European Optical Society

Abstract Applications for additively manufactured (AM) metal parts, particularly via laser-based powder bed fusion (PBF-LB/M), have been growing significantly in industries with high level of requirements such as aerospace, nuclear plant, automotive, energy, and medical industry. However, PBF-LB/M parts often require welding to other components due to their limited size. Thus, the weldability of PBF-LB/M parts is of interest, particularly due to the microstructural differences between PBF-LB/M and conventionally manufactured parts. This study investigates the microstructure and mechanical properties of laser-welded PBF-LB/IN718 and compares the results with laser-welded sheet metal IN718. In addition, the effect of heat treatment before welding on the weldability of PBF-LB/IN718 samples was evaluated. Both the heat-treated and as-built PBF-LB/IN718 welds had lower microhardness at the fusion zone (FZ) than the base metals, whereas the sheet metal IN718 weld showed higher microhardness at FZ than the base metal. This was attributed to the distinct secondary phases and microstructure of the conventional IN718 and PBF-LB/IN718 samples. Nevertheless, the ultimate tensile strength and yield strength of PBF-LB/IN718 welds were higher than the conventional IN718 welds, proving that laser welding is a viable method of joining PBF-LB/IN718 parts. Finally, the fatigue strength of the PBF-LB/IN718 welds, assessed at 10 6 cycles, was inferior to that of the conventional IN718 welds, owning to the defects such as lack of fusion in the base metal of PBF-LB/IN718 samples.

ABSTRACT This pilot study develops a process to evaluate in-situ defect detection and self-healing in Ti-6Al-4V fabricated using laser-based powder bed fusion. A tailor-made test specimen was designed and manufactured for the nanofocus tube X-ray computed tomography (XCT) system. In situ optical tomography was used to capture infrared images containing heat signatures of the hot laser interaction zone. Depicting natural process variation, defective regions were seeded using process manipulation (up to ±30%) in proximity of the experimental standard volumetric energy density (VED). The concomitant defects and heat signatures were both spatially and temporally captured. The results indicate that porosity significantly grows from an average value of 27 parts per million (PPM) to a value of 337 PPM comprising defect sizes of <112 µm when the VED increases by 30%. The outcome confirmed that Ti–6Al–4V can self-heal these defective regions by up to 7 ± 1 layers using the standard VED. A convolutional neural network was trained (n = 211) and was verified with XCT. The model demonstrated prediction accuracy of 94% for the six classes of unfamiliar defective regions. This work enables in-situ detection and healing of defective regions caused by process uncertainty that can shift the quality frontier of novel product design and development.

Introdução: Este artigo traz uma reflexão sobre a Educação de Jovens e Adultos numa perspectiva de pensar sobre as dificuldades encontradas nessa modalidade de ensino e as possibilidades de trazer interesse e motivação desse público especial, que não completou suas aprendizagens na idade própria e retorna às salas de aula por motivos diversos. Para realização da pesquisa, lançou-se mão de uma revisão de literatura, que contou com o aporte teórico de autores como Freire (1979; 1996; 2005), Gadotti (1996, 2008) e Marchesi (2004), dentre outros, que foram de fundamental importância para este estudo. Além disso, foram visitadas as legislações brasileiras que tratam da EJA. Com isso, observou-se que a modalidade educacional direcionada à jovens e adultos carrega uma história própria, cheia de lacunas, avanços e retrocessos. Os discentes, por sua vez, trazem consigo histórias de exclusão e baixa autoestima, o que dificulta muitas vezes a crença de que aprender pode ser bom. Isso é mais uma dificuldade encontrada pelos professores que trabalham com a EJA. Nesse sentido, esses profissionais, geralmente despreparados, recebem a missão de buscar caminhos motivadores para que a consecução de aprendizagens seja uma experiência significativa para os aprendentes.

Italy can boast a very diversified and lively panorama of educational, research and industrial activities pivoted about Optics and Photonics. Significant advancements in laser technology, optical communication, and optical materials are driving innovation in healthcare, manufacturing, agrifood and generally in promoting digital transition. The National Recovery and Resilience Plan is expected to greatly enhance the country competitiveness on a global scale.

Powder bed fusion using a laser beam (PBF-LB/M) is considered one of the most versatile additive manufacturing methods as the parts printed have high resolution thanks to the low layer thickness used. The powder packing density (PD) of the powder layer has a significant impact on the density, surface roughness and other mechanical properties of the built parts. Due to the difficulty of characterizing the powder bed in situ, simulation has often been used to study the powder behavior on the powder bed. However, in order for the simulation to have practical value, there must be some way of confirming the results via experimental methods, also called validation. The aim of this study was to develop a powder packing density-based validation method for a powder bed simulation. The developed method featured a simplistic “open cup” style sample which traps powder inside for PD measurement. The samples were built with an EOS M 290 PBF-LB/M system using Alloy 718 (also known as “IN718” or “Inconel”) powder. Average PD over the five built samples was 52.4 %, with a standard deviation of 0.2 %. The method was used to successfully validate a powder bed simulation with four recoated powder layers, modelled using FLOW-3D DEM simulation software from Flow Science Inc. Similar methods for PD characterization were found in literature, but in many cases the method does not fully correspond to the conditions of a simulated powder bed, the scale is very small, or the reliability of the PD measurement is not confirmed. The method presented in this study corresponds to typical powder bed simulation conditions, while retaining high reliability and repeatability of results.

Additively manufactured Aluminum-Copper alloys are attracting interest because of their high tensile strength. Nevertheless, the presence of Cu strongly affects the corrosion performances. In this work, the corrosion behavior of an innovative laser powder bed fusion-processed 2139 alloy was investigated, and its corrosion performances were compared to the well-consolidated AlSi10Mg alloy, as well as the parent wrought alloy. Electrochemical, Kelvin probe microscopy and intergranular corrosion tests were performed. The unique corrosion morphology at melt pool boundaries are presented and discussed alongside with the effect of surface finishing and heat treatments.

Este estudo é parte da minha dissertação e nasce de implicações pessoais e acadêmicas, tendo como base os trajetos e as performatividades de jovens gays nos contextos escolares. Objetivo geral analisar a percepção de si de jovens gays nas performatividades presentes nos trajetos escolares de resistências que problematizam os valores pré-estabelecidos e rompem com a invisibilidade na escola. O estudo tem como método a Sociopoética. A oficina de negociação e da produção dos dados me possibilitou um encontro com meus pares, o grupo-pesquisador. O corpo gay é atravessado por cicatrizes, práticas e pedagogias da exclusão, seja na escola, seja fora dela, esse corpo está mais suscetível à violência. O pensamento coletivo do grupo tem a seguinte dimensão - Corpos de jovens gays: invisibilidades e resistências na escola apresentam “problemas do corpo giz do jovem gay” na relação consigo mesmo, com a família e com outros; performatividades que problematizam os valores pré-estabelecidos; percepções de si.

Este texto investiga o circuito cultural e geográfico do movimento Poetry Slam em Portugal. Esta competição de poesia falada implica encontros espaciais, gerando dinâmicas geográficas discutidas neste artigo. Os procedimentos metodológicos foram trabalhos de campo, observações participantes, entrevistas com mulheres poetas e elaboração de mapas. Apresento assim uma caracterização do Poetry Slam, a geografia desse movimento poético e o contexto contemporâneo português por meio de sua espacialização e interpretação. O argumento central é de que há um circuito cultural, poético e geográfico de escala internacional que envolve distintos corpos poéticos (nacionais e imigrantes).

A pandemia da COVID-19 provocou mudanças no estilo de vida das pessoas no último biênio, o confinamento levou ao uso excessivo de telas como celulares e notebooks. A interação humana sofreu enorme alteração promovida por meios eletrônicos e os écrans. Alterações no estilo de vida historicamente são acompanhadas de fatores maléficos imensuráveis. A exposição prolongada a luzes violetas ou azuis pode prejudicar os olhos, bem como a pele e a retina. O sol é o produtor de energia mais importante, é também a principal fonte de energia que emite radiação, entretanto diversos eletrônicos também emitem ondas radioativas. Através de revisão bibliográfica, esta pesquisa buscou demonstrar a aplicação de filtros aplicados em lentes para a diminuição da astenopia e alterações no ciclo circadiano.