Добірка наукової літератури з теми "Magnetomechanical phenomena"

A review of the latest theoretical advances in the description of magnetomechanical effects and phenomena observed in magnetoactive elastomers (MAEs), i.e., polymer networks filled with magnetic micro- and/or nanoparticles, under the action of external magnetic fields is presented. Theoretical modeling of magnetomechanical coupling is considered on various spatial scales: from the behavior of individual magnetic particles constrained in an elastic medium to the mechanical properties of an MAE sample as a whole. It is demonstrated how theoretical models enable qualitative and quantitative interpretation of experimental results. The limitations and challenges of current approaches are discussed and some information about the most promising lines of research in this area is provided. The review is aimed at specialists involved in the study of not only the magnetomechanical properties of MAEs, but also a wide range of other physical phenomena occurring in magnetic polymer composites in external magnetic fields.

The annealing behaviour of temperature-dependent mechanical spectra (vibrating-reed technique) was studied on electrodeposited ultrafine-grained nickel as well as on Ni nanocomposites with small (7 nm) SiO2or larger (25 nm) Al2O3nanoparticles. From the response of the different phenomena involved – Young’s modulus, high-temperature damping background, dislocation-and hydrogen-induced low-temperature loss peaks, and magnetomechanical effects – information is obtained on processes such as recovery, grain growth, hydrogen trapping, and dislocation generation by thermal stresses, which are influenced by both kinds of nanoparticles in different ways.

The current state of technology is characterized by the mass use of electricity, the use of various electrical, electronic and radio devices. This causes expansion of magnetic measurements and the need to develop new highly sensitive measuring equipment for a wide range of frequencies. One of its main elements, that largely determines the accuracy, frequency and dynamic ranges, are the primary measuring sensors of strength (induction) of alternating magnetic fields. Many works have been devoted to the analysis and development of various sensors of strength (induction) of magnetic fields. At the same time, it can be noted the lack of a systematic approach to the measurement of alternating magnetic fields. The problem of the general classification of methods of measurement of alternating magnetic fields and, accordingly, primary measuring sensors of strength (induction) of alternating magnetic fields is not solved. In most cases, separate issues of measuring alternating magnetic fields and certain types of sensors are considered. That does not allow obtaining a holistic picture in this area and make the right choice of direction for solving assigned tasks. The comprehensive analysis of methods of measuring alternating magnetic fields was carried out in this work. Based on it, the classification of primary measuring sensors of strength (induction) of alternating magnetic fields, on the physical principles of transformation was proposed. Accordingly, the available measuring sensors of alternating magnetic fields following to the group of used physical phenomena can be divided into: magnetomechanical, induction, galvanomagnetic, quantum, magneto-optical and photomagnetic. Depending on the characteristics of each of these phenomena, separate measurement methods and types of measuring sensors were highlighted. The current state of development of each of the types of measuring sensors of strength of alternating magnetic fields was analyzed, their advantages and disadvantages were determined, the limits of dynamic and frequency ranges, the maximum values of errors were outlined. The obtained results allow to significantly simplify and reduce the time of choosing the necessary method of strength (induction) of alternating magnetic fields measuring and to choose the necessary type of measuring sensor to effectively solve the tasks.

The main objective of this contribution is the theoretical modelling of magnetizable materials that exhibit viscoelastic properties. The current state of the art in the mathematical modelling of non-linear magnetomechanics in deformable media can be easily integrated within the unified framework of continuum thermodynamics, which is crucial in setting the convenient forms for the constitutive laws and evolution equations. Owing to the soft nature of the materials we have in mind, the finite strain range is adopted a priori and, in this first approach, only isotropic materials are considered. We adopt the currently well-accepted multiplicative split of the deformation gradient, which, moreover, gives rise to an intermediate configuration. Herein, the novelty resides in the fact that the magnetic field vectors are transported onto the aforementioned intermediate configuration and, therefore, can be implicitly decomposed. The proposed formulation is based on the magnetic induction as the main independent variable for the magnetic part of the problem. An alternative formulation based on the magnetic field as main independent variable can easily be deduced, but this latter will not be considered in this paper for the sake of clarity. A very simple model example that agrees with the laws of thermodynamics is proposed for the purpose of demonstration to study some phenomena qualitatively.

We report focused light-induced activation of intense magnetic microconvection mediated by suspended magnetic nanoparticles in microscale two-dimensional optothermal grids. Fully anisotropic control of microflow and mass transport fluxes is achieved by engaging the magnetic field along one or the other preferred directions. The effect is based on the recently described thermal diffusion–magnetomechanical coupling in synthetic magnetic nanofluids. We expect that the new phenomenon can be applied as an efficient all-optical mixing strategy in integrated microfluidic devices. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

