SEARCH · Search NASA
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.
Formulas are derived for calculation of the grinding force in the presence of ultrasound whose amplitude changes the microcutting kinematics of the abrasive grains. The formulas are verified experimentally.
An algorithm is outlined for the design of abrasive tools of optimal structure for a specific grinding operation, ensuring maximum productivity and minimum cost. Systems analysis is employed. Mathematical models for the design calculation are presented, and an example is given to illustrate the optimization of grinding tools.
Methods of cutting thick titanium-alloy plates and slabs are considered. The surface quality of the cut and the productivity are estimated. Abrasive cutting by means of water jets is the most universal method and yields satisfactory surface quality at moderate cost.
Abstract—The failure of cutting tools is investigated. A generalized approach to describing failure is proposed, on the basis of the theory of random point processes. Two mechanisms by which the abrasive particles act on the tool’s cutting edge are considered. The corresponding dynamics of damage accumulation is described.
Software for recording machining tracks in abrasive lapping is described. The software permits prediction of the shape and magnitude of the tool’s surface wear at the stage of process design, on the basis of the dimensions of the workpiece and the lap, their relative velocity, and the machining trajectory.
Cleaning of surfaces by ion bombardment and abrasion, and measuring of surface cleanliness
From the practical point of view, this analysis shows that each problem of friction or wear requires its particular solution. There is no universal solution; one or other of the factors predominates and defines the choice of the solution. In certain cases, copper alloys of great thermal conductivity are preferred; in others, plastics abundantly supplied with water. Sometimes, soft antifriction metals are desirable to distribute the load; at other times, hard metals with high resistance to abrasion or heat.
Lunar dust known as regolith is a huge challenge for lunar exploration missions. Formed over millennia by a complex process involving impacts of meteoroids and micrometeoroids on the lunar surface, lunar dust is porous, highly abrasive with sharp jagged edges, chemically reactive, electrostatically charged and sometimes magnetic. The chemical composition and thickness of the dust layer also varies in different regions of the lunar surface. From samples obtained by previous lunar missions, the average particle size is below 100 microns. This dust has the tendency to strongly adhere to any exposed surfaces, and often degrades the material functionality to eventually cause failure. Any material on the lunar surface is also subject to harsh temperature cycles ranging from -178 ̊C to + 123 ̊C and extreme ultraviolet radiation. While on the lunar surface, different classes of materials would be required for different applications. Advanced materials have been and will be used throughout the lunar lander, habitat, and mission equipment. Examples include: polymeric materials for astronaut protective clothing; metals and ceramics for the lunar lander legs and habitats, and excavating equipment; and semiconductors for solar panels and on-board electronics. In all these applications, the surfaces of the materials are expected or understood to be exposed to the extreme lunar environment condition that includes the regolith dust. During the Apollo missions, the dust clung to and abraded the astronaut’s suits, degraded seals, optics, clogged sensors and reduced performance of thermal radiators. The lunar dust adheres to the surface by various mechanisms, which include electrostatic and Coulombic interactions, Van-der-Waals forces, magnetic forces, mechanical interlocking, chemical bonding and donor-acceptor interactions. There are three primary strategies for developing technologies to minimize the lunar dust adhesion: active, passive and a combination of active and passive. In the active approach, an external energy is needed to prevent or remove particles from collecting on the surface. Mechanically powered brushes and electrodynamic dust screens are two examples. In the passive approach, no external power is needed, and the material surface properties are able to mitigate dust adhesion. A well-known example of this strategy is the low work function coatings for non-stick surfaces. In most cases a combination