Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “STIRRING”

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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Effect of the surface preparation techniques on the EBSD analysis of a friction stir welded AA1100-B{sub 4}C metal matrix composite

Aluminum based metal matrix composites (MMCs) have been used in various automobile, aerospace and military industries. Yet characterization of the microstructure in these materials remains a challenge. In the present work, the grain structure in the matrix of B{sub 4}C particulate reinforced MMCs and their friction stir welds is characterized by using optical metallography and the electron backscatter diffraction (EBSD) technique. Optical metallography can partially reveal the grain structure in the matrix of AA1100-16 vol.% B{sub 4}C composite. The EBSD technique has been successfully applied to characterize the grain structure in the AA1100-16 vol.% B{sub 4}C friction stir welds, which provides a powerful tool to follow the microstructural evolution of MMC materials during friction stir welding (FSW). Both mechanical polishing and ion beam polishing are used for the EBSD sample preparation. The effect of the sample preparation on the EBSD data acquisition quality is studied. Some typical examples, such as the identification of grains and subgrains, grain size distribution, deformation fields and the texture components are given. - Highlights: {yields} EBSD has been used to characterize the grain structure of Al-B{sub 4}C MMCs. {yields} Mechanical and ion beam polishing are compared for EBSD sample preparation of MMCs. {yields} EBSD shows great advantages over optical microscopy for microtexture analysis of MMCs.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Friction stir welding joint of dissimilar materials between AZ31B magnesium and 6061 aluminum alloys: Microstructure studies and mechanical characterizations

Friction stir welding is an efficient manufacturing method for joining dissimilar alloys, which can dramatically reduce grain sizes and offer high mechanical joint efficiency. Lap FSW joints between dissimilar AZ31B and Al 6061 alloy sheets were made at various tool rotation and travel speeds. Rotation and travel speeds varied between 560–1400 r/min and 16–40 mm/min respectively, where the ratio between these parameters was such that nearly constant pitch distances were applied during welding. X-ray diffraction pattern (XRD), optical microscopy images (OM), electron probe microanalysis (EPMA) and scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS) were used to investigate the microstructures of the joints welded. Intermetallic phases including Al{sub 12}Mg{sub 17} (γ) and Al{sub 3}Mg{sub 2} (β) were detected in the weld zone (WZ). For different tool rotation speeds, the morphology of the microstructure in the stir zone changed significantly with travel speed. Lap shear tensile test results indicated that by simultaneously increasing the tool rotation and travel speeds to 1400 r/min and 40 mm/min, the joint tensile strength and ductility reached a maximum. Microhardness measurements and tensile stress–strain curves indicated that mechanical properties were affected by FSW parameters and mainly depended on the formation of intermetallic compounds in the weld zone. In addition, a debonding failure mode in the Al/Mg dissimilar weld nugget was investigated by SEM and surface fracture studies indicated that the presence of intermetallic compounds in the weld zone controlled the failure mode. XRD analysis of the fracture surface indicated the presence of brittle intermetallic compounds including Al{sub 12}Mg{sub 17} (γ) and Al{sub 3}Mg{sub 2} (β). - Highlights: • Dissimilar Al/Mg joint was obtained by lap friction stir welding technique. • Effect of rotation and travel speeds on the formation of intermetallic compounds • Microstructure and chemical studies including metallography, XRD, SEM-EDS, and EPMA • Mechanical property tests such as stress–strain curves, failure load and hardness • IMCs as Al{sub 3}Mg{sub 2} and Al{sub 12}Mg{sub 17} were identified in weld nugget and at Al/Mg interface.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure and wear characterization of aluminum matrix composites reinforced with industrial waste fly ash particulates synthesized by friction stir processing

