Improved productivity in fusion welding : executive summary

This document is an Executive Summary of individual submissions of work that the author has submitted towards the degree of Engineering Doctorate. The work comprises three main themes, which can be demonstrated in a broader sense as contributing towards improved productivity in fusion welding: i) The use of active fluxes for Tungsten Inert Gas (TIG) welding. ii) An investigation into the reduction of porosity when Metal Active Gas (MAG) welding galvanneal coated steel sheet used in the automotive industry. iii) The use of high power Nd:YAG laser welding for the production of large diameter, long distance land pipelines. Active fluxes give improved productivity by increasing the penetration depth of the TIG welding process by the simple addition of a flux applied to the surface. Although the productivity benefits of the process had been proven through a joint TWIIindustry project, the mechanism by which the fluxes produced this improvement was not fully understood. The first theme investigated the mechanisms at work in providing increased penetration and concluded that the primary mechanism responsible for the action of the fluxes was not due to a change in the flow of the molten pool but, as others had suggested, due to arc constriction. This work contributed to a greater understanding of the welding process and, furthermore, a greater understanding of the potential opportunities and limitations of the process when designing new fluxes for other alloy systems. MAG welds in coated steel sheet used in the automotive industry are prone to porosity leading to high reject rates. The second phase of work reported here determined welding procedures capable of delivering low porosity welds developed through statistical experimental design. These procedures demonstrated how low porosity welds could be made using conventional MAG welding techniques on steels that had been galvanneal coated to provide corrosion resistance. The procedures developed could be easily implemented at high production rates in an industrial manufacturing environment to reduce defect levels, and thus costly repairs or high scrap rates. The third theme of the work demonstrated how Nd:YAG laser welding could potentially be used to replace conventional arc welding techniques for land lay of gas transmission pipelines. The application of a single laser fill pass, made at high production rates, could replace the use of multiple MAG welding stations greatly reducing the costs associated with pipeline fabrication. BP has claimed that half pipeline cost savings of up to $300 million dollars are achievable through the implementation of such a technique. The justification for the use of lasers in pipelines is discussed in terms of both technical and economic suitability. Preliminary experimental work showed that high power Nd:YAG laser welds could achieve productivity targets, although in order to reduce defects and achieve the necessary structural performance it would be necessary to combine laser welding with a MAG welding process

Pericardial Adhesions in the Cobia Rachycentron canadum (Linnaeus)

Pericardial adhesions are reported in diseased hearts of the cobia Rachycentron canadum (Linnaeus). The epicardium and pericardium are either tightly fused or connected by numerous thick collagenous adhesions over most of the heart surface

Pericardial Adhesions in the Cobia Rachycentron canadum (Linnaeus)

Pericardial adhesions are reported in diseased hearts of the cobia Rachycentron canadum (Linnaeus). The epicardium and pericardium are either tightly fused or connected by numerous thick collagenous adhesions over most of the heart surface

Active and driven hydrodynamic crystals

Motivated by the experimental ability to produce monodisperse particles in microfluidic devices, we study theoretically the hydrodynamic stability of driven and active crystals. We first recall the theoretical tools allowing to quantify the dynamics of elongated particles in a confined fluid. In this regime hydrodynamic interactions between particles arise from a superposition of potential dipolar singularities. We exploit this feature to derive the equations of motion for the particle positions and orientations. After showing that all five planar Bravais lattices are stationary solutions of the equations of motion, we consider separately the case where the particles are passively driven by an external force, and the situation where they are self-propelling. We first demonstrate that phonon modes propagate in driven crystals, which are always marginally stable. The spatial structure of the eigenmodes depend solely on the symmetries of the lattices, and on the orientation of the driving force. For active crystals, the stability of the particle positions and orientations depends not only on the symmetry of the crystals but also on the perturbation wavelengths and on the crystal density. Unlike unconfined fluids, the stability of active crystals is independent of the nature of the propulsion mechanism at the single particle level. The square and rectangular lattices are found to be linearly unstable at short wavelengths provided the volume fraction of the crystals is high enough. Differently, hexagonal, oblique, and face-centered crystals are always unstable. Our work provides a theoretical basis for future experimental work on flowing microfluidic crystals.Comment: 10 pages, 10 figure

Insights into the influence of solvent polarity on the crystallization of poly(ethylene oxide) spin-coated thin films via in situ grazing incidence wide-angle X-ray scattering

