1,721,017 research outputs found
Predicting the roughness of overhanging surfaces in laser powder bed fusion via in-situ thermal imaging
Full text linkThe production of overhanging surfaces in Laser Powder-Bed Fusion (LPBF) has long been a challenging task due to poor heat dissipation and lack of support of loose powder, resulting in surface defects and increased roughness due to dross formation and sintering. Surface quality is a critical aspect of AM mechanical components that undergo fatigue loading, as a rough surface can act as a preferential crack initiation site and lead to premature failure. Predicting the quality of the as-built surfaces could be used to identify critical areas that require rework or post-processing, or to find regions that require optimization of the process parameters to improve the final quality. The orientation of the surface itself (i.e., the degree of inclination of the surface) could be used to predict the final surface quality and will be employed as benchmarking reference throughout the work (referred to as “geometry-based” model). This study demonstrates the effectiveness of using data mining on high-speed thermal video images to create a real-time predictive model based on “in-situ” data for estimating surface roughness (Sa) of overhanging surfaces printed at different inclinations. The results showed that the model based on “in-situ” data has a prediction accuracy that is more than 2 times higher than the one obtained with a model that is purely based on geometric data, i.e., a model that relies only on the inclination angle of the surface during the print. The proposed method is tested on different materials (AISI 316L stainless steel and AlSi10Mg) and process conditions (continuous and pulsed laser, low and high power) to show the flexibility and extended applicability of the proposed solution. The newly developed method opens new possibilities for in-situ quality control and process optimization of surface quality in Laser Powder Bed Fusion (LPBF)
A new method for in-situ process monitoring of AM cooling rate-related defects
Full text linkThe increasing popularity of additive manufacturing (AM) is pushing the industry to provide new solutions to improve the process stability. In the past, process monitoring and control has proved to be a fundamental tool to enhance the repeatability of many manufacturing processes, however the typical AM fast dynamics require a high spatiotemporal resolution data flow to accurately describe the process and these new types of data are presenting new challenges for standard statistical process monitoring (SPM) techniques. In this work, the capabilities of a new machine learning (ML) based framework for the detection of cooling rate-related defects in metal additive manufacturing processes via in-situ high-speed cameras are presented and discussed
Effect of overhanging surfaces on the evolution of substrate topography and internal defects formation in laser powder bed fusion
Full text linkOverhanging (a.k.a. down-facing) surfaces are typically found in complex metal parts built with laser powder bed fusion (L-PBF). When these surfaces exceed a certain extension or inclination with respect to the build plate, they need to be supported with external structures to avoid failure and macro-geometrical errors. However, a relatively large portion of the slice gets printed directly over loose powder, thus facing a substrate with significantly different wetting and heat transfer characteristics from solid/bulk. Several quality aspects (e.g., internal defects, surface topography) can be affected by the presence of overhangs, but their evolution during the process is still a relatively unexplored field. In this work, a new strategy based on process interruption is proposed for analyzing the evolution of defects produced during the printing of down-facing surfaces. Ex-situ high-accuracy characterization equipment was used to study their effect on the evolution of printed surface topography, internal defects, melted and sintered thickness. Results show that the process gradually recovers from the disturbance introduced by the overhang, but the peculiar structure of the internal defects observed in those regions reveals that even small unsupported areas can be detrimental to the as-built quality of the part. The combined use of surface topography data and volume reconstruction also allowed developing and validating a physics-based model for predicting the evolution of surface topography and effective layer thickness in overhangs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Unlocking New In-Situ Defect Detection Capabilities in Additive Manufacturing with Machine Learning and a Recoater-Based Imaging Architecture
Full text linkAdditive manufacturing (AM) has the potential to revolutionize the way products are designed and produced in a wide range of industries. However, ensuring the quality and reliability of AM parts remains a challenge, as defects can occur during the building process. In-situ monitoring is a promising approach for detecting and classifying these defects for in-process part qualification. In this paper, we present a novel approach for in-situ monitoring of laser powder bed fusion (LPBF) processes using a recoater-based imaging sensor and machine learning algorithms. The new sensor architecture is a recoater-mounted contact image sensor (CIS) and allows for high-resolution imaging of the build area during the recoating process, enabling the observation of a wide range of part and process-related defects. We demonstrate the effectiveness of using machine learning for image analysis on a series of experiments on a commercial AM system, showing significant improvements in defect detection accuracy compared to existing methods. Our results demonstrate the potential of the recoater-based sensor architecture for unlocking new capabilities for in-situ monitoring and quality control in powder bed-based AM processes
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Molecular pathology demonstration of sars-cov-2 in cytotrophoblast from placental tissue with chronic histiocytic intervillositis, trophoblast necrosis and covid-19
No full textA subset of placentas from pregnant women having the SARS-CoV-2 infection have been found to be infected with the coronavirus using molecular pathology methods including im-munohistochemistry and RNA in situ hybridization. These infected placentas can demonstrate several unusual findings which occur together—chronic histiocytic intervillositis, trophoblast necrosis and positive staining of the syncytiotrophoblast for SARS-CoV-2. They frequently also have increased fibrin deposition, which can be massive in some cases. Syncytiotrophoblast is the most frequent fetal-derived cell type to be positive for SARS-CoV-2. It has recently been shown that in a small number of infected placentas, villous stromal macrophages, termed Hofbauer cells, and villous capillary endothelial cells can also stain positive for SARS-CoV-2. This report describes a placenta from a pregnant woman with SARS-CoV-2 that had chronic histiocytic intervillositis, trophoblast necrosis, increased fibrin deposition and positive staining of the syncytiotrophoblast for SARS-CoV-2. In addition, molecular pathology testing including RNAscope and immunohistochem-istry for SARS-CoV-2 and double-staining immunohistochemistry using antibodies to E-cadherin and GATA3 revealed that cytotrophoblast cells stained intensely for SARS-CoV-2. All of the cytotro-phoblast cells that demonstrated positive staining for SARS-CoV-2 were in direct physical contact with overlying syncytiotrophoblast that also stained positive for the virus. The pattern of cytotro-phoblast staining for SARS-CoV-2 was patchy, and there were chorionic villi having diffuse positive staining of the syncytiotrophoblast for SARS-CoV-2, but without staining of cytotrophoblast. This first detailed description of cytotrophoblast involvement by SARS-CoV-2 adds another fetal cell type from infected placentas that demonstrate viral staining
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