Heat treatment effects on sensitivity and hysteresis loops of magnetoelastic torque transducers

Abstract

Recent experiments have indicated that a torque transducer can be constructed based on local bands of naturally stabilized remanent circumferential magnetization within a hollow steel shaft. A strong coercive force along with the crystalline anisotropy combine to stabilize the circumferential magnetization of the sensing area of the shaft. A torqued shaft has its magnetic axis tilted into a helical orientation, which generates an axial field signal linearly proportional to the applied torque that can be sensed externally to the shaft. Our research has shown that the transducer function can be improved by appropriate sequential heat treatments in a helium atmosphere. Subsequent to all heat treatment steps, the test shafts were measured to determine the changes in axial and circumferential magnetic hysteresis properties and to track the development of the magnetic sensing area to applied torque ͑sensitivity͒. Although little change was produced in the originally narrow axial hysteresis loops, a 10%-20% decrease was observed in both axial coercive force and remanent magnetization, and correspondingly, a 50% increase was observed in sensitivity, accompanied by a higher linear saturation limit. Additionally, the heat treatment cycle significantly widened the originally broad circumferential hysteresis loops, resulting in a substantial increase in circumferential coercive force, which improves the stability of the sensory region.

Low temperature heat capacity of the high-pressure-phase of SiO2, coesite, and calculation of theα-quartz-to-coesite equilibrium boundary

“…In order to compare the calculated phase boundary with those from direct experimental determinations, figure 6 also includes several representative boundaries of α-quartz-coesite determined by high-pressure and high-temperature experiments. (13)(14)(15) As shown in the figure, the calculated boundary is consistent with that of Bose and Ganguly. (15) Because the position of the calculated boundary is sensitive to the data used, and the error of the enthalpy is relatively large, the uncertainty in pressure of the calculated boundary is about ±0.3 GPa.…”

“…Calculated phase boundary of (α-quartz, coesite). B-E, Boyd and England; (13) B-B, Bohlen and Boettcher; (14) B-G, Bose and Ganguly. (15) quartz-to-coesite transition of (3.40 ± 0.56) kJ · mol −1 at T = 298.15 K by Akaogi et al (5) is also used in the calculation.…”

Fossilized high pressure from the Earth's deep interior: The coesite-in-diamond barometer

“…Although coesite-and diamond-bearing rocks (9-12) undoubtedly have a high-pressure origin, individually, coesite and diamond cover a wide P-T domain of stability (13,14) that precludes their use as a precise and accurate geobarometer, because they give only a lower bound on the pressure of formation. In many cases, much higher pressures are suggested (15) based on mineral equilibria data, including SiO 2 solubility in garnets (16) or K 2 O solubility in clinopyroxenes (17).…”

The effects of heat treatment on the magnetic behavior of ring-type magnetoelastic torque sensors

“…The physical property changes observed to accompany the heat treatment carried out in this work can be successfully explained by a two-dimensional (axial and circumferential) model already described in an earlier publication by the authors and well-documented in the literature [5,7]. The larger sensitivity values observed subsequent to heat treatment for a given applied shearing stress correspond to larger rotations of the magnetization vector in order to achieve a minimum in the total energy per unit volume.…”

“…This stability is partially provided by the associated tensile "hoop" stress in the sensory ring [4], but a large circumferential coercive force in the material of the ring is also essential to the successful performance and durability of the transducer, as has been previously shown in the literature [5]. While the coercive force is a single-valued function of the chemical, metallurgical, structural, and geometric properties of a sample [6], we herein describe a method of enhancing the circumferential coercive force through a series of heat treatments in one of the major alloys used for the sensory ring.…”