Fly ash (FA) is a waste product of coal combustion in thermal power plants which is available in massive quantities all over the world causing land pollution. This paper reports the characterization of AA6061 aluminum matrix composites (AMCs) reinforced with FA particles synthesized using friction stir processing (FSP). The volume fraction of FA particles was varied from 0 to 18 in steps of 6. The prepared AMCs were characterized using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diagram (EBSD). The wear rate was estimated using a pin-on-disc wear apparatus. FA particles were observed to be distributed homogeneously in the AMC irrespective of the location within the stir zone. The EBSD micrographs revealed remarkable grain refinement in the AMC. The incorporation of FA particles enhanced the microhardness and wear resistance of the AMC. The strengthening mechanisms of the AMC were discussed and correlated to the observed microstructures. The wear mechanisms were identified by characterizing the wear debris and worn surfaces. - Highlights: •Industrial waste fly ash was used to produce aluminum matrix composites. •Friction stir processing was used to produce AA6061/Fly Ash composite. •Fly ash particles refined the grains of aluminum matrix. •Fly ash particles enhanced the hardness and wear resistance. •Successful utilization of fly ash to make aluminum composites reduces land pollution.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Defect features, texture and mechanical properties of friction stir welded lap joints of 2A97 Al-Li alloy thin sheets

1.4 mm 2A97 Al-Li alloy thin sheets were welded by friction stir lap welding using the stirring tools with different pin length at different rotational speeds. The influence of pin length and rotational speed on the defect features and mechanical properties of lap joints were investigated in detail. Microstructure observation shows that the hook defect geometry and size mainly varies with the pin length instead of the rotational speed. The size of hook defects on both the advancing side (AS) and the retreating side (RS) increased with increasing the pin length, leading to the effective sheet thickness decreased accordingly. Electron backscatter diffraction analysis reveals that the weld zones, especially the nugget zone (NZ), have the much lower texture intensity than the base metal. Some new texture components are formed in the thermo-mechanical affected zone (TMAZ) and the NZ of joint. Lap shear test results show that the failure load of joints generally decreases with increasing the pin length and the rotational speed. The joints failed during the lap shear tests at three locations: the lap interface, the RS of the top sheet and the AS of the bottom sheet. The fracture locations are mainly determined by the hook defects. - Highlights: • Hook defect size mainly varies with the pin length of stirring tool. • The proportion of LAGBs and substructured grains increases from NZ to TMAZ. • Weld zones, especially the NZ, have the much lower texture intensity than the BM. • Lap shear failure load and fracture location of joints is relative to the hook defects.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Comparison of microstructural and mechanical properties of friction stir spot welded ultra-high strength dual phase and complex phase steels

Highlights: • The microstructure and mechanical properties of FSSW of ultra high strength DP and CP steels are compared. • The stir zone (SZ) of CP steel mainly consists of bainite and martensite; no bainite is identified in the SZ of DP steel. • The cooling was not fast enough for the CP steel to suppress the effect of chemical composition on phase transformation. - Abstract: The microstructure and mechanical properties of friction stir spot welding of ultrahigh strength dual phase (DP) and complex phase (DP) steels are compared based on the experimental results. For both DP and CP steels, FSSW joints are successfully fabricated using the same process parameter set. While the microstructure of joints are characterized in detail using scanning electron microscopy, electron back scattered diffraction, and transmission electron microscopy, the mechanical property of joints are evaluated by shear tensile tests. The result of the microstructural analysis shows that the stir zone (SZ) of CP steel mainly consists of bainite and martensite, while no bainite is identified in the SZ of DP steel. The existence of bainite in the SZ of CP steel suggests that the cooling rate, which is nearly identical for both CP and DP steels, was not fast enough to suppress the effect of the alloying composition, particularly that of Mn, on the phase transformation. The result of the present study contributes to the development of solid state joining process of the ultrahigh strength steels.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Correlation between corrosion resistance, anodic hydrogen evolution and microhardness in friction stir weldment of AA2198 alloy

Highlights: • There is a relationship between hardness, corrosion and H{sub 2} evolution in AA2198-T851 alloy friction stir weldment • Variation in the population density of T1 particles is the correlating factor for the relationship • The parent material is the region that is most susceptible to corrosion. • The weld zones of AA2198-T851 alloy friction stir weldment exhibit different forms of corrosion. - Abstract: Correlation between corrosion resistance, anodic hydrogen evolution and microhardness in the friction stir weldment of AA2198-T851 alloy has been investigated. Different microscopy techniques, scanning vibrating electrode technique (SVET) and potentiodynamic polarization tests were employed in the investigation. Unlike other 3rd generation Al-Cu-Li alloys where the regions that are most susceptible to corrosion are always within the weld region, the results reveal that the parent material is the most susceptible in this case. There is a direct correlation between corrosion resistance, anodic hydrogen evolution and microhardness in the weldment, and the T{sub 1} phase is associated with the direct correlation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Friction stir welding of multi-walled carbon nanotubes reinforced Al matrix composites

