| 191. |
- Powell, John, et al.
(författare)
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The sensitivity of hybrid laser welding to variations in workpiece position
- 2011
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 12:1, s. 188-193
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Tidskriftsartikel (refereegranskat)abstract
- High speed imaging has been used to analyze the sensitivity of the Hybrid laser welding process to variations in the laser-arcworkpiece geometry along the axis of the laser beam. The welding process was found to be stable within a certain range of workpiece positions. Outside of this range the process became unstable. If the workpiece was too close to the laser/arc combination, the two energy sources did not supplement each other sufficiently. If the workpiece was too far away the droplets from the arc interfered with the laser-keyhole interaction.
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| 192. |
- Powell, John, et al.
(författare)
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Weld root instabilities in fiber laser welding
- 2015
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 27:Suppl. 2
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Tidskriftsartikel (refereegranskat)abstract
- Fiber laser welding and fiber laser-arc hybrid welding have been developed into very useful industrial processes over the past few years. However, the use of fiber lasers can be associated with quality problems at the weld root such as intermittent penetration, melt ejection, and humping. This paper explains the mechanisms which create these instabilities and suggests a repair technique which would alleviate the problems in some cases. The main difference between fiber and CO2 laser welding is that during fiber laser welding there is a strong downward thrust on the melt in the keyhole.(This is not the case during CO2 laser welding.) The downward thrust on the melt is generated as a result of the fiber laser evaporating the top faces of bumps on the melt surface. The downward flow has two main effects;(a) the melt can achieve velocities which result in melt ejection from the root of the weld-which can result in intermittent penetration,(b) the supply of hot metal to the bottom of the weld makes the process much more thermally uniform at the top and bottom of the weld. This uniformity means that the melt is extended backward several millimeters on the top and bottom surfaces-which can result in melt humping in the weld root as well as on the top surface. This paper examines these weld root instabilities and also describes a technique of weld root remelting which has been shown to be effective in smoothing out the root of the weld to improve its tensile and fatigue properties
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| 193. |
- Ring-Groth, Margareta, et al.
(författare)
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Fatigue properties of weldbonded stainless steel joints
- 2000
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Ingår i: Journal of Advanced Materials. - 1070-9789. ; 32:1, s. 21-27
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Tidskriftsartikel (refereegranskat)abstract
- Weldbonding of stainless steel with an epoxy adhesive has been investigated with respect to fatigue life. Factors affecting joint strength have been identified and summarized. The weld-bonded joints were mechanically pre-treated, and weld-bonded as flanged single-overlap and cross-tension specimens. The results were compared with spot welded specimens of identical configuration. The weld-bonded specimens have better fatigue properties than spot welded specimens.
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| 194. |
- Ring-Groth, Margareta, et al.
(författare)
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Weldbonding of stainless steel : An introduction
- 1998
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Ingår i: Journal of Advanced Materials. - 1070-9789. ; 30:1, s. 36-39
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Tidskriftsartikel (refereegranskat)abstract
- Weldbonding is a method which combines the best mechanical features of resistance spot welding and adhesive bonding. For adhesive users, the technique simplifies the curing stage since no fixtures are needed for the period when the adhesive develops handling strength, and for spot weld users, the technique gives a joint a better mechanical properties and a sealed joint line. The bonds created are similar to normal spot welds but the joint is constrained by the adhesive at the interface. The adhesive is not present in the area surrounding the spot weld, since the heat generated between the stainless steel sheets burns the adhesive in that area
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| 195. |
- Roy, Sushmita, et al.
(författare)
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Identification of functional elements and regulatory circuits by Drosophila modENCODE.
- 2010
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 330:6012, s. 1787-1797
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Tidskriftsartikel (refereegranskat)abstract
- To gain insight into how genomic information is translated into cellular and developmental programs, the Drosophila model organism Encyclopedia of DNA Elements (modENCODE) project is comprehensively mapping transcripts, histone modifications, chromosomal proteins, transcription factors, replication proteins and intermediates, and nucleosome properties across a developmental time course and in multiple cell lines. We have generated more than 700 data sets and discovered protein-coding, noncoding, RNA regulatory, replication, and chromatin elements, more than tripling the annotated portion of the Drosophila genome. Correlated activity patterns of these elements reveal a functional regulatory network, which predicts putative new functions for genes, reveals stage- and tissue-specific regulators, and enables gene-expression prediction. Our results provide a foundation for directed experimental and computational studies in Drosophila and related species and also a model for systematic data integration toward comprehensive genomic and functional annotation.
