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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of interfacial transition zone on the Young's modulus of carbon nanofiber reinforced cement concrete

Identifying the properties of the region where the cement paste meets the aggregate surface (interfacial transition zone, ITZ) is critical to understanding the strength and fracture behavior of carbon nanofiber (CNF) reinforced cement concrete. In this study, the finite element method is employed to investigate the effect of the ITZ on the Young's modulus of cement concrete made with CNF. The numerical models for cement concrete with and without CNF are constructed based on the digital image processing technique. To consider the interface effect, the concept of ''effective aggregate'' is put forward, namely, the Young's modulus and Poisson's ratio for each aggregate particle are replaced by an effective Young's modulus and effective Poisson's ratio, in which the effect of thickness and the Young's modulus of ITZ is taken into account in an averaged manner. Then, the quantitative nanomechanical mapping (based on atomic force microscopy) technique is adopted to measure the Young's modulus and thickness of ITZ with and without CNFs, which are further used as the input parameters in the numerical model. The numerical simulation results are verified by experimental testing, which indicates that the ITZ effect should be considered when implementing the numerical simulation. In addition, this analysis shows that compared with the plain cement concrete, CNFs can greatly enhance the mechanical properties of ITZ, which will in turn improve the Young's modulus of cement concrete significantly. Finally, the effect of thickness and Young's modulus of ITZ on the Young's modulus of CNF reinforced cement concrete is also discussed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Reinforced double-threaded slide-ring networks for accelerated hydrogel discovery and 3D printing

Traditionally, slide-ring gels are stretchable but soft as a result of an elasticity-stretchability trade-off. Herein, we introduce a new approach to breaking this trade-off and creating reinforced slide-ring networks with mobile crosslinkers. Our approach involves the construction of a polyethylene glycol double-threaded γ-cyclodextrin-based pro-slide-ring crosslinker that serves as a modular component for 3D printing and copolymerization. The resulting crystalline-domain-reinforced slide-ring hydrogels, or CrysDoS-gels, exhibit both high elasticity and high stretchability. The modular synthesis allows for high-throughput synthesis of CrysDoS-gels, generating a large amount of data for structure-property analysis. Here, by employing data science techniques, such as machine learning and linear regression, not only were we able to identify which chemical components influence the mechanical properties of CrysDoS-gels, but this analysis also aided in the discovery of better-performing CrysDoS-gels. Finally, we demonstrate the potential application of the newly discovered CrysDoS-gels as sensing devices by 3D printing them as stress sensors with high sensitivity and a broad detection range.

3D-printing↗
DOE OSTI2014

Crashworthiness characteristics of a carbon fiber reinforced dual-phase epoxy–polyurea hybrid matrix composite

In this paper, the crashworthiness characteristics of rectangular tubes made from a Carbon-fiber reinforced Hybrid-Polymeric Matrix (CHMC) composite were investigated using quasi-static and impact crush tests. The hybrid matrix formulation of the CHMC was created by combining an epoxy-based thermosetting polymer with a lightly crosslinked polyurea elastomer at various cure-time intervals and volumetric ratios. The load–displacement responses of both CHMC and carbon-fiber reinforced epoxy (CF/epoxy) specimens were obtained under various crushing speeds; and crashworthiness parameters, such as the average crushing force and specific energy absorption (SEA), were calculated using subsequent load–displacement relationships. The CHMC maintained a high level of structural integrity and post-crush performance, relative to traditional CF/epoxy. The influence of the curing time and volumetric ratios of the polyurea/epoxy dual-hybridized matrix system on the crashworthiness parameters was also investigated. The results reveal that the load carrying capacity and total energy absorption tend to increase with greater polyurea thickness and lower elapsed reaction curing time of the epoxy although this is typically a function of the loading rate. In conclusion, the mechanism by which the CHMC provides increased damage tolerance was also investigated using scanning electron microscopy (SEM).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Factors affecting direct lightning strike damage to fiber reinforced composites: A review

In recent years, Carbon Fiber Reinforced Plastics (CFRP) or Glass Fiber Reinforced Plastics (GFRPs) have become a very common material for aircraft and wind turbine structures. These structures are often protected from lightning strikes using conventional metal-based protective films/foils. Non-conventional, non-metallic lightning strike protection (LSP) technologies have not yet been fully realized, but research on non-conventional LSP systems for CFRPs has gained momentum in the last few years. The discovery of new structural conductive materials and improvements in the processing of carbon nano-filler based composites have challenged the conventional metal-based LSP systems by providing the potential for lightweight, non-metallic alternatives. However, a major challenge in using non-conventional LSP is the complex nature of a lightning strike event and its complicated thermal and mechanical impact on CFRP structures. Understanding the direct effect of a lightning strike on a CFRP structure requires understanding multiple transient loads, such as electrical, thermal, magnetic, acoustics, shock, and inertia. This review article focuses on new findings and discusses the complex direct effects of lightning on CFRPs. Specifically, the focus is to find the important factors that regulate and control the damage to FRPs are classified and discussed with the help of available literature based on experimental results. Finally, possibilities and limitations to these new findings are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A machine learning approach to determine the elastic properties of printed fiber-reinforced polymers

This work focuses on the simultaneous determination of the elastic constants and the fiber orientation state for a short fiber-reinforced polymer composite by performing a minimum of experimental tests. Here we introduce a methodology that enables the inverse determination of fiber orientation state and the in-situ polymer properties by performing tensile tests at the composite coupon level. We demonstrate the approach for the extrusion deposition additive manufacturing (EDAM) process to illustrate one application of the methodology, but the development is such that it can be applied to short fiber-reinforced polymer (SFRP) systems processed via other methods. Currently, developing composites additive manufacturing digital twins require extensive material characterization. In particular, the mechanical characterization of the orthotropic elastic properties of a composite involves extensive sample preparation and testing, therefore the elasticity tensor is generally populated using a micromechanics model. This, however, requires measuring the fiber orientation state in addition to knowing the constituent material properties. Experimentally measuring the fiber orientation state can be tedious and time consuming. Further, optical methods are limited to resolving the orientation of cylindrical fibers or cluster of non-cylindrical fibers, and computed tomography (CT) methods scan regions of volume that are much smaller than a full printed bead. Therefore, we propose a methodology, accelerated by machine learning, to identify the anisotropic mechanical properties and fiber orientation state at the same time. Early results show that inference of the fiber orientation and composite properties is possible with as few as three tensile tests. Our results show that a combination of the choice of the micromechanics model and reliable set of experiments can yield the nine elastic constants, as well as, the fiber orientation state.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of reinforcement phase on the mechanical property of tungsten nanocomposite synthesized by spark plasma sintering

Nanostructured tungsten composites were fabricated by spark plasma sintering of nanostructured composite powders. The composite powders, which were synthesized by mechanical milling of tungsten and Ni-based alloy powders, are comprised of alternating layers of tungsten and metallic glass several hundred nanometers in size. The mechanical behavior of the nanostructured W composite is similar to pure tungsten, however, in contrast to monolithic pure tungsten, some macroscopic compressive plasticity accompanies the enhanced maximum strength up to 2.4 GPa by introducing reinforcement. As a result, we have found that the mechanical properties of the composites strongly depend on the uniformity of the nano-grained tungsten matrix and reinforcement phase distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Refinement of Mg{sub 2}Si reinforcement in a commercial Al–20%Mg{sub 2}Si in-situ composite with bismuth, antimony and strontium

Refinement by addition elements of Al–Mg{sub 2}Si alloys is known to result in a change of primary Mg{sub 2}Si morphology. In this paper, the effects of Bi, Sb and Sr on the characteristic parameters of Al–20%Mg{sub 2}Si in-situ composite have been investigated by computer aided cooling curve thermal analysis and microstructural inspection. Size, density and aspect ratio measurements showed that additions of 0.4 wt.% Bi, 0.8 wt.% Sb and 0.01 wt.% Sr refined the Mg{sub 2}Si reinforcement. Exceeding these concentrations, however, resulted in coarsening of Mg{sub 2}Si particles with no change in the morphology. The results also showed that addition elements caused a decrease in the nucleation and growth temperatures of Mg{sub 2}Si particles. The refining effect of Bi, Sb and Sr is likely to be related to the effect of oxide bifilms suspended in the composite melt as favored nucleation substrates for Mg{sub 2}Si particles. - Highlight: • 0.4 wt.%, 0.8 wt.% and 0.01 wt.% is the optimum content for Bi, Sb and Sr addition. • Exceeding optimum concentration resulted in the coarsening of reinforcements. • Nucleation and growth temperatures decrease with addition of Bi, Sb and Sr. • The refining effect of Bi, Sb and Sr is likely to be related to the oxide bifilms.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites

The interfacial microstructure of SiC{sub p} or YAl{sub 2p} reinforced Mg–14Li–3Al matrix composites was comparatively characterized by scanning electron microscopy and electron probe microanalysis. A nanoindentation combined with scanning electron microscopy technique was used to characterize the interfacial mechanical properties between the reinforcements and matrix. The interfacial strength and failure behaviors for the composites were analyzed from the load–penetration curves and corresponding images. In situ tensile tests were used to observe the fracture and deformation processes with the aid of scanning electron microscopy. The results show that both the chemical and mechanical compatibilities between the YAl{sub 2} particles and LA143 matrix are better than those between the SiC particles and LA143 matrix. The interfacial breakage load for the SiC/LA143 composite is lower than that for the YAl{sub 2}/LA143 composite because of the worse chemical and mechanical compatibilities between the ceramic particles and metal matrix. Interfacial breakage is the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanism for the YAl{sub 2}/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix. - Highlights: • The compatibility for YAl{sub 2} particle with LA143 matrix is better than SiC particle. • The strength of the YAl{sub 2}/LA143 interface is higher than the SiC/LA143 interface. • The main failure behavior for the SiC/LA143 composite is interfacial breakage. • The main failure behavior for YAl{sub 2}/LA143 composite is particle and matrix breakage. • The interfacial strength plays an important role on the composite failure behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure and mechanical properties of aluminium matrix composites reinforced by Al{sub 62}Cu{sub 25.5}Fe{sub 12.5} melt spun ribbon

Aluminium matrix composites containing 15, 30 and 50 vol.% of pulverized Al{sub 62}Cu{sub 25.5}Fe{sub 12.5} (in at.%) melt spun ribbons have been prepared by a vacuum hot pressing (T = 673 K, P = 600 MPa). The microstructure of the initial ribbon and the composites was investigated using X-ray, scanning and transmission electron microscopy. In the as-spun ribbon the quasicrystalline icosahedral phase (i-phase) coexisted with the cubic copper rich β-Al(Cu, Fe) intermetallic compound. The phase composition of Al-Cu-Fe particles changed after consolidation process and the i-phase transformed partially to the ω-Al{sub 70}Cu{sub 20}Fe{sub 10} phase. Additionally, the Θ-Al{sub 2}Cu phase formed at the α(Al)/Al-Cu-Fe particle interfaces. With an increase in volume fraction of the reinforcement the hardness of the composites increased up to HV = 180 for the highest amount of added particles. The ultimate compression strength of the same sample reached the value of 545 MPa. - Highlights: • Al and 15, 30, 50% of pulverized Al{sub 62}Cu{sub 25.5}Fe{sub 12.5} melt spun ribbon were consolidated. • The initial ribbon consisted of the icosahedral i-phase and copper rich β-Al(Cu, Fe). • The i-phase partially transforms to ω-Al{sub 7}Cu{sub 2}Fe phase in all composites. • Increase of microhardness and compressive strength with content of reinforcement • Ultimate compression strength 545 MPa for 50% of added particles.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Wood-reinforced composites by stereolithography with the stress whitening behavior

In this study, poplar wood flour at various concentrations (1–10 wt%) is incorporated into a methacrylate-based resin via solution blending to fabricate wood-reinforced composites using stereolithography apparatus (SLA) 3D printing. Differential scanning calorimetry (DSC) along with Fourier transform infrared spectroscopy (FTIR) analysis shows the presence of a small amount of residual monomer in the printed samples. For the printed composites, the glass transition temperature (T g ) from dynamic mechanical analysis (DMA) decreases as more wood flour is incorporated, which indicates an increase in free volume occupied by polymer chains. The tensile strength is improved up to 17.3% from 21.1 MPa (no wood flour) to 24.7 MPa (1.0 wt% wood flour). The highest Young’s modulus reaches 323.8 MPa (2.0 wt% wood flour), which is 1.9-fold of that of the sample without wood flour. Moreover, the composites show “stress whitening” with the addition of wood flour during the uniaxial drawing. Morphology analysis of the tested samples show that the formation of microcraze and microvoids likely causing the stress whitening. This is the first study that demonstrates wood flour can be utilized in SLA 3D printed wood plastic composites (WPC) which can reinforce the printed products with a modest loading amount.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microwave combustion synthesis of in situ Al{sub 2}O{sub 3} and Al{sub 3}Zr reinforced aluminum matrix composites

Al{sub 2}O{sub 3} and Al{sub 3}Zr reinforced aluminum matrix composites were fabricated from Al and ZrO{sub 2} powders by SiC assisted microwave combustion synthesis. The microstructure and reaction pathways were analyzed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results showed that the heating rate during microwave synthesis was very high and the entire process took several minutes and that the ignition temperature of the reaction was much lower than that of conventional methods. In addition, the resulting microstructure was found to be finer than that prepared by the conventional methods and no cracks can be seen in the Al{sub 3}Zr reinforcements. As such, the newly developed composites have potential for safety-critical applications where catastrophic failure is not tolerated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Reinforcing blade-cast photocatalytic-titania thin film by titanate nanotubes

Highlights: • Suspension-based photocatalysts are inferior to thin-films due to separation issues. • Hydrothermal TiO{sub 2} nanotubes and sol-gel Ti(n-OBu){sub 4} blends were tape casted on glass. • Optimum blend composition yields mechanical stability due to the tubes reinforcing effect. • At optimum gel content the nanotube bundles are smoothed without stabilizers added. • Surface accessibility and mass transfer dominate the photocatalytic dye degradation. - Abstract: Titanate nanotubes/titania gel blends were prepared as composite sol-gel material, deposited on a glass substrate using a doctor blade and calcined in order to create thin films. In order to get an insight in titania nanotubes’ ability to reinforce thin films, drying control chemical agents were not used. The effects of titanate nanotubes to titanium n-butoxide ratio on surface morphology, phase composition, mechanical stability and photocatalytic activity were studied. Characterization of the thin films was carried out by means of optical and scanning electron microscopy, powder X-ray diffraction, synchrotron radiation grazing incidence X-ray diffraction and mechanical stability testing. Photocatalytic properties of the obtained thin films were evaluated on the basis of methylene blue degradation. Moderate blends exhibit favourable microstructural features while the dye degradation rate was greater for films with a greater amount of titanate nanotubes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

PBI nanofiber mat-reinforced anion exchange membranes with covalently linked interfaces for use in water electrolysers

Anion exchange membranes (AEM) are key components in anion exchange membrane water electrolysers. Recently developed materials are less susceptible to the alkaline degradation of the polymer backbone and quaternary ammonium groups. A remaining challenge is the mechanical stability in contact with hot water and dimensional stability when the temperature of the feed solution changes. One solution is to reinforce membranes with a porous support. Since support materials like PEEK or PTFE have a different swelling behavior than the matrix and no strong interactions with the matrix, voids can form, and gas crossover increases. In this work, we approach this issue by pore filling polybenzimidazole nanofiber mats with the bromomethylated precursor of mTPN, an ultra-stable AEM material. During drying, a covalent interaction between support (PBI amine groups) and matrix (-CH 2 Br) is established. After quaternization, the optimized PBI/mTPN-50.120 composite membrane still shows a high conductivity of 62 mS cm –1 , but 37% reduced length swelling in comparison to the non-reinforced membrane. Tensile strength and Young's modulus increase 17% and 56% to 49 MPa and 680 MPa, respectively. In an electrolyser, a stable voltage of 1.98V at 0.25 A cm –2 was achieved, and no change in membrane resistance was observed over the test time of 200 h (50°C, 1 M KOH, catalysts based on Ni/Fe and Mo).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Anion exchange membranes: The effect of reinforcement in water and electrolyte

Alkaline anion-conducting polymer-based CO 2 electrolysis and water electrolysis are among two emerging renewable energy conversion technologies. Their system design and integration offer promise of lower capital cost due to utilization of low-cost catalysts, in contrast to platinum group metal catalysts required for cation-conducting polymer-based devices. However, a critical component, the polymer electrolyte membrane, remains an obstacle hampering system performance and durability. In this study, commercially-available Sustainion® membranes with and without PTFE-reinforcement were investigated to understand previously unreported origins of improved device performance when compared to alternative membrane chemistries. We report critical membrane properties, such as morphology, thermal stability, as well as temperature-, hydration-, and counter-ion dependent ion conductivity. Moveover, the changes in uptake and conductivity of membranes in supporting electrolytes of K 2 CO 3 and KOH investigated as a function of their concentration. Presence of reinforcement and supporting electrolyte type alter the membrane's transport functionality, which could help guide device design for improved performance. In conclusion, the obtained results not only show how Sustainion® properties change with operating environment for CO 2 and water electrolysis applications, but also provide understanding for internal and external factors controlling anion-exhcnage membrane functionality in electrochemical devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

New class of tritium breeders for fusion applications: Metal-reinforced composite breeders

