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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Effects of Core-Shell Rubber (CSR) Nanoparticles on the Cryogenic Fracture Toughness of CSR Modified Epoxy

This study investigated the effects of core-shell rubber (CSR) nanoparticles on the mechanical properties and fracture toughness of an epoxy resin at ambient and liquid nitrogen (LN2) temperatures. Varying amounts of Kane Ace(Registered TradeMark) MX130 and Kane Ace(Registered TradeMark) MX960 toughening agent were added to a commercially available EPON 862/Epikure W epoxy resin. Elastic modulus was calculated using quasi-static tensile data. Fracture toughness was evaluated by the resulting breaking energy measured in Charpy impact tests conducted on an instrumented drop tower. The size and distribution of the CSR nanoparticles were characterized using Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS). Scanning Electron Microscopy (SEM) was used to study the fracture surface morphology. The addition of the CSR nanoparticles increased the breaking energy with negligible change in elastic modulus and ultimate tensile stress (UTS). At ambient temperature the breaking energy increased with increasing additions of the CSR nanoparticles up to 13.8wt%, while at LN2 temperatures, it reached a plateau at much lower CSR concentration.

Wang, Jun↗
NASA NTRS1979

Evaluation of urethane for feasibility of use in wind turbine blade design

A preliminary evaluation was conducted of the use of cast urethane as a possible material for low-cost blades for wind turbines. Specimen test data are presented for ultimate tensile strength, elastic modulus, flexural strain, creep, and fatigue properties of a number of urethane formulations. Data are also included for a large-scale urethane blade section composed of cast symmetrical half-profiles tested as a cantilever beam. Based on these results, an analysis was conducted of a full-scale blade design of cast urethane that meets the design specifications of the rotor blades for the NASA/DOE experimental 100-kW MOD-0 wind turbine. Because of the low value of elastic modulus for urethane (around 457 000 psi), the design loads would have to be carried by metal reinforcement. Considerations for further evaluation are noted.

Lieblein, S.↗
DOE OSTI2019

The Critical Role of Electron-Donating Thiophene Groups on the Mechanical and Thermal Properties of Donor–Acceptor Semiconducting Polymers

Organic semiconducting donor–acceptor polymers are promising candidates for stretchable electronics owing to their mechanical compliance. However, the effect of the electron-donating thiophene group on the thermomechanical properties of conjugated polymers has not been carefully studied. Here, thin-film mechanical properties are investigated for diketopyrrolopyrrole (DPP)-based conjugated polymers with varying numbers of isolated thiophene moieties and sizes of fused thiophene rings in the polymer backbone. Interestingly, it is found that these thiophene units act as an antiplasticizer, where more isolated thiophene rings or bigger fused rings result in an increased glass transition temperature (T g ) of the polymer backbone, and consequently elastic modulus of the respective DPP polymers. Detailed morphological studies suggests that all samples show similar semicrystalline morphology. This antiplasticization effect also exists in para-azaquinodimethane-based conjugated polymers, indicating that this can be a general trend for various conjugated polymer systems. Using the knowledge gained above, a new DPP-based polymer with increased alkyl side chain density through attaching alky chains to the thiophene unit is engineered. The new DPP polymer demonstrates a record low T g , and 50% lower elastic modulus than a reference polymer without side-chain decorated on the thiophene unit. Finally, this work provides a general design rule for making low-T g conjugated polymers for stretchable electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Two-scale model for the effect of physical aging in elastomers filled with hard nanoparticles

A two-scale model is developed, and solved numerically, to describe the mechanical behavior of elastomers filled with hard nanoparticles. Of particular interest is the slow recovery of the elastic modulus after large-amplitude oscillatory deformation. To account for this effect, the physical aging of the glassy bridges between the filler particles is captured with two thermal degrees of freedom for the matrix material, namely a kinetic and a configurational one. Formulating the two-scale model enriched with aging in a nonequilibrium thermodynamics context, first results in a constitutive relation for the Cauchy stress tensor. Second, the dynamics of physical aging is described, which eventually results in the slow recovery of the elastic modulus with waiting time. The proposed model is investigated numerically under large amplitude oscillatory shear deformation. Of particular interest in this respect is the coupling of the micro-scale dynamics with the physical aging on the macroscopic scale. This coupling is examined in detail, both in an approximate way using a Gaussian approximation, as well as numerically, under specific conditions. It turns out that the CONNFFESSIT approach (Laso and Öttinger 1993 ) can not be employed for the numerical solution of the model under arbitrary loading conditions because of the novel structure of the two-level coupling term. While a procedure for solving the model numerically for the case of strong applied deformation is presented in this paper, other solution methodologies need to be sought for the cases of weak and no applied deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Sub-cellular force microscopy in single normal and cancer cells

