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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Statistical Analyses of Raw Material Data for MTM45-1/CF7442A-36% RW: CMH Cure Cycle

This report describes statistical characterization of physical properties of the composite material system MTM45-1/CF7442A, which has been tested and is currently being considered for use on spacecraft structures. This composite system is made of 6K plain weave graphite fibers in a highly toughened resin system. This report summarizes the distribution types and statistical details of the tests and the conditions for the experimental data generated. These distributions will be used in multivariate regression analyses to help determine material and design allowables for similar material systems and to establish a procedure for other material systems. Additionally, these distributions will be used in future probabilistic analyses of spacecraft structures. The specific properties that are characterized are the ultimate strength, modulus, and Poisson􀂶s ratio by using a commercially available statistical package. Results are displayed using graphical and semigraphical methods and are included in the accompanying appendixes.

Coroneos, Rula↗
NASA NTRS2004

Gear Performance Improved by Coating

Gears, bearings, and other mechanical elements transmit loads through contacting surfaces. Even if properly designed, manufactured, installed, and maintained, gears and bearings will eventually fail because of the fatigue of the working surfaces. Economical means for extending the fatigue lives of gears and bearings are highly desired, and coatings offer the opportunity to engineer surfaces to extend the fatigue lives of mechanical components. A tungsten-containing diamondlike-carbon coating exhibiting high hardness, low friction, and good toughness was evaluated for application to spur gears. Fatigue testing was done at the NASA Glenn Research Center on both uncoated and coated spur gears. The results showed that the coating extended the surface fatigue lives of the gears by a factor of about 5 relative to the uncoated gears. For the experiments, a lot of spur test gears made from AISI 9310 gear steel were case-carburized and ground to aerospace specifications. The geometries of the 28-tooth, 8-pitch gears were verified as meeting American Gear Manufacturing Association (AGMA) quality class 12. One-half of the gears were randomly selected for coating. The method of coating was selected to achieve desired adherence, toughness, hardness, and low-friction characteristics. First the gears to be coated were prepared by blasting (vapor honing) with Al2O3 particles and cleaning. Then, the gears were provided with a thin adhesion layer of elemental chromium followed by magnetron sputtering of the outer coating consisting of carbon (70 at.%), hydrogen (15 at.%), tungsten (12 at.%), and nickel (3 at.%) (atomic percent at the surface). In total, the coating thickness was about 2.5 to 3 microns. As compared with the steel substrate, the coated surface was harder by a factor of about 2 and had a smaller elastic modulus. All gears were tested using a 5-centistoke synthetic oil, a 10,000-rpm rotation speed, and a hertzian contact stress of at least 1.7 GPa (250 ksi). Tests were run until either surface fatigue occurred or 300 million stress cycles were completed. Tests were run using either a pair of uncoated gears or a pair of coated gears (coated gears mated with uncoated gears were not evaluated). The fatigue test results, shown on Weibull coordinates in the graph, demonstrate that the coating provided substantially longer fatigue lives even though some of the coated gears endured larger stresses. The increase in fatigue life was a factor of about 5 and the statistical confidence for the improvement is high (greater than 99 percent). Examination of the tested gears revealed substantial reductions of total wear for coated gears in comparison to uncoated gears. The coated gear surface topography changed with running, with localized areas of the tooth surface becoming smoother with running. Theories explaining how coatings can extend gear fatigue lives are research topics for coating, tribology, and fatigue specialists. This work was done as a partnership between NASA, the U.S. Army Research Laboratory, United Technologies Research Corporation, and Sikorsky Aircraft.

