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At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

DOE OSTI2012

Friction surfaced Stellite6 coatings

Solid state Stellite6 coatings were deposited on steel substrate by friction surfacing and compared with Stellite6 cast rod and coatings deposited by gas tungsten arc and plasma transferred arc welding processes. Friction surfaced coatings exhibited finer and uniformly distributed carbides and were characterized by the absence of solidification structure and compositional homogeneity compared to cast rod, gas tungsten arc and plasma transferred coatings. Friction surfaced coating showed relatively higher hardness. X-ray diffraction of samples showed only face centered cubic Co peaks while cold worked coating showed hexagonally close packed Co also. - Highlights: Black-Right-Pointing-Pointer Stellite6 used as coating material for friction surfacing. Black-Right-Pointing-Pointer Friction surfaced (FS) coatings compared with casting, GTA and PTA processes. Black-Right-Pointing-Pointer Finer and uniformly distributed carbides in friction surfaced coatings. Black-Right-Pointing-Pointer Absence of melting results compositional homogeneity in FS Stellite6 coatings.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener-Hollomon parameter during friction surfacing. - Highlights: Black-Right-Pointing-Pointer Dynamic recrystallization in alloy 316L friction surfaced coatings is examined. Black-Right-Pointing-Pointer Friction surfacing leads to discontinuous dynamic recrystallization in alloy 316L. Black-Right-Pointing-Pointer Strain rates in friction surfacing exceed 400 s{sup -1}. Black-Right-Pointing-Pointer Estimated grain size matches well with experimental observations in 316L coatings.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Internal friction sensitivity to precipitation in Al-12 wt% Mg alloy

Highlights: • Internal friction is sensible to semi coherent and non-coherent phases (β′ and β). • Internal friction is not enough sensible to coherent GP zones formation in Al-12 wt% Mg. • Appearance of two IF peaks is due to β′ and β phases formation and dissolution. - Abstract: In order to improve the understanding of the sensibility of the internal friction phenomena to different stages of precipitation in Al-Mg alloys, the ageing effect of a supersaturated solid solution on the Temperature Dependent Internal Friction (TDIF) spectra has been studied. The research showed that the dissolution of the β phase and the transfer of Mg atoms to a solid solution and the formation of β′ metastable phase have an effect on internal friction. Thus, it was proved that the precipitation or the dissolution of β phase plays an important role in the anelasticity of Al-Mg alloys. A detailed TDIF analysis revealed the sensibility of the internal friction technique to the formation of semi-coherent and non-coherent phases (β′ and β) but it is not sensitive enough to the formation of coherent phases (GP zones). Several observations on the nature and the shape of the precipitates are also discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Multidimensional modeling of fuel-cladding friction in an LWR fuel rod

Solving finite element problems with friction often increases the level of difficulty to obtain properly converged solutions. This type of challenge becomes more salient when advanced, possibly multiscale, material models are employed to capture the thermomechanical behavior of fuel and cladding materials. Here the present work details our recent developments in a nuclear fuel performance finite element code for the systematic consideration of friction in nuclear reactor finite element simulations. We show the application of friction and its effects on the mechanics of light-water reactor rods accounting for various fuel constitutive modeling techniques, model dimensionalities, pellet assumed geometries, and power conditions. In particular, we focus on the fuel rod mechanical behavior as it relates to fuel constitutive models, sensitivity to the coefficient of friction, pellet states of stress, and rod elongation. We discuss the trade-offs between the various multidimensional modeling options and highlight the relevance of frictional effects in the prediction of the fuel rod deformation and interfacial stresses. To relate our modeling results with actual reactor operation, simulations including frictional effects are compared with fuel rod elongation experimental data and some challenges for carrying out a full validation of the axial mechanics are discussed.

42 ENGINEERING↗

DOE OSTI2014

Effects of Stone-Wales and vacancy defects in atomic-scale friction on defective graphite

Graphite is an excellent solid lubricant for surface coating, but its performance is significantly weakened by the vacancy or Stone-Wales (SW) defect. This study uses molecular dynamics simulations to explore the frictional behavior of a diamond tip sliding over a graphite which contains a single defect or stacked defects. Our results suggest that the friction on defective graphite shows a strong dependence on defect location and type. The 5-7-7-5 structure of SW defect results in an effectively negative slope of friction. For defective graphite containing a defect in the surface, adding a single vacancy in the interior layer will decrease the friction coefficients, while setting a SW defect in the interior layer may increase the friction coefficients. Our obtained results may provide useful information for understanding the atomic-scale friction properties of defective graphite.

