1,721,396 research outputs found
On the Choice of Tool Material in Friction Stir Welding of Titanium Alloys
No full textFriction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, is now being successfully used also for magnesium alloys, copper and steels. The wide diffusion the process is having is due to the possibility to weld both materials traditionally considered difficult to be welded or "unweldable" by traditional fusion welding processes due to peculiar thermal and chemical material properties, and complex geometries as sandwich structures and straightening panels. Recently, research is focusing on titanium alloys thanks to the high interest that such materials are getting from the industry due to the extremely high strength-weight ratio together with good corrosion resistance properties. At the moment, the main limit to the industrial applicability of FSW to titanium alloys is the tool life, as ultra wear and deformation resistant materials must be used. In this paper a, experimental study of the tool life in FSW of titanium alloys sheets at the varying of the main process parameters is performed. Numerical simulation provided important information for the fixture design and analysis of results. Tungsten and Rhenium alloy W25Re tools are found to be the most reliable among the ones considered
Animal-mediated interactions for pollination in saltmarsh communities
Full text linkAmong the wide variety of biotic interactions, animal-mediated pollination plays a crucial role in the maintenance of the integrity of plant communities. Thus, there is increasing concern about the possible effects that the growing loss of pollinators (i.e., pollinator crisis phenomenon) might have on plant communities. Recent studies revealed that pollination interactions often occur at the landscape scale, with plant species of different communities interacting through pollinator sharing. Saltmarshes provide a suitable example of plant communities spatially co-occurring at the landscape scale, with the micro-topography determining a precise zonation of ecologically distinct halophytic communities. However, little is still known about pollination interactions in saltmarshes. The aim of the present study was to assess which halophytic community contribute best to pollinator species richness in saltmarshes and whether plant species of different halophytic communities interact through pollinator sharing. To this aim we placed 20 permanent plots per plant community and monitored pollination interactions between plants and pollinators once a month during the overall flowering season. Our results revealed that animal-mediated pollination occurred in only two halophytic communities, with three species depending on animals for their pollination. When comparing halophytic communities in terms of richness of pollinator species, the vegetation of sandbanks, mudflats and sandflats emerged as the richest one. Animal-pollinated species of saltmarshes only partially shared pollinator species, revealing an overall low exchange of pollinators between different halophytic communities. In conclusion, the high complementarity in the spectrum of pollinators showed by animal-pollinated species of different halophytic communities makes all halophytic communities hosting animal-pollinated species important for the conservation of pollinators
Osservazioni sulla caratterizzazione dell'essenza lignea della legatura del Codice C mediante l'impiego di tecniche di indagine non invasive
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Valutazione della funzionalità dei boschi planiziali relitti della pianura veneta orientale nella conservazione delle specie nemorli erbacee
No full textSelective Laser Melting of Ti6Al4V: Effects of Heat Accumulation Phenomena Due to Building Orientation
Full text linkTitanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland
Caratterizzazione del pattern lipidico e degli acidi grassi del muscolo dell’ibrido Acipenser naccarii (Bonaparte, 1836) x A. baerii (Brandt, 1869) e del reciproco A. baerii x A. naccarii.
No full textMuscle phospholipids and tryglicerides were measured in two sturgeon (Acipenseridae) hybrids. Fatty acid composition of the two lipidic fractions showed a strong similarity between the two hybrids
On the role of intermetallic and interlayer in the dissimilar material welding of Ti6Al4V and SS 316L by friction stir welding
Full text linkJoining titanium with stainless steel can lighten the structure of numerous industrial applications. However, a vast disparity of thermal, physical, and chemical properties between these alloys leads to defects in conventional arc welding techniques, viz., brittle intermetallic compounds, pores, cracks, etc. Friction stir welding (FSW) is a renowned solid-state joining technology for creating dissimilar material joints producing visco-plastic material flow at the interface. The present investigation compares the intermetallic layer thickness and properties as a function of the thickness of the Cu interlayer sandwiched in lap joints. Macrostructural and microstructural characterizations were carried out to understand the localized microstructural evolution comprising intermetallic, grain refinement, defects, etc. Mechanical properties were also evaluated for prepared lap joints
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