Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “particle cracking”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A new woven composite constitutive model validated by shock wave experiments

In this paper, we present results of plate impact simulations of shock compressed woven glass fiber-reinforced plastic (GRP) performed using the Arbitrary Lagrangian–Eulerian three-dimensional finite element code. A hyperelastic large-strain-based empirical Continuum Damage Mechanics (CDM) formulation is employed to describe damage initiation and growth in the shock-compressed GRP. The model parameters calibration scheme utilizes the Velocity Interferometer System for Any Reflector normal particle velocity measurements at the free surface of the GRP target plates. The impact velocity in the experiments ranged from 8.5 to 418 m/s. The finite element model considered planar 0°/90° bidirectional plies with an individual ply thickness of 0.68 mm, stacked to reach a total laminate thickness of 6.8 mm. The anisotropic elastic strains were estimated from the experimentally determined tetragonal symmetry stiffness matrix for the GRP. The strain-based damage model captures several salient features observed in the measured free surface particle wave profiles, including the shock rise time, onset of Elastic—Elastic Cracking, and the shape of the nonlinear portion of the experimental particle velocity profiles. Furthermore, the CDM model predicts the dominant damage mode to be matrix microcracking due to shear and the associated bulk expansion (bulking) under the global compressive loading in the plate impact configuration.

42 ENGINEERING↗
DOE OSTI2025

Comparative Study of Vinylene Carbonate and Lithium Difluoro(oxalate)borate Additives in a SiO x /Graphite Anode Lithium-Ion Battery in the Presence of Fluoroethylene Carbonate

The SiO x /graphite composite is recognized as a promising anode material for lithium-ion batteries (LIBs), owing to the high theoretical capacity of SiO x combined with the excellent stability of graphite. However, the inherent disadvantage of volume expansion in silicon-based anodes places significant challenges on the solid electrolyte interphase (SEI) and severely degrades the electrochemical performance. Rational formulation of electrolyte, including its additives, is crucial in accommodating and optimizing the composition of the SEI and enhancing the cell performance. In this work, we present a comparative study of vinylene carbonate (VC) and lithium difluoro(oxalate)borate (LiDFOB) additives combined with fluoroethylene carbonate (FEC) in the electrolyte for SiO x /graphite∥LiNi 1–x–y–z Co x Mn y Al z O 2 full cells. VC outperformed LiDFOB as an additive, delivering higher capacity cycling, higher Coulombic efficiency, and better cycle stability up to 400 cycles. XPS and impedance analyses reveal that LiDFOB contributed to SEI/CEI with both a lower proportion of LiF and a higher proportion of poly(VC), which tended to produce higher cell impedance. XRD and XANES further indicated that using the LiDFOB additive, the NCMA cycled to a shallower degree than that of the VC additive. Although the VC additive maintained a higher capacity up to 400 cycles, microstrain and SEM analyses show a higher strained NCMA along with clear evidence of cracking over the surface of the NCMA particle in VC-based electrolyte but not in LiDFOB. In conclusion, this suggests that the negative influence of LiDFOB at the anode (inferior SEI) supersedes the negative impact of both a cracked NCMA and a deeper cycled NCMA and SiO x -based anode.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Crack width control and mechanical properties of low carbon engineered cementitious composites (ECC)

Engineered Cementitious Composites (ECC) have superior properties with high tensile ductility and tight crack width compared to conventional concrete. The properties of ECC are significantly influenced by the material composition which can be tailored to enhance the sustainability of ECC. Towards this goal, recycled crumb rubber (CR) and silica fume (SF) were used to tailor the properties of a polypropylene-fiber reinforced ECC with a low carbon binder based on limestone calcined clay cement (LC3) in this study. Crumb rubber was found to be effective in enhancing strain-hardening performance and reducing the width of the multiple microcracks. However, a loss of compressive strength was accompanied by an increasing amount of CR. While silica fume or lower w/b ratio enhanced the compressive strength, the crack width of ECC increased at higher SF content or lower w/b. The underlying mechanisms of these trends were traced to the alteration of the matrix fracture toughness and fiber/matrix interfacial bond. Rubber particle bridging was found to contribute to crack width control. Finally, the combined use of the LC3 green binder and CR led to a lowering of the embodied and operational carbon footprint of ECC.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Investigation of deformation mechanisms in an advanced FeCrAl alloy using in-situ SEM-EBSD testing

