Papers by Keyword: Magnetic Field

Abstract: Aluminium metal matrix composites (AMC) are perspective materials for a wide range of applications in automotive, aerospace and other industries where material mechanical properties and weight ratio is crucial. In AMC manufacturing through metallurgical process the main obstacle for particle introduction into the melt is poor particle wettability and their tendency to form agglomerates due to van der Waals and interfacial forces. Most of currently used AMC manufacturing methods through metallurgical route are effective only for small quantities or are time consuming, even though metallurgical AMC production route would promise significant cost savings. In this study we propose a permanent magnet stirring technology developed by IP UL as tool for alternative realization of stir- and compo-casting methods for AMC production. First results of contactless stirred semi-solid aluminium alloys show effective alloy stirring in melt volume and intense surface deformations that can break the oxide layer and stir in the reinforcement material from the melt surface.

Abstract: The viscoelastic and creep and recovery behaviors of a carbonyl iron (CI)-water-based magnetorheological fluid (MRF) were studied under dynamic and constant loading conditions. The feature of MR fluid is to change from liquid to semi-solid state just in a few milliseconds after applying a magnetic field. ThereforeMR fluid is a kind of smart material whose rheological properties change with step-change in a magnetic field. We prepared MR fluids comprising CI 65 wt%, water 35 wt %, bentonite 3 wt %, and oleic acid 1 wt %. Because bentonite with nanosized fills the voids between the CI particles, it was used with oleic acid to enhance the MR response of the CI/water suspension. The strain amplitude tests reveal that MR fluid behaves as a viscoelastic material in the LVE range and a transition of fluid occurred from linear viscoelastic to non-linear viscoelastic behavior at the critical strain of 0.1%. Its storage moduli confirmed a steady plateau region for the entire angular frequency range, suggesting the well-known solid-like behavior of the MR suspension. The creep and recovery result signified that as the magnetic field increased, the instantaneous creep strain contributions decreased dramatically.

Abstract: The relationship between the interaction of ferromagnetically ordered clusters in austenite with dislocations, twinning and nucleation of the martensite phase is considered. It is shown that the regions with short-range order existing in austenite affect the dislocation structure. In turn, dislocations are involved in the formation of twins and martensite nuclei. The imposition of an external magnetic field enhances the magnetic inhomogeneity of austenite and the effects of magnetoelastic interaction between clusters and dislocations.

Abstract: The article contains the results of experiments carried out on laser irradiation of steels in a constant magnetic field. The experiment shows it possible to increase the cooling speed while heat transfer decreases from the surface into lower metal layers, which slightly reduces laser-hardened layer depth, increases convective mixing of the fusion area, which have a positive impact on the surface layers quality of steel and alloys. This has a positive effect on strength product properties. Magnetic field processing of metal reduces the degree of local plastic deformation of irradiated layer due to magnetostriction phenomenon. Magnetic field superimposition contributes to two-phase decay of the martensite, and reduces residual stresses and crack risk.

Abstract: The formation energy of martensite nuclei in the austenite matrix is calculated. Nanoclusters with ferromagnetic order, which exist in austenite above the Curie temperature, reduce the formation energy of a critical martensite nucleation center when exposed to an external magnetic field. The data obtained are explained by the magnetic separation of the initial phase under the action of a magnetic field. A fluctuation increase in nanovolumes with a ferromagnetic order in austenite increases the energy in a atoms group of the matrix phase with a parallel spins arrangement. As a result, the nucleation rate of the martensite phase increases and the martensitic transformation proceeds more completely.