This work investigates the biomechanical properties of sub-cellular structures of breast cells using atomic force microscopy (AFM). The cells are modeled as a triple-layered structure where the Generalized Maxwell model is applied to experimental data from AFM stress-relaxation tests to extract the elastic modulus, the apparent viscosity, and the relaxation time of sub-cellular structures. The triple-layered modeling results allow for determination and comparison of the biomechanical properties of the three major sub-cellular structures between normal and cancerous cells: the up plasma membrane/actin cortex, the mid cytoplasm/nucleus, and the low nuclear/integrin sub-domains. The results reveal that the sub-domains become stiffer and significantly more viscous with depth, regardless of cell type. In addition, there is a decreasing trend in the average elastic modulus and apparent viscosity of the all corresponding sub-cellular structures from normal to cancerous cells, which becomes most remarkable in the deeper sub-domain. The presented modeling in this work constitutes a unique AFM-based experimental framework to study the biomechanics of sub-cellular structures. - Highlights: • The cells are modeled as a triple-layered structure using Generalized Maxwell model. • The sub-domains include membrane/cortex, cytoplasm/nucleus, and nuclear/integrin. • Biomechanics of corresponding sub-domains are compared among normal and cancer cells. • Viscoelasticity of sub-domains show a decreasing trend from normal to cancer cells. • The decreasing trend becomes most significant in the deeper sub-domain.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Durable aluminate toughened zirconate composite thermal barrier coating (TBC) materials for high temperature operation

Research on advanced thermal barrier coating (TBC) materials capable of operating beyond 1200°C has primarily focused on the rare earth zirconate pyrochlores, particularly gadolinium zirconate (Gd 2 Zr 2 O 7 – GZO). The drawback of this material is a significant reduction in durability due to a low fracture toughness. This study investigates utilization of a thermodynamically compatible gadolinia alumina perovskite (GdAlO 3 – GAP) toughening phase to improve the durability of GZO. Dense pellets were fabricated to assess the material properties with minimal microstructural influence. Thermal stability, elastic modulus, hardness, indentation fracture resistance and erosion durability were evaluated for GZO, GAP, and composite pellets containing 10, 30, and 50 wt.% GAP. It was demonstrated that GAP and GZO are thermodynamically compatible through 1600°C and thus capable of operating well beyond the limits of traditional 7 wt.% yttria stabilized zirconia (YSZ). Grain sizes are maintained due to a lack of diffusion, and thus microstructural stability is enhanced. The GAP fracture toughness was shown to be over 2X that of GZO while exhibiting a lower elastic modulus and similar hardness. The 50:50 GZO-GAP composite exhibited a 63% reduction in the absolute erosion rate, demonstrating the immense toughening capabilities of this system. The implications for composite TBCs utilizing this system are discussed, along with future research.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus. -- Highlights: •Parameter study on material characteristics influencing overlay cracking. •Analytical model gives good quantitative indication of overlay cracking. •Ring test presents good qualitative indication of overlay cracking. •Curing duration has little effect on overlay cracking.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synergistic role of carbonaceous reinforcements on multi length scale tribology of electrophoretically deposited nickel-boron nitride coatings

Highlights: • Electrophoretic deposition of Ni-BN coating. • Reinforcement of Ni-BN with carbon allotropes (diamond, carbon nanotubes and graphene). • Enhanced hardness and elastic modulus in Ni-BN-D than Ni-BN-CNT and Ni-BN-Gr. • High wear resistance (0.45 × 10{sup −8} m{sup 3}) from fretting and micro-scratch testing of Ni-BN-D. • High compressive stress (−601 MPa) exist in Ni-BN-D coating which restricts wear. - Abstract: Electrophoretically deposited Ni-BN composite coating was strengthened with graphene (Ni-BN-Gr), carbon nanotubes (Ni-BN-CNT) and diamond (Ni-BN-D) carbonaceous reinforcements. Highest hardness (2.0 GPa) and elastic modulus (133.5 GPa) of Ni-BN-D coating than Ni-BN-CNT (1.96 GPa and 102.1 GPa, respectively), Ni-BN-Gr (1.94 GPa and 92.0 GPa respectively) and also from Ni-BN (1.89 GPa and 91.5 GPa, respectively) coatings was linked through high compressive stress (−601 MPa), dislocation density (8.9 × 10{sup 15} m{sup −2}) and yield strength (4.4 GPa). The micro-scratching damage was contributed by ploughing and adhesion components, which were compared with that of experimental frictional values. Addition of graphene, CNT and diamond in Ni-BN composite showed a decrease in wear volume (from 1.66 × 10{sup −8} m{sup 3} to 0.45 × 10{sup −8} m{sup 3}) due to the synergetic lubricating effect of BN and carbonaceous reinforcements. Thus, Ni-BN-D restrict inception of multiscale wear and can be a potential three phase metal-ceramic coating for engineering and industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of particle inclusions on cracking in ultrathin barrier films

