting and interfacial bonding between high modulus carbon fibers and high-temperature polyimide resins. Sizings commercially supplied on most carbon fibers are not compatible with polyimides. In this study, the chemistry of sizings on two high-modulus carbon fibers (M40J and M60J, Toray) was characterized as was the chemistry of PMR-II-50 fluorinated polyimide resin. The carbon fibers were characterized using single filament wetting, scanning electron microscopy, fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopic measurements. The polyimide matrix resins were coated onto glass filaments for characterization by wetting measurements. Surface energy components were obtained by wetting with nondispersive (methylene iodide), acidic (ethylene glycol), and basic (formamide) probes. A continuous desizing system that uses an environmentally friendly chemical-mechanical process was developed for tow level fiber. Composites were fabricated with fibers containing the manufacturer's sizing, desized, and further treated with a reactive finish. Results of room-temperature tests after thermal aging show that the reactive finish produces a higher strength and more durable interface compared to the manufacturer's sizing. When exposed to moisture blistering tests, however, the better bonded composite displayed a tendency to delaminate, presumably due to trapping of volatiles.

Allred, Ronald E.↗

NASA NTRS2003

Effect of Sizings on the Durability of High Temperature Polymer Composites

To increase performance and durability of high-temperature composite for potential rocket engine components, it is necessary to optimize wetting and interfacial bonding between high modulus carbon fibers and high-temperature polyimide resins. Sizing commercially supplied on most carbon fiber are not compatible with polyimides. In this study, the chemistry of sizing on two high modulus carbon fiber (M40J and M60J, Tiray) was characterized. A continuous desizling system that uses an environmentally friendly chemical-mechanical process was developed for tow level fiber. Composites were fabricated with fibers containing the manufacturer's sizing, desized, and further treated with a reactive finish. Results of room-temperature tests after thermal aging show that the reactive finish produces a higher strength and more durable interface compared to the manufacturer's sizing. When exposed to moisture blistering tests, however, the butter bonded composite displayed a tendency to delaminate, presumably due to trapping of volatiles.

Allred, Ronald E.↗

NASA NTRS2015

An Analysis Methodology to Predict Damage Propagation in Notched Composite Fuselage Structures

A new methodology is proposed for predicting damage propagation in notched composite skin-stiffened structures. The proposed approach considers the interaction of damage propagation in the skin with delamination of the stiffener in order to assess the damage containment behavior of the structure. The damage propagating from a notch within a thin fiber-reinforced polymer skin is idealized as a through-the-thickness cohesive crack. The cohesive law for the through-the-thickness crack is characterized using a compact tension test. The approach was applied to a full-scale pultruded rod stitched efficient unitized structure (PRSEUS) concept fuselage panel that was tested recently. The stitched skin/stringer interfaces, a key feature of the PRSEUS concept, were modeled to assess the effectiveness of the stitching at containing damage propagation. Comparison between the predicted and observed damage extension shows acceptable agreement throughout loading. These results indicate that the model can represent accurately the complex interactions between a through-the-thickness crack in the skin and delamination between the skin and stringer. The model is used to demonstrate that the skin-stiffener interface toughness is critical to damage containment capability

Bergan, A.↗

DOE OSTI2022

Leak-tight crack repair for 304L stainless steel using friction surfacing

Here, friction surfacing (FS) was investigated as a method for sealing 50 μm wide thru-cracks in 3-mm-thick 304L stainless steel (304L) plate. Friction surfacing was performed using two sizes of 304L consumable rod, with diameters of 9.52 mm and 12.7 mm, on two substrate conditions (clean and oxidized). Friction surfacing was able to deposit a 600 μm thick coating and repair cracks to a depth of 100 μm - 200 μm below the original surface, when using the 12.7-mm-diameter consumable rod for both substrate conditions. Helium leak rates of 10 -10 atm-cc/s were achieved on crack repairs, designating them as leak-tight by the ANSI N14.5 standard. Optical and scanning electron microscopy were used to investigate the coating microstructure and bond interfaces. In this study, the 12.7-mm-diameter rod performed better with disruption of the oxide layer on the oxidized substrate and providing a more homogenous coating. Mechanical properties of the coated samples were evaluated by performing micro-indentation, tensile, bending, and adhesion testing. Higher hardness in the coatings was observed due to the fine equiaxed grains resulting from dynamic recrystallization. Complete consolidation of plastically deformed material on the substrate and a strong diffusion bond across the interface was observed. This was reflected in tensile and bending properties of the FS coatings being comparable to those of uncoated specimen. No delamination of the FS coating was observed during adhesion testing. The results demonstrate that friction surfacing is a viable option to seal cracks in stainless steels.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Optimization of thermal barrier coating performance and durability over a drive cycle