Abstract: The study is concerned with the effects of slip velocity on a non-uniform rotating electroosmotic flow in a micro-channel. Electroosmotic driven fluid flow is obtained by the application of a potential electric field which describes the nonlinear Poisson-Boltzmann equation. The external electric potential is applied along the x and y directions which provides the necessary driving force for the electroosmotic flow. Two semi analytical techniques were employed to obtain the solution of the nonlinear Poisson-Boltzmann equation. The first method incorporates the complex normalized function into the Laplace transform and the second method is the combination of the Laplace transform and D’Alembert technique. Further, the complex normalized function became difficult to invert in closed form, hence we resort to the use of numerical procedure based on the Stehfest's algorithm. The graphical solutions to the axial velocities on both x and y components have been obtained and analyzed for the effects of the slip parameter and the amplitude of oscillation of the micro-channel walls. The solutions show that the rotating electroosmotic flow profile and the flow rate greatly depend on time, rotating parameter and the electrokinetic width. The results also indicate that the applied electric field and the electroosmotic force, play vital role on the velocity distribution in the micro-channel. The fact is that the solutions obtained in this study synthesize most of the solutions available in the previous studies. Finally, this study will be relevant in biological applications particularly in pumping mechanism to help transport substances within different parts of the systems.

Abstract: The time-dependent hydromagnetic boundary layer flow across a vertical surface with internal heat regeneration in porous media is investigated. The flow problem has been modelled mathematically in partial differential equations along with appropriate defined boundary conditions. These equations were expressed in dimensionless form using suitable similarity variables. The resulting dimensionless equations along with the conditions defined at the boundaries are solved by means of the Laplace transform methods. Results of the study are graphically illustrated for various quantities of practical importance. It was concluded that time positively influence the flow as a reduced skin friction coefficient was observed. Furthermore, the magnetic parameter, the radiation parameter, the heat absorption parameter and the permeability of the porous media can be used to influence the characteristics of a flow in porous media.

Abstract: Preservation of materials using liquid nitrogen media has been widely used. One of them is used in the medical field, namely cryonic technology. Cryonics is a method of preservation at cold temperatures using a cryoprotectant in liquid nitrogen. To maintain the quality of the material, a sensor that can detect the temperature of liquid nitrogen is needed. Low temperature sensors with Cu and Ni based Resistance Temperature Detector with layers (RTD) have been made, but these sensors have a layer of Ni deposits that are not yet homogeneous. So quality improvement is needed by adding an external magnetic field. Based on this, the aim of this research is to synthesize a thin layer of Cu / Ni using electroplating method assisted by external magnets parallel to the ion currents

Abstract: Magnetorheological braking devices function due to the organization of domain structures between liquid and solid magnetic materials under the action of an electromagnetic or magnetic field. The disc is most widely used as a rotating braking element that made of a solid magnetic material due to the large area of contact with a magnetorheological fluid. Many factors affect the braking characteristics of the magnetorheological disc brake. Specifically, the value of the magnetic field and how the field is distributed across the work element is significantly affected at the braking torque. There are different ways to generate a magnetic field. In this study, the method of installation of permanent magnets into the construction, allowing to increase the braking torque of the magnetorheological disc brake is proposed. Simulation modelling showing the distribution of the magnetic field across the disk depending on the installation of permanent magnets with different pole orientations were carried out. The model takes into account the possibility of increasing the gap between solid magnetic materials of the structure, inside them which the magnetorheological fluid is placed. Comparative estimation of the distribution of the magnetic fields depending on the chosen method of installation of permanent magnets with different orientations of their poles is carried out. Further research is planned to focus on a comparative assessment of the distribution of magnetic fields depending on the selected material of the braking chamber.

Abstract: During heat treatment of machine parts and tools, besides the usual task of ensuring a high complex of mechanical and operational properties, there is a problem of distortion of products in the process of heat treatment and the need for editing operations (which are carried out manually and require significant labor costs). The known methods do not solve the problem of removing distortion for thin-walled parts of the ring shape completely. This paper shows the technical possibility of using the energy of a constant magnetic field for the "internal" straightening of products during heat treatment in the temperature range of super-plasticity of transformation. The use of special equipment makes it possible to eliminate virtually the distortion of thin-walled parts of the ring shape and to improve their mechanical properties.