Here, the effects of particle inclusions with different mechanical properties on the development of cracks in ultra-thin barrier films have been studied. Two types of particles, alumina and poly(styrene-b-methyl methacrylate) with large differences in their elastic modulus were used, representing both hard and soft inclusions. Particles were seeded onto polyethylene naphthalate substrates and subsequently coated with atomic layer deposited Al 2 O 3 as a barrier film. Ca corrosion tests used to determine the performance of the barrier films revealed that soft polymer particle inclusions severely affect the development of cracking in barrier films as compared to stiff ceramic particles. Tensile tests also confirmed that the barrier films with polymer particle inclusions have the lowest value of critical onset strain. Parametric simulations, conducted by varying the elastic modulus of the particle inclusions over a wide range, resulted in a larger strain energy release rate near particle inclusions which promotes crack formation and negatively impacts the performance of barrier films with softer particle inclusions. Thus, the combination of high residual stresses in the barrier films with the presence of soft particle inclusions is found the most detrimental for the development of high-performance ultrathin barrier films.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The effect of Sn addition on phase stability and phase evolution during aging heat treatment in Ti–Mo alloys employed as biomaterials

Increases in life expectancy and improvements in necessary healthcare attach great importance to the development of biomaterials. Ti alloys containing β stabilizing elements are often used as biomaterials due to their high specific strength, high corrosion resistance, unusual biocompatibility and low elastic moduli, which benefit bone tissues close to an implant. This study deals with phase stability in β Ti–Mo–Sn alloys processed under different conditions and was performed according to the following steps: a study of the effect of Sn content (a) on phase stability in Ti–Mo alloys, (b) on the suppression of α″ and ω phase precipitation; (c) on α-phase precipitation during aging heat treatments and (d) on mechanical properties, including the elastic modulus, as measured using tensile tests and acoustic techniques. The alloys were prepared by arc melting under a controlled atmosphere followed by homogenization heat treatment and hot rolling. Optical microscopy, scanning and transmission electron microscopy, X-ray diffraction and differential scanning calorimetry were employed for characterization purposes. Samples were also submitted to solution treatment above the β transus temperature and aging heat treatments under a controlled atmosphere. The results suggest that Sn suppresses the formation of the ω and α″ phases in Ti–Mo system. - Highlights: • Sn addition to Ti alloys decreases elastic modulus by suppressing ω phase precipitation. • Sn addition decreases the temperature of martensite decomposition. • Sn addition decreases the temperature of α phase precipitation and β transus. • Mechanical strength decreases with increasing Sn content.

36 MATERIALS SCIENCE↗
NASA NTRS2011

Resilient and Corrosion-Proof Rolling Element Bearings Made from Superelastic Ni-Ti Alloys for Aerospace Mechanism Applications

Mechanical components (bearings, gears, mechanisms) typically utilize hard materials to minimize wear and attain long life. In such components, heavily loaded contact points (e.g., meshing gear teeth, bearing ball-raceway contacts) experience high contact stresses. The combination of high hardness, heavy loads and high elastic modulus often leads to damaging contact stress. In addition, mechanical component materials, such as tool steel or silicon nitride exhibit limited recoverable strain (typically less than 1 percent). These material attributes can lead to Brinell damage (e.g., denting) particularly during transient overload events such as shock impacts that occur during the launching of space vehicles or the landing of aircraft. In this paper, a superelastic alloy, 60NiTi, is considered for rolling element bearing applications. A series of Rockwell and Brinell hardness, compressive strength, fatigue and tribology tests are conducted and reported. The combination of high hardness, moderate elastic modulus, large recoverable strain, low density, and intrinsic corrosion immunity provide a path to bearings largely impervious to shock load damage. It is anticipated that bearings and components made from alloys with such attributes can alleviate many problems encountered in advanced aerospace applications.