This thesis focuses on three areas of nonclassical continuum mechanics of solids. In the first part, we develop a few peridynamics (PD) models and solution strategies for discretized PD equations in the context of the mechanics of solids and structures. A strategy for removal of zero energy modes in PD correspondence models is presented in the second part of this thesis and a way of modelling solid continua with defects is outlined drawing upon analogies from gauge theory. In the last part, exploring conformal gauge symmetries in elastic solids, we show how several electromechanical and magnetomechanical phenomena can emerge solely from local conformal symmetry considerations of the Lagrangian. We start with formulating a PD theory for thick linear elastic shells to model fracture and fragmentation in these structures. Effects of shear deformation and coupling between surface wryness with in-plane stress resultants and surface strain with moment resultants are considered. A few numerical simulations on thick plate, thick cylindrical shell and quasi-static fracture propagation on thick cylindrical shell are presented. Next, a reduced dimensional PD theory is developed for axisymmetric structures. Apart from reduction of computational burden, it eliminates stress singularity near the axis of symmetry due to the nonlocality in PD. We furnish a few numerical simulations on Taylor impact test with copper and steel specimens and compared them with experimental observations. After that, inelastic response of ceramics is investigated using phase field based PD theory to eliminate some of the limitations of Deshpande-Evans (DE) ceramics constitutive model. A macroscopic PD phase field based integro-differential damage evolution rule is used replacing DE crack growth law which removes possible mesh dependent solutions. We numerically solve a spherical cavity expansion problem using dimensional reduction and demonstrate evolution of damage and plastic fronts. Next, a general procedure for solving discretized PD continuum and atomic systems is presented using Hamilton-Jacobi theory and time-dependent perturbation techniques. Here, approximate analytical solutions of positions and momenta are obtained as functions of initial conditions and time with which separate analysis for each initial condition can be eliminated resulting in saving in computational time. A few simulations on linear discretized PD problems are furnished to demonstrate the efficacy of our method. We also solved graphene sheets under tension and shear loading using simplified Tersoff potential for given initial conditions. After that, flexoelectricity – an electromechanical coupling phenomenon is modeled in PD to investigate nanoscale fracture propagation in dielectrics. An analytical solution is presented for an infinite 3D body considering bond based case. Incorporating damage through phase field theory, we present a few numerical simulations on damage propagation in a flexoelectric plate. In the second part of the thesis, we develop a sub-horizon based PD theory to eliminate zero-energy and other unphysical deformation modes from the correspondence framework of non-ordinary state based PD which requires only a minor alteration of the conventional PD correspondence equations and little additional computational demand. With this, one may study convergence of the solutions for a fixed horizon size with increasing particle density and obtain meaningful nonlocal solutions. We also outlined a way to model defective continua in this framework drawing upon analogies from a translation invariant gauge theory of solids. In the last part, a conformal gauge theory of solids is laid out. We note that, if the pulled back metric of the current configuration (right Cauchy-Green tensor) is scaled with a constant, the volumetric part of Lagrange density changes but the isochoric part remains invariant. However, under a position dependent scaling, isochoric part loses its invariance. In order to restore invariance of the isochoric part, we introduce a 1-form compensating field and modify the definition of derivative to a gauge covariant one (minimal replacement). Noting close connection with Weyl geometry, we impose Weyl condition through the Lagrangian and for the evolution of 1-form, a minimal coupling is constructed. We obtain Euler-Lagrange equations from Hamilton’s principle and noticed a close similarity with flexoelectricity governing equations interpreting the exact part of 1-form with electric field and the anti-exact part with the polarization vector. Next, piezoelectricity and electrostriction phenomena are modeled through contraction of Weyl condition in various manners. We also modeled magnetomechanical phenomena applying Hodge decomposition theorem on the 1-form which leads to curl of a pseudo-vector field and a vector field. Identifying the pseudo-vector field with the magnetic potential and vector part with magnetization, flexomagnetism, piezomagnetism and magnetostriction phenomena are modeled.

High cycle fatigue (HCF) is the main cause of failure in rotating machinery especially in aircraft engines which results in the loss of human life as well as billions of dollars. More than 60 percent of aircraft accidents are related to High cycle fatigue. Major reason for HCF is vibratory stresses induced in the blades at resonance. Damping is needed to avoid vibratory stresses to reach the failure level. High speed rotating machinery has to pass through the resonance in order to reach the operational speed and chances of failure are high at resonance level. It is therefore required to suppress the vibrations at resonance level to avoid any damage to the structure. Application of coating to suppress vibrations is a current area of research. Various types of coatings have been studied recently. This includes plasma graded coatings, viscoelastic dampers, piezoelectric material damping, and magnetomechanical damping. In this research, the phenomenon of damping using a coating of nickel alloy on a steel beam is studied experimentally and numerically to reduce vibratory stresses by enhancing damping characteristics to avoid aircraft engine and rotating machinery failure. For this purpose, uncoated and nickel alloy coated steel beams are fabricated. The coating procedure was performed using plasma arc method. The beams were then mounted in a cantilevered position and bump and vibration shaker tests were conducted to determine the natural frequencies and mode shapes. One of the most important parameter to measure the damping of a system is the damping ratio. In order to determine the damping ratio, vibration analyzer mode was adjusted in time domain and beam was excited by using a hammer. The vibration analyzer showed the vibration decay as a function of time. Using that decay, damping ratio was calculated by using logarithmic decrement method. In order to investigate and compare the damping characteristics of un-coated and coated beams, forced response method was employed. In this method, beams were excited at 1st and 2nd bending mode natural frequencies using vibration shaker. Results were very encouraging and showed a significant improvement in damping characteristics. The experimental results were then endorsed by numerical results which were achieved by performing modal and forced response analysis using finite element analysis techniques.