The deformation mechanisms associated with uniaxial tensile testing are observed by conducting tensile experiments of an FeCrAl alloy using scanning electron microscopy (SEM) coupled with electron backscattered diffraction (EBSD). Prior to the deformation, investigated alloy was consisting grain and precipitate size of ~63.0 μm and ~6.7 μm, respectively. The recorded SEM micrographs and EBSD data at increasing levels of strains revealed the complex phenomena of slip bands’ formation in the presence of surface grain morphology evolution and their (001), (110) and (111) crystallographic planes distortions. The grains with orientation (110)||tensile direction (TD) shows higher shape change; however, (001)||TD and (111)||TD oriented grains show higher lattice gradient formation. Extracted information from the EBSD indicates that the crystallographic rotations drive towards specific, fiber-like texture in relation to the loading direction. Postmortem analysis of the recorded microstructure during the tensile deformation explains the phenomena of crack formation in the hard-intermetallic particles before the ultimate tensile strength (UTS). However, after the UTS, pores were identified in the neck that resulted from extensive plastic deformation. In-depth analysis was carried out to identify the cause of cracks and pores formation phenomena during the tensile test.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Fracto-emission from graphite/epoxy composites

Fracto-emission (FE) is the emission of particles and photons during and following crack propagation. Electrons (EE), positive ions (PIE), and excited and ground state neutrals (NE) were observed. Results of a number of experiments involving principally graphite/epoxy composites and Kevlar single fibers are presented. The physical processes responsible for EE and PIE are discussed as well as FE from fiber- and particulate-reinforced composites.

Dickinson, J. T.↗
NASA NTRS2018

High Strength Ceramic Fibers and Methods of Fabrication

A method and apparatus for forming a plurality of fibers from (e.g., CVD) precursors, including a reactor adapted to grow a plurality of individual fibers; and a plurality of independently controllable lasers, each laser of the plurality of lasers growing a respective fiber. A high performance fiber (HPF) structure, including a plurality of fibers arranged in the structure; a matrix disposed between the fibers; wherein a multilayer coating is provided along the surfaces of at least some of the fibers with an inner layer region having a sheet-like strength; and an outer layer region, having a particle-like strength, such that any cracks propagating toward the outer layer from the matrix propagate along the outer layer and back into the matrix, thereby preventing the cracks from approaching the fibers. A method of forming an interphase in a ceramic matrix composite material having a plurality of SiC fibers, which maximizes toughness by minimizing fiber to fiber bridging, including arranging a plurality of SiC fibers into a preform; selectively removing (e.g., etching) silicon out of the surface of the fibers resulting in a porous carbon layer on the fibers; and replacing the porous carbon layer with an interphase layer (e.g., Boron Nitride), which coats the fibers to thereby minimize fiber to fiber bridging in the preform.

Pegna, Joseph↗
DOE OSTI2020

Plasma and X-ray radiation-induced damage mechanisms in a tungsten heavy alloy

Tungsten-based materials are among the main candidate plasma-facing materials for future fusion reactors where extreme conditions of thermomechanical stresses, radiation, and energetic particles must be withstood. Here a hybrid X-pinch platform combined with a pulsed power machine was used to study damage mechanisms in 90W–4Cu–6Ni tungsten heavy alloy as a result of exposure to high energy density plasma, X-ray radiation, and the resulting thermal shock. It was found that the plasma-facing surface of the material undergoes severe melting and ablation with the extent of ablation being higher in the Cu–Ni phase than the W particles. Rapid melting and solidification transform the W particles into fine dendrite morphologies embedded in the Cu–Ni solid solution. Cracking was also observed in the subsurface layers at the interfaces between the W particles and the Cu-rich phase of the Cu–Ni matrix. X-ray radiation, on the other hand, cause slight melting on the surface without significant ablation and no cracking.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Microstructural Preparation and Examination of Polymer-Matrix Composites