of active and passive methods might be needed to optimally manage the lunar regolith. The passive method is significantly more attractive as it does not require any external power or an additional control subsystem. These approaches optimize the mission payload and reduce risk. Surface modification to minimize the dust adhesion is thus very important to lunar missions. Here, naturally evolved surface structures might provide guidance for solutions. There are several factors that have to be considered for minimizing particle adhesion to a surface. These include the substrate material properties, surface topography, chemistry, and the characteristics of the adhering particles. When engineering a surface, the substrate material chosen would be dependent on the needs of the application. Tailoring the surface microstructure or chemistry opens up more possibilities for its optimal utilization
As humanity expands its ventures into lunar and planetary exploration, the demand intensifies for resilient materials capable of enduring extreme environmental and service conditions. The Moon’s surface presents numerous challenges, including ultra-high vacuum exposure, temperature extremes and intense radiation. Additionally, lunar regolith poses a significant threat to component durability and reusability due to its abrasive nature. Lunar dust particles scoring, adhering, or embedding into surfaces and within device-confined geometries, such as bearings, drive mechanisms and connectors, can cause premature component wear or failure. Furthermore, the interaction between the rocket plume and the surface during vehicle landings and ascents creates severe erosive conditions near critical vehicle components and adjacent infrastructure. A key barrier hindering materials discovery for lunar dust tolerant applications is a lack of standard laboratory methods to evaluate material properties and performance under representative operating conditions. A case will be presented for research activities supporting identification, processing and characterization of candidate materials in conjunction with innovations in standardized testing and qualification. Results will highlight current and emerging test methods for simulating lunar dust exposure and component degradation, paving the way for a new generation of robust materials and coatings for space exploration.
As humanity expands its ventures into lunar exploration, the demand intensifies for materials capable of enduring extreme environmental and service conditions. The Moon’s surface presents numerous challenges, including ultra-high vacuum exposure, temperature extremes and intense radiation. Additionally, lunar regolith threatens component durability and reusability due to its abrasive nature. Lunar dust particles scoring, adhering or embedding into surfaces and within device-confined geometries, such as bearings, drive mechanisms and connectors, can cause premature component wear or failure. Furthermore, the interaction between the rocket plume and surface during vehicle landings and ascents creates severe erosive conditions near critical vehicle components and adjacent infrastructure. A key barrier hindering materials discovery for lunar dust tolerant applications is a lack of standard laboratory methods to evaluate material properties and performance under representative operating conditions. A case will be presented for research activities supporting identification, processing and characterization of candidate materials in conjunction with innovations in standardized testing and qualification. Results will highlight current and emerging test methods for simulating lunar dust exposure and component degradation, paving the way for a new generation of robust materials and coatings for space exploration.
The aim of this works is sharing the research conducted by NREL in the past three years on photovoltaic soiling. Soiling is an issue affecting PV systems worldwide and causing reduction in performance and increase in O&M costs. NREL has been working closing with he community to (i) develop models to predict soiling, in order to help PV owners to better plan optimal cleaning schedules, and identify soiling trends from PV performance data, without the need of expensive soiling detectors, (ii) understand the abrasive effects of soiling and cleanings on PV glasses, (iii) investigate the effectiveness of different cleaning methods. The most important results and some of the resources made available by the NREL research team will be presented.
