1,720,973 research outputs found
Additive manufacturing and joints: Design and methods
No full textThe industrialization of the Additive Manufacturing (AM) processes is enabling the use of AM components as final product in several applications. These processes are particularly relevant for manufacturing components with optimized custom-tailored geometries. However, to fully exploit the potentiality of AM, the development of knowledge aimed to produce dedicated design methods is needed. Indeed, even if AM enables the manufacturing of new kinds of structures, e.g. 3D lattice structures, it introduces process-specific design input and limitations that needs design methods different to from the ones for subtractive manufacturing.
Design for AM (DfAM) is a design methodology that aims to take advantage of new buildable geometries but taking into account also AM processed materials anisotropy and 3D printing constraints.
Recent literature focused on the assembly of AM components and on the AM components joining to a main structure. The conclusion was that adhesive bonding is a promising joining process, especially considering its improved stress distribution compared to fastening, but at the time of writing a method that combines DfAM and adhesive bonding knowledge is not available.
The work presented in this thesis focused on developing knowledge on design for AM and bonded joints.
First step was evaluating testing methods for AM and producing data on materials properties.
Secondly, the early works on tailoring approaches for AM joints, published recently in scientific literature, were analyzed. Then AM dedicated designs, modifications and testing methods were proposed both for the adherends (in the thickness and on the surfaces) and the joints. Specifically, an innovative joint design concept was introduced, i.e. using the 3D printing parameters as bonded joint design factors.
Eventually, feasibility of performing joints using multi-material AM with conductive polymer to embed heating elements was assessed. The 3D printed through the thickness circuits is a cutting-edge approach to enable new solutions for joints structural monitoring and self-healing
Modeling the strength of laminated parts made by fused filament fabrication additive manufacturing
No full textFused filament fabrication (FFF, also known as fused deposition modeling) is the most popular 3D printing additive manufacturing technology: cheap 3D printers are largely widespread and most polymeric materials can be used. It is probably the most versatile additive manufacturing technology. The applications range from prototyping to the production of custom parts with structural capabilities: fiber reinforced plastics can also be used. However, the knowledge of the FFF materials and the design criteria for fused filament fabricated parts are scarcely known and this results in a very common skepticism in adopting this technology for technical structural components. As for the other processing technologies for plastics, included injection molding, the mechanical properties of the components strongly depend on the manufacturing parameters. As shown by some authors, since production by FFF produces a layered structure, it is possible to model the mechanical behavior by means of the classical lamination theory largely verified and known for composites. In those papers, it was shown that the equivalent elastic properties could be predicted as a function of the lamination stacking and angles. In this paper, based on experimental results obtained on symmetric balanced angle-ply laminated samples made of polyethylene terephthalate with added glycol (PETG) and polyamide (PA) subject to tensile loads, the Tsai-Hill criterion was applied to predict the strength. After identification of the strength parameters, a good correlation of the experimental with the model parameters, for all lamination angles, was obtained
An improved model to describe the repeated loading-unloading in compression of cellular materials
No full textCellular materials, often referred as foams or structural foams when used for energy absorption, are largely used to protect people and goods in the case of shocks and impacts. The detailed knowledge of their behavior is fundamental to design components for this aim. Peroni et al. (2008)-(2009) proposed a model able to describe the mechanical compression behavior of some polymeric material. Such model, based on the work by Rusch (1970), described the stress-strain curve as a sum of two contributions, the first for the elastic part and the second for the densification. More recently Avalle and Belingardi (2018) presented a more general model where the stress is calculated as a sum of three terms, one for the elasto-plastic phase, the second for the plateau, and a third for the densification. The model could include effects like density and strain-rate. However, those models allow to describe only the monotonic compression behavior: in several situations repeated impacts can happen with unloading followed by further reloading. Unfortunately unloading cannot be described by a linear relation between stress and strain (as is usually considered for metals). Unloading follows a non-linear law with a variable relation between stress and strain in the successive cycles: this requires a particularly complex model. In this work, a new model able to effectively reproduce the compression behavior of some polymeric cellular materials is presented. The model is validated and tuned on the basis of experimental tests with specimen subject to complex cycles of repeated loading and unloading. The model describes both the loading from different levels of residual compression and unloading from any value of compression level. The application to several materials justifies the generality of the method
Design and fabrication of resistive sensor using additive manufacturing techniques for robotic application
No full textDevelopment of a wearable device for the early diagnosis of neurodegenerative diseases
No full textThe progressive evolution of information and sensing technologies is giving pulse to the development of wearable mobile devices in search of life quality improvement. A relevant field of application is healthcare, with the development of wireless unobtrusive wearable solutions for the continuous remote health monitoring of patients. These wearable devices are particularly important for neurodegenerative diseases due to the possibility of early stage diagnoses through continuous monitoring to collect earlier significant data. Discovering specific symptoms and early defining medical treatments can delay, if not stop, the pathology progress whereas, once major symptoms like restricted or impaired mobility has appeared, the patients already underwent relevant and irreversible brain damage. The aim of this work is to show the development of the Neuroglass, a wearable smart glasses device for early stage diagnosis and monitoring of Parkinsonian-type neurodegenerative diseases. The designed frame is compliant to the standards and in order to embed the sensors to collect data from head and eyes movements since one of the early symptoms of Parkinson's disease has proven to be eye tremors. Preliminary laboratory tests, e.g. head accelerations measurements for different body movements, were carried out in order to choose properly the characteristics and positioning of the sensors; afterwards the device’s frame was designed by means of a 3D parametric CAD and built by additive manufacturing. The design was validated by first experimental test on monitoring eye movements and blinks
Development of a gripper for garment handling designed for additive manufacturing
No full textThe paper presents how a robotic gripper specific for grasping and handling of textiles and soft flexible layers can be miniaturized and improved by polymeric additive manufacturing-oriented re-design. Advantages of polymeric additive manufacturing are to allow a re-design of components with integrated functions, to be cost-effective equipment for small batches production and the availability of suitable materials for many applications. The drawback is that for design validation extended testing is still necessary because of lacks in standardization and that the mechanical properties are building parameters dependent. The outcomes are a lower complexity of the design overall and lower number of components. These are pursued taking advantage of the anisotropy of the additive manufacturing processed polymer and assigning appropriate shapes and linkages in the mechanisms. Set of common materials (polylactide, polyethylene terephthalate, acrylonitrile butadiene styrene) and technical (acrylonitrile styrene acrylate, polycarbonate/polybutylene terephthalate blend) are tested to obtain data for the modelling
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
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
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