On the shear test of a MR elastomer under magnetic field applied at various angles

In this paper the influence of the angle between the applied external magnetic field and the mechanical shear direction on the measured elasticity of a magnetorheological (MR) elastomer is addressed. The whole range of magnetic field angles from 0○ to 90○ is analyzed in steps of 5○. Though this dependence is of highest importance for practical applications this issue is rather neglected in previous studies. The work uses MR elastomer specimens based on a silicone rubber matrix containing iron powder in weight fractions of 82 wt.% and 89 wt.%. It has been shown that the measured modulus of elasticity of such composites decreases as the angle between an external magnetic field and applied shear deformation increases. As the framework for the discussion of the findings a macroscopic explanation associated with the magneto-deformation effect as well as an influence of the demagnetizing factor are considered.

Remarks on Selecting Length of Cylindrical Sample to Determine Magnetic Properties of its Material

When experimentally studying magnetic properties of the ferromagnetic materials, preferences are often given to a more convenient method involving the use of sufficiently long cylindrical samples with the L length and the D diameter placed in the solenoid field as an alternative to the method based on using classical samples of the toroidal shape (to exclude manifestations of the demagnetizing factor). Currently, required justification is practically missing for specific values of the relative L/D length, which would indicate such [L/D] values (for L/D ≥ [L/D]), at which magnetic properties of a sample (already long enough) correspond to magnetic properties of its material. While the existing recommendations such as [L/D] = 50 are postulated, let us note that relevant experimental studies of magnetic properties of the cylindrical samples with the L/D parameter targeted variation were not made. An attempt was made to fill this gap. For cylindrical steel samples with the different L/D values (from 1 to 50), families of the B magnetic induction and of the μ permeability field dependencies were obtained experimentally using the ballistic method. The sought [L/D] values were determined from the B and μ dependencies on the L/D by the junction abscissa of the ascending and self-similar branches. It was established that in the accepted field strength in the range of H = 0.94--54.2 kА/m magnetizing field, the [L/D] parameter is a variable substantially depending on H (and/or μ). It varies from [L/D] = 10--15 at H = 54.2 kA/m (μ = 30) to [L/D] = 50--60 at H = 4.7 kA/m (μ = 270). And at H < 4.7 kA/m, [L/D] > 50--60, i.e., more than is commonly believed. Thus, it was stated that the data on magnetic properties obtained when using even long samples (L/D = 50) and declared as data on the magnetic properties of the corresponding material, are only close to those with H < 4.7 kA/m. Phenomenological expressions were obtained for the [L/D] determination: exponential with the H argument and logarithmic with the μ argument

Метод расчета поверхностных механических напряжений в осесимметричных магнитных системах

A method is proposed for calculating the mechanical stresses of magnetic and current systems, calculated from the energy density of a uniformly magnetized cylinder. For the calculation, an average in volume demagnetizing factor of the cylinder is introduced, which is proportional to the ratio of the cylinder diameter to its length . It is shown that the demagnetization energy , negligible for a "long" cylinder , ( ), becomes decisive in the formation of stresses at . The radial and axial stresses are investigated in a wide range of ratios.

Research of the properties of magnetic fillers of cylindrical shape

It has been noted that the information on magnetic properties of specific magnets available in the design and operation of magnetic separators/analyzers using magnetic fillers in the form of balls as the working body (polygradient type) is extremely limited, especially for magnets with varying sphericity coefficients (mutual ratios of characteristic sizes). Experiments using cylindrical samples (porous) as a ferromagnetic matrix rendered the induction data subsequently applied to establish the magnetic permeability, susceptibility, and magnetization values for the samples at various values of the length-todiameter ratio of φ = 1–16. The demagnetizing factor N was obtained and analyzed for the «short» samples (1 ≤ φ [φ]) in the range of magnetizing field strengths of 9–47 kA/m, taking into account the established transient value of φ = [φ] = 10–12 (when, at φ ≥ [φ], the magnetic properties of the sample correspond to the magnetic properties of its quasi-solid material). The analysis results for these data, required when assessing the actual magnetic properties of «short» working bodies, characteristic of polygradient magnetic separators/ analyzers, demonstrate the validity of the exponential dependence (decreasing with increasing) of their demagnetizing factor. The research was carried out with the financial support of the Ministry of Education and Science of the Russian Federation within the framework of the State Assignment in the field of science (project No. 0706-2020-0024) and of the Russian Foundation for Basic Research and the Royal Society of London under research project No. 20-52-10006.

Метод расчета взаимной индуктивности системы катушек c использованием модели аксиально намагниченного цилиндра

Proposed is a method of computing a mutual inductance of a dense winding coil system using energy of axial magnetic cylinders. Obtained formulas of computing 3-D fields of the cylinder and coils expressed in elliptic integrals. Demonstrated that an average in volume demagnetizing factor is equal to Nagaoka coefficient for self-inductance of short coils

Size Dependence of the Magnetoelastic Properties of Metallic Glasses for Actuation Applications

We present an exhaustive study of the magnetoelastic properties of 24 strips with different rectangular dimensions, cut from a long ribbon of Metglas® 2826MB3. The strips have a length-to-width ratio R = L/w ranging from 2 to over 20. Significant variations of the apparent saturation Young’s modulus and the ΔE effect with strip geometry, changing from 160 GPa and 4% for L = 10 mm, w = 5 mm and R = 2, to 164 GPa and 9.6% for L = 35 mm, w = 1.7 mm and R = 20.6, have been observed. In order to obtain the highest values of the ΔE effect, the magnetomechanical coupling coefficient, k, and the quality factor of the resonance, Q, a value R > 14 is needed. The effective anisotropy field Hk*, taken as the minimum of the E(H) curve, and its width ΔH, are not as strongly influenced by the R value, and a value of R > 7 is enough to reach the lowest value. From our measurements we infer that the formerly predicted value of R > 5 needed for a good magnetic and magnetoelastic response of the material must be actually regarded as the lowest limit for this parameter. In fact, we show that the demagnetizing factor N, rather than the length-to-width ratio R, is the parameter that governs the magnetoelastic performance of these strips.