Krantz, Timothy L.↗
DOE OSTI2023

High‐Throughput Evaluation of Hardening Coefficients of Eight Alloying Elements in Magnesium

Liquid–solid diffusion couples (LSDCs) are employed to generate a composition gradient in the single‐phase hexagonal closed‐packed (hcp) solid solution with compositions up to the solubility limit of various solutes in Mg. Nanoindentation scanning across the composition gradient in LSDCs allows effective evaluation of composition‐dependent hardness of eight alloying elements (Al, Ca, Ce, Gd, Li, Sn, Y, and Zn) in the hcp Mg phase. The hardening coefficients, an indicator of the potency of solid‐solution hardening, are evaluated from the measured composition‐hardness data and correlated with various materials properties such as atomic radius, shear modulus, and elastic modulus of the solutes. The rank of hardening potency of Al, Gd, Sn, Y, and Zn measured by nanoindentation is in good agreement with that measured by microindentation reported in the literature. The hardening coefficient (potency) from the strongest to the weakest is Ce > Ca > Y ≈ Gd > Zn > Al ≈ Sn > Li in Mg‐based hcp binary solid solutions. The hardening coefficient is found to be closely correlated with the strengthening potency.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-Pressure Structural and Thermodynamic Properties of Cerium Orthosilicates (CeSiO 4 )

Pressure-induced phase transitions from the zircon structure-type (I4 1 /amd) to the scheelite structure type (I4 1 /a) are known for many ternary oxides systems (ABO 4 ). In this work, we present the first high-pressure study on synthetic stetindite (CeSiO 4 ) by a combination of in situ high-pressure synchrotron powder X-ray diffraction up to 36 GPa, implemented with and without dual sided laser heating, and in situ high-pressure Raman spectroscopy up to 43 GPa. Two phase transitions were identified: zircon to a high-pressure low-symmetry (HPLS) phase at 15 GPa and then to a scheelite at 18 GPa. The latter from HPLS scheelite phase was found irreversible; i.e., scheelite is fully quenchable at ambient conditions, as in other zircon-type phases. The bulk moduli (K 0 ) of stetindite, HPLS, and high-pressure scheelite phases were determined, respectively, as 171(5), 105(4), and 221(40) GPa by fitting to a second-order Birch-Murnaghan equation of state. The pressure derivatives of vibrational modes and Gru''neisen parameters of the zircon-structured polymorph are similar to those of other orthosilicate minerals. In conclusion, due to the larger ionic radii of Ce 4+ , with respect to Zr 4+ , stetindite was found to possess a softer bulk modulus and undergo the phase transitions at a lower pressure than zircon (ZrSiO 4 ), such observations are consistent with what were found in coffinite (USiO 4 ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Structural, Thermal, and Mechanical Characterization of a Thermally Conductive Polymer Composite for Heat Exchanger Applications

Polymer composites are being considered for numerous thermal applications because of their inherent benefits, such as light weight, corrosion resistance, and reduced cost. In this work, the microstructural, thermal, and mechanical properties of a 3D printed polymer composite with high thermal conductivity are examined using multiple characterization techniques. Infrared spectroscopy and X-ray diffraction reveal that the composite contains a polyphenylene sulfide matrix with graphitic fillers, which is responsible for the high thermal conductivity. Furthermore, differential scanning calorimetry determines that the glass transition and melting point of the composite are 87.6 °C and 285.6 °C, respectively. Thermogravimetric analysis reveals that the composite is thermally stable up to ~400 °C. Creep tests are performed at different isotherms to evaluate the long-term performance of the composite. The creep result indicates that the composite can maintain mechanical integrity when used below its glass transition temperature. Nanoindentation tests reveal that modulus and hardness of the composite is not significantly influenced by heating or creep conditions. These findings indicate that the composite is potentially suitable for heat exchanger applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Experimental Comparison of Elastomeric Materials for Hydraulic Seal Durability under Reciprocating Conditions

