Extended Double Lattice BRST, Curci-Ferrari Mass and the Neuberger Problem

We present Extended Double BRST on the lattice and extend the Neuberger problem to include the ghost/anti-ghost symmetric formulation of the non-linear covariant Curci-Ferrari (CF) gauges. We then show how a CF mass regulates the 0/0 indeterminate form of physical observables, as observed by Neuberger, and discuss the gauge-parameter and mass dependence of the model.Comment: Prepared for 7th Conference on Quark Confinement and the Hadron Spectrum, Ponta Delgada, Azores, Portugal, 2-7 Sep 2006. 3p

Finite element simulation of semi-finishing turning of Electron Beam Melted Ti6Al4V under dry and cryogenic cooling

open6noIn the last few years, important step forwards have been made on Finite Element Simulation of machining operations. Wrought Ti6Al4V alloy has been deeply investigated both numerically and experimentally due to its wide application in the industry. Recently, Additive Manufacturing technologies as the Electron Beam Melting and the Direct Melting Laser Sintering are more and more employed in the production of biomedical and aeronautical components made of Ti6Al4V alloy. Fine acicular microstructures are generated by the application of additive manufacturing technologies, affecting the mechanical properties and the machinability. By the consequence, this peculiarity has to be considered in modelling the material behaviour. In this work, a numerical analysis of cylindrical external turning on Electron Beam Melted (EBM) Ti6Al4V alloy is presented. A Johnson-Cook constitutive equation was implemented as a flow stress model and adapted with respect to the wrought Ti6Al4V alloy. The model was calibrated and validated through the cutting forces and temperatures measurements acquired under dry and cryogenic lubricating conditions.openBordin, A; Imbrogno, S.; Rotella, G.; Bruschi, S.; Ghiotti, A.; Umbrello, D.Bordin, Alberto; Imbrogno, S.; Rotella, G.; Bruschi, Stefania; Ghiotti, Andrea; Umbrello, D

ultrasonic vibration turning to increase the deposition efficiency of a silica based sol gel coating

Abstract Magnesium alloys are attracting more and more attention for producing temporary prosthetic devices thanks to their bioresorbable characteristics in human environment. However, they present a reduced corrosion resistance to body fluids, which still limits their applications to a great extent. One possible way to increase the corrosion performances is to coat the device with a suitable coating that provides a barrier to the body fluids corrosion. In this work, Ultrasonic Vibration Turning (UVT) is used to create a surface texture to the AZ31 magnesium alloy with the aim of improving the surface wettability and therefore helping the subsequent coating deposition. The obtained results showed that the surface texture induced by UVT contributed to increase the surface wettability of approximately 17% compared to the conventional turning case, regardless of the adopted cutting parameters. The UVT texture proved to improve the efficiency of the coating deposition since the thickness of the deposited sol-gel coating was increased when applied to UVT surfaces, especially at the lowest depth of cut and highest cutting speed that contributed to generate deeper dimples

on the surface integrity of electron beam melted ti6al4v after machining

Abstract The Additive Manufacturing process known as Electron Beam Melting (EBM) is increasingly used to produce Ti6Al4V biomedical parts, whose functional surfaces, however, need to be machined afterwards. The paper addresses the fundamental issue of surface integrity of EBM parts when subjected to machining operation under dry, flood and cryogenic cooling conditions. The machined surface integrity is evaluated in terms of microstructural and mechanical features, residual stresses, surface topography and defects. Results are then compared to the outcomes of the same machining tests carried out on the conventional wrought alloy. This study points out the different machinability of the two investigated alloys, highlighting that new insights into optimization of parameters for machining AM alloys are needed

the effect of cooling strategies and machining feed rate on the corrosion behavior and wettability of az31 alloy for biomedical applications

Abstract In this work, the corrosion rate of the AZ31 magnesium alloy in physiological environment was improved by optimized machining process parameters. Cryogenic turning was exploited to obtain a featureless layer in the machined sub-surface, while the feed rate was modified to reduce the aspect ratio of the feed marks characteristic of the turning operation, achieving a decrease of the alloy wettability. The obtained results showed that the aforementioned combined aspects acted as an efficient strategy to enhance the AZ31 poor corrosion behavior, which represents the major obstacle of its effective application in the biomedical field

large strain extrusion machining of magnesium alloys for biomedical applications

Abstract Recently, magnesium alloys are attracting more and more attention as degradable materials for manufacturing temporary biomedical devices, although their rapid degradation in physiological environment limits their clinical applications to a great extent. Different Severe Plastic Deformation (SPD) processes have been recently applied to magnesium alloys in order to improve the surface integrity, which is directly correlated to their corrosion resistance. The current study investigates the possibility of exploiting Large Strain Extrusion Machining (LSEM) as a processing route to increase corrosion resistance of magnesium alloys for biomedical applications. Different cooling conditions and cutting speeds were adopted during LSEM and their effects on the surface integrity and corrosion resistance on both the machined workpiece and obtained chips were studied. For the first time, liquid nitrogen was used as cooling medium in LSEM and its effect was properly investigated. Results showed that LSEM, regardless of the adopted cutting parameters, is an effective method to obtain a workpiece with improved functional performances. Similar results pertain to the chips, but a careful choice of process parameters is even more mandatory than in the case of the workpiece