The existing Hanford Tank Farms Waste Transfer System has several models of ball valves used for double valve isolation (DVI) that have been installed for 10 or more years. The safety function of the safety-significant valves is to limit leakage of waste past the valves in order to decrease the consequences of a fine spray release due to a transfer misroute. While previous leak testing of the valves has been conducted, the testing did not address concerns in the Documented Safety Analysis concerns about the impact on valve operation and service life of the potential abrasive/erosive properties of the tank waste on the valves when cycled. Pacific Northwest National Laboratory (PNNL) conducted DVI tests at their Multi-Phase Transport Evaluation Loop Facility. Testing evaluated the leak rate of safety-significant isolation valves for DVI as a function of simulated operating cycles. PNNL developed a performance-based simulant specifically for this test program. The test environment simulated the abrasive characteristics of the Hanford Tank Farms Waste Transfer System during single-shell tank retrieval and waste feed delivery to the Hanford Tank Waste Treatment and Immobilization Plant. The testing consisted of periodically measuring leak rates and maximum operational torques on the DVI valves after prescribed numbers of valve operational cycles (open and close). The test results from the simulant cycle tests provide Washington River Protection Solutions with performance characteristics that can be used to verify compliance with the Documented Safety Analysis limits for valve seat leakage. (authors)
A cleaning method using a laser ablation technology is widely used in various industries such as automobile, aviation, and semiconductor industries. Recently, applying this technology to decontamination works has been receiving attention as a useful and effective decontamination method. The laser decontamination method allows for decreasing a generation of secondary radioactive waste because materials like abrasive and water are not required. This is one of big advantages in use for decontamination works. Additionally, the system is compact and requires less than 100 W electric power. These features provide a low running cost. Remote operation obviously plays an important role in terms of a dose reduction in highly-radioactive and contaminated environment. The laser decontamination method is also suitable for remote works using manipulators as the laser head is light and compact, and a reaction force during operation is small, compared to the other types of decontamination tools. This paper provides an outline and a capability of the remote laser decontamination system developed by IHI Corporation (IHI) with some results of component tests for this system. (authors)
Structural health of waste transfer infrastructure is of utmost importance to DOE and communities surrounding their active sites. A Fitness-for-Service (FFS) program for the Waste Transfer System has been implemented by the US Department of Energy (DOE) for the purposes of evaluating and quantifying the degradation of critical components. Currently, the method of approach is to section and evaluate pipelines that have been removed at end service. In order to augment data collection methods applied to making lifespan estimates of waste transfer system components, Florida International University (FIU) has been investigating new-technology based strategies for quantifying the rate of degradation. Present research considers the option of a coupon system installed on a section of pipe at points of interest that will provide easy access to high resolution measurements of erosion/corrosion rates during operation. Researchers at Savannah River National Laboratory (SRNL) have developed this novel solution for in situ erosion and corrosion measurements in many applicable locations such as tanks, pipes, ducts, and injection points. The coupons are approximately 12.7 mm (1/2 inch) in diameter and 25.4 mm (1 inch) in length and can be placed in the pipe sections using Swagelok compression fittings. The coupon design allows for monitoring of the total degradation resulting from corrosion and erosion. High-resolution Ultrasonic Thickness (UT) testing allows in-situ monitoring of both degradation mechanisms. When removed from the system mass loss resulting from corrosion and erosion may also be evaluated. Experimental testing at FIU implemented the SRNL coupon system in a 6.10 meter (20 foot) pipe loop system comprised of 50.8 mm (2 inch) and 76.2 mm (3 inch) pipe sections in order to replicate expected use cases at the sites. Operational conditions were emulated by pumping abrasive materials through the pipeline at full capacity and collecting measurements from the SRNL coupons. Initial testing was conducted by circulating water followed by a mixture of sand and water for uniform wear rates. Thickness changes and mass loss were measured, and the surface exposed to the process fluid was observed for visual evidence of characteristic wear patterns resulting from an erosive environment. The test matrix consisted of several hours of operation and using fine, medium and coarse grain sands. Test results were analyzed to check for all three parameters (mass loss/gain, thickness change and surface patters) which could provide estimates of the remaining useful life of the pipe sections. Thus, the research presents the findings of this evaluation of the SRNL coupons as a means for conducting high accuracy, cost effective in-situ analysis of pipeline and waste transfer systems for erosion and corrosion susceptibility. (authors)
