Materials Science Forum Vol. 856

Abstract: This study reports on effects of tapered metering pins on a magnetorheological (MR) fluid subjected to shock loading. Using four types of tapered metering pins, we conducted drop impact tests and qualitative analysis of effects of tapered pins on an MR fluid with a magnetic field applied around an orifice area. We measured the displacement of a piston and calculated velocity and acceleration from the measured displacement. The four different tapered pins changed a piston stroke to bring the impacting mass to rest. The results indicated that the shape of the pins has an effect on the entire process of shock absorption, whereas magnetic field strength has an effect on the post-peak behavior only. These results show that a tapered metering pin has applicability to a shock absorber using an MR fluid.

Abstract: Behaviors of both micrometer-size nonmagnetic abrasive particles and micrometer-size magnetic particles in a magnetic fluid are investigated by using the discrete particle method which is based on the simplified Stokes dynamics. Sheet-like clusters of nonmagnetic particles and sheet-like clusters of magnetic particles alternately appear one after another in the axis direction when the flow velocity is small.

Abstract: Responses of a magnetic fluid interface adsorbed on a small permanent magnet in water container subjected to an alternating magnetic field were studied with a high-speed video camera system. The directions of the external alternating magnetic field were parallel and anti-parallel to that of the permanent magnet. It was found that the interface of water-magnetic fluid responds to the external alternating magnetic field in elongation and contraction with Rosensweig instability at the interface. Frequency characteristics of the interface response of water-magnetic fluid system subjected to alternating magnetic field were revealed over a wide frequency band experimentally.

Abstract: A magnetic-fluid tuned liquid column damper (MF-TLCD) is a semi-active damper that has a magnetic fluid column in U-pipe as an additional vibration system. An MF-TLCD can suppress structural vibrations at a wide frequency range by applying a magnetic field. In this study, we performed vibration experiments for three types of U-pipes and assessed the effects on MF-TLCD performance caused by different damping forces on the liquid column.

Abstract: Response characteristics in the opening and closing operations of the micro magnetic fluid diaphragm mechanism by the alternating magnetic field are described. The micro magnetic fluid diaphragm mechanism was composed of a ring shaped permanent magnet and kerosene-based magnetic fluid. The driving principle of micro magnetic fluid device was based on the surface phenomena of magnetic fluid adsorbed on a permanent magnet. The opening and shutting time of diaphragm mechanism in the alternating magnetic field was measured by high-speed video camera system. The details of magnetic fluid surface response in the opening and closing operations of magnetic fluid hole were revealed experimentally.

Abstract: Fault current limiters (FCL) require superconducting (SC) materials which can provide a definite rate of response to a fault event resulting in the SC – normal state reversible transition. The main characteristics determined the material suitability are the critical current density, j_c, thermal conductivity and capacity which are strongly determined by manufacturing technology, in particular, of MgB₂. In the paper we estimate the j_c of bulk MgB₂ samples by the vibrating magnetometer and inductive, contactless transformer, method using ring samples. The bulk MgB₂ samples were produced under 30 MPa (hot pressing) and 2 GPa (quasihydrostatic pressing) at 800-1050 ^оС from different initial ingredients (Mg and B or MgB₂ with and without additions). It is shown that the technology process and initial ingredients strongly influence the distribution of boron-and oxygen-enriched nanosized inhomogenities in MgB₂ matrix, connectivity between SC grains, material porosity and, as result, the SC properties. The transformer method gives the j_c in the range from 1.6·10⁴ up to 6.3·10⁴ A/cm² at about 4 K while using magnetometer measurements the j_c is estimated from 2.24·10⁵ up to 5.1·10⁵ A/cm² at 10 K in self-magnetic fields. The contradictions in the j_c estimated by different methods can be explained by instability of the SC state of MgB₂, caused by variation of the applied magnetic field. Using the transformer method AC losses per a cycle before quenching for the best materials were estimated around 0.75-1 J/cm³, while the power of losses was about 200 W. The FCL model with rings cut out from SC MgB₂ materials prepared using various technologies demonstrated that MgB₂ is a promising material for application in inductive FCLs.

Abstract: The paper is devoted to testing of a brushless exciter intended for a 1 MVA high-temperature superconductive (HTSC) synchronous generator. It was decided to make a ambient-temperature version on the 1-st stage with a latter transaction to a cryogenically-cooled version. The exciter incorporates a number of nanomaterials: rare-earth Nd-Fe-B magnets and magnetic cores, manufactured of amorphous alloy tape.

Abstract: The paper describes results of testing of magnetic loss and saturation of magnetic system for superconductive electrical devices, manufactured of AMAG 225 AMAG 170 amorphous alloys produced by the Open Joint-Stock Company “Mstator”. Note that annealing of the cores was not carried out, since previous experience shows that annealing process makes steel crispy, and, furthermore, in case of thermal cycling, which occurs in cryogenic machines and devices, the destructive process is accelerating and results in the total destruction of amorphous tape. Manufacturing of the cores of different superconductive electrical devices requires testing with 2NSR, 5BDSR amorphous alloys, AMAG 200 nanocrystalline tape, (unannealed and annealed). The results of these investigations were published previously.

Abstract: New applications of nanoscale powders of Si, SiO₂ and BaTiO_3, etc. have been developed for vacuum sealing, reflectors in LED devices and thermally cooling membranes from metal surface. The optical transparency and good vacuum sealing were formed in baking temperatures as low as 150°C, 1hr by using nanoscale powders of these materials. We show the several applications of capacitors with the material thicknesses between 1 and 10 μm, and show the thermally cooling enhancements in several metals of Al, Fe and stainless steel up to 2.5deg/s in the metal temperature range higher than 50°C.