Adapting procedures widely used in the metallographic characterization of metals and alloys, the microstructural preparation and examination of three polymer-matrix composites (PMC's) is described. The materials investigated contained either hollow ceramic filler particles or woven, continuous carbon/graphite fibers. Since the two particulate composites were considered to be isotropic, only one sample orientation was prepared. For the fiber composite, both longitudinal and planar orientations were studied. Once prepared, the samples were examined using reflected light microscopy. A number of microstructural features were evaluated qualitatively, including porosity and cracks, filler-matrix interfacial bonding, filler particle characteristics (shape, size, size distribution, and loading variation) and fiber characteristics (orientation, packing variation, and discontinuities).

Elban, Wayne L.↗
DOE OSTI2020

Microstructural evolution of Mo-UO 2 cermets under high temperature hydrogen environments

Ceramic-metallic (cermet) materials show promise for use in nuclear thermal propulsion applications due to attractive thermophysical properties including high temperature stability and high thermal conductivity. In this work, molybdenum-uranium dioxide (Mo-UO 2 ) cermet fuel elements were fabricated by means of spark plasma sintering (SPS) and were subsequently exposed to hydrogen at high temperatures (2500 K). Mo-UO 2 samples pre- and post-exposure were characterized by means of optical microscopy, scanning electron microscopy, and X-ray diffraction (XRD). Microscopy analyses of the as-produced material displayed microscopic cracking on the interior of the spherical UO 2 fuel particles but confirmed that the fuel particles were fully encapsulated in the Mo matrix. The results further showed mass loss, macroscopic swelling, and cracking in the cermet samples which occurred during high temperature hydrogen testing. Nanoscale swelling was evidenced by XRD in the Mo matrix and UO 2 fuel structure due to the incorporation of defects and accompanied microstrain.

36 MATERIALS SCIENCE↗
NASA NTRS1981

The generation and morphology of single-crystal silicon carbide wear particles under adhesive conditions

Sliding friction experiments were performed in vacuum at room temperature on a plane-type SiC surface in contact with iron-based binary alloys. Multiangular and spherical wear particles were found to form as a result of multipass sliding. The multiangular particles were produced by primary and secondary cracking of the 0001, 10(-)10, and 11(-)20 plane-type cleavage planes under the Hertzian stress field or local inelastic deformation zone. When alloy surfaces are in contact with silicon carbide under a load of 0.2 N, the alloy around the contact area is subjected to stresses that are close to the elastic limit in the elastic deformation region and/or exceed it. It was also found that spherical wear particles may be produced by two mechanisms: a penny-shaped fracture along the circular stress trajectories under the local inelastic deformation zone, and the attrition and fatigue of wear particles.

Miyoshi, K.↗
DOE OSTI2020

Crack-Free Silicon Monoxide as Anodes for Lithium-Ion Batteries

The volume expansion of Si and SiO particles was investigated using a single-particle battery assembled with a focused ion beam and scanning electron microscopy (FIB-SEM) system. Single Si and SiO particles were galvanostatically charged and discharged as in real batteries. Microstructural changes of the particles were monitored in situ using FIB-SEM from two different angles. The results revealed that the volume expansion of micrometer size particle SiO was not only much smaller than that of Si, but it also kept its original shape with no sign of cracks. Additionally, this isotropic mechanical property of a SiO particle can be attributed to its microstructure: nanosized Si domains mixed with SiO 2 domains. The nanosized Si domains can mitigate the anisotropic swelling caused by the orientation-dependent lithium-ion insertion; the surrounding SiO 2 domains can act as a buffer to further constrain the localized anisotropic swelling.