Commercial fusion reactors operating on a D-T fuel cycle will require a steady supply of tritium to maintain the burning plasma required for continuous power generation. Since tritium has a short half-life, there is negligible natural abundance which necessitates fusion reactors to produce their own source of tritium. Tritium is most easily produced by surrounding a fusion reactor core with lithium (Li), which reacts under the intense neutron flux leaving the reactor core to form tritium and helium. Due to the hazards and technical challenges associated with surrounding a fusion reactor core with many tons of molten Li, other Li-bearing tritium breeder materials have been pursued. Unfortunately, most of the liquid breeders historically examined are exceedingly corrosive to reactor structural materials while many solid breeders in the form of ceramics are forced to make tradeoffs between Li content and mechanical integrity. In this work, to break the historic limit between Li-density and mechanical integrity of traditional solid breeders, a new class of solid tritium breeders is developed: metal-reinforced composite (MERC) breeders. Specifically, the high Li-density of lithium oxide (Li 2 O) is exploited through the addition of a metal reinforcing phase, producing a composite breeder material exhibiting high splitting tensile strength and quasi-ductility with a Li-density greater than other leading solid breeder candidates, including lithium orthosilicate (Li 4 SiO 4 ) and lithium metatitanate (Li 2 TiO 3 ). Mechanical testing, microstructural characterization, and neutronic simulation results are presented and discussed in light of fusion reactor design considerations.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Reinforcing the exit hole from friction stir welding and processing

After friction stir welding/processing (FSW/P), an exit hole remains at the end of the run, which can be the weakest region of the welded/processed workpiece. In addition, tensile residual stress around the exit hole resulting from heating during FSW/P facilitates incipient crack initiating from the exit hole under external loading. Current solutions include removing or repairing the exit hole, which are time-consuming and costly. Here, we propose a novel method to reinforce the exit hole by applying an additional FSW/P pass around it, in a way that replaces preexisting tensile residual stress with compressive residual stress. Under external loading, there is no evident strain accumulation around the exit hole, and the workpiece ultimately fails along the FSW/P heat affected zone. This method provides a more convenient way to reinforce the exit hole than the current exit-hole repair or removal methods for industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

RLMolLM: Reinforcement Learning-Enhanced Language Model Framework for Inverse Molecular Design

Inverse molecular design faces significant challenges due to vast chemical space and complex property requirements. While language models show promise for molecular generation, they struggle with validity, multi-property optimization, and structural constraints. This work presents RLMolLM, a reinforcement learning framework combining Proximal Policy Optimization (PPO) with genetic algorithms to address these limitations. Our approach optimizes multiple user-specified properties including quantitative estimates of drug-likeness (QED), synthetic accessibility (SA), and ADMET (absorption, distribution, metabolism, excretion, and toxicity) endpoints without requiring complete model retraining, while maintaining capability for scaffold-constrained generation where specific substructures must be preserved. We outperform state-of-the-art methods for molecular optimization, achieving best QED scores across GDB13, Moses, and Zinc datasets with up to 31% improvement over previous methods while maintaining excellent validity, uniqueness, and novelty metrics. For simultaneous multi-property optimization, our framework achieves substantial improvements in ADMET properties including 4.5-fold reduction in hERG toxicity and enhanced Caco-2 permeability compared to Moses dataset. Under structural constraints, the framework significantly improves molecular validity while preserving scaffolds and effectively optimizing properties. In conclusion, this versatile solution advances pharmaceutical and materials molecular design through effective integration of reinforcement learning and genetic algorithms with multi-property optimization and scaffold preservation.

Genetic algorithms↗
DOE OSTI2019

Poplar as Biofiber Reinforcement in Composites for Large-Scale 3D Printing

The economic viability of the biofuel industry could be improved by adding a high-value revenue stream for biomass supply chains: bioderived composites for the rapidly expanding large-scale additive manufacturing industry (i.e., 3D printing). Using fibrillated fibers derived from biomass (e.g., Populus ) to reinforce polymers for 3D printing applications would be less expensive compared to using conventional carbon fibers. Poplar fibers of different mesh sizes (<180, 180–425, 425–850, and 850–2360 μm) were used to prepare poplar–polylactic acid (PLA) composites. The poplar/PLA composites were successfully printed using a large-scale 3D printer to create a podium support. The tensile strength of the composites increased from 34 to 54 MPa as the poplar fiber size decreased. Here, the fracture surfaces of composites derived from smaller poplar fibers (<180 μm) were more compact with fewer voids compared with the composites made with larger poplar fibers. Because of the porous and hollow microstructures, smaller poplar fibers contained more pores on their outer surfaces, which were available for the access and penetration of PLA. Poplar has potential for use as a thermoplastic reinforcement for large-scale 3D printing.

36 MATERIALS SCIENCE↗