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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Flexural Fatigue Testing and Qualification of Hybrid PAN-pitch Composite Materials with High Through-Thickness Thermal Conductivity

Carbon-fiber-reinforced polymers (CFRPs) considered for motor components within future electric vertical takeoff and landing (eVTOL) vehicles require not only a high strength-to-weight ratio but also a high through-thickness thermal conductivity (TC) to dissipate heat. Previously, CFRPs incorporating pitch CF interleaves demonstrated an increased through-thickness TC relative to the baseline composite, but the effect on flexural fatigue life was not evaluated. For this work, T700S/TC275–1 braided carbon fiber/epoxy prepreg baseline (no interleave), YSH–60A pitch interleave, and YS–80A pitch interleave configurations were tested for fatigue life. A combination of ASTM International Standards D7264 and D3479 were used to develop a reliable testing method. An Instron® (Illinois Tool Works Inc.) 8501 servohydraulic system with a fatigue test fixture was set up with a 16:1 span:thickness ratio, load ratio R set to 0.1, and frequency of 4 Hz. High-cycle fatigue testing was completed, and it was found that YSH–60A interleave performed slightly better than YS–80A below 100,000 cycles but showed no differences above 100,000 cycles. In all cases, the baseline CFRP had superior fatigue life performance both in terms of stress handled and total cycles to failure. These fatigue testing data will inform future use of hybrid CFRP materials by highlighting the tradeoff between increased through-thickness TC and fatigue life. Testing guidelines, equipment, and parameters for static and fatigue tests were successfully outlined for CFRPs.

composites↗
DOE OSTI2012

Thickness limitations in carbon nanotube reinforced silicon nitride coatings synthesized by vapor infiltration

Chemical vapor infiltration is a convenient method for synthesizing carbon nanotube (CNT)-reinforced ceramic coatings. The thickness over which infiltration is relatively uniform is limited by gas phase diffusion in the pore structure. These effects were investigated in two types of silicon nitride matrix composites. With CNTs that were distributed uniformly on the substrate surface dense coatings were limited to thicknesses of several microns. With dual structured CNT arrays produced by photolithography coatings up to 400 gm thick were obtained with minimal residual porosity. Gas transport into these dual structured materials was facilitated by creating micron sized channels between "CNT pillars" (i.e. each pillar consisted of a large number of individual CNTs). The experimental results are consistent with basic comparisons between the rates of gas diffusion and silicon nitride growth in porous structures. This analysis also provides a general insight into optimizing infiltration conditions during the fabrication of thick CNT-reinforced composite coatings. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

carbon nanotubes↗
DOE OSTI2018

DEVELOPMENT OF A SCALABLE THERMOMECHANICAL PROCESS (TMP) FOR THICK BAINITIC ARMOR STEEL

A bainite phase-based alloy and associated thermomechanical process were developed to produce (2.5 to over 5 cm) thick armor-grade steel with uniform through-thickness high hardness and strength. The alloy composition and the final-critical (austenite to bainite) isothermal transformation step were specifically designed to utilize a simple and versatile air-cool/quench method to keep a low upfront capital cost and to provide the ability to continuously control the cooling rate in real time, in order to produce maximum volume fraction of bainite phase, and promote uniformly distributed strength and hardness. Final thickness of 2.5 cm and 5.7 cm steel plates were fabricated for characterization, testing and evaluation and found to possess uniform through-thickness hardness between 53 to 55 HRC and dynamic compressive strength of up to 2 GPa.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Study of influence of plastic scintillators thicknesses to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources

The Nuclear and Energy Research Institute - IPEN, offers post-graduate programs, namely: Nuclear Technology - Applications (TNA), Nuclear Technology - Materials (TNM), Nuclear Technology - Reactors (TNR). The Institute programs mission is to form expert technicians, physicists and engineers with a strong knowledge in their discipline to work in the nuclear area. The course: 'Theoretical Fundamentals and Practices of the Instrumentation used in Nuclear Data Acquisition' covers the use of laboratory nuclear instrumentation and the accomplishment of experiments to obtain nuclear parameters. One of these experimental exercises is object of this work: 'Study of influence of plastic scintillators to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources'. The use of scintillators plastic for the detection has the advantage of low cost, high mechanical strength, is not hygroscopic and can be manufactured in large volumes. This work aims to present the analysis of relative efficiency of detection of plastic scintillators of various thicknesses for beta particles and gamma radiation by the spectrum of {sup 137}Cs and {sup 90}Sr. Due to lack of resolution of the detectors plastic scintillators we worked with relative efficiency. The evaluation was done by reading deposited energy, using the software MAESTRO, for each detector thickness. For beta particles was observed an ideal thickness around 3 mm and the better photon efficiency was observed with increasing the thickness of the detector. The present experiment does not intend to establish a new technique for this subject: it solely aims student's practical exercises in nuclear properties of elements and detectors being part of the nuclear experimental course. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Comparing Measured (a,n) Thick Target Yields to MCNP6 using TENDL 2012 Libraries - Paper 31

MCNP6, due to the heritage of MCNPX, has always possessed the capability to transport the light ions, such as alpha particles. Two types of competing physics take place during the particle transport: atomic and nuclear physics. Charged particles lose energy to media due to Coulombic interactions. MCNP6 models Coulombic interactions through the use of the continuous slowing down approximation. Stopping powers are calculated at a variety of energies using the Bethe-Bloch formula with Sternheimer and Peierls density effect correction. For energies less than 1.31 MeV/AMU, a low-energy SPAR model is used. When the energy of the particle is high enough, there is a transition from nuclear interactions to nucleon interactions. MCNP6 possess various physics models to account for these types of intra-nuclear cascades. These models are less accurate at low energies. Even though MCNP6 will transport these light ions to low energies (i.e. less than 20 MeV), most of the available model physics in MCNP6, for nuclear interactions, has a suggested minimum energy of ∼20-200 MeV. The result of the poorer prediction at low energies causes important light ion events, such as F-19(a,n)Na-22 from U-234 decay in UF{sub 6}, to produce orders of magnitude fewer neutrons in MCNP6 than should be emitted. As with neutrons, ACE (A Compact ENDF) formatted light ion libraries have been developed from several different evaluations. These libraries possess better physics at low energies where the physics models break down. The TENDL 2012 evaluations possess alpha transport libraries, in ACE format, such that they can easily be used with codes like MCNP6 that read ACE formatted cross sections. As a result, a capability was developed for MCNP6 to read and implement these library cross sections when the light ion reached energies below the library upper energy cutoff. Perfectly modelling an experiment for benchmark comparisons to a code calculation can be tricky. For complex setups, systematic error is always possible; and usually a hefty uncertainty analysis is required to quantify just the geometry setup and material combination choices. For an (a,n) interaction, a thick target yield is defined as the amount of neutrons emitted given that the alpha ranges out in the material. For alpha transport at low energy <10 MeV, in reasonably dense materials (>1-2 g/cc), with a material dimension length larger than a few hundred microns, alpha particles will tend to completely stop and range out in the material. For Li, Be, B, C, N, O, F, Na, Mg and Al thick target yields exist in 200 keV intervals from 1 to 9.8 MeV (most of the elements do have (a,n) thresholds above 1 MeV). Because modelling a thick target yield in MCNP6 is much easier than attempting to account for the complexity of systematic error from a full out experiment, we present here comparisons of (a,n) thick target yields to those calculated in MCNP6 using the TENDL 2012 alpha library evaluations.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Determining thickness and refractive index from free-standing ultra-thin polymer films with spectroscopic ellipsometry

It is a well-known challenge to determine refractive index (n) from ultra-thin films where the thickness is less than about 10 nm. In this paper, we discovered an interesting exception to this issue while characterizing spectroscopic ellipsometry (SE) data from isotropic, free-standing polymer films. Ellipsometry analysis shows that both thickness and refractive index can be independently determined for free-standing films as thin as 5 nm. Simulations further confirm an orthogonal separation between thickness and index effects on the experimental SE data. Effects of angle of incidence and wavelength on the data and sensitivity are discussed. Finally, while others have demonstrated methods to determine refractive index from ultra-thin films, our analysis provides the first results to demonstrate high-sensitivity to the refractive index from ultra-thin layers.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Thickness Effect of Al-Doped ZnO Window Layer on Damp Heat Stability of CuInGaSe2 Solar Cells: Preprint

