Concentric Scanning Strategies for Laser Powder Bed Fusion: Porosity Distribution in Practical Geometries

Besides the optimisation of process parameters such as laser power or scan speed, the choice of the scan path represents a possibility to optimise the laser powder bed fusion process even further. The usual hatching strategy creates a homogeneous microstructure but makes it necessary to switch the laser off and on after each scan vector, which can slow down the fabrication. Moreover, the end of each scan vector is a location susceptible to the creation of keyhole pores. In this work, these disadvantages were meant to be avoided by using scan strategies that consist of longer paths and thus less end of track points. To this end, an open-source tool to tailor the LPBF G-code to geometric part features and advanced path configurations was developed and embedded into a co-visualization platform. With this tool, specimens built with four different types of paths were fabricated and the effect of these alternative scan strategies on pore distributions and path neighbourhood was investigated using micro-computed tomography. In the examined example geometry, a spiral scan pattern reduced the distance the laser had to jump between scanning by 78%. However, with the alternative path patterns, the defect architecture was strongly dependant on the part geometry and increased the overall porosity to 0.42%. Respective alleviation approaches are therefore necessary and are discussed in the remainder of this work

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The effect of surface patterning and unidirectional roughness on corrosion of metals

In this study two different surface modification methods, namely surface patterning and unidirectional roughness, were applied to nickel and mild steel specimens to investigate the effect of surface roughness on the corrosion resistance. The goal is to decrease the contact area between the corrosive electrolyte and the substrate by creating different surface morphologies using different methods including surface patterns by laser ablation and unidirectional surface roughness through using SiC papers with different grits (G60- to G1200) on nickel and mild steel with different passivation behaviours. Electrochemical impedance spectroscopy measurements (EIS), potentiodynamic polarization and different surface characterization methods were performed to investigate the protection performance of the metals. In the first phase, patterns of holes with specific diameters (D) and inter-hole spacings (L) were created by laser ablation on nickel and corrosion tests were carried out in a 0.5 M H 2 SO 4 solution. The corrosion potential, E Corr , and current density (I Corr ) were determined and compared for different ratios of (D/L). Energy dispersive spectroscopy (EDS) was performed on the surface of the samples to investigate the chemical composition, specifically the oxygen content of different regions of the patterned area before and after corrosion testing. By creating such patterns we are able to produce a surface with heterogeneous wetting properties, to decrease the contact area between the liquid and the substrate. It has been shown that for a few specific patterns the corrosion resistance can be increased by orders of magnitude. In the next phase, the effect of unidirectional surface roughness on the corrosion of nickel and mild steel was investigated using EIS and potentiodynamic polarization techniques. Scanning electron micrographs were also taken and roughnesses were measured before and after corrosion testing with a profilometer. EDS also measured oxygen concentration. By decreasing the roughness, the corrosion resistance of nickel and mild steel increased and decreased respectively. The patterned sample showed the best corrosion resistance as a result of the heterogeneous wetting phenomenon that happened on the surface. Surface patterning also can achieve a much larger improvement in corrosion resistance compared to unidirectional roughness

Genetic improvement of tomato by targeted control of fruit softening

Controlling the rate of softening to extend shelf life was a key target for researchers engineering genetically modified (GM) tomatoes in the 1990s, but only modest improvements were achieved. Hybrids grown nowadays contain 'non-ripening mutations' that slow ripening and improve shelf life, but adversely affect flavor and color. We report substantial, targeted control of tomato softening, without affecting other aspects of ripening, by silencing a gene encoding a pectate lyase

Compressive behavior of masonry columns confined with steel reinforced grout (SRG) composite

In this study, a new type of composite comprised of steel fiber cords embedded in a natural hydraulic lime mortar matrix, known as steel reinforced grout (SRG), is explored for the use in confinement of masonry columns. An experimental study was carried out to understand the behavior of solid clay brick masonry columns confined by SRG jackets. Twenty-four confined and seven unconfined columns with a square cross-section were tested to failure under a monotonic concentric compressive load. Test parameters considered were the column corner condition, number of fiber jacket layers, and number of fiber overlapping faces. SRG confinement improved the compressive strength, ultimate axial strain, and energy absorption of the masonry columns relative to the unconfined condition. Results showed that increasing the number of fiber layers increased the confined compressive strength, however the increase in confined strength was not proportional to the number of fiber layers. Rounding the column corners slightly increased the confined compressive strength. Increasing the number of fiber overlapping faces also increased the confined compressive strength. Models from the literature for FRP-confined masonry were examined for their applicability to predict the strength increase from SRG jackets. Considering the specimens included in this thesis work and supplemented with others collected from the literature, it was found that the model for the Italian CNR-DT 200 provided the closest predictions of the increase in compressive strength provided by the SRG jacket (within 33% of the experimental values). More work is needed to improve the predictions of the increase in compressive strength provided by SRG jackets and to predict the ultimate strain in the jacket --Abstract, page iii

Winning and losing in the creative industries: an analysis of creative graduates' career opportunities across creative disciplines

Following earlier work looking at overall career difficulties and low economic rewards faced by graduates in creative disciplines, the paper takes a closer look into the different career patterns and economic performance of “Bohemian” graduates across different creative disciplines. While it is widely acknowledged in the literature that careers in the creative field tend to be unstructured, often relying on part-time work and low wages, our knowledge of how these characteristics differ across the creative industries and occupational sectors is very limited. The paper explores the different trajectory and career patterns experienced by graduates in different creative disciplinary fields and their ability to enter creative occupations. Data from the Higher Education Statistical Agency (HESA) are presented, articulating a complex picture of the reality of finding a creative occupation for creative graduates. While students of some disciplines struggle to find full-time work in the creative economy, for others full-time occupation is the norm. Geography plays a crucial role also in offering graduates opportunities in creative occupations and higher salaries. The findings are contextualised in the New Labour cultural policy framework and conclusions are drawn on whether the creative industries policy construct has hidden a very problematic reality of winners and losers in the creative economy