Controlling polymer thin-film morphology and crystallinity is crucial for a wide range of applications, particularly in thin-film organic electronic devices. In this work, the crystallization behavior of a model polymer, poly(ethylene oxide) (PEO), during spin-coating is studied. PEO films were spun-cast from solvents possessing different polarities (chloroform, THF, and methanol) and probed via in situ grazing incidence wide-angle X-ray scattering. The crystallization behavior was found to follow the solvent polarity order (where chloroform chloroform > methanol). When spun-cast from nonpolar chloroform, crystallization largely followed Avrami kinetics, resulting in the formation of morphologies comprising large spherulites. PEO solutions cast from more polar solvents (THF and methanol) do not form well-defined highly crystalline morphologies and are largely amorphous with the presence of small crystalline regions. The difference in morphological development of PEO spun-cast from polar solvents is attributed to clustering phenomena that inhibit polymer crystallization. This work highlights the importance of considering individual components of polymer solubility, rather than simple total solubility, when designing processing routes for the generation of morphologies with optimum crystallinities or morphologies

Periodic and Quasiperiodic Motion of an Elongated Microswimmer in Poiseuille Flow

We study the dynamics of a prolate spheroidal microswimmer in Poiseuille flow for different flow geometries. When moving between two parallel plates or in a cylindrical microchannel, the swimmer performs either periodic swinging or periodic tumbling motion. Although the trajectories of spherical and elongated swimmers are qualitatively similar, the swinging and tumbling frequency strongly depends on the aspect ratio of the swimmer. In channels with reduced symmetry the swimmers perform quasiperiodic motion which we demonstrate explicitely for swimming in a channel with elliptical cross section

Deconstructing the outsider puzzle: The legitimation journey of novelty

The proposition that outsiders often are crucial carriers of novelty into an established institutional field has received wide empirical support. But an equally compelling proposition points to the following puzzle: the very same conditions that enhance outsiders' ability to make novel contributions also hinder their ability to carry them out. We seek to address this puzzle by examining the contextual circumstances that affect the legitimation of novelty originating from a noncertified outsider that challenged the status quo in an established institutional field. Our research case material is John Harrison's introduction of a new mechanical method for measuring longitude at sea-the marine chronometer- which challenged the dominant astronomical approach.We find that whether an outsider's new offer gains or is denied legitimacy is influenced by (1) the outsider's agency to further a new offer, (2) the existence of multiple audiences with different dispositions toward this offer, and (3) the occurrence of an exogenous jolt that helps create a more receptive social space. We organize these insights into a multilevel conceptual framework that builds on previouswork but attributes a more decisive role to the interplay between endogenous and exogenous variables in shaping a field's shifting receptiveness to novelty. The framework exposes the interdependencies between the micro-, meso-, and macro-level processes that jointly affect an outsider's efforts to introduce novelty into an existing field

Older Workers and Care-Giving in England: the Policy Context for Older Workers’ Employment Patterns

This article considers recent changes in the incidence of caring among people aged 50-64 in England and the policy context in which these have occurred. After introducing the topic, research questions addressed and methods used, it outlines findings from other research on how older workers experience and manage caring roles. It then sets out relevant public policy developments since carers were first accorded rights to recognition and services in 1995, focusing on workplace support, local services and financial help for people who reduce or quit their paid work to care. The article presents new analyses of the population censuses conducted in England in 2001 and 2011, focusing on people aged 50-64 and especially on those aged 60-64, the group in which the largest changes were seen. Theses show growth in caring at higher levels of intensity for older workers, and increases in the incidence of caring alongside paid work. To deepen understanding of these changes, the analysis also draws on data from a government survey of carers conducted in 2009-10. The concluding discussion argues that although the modest policy changes implemented since 1995 have provided some support to older workers managing work and care, more policy attention needs to be given following the sharp increase in the incidence of caring seen among people aged 50-64 in England between 2001 and 2011

Boundaries can steer active Janus spheres

The advent of autonomous self-propulsion has instigated research towards making colloidal machines that can deliver mechanical work in the form of transport, and other functions such as sensing and cleaning. While much progress has been made in the last 10 years on various mechanisms to generate self-propulsion, the ability to steer self-propelled colloidal devices has so far been much more limited. A critical barrier in increasing the impact of such motors is in directing their motion against the Brownian rotation, which randomizes particle orientations. In this context, here we report directed motion of a specific class of catalytic motors when moving in close proximity to solid surfaces. This is achieved through active quenching of their Brownian rotation by constraining it in a rotational well, caused not by equilibrium, but by hydrodynamic effects. We demonstrate how combining these geometric constraints can be utilized to steer these active colloids along arbitrary trajectories