Highlights: • Al/MWCNT composites were successfully welded using friction stir welding. • After FSW, the composites possessed an excellent balance of mechanical properties. • High tensile strength and elongation over BM owing to MWCNTs after FSW. • Microstructures were investigated according to MWCNT contents and FSW conditions. - Abstract: In this study, we prepared composites between Al and multi-walled carbon nanotubes (MWCNTs) using the friction stir welding (FSW) method and investigated their microstructural evolution and mechanical properties by controlling the amount of MWCNT (1 and 3 vol%) and the plunging load (400 and 600 kg) used. After the FSW process, MWCNT showed slight coarsening of grain with random shear textures and accumulated dislocations; the differences obtained by varying the plunging load and MWCNT amount were insignificant. The friction-stir welded composite obtained using 3 vol% MWCNT and a plunging load of 600 kg possessed two-times better balance between strength and ductility than the base metal, due to the presence of both MWCNTs and the partially decomposed Al{sub 4}C{sub 3} in the composite.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Isopycnal Submesoscale Stirring Crucially Sustaining Subsurface Chlorophyll Maximum in Ocean Cyclonic Eddies

Abstract Mesoscale and submesoscale processes have crucial impacts on ocean biogeochemistry, importantly enhancing the primary production in nutrient‐deficient ocean regions. Yet, the intricate biophysical interplay still holds mysteries. Using targeted high‐resolution in situ observations in the South China Sea, we reveal that isopycnal submesoscale stirring serves as the primary driver of vertical nutrient transport to sustain the dome‐shaped subsurface chlorophyll maximum (SCM) within a long‐lived cyclonic mesoscale eddy. Density surface doming at the eddy core increased light exposure for phytoplankton production, while along‐isopycnal submesoscale stirring disrupted the mesoscale coherence and drove significant vertical exchange of tracers. These physical processes play a crucial role in maintaining the elevated phytoplankton biomass in the eddy core. Our findings shed light on the universal mechanism of how mesoscale and submesoscale coupling enhances primary production in ocean cyclonic eddies, highlighting the pivotal role of submesoscale stirring in structuring marine ecosystems.

Cao, Haijin↗
DOE OSTI2015

Friction stir processing on high carbon steel U12

Friction stir processing (FSP) of high carbon steel (U12) samples has been carried out using a milling machine and tools made of cemented tungsten carbide. The FSP tool has been made in the shape of 5×5×1.5 mm. The microstructural characterization of obtained stir zone and heat affected zone has been carried out. Microhardness at the level of 700 MPa has been obtained in the stir zone with microstructure consisting of large grains and cementitte network. This high-level of microhardness is explained by bainitic reaction developing from decarburization of austenitic grains during cementite network formation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Friction stir scribe welding technique for dissimilar joining of aluminium and galvanised steel

Friction stir scribe technology, a derivative of friction stir welding, was applied for the dissimilar lap welding of an aluminum alloy and galvanized mild steel sheets. During the process, the rotating tool with a cobalt steel scribe first penetrated the top material — aluminum — and then the scribe cut the bottom material — steel. The steel was displaced into the upper material to produce a characteristic hook feature. Lap welds were shear tested, and their fracture paths were studied. Welding parameters affected the welding features including hook height, which turned out to be highly related to fracture position. Therefore, in this paper, the relationships among welding parameters, hook height, joint strength and fracture position are presented. In addition, influence of zinc coating on joint strength was also studied. Keywords: friction stir scribe technology; dissimilar material welding; zinc coating; hook height; joint strength; fracture position

Aluminum↗
DOE OSTI2012

HOW TO MAKE AN ULTRA-FAINT DWARF SPHEROIDAL GALAXY: TIDAL STIRRING OF DISKY DWARFS WITH SHALLOW DARK MATTER DENSITY PROFILES