DellaCorte, Christopher↗
DOE OSTI2015

Propensity of bond exchange as a window into the mechanical properties of metallic glasses

We investigated the mechanical properties of Zr-Cu-Al bulk metallic glasses, by compression experiment and molecular dynamics simulations. From the simulation, we found that the large, solvent atom, Zr, has high propensity of bond exchange compared to those of the smaller solute atoms. The difference in bond exchange is consistent with the observed disparity in mechanical behaviors: Zr-rich metallic glass exhibits low elastic modulus and large plastic strain. Furthermore, X-ray photoelectron spectroscopy measurements suggest that the increased propensity in bond exchange is related to the softening of Zr bonds with increasing Zr content.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Influence of extended exposure in space on mechanical properties of high-toughness graphite-epoxy composite material (A0019)

Graphite-epoxy composites are promising candidates for structural use in space vehicles because of their high strength and elastic modulus properties. The problem of low fracture toughness was solved by use of recently developed techniques of intermittent interlaminar bonding. Before this material can be adapted for space use, however, confidence must be gained that its mechanical properties are not degraded by exposure to the space environment. The objective of this experiment is to test the effect of extended exposure to a space environment on the mechanical properties of a specially toughened T300/5208 graphite-epoxy composite material. Specimens made by recently developed techniques of intermittent interlaminar bonding will be exposed and afterward tested for fracture toughness, tensile strength, and elastic modulus. The approach of this experiment is to provide a frame on which the specimens can be mounted with their flat sides normal to the Long Duration Exposure Facility radius, each specimen with an unobstructed exposure of about 2 pi sr. The specimens will be mounted so that they neither fracture from high stress nor fail from excessive heating during launch and return.

Felbeck, D. K.↗
DOE OSTI2011

Evaluation of Fibrinogen Self-assembly: Role of its alphaC Region

Background: Exposure of cryptic, functional sites on fibrinogen upon its adsorption to hydrophobic surfaces of biomaterials has been linked to an inflammatory response and fibrosis. Such adsorption also induces ordered fibrinogen aggregation which is poorly understood. Objective: To investigate hydrophobic surface-induced fibrinogen aggregation. Methods: Contact and lateral force scanning probe microscopy, yielding topography, image dimensions and fiber elastic modulus measurements were used along with transmission and scanning electron microscopy. Fibrinogen aggregation was induced under non-enzymatic conditions by adsorption on a trioctyl-surface monolayer (trioctylmethylamine) grafted onto silica clay plates. Results: A more than one molecule thick coating was generated by adsorption on the plate from 100 to 200 {mu}g mL{sup -1} fibrinogen solutions, and three-dimensional networks formed from 4 mg mL{sup -1} fibrinogen incubated with uncoated or fibrinogen-coated plates. Fibrils appeared laterally assembled into branching and overlapping fibers whose heights from the surface ranged from approximately 3 to 740 nm. The elastic modulus of fibrinogen fibers was 1.55 MPa. No fibrils formed when fibrinogen lacking {alpha}C-domains was used as a coating or was incubated with intact fibrinogen-coated plates, or when the latter plates were sequentially incubated with anti-A{alpha}529-539 mAb and intact fibrinogen. When an anti-A{alpha}241-476 mAb was used instead, fine, long fibers formed. Similarly, sequential incubations of fibrinogen-coated plates with recombinant {alpha}C-domain (A{alpha}392-610 fragment) or {alpha}C-connector (A{alpha}221-372 fragment) and fibrinogen resulted in distinctly fine fiber networks. Conclusions: Adsorption-induced fibrinogen self-assembly is initiated by a more than one molecule-thick surface layer and eventuates in three-dimensional networks whose formation requires fibrinogen with intact {alpha}C-domains.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Size Effects on Deformation and Fracture of Scandium Deuteride Films.

Metal hydride films have been observed to crack during production and use, prompting mechanical property studies of scandium deuteride films. The following focuses on elastic modulus, fracture, and size effects observed in the system for future film mechanical behavior modeling efforts. Scandium deuteride films were produced through the deuterium charging of electron beam evaporated scandium films using X-ray diffraction, scanning Auger microscopy, and electron backscatter diffraction to monitor changes in the films before and after charging. Scanning electron microscopy, nanoindentation, and focused ion beam machined micropillar compression tests were used for mechanical characterization of the scandium deuteride films. The micropillars showed a size effect for flow stress, indicating that film thickness is a relevant tuning parameter for film performance, and that fracture was controlled by the presence of grain boundaries. Elastic modulus was determined by both micropillar compression and nanoindentation to be approximately 150 GPa, Fracture studies of bulk film channel cracking as well as compression induced cracks in some of the pillars yielded a fracture toughness around 1.0 MPa-m1/2. Preliminary Weibull distributions of fracture in the micropillars are provided. Despite this relatively low value of fracture toughness, scandium deuteride micropillars can undergo a large degree of plasticity in small volumes and can harden to some degree, demonstrating the ductile and brittle nature of this material

