Search results for " Technology"
showing 10 items of 23337 documents
OPTIMIZATION OF A NOVEL MAGNETO-RHEOLOGICAL DEVICE WITH PERMANENT MAGNETS
2017
In this paper a novel evolutionary algorithm is used for the optimization of the performance of a magnetorheological (MR) device, capable to transmit torque between two shafts and powered by a system of Permanent Magnets (PMs). The stochastic, evolutionary, global optimization algorithm is based on a modified version of the self-organizing map. It uses a dedicated simplified analytical model of the device, developed in order to obtain a fast and accurate evaluation of the torque. Then, by means this model, the cost function to find the optimal parameters of the device is defined. Once the optimal parameters are identified, the performance of the proposed device is simulated by means of a FE…
How activator ion concentration affects spectroscopic properties on Ba4Y3F17: Er3+, Yb3+, a new perspective up-conversion material
2018
Abstract Ba4Y3F17 with Er3+ and Yb3+, a promising material for up-conversion luminescence, was synthesized. Excellent isomorphic capacity was detected. Low-temperature measurements show that erbium ions are incorporated in multiple lattice positions, which is inconsistent with the current model of Ba4Y3F17 crystal lattice structure. Activator ion concentration has a different impact on 4S3/2 and 4F9/2, states (for the green and red luminescence, respectively) depopulation. Energy transfer from Er3+ 4S3/2 state to Yb3+ is observed even at low temperature (15 K) while Er-Er cross-relaxation is observed from 120 K and above. Yb3+ concentration has a great impact to red-to-green up-conversion l…
EBSD, XRD and SRS characterization of a casting Al-7wt%Si alloy processed by equal channel angular extrusion: Dislocation density evaluation
2019
Abstract Aluminum‑silicon (Al Si) alloys of high silicon contents are composite materials; they are used whenever high casting properties are required. They are slightly ductile below 8wt%Si. An increase in ductility can be obtained by refining Si-crystals in elaboration or by a further hot working. In the present work, an Al-7wt%Si alloy was processed by Equal Channel Angular Extrusion (ECAE) at temperatures 20 °C and 160 °C up to three passes. The die was formed by two cylindrical channels with characteristic angles Φ = 110° and Ψ = 0. EBSD, X ray diffraction (XRD) and Strain Rate Sensitivity (SRS) were used to characterize the microstructure and the mechanical properties. High levels of …
Experimental and numerical investigation on a new FSW based metal to composite joining technique
2018
Abstract In the last decades, different techniques were proposed to join aluminum sheets with composites materials. Each of them has advantages and weak points over the others and new techniques and patents are continuously developed to overcome these difficulties. In this paper an experimental and numerical investigation on a new Friction Stir Welding based approach to mechanically join AA6082-T6 to self-reinforced polypropylene is presented. The aluminum sheet is pre-holed along both the sides of the weld line and a pinless tool generates the heat and pressure needed to prompt back-extrusion of the composite. New experimental fixtures and hole designs were investigated in order to enhance…
Influence of spray trajectories on characteristics of cold-sprayed copper deposits
2021
Abstract Industrial robots are widely used in cold spray (CS) as well as thermal spray to produce various coatings by precisely controlling kinematic parameters during the process. However, the robot trajectory and its effect on the characteristics of CS deposits are important, but not fully studied. This article introduces four typical spray trajectories, including zigzag path, cross path, parallel path, and spiral path, to elaborate thick CS Cu deposits, and characterizes the corresponding Cu deposits, respectively. The experimental results revealed that the spray trajectories have a major influence on the associated thermal history and the residual stress distribution. However, no signif…
High temperature oxidation of Mg2(Si-Sn)
2016
Abstract High temperature oxidation of Mg 2 Si 1- x Sn x alloys ( x = 0.1 ⿿ 0.6) has been investigated. The oxidation rate was slow for temperatures below 430 °C. In the temperature range between 430⿿500 °C all the alloys exhibited breakaway oxidation. The onset temperature of the breakaway region in general decreased with increasing level of Sn in the alloy. The breakaway behavior is explained by a combination of the formation of a non-protective MgO layer and the formation of Sn-rich liquid at the interface between the oxide and Mg depleted Mg 2 Sn.
Melting temperature prediction by thermoelastic instability: An ab initio modelling, for periclase (MgO)
2021
Abstract Melting temperature (TM) is a crucial physical property of solids and plays an important role for the characterization of materials, allowing us to understand their behavior at non-ambient conditions. The present investigation aims i) to provide a physically sound basis to the estimation of TM through a “critical temperature” (TC), which signals the onset of thermodynamic instability due to a change of the isothermal bulk modulus from positive to negative at a given PC-VC-TC point, such that (∂P/∂V)VC,TC = -(∂2F/∂V2) VC,TC = 0; ii) to discuss the case of periclase (MgO), for which accurate melting temperature observations as a function of pressure are available. Using first princip…
Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source
2020
The production of negative ions in cesium sputter ion sources is generally considered to be a pure surface process. It has been recently proposed that ion pair production could explain the higher-than-expected beam currents extracted from these ion sources, therefore opening the door for laser-assisted enhancement of the negative ion yield. We have tested this hypothesis by measuring the effect of various pulsed diode lasers on the O − beam current produced from Al 2O 3 cathode of a cesium sputter ion source. It is expected that the ion pair production of O − requires populating the 5d electronic states of neutral cesium, thus implying that the process should be provoked only with specific …
EPR in glass ceramics
2019
Abstract The development of novel materials requires a profound understanding of the relationship between a material's performance and its structural properties. Electron paramagnetic resonance (EPR) is a well-established technique for a direct detection and identification of paramagnetic defects in solids. This chapter provides an overview of the applicability of continuous wave EPR spectroscopy in the studies of glass ceramics focusing on transition metal (Mn2 +, Cu2 +, Cr3 +) and rare earth (Gd3 +, Eu2 +, Er3 +, Yb3 +) ion local structure analysis. EPR spectra features of the above-mentioned paramagnetic probes in glasses and glass ceramics are compared and discussed in detail. The chapt…
Effect of surface finishing on the oxidation behaviour of a ferritic stainless steel
2017
Abstract The corrosion behaviour and the oxidation mechanism of a ferritic stainless steel, K41X (AISI 441), were evaluated at 800 °C in water vapour hydrogen enriched atmosphere. Mirror polished samples were compared to as-rolled K41X material. Two different oxidation behaviours were observed depending on the surface finishing: a protective double (Cr,Mn) 3 O 4 /Cr 2 O 3 scale formed on the polished samples whereas external Fe 3 O 4 and (Cr,Fe) 2 O 3 oxides grew on the raw steel. Moreover, isotopic marker experiments combined with SIMS analyses revealed different growth mechanisms. The influence of surface finishing on the corrosion products and growth mechanisms was apprehended by means o…