Magneto-resistance, stress effects, and a self-similar expansion model for the magnetization processes in amprphous wires
The outer shell magnetization process was investigated from the point of view of its effects on longitudinal and transverse magnetoresistance (MR), magnetization, and domain structure observations as well as their stress effects for a Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous wire with a diameter of 125 mu m prepared by rapid quenching in rotating water. The unusual behavior of the initial negative slope observed in the longitudinal MR is explained in terms of a realistic domain structure. A self-similar expansion model is proposed to explain the dynamical response of such a structure under applied fields and/or tensile stresses. It is suggested that the zig-zag domains of the outer shell are stabilized by a square closure domain which expands uniformly while maintaining a self-similar shape up to a threshold field of about 20 Oe and then deforms towards the saturation magnetization. However, this domain structure was destroyed or much deformed by a tensile stress along the wire axis of about 170 MPa in the sample. Such a critical stress depends on the diameter, quenching conditions, alloy composition, etc. This behavior and stabilization of the zig-zag domain by the closure domains give a novel mechanism for the magnetization processes which follow the re-entrant reversal, and are thus useful for the understanding of re-entrant reversal phenomena themselves. >
Influence of applied tensile and compressive stress on large Barkhausen and Matteucci effects in amorphous wires
Investigation for establishing a residual stress distribution and domain model for amorphous magnetostrictive alloy wires were carried out. Therefore, voltage pulse generation due to the large Barkhausen jump (e p ) and the Matteucci effect (e p ') was studied as a function of tensile and compressive stress applied in the axial direction. The wires had a composition of Fe 77.5 Si 7.5 B 15 , made by the in-water quenching technique. The amplitude of the voltage pulses (e p and e p ') and domain nucleation field (H*), are found to decrease smoothly to zero at a critical compressive stress of 5 kg/mm2for the as-cast wires. A reduction in the critical stress to 3 kg/mm2is observed after altering the wire diameter from 125 to 95 µm by etching. Tensile stress above 20 kg/mm2was found to increase e p and H*. Squareness ratio (B r /B s ) is observed to be a continous increasing function of applied stress in the range from compressive, zero to tensile stress, being about 0.5 at zero stress. By reducing the diameter by 50% through etching, B r /B s is found to increase by about 20%. The observed results is indicating a gradually varying residual stress such that the core has a stress induced axial anisotropy and the outer layers has an anisotropy perpendicular to the axis, caused by positive magnetostriction.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME