1,720,963 research outputs found
HCF resistance of AlSi10Mg produced by SLM in relation to the presence of defects
Get PDFBeing able to predict the fatigue resistance of parts produced by additive manufacturing (AM) is a very actual and frequent open issue. The qualification of AM structural parts needs a very costly and time consuming series of fatigue tests, on both samples and full-scale parts. A proper control of the AM process allows obtaining comparable and even better fatigue resistance than standard manufacturing. Despite this, the experimental results often show a large scatter, mostly due to the presence of defects. In this framework, this work summarizes a research activity aiming at modelling the high cycle fatigue (HCF) resistance in presence of defects, focusing on AlSi10Mg produced by selective laser melting (SLM). Two batches of samples were investigated by computed tomography (CT) and tested. A lower bound resistance curve was obtained introducing artificial defects. A fatigue crack growth simulation model based on the maximum defect size is proposed, able to estimate both the life and the scatter of the data in the fully-elastic region. Moreover, knowing the size and position of all the defects inside the samples, it was possible to foresee the defect at the origin of fatigue failure and to draw a hazard ranking based on the applied stress intensity factor
Quality control of AlSi10Mg produced by SLM: Metallography versus CT scans for critical defect size assessment
Get PDFWhile the adoption of metal additive manufacturing (AM) is growing exponentially owing to its wide range of potential applications, its application to safety-critical and structural parts is significantly impeded by the lack of standards. Quality assessment of AM products is a crucial requirement, as the AM process induces internal defects that can have detrimental effects on the fatigue resistance.By evaluating the defect distribution, it is possible to perform a fracture mechanics assessment to estimate the fatigue strength and service lifetime of AM materials. This strategy has been successfully applied to selective laser-melted AlSi10Mg by performing X-ray micro-computed tomography (mu CT) and applying suitable statistical methods (i.e., statistics of extremes). However, it remains unclear whether complex and expensive nondestructive inspection methods (e.g., mu CT) are necessary and whether simpler and more conventional approaches (i.e., microscopy of polished sections (PSs), as prescribed by ASTM E2283) would provide equivalent information for the estimation of internal defects.In this study, the size of the most detrimental defect was estimated by performing both light microscopy on PSs and mu CT on three batches of fatigue specimens characterized by different internal porosities. The results showed that both techniques were able to pinpoint a significant difference in the prospective largest defect in a material volume corresponding to the gauge section of a specimen. However, extrapolation of the critical defect size for fatigue failure using PS data was less accurate and less conservative than that using CT data. An evaluation of the techniques with regard to time and cost indicated that mu CT allowed the investigation of larger sample volumes and the reduction of both man hours and cost
Additive manufacturing in the new space economy: Current achievements and future perspectives
No full textIn recent years, the realm of space exploration has undergone a transformative shift, marked by the emergence of a thriving new space economy. This evolution has not only redefined existing space infrastructures and services but has also democratized access to space, accelerating exploration endeavors. At the core of such evolution is additive manufacturing (AM), a groundbreaking technology that has fundamentally altered the landscape of designing and producing launchers and space systems. AM not only enhances the efficiency of existing space missions but also unlocks novel avenues for space exploration and the establishment of sustainable human settlements beyond Earth. This paper provides a comprehensive and current exploration of the industrial catalysts driving AM adoption across key space domains. It delves into existing applications and uncharted frontiers, exploring innovative advancements while spotlighting industry gaps and obstacles. Motivated by the maturation of AM technologies, the proven track record of additively manufactured components in space missions, and the surge in research and investments aligning with major space market trends, this paper aims to provide aerospace and manufacturing communities with a panoramic view of present and future opportunities for AM within the rapidly expanding new space economy. Additionally, it sheds light on the profound impact and momentum gathering in this field, all the while examining the significant challenges that demand concerted attention
A benchmark activity on the fatigue life assessment of AlSi10Mg components manufactured by L-PBF
Get PDFOne of the challenges associated with additive manufacturing (AM) is the definition of an assessment route which considers the main process signatures of the AM process. To this end, this work presents a complete benchmark activity for the assessment of an AlSi10Mg component produced by a laser pow- der bed fusion process, aimed at advancing the understanding of the fatigue resistance of AM materials with particular focus on the comparison between the fatigue performances of small coupons and demon- strators. Four builds of AlSi10Mg specimen geometries were manufactured to: (i) determine the fatigue curves for both as-built and machined conditions; (ii) measure the fatigue crack growth rate; (iii) produce and test under fatigue a benchmark component used as a reference for the validation of the fatigue assessment procedure. Tools and concepts of flaw tolerance were then used to perform the fatigue assess- ment of the benchmark component and were shown to be successful in the life prediction. Results obtained from this wide database (related to internal defects and surface features) show that only a fracture-based fatigue assessment is able to provide precise life estimates consistent with material crack growth properties. Eventually, all the experimental results including specimens design, analysis of frac- ture surfaces and raw tests’ data will be made available in a database which can be accessed and used by the industrial and scientific communities to calibrate and validate alternative fatigue assessment proce- dures of AM parts
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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