1,720,980 research outputs found
The effect of thickness of Nylon 6,6 nanofibrous mat on Modes I–II fracture mechanics of UD and woven composite laminates
No full textThis paper presents an experimental investigation on epoxy resin-carbon fibers composites interleaved with Nylon 6,6 nanofibers. In particular, the paper focuses on the effect of the thickness of the nanoreinforce into two types of laminae: unidirectional (UD) and plain wave (PW). The effectiveness of the nanoreinforce has been addressed by comparing critical and propagation energy release rates, calculated by testing samples under Mode I and Mode II fracture mechanic loads. Experiments show a general improvement in delamination resistance when the nanofibers are interleaved. Nevertheless slightly different behaviour has been found between the two types of lamina: micrographs of crack paths have been used to explain the reinforce mechanisms and such differences, suggesting a strong interaction between the nature of the fabric and the thickness of the nanointerlayer
Experimental study on a new generation of recycled composite laminates
Full text linkComposite manufacturing processes generate a significant amount of waste due to the raw material being supplied in sheet form and cut-outs. The unused scraps of prepreg are typically discarded, leading to the disposal of up to 35% of the purchased material, accompanied by economic losses and negative environmental impacts. The authors propose collecting these scraps, cutting them into smaller, regular patches, and assembling them into a new, patched prepreg sheet. This study presents an experimental investigation into the mechanical properties of such patched material, assembled using two different architectures and three patch geometries. Five different configurations are designed, manufactured, and tested, with results compared to samples made from the original unpatched material through four-point bending tests. When patches are assembled in a regular geometry, the new material possesses around 50% and 90% of the original strength and stiffness respectively, demonstrating potential for use in load-bearing applications. The methods of assembling the patches following a regular pattern also resulted in significantly better properties than a random deposition, which despite its lower cost to implement does not retain relevant mechanical characteristics. Of the two arranged investigated architectures, the one being more complex to manufacture shows 9% and 5% higher stiffness and strength, respectively, than the simpler one. Fracture analysis shows that failure mainly takes place in between of a patch, rather than the superposition areas
Electrospun nanofibers as reinforcement for composite laminates materials – a review
Full text linkIn the last few decades nanofibers have been developed and introduced in a vast number of industrial and research applications. One of their most effective use is as interleaved reinforcement for composite laminate materials against delamination. Nanofibrous mats have the ideal morphology to be embedded between two plies of a laminate, and a vast and deep research has been carried out investigating their effect on the global behaviour of a composite laminate. This review is the first of its kind to date which presents a detailed state-of-the-art on the effect of nanofibrous interleaves into composite laminates with focus on the mechanical performances and behaviours of nanomodified materials. A detailed description of the working mechanisms of the nanointerleave under different load cases is presented, and a comparative analysis between papers in literature will provide readers with a powerful tool to understand and use nanofibers for reinforcing purposes
Vibration-based delamination diagnosis and modelling for composite laminate plates
No full textThis study suggests a methodology for damage diagnosis in structures, which is based on a multivariate statistical procedure and uses the measured time domain structural vibration response. In this paper the methodology is developed for the purposes of delamination assessment in free vibrating composite laminate plates. It applies singular spectrum analysis to the measured strains in order to decompose and compress the information contained in these responses into a smaller number of independent variables. The method works on the principle of clusterization between healthy and delaminated plates with different delamination sizes and locations. The developed methodology is then applied and verified on numerically simulated and experimentally obtained results for composite laminate plates. The results demonstrate a good capability for clusterization between different delamination scenarios in composite laminate plates
Influence of electrospun nanofibers on the interlaminar properties of unidirectional epoxy resin/glass fiber composite laminates
No full textNylon 6,6 nanofibers were interleaved in the mid-plane of glass fiber/epoxy matrix composite laminates for Mode I and II fracture mechanic tests. The present study investigates the effect of the nanofibers on the laminates' mechanical response. Results showed that Nylon 6,6 nanofibers improved specimen's fracture mechanic behavior: the initial energy release rates GIC and GIIC increased 62% and 109%, respectively, when nanofibrous interlayer was used. Scanning electron microscope micrographs showed that nanofiber bridging mechanism enhances performances of the nanomodified specimens, still able to link the layers when the matrix is broken
Noise and vibration of permanent magnet synchronous electric motors: A simplified analytical model
Full text linkDesign of electric motors, especially for automotive applications where early design choices have significant impacts on the final results, in terms of both cost and performances, is a matter of primary importance, with direct consequences on the entire vehicle. Common practice lacks simple, yet reliable, analytical method to evaluate vibration and noise emission of permanent magnet synchronous motors (PMSMs), and this is the gap that the work here proposed aims to fill. In particular, electric vehicles’ noise requirements have added a design opportunity to manufacturers, which, depending on the type of costumers they are selling their products to, need to comply with different preferences. Accurately estimating noise emissions of such complex machines is a difficult matter, which can be fully exploited only at the end of the design process. The article aims to provide a simple, yet accurate enough, tool to estimate the noise emission of electrical motors at the early stage of the design, giving engineers and researchers a tool to drive their choices. An equivalent curved beam model is used for modeling the structural vibration of the stator when subjected to electromagnetic forces. The sound pressure amplitudes are analytically derived based on the acoustic solution for infinitely long cylindrical radiators. Part of the innovation lays on the fact that the contributions of both the radial and tangential forces are taken into account, and a discussion on the effect and influence of the latter on the stator acoustic emission is presented. The sound pressure radiated from the outer surface of the stator is calculated, and a unique indicator of sound emission, named sound pressure level (SPL), is determined. The proposed method is validated against data of two PMSMs from literature, showing good agreement with the experiments, proving the method is a reliable tool for electric motor designers to be used especially during the early stage of design
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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