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High Speed Friction Stir Spot Welding on DP 980 Steel:Joint Properties and Tool WearSaunders, Nathan David 12 March 2012 (has links) (PDF)
With the desire to improve passenger safety and fuel efficiency, Ultra High Strength Steels (UHSS) have been developed for use in the automotive industry. UHSS are high strength steels with high ductility and strength. DP 980 is one of these UHSS being applied in automobile manufacturing. DP 980 is difficult to join with Resistance Spot Welding (RSW) because of the high carbon content and alloying in this material. The weld becomes brittle when it solidifies during the welding process. With the desire and motivation of widely using UHSS, new welding processes are needed to be developed in order to effectively join DP 980. Friction Stir Spot Welding (FSSW) is a developing welding process aimed to replace RSW in the automotive industry because of its ability to join materials at a lower temperature. Currently the welding loads of the tools are higher than 2000 pounds, ranging from 3,000 to 5,000 pounds, which exceeds the limit of the welding robots in the automotive factories. It is proposed that the welding loads can be reduced by increasing the spindle speed of the FSSW tool. Other focuses in the research include increasing the life of the tool and developing acceptable welding parameters for High Speed FSSW. The experimental work done for this thesis provided support that weld strength can be obtained at levels above the acceptable standard for DP 980 material (greater than 2400 pound lap shear fracture load for 1.2 mm material) while keeping the vertical load on the welding machine spindle below 2000 lbs.
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Microstructural Evaluation in Friction Stir Welded High Strength Low Alloy SteelsAbbasi Gharacheh, Majid 04 November 2011 (has links) (PDF)
Understanding microstructural evolution in Friction Stir Welding (FSW) of steels is essential in order to understand and optimize the process. Ferritic steels undergo an allotropic phase transformation. This makes microstructural evolution study very challenging. An approach based on Electron Backscattered Diffraction (EBSD) and phase transformation orientation relationships is introduced to reconstruct pre-transformed grain structure and texture. Reconstructed pre-transformed and post-transformed grain structures and textures were investigated in order to understand microstructural evolution. Texture results show that there is evidence of shear deformation as well as recrystallization in the reconstructed prior austenite. Room temperature ferrite exhibits well-defined shear deformation texture components. Shear deformation texture in the room temperature microstructure implies that FSW imposes deformation during and after the phase transformation. Prior austenite grain boundary analysis shows that variant selection is governed by interfacial energy. Variants that have near ideal BCC/FCC misorientation relative to their neighboring austenite and near zero misorientation relative to neighboring ferrite are selected. Selection of coinciding variants in transformed prior austenite Σ3 boundaries supports the interfacial-energy-controlled variant selection mechanism.
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The role of stirring time on the metallurgical and mechanical properties during modified friction stir clinching of AA6061-T6 and AA7075-T6 sheetsMemon, S., Paidar, M., Ojo, O.O., Cooke, Kavian O., Babaei, B., Masoumnezhad, M. 25 November 2020 (has links)
Yes / In this study, the modified friction stir clinching process was successfully utilized to weld the AA7075-T6 to AA6061-T6 aluminum alloys. The approach of this study was to appraise the influence of the stirring time (6, 12, and 18 s) on the metallurgical and mechanical behavior of the welded samples. The microstructural study demonstrated that stirring time significantly affected joint properties and material flow, which can be ascribed to the discrepancy in the properties of the Al alloys used in this study. Void, local melting and defect-free joints were produced under the stirring times of 6 s, 18 s, and 12 s respectively. It was found that tensile/shear strength increased significantly from 63.5 MPa to 109 MPa as the stirring time increased from 6 s to 12 s, while a further increase in the stirring time to 18 s significantly decreased the joint's strength to 76.1 MPa. The observed failed samples showed that stirring time did not influence fracture mode.
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Friction Stir Welding and Microstructure Simulation of HSLA-65 and Austenitic Stainless SteelFailla, David Michael, II 08 September 2009 (has links)
No description available.
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Friction Stir Processing of Nickel-base AlloysRodelas, Jeffrey M. 13 August 2012 (has links)
No description available.
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Frequency Response Modeling of Additive Friction Stir Deposition Parts with Print DefectsPennington, Brett Kenneth 03 June 2024 (has links)
A change in a part's response to vibrations can be measured and utilized as a non-destructive testing method to detect deviations in the part's materials or geometry through processes such as laser acoustic resonance spectroscopy. This work focuses on leveraging vibration resonance to detect flaws in prints produced through additive friction stir deposition that arise through environmental contamination. More specifically, the use case considered is the printing of AA7075 in an iron oxide rich environment, where iron oxide dust or powder could accidentally be stirred into the printed material creating a print flaw. The modeling of printed parts contaminated with iron oxide to predict their natural frequencies is examined. Two different finite element models are discussed, which were created to represent contamination flaws with and without voids. The first model considers the case where a part is void-free. In this case, the model assumes a solid, homogeneous material condition in the stir region. The second model considers the case where voids are present in the part. This model leverages x-ray computed tomography data to build a representative mesh. These models show that with a well-understood part and corresponding flaw, it is possible to predict the natural frequencies of a flawed part. By leveraging the part vibration measurements and model predictions of known defects, it may be possible to gain insights into and characterize unknown print flaws. / Master of Science / An important aspect of product or part creation is checking consistency between parts. Methods that can verify a part is good without damaging the part are valuable, especially when only a few parts are being made, or there is a high chance of something going wrong. One way of checking a part is to shake it and watch how it reacts and bends. If there is a difference in how a part reacts to the shaking from a known good part, then there is a problem. This work examines creating computer simulations to predict how a part should react to shaking when it is good and how it should react when it has flaws. This work considers flaws caused by debris from the environment during part creation. This work also considers whether such debris causes holes or voids to form in the parts and conducts predictions with the holes included.