Wave Energy Converters (WECs) rely on hydraulic Power Take-Off (PTO) systems to transform the kinetic energy of ocean waves into electricity, where hydraulic seals play a critical role in preventing fluid leakage and ensuring watertight operation under harsh marine conditions. However, seal degradation due to wear, fatigue, and corrosion remains a key challenge limiting system reliability and increasing maintenance costs. In this study, the tribological performance of elastomeric materials for hydraulic sealing applications that are based on commercial polyurethane and custom-compounded Ethylene Propylene Diene Monomer (EPDM) is investigated. Using a CSM tribometer, reciprocating wear tests were conducted in accordance with ASTM G133 under dry sliding conditions, with normal loads ranging from 3 to 10 N, and sliding speeds of 10 to 30 mm/s. Coefficient of friction (COF), specific wear rate, and worn surface morphology are evaluated to understand how load, velocity, and material composition affect seal durability. Improved wear stability and high Shore A hardness (93–94) were demonstrated by the commercial thermoplastic polyurethane (Duralast 4203 and 4758). EPDM-based compounds showed different filler-dependent behaviors, formulations filled with carbon black (E3) had the lowest wear rate (1.45 × 10?4 mm³ N?¹ m?¹) and increased load-bearing capacity, while samples modified with silica and plasticizer (E4, E5) had better conformability and damping but less hardness. Compounded EPDMs showed wider deformation zones because of their lower modulus and filler-matrix interfacial fluctuations, while commercial grades exhibited shallower wear scars (= 380 µm), according to optical profilometry. The Archard model-based lifetime estimation showed that, under 10 N and 30 mm/s, operational endurance ranged from 3.1 to 6.2 years. Because of its low wear rate and steady interfacial behavior, E3 had the longest anticipated life. For medium-load hydraulic sealing applications, these results demonstrate the possibility of customized EPDM formulations as affordable substitutes for commercial polyurethanes. They also offer a quantitative foundation for material selection and lifespan prediction.

Durability↗
NASA NTRS1998

Effect of Composite Fabrication on the Strength of Single Crystal Al2O3 Fibers in Two Fe-Base Alloy Composites

Continuous single-crystal Al2O3 fibers have been incorporated into a variety of metal and intermetallic matrices and the results have consistently indicated that the fiber strength had been reduced by 32 to 50% during processing. Two iron-based alloys, FeNiCoCrAl and FeAlVCMn, were chosen as matrices for Al2O3 fiber reinforced metal matrix composites (MMC) with the goal of maintaining Al2O3 fiber strength after composite processing. The feasibility of Al2O3/FeNiCoCrAl and Al2O3/FeAlVCMn composite systems for high temperature applications were assessed in terms of fiber-matrix chemical compatibility, interfacial bond strength, and composite tensile properties. The strength of etched-out fibers was significantly improved by choosing matrices containing less reactive elements. The ultimate tensile strength (UTS) values of the composites could generally be predicted with existing models using the strength of etched-out fibers. However, the UTS of the composites were less than desired due to a low fiber Weibull modulus. Acoustic emission analysis during tensile testing was a useful tool for determining the efficiency of the fibers in the composite and for determining the failure mechanism of the composites.

Draper, Susan L.↗
NASA NTRS2014

Increased Tensile Strength of Carbon Nanotube Yarns and Sheets through Chemical Modification and Electron Beam Irradiation

The inherent strength of individual carbon nanotubes offers considerable opportunity for the development of advanced, lightweight composite structures. Recent work in the fabrication and application of carbon nanotube (CNT) forms such as yarns and sheets has addressed early nanocomposite limitations with respect to nanotube dispersion and loading; and has pushed the technology toward structural composite applications. However, the high tensile strength of an individual CNT has not directly translated to macro-scale CNT forms where bulk material strength is limited by inter-tube electrostatic attraction and slippage. The focus of this work was to assess post processing of CNT sheet and yarn to improve the macro-scale strength of these material forms. Both small molecule functionalization and e-beam irradiation was evaluated as a means to enhance tensile strength and Youngs modulus of the bulk CNT material. Mechanical testing results revealed a tensile strength increase in CNT sheets by 57 when functionalized, while an additional 48 increase in tensile strength was observed when functionalized sheets were irradiated; compared to unfunctionalized sheets. Similarly, small molecule functionalization increased yarn tensile strength up to 25, whereas irradiation of the functionalized yarns pushed the tensile strength to 88 beyond that of the baseline yarn.

composites↗
DOE OSTI2025

Polypropylene Composites Reinforced With Recycled Waste Cellulosic Fiber/Fine Mixture: The Impact of Cellulose Sieving on Performance