In recent years the Sloan Digital Sky Survey has unraveled a new population of ultra-faint dwarf galaxies (UFDs) whose origin remains a puzzle in the vicinity of the Milky Way (MW). Using a suite of collisionless N-body simulations, we investigate the formation of UFDs in the context of the tidal stirring model for the formation of dwarf spheroidal galaxies in the Local Group (LG). Our simulations are designed to reproduce the tidal interactions between MW-sized host galaxies and rotationally supported dwarfs embedded in 10{sup 9} M{sub Sun} dark matter (DM) halos. We explore a variety of inner density slopes {rho}{proportional_to}r{sup -{alpha}} for the dwarf DM halos, ranging from core-like ({alpha} = 0.2) to cuspy ({alpha} = 1), and different dwarf orbital configurations. Our experiments demonstrate that UFDs can be produced via tidal stirring of disky dwarfs on relatively tight orbits, consistent with a redshift of accretion by the host galaxy of z {approx} 1, and with intermediate values for the halo inner density slopes ({rho}{proportional_to}r{sup -0.6}). The inferred slopes are in excellent agreement with those resulting from both the modeling of the rotation curves of dwarf galaxies and recent cosmological simulations of dwarf galaxy formation. Comparing the properties of observed UFDs with those of their simulated counterparts, we find remarkable similarities in terms of basic observational parameters. We conclude that tidal stirring of rotationally supported dwarfs represents a viable mechanism for the formation of UFDs in the LG environment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Corrosion Testing of Friction Stir Welded 304L Stainless Steel

A preliminary study on the microstructural characteristics and stress corrosion cracking susceptibility of a friction stir welded (FSW) 304L stainless steel plate was carried out. The weld examined was characterized by several typical microstructural features of friction stir welds including a gradient of dynamically recrystallized microstructure with distinct material flow patterns reflective of the complex distribution of thermomechanical histories. Evidence of process-induced microstructural sensitization was lacking Immersion testing of the friction stir welded plate in boiling magnesium chloride solution indicated the FSW region was more susceptible to SCC than the base 304L material, especially along the weld toes. The microstructural origins of this SCC susceptibility are not clear, but it is likely driven by residual stress imparted by the welding process. Future work will focus on direct examination of the SCC damaged microstructure and residual stress of the weld zone to further clarify the operative characteristics controlling SCC susceptibility.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

ETF Grout Expansion: Effects of Different Slags and Struvite Precipitation Protocols (Stirring Time)

The ETF ammonia tolerant grout waste form was developed by the Vitreous State Laboratory (VSL) to stabilize ammonium and thereby prevent emission of ammonia vapor during solidification of an ammonium-rich, concentrated sodium sulfate aqueous waste stream generated at the Hanford Effluent Treatment Facility (ETF). VSL personnel did not observe expansion in samples prepared during the waste form development work. However, Savannah River National Laboratory (SRNL) personnel detected expansion, in a few ETF grout samples, up to ~ 20 percent vertical expansion, while preforming work scope to evaluate the effect of ETF brine compositional ranges on the precipitation and solidification processes. The initial work requests can be found in Washington River Protection Services (WRPS) Statement of Work (SOW, Requisitions #: 339922 Revisions 0 and 1, March 11, 2021, and November 2021, respectively. As a result of the waste form expansion observed by SRNL, additional evaluation was requested by WRPS SOW Requisitions #: 356730 Revision 0 and Revision 1, February 1, 2022, and July 11, 2022, respectively. The goal of these requests was to determine whether differences in the slags and / or in sample preparation protocols used by VSL and SRNL were the cause of the expansion observed in the SRNL samples. G. Chen, WRPS, arranged a materials exchange between VSL and SRNL and coordinated the VSL protocol(s) for grouting and curing 1L batches of Base Case ETF base case simulant. Materials were exchanged between VSL and SRNL. Both laboratories performed the VSL struvite precipitation-solidification protocol and cured samples for at least 28 days. Differences in VSL and SRNL slag compositions, mineralogy and particle size results in themselves or combined were determined to not be the cause of the expansion because all samples expanded regardless of whether the VSL or SRNL slags were used. The fundamental cause of the observed expansion could not be attributed to minor variations in the following: 1) chemistry of the slag and other reagents, 2) container wall thickness, 3) ambient bench top curing conditions at VSL and SRNL, 4) pH adjustments to 7 ± a few tenths of unit, nor 5) stirring time between the precipitation and solidification process steps. Additional observations include: grout samples prepared with VSL slag expanded less than those prepared with the SRNL slag and, based on a very limited sample set, some samples stirred for longer times expanded less than those stirred for 20 minutes.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

A priori examination of reduced chemistry models derived from canonical stirred reactors using three-dimensional direct numerical simulation datasets

