Generation mechanism and empirical model of eddy current force and torque in drum-type eddy current separation.

Enhancing the recovery efficiency of non-ferrous metals in eddy current separation is of great significance. In this study, the accuracy of the simulation model was verified by comparing the eddy current force. The transformation mechanism of the Lorentz forces into the eddy current force and torque in non-ferrous metal particles was revealed by analyzing various physical fields. Then, the influence of magnetic field parameters on eddy current, eddy current force, and torque was studied. It shows that the eddy current force and torque are affected by the vector gradient of the magnetic field and the magnetic flux density, respectively. Additionally, the time derivative of the magnetic field impacts the magnitude of the eddy current force and torque by controlling the eddy current. On this basis, the empirical models of eddy current force and torque were established by similarity theory. The results obtained can improve and expand the application of eddy current separation.

Redesigning axial-axial (biaxial) cruciform specimens for very high cycle fatigue ultrasonic testing machines.

The necessity to increase performances in terms of lifetime and security in mechanical components or structures is the motivation for intense research in fatigue. Applications range from aeronautics to medical devices. With the development of new materials, there is no longer a fatigue limit in the classical sense, where it was accepted that the fatigue limit is the stress level such that there is no fracture up to 1E7 cycles. The recent development of ultrasonic testing machines where frequencies can go as high as 20 kHz or over enabled tests to be extended to ranges larger than 1E9 in just a few days. This area of studies is now known as Very High Cycle Fatigue (VHCF). On the other hand, most of the existing test equipment in the market for both classical and VHCF are uniaxial test machines. However, critical components used in Engineering applications are usually subjected to complex multi-axial loading conditions. In this paper, it is presented the methodology to redesigning existing cruciform test specimens that can be used to create an in-plane biaxial state of stress when used in 'uniaxial' VHCF ultrasonic testing machines (in this case, the term 'uniaxial' is used not because of the state of stress created at the centre of the specimen, but because of the direction at which the load is applied). The methodology is explained in such a way that it can be expanded to other existing designs, namely cruciform designs, that are not yet used in VHCF. Also, although the approach is presented in simple and logical terms, it may not be that obvious for those who have a more focused approach on fatigue rather than on modal analysis. It is expected that by contributing to bridging the gap between the sciences of modal analysis and fatigue, this research will help and encourage others exploiting new capabilities in VHCF.

A study on the influence of Ni-Ti M-Wire in the flexural fatigue life of endodontic rotary files by using Finite Element Analysis.

The aim of this paper is to analyze the cyclic performance of two different Ni-Ti endodontic rotary files made from different alloys under bending using Finite Element Analysis (FEA). When experimentation is not available, this is not a trivial task and most papers on the subject rely on static analysis only. Two Ni-Ti rotary instruments are selected, ProFile GT and a GT Series X (GTX). The latter file is made from M-Wire, which has been thermo-mechanically processed to have larger flexibility, according to its manufacturer. The mechanical response was studied by considering different scenarios in the FEA package, in which the material properties were introduced according to existing literature. The method and results are presented and discussed so that this paper can be used as a guideline for future works. Although not fully reflective of the instrument's behavior in a dynamic rotation intra-canal system, the models used constitute a good approximation when a comparison between two instruments is at stake. It is shown that the GTX file has a lower risk of fatigue fracture during its clinical use when compared to the GT file, especially when the root canal makes the file deform into an extreme geometry. However, if the root canal does not make the file deform more than a certain amount, the GT file is equally good from the point of view of mechanical endurance.

Structural characterisation and mechanical FE analysis of conventional and M-Wire Ni-Ti alloys used in endodontic rotary instruments.

The purpose of this study is to understand how the M-Wire alloy conditions the mechanical flexibility of endodontic rotary files at body temperature.Two different rotary instruments, a Profile GT 20/.06 and a Profile GT Series X 20/.06, were selected due to their geometrical similarity and their different constituent alloy. GT series X files are made from M-Wire, a Ni-Ti alloy allegedly having higher flexibility at body temperature. Both files were analysed by X-Ray Diffraction and Differential Scanning Calorimetry to investigate phase transformations and the effects of working temperature on these different alloys. Mechanical behaviour was assessed by means of static bending and torsional Finite Element simulations, taking into account the nonlinear superelastic behaviour of Ni-Ti materials. It was found that GT files present austenitic phase at body temperature, whereas GT series X present R-phase at temperatures under 40 °C with a potential for larger flexibility. For the same load conditions, simulations showed that the slight geometrical differences between the two files do not introduce great disagreement in the instruments' mechanical response. It was confirmed that M-Wire increases the instrument's flexibility, mainly due to the presence of R-phase at body temperature.

Numeric comparison of the static mechanical behavior between ProFile GT and ProFile GT series X rotary nickel-titanium files.

INTRODUCTION: This article aims to evaluate how different superelastic nickel-titanium (NiTi) alloys determine the static mechanical performance of endodontic files during bending and torsion. METHODS: Two NiTi rotary instruments with similar geometries and equal cross sections, ProFile GT (GT) and a GT Series X (GTX), were selected. The latter file is made from M-Wire, a NiTi alloy that, according to its manufacturer, has been thermomechanically processed to have larger flexibility at body temperature. The mechanical response was studied for a series of static bending and torsional loads by using finite element (FE) models. The materials were characterized according to previously published stress-strain curves. RESULTS: For the same load and boundary conditions, the GTX material significantly increased the instrument's performance. For instance, the deflection for a 1N force at the tip of the file was found to be 28.5% larger for the GTX file, whereas the maximum stress decreased 13.2%. CONCLUSIONS: Although not fully reflective of the instrument's behavior in a dynamic rotation intracanal system, the static results showed that the GTX file is more flexible and capable of stress relief at the most critical sections than the GT file, suggesting that it has a lower risk of fracture inside the root canals during its clinical use.