This study explores how a sieving step of waste cellulosic fiber and fine (WCFF) mixture affects the performance of WCFF‐loaded polypropylene (PP) composites and whether the separation of fines from fibers offers an added benefit. The WCFF samples were downsized, and four different filler size ranges were sieved using a series of mesh sizes from 4 to 0.85 mm. The WCFF/PP composites were then compounded at 20 wt.% loading of WCFF using a twin‐screw extruder. Incorporating WCFF increased the tensile strength to 41.28 MPa and the modulus to 3207 MPa, accounting for 28% and 38% enhancements, respectively. Interestingly, the greatest improvements were associated with the nonsieved WCFF case, and the sieved WCFF fibers provided only marginal enhancements over virgin PP. The outperformance of nonsieved WCFF was attributed to the synergistic reinforcement of hybrid fibers and fines as well as the maintenance of longer fibers in the system. However, the strain at break and impact strength of PP decreased after introducing WCFF. Moreover, the complex viscosity and storage modulus increased with an increase in the filler size, due to the formation of a more effective percolative network. The PP's crystallinity exhibited a relatively strong dependency on the sieving, where WCFF samples with short‐aspect‐ratio fillers promoted the crystallinity significantly. It was also found that the WCFF degradation onset temperature increased once it was incorporated into PP. This study suggests that waste cellulosic feedstocks can be utilized as a reinforcement without additional sieving to manufacture high‐performance and cost‐effective composites.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Evaluating Use of Boron- and Hafnium-Modified Polysilazanes for Ceramic Matrix Minicomposites

In this study, the potential of polymer-derived Ceramic Matrix Composites (CMCs) is demonstrated by addition of thin ceramic coatings on Carbon Fiber (CF) bundles. Boron- and hafnium- modified polysilazane liquid precursors were synthesized and used to infiltrate the fiber bundles of CF to fabricate lab-scale Si(B)CN/CF and Si(Hf)CN/CF CMC mini-composites, respectively. The precursor-to-ceramic conversion process was achieved at 800°C with crosslinked precursor to ceramic yield of approx. 90% in Ar environment. The Si(B)CN/CF contained Si-N and B-N bonds, while Si-N and Hf-O-Si bonds were observed for Si(Hf)CN/CF sample with uniform and dense surfaces. Room-temperature tensile tests showed that the Si(Hf)CN/CF sample could reach a tensile strength of ~790 MPa and elastic modulus of 66.88 GPa among the composites. Oxidation study of the Si(Hf)CN/CF mini-composites showed higher stability compared to SiCN/CF and Si(B)CN/CF mini-composites up to 1500°C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1991

Simplified micromechanical equations for thermal residual stress analysis of coated fiber composites

The fabrication of metal matrix composites poses unique problems to the materials engineer. The large thermal expansion coefficient (CTE) mismatch between the fiber and matrix leads to high tensile residual stresses at the fiber/matrix (F/M) interface which could lead to premature matrix cracking during cooldown. Fiber coatings could be used to reduce thermal residual stresses. A simple closed form analysis, based on a three phase composite cylinder model, was developed to calculate thermal residual stresses in a fiber/interphase/matrix system. Parametric studies showed that the tensile thermal residual stresses at the F/M interface were very sensitive to the CTE and thickness of the interphase layer. The modulus of the layer had only a moderate effect on tensile residual stresses. For a silicon carbide titanium aluminide composite, the tangential stresses were 20 to 30 pct. larger than the axial stresses, over a wide range of interphase layer properties, indicating a tendency to form radial matrix cracks during cooldown. Guidelines for the selection of appropriate material properties of the fiber coating were also derived in order to minimize thermal residual stresses in the matrix during fabrication.