Generated by abrasion of fuel spheres, graphite dust is an important issue for the operation and maintenance of high-temperature gas-cooled reactor (HTGR), since the transport of fission product is closely coupled with graphite dusts. AVR experiments on dust specific radioactivity indicate that graphite dust deposition on steam generator (SG) should be of special interest. Most previous simulations on graphite dust deposition assume a hit-and-stick nature for particles, which may overestimate the deposition rate. In this work we uses a critical velocity model to account for particle-wall interaction. Combined with computational fluid dynamics simulation and discrete phase method, the deposition of graphite dust in the upper 22 layers of SG tubes was studied with particle-wall interaction considered. The result shows that the deposition rate is highly overestimated if hit-and-stick is assumed. For particles larger than 5 {mu}m, the difference can be as large as 3 times. Particle deposition rate reaches maximum at about 3 {mu}m. As for the spatial distribution, few particles deposit on the first layer of tubes due to relative low Stokes number while more depositions occur after entering bundle zone, which indicates that the unsteady wake among tubes could be a major mechanism for the deposition. (authors)
Fragmenting of high-energy heavy ions in nuclear collisions is an important process in space radiation transport, shielding and risk assessment since the secondary particles produced by these collisions have ranges greater than their parent nucleus, and are damaging to humans and spacecraft components. This work uses a quantum-mechanical optical potential abrasion-ablation collision-modeling concept in which nucleons in both the projectile and target are removed by a combination of knockout and evaporation processes in these collisions. In the knockout stage, the collision results in some of the struck projectile nucleons exiting the nucleus and leaving an excited pre-fragment, which then deexcites by a emitting photons, nucleons and light ions by a cascade-evaporation process. The main thrust of this work is to investigate differences in isotope and element production cross sections as a result of utilizing two very different models of charge-to mass ratios for the projectile pre-fragments produced by the abrasion/knockout process. (authors)
Materials with superior hardness can be categorized as ultrahard (Vickers hardness, H v ≥ 80 GPa) and superhard (H v ≥ 40 GPa). These materials are commonly used as cutting tools and abrasives in the machining and manufacturing industries. With its extreme hardness, diamond is the best known and most used ultrahard material for industrial applications. However, it is ineffective at cutting and drilling ferrous alloys due to diamond's high reactivity with iron and poor thermal stability in air. Additionally, the synthesis of diamond requires both high pressure (HP) and high temperature, making it an expensive process. These limitations have driven the search for alternative superhard materials that are capable of cutting steels and other materials at lower costs. This article reviews the concept of hardness and summarizes advancements in the synthesis and mechanical properties of hard materials. It begins with a review of methods to measure hardness, adding HP diffraction methods to more conventional hardness measurements. It then considers new ultrahard materials that exist within the B–C–N ternary system, with hardness approaching diamond but improved chemical stability. Finally, it surveys superhard nitrides, oxides, and borides as potential alternative materials, focusing on transition metal boride systems where the synthesis can be readily achieved at ambient pressure and scaled for industrial applications. We hope that this article serves as an overview of hard materials and guide for the comparison of data reported in the literature.
In recent decades, nanoparticles have received substantial scientific attention due to their novel behavior and industrial applications, from quantum dots to catalysis.Synthesis of nanoparticles is often challenging, since they exist far from equilibrium with a high surface to volume ratio. This work investigates a novel nanoparticle fabrication methodology: combined reaction and acoustic cavitation abrasion of a solid in contact with a liquid. A mechanism is proposed by which particles are generated more effectively by the combination of reaction and cavitation than by either independently. In the current study, a novel method known as Magneto-Acoustic Mixing Technology (MAMT)[3] is used to produce nanometer to micron sized particles by chemical and acoustic mechanisms between diamond particles and a stainless steel surface in the presence of a metallic liquid, in this application Mg. This method demonstrates a number of advantages, including fabrication of novel chemistries and continuous particle production. This methodology is also easily adaptable to an in-situ nanoparticle generation mechanism for the production of metal matrix nanocomposites (MMnCs). In-situ particle generation methods like MAMT inherently limit particle agglomeration and improve the safety of nanocomposite fabrication by eliminating environmental contamination. In the current study, particle size, volume fraction, and chemistry are investigated, as well as the interaction of sonic power and chemical reaction.