1,720,961 research outputs found
Peck drilling of CFRP/titanium stacks: effect of tool wear on hole dimensional and geometrical accuracy
No full textThe effect of tool wear on dimensional and geometrical accuracy of holes machined by peck drilling in carbon fibre reinforced plastic (CRFP) and titanium (Ti) stacks is studied. Coated and uncoated tungsten carbide drills of both fine and ultra-fine microstructures are employed to assess the importance of grain size and coating on hole accuracy. Hole profiles show two maxima: one at the hole entry and the other at the CFRP/Ti interface. Hole cylindricity as function of tool wear shows a minimum. It firstly decreases due to flank wear and subsequent reduction of the drill diameter. Then the rise of tool instability prevails with the result that an increase of the cylindricity with tool wear is brought about. Less wear-resistant drills attain this minimum in a shorter time of cutting
Set-up of an experimental procedure for the surface smoothing of FDM parts through acetone vapor
No full textFused deposition modeling (FDM) is an additive manufacturing technology where three-dimensional physical models are manufactured by layer-by-layer deposition. However, the layered surface built with FDM suffers from poor surface quality and dimensional accuracy even for basic part geometries. This proves to be unacceptable and not satisfactory for most general purposes with the consequence of a decreased value of the final product. Several methods for post-processing were proposed to achieve fine surface of manufactured components. In particular, for components manufactured with polylactic acid (PLA) the chemical post-processing with dimethyl ketone (acetone), named vapor smoothing process, seems to be very promising to significantly improve the surface roughness. Moreover, acetone has the main advantage to have a low cost, low toxicity and high diffusion rate. However, this polishing procedure may dissolve the outer surface of the parts affecting the structural reliability of the part. In this work, a novel device, consisting of a cylindrical chamber in Pyrex, is set-up for the vapor smoothing process with acetone. The system is designed to permit the injection of a gas containing acetone at different concentrations and at different operating conditions (temperature, contact time). The samples used for the test are truncheon design manufactured using different printer settings; each truncheon is built at inclination angles varying from 0o to 45o in step of 5o. The variation of the surface roughness was investigated using a confocal microscope Leica DCM3D, equipped with the software LeicaScan and LeicaMap
Surface and mechanical characterization of stationary shoulder friction stir welded lap joints: experimental and numerical approach
No full textFriction Stir Welding (FSW) is one of the most used solid-state welding processes in the aeronautical, aerospace, ground transportation and naval fields. Stationary Shoulder Friction Stir Welding (SSFSW) is a recently introduced variant of the process allowing lower heat input into the joints, with beneficial effects in terms of joint mechanical properties, microstructure and top surface finish. In the paper, lap joints produced by SSFSW and made out of AA6082-T6 aluminum alloy sheets have been analyzed with the aim to investigate the effect of the stationary shoulder on the lap joints surface, metallurgical, and mechanical properties. The lap joints produced by SSFSW have been compared to the ones produced by “conventional” FSW in order to highlight the differences between the two processes. The top surface of the joints obtained with the two processes has been quantitatively evaluated. Finally, a dedicated numerical model has been utilized to highlight the causes of the observed differences through the distributions of the main field variables, namely temperature, strain and strain rate. It was found that SSFSW results in narrower weld nugget and smaller areas involved by micro hardness reduction caused by smaller peak temperature and high temperature zone. Additionally, better surface quality was found for the joint welded by SSFSW with lower heights and flash, allowing to avoid subsequent finishing operations needed for most industrial applications
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
Effect of different surface treatments on titanium dental implant micro-morphology
No full textBackground: Titanium dental implants are today widely used with osseointegration mainly dependently on the implant surface properties. Different processing routes lead to different surface characteristics resulting, of course, in different in situ behaviors of the implants. Materials: The effect of different treatments, whether mechanical or chemical, on the surface morphology of titanium implants were investigated. To this aim, various experimental methods, including roughness analysis as well scanning electron microscope (SEM) observations, were applied. Results: The results showed that, in contrast to the mechanical treatments, the chemical ones gave rise to a more irregular surface. SEM observations suggested that where commercial pure titanium was used, the chemical treatments provided implant surfaces without contaminations. In contrast, sandblasted implants could cause potential risks of surface contamination because of the presence of blasting particles remnants. Conclusions: The examined implant surfaces showed different roughness levels in relation to the superficial treatment applied. The acid-etched surfaces were characterized by the presence of deeper valleys and higher peaks than the sandblasted surfaces. For this reason, acid-etched surfaces can be more easily damaged by the stress produced by the peri-implant bone during surgical implant placement
Effect of plasma surface treatment on the impact behavior of basalt/epoxy composites
No full textIn this study, the effects of surface treatment of a low-temperature atmospheric oxygen plasma on basalt/epoxy composites were investigated to improve the hydrophobility of the composite surface. After the plasma treatment, the unmodified and surface treated composite laminates have been experimentally characterized by performing contact angle measurements, low-velocity impact tests and indentation depth on the impacted laminates. Results have showed a dependence of such composite properties on the plasma coating deposition and on the treatment parameters outlining the need to optimize both the plasma power and exposition time to plasma in order to assess the efficiency of the plasma treatment and establish the optimal processing conditions
Low-temperature effect on the impact and flexural behaviour of basalt composite laminates
No full textEpoxy based laminates reinforced with woven basalt fibres have been manufactured and characterized by quasi-static mechanical tests and low-velocity impact tests. Samples were prepared by infusion of 16 plies of basalt under pre-optimized conditions. All the interlaminar shear strength, flexural and impact tests were carried out at room temperature, −25 °C and −50 °C to investigate the effect of temperature on the mechanical characteristics and the impact damage onset and propagation. Ultrasonic technique were adopted to provide information on the shape and the extent of the internal damage. The final aim was to be able to predict impact energy and delamination under different temperature conditions and to assess the influence of the resin matrix stiffening at low temperature on the composite behaviour. Results show that at low temperature due to the stiffening of the resin matrix, the composite tested is more resistant and less deformable. It is interesting since, at low temperatures, it is more straightforward the damage propagation. In particular, ILSS and flexural tests show a maximum increase of 39% and 12.78% respectively at T = −50 °C compared to the value at room temperature. A delamination area increase of wholly 40% at T = −50 °C, is detected
- …