25 ENERGY STORAGE↗
NASA NTRS2015

Methodology for Producing a Uniform Distribution of UO2 in a Tungsten Matrix

Current work at NASA's Marshall Space Flight Center (MSFC) is focused on the development CERMET fuel materials for Nuclear Thermal Propulsion (NTP). The CERMETs consist of uranium dioxide (UO2) fuel particles embedded in a tungsten (W) metal matrix. Initial testing of W-UO2 samples fabricated from fine angular powders performed reasonably well, but suffered from significant fuel loss during repeated thermal cycling due to agglomeration of the UO2 (1). The blended powder mixtures resulted in a non-uniform dispersion of the UO2 particles in the tungsten matrix, which allows rapid vaporization of the interconnected UO2 from the sample edges into the bulk material. Also, the angular powders create areas of stress concentrations due to thermal expansion mismatch, which eventually cracks the tungsten matrix. Evenly coating spherical UO2 particles with chemical vapor deposited (CVD) tungsten prior to consolidation was previously demonstrated to provide improved performance. However, the CVD processing technology is expensive and not currently available. In order to reduce cost and enhance performance, a powder coating process has been developed at MSFC to produce a uniform distribution of the spherical UO2 particles in a tungsten matrix. The method involves utilization of a polyethylene binder during mixing which leads to fine tungsten powders clinging to the larger UO2 spherical particles. This process was developed using HfO2 as a surrogate for UO2. Enough powder was mixed to make 8 discs (2cm diameter x 8mm thickness) using spark plasma sintering. A uniaxial pressure of 50 MPa was used at four different temperatures (2 samples at each temperature). The first two samples were heated to 1400C and 1500C respectively for 5 minutes. Densities for these samples were less than 85% of theoretical, so the time at temperature was increased to 20 minutes for the remaining samples. The highest densities were achieved for the two samples sintered at 1700C (approx. 92% of theoretical). Scanning electron microscopy (SEM) of the mixed powders and the sintered samples along with energy dispersive x-ray analysis was obtained. The SEM of the powders clearly show the fine W powder adhered to the larger HfO2 particles and a uniform distribution of HfO2 particles in a tungsten matrix upon densification. Vicker's Microhardness testing was also performed on all samples using 0.5, 1.0 and 2.0 kg loads. Five indents were made at each load level. All indents were placed in the tungsten matrix to assist as a proxy in measuring densification. The highest hardness value was obtained for the 1700C specimens. The hardness average for these samples was 312.14 MPa. This powder processing method has been applied to W/UO2 powders with the SEM of the powders appearing similar to the W/HfO2 powder images.

Tucker, Dennis S.↗
NASA NTRS1999

Fatigue Analyses Under Constant- and Variable-Amplitude Loading Using Small-Crack Theory

Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily "crack growth" from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using "small-crack theory" under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta-Keff) under constant-amplitude loading. Modifications to the delta-Keff-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small-and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.

Newman, J. C., Jr.↗
NASA NTRS1999

Analyses of Fatigue and Fatigue-Crack Growth under Constant- and Variable-Amplitude Loading

Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily crack growth from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using small-crack theory under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta K(sub eff)) under constant-amplitude loading. Modifications to the delta K(sub eff)-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.

Newman, J. C., Jr.↗
DOE OSTI2024

Assessing the release, transport, and retention of radioactive aerosols from hypothetical breaches in spent fuel storage canisters