A methodology to thermo-mechanically optimize a piston thermal barrier coating over a full drive cycle was established. The optimization objective was to minimize the heat transfer to the engine wall while maintaining structural integrity of the coating. Over 800 candidate materials were investigated and the optimization required more than one million non-road transient drive cycle calculations; real materials were investigated to ensure a realizable result and the existence of thermal and mechanical properties. High computational efficiency was achieved using a recently developed analytical heat transfer technique for multilayer engine walls. An uncoupled approach was utilized for the optimization, wherein the gas temperature and heat transfer coefficient profiles from a fully coupled and calibrated baseline model over the 20-min drive cycle were employed. The coating/piston interface temperature was constrained to be below the maximum piston service temperature limit. The durability was assessed using a recently developed analytical coating delamination framework for engine in-cylinder coatings based on the energy release rate when a crack forms. Results are presented for a mechanically unconstrained optimization and for cases constrained to three fixed levels of drive-cycle maximum energy release rate, and also constrained by the individual material’s toughness. The best-performing coating materials identified were verified using the fully coupled system-level model, which compared well to the uncoupled predictions. A study on the effect of adding a sealing layer to some high-performing, but porous, coatings showed a reduction in fuel consumption benefit and an increased exhaust temperature over the cycle, but the system still outperformed the uncoated case. The results of the study elucidate the importance of including engine performance and mechanical failure considerations in thermal barrier coating design.

Engineering↗

DOE OSTI2026

Influence of Shear Strength Assumptions on BISON Debonding Simulations

Accurately predicting the thermomechanical response of buffer–IPyC debonding in TRISO fuel particles requires reliable mechanical property inputs for each coating layer, particularly the normal and shear strengths that influence interlayer delamination and stress concentrations. Micro tensile testing of AGR-2 fuel particles provided experimentally measured normal strengths for the buffer, IPyC, and buffer–IPyC interface; however, shear strength was not measured. As a result, BISON simulations of interface debonding must rely on assumed shear strength values, typically estimated as 20–40% of the measured ultimate tensile strength. This study evaluates how these assumed shear strength values influence cohesive zone model (CZM) predictions of buffer–IPyC separation in AGR 2 TRISO particles. Using micro tensile data from three AGR 2 compacts (2 1 3, 5 1 3, and 6 3 3), BISON simulations were performed with multiple shear strength assumptions to quantify their effect on radial and tangential stress evolution, debonding, and gap propagation. The results show that shear strength is a high sensitivity parameter: increasing the assumed shear strength significantly alters the stress distribution at the buffer–IPyC junction, shifts the predicted debonding location, and changes the extent of partial gap formation. While normal strength controls the initiation of interface separation, shear strength strongly influences the mode mixity of the failure process and the resulting stress concentrations transmitted to the IPyC and SiC layers. These findings highlight a critical gap in current TRISO mechanical characterization. Without experimentally measured shear strength, BISON simulations must rely on approximations that introduce uncertainty into predictions of coating layer integrity and fission product barrier performance. Future fuel qualification campaigns should therefore consider measurement of shear strength at the interlayer interfaces to reduce model uncertainty and improve the fidelity of TRISO fuel performance simulations.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2025

Self‐Lubricating Tribo‐Catalytic Activity of 2D High Entropy Alloy Nanoflakes

High Entropy Alloys (HEAs) have garnered attention due to their remarkable tribological attributes. Predominantly, failure mechanisms in HEAs emanate from stress‐induced dislocations, culminating in crack propagation and film delamination. In this study, we report on the synthesis of 2D HEA of (MoWNbTaV) 0.2 S 2 which facilitates shear‐induced energy dissipation at sliding interfaces. The ball‐on‐disk tribological investigations demonstrate unprecedentedly low average coefficients of friction (0.076) and wear rates (10 −9 mm 3 (N∙m) −1 ) under high contact pressures (0.936 GPa) within ambient conditions. Employing multi‐scale characterizations alongside molecular dynamic simulations, we elucidate that the presence of the HEA triggers tribocatalytic activity under high contact pressures emerging as a pivotal factor in extending lubricant lifespan during tribological tests. The resilient lubriciousness coupled with the facile spray coating methodology of (MoWNbTaV) 0.2 S 2 in ambient environments paves the way for the development of a new class of solid lubricants based on 2D HEA.

2D solid lubricant↗

DOE OSTI2024

Interfacial charge transfer driven by surface termination-controlled Ti 2 C MXene for enhanced hydrogen storage in magnesium

Two-dimensional transition metal carbides and nitrides (MXenes) with layered structure and high conductivity have been effectively utilized in various energy materials, including as a catalytic support of MgH 2 for hydrogen storage. However, the terminal groups formed on the surface during the etching step tend to deactivate reactive Mg metal and add dead mass, thereby deteriorating the catalytic role of MXene in hydrogen sorption of Mg. For this work, we exploited a molten-salt derived MXene with easily modifiable –Cl terminations, compared to conventional –O, –OH and –F groups, and synthesized a composite of Mg and delaminated Ti 2 CCl x MXene to improve the hydrogen storage performance of Mg through charge transfer. This strategy enables the formation of an intimate interface between Mg and MXene, facilitating charge transfer and thereby boosting the catalytic effect. The resulting composite demonstrates significantly enhanced hydrogen sorption kinetics by modulating Mg–H bond strength. This novel approach of modifying surface terminations leverages the unique properties of MXene as a superior support for active materials, offering broader applications in energy materials.

2D material↗