Naik, R. A.↗
NASA NTRS2000

Thermophysical and Thermomechanical Properties of Thermal Barrier Coating Systems

Thermal barrier coatings have been developed for advanced gas turbine and diesel engine applications to improve engine reliability and fuel efficiency. However, the issue of coating durability under high temperature cyclic conditions is still of major concern. The coating failure is closely related to thermal stresses and oxidation in the coating systems. Coating shrinkage cracking resulting from ceramic sintering and creep at high temperatures can further accelerate the coating failure process. The purpose of this paper is to address critical issues such as ceramic sintering and creep, thermal fatigue and their relevance to coating life prediction. Novel test approaches have been established to obtain critical thermophysical and thermomechanical properties of the coating systems under near-realistic temperature and stress gradients encountered in advanced engine systems. Emphasis is placed on the dynamic changes of the coating thermal conductivity and elastic modulus, fatigue and creep interactions, and resulting failure mechanisms during the simulated engine tests. Detailed experimental and modeling results describing processes occurring in the thermal barrier coating systems provide a framework for developing strategies to manage ceramic coating architecture, microstructure and properties.

Zhu, Dongming↗
DOE OSTI2026

Validated Reactive Force Field Quantifies MXene Interfacial Properties, Mechanics, and Thermal Transport

MXenes combine rich surface chemistry, mechanical strength, and high conductivity for a multitude of emerging applications. Predictive modeling supports accelerated materials designs and has been limited by the absence of validated and transferable force fields. Here, we introduce an interpretable, reactive INTERFACE force field (IFF and IFF-R) for Ti 3 C 2 T x MXenes that is trained based on chemical knowledge and achieves quantitative agreement with experiments across lattice parameters (<0.5%), density (<0.2%), liquid contact angles, Raman spectra, and the in-plane elastic modulus (∼320 GPa). The models cover surface terminations from hydroxyl (−OH) to fluorine (−F) groups and are extensible to other chemistries. We introduce pH-resolved surface chemistry and identify dopamine adsorption mechanisms at MXene–aqueous interfaces supported by QCM-D and UV–Vis experiments. The data reveal coplanar and perpendicular binding modes and concentration-dependent multilayer assembly. We predict previously inaccessible properties, including termination-dependent cleavage energies, interlayer shear moduli and dynamic shear failure, nanoindentation and brittle fracture, anisotropic in-plane and out-of-plane thermal conductivities, including the role of defects. Agreement with available experimental data is consistently close and exceeds DFT accuracy across the benchmark properties examined. The IFF/IFF-R model is compatible with CHARMM, AMBER, OPLS, and CVFF force fields for simulations of MXenes with diverse surface terminations, electrolyte interfaces, biointerfaces, and polymer composites without additional parameters. Parameter sets, 3D models, and analysis scripts are provided for community use. The validated, reactive, and transferable IFF framework facilitates predictive design of MXene-based films, membranes, sensing interfaces, and composites.

MXene↗
NASA NTRS1972

Applications of the direct photon absorption technique for measuring bone mineral content in vivo. Determination of body composition in vivo

The bone mineral content, BMC, determined by monoenergetic photon absorption technique, of 29 different locations on the long bones and vertebral columns of 24 skeletons was measured. Compressive tests were made on bone from these locations in which the maximum load and maximum stress were measured. Also the ultimate strain, modulus of elasticity and energy absorbed to failure were determined for compact bone from the femoral diaphysis and cancellous bone from the eighth through eleventh thoracic vertebrae. Correlations and predictive relationships between these parameters were examined to investigate the applicability of using the BMC at sites normally measured in vivo, i.e. radius and ulna in estimating the BMC and/or strength of the spine or femoral neck. It was found that the BMC at sites on the same bone were highly correlated r = 0.95 or better; the BMC at sites on different bones were also highly interrelated, r = 0.85. The BMC at various sites on the long bones could be estimated to between 10 and 15 per cent from the BMC of sites on the radius or ulna.

Cameron, J. R.↗
NASA NTRS1996

Control of Thermal Deflection, Panel Flutter and Acoustic Fatigue at Elevated Temperatures Using Shape Memory Alloys