Teresi, C. S.↗
DOE OSTI2016

Microstructures and martensitic transformation behavior of superelastic Ti-Ni-Ag scaffolds

Highlights: • The B2-R-B19′ transformation occurred in 49Ti-50.3Ni-0.7Ag alloy fibers. • Annealing treated alloy fibers showed superelastic recovery ratio of 93%. • Ageing treated scaffold had an elastic modulus of 0.67 GPa. • Ageing treated scaffold exhibited good superelasticity at human body temperature. - Abstract: Ti-Ni-Ag scaffolds were prepared by sintering rapidly solidified alloy fibers. Microstructures and transformation behaviors of alloy fibers and scaffolds were investigated by means of electron probe micro-analyzer (EPMA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The B2-R-B19′ transformation occurs in alloy fibers. The alloy fibers have good superelasticity with superelastic recovery ratio of 93% after annealing heat treatment. The as-sintered Ti-Ni-Ag scaffolds possess three-dimensional and interconnected pores and have the porosity level of 80%. The heat treated Ti-Ni-Ag scaffolds not only have an elastic modulus of 0.67 GPa, which match well with that of cancellous bone, but also show excellent superelasticity at human body temperature. In terms of the mechanical properties, the Ti-Ni-Ag scaffolds in this study can meet the main requirements of bone scaffold for the purpose of bone replacement applications.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Properties of Bulk Sintered Silver As a Function of Porosity

This report summarizes a study where various properties of bulk-sintered silver were investigated over a range of porosity. This work was conducted within the National Transportation Research Center's Power Device Packaging project that is part of the DOE Vehicle Technologies Advanced Power Electronics and Electric Motors Program. Sintered silver, as an interconnect material in power electronics, inherently has porosity in its produced structure because of the way it is made. Therefore, interest existed in this study to examine if that porosity affected electrical properties, thermal properties, and mechanical properties because any dependencies could affect the intended function (e.g., thermal transfer, mechanical stress relief, etc.) or reliability of that interconnect layer and alter how its performance is modeled. Disks of bulk-sintered silver were fabricated using different starting silver pastes and different sintering conditions to promote different amounts of porosity. Test coupons were harvested out of the disks to measure electrical resistivity and electrical conductivity, thermal conductivity, coefficient of thermal expansion, elastic modulus, Poisson's ratio, and yield stress. The authors fully recognize that the microstructure of processed bulk silver coupons may indeed not be identical to the microstructure produced in thin (20-50 microns) layers of sintered silver. However, measuring these same properties with such a thin actual structure is very difficult, requires very specialized specimen preparation and unique testing instrumentation, is expensive, and has experimental shortfalls of its own, so the authors concluded that the herein measured responses using processed bulk sintered silver coupons would be sufficient to determine acceptable values of those properties. Almost all the investigated properties of bulk sintered silver changed with porosity content within a range of 3-38% porosity. Electrical resistivity, electrical conductivity, thermal conductivity, elastic modulus, Poisson's ratio, and yield stress all depended on the porosity content in bulk-sintered silver. The only investigated property that was independent of porosity in that range was coefficient of thermal expansion.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of Encapsulant Properties on the Thermo-Mechanical Reliability of Double-Side Cooled Power Modules for Traction Inverters

Double-side cooled power modules are being developed for next-generation traction inverters due to their better heat extraction, lower profile, and lower parasitic inductances. However, due to their rigid structure, they cause reliability concerns arising from high thermo-mechanical stresses at the interconnection joints in the module. In this work, a materials-based approach using rigid encapsulants is presented for reducing thermo-mechanical fatigue. Finite-element thermo- mechanical simulations were performed to examine the effects of the elastic modulus and coefficient of thermal expansion of epoxy- based encapsulants on the bond deformation inside a double-side cooled power module. It was found that a rigid encapsulant with a high modulus of 6.0 GPa or above and a coefficient of thermal expansion around 20 ppm/oC would improve the thermo- mechanical reliability of double-side cooled power modules by decreasing the permanent bond deformation inside the modules by 50-60%.

ADVANCED PROPULSION SYSTEMS↗