We investigated the damp heat (DH) stability of CuInGaSe2 (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 ..mu..m to a modest 0.50 ..mu..m over an underlying 0.10-..mu..m intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 ..mu..m/3 ..mu..m)metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85oC and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cellsexhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

14 SOLAR ENERGY↗
DOE OSTI2022

16.52% Efficiency All-Polymer Solar Cells with High Tolerance of the Photoactive Layer Thickness

All-polymer solar cells (all-PSCs) have drawn growing attention and achieved tremendous progress recently, but their power conversion efficiency (PCE) still lags behind small-molecule-acceptor (SMA)-based PSCs due to the relative difficulty on morphology control of polymer photoactive blends. Here, in this work, low-cost PTQ10 is introduced as a second polymer donor (a third component) into the PM6:PY-IT blend to finely tune the energy-level matching and microscopic morphology of the polymer blend photoactive layer. The addition of PTQ10 decreases the π–π stacking distance, and increases the π–π stacking coherence length and the ordered face-on molecular packing orientation, which improves the charge separation and transport in the photoactive layer. Moreover, the deeper highest occupied molecular orbital energy level of the PTQ10 polymer donor than PM6 leads to higher open-circuit voltage of the ternary all-PSCs. As a result, a PCE of 16.52% is achieved for ternary all-PSCs, which is one of the highest PCEs for all-PSCs. In addition, the ternary devices exhibit a high tolerance of the photoactive layer thickness with high PCEs of 15.27% and 13.91% at photoactive layer thickness of ≈205 and ≈306 nm, respectively, which are the highest PCEs so far for all-PSCs with a thick photoactive layer.

14 SOLAR ENERGY↗
DOE OSTI2018

Improved Superconducting Properties of Thick YBa{sub 2}Cu{sub 3}O{sub 7−δ} Film by Adding Amino-Rich Polyethyleneimine in Precursor Solution

Polyethyleneimine (PEI) with an amount of –NH{sub 2} groups used in precursor solution could effectively reduce Cu{sup 2+} volatilization during the pyrolysis process. Thermogravimetric analysis shows that the temperature window of low-temperature pyrolysis for precursor solution with PEI (PEI-YBCO) is widened significantly. The slower pyrolysis process can enrich Cu{sup 2+} and improve critical current density (J{sub c}) of PEI-YBCO films. The highest J{sub c} is 3.03 MA/cm{sup 2} at 77 K when the amount of PEI is 0.5 g/10 mL and the film thickness is 400 nm. Then the thickness increases from 0.4 to 2.0 μm by changing the coating times. The J{sub c} values of PEI-YBCO films decrease gradually with the thickness increase. However, the critical current (I{sub c}) can be up to 197 A/cm (at 77 K, self-field) and J{sub c} can still keep 1.68 MA/cm{sup 2} at 1.2 μm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Flux Pinning Mechanism in BaSnO{sub 3}-Added GdBa{sub 2}Cu{sub 3}O{sub 7-x} Films with Different Thickness

Types of flux pinning mechanism in pure and BaSnO{sub 3} (BSO)-added GdBa{sub 2}Cu{sub 3}O{sub 7-x} (GdBCO) superconducting films have been determined by using the Dew-Hughes model. We have found that as the BSO content increases up to 4 wt%, dominant pinning mechanism of GdBCO films has changed from normal surface pinning due to intrinsic linear defects to normal point pinning by BSO addition. Careful analysis on the scaling of the flux pinning for the 4 wt% BSO-doped GdBCO films with various film thicknesses revealed that the pinning mechanism came from the hybrid pinning of two kinds of pinning types. In addition to the normal point pinning by BSO addition, another type of Δκ-pinning was observed to be prominent in the thinner films in low magnetic field region as normal point pinning was deteriorated. Through the EXAFS analysis, it was found that the Δκ-pinning is possibly originated from the oxygen deficiency in localized position. These results suggested that film thickness directly affects the flux pinning mechanism of the BSO-doped GdBCO films, and in the application point of view, an optimization of the film thickness may be crucial to operate normal point pinning induced by BSO addition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Optimal absorber thickness in long-wave multiple-stage detector

