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Environmental magnetism: measuring, monitoring and modelling urban street dust pollution

Sun, 01 Jan 2006 00:00:00 GMT

Title: Environmental magnetism: measuring, monitoring and modelling urban street dust pollution Authors: Shilton, Vaughan F.; Fullen, Michael A.; Booth, Colin A.; Walden, John; Worsley, Annie T.; Power, A.L. Abstract: Urban street dusts have been monitored monthly for one year (May 2000 to April 2001), their magnetic properties measured and their multivariate relationships modelled by Simultaneous R- and Q-mode Factor Analysis, so as to differentiate dusts from three urban roads (two in Wolverhampton and one in Dudley) in the West Midlands (U.K.). Results show the street dusts contain a large range of magnetic concentrations, magnetic mineralogy and magnetic domain sizes, which has enabled significant differences (p < 0.001) to be identified between individual roads. Whilst soil is proposed as a notable provenance for the dust, magnetic values in this study are much higher than those previously reported for topsoils and thus, indicate the influence of other sources, such as anthropogenic pollutants. This indicates the potential of magnetic methodologies as a valuable means of contributing to local and national road pollution monitoring schemes. Furthermore, Factor Analysis aided the interpretation of dust variations and simplified the inter-relationships between magnetic parameters, which highlights its potential for classifying and discriminating urban street dust sources.

Finite Element Modelling of Multipass Fusion Welding with Application to Complex Geometries

Mon, 01 Jan 2007 00:00:00 GMT

Title: Finite Element Modelling of Multipass Fusion Welding with Application to Complex Geometries Authors: Jiang, Wei; Yahiaoui, Kadda Abstract: The current paper presents recently completed work in the development of advanced multi-pass weld modelling procedures, with the ultimate objective of predicting weld residual stress distributions in thick-walled complex geometries. The modelling technique was first developed using simple three-dimensional geometries, for which experimental data was available for validation purposes. All the non-linearities associated with welding, including geometry, material, and boundary non-linearities, as well as heat source movement were taken into account. The element removal/reactivate technique was employed to simulate the deposition of filler material. Combined with a newly developed meshing technique, the model was then applied to predict residual stress distributions for a relatively thick stainless steel piping branch junction. Finally, a parametric study was conducted to assess the effects of various manufacture-related welding parameters on the final residual stress fields. The interpass temperature and cooling rate were found to be the two most sensitive parameters affecting resultant residual stresses. The residual stress profiles can be optimized relatively easily by adjusting these parameters. This research demonstrated that the developed modelling technique has potential in multi-pass welding process optimization and wide industrial applications including weld repairs.(Professional Engineering Publishing) Description: The Journal’s editorial board deemed it timely to dedicate an issue to address recent developments in the field and to highlight challenges to industry to exploit state-of-the-art modelling techniques. This paper was included in the special issue and describes the application of commercial finite element software to model the multipass fusion welding process.

Finite Element Simulation of Multipass Welding: Full Three-Dimensional Versus Generalized Plane Strain or Axisymmetric Models

Sat, 01 Jan 2005 00:00:00 GMT

Title: Finite Element Simulation of Multipass Welding: Full Three-Dimensional Versus Generalized Plane Strain or Axisymmetric Models Authors: Jiang, Wei; Yahiaoui, Kadda; Laoui, Tahar Abstract: A full three-dimensional (3D) thermo-mechanical finite element (FE) model has been developed to simulate the step-by-step multipass welding process. Non-linearities associated with welding, such as a moving heat source, material deposition, temperature-dependent material properties, latent heat, and large deformations, were taken into account. The model was applied to multipass butt-welded mild steel plate and girth butt-welded stainless steel pipe for validation. The simulation results were compared with independently obtained experimental data and numerical predictions from two-dimensional (2D) generalized plane strain and axisymmetric models. Good agreements between the 3D predictions and experimental data have been obtained. The computational model has the potential to be applied to multipass welded complex geometries for residual stress prediction. (Professional Engineering Publishing) Description: A three-dimensional thermo-mechanical finite element model has been developed and applied to multipass butt-welded mild steel plate and girth butt-welded stainless steel pipe. The simulation results were validated with independently obtained experimental data. The computational model has the potential to be applied to multipass welded complex geometries for residual stress prediction.

Finite Element Prediction of Residual Stress Distributions in a Multipass Welded Piping Branch Junction

Mon, 01 Jan 2007 00:00:00 GMT

Title: Finite Element Prediction of Residual Stress Distributions in a Multipass Welded Piping Branch Junction Authors: Jiang, Wei; Yahiaoui, Kadda Abstract: Piping branch junctions and nozzle attachments to main pressure vessels are common engineering components used in the power, oil and gas, and shipbuilding industries amongst others. These components are usually fabricated by multipass welding. The latter process is known to induce residual stresses at the fabrication stage, which can have severe adverse effects on the in-service behavior of such critical components. It is thus desirable if the distributions of residual stresses can be predicted well in advance of welding execution. This paper presents a comprehensive study of three dimensional residual stress distributions in a stainless steel tee branch junction during a multipass welding process. A full three dimensional thermomechanical finite element model has been developed for this purpose. A newly developed meshing technique has been used to model the complex intersection areas of the welded junction with all hexahedral elements. Element removal/reactivate technique has been employed to simulate the deposition of filler material. Material, geometry, and boundary nonlinearities associated with welding were all taken into account. The analysis results are presented in the form of stress distributions circumferentially along the weld line on both run and branch pipes as well as at the run and branch cross sections. In general, this computational model is capable of predicting three dimensional through-thickness welding residual stress, which can be valuable for structural integrity assessments of complex welded geometries. (ASME) Description: The research presented extends that on stress and temperature distributions in welded oil/gas steel pipe junctions, research that has resulted in Yahiaoui being invited to present to: Ecole de Technologie Supérieure, University of Québec, Montreal, August 2006, and The Structural Technology and Materials Group of the Institute of Mechanical Engineers October 2006.