Effect of Magnetostatic Interactions on Twin Boundary Motion in NiMnGa Magnetic Shape Memory Alloy
We investigated the effect of magnetostatic interactions on the field-induced reorientation of martensite variants in Ni50.0Mn27.5Ga22.5. The reorientation, achieved by sweeping a single Type-II twin boundary along the sample, was triggered by a twinning stress of about 0.1 MPa. However, depending on the initial position of the twin boundary, the magnetic field providing the critical stress varied in the range 832 kA/m. By taking into account the variants sizes and their mutual interactions, we explained the observed dependence of the switching field on the location of the boundary. The resulting match between model predictions and measurements illustrates the fundamental role played by demagnetization effects and magnetostatic interactions in magnetic shape memory effect.
Magnetic Domain Structure and Magnetically-Induced Reorientation in Ni-Mn-Ga Magnetic Shape Memory Alloy
Magnetization process during magnetically induced reorientation and related magnetic domains of cuboid Ni50Mn28.5Ga21.5 single crystal with {100} faces was investigated. Magnetic domains were visualized using magneto-optical indicator. The domains pattern is determined by strong uniaxial magnetic anisotropy of Ni– Mn–Ga martensite. Thanks to magnetically induced reorientation the domains arrangements for all three crystal orientations could be obtained and we showed that the size of domains scales with square root of the thickness and penetrates through whole crystal. Visualization of magnetic domains on all faces of cuboid provides the 3D model of magnetic domains.
Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact
There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.