The detectivity characteristics of interband cascade infrared type-II superlattice detectors for long-wave infrared detection (λ{sub cut-off} = 8 μm at room temperature) are discussed. We present comparison of two superlattices: InAs/GaSb and InAs/InAsSb, assuming the characteristic parameters—absorption coefficients α and carrier lifetimes τ published in literature. Dependence of the Johnson-noise limited detectivity on the absorber thickness for a different number of stages is reported. Higher detectivity D{sup *} value can be achieved by increasing the carrier lifetime. However, for detectors based on type-II InAs/GaSb superlattice increasing the carrier lifetime up to 25 ns leads to a situation in which one stage is preferred, i.e. for detector with a single absorber, we obtain the highest detectivity value. In the case of InAs/InAsSb material, the situation is similar for τ ≥ 80 ns. We have shown that the optimal absorber thickness at which the highest detectivity values are obtained depends not only on the absorption coefficient α and the number of stages N{sub S}, but also on the carrier diffusion length L. According to a calculations, cascade detectors based on Ga-free material should have much higher optimal absorber thicknesses than materials based on InAs/GaSb.

42 ENGINEERING↗
DOE OSTI2018

Numerical Simulation of Bulging Deformation for Wide-Thick Slab Under Uneven Cooling Conditions

In the present work, the bulging deformation of a wide-thick slab under uneven cooling conditions was studied using finite element method. The non-uniform solidification was first calculated using a 2D heat transfer model. The thermal material properties were derived based on a microsegregation model, and the water flux distribution was measured and applied to calculate the cooling boundary conditions. Based on the solidification results, a 3D bulging model was established. The 2D heat transfer model was verified by the measured shell thickness and the slab surface temperature, and the 3D bulging model was verified by the calculated maximum bulging deflections using formulas. The bulging deformation behavior of the wide-thick slab under uneven cooling condition was then determined, and the effect of uneven solidification, casting speed, and roll misalignment were investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

An Artificial Neural Network Model to Predict the Bainite Plate Thickness of Nanostructured Bainitic Steels Using an Efficient Network-Learning Algorithm

Nanostructured bainitic steel has an extraordinary ultrahigh strength of about 2.0 GPa along with good toughness of 30 MPa m{sup 1/2}. The finer thickness of plate 20-80 nm is largely responsible for achieving such a large hardness of 690-720 HV. In this work, a multilayer perceptron-based artificial neural network (ANN) model has been developed to predict the thickness of bainite plate pertaining to nanostructured bainitic steels. The inputs of the ANN model are, namely, Gibbs free energy for bainitic transformation, austenite strength, transformation temperature for bainite and carbon concentration in the steel. The model prediction revealed that the bainite plate thickness critically depends on austenite strength and Gibbs free energy. From the neural prediction, it is concluded that formation of nanostructured bainitic steel is feasible only if sufficient austenite strength (above 165 MPa) has been achieved. This can be accomplished with a minimum carbon content of 0.5 wt.% in steel and transformation temperature below 300 °C. Higher driving force (Gibbs free energy) below − 1800 J/mol is another prerequisite condition of formation of nanostructured bainite steel. The network-learning architecture has been optimized using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm to minimize the network training error within eight training cycles. The algorithm facilitates a faster convergence of network training and testing errors.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Elastic Modulus Estimation for Copper Syntactic Foams Reinforced with Iron Hollow Spheres of Different Wall Thicknesses

The present study estimates the effect on Young’s modulus of the percentage and thickness of iron hollow spheres reinforcing copper syntactic foams. The resulting materials were modeled by inserting hollow spheres in a random arrangement, using a combination of Discrete Element Method (DEM) for generating the sphere location coordinates and Finite Element Analysis (FEA). Estimations for syntactic foams were compared to those obtained for conventional copper foams with the same porosity. Results showed that the elastic modulus of both syntactic and conventional foams drops significantly as the percentage of spheres or porosity increases. Furthermore, the increase in the wall thickness of the iron hollow spheres leads to significant rises in the Young’s modulus. Depending on the desired mechanical properties, the outcomes presented in this work could be used for selecting the kind of foam (syntactic or conventional) and predesign some characteristics such as porosity or thickness of the spheres or pores.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Modeling of deformation of battery cells using thick shell element formulation

