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 shape memory fatigue
Single crystal specimens of having compositions close to Ni2MnGa and exhibiting magnetic shape memory effect (MSME) were tested in a rotating magnetic field at a frequency of 5.7 Hz. The applied magnetic field, about 0.7 T was strong enough to induce the MSME. Test of one specimen was discontinued because of the structural failure of the specimens after 0.5 million cycles. Second specimen was tested up to 37 millions cycles. The evolution of the martensitic morphology and crack propagation were observed by optical microscopy. To characterize the magnetic shape memory behavior the simultaneous measurements of the field-induced strain and magnetization as a function of the magnetic field and external load was used. The full MSM effect, about 6% obtained prior the test, decreased to about 3% during the first million cycles. This value stayed then approximately constant up to 37 millions cycles of rotating magnetic field. The magnetic field needed to initiate the MSME increased. The observed behavior is discussed within the framework of observed martensitic band structure in the specimens and the existence of initial cracks and other obstacles for martensitic twin boundary motion.
Relationships Between Food Preferences and Food Acceptance Ratings
A study was conducted to assess relationships between food preference ratings and food acceptability ratings. Acceptability ratings for each of two discriminably different samples of nine food items were obtained using the 9-point hedonic scale. Regression analysis indicated that no linear relationship existed between these ratings and either hedonic or frequency preference ratings of the foods. In addition, the range of acceptability ratings was smaller than the range of corresponding’preference ratings. Panelists’expressed preferences had no effect on their assignment of differential acceptance ratings to different samples of the items. Correlations between preference ratings of laboratory panelists and military field panelists were good, in spite of higher absolute preference ratings assigned by the laboratory panel.