36 MATERIALS SCIENCE↗

NASA NTRSDate not supplied

Skin Friction Measurement on a Swept NACA 0015 Wing Using Oil Film Interferometry

An application of oil film interferometry (OFI) to measure skin friction on the 3D flow over an NACA 0015 airfoil with 30° of sweep is presented. Local flow direction must be known to apply OFI to complex 3D flows such as this. A recently developed surface flow vector extraction method was integrated into the OFI analysis algorithm. Surface flow vectors were used to calculate the surface streamlines and hence provided local flow direction to the OFI analysis. After calibration using photogrammetry, the surface flow vectors also enabled decomposition of the skin friction coefficient into different components (such as chordwise and spanwise). The presented method successfully measured skin friction at locations with different flow characteristics such as high skin friction regions, strong spanwise flow regions, and 3D flow separated regions. In the current OFI analysis, multiple interferogram images acquired at different times were analyzed for the same location. The multiple interferogram analysis enabled averaging, which reduced the scatter the skin friction data. The results presented herein demonstrate the capability of the current approach, thereby extending OFI skin friction measurements to complex 3D flows.

Skin friction measurement↗

NASA NTRSDate not supplied

Skin Friction Measurement on a Swept NACA 0015 Wing Using Oil Film Interferometry

Skin friction measurement↗

DOE OSTI2016

Friction Stir Cutting for Decommissioning - 16130

Safe and cost effective decommissioning of redundant nuclear plant is a primary consideration to countries and companies with aging nuclear facilities. The wider media coverage of nuclear issues and strong public feeling is ensuring decommissioning options are also considered prior to development of new nuclear facilities. A project has been undertaken to demonstrate the feasibility of applying friction stir cutting, a non-fusion, non-machining, method of separating materials for size reduction of redundant metallic nuclear plant, specifically as a flexible low cost tool for plant dismantling. The research program was designed to provide a fast and effective approach to the assessment of process feasibility in stainless steels. Friction stir cutting may begin by traversing the rotating tool into the edge of the plate, or alternatively, by piercing the plate with a suitably profiled rotating friction stir cutting tool. Plate piercing trials were conducted to determine the down-force required to pierce the plate and to identify the appropriate tool tip profile for efficient piercing. The friction stir cutting process has been successfully demonstrated in 3 mm and 6 mm thick stainless steel plate. Provided sufficient torque is available, the friction stir cutting process is suitable for robotic application. The process is suitable for submerged applications such as the removal of pond furniture. Special attention was given towards any fume generation or particulate emissions during cutting. Friction stir cutting of bare steel plate does not generate fume, results in a relatively smooth edge profile and produces minimal loose debris. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2019

Graphene - MoS 2 ensembles to reduce friction and wear in DLC-Steel contacts

Recent demonstration of two dimensional (2D) solid lubricant materials to minimize friction to unmeasurable levels (superlubricity) and reduce wear at macroscale propelled further research investigations in the direction of exploring their potential in industrially relevant material combinations such as steel and diamond-like-carbon (DLC) in sliding contact. In this study, we have used a combination of 2D materials i. e. Graphene and MoS 2 as a solid lubricant to reduce friction and wear in steel-hydrogenated DLC contacts even at high contact pressures and sliding speed. Sliding friction tests conducted under dry nitrogen conditions shows a reduction of friction and wear by 16 and 29 times, respectively as compared to Steel vs H-DLC (baseline) experiments and friction and wear by a factor of 43 and 434, respectively, compared to self-mated steel vs steel experiments. In conclusion, optical and Raman investigations of the material pairs and the wear debris analysis in TEM indicated the formation of amorphous carbon mixed graphene layers at the sliding interface leading to such dramatic reductions in friction and wear.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Liquids with Lower Wettability Can Exhibit Higher Friction on Hexagonal Boron Nitride: The Intriguing Role of Solid–Liquid Electrostatic Interactions