Here, we describe a new approach for modeling nonlinear deformation and stress distribution of battery cells using a new thick shell finite element formulation with a through-thickness calculation of stresses and strains that satisfy equilibrium conditions. Battery cells are transversely layered materials that contain numerous thin layers in a repeating sequence. The layers are made of materials with significantly different mechanical responses. Explicit discretization of the layers is computationally impractical except for very small domains, while homogenized material models cannot account for stress and strain variations and partition through the thickness. The new formulation allows for calculation of the transverse and interlayer stresses based on the material properties of the individual cell layers. The application to problems where the transverse stresses have strong influence is also possible.

25 ENERGY STORAGE↗
DOE OSTI2011

Effect of Substrate Thickness on Oxide Scale Spallation for Solid Oxide Fuel Cells

In this paper, the effect of the ferritic substrate's thickness on the delamination/spallation of the oxide scale was investigated experimentally and numerically. At the high-temperature oxidation environment of solid oxide fuel cells (SOFCs), a combination of growth stress with thermal stresses may lead to scale delamination/buckling and eventual spallation during SOFC stack cooling, even leading to serious degradation of cell performance. The growth stress is induced by the growth of the oxide scale on the scale/substrate interface, and thermal stress is induced by a mismatch of the coefficient of thermal expansion between the oxide scale and the substrate. The numerical results show that the interfacial shear stresses, which are the driving force of scale delamination between the oxide scale and the ferritic substrate, increase with the growth of the oxide scale and also with the thickness of the ferritic substrate; i.e., the thick ferritic substrate can easily lead to scale delamination and spallation. Experimental observation confirmed the predicted results of the delamination and spallation of the oxide scale on the ferritic substrate.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Coupling of multiscale imaging analysis and computational modeling for understanding thick cathode degradation mechanisms

Here, using a thick NMC811 (LiNi 0.8 Mn 0.1 Co 0.1 O 2 ) electrode as an example, we present a macro- to nanoscale 2D and 3D imaging analysis approach coupled with 4D (space + time) computational modeling to probe its degradation mechanism in a lithium-ion battery cell. Particle cracking increases and contact loss between particles and carbon-binder domain are observed to correlate with the cell degradation. This study unravels that the reaction heterogeneity within the thick cathode caused by the unbalanced electron conduction is the main cause of the battery degradation over cycling. The increased heterogeneity in the system will entail more cathode regions where the degree of active material utilization is uneven, leading to higher probabilities of particle cracking. These findings shed light on the crucial role of the electronic and ionic transportation networks in the performance deterioration of the thick cathode. They also provide guidance for cathode architecture optimization and performance improvement.

25 ENERGY STORAGE↗
DOE OSTI2021

Impact of electrode porosity architecture on electrochemical performances of 1 mm-thick LiFePO4 binder-free Li-ion electrodes fabricated by Spark Plasma Sintering

Thick electrodes with high active material loadings have been intensively studied over the last couple of decades in pursuit of achieving high energy density systems. To optimize and enhance the electrochemical performance of such electrodes, one has to control the pore morphology by, for example, varying the pore size and shape, and the level of porosity. In the present work, the fabrication of thick binder-free LiFePO4 (LFP) electrodes with two different pore sizes (12 and 20 mu m) and porosities (21 vol% and 44 vol%) using Spark Plasma Sintering (SPS) and templating approach is reported. The well-controlled porous architecture inside the thick electrodes is realized by fine-tuning experimental parameters. The impact of porosity architecture on electrochemical performance is quantified and correlated with the 3D tortuosity values determined from both micro-computed tomography and electrochemical impedance-based experimental methods. Based on the micro-computed tomography data analysis, estimated tortuosity values along X, Y, and Z axes reveal an anisotropic effect perpendicularly to the SPS compression axis (Z-direction). This is particularly profoundly observed in the samples with larger pores (20 mu m). The correlation between morphological properties and the rate capability performance is established indicating that the capacity loss happens mainly due to the Li-ion diffusion limitations.

Cathode material↗