The High Speed Civil Transport (HSCT) will have to be designed to withstand high aerodynamic load at supersonic speeds (panel flutter) and high acoustic load (acoustic or sonic fatigue) due to fluctuating boundary layer or jet engine acoustic pressure. The thermal deflection of the skin panels will also alter the vehicle's configuration, thus it may affect the aerodynamic characteristics of the vehicle and lead to poor performance. Shape memory alloys (SMA) have an unique ability to recover large strains completely when the alloy is heated above the characteristic transformation (austenite finish T(sub f)) temperature. The recovery stress and elastic modulus are both temperature dependent, and the recovery stress also depends on the initial strain. An innovative concept is to utilize the recovery stress by embedding the initially strained SMA wire in a graphite/epoxy composite laminated panel. The SMA wires are thus restrained and large inplane forces are induced in the panel at elevated temeperatures. By embedding SMA in composite panel, the panel becomes much stiffer at elevated temperatures. That is because the large tensile inplane forces induced in the panel from the SMA recovery stress. A stiffer panel would certainly yield smaller dynamic responses.

Mei, Chuh↗
NASA NTRS2011

AC Electric Field Activated Shape Memory Polymer Composite

Shape memory materials have drawn interest for applications like intelligent medical devices, deployable space structures and morphing structures. Compared to other shape memory materials like shape memory alloys (SMAs) or shape memory ceramics (SMCs), shape memory polymers (SMPs) have high elastic deformation that is amenable to tailored of mechanical properties, have lower density, and are easily processed. However, SMPs have low recovery stress and long response times. A new shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive fillers to enhance its thermo-mechanical characteristics. A new composition of shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive functionalized graphene sheets (FGS) to enhance its thermo-mechanical characteristics. The elastic modulus of LaRC-SMPC is approximately 2.7 GPa at room temperature and 4.3 MPa above its glass transition temperature. Conductive FGSs-doped LaRC-SMPC exhibited higher conductivity compared to pristine LaRC SMP. Applying an electric field at between 0.1 Hz and 1 kHz induced faster heating to activate the LaRC-SMPC s shape memory effect relative to applying DC electric field or AC electric field at frequencies exceeding1 kHz.

Kang, Jin Ho↗
NASA NTRS1988

High performance composites research at NASA-Langley

Barriers to the more extensive use of advanced composites in heavily loaded structures on commercial transports are discussed from a materials viewpoint. NASA Langley matrix development activities designed to overcome these barriers are presented. These include the synthesis of processable, tough, durable matrices, the development of resin-property/composite-property relationships which help guide the synthesis program, and the exploitation of new processing technology to effectively combine reinforcement filaments with polymer matrices. Examples of five classes of polymers being investigated as matrix resins at NASA Langley are presented, including amorphous and semicrystalline thermoplastics, lightly crosslinked thermoplastics, semiinterpenetrating networks, and toughened thermosets. Relationships between neat resin modulus, resin fracture energy, interlaminar fracture energy, composite compression strength, and postimpact compression strength are shown. Powder and slurry processing techniques are discussed.

Saint Clair, Terry L.↗
DOE OSTI2022

Failure evaluation of neutron-irradiated SiC/SiC composites by underwater acoustic emission

Here, understanding the statistical properties of mechanical properties of non-irradiated and neutron-irradiated SiC/SiC composites is essential for component design. This study aims to evaluate the detailed damage accumulation behavior of composites focusing on two fracture parameters: proportional limit stress (PLS) and acoustic emission (AE) onset stress. The developmental underwater AE technique, which is benefit in non-contact in-situ failure monitoring method during mechanical testing and in handle of the irradiated material, was first applied to evaluate damage accumulation behavior. Two types of chemical vapor infiltration SiC/SiC composites were used: one reinforced with Hi-Nicalon Type-S SiC fiber and one reinforced with Tyranno-SA3 SiC fiber in the form of satin-woven 2D fabrics with pyrolytic carbon interface. Neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory reached a fluence of 30 dpa at a temperature of 620–670°C. Four-point flexural tests were conducted to evaluate post-irradiation strength. Weibull statistics did not suggest marked degradation of composite strength. Detailed failure behavior evaluated by AE demonstrated no irradiation-induced change of the AE onset stress (i.e., crack initiation equivalent stress). Failure probability analysis suggests that increasing the reliability of composites (i.e., the Weibull modulus rather than strength itself) is essential to expanding the design margin and benefiting from a probabilistic design approach.

36 MATERIALS SCIENCE↗