Here, we investigate the wetting and frictional behavior of polar (water and ethylene glycol) and nonpolar (diiodomethane) liquids on the basal plane of hexagonal boron nitride (hBN) using molecular dynamics simulations. Our results for the wettability of water on the hBN basal plane (contact angle 81°) are in qualitative agreement with the experimentally deduced mild hydrophilicity of the hBN basal plane (contact angle 66°). We find that water exhibits the lowest wettability, as quantified by the highest contact angle, but the highest friction coefficient of (1.9 ± 0.4) × 10 5 N-s/m 3 on the hBN basal plane among the three liquids considered. This intriguing finding is explained in terms of the competition between dispersion and electrostatic interactions operating between the hBN basal plane and the three liquids. We find that electrostatic interactions do not affect the wetting behavior appreciably, as quantified by a less than 3° change in the respective contact angles of the three liquids considered. On the other hand, electrostatic interactions are found to increase the friction coefficients of the three liquids in contact with hBN to different extents, indicating that despite the increased friction of water on hBN, relative to that on graphene, nonpolar liquids may exhibit similar friction coefficients on hBN and graphene. Our findings reveal that the increase in the friction coefficient, upon incorporation of solid–liquid electrostatic interactions, is brought about by a greater increase in the solid–liquid mean-squared total lateral force, as compared to a smaller reduction in the decorrelation time of the solid–liquid force.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

The Role of Mineral Composition on the Frictional and Stability Properties of Powdered Reservoir Rocks

The growing hazard of induced seismicity driven by the boom in unconventional resources exploitation is strongly linked to fault activation. We perform laboratory measurements on simulated fault gouges comprising powdered reservoir rocks from major oil and gas production sites in China, to probe the control of mineral composition on fault friction and stability responses during reservoir stimulation. Double direct shear experiments were conducted on gouges with phyllosilicate content ranging from 0 to 30 wt.% and grain sizes <150 μm, at constant normal stresses of 10–40 MPa and conditions of room temperature and water saturation. The velocity step and slide-hold-slide sequences were employed to evaluate frictional stability and static healing, respectively. Results indicate that the mineralogy of the gouges exhibit a strong control on the frictional strength, stability, and healing. Phyllosilicate-rich samples show lower frictional strength μ and higher values of (a – b ), promoting stable sliding. For the gouges studied, the frictional strength decreases monotonically with increasing phyllosilicate content, and a transition from velocity weakening to velocity strengthening behavior is evident at 15 wt.% phyllosilicates. Intermediate healing rates are common in gouges with higher content of phyllosilicates, with high healing rates predominantly in phyllosilicate-poor gouges. As an indispensable component in reservoir rocks, the carbonates are shown to affect both the frictional stability and healing response. These findings can have important implications for understanding the effects of mineralogy on fault behavior and induced seismic potential in geoengineering activities, particularly in reservoirs in China.

58 GEOSCIENCES↗

DOE OSTI2015

Solid friction between soft filaments

Any macroscopic deformation of a filamentous bundle is necessarily accompanied by local sliding and/or stretching of the constituent filaments. Yet the nature of the sliding friction between two aligned filaments interacting through multiple contacts remains largely unexplored. Here, by directly measuring the sliding forces between two bundled F-actin filaments, we show that these frictional forces are unexpectedly large, scale logarithmically with sliding velocity as in solid-like friction, and exhibit complex dependence on the filaments’ overlap length. We also show that a reduction of the frictional force by orders of magnitude, associated with a transition from solid-like friction to Stokes’s drag, can be induced by coating F-actin with polymeric brushes. Furthermore, we observe similar transitions in filamentous microtubules and bacterial flagella. In conclusion, our findings demonstrate how altering a filament’s elasticity, structure and interactions can be used to engineer interfilament friction and thus tune the properties of fibrous composite materials.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Incorporation of velocity-dependent restitution coefficient and particle surface friction into kinetic theory for modeling granular flow cooling

Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009)]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Evolution of Friction and Permeability in a Propped Fracture under Shear

We explore the evolution of friction and permeability of a propped fracture under shear. We examine the effects of normal stress, proppant thickness, proppant size, and fracture wall texture on the frictional and transport response of proppant packs confined between planar fracture surfaces. The proppant-absent and proppant-filled fractures show different frictional strength. For fractures with proppants, the frictional response is mainly controlled by the normal stress and proppant thickness. The depth of shearing-concurrent striations on fracture surfaces suggests that the magnitude of proppant embedment is controlled by the applied normal stress. Under high normal stress, the reduced friction implies that shear slip is more likely to occur on propped fractures in deeper reservoirs. The increase in the number of proppant layers, from monolayer to triple layers, significantly increases the friction of the propped fracture due to the interlocking of the particles and jamming. Permeability of the propped fracture is mainly controlled by the magnitude of the normal stress, the proppant thickness, and the proppant grain size. Permeability of the propped fracture decreases during shearing due to proppant particle crushing and related clogging. Proppants are prone to crushing if the shear loading evolves concurrently with the normal loading.