Interim dry storage of spent nuclear fuel involves storing the fuel in welded stainless-steel canisters. Under certain conditions, the canisters could be subjected to environments that may promote stress corrosion cracking leading to a risk of breach and release of aerosol-sized particulate from the interior of the canister to the external environment through the crack. Research is currently under way by several laboratories to better understand the formation and propagation of stress corrosion cracks, however little work has been done to quantitatively assess the potential aerosol release. The purpose of the present work is to introduce a reliable generic numerical model for prediction of aerosol transport, deposition, and plugging in leak paths similar to stress corrosion cracks, while accounting for potential plugging from particle deposition. The model is dynamic (changing leak path geometry due to plugging) and it relies on the numerical solution of the aerosol transport equation in one dimension using finite differences. The model’s capabilities were also incorporated into a Graphical User Interface (GUI) that was developed to enhance user accessibility. Model validation efforts presented in this paper compare the model’s predictions with recent experimental data from Sandia National Laboratories (SNL) and results available in literature. We expect this model to improve the accuracy of consequence assessments and reduce the uncertainty of radiological consequence estimations in the remote event of a through-wall breach in dry cask storage systems.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2019

Development and Characterization of Hot-Pressed Matrices for Engineered Ceramic Matrix Composites (E-CMCs)

The present research effort was undertaken to develop a new generation of SiC fiber-reinforced engineered ceramic matrix composites (E-CMCs). In contrast to traditional CMCs with a brittle SiC matrix, an E-CMC is designed to consist of a matrix engineered to possess sufficient high temperature plasticity to minimize crack propagation, relatively high fracture toughness, and self-healing capabilities to prevent oxygen ingress to the BN-coated fibers through surface-connected cracks. The present paper discusses the bend strength, isothermal oxidation, microstructures and self-healing properties of several silicide-behaved engineered matrices. Based on the oxidation tests, where it was observed that some of the matrices exhibited either catastrophic oxidation ("pesting") or spalling of the oxide scale, two engineered matrices, CrSi2/SiC/Si3N4 and CrMoSi/SiC/Si3N4, were down-selected for further investigation. Four-point bend tests were conducted on these two engineered matrices between room temperature and 1698 degrees Kelvin. Although these matrices were brittle at low temperatures, it was observed that the bend strengths and bend ductility increased at high temperatures as the silicide particles became more ductile, which was qualitatively consistent with the theoretically expected behavior that crack blunting at these particles should increase the matrix strength. Additional studies were conducted to study the effects of different additives on the self-healing properties of the engineered matrices, which helped to identify the most effective additives.

Composite Materials↗
DOE OSTI2022

Isothermal and Cyclic Oxidation of Haynes 282 Processed by Electron Beam Melting (EBM) and Laser Powder Bed Fusion (LPBF) in Dry Air at 800 and 950°C

Here, the isothermal and cyclic oxidation behavior of Haynes 282 (H282) processed by laser powder bed fusion and electron beam melting was compared to its cast counterpart during exposures in air at 800 and 950°C. The specific microstructure of the AM alloys compared to coarse-grain cast 282 resulted in differences in oxidation rates, internal oxidation and spallation behavior. At 800°C, faster Ti diffusion to the surface due to the smaller grain size of the AM alloys led to Ti doping of the Cr 2 O 3 scale and faster oxidation rates. The higher density of grain boundaries also resulted in more pronounced internal oxidation. At 950°C, a duplex Cr 2 O 3 scale was observed with a dense inner layer and porous cracked outer layer with embedded TiO 2 particles. The impact of the external and internal oxide compositions and oxidation-induced elemental depletions on the oxidation lifetime, creep properties and spallation behavior is discussed.

36 MATERIALS SCIENCE↗
NASA NTRS1984

A study of fatigue damage mechanisms in Waspaloy from 25 to 800 C

The objective of the study was to examine the effect of various microstructures on the fatigue and damage accumulation behavior of Waspaloy, a nickel-base alloy commonly used in aircraft engines. Shearing was the dominant deformation mode in specimens with coarse grains and small (50-80 A) gamma prime particles, whereas Orowan looping was dominant in fine-grained specimens with large (about 900 A) gamma prime particles. At temperatures up to 500 C, cracks initiated transgranularly, while at 800 C the failure process was intergranular for both coarse-grained and fine-grained specimens. At temperatures above 500 C, a significant decrease in the fatigue life was observed for both coarse-grained and fine-grained material.

Lerch, B. A.↗