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| 196. |
- Sarady, Istvan, et al.
(författare)
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The manufacture of high precision parts by Nd:YAG laser welding
- 1994
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Ingår i: Proceedings of the Laser Materials Processing Conference. - Orlando, Fla : Laser institute of America. - 0912035528 ; , s. 396-404
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Konferensbidrag (refereegranskat)abstract
- The mechanisms of laser welding are explained and three examples are described to illustrate the flexibility of Nd:YAG laser welding in production of small components. Explanations are given of the principles of condition-limited welding, deep penetration welding and braze welding. The production line examples given relate to: cutting, laser seam welding and laser spot welding of stainless steel housings of gyros for aeronautical navigation; laser spot welding a cobalt alloy torsion spring onto a stainless steel gyro housing; and braze welding of a tungsten alloy to an iron-cobalt alloy, involving melting the latter to make the joint. Workpieces, procedures and results obtained are detailed
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| 197. |
- Sundqvist, Jesper
(författare)
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Aspects of Heat Flow in Laser Processing of Metals
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the laser was invented in 1960, its use in manufacturing industry has been growing rapidly. Laser processing of metals is based on the flow of heat that is generated by the absorbed laser beam. One outstanding aspect of laser beams is high precision along with high controllability of energy transfer, which includes creative techniques of shaping the beam and in turn the process. The thesis presents six Papers A-F on different metal processing techniques, namely welding, hardening and cutting, the latter combined with additive manufacturing. For each respective technique it was studied how desired properties can be optimized by controlled use of the laser beam and in turn of the temperature field. Addressing their different complexity of the heat transfer, various theoretical and experimental analysis methods were applied.Laser beam welding is usually conducted with standard beam shapes, i.e. Gaussian or top-hat like, which is not always optimal for the process. Identification of an optimised weld pool shape or temperature cycle could increase the quality of welded products or even enable new applications. Papers A and B aim to increase the knowledge for non-standard beam shapes, particularly for single-pulse conduction mode welding. Paper A presents an investigation on an industrial application where a C-shaped weld joint is desired. The sensitivity to and optimization of different C-shaped beam irradiation profiles is discussed. The analysis is mainly carried out by applying Finite Element Analysis, FEA, to calculate the heat conduction contributions, showing unexpected sensitivity in certain regimes. Paper B presents a semi-analytical model for fast calculation of the temperature field from different beam profiles. Examples include multi-spots or the misalignment sensitivity of Diffractive Optical Elements.In Paper C, for laser hardening of 11% Cr ferritic stainless steel the temperature field was studied to enable hardening. It was shown that single-track hardening without sensitisation could be achieved but overlapping tracks had a continuous network of ditched grain boundaries and is thereby at risk for sensitisation. The sensitised area is caused by a reheating cycle.The same mechanism for the same material was studied in Paper D when applying a recently developed drop deposition technique, where additive manufacturing is fed by laser cutting. The same reheating isotherm becomes critical, but here sensitisation tests show a discontinuous network of ditched grain boundaries in the added material. The solid heat-affected zone on the other hand has a continuous network of ditched grain boundaries, which implies a sensitisation risk. The continuous network is however not in contact with the surface. The tested parameters is thus not at risk for intergranular corrosion through sensitisation.For friction stir welding of dissimilar metals, Ti-6Al-4V with AISI 304L stainless steel, Paper E, the influence of a laser-induced preheating temperature field on the tool forces was investigated through numerical simulation. By suitable application of laser preheating, the forces acting on the tool can be substantially lowered, in a robust manner.The temperature field from seam welding induces a residual stress field. In Paper F, for continuous wave laser keyhole welding of high strength steel butt joints, a method is presented to identify the residual stress behaviour of laser welded sheets by measurement of the fatigue crack growth rate during testing, by deriving the crack acceleration. The analysis was confirmed by hole drilling tests and by FEA.The knowledge and methods of the above different experimental and theoretical studies complement each other. They contribute to further optimize certain aspects through laser-induced temperature fields, for different manufacturing techniques.