Data-driven approaches to construct reduced chemical kinetic models, that rely heavily on thermo-chemical datasets with full chemical kinetics, have been gaining popularity. Datasets from direct numerical simulations (DNS) under three-dimensional (3-D) realistic turbulent flow conditions are desirable but limited to carefully designed parametric conditions due to the computational cost. Constructing datasets from a large ensemble of zero-dimensional stirred reactors like perfectly stirred reactor (PSR) and partially stirred reactor (PaSR) is a computationally efficient solution to consider the turbulence-chemistry interactions and cover a broad range of parametric conditions. In this paper, we derive reduced chemistry models from solutions of a large number of PSR and PaSR reactors using autoencoder (AE) neural networks and principal component analysis (PCA), and conduct a priori examination of the reduced models in three temporally evolving 3-D DNS jet flames featuring local extinction and re-ignition. The results show that the reduced models derived from PaSR datasets, i.e., AE-PaSR and PCA-PaSR, generally show significant improvement over the ones derived from PSR datasets. Among all the reduced models, AE-PaSR shows the best agreement with DNS results on the reconstruction accuracy and the representation of temporally evolving local extinction and re-ignition events.

Zhang, Pei↗
NASA NTRS1975

Additional experiments with a four-bladed cyclic pitch stirring model rotor, part 2 of second yearly report

The four bladed pitch stirring rotor model was used in a rotor dynamic wake survey at zero advance ratio, covering 2 deg, 5 deg and 8 deg collective pitch settings. Dynamic wake data were taken in planes .12 and .20 radii below the rotor disk and are to be compared with analytical wake data with parameters to be identified from pitch stirring transients. The model was modified to perform such transients. The instrumentation developed for this purpose is described together with the method of data acquisition and with the test procedures. The hardware and software for several data handling systems are discussed. These systems extract from pitch stirring transients the parameters of analytical dynamic rotor wake models.

Hohenemser, K. H.↗
NASA NTRS1985

Planar oscillatory stirring apparatus

The present invention is directed to an apparatus for stirring materials using planar orthogonal axes oscillations. The apparatus has a movable slide plate sandwiched between two fixed parallel support plates. Pressurized air is supplied to the movable slide plate which employs a tri-arm air bearing vent structure which allows the slide plate to float and to translate between the parallel support plates. The container having a material to be stirred is secured to the upper surface of the slide plate through an aperture in the upper support plate. A motor driven eccentric shaft loosely extends into a center hole bearing of the slide plate to cause the horizontal oscillations. Novelty lies in the combination of elements which exploits the discovery that low frequency, orthogonal oscillations applied horizontally to a Bridgman crucible provides a very rigorous stirring action, comparable with and more effective by an order of magnitude than the accelerated crucible rotation technique.

Wolf, M. F.↗
NASA NTRS1987

Low frequency vibrational stirring - A new method for rapidly mixing solutions and melts during growth

A new method for rapidly stirring liquids has been developed which may be useful in crystal growth applications. The method involves the introduction of orthogonally coupled low frequency vibrations to fluids contained in cylindrical crucibles. A mathematical model has been developed to describe the influence of this vibrational stirring method on fluid flow. The optimum sloshing frequencies calculated for a specific system geometry were very close to those observed experimentally. A systematic study of the fluid flow induced by the vibrational motion was carried out at room temperature using aqueous solutions containing glycerine. Preliminary experiments were carried out to study the effect of vibrational stirring on interface shape and position during the Bridgman growth of CsCdCl3, a model system.

Liu, W.-S.↗
NASA NTRS1987

Infrared properties of an anisotropically stirred fluid

A renormalization group is developed for the Navier-Stokes equations driven by an anisotropically correlated random stirring force. The stirring force generates homogeneous turbulence with a preferred direction. The force correlation is the sum of a small anisotropic perturbation and an isotropic correlation chosen, so that the fixed point of renormalization group has a k exp -5/3 energy spectrum. Fixed points for the anisotropic correlation are found near this isotropic fixed point. Two types of anisotropy are analyzed. when the additional stirring is in the plane perpendicular to the preferred direction, the renormalized viscosity is increased. When it is aligned with the preferred direction, the viscosity is decreased. A possible connection with the inverse energy cascade of two-dimensional turbulence is discussed.

Rubinstein, Robert↗