42 ENGINEERING↗

DOE OSTI2018

Role of Surface Friction on Shallow Nonprecipitating Convection

The role of surface friction on shallow nonprecipitating convection is investigated using a series of large-eddy simulations with varying surface friction velocity and with a cloud identification algorithm. As surface friction intensifies, convective rolls dominate over convective cells and secondary overturning circulation becomes stronger in the subcloud layer, thus transporting more moisture upward and more heat downward between the subcloud and cloud layers. Identifying individual clouds, using the identification algorithm based on a three-dimensional topological analysis, reveals that intensified surface friction increases the number of clouds and the degree of tilting in the downstream direction. Highly intensified surface friction increases wind shear across the cloud base and induces cloud tilting, which leads to a vertically parabolic profile of liquid water mixing ratio instead of the classical two-layer structure (conditionally unstable and trade inversion layers). Furthermore, cloud tilting induces more cloud cover and more cloud mass flux much above the cloud base (e.g., 0.8 < z < 1.2 km), but less cloud cover and less cloud mass flux in the upper cloud layer (e.g., z > 1.2 km) because of increased lateral entrainment rate. Similarly, profiles of directly measured entrainment and detrainment rates show that detrainment in the lower cloud layer becomes smaller with stronger surface friction.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2020

Calculation of Friction Factors in Heat Pipes Using CFD in Support of the Sockeye Code

A heat pipe is two-phase heat transfer device which relies on surface tension and capillary pressure to provide a very efficient heat transfer mechanism. Currently, there is interest in designing micro nuclear power reactors using high temperature heat pipes to provide totally passive cooling. To support this, Sockeye is being developed as a heat pipe simulation capability. To support the development of Sockeye, individual phenomena must be tested. This work focuses on applying a CFD model to evaluate friction factors for use in Sockeye. A CFD model has been developed in Nek5000 which simulates each component fluid, i.e. sodium liquid and vapor, independently and captures the effects of the wick on friction factor. The model tests the effect of the wick permeability and the thickness of the wick occupied by each fluid component. The thickness of the wick occupied by each component can be directly related to the local vapor volume fraction from the Sockeye heat pipe model. Results from the CFD model indicate that friction factor in the liquid flow decreases with increasing wick permeability, while the friction factor in the vapor flow increases with increasing wick permeability. In the liquid, this is likely a direct result of the increased cross sectional area available for the flow. For the vapor, this is explained as the wick acting like a rough wall, while the increased area has only a negligible impact. Results for the tests of the thickness of the wick occupied by each fluid showed a thresholding behavior for both liquid and vapor. When the thickness of the wick occupied by each fluid was increased, it increased the effect of the wick, but only up to a certain point. Once a certain thickness was reached, the friction factors remained constant. When the fluid occupied only a very small fraction of the wick, friction factors returned to nominal values.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS1971

Exploratory study of friction welds in Udimet 700 and TD-Nickel bar

Friction welded butt joints were made in both Udimet 700 and TD-Nickel bar. Also, dissimilar metal friction welds were made between these materials. Friction welding of Udimet 700 shows great promise because the welds were found to be as strong as the parent metal in stress rupture and tensile tests at 760 and 980 C. The weld line was not detectable metallographically in the heat treated condition. Friction welding for TD-Nickel, however, holds little if any promise. TD-Nickel friction weldments could support only 9 percent as much stress as the base metal for a 10-hour stress-rupture life at 1090 C. Dissimilar Udimet 700/TD-Nickel friction welds could sustain only 15 percent as much stress as the TD-Nickel parent metal for a 10-hour rupture life at 930 C.

Moore, T. J.↗

NASA NTRS1974

Friction behavior of 304 stainless steel of varying hardness lubricated with benzene and some benzyl structures

The lubricating properties of some benzyl and benzene structures were determined by using 304 stainless steel surfaces strained to various hardness. Friction coefficients and wear track widths were measured with a Bowden-Leben type friction apparatus by using a pin-on-disk specimen configuration. Results obtained indicate that benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol resulted in the lowest friction coefficients for 304 stainless steel, while benzyl ether provided the least surface protection and gave the highest friction. Strainhardening of the 304 stainless steel prior to sliding resulted in reduced friction in dry sliding. With benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol changes in 304 stainless steel hardness had no effect upon friction behavior.

Buckley, D. H.↗