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| 198. |
- van de Giessen, Elsmarieke, et al.
(författare)
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Association study on glutathione S-transferase omega 1 and 2 and familial ALS
- 2008
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Ingår i: Amyotrophic Lateral Sclerosis and other Motor Neuron Disorders. - : Informa UK Limited. - 1466-0822 .- 1743-4483. ; 9:2, s. 81-84
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Tidskriftsartikel (refereegranskat)abstract
- Glutathione S-transferase omega 1 and 2 (GSTO1 and 2) protect from oxidative stress, a possible pathogenic mechanism underlying the pathogenesis of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. Significant association of age of onset in Alzheimer's patients with GSTO1 and 2 had recently been identified, suggesting a possibly similar association with ALS. In this study 12 Hapmap tagged SNPs in GSTO1 and 2 were genotyped in 251 Caucasian British, Australian and Swedish familial ALS (FALS) cases. No association was found for age of onset and survival of FALS in the British and Australian patients. In the Swedish patients, association for age of onset was found with several SNPs (p = 0.003-0.048). These results suggest a possible effect of the GSTO1 and 2 locus on age of onset of FALS.
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| 199. |
- Wills, John W., et al.
(författare)
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Image-Based Cell Profiling Enables Quantitative Tissue Microscopy in Gastroenterology
- 2020
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Ingår i: Cytometry Part A. - : WILEY. - 1552-4922 .- 1552-4930. ; 97:12, s. 1222-1237
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Tidskriftsartikel (refereegranskat)abstract
- Immunofluorescence microscopy is an essential tool for tissue-based research, yet data reporting is almost always qualitative. Quantification of images, at the per-cell level, enables "flow cytometry-type" analyses with intact locational data but achieving this is complex. Gastrointestinal tissue, for example, is highly diverse: from mixed-cell epithelial layers through to discrete lymphoid patches. Moreover, different species (e.g., rat, mouse, and humans) and tissue preparations (paraffin/frozen) are all commonly studied. Here, using field-relevant examples, we develop open, user-friendly methodology that can encompass these variables to provide quantitative tissue microscopy for the field. Antibody-independent cell labeling approaches, compatible across preparation types and species, were optimized. Per-cell data were extracted from routine confocal micrographs, with semantic machine learning employed to tackle densely packed lymphoid tissues. Data analysis was achieved by flow cytometry-type analyses alongside visualization and statistical definition of cell locations, interactions and established microenvironments. First, quantification of Escherichia coli passage into human small bowel tissue, following Ussing chamber incubations exemplified objective quantification of rare events in the context of lumen-tissue crosstalk. Second, in rat jejenum, precise histological context revealed distinct populations of intraepithelial lymphocytes between and directly below enterocytes enabling quantification in context of total epithelial cell numbers. Finally, mouse mononuclear phagocyte-T cell interactions, cell expression and significant spatial cell congregations were mapped to shed light on cell-cell communication in lymphoid Peyers patch. Accessible, quantitative tissue microscopy provides a new window-of-insight to diverse questions in gastroenterology. It can also help combat some of the data reproducibility crisis associated with antibody technologies and over-reliance on qualitative microscopy. (c) 2020 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.
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| 200. |
- Wouters, Marc, et al.
(författare)
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The influence of joint gap on the strength of hybrid Nd:yttrium-aluminum-garnet laser-metal inert gas welds
- 2006
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 18:3, s. 181-184
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Tidskriftsartikel (refereegranskat)abstract
- This article presents the results of an experimental and theoretical analysis of the effect of joint gap on the strength of hybrid laser-metal inert gas welds. The welds were of the partial penetration butt type with various joint gaps but identical weld penetration. Impact testing established that a zero gap gave a weak weld because the weld geometry contained the equivalent of a sharp crack where the unwelded parts met each other. A small gap between the workpieces improved the weld impact strength as the sharp crack effect became dissipated. Further increases in gap width resulted in a weakening of the joint and this is the subject of a discussion on joint gap optimization
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