1,720,959 research outputs found
Numerical investigation of polymeric hollow extrudate for optimized 3D printing of complex structures
No full textMechanical behaviors at 77K of Zr-modified Al 7075 alloy printed by L-PBF
No full textDecreasing the mass of structure is the main goal of aerospace industries. One solution to do so is to remove all unnecessary parts when designing them. Classical fabrication methods do not allow such new designs to be easily implemented. Recent development of additive manufacturing technologies allows huge mass reduction in those industries. Optimization of printing strategies for different alloys has been of great importance in recent research (1,2). Recent works focuses on the development of printing strategies for Al 7075 series (3,4), a high-strength aluminum alloy. As printing strategies are now better understood, it becomes important to determine their mechanical properties at their working temperature. Using a home-made tensile device working at cryogenic temperatures, the mechanical characterization of Zr-modified Al7075 alloys has been carried out. The results are promising when compared to classical Al7075-T6 . The AB samples have a yield stress of 415 MPa at RT and 476 MPa at 77K with correct elongation values (>14% at both temperatures) while T6 samples presents values of 550MPa and 650MPa at those temperature respectively. However, through optimized thermal treatment, we achieve the stress level of 526MPa and 668MPa at both RT and cryogenic temperatures for the printed samples. X-ray tomography analysis and Scanning Electron Microscopy characterization have been carried out to understand the deformation mechanisms taking place at cryogenic temperature compared to room temperature
Properties of 7075 aluminium chips deposition produced by multi-layer friction surfacing
No full textThe solid-state additive manufacturing process of multi-layer friction surfacing is ideal for building three-dimensional parts from high-strength precipitation-hardened 7075 Aluminium chips. This process can be efficient for aluminum recycling, bypassing the resource-hungry recycling fusion process and maintaining material properties despite the use of chips as raw material. The current study shows that the fully softened chips provide high deposition density. The microstructure retains the elements as the original 7075 aluminium alloy. Thanks to the knowledge already acquired with dense rods, hardening precipitation can be restored with post-T6 heat treatment. This implies a significant improvement in microhardness, effects on microstructure and mechanical properties
WAAM of high strength 7075 Al alloy: challenges, microstructural and mechanical characterization
No full textWire Arc Additive Manufacturing (WAAM) of aluminum alloys, particularly high-strength alloys like 7xxx series, presents significant challenges. This study, part of the Win2Wal WAALU project, focuses on the challenges associated with WAAM of 7075 Al alloy, including issues related to defects, microstructure, mechanical performance, and post-deposition heat treatments. The present work discusses the impact of wire quality, WAAM deposition strategies, and manufacturing conditions on the performance of the resulting structures. WAAM is performed using a 6-axis Kuka robot coupled with a Fronius welding source. The initial filler metal consists of ER7075 aluminum wires with diameters of 1.6 mm and 1.2 mm. Post weld heat treatments are applied to achieve the peak-aged T6 state for the ER7075 WAAM manufactured parts. X-ray tomography is used to identify internal defects in the printed structures. By correlating these defects with the WAAM deposition conditions, the study provides valuable insights into the key factors influencing print quality. Guidelines for successfully printing 7075 aluminum alloy using WAAM are proposed. Hot cracking is mitigated through careful management of the deposition strategy and heat input, while porosity is minimized by using higher-quality feedstock wire and efficient thermal control. The optimized WAAM conditions are further explored by evaluating the tensile strength and fatigue life of the printed ER7075 parts. These results are compared to those of equivalent wrought EN AW 7075 plates in the peak-aged T6 condition. The findings of this work contribute to advancing the industrial application of WAAM for high-strength aluminum alloys
Roughness vs. Sub-Surface Porosities: Key Factors in Fatigue Behavior of AlSi10Mg LPBF Alloy
No full textThe presence of porosities and poor surface quality in samples produced by L-PBF significantly impacts mechanical performance, particularly under cyclic loading. To ensure reliable performance in engineering applications without resorting to time-intensive post-processing, efforts have focused on optimizing the L-PBF process to reduce both porosity and surface roughness [1, 2]. This study investigates the interplay between surface roughness and sub-surface porosities in determining the fatigue behavior of AlSi10Mg LPBF samples. Previous work has demonstrated that minimizing the surface roughness of AlSi10Mg often comes at the cost of introducing sub-surface porosities [2]. Specifically, employing the keyholing mode for contouring can reduce roughness to below 5 microns but simultaneously creates keyhole-induced porosities in the contours. To evaluate the trade-off between reducing surface roughness and introducing sub-surface porosities, fatigue tests were conducted on three types of as-build samples: (1) high roughness (2) medium roughness (3) low roughness with sub-surface porosities. The roughness was controlled by using different contouring strategies. To highlight the impact of sub-surface porosities and thus dissociate it from the influence of roughness, the three sets of samples were also tested in their mirror-polished state. The three types of as-built samples and polished samples were then compared to sandblasted samples, which represent the standard surface treatment for improving fatigue performance. While the low-roughness samples showed better fatigue properties, the results indicate that the fatigue resistance of all three sample types remains poor, making post-treatment necessary. It also shows that, while sandblasting slightly increases the roughness of the low-roughness sample, it significantly improves the fatigue resistance of the samples
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Effect of thermal history on defects in brittle Fe-6.5wt%Si soft magnetic alloy produced by Laser Powder Bed Fusion
No full textOptimization of radial flux machines with punched laminated sheets of electrical steel is well covered in the literature. Additive manufacturing, and in particular Laser Powder Bed Fusion (L-PBF), of soft magnetic should enable a less restrictive design of electrical machines, particularly for axial flux machines whose flux path is fundamentally 3D. Fe-6.5wt%Si is a good candidate in terms of magnetic and electrical properties as well as material cost. As a first step towards designing such complex parts, this alloy needs to be well characterized both mechanically, electrically and magnetically. However, this material tends to exhibit cracking, due to its brittleness, and pores during LPBF manufacturing. First, a detailed comparison of process parameters is carried out to understand the appearance of cracks and pores. Different parameters, laser scanning strategies as well as support structures are compared. Secondly, a thermal dynamic finite element method (FEM) simulation of L-PBF process is developed. It is validated using in-situ thermal measurements by a thermal camera. Subsequently, both mechanical and magnetic properties are measured on the best samples and compared based on their thermal history
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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