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Tool Life Characterization in Refill Friction Stir Spot WeldingBelnap, Ruth Guadalupe 20 June 2024 (has links) (PDF)
As light-weighting becomes a priority for the automotive industry, refill friction stir spot welding emerges with enormous potential to supplement or replace conventional spot joining processes. This thesis addresses the limitations of current tooling options by examining materials beyond steel for use in RFSSW. Contained herein is an analysis of weld quality as a function of tool material, a production evaluation of RFSSW using various tool materials, and an assessment of long-term performance of a tungsten carbide tool. Over the course of this research, tungsten carbide emerged as a viable candidate for long-lasting RFSSW tooling.
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Ex-situ Inspection and Ultrasonic Metamaterial Lens Enabled Noncontact In-situ Monitoring of Solid-state Additive Manufacturing Process for Aluminum Alloy 6061Yang, Teng 05 1900 (has links)
Additive friction stir deposition (AFSD) is an innovative solid-state manufacturing process capable of producing parts with fine, equiaxed grains. However, due to the complexity of extensive plastic deformation and the viscoplastic behavior of metallic materials at elevated temperatures, the analysis of material flow and stress evolution during AFSD remains at a rudimentary stage. As a developing technology, gaining a deeper understanding of the underlying physical behaviors behind the processing is appreciable. This study comprises three objectives: investigating microstructure and stress-induced acoustic wave propagation behaviors, implementing non-contact in-situ monitoring in AFSD of aluminum alloy 6061 using a far-collimation acoustic metamaterial lens, and ex-situ analysis of parameter-dependent mechanics influences in AFSD of aluminum alloys 6061. To achieve this, a novel ultrasound in-situ monitoring method, along with ex-situ residual stress measurements, is facilitated by MD and FEA simulations and been experimentally verified. Real-time asymmetric property distribution and abnormal parameter-dependence acoustic wave phase change during the AFSD of aluminum alloy 6061 were identified through the in-situ monitoring and further investigated in detail through ex-situ inspection. A key parameter, effective viscosity, was introduced to the parameter windows selections, which can affect the thermo-fluidic mechanics during the process, thereby altering the physical aspects, mechanical properties, and microstructures.
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Stir bar sorptive extraction for the analysis of beverages and foodstuffsTredoux, A. G. J. 03 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / The main goal of this study was the development of new technologies based on modern
analytical techniques for analysis of volatiles in wines. Due to the exponential growth of
the wine industry and consumer demands for an enjoyable, safe-to-consume, and high
quality product, the need for arose for methodologies aiding the understanding of wine
better arose. Chemical analysis is a valuable way of studying the composition of wine in
depth. Very sophisticated instrumentation is available nowadays but almost always the
sample needs to be cleaned up or concentrated before such analysis. This study
investigates the use of stir bar sorptive extraction (SBSE) as such a technique. It is shown
that SBSE combined with gas chromatography-mass spectrometry (GC-MS) is extremely
suited for a wide number of analyses and during the course of the study the technique was
applied for troublesome analytical challenges in various beverages and foodstuffs. The
study focuses on the development of a screening technique for volatiles in wine using
SBSE and the application of the data to various chemometrical techniques for
classification purposes. A second part of the study shows the applicability of SBSE for
extraction of pesticides, contaminants and preservatives from wine, water, lemon
flavoured beverages and yoghurt. The method is also elaborated upon by development of
faster analysis methods for wine and beer and the investigation of using SBSE for
headspace sampling of wine. In all the applications, SBSE technology was shown to be
sensitive, repeatable, robust and very simple to use.
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Microstructure characterization of friction-stir processed nickel-aluminum bronze through orientation imaging microscopyCuevas, Assunta Mariela. 09 1900 (has links)
Approved for public release, distribution is unlimited / The effect of friction-stir processing (FSP) on the microstructure of a cast nickel-aluminum bronze (NAB) material has been characterized by various micro-analytical methods including orientation imaging microscopy (OIM). Cast NAB is widely utilized in the production of propellers for the surface ships and submarines of the U.S. Navy due to excellent corrosion-resistance. New applications require improved mechanical properties that may be attainable using FSP to achieve localized microstructure modification. Friction between a rotating tool and the surface of the material results in a *stirring* action that, in turn, produces adiabatic heating and local softening of the material. The tool rotation results in very large shear deformations in the softened regions and thus microstructure refinement and homogenization; in effect FSP may convert an as-cast microstructure to a wrought condition in the absence of macroscopic shape change. In as-cast material, results of optical and scanning electron microscopy (using energy dispersive analysis) show an ` (FCC) matrix containing globular and particulate dispersions that correspond to the *I, *II and *IV second phases; these represent various morphologies of the Fe3Al intermetallic compound, which has a D03 structure. Also present are lamellar particles of *III, which is NiAl and has a B2 structure. The grain size in the ` matrix is ~ 1 mm. In OIM, the microtexture and microstructure in the ` (FCC) matrix may be readily obtained and analyzed. However, interatom distances in the Fe3Al and NiAl phases differ by only about one percent and so these phases are not distinguishable from one another during OIM. Altogether, microstructure and microtexture analysis showed that there are several regions in the thermomechanically affected zone (TMAZ) of a material subjected to FSP. From base material inward toward the TMAZ, these include: annealing effects in undeformed base material; a region just inside the TMAZ in which grain deformation and C-type shear deformation textures are observed; regions of highly refined and recrystallized grains further inside the TMAZ, wherein the grain size is < 5æm; and, finally, regions of elongated, banded and twinned grain structures that suggest grain growth following recrystalliztion. / Lieutenant, United States Navy
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