Application of a new ultrasonic sing around system to the study of magnetoelastic effects in some heavy rare earths

The development of a new ultrasonic sing around system has been described. The equipment has been used to investigate the behaviour of the second order eleastic moduli of single crystal specimens of Gadolinium, Terbium, Dysprosium and Erbium under conditions of varying temperature, pressure and magnetic field .From the results, some indication of the performance of the new system has been obtained. The behaviour of the elastic properties as a function of magnetic field has allowed critical fields to be determined, and the variation of the elastic moduli with pressure have allowed the Grüneisen parameters and third order elastic constants to be calculated. Results have been compared where possible with earlier published findings

Application of the Preisach and Jiles–Atherton models to the simulation of hysteresis in soft magnetic alloys

his article describes the advances in unification of model descriptions of hysteresis in magnetic materials and demonstrates the equivalence of two widely accepted models, the Preisach (PM) and Jiles–Atherton (JA) models. Recently it was shown that starting from general energy relations, the JA equation for a loop branch can be derived from PM. The unified approach is here applied to the interpretation of magnetization measured in nonoriented Si–Fe steels with variable grain size ⟨s⟩, and also in as-cast and annealed Fe amorphous alloys. In the case of NO Fe–Si, the modeling parameter k defined by the volume density of pinning centers is such that k≈A+B/⟨s⟩, where the parameters A and B are related to magnetocrystalline anisotropy and grain texture. The value of k in the amorphous alloys can be used to estimate the microstructural correlation length playing the role of effective grain size in these materials

Evaluation of Low-Cylce Fatigue Damage in Steel Structural Components by a Magnetic Measurement Technique

Fatigue is one of the leading causes of failure in structural components. The development of a viable NDE technique which can detect fatigue damage in its early stages of development, monitor its progress and be capable of predicting the onset of catastrophic failure is very essential. If the damage can be detected at an early stage, corrective measures can be taken either in the form of repairs to, or replacement of, the damaged part

Enhanced differential magnetostrictive response in annealed Terfenol‐D

The field and pressure dependencies of the magnetostriction of Tb0.316Dy0.684Fe1.982 have been measured in a grain‐oriented rod after thermally annealing for 1 day at 850 °C and for 4 days at 950 °C in an argon atmosphere. The results of the heat treatment are a fivefold increase in the strain coefficient d 33(=dλ/dH) and a 100% increase in the maximum strain (λ). There was also an increase in the λ‐vs‐Hhysteresis. Under compressive uniaxial stress there was virtually no bulk change in magnetostrictive strain until the field exceeded a critical value which depended on the applied stress, for instance ∼12 kA/m under a stress of 6 MPa

Detection of Expended Fatigue Life of AISI 4140 Steels from Magnetic Measurements

The objective of this study was to determine how magnetic properties such as coercivity, hysteresis loss and initial susceptibility of AISI 4140 steels depended on the expended fatigue life. If one or more of these magnetic properties was found to be sensitive to fatigue cycling, then it should be possible to devise a magnetic NDE technique based on these results, for monitoring of in-service components subjected to fatigue cycling

Magnetostrictive magnetometer

A magnetometer which employs a rod of magnetostrictive material comprising a ternary alloy of dysprosium, terbium and iron wherein the grains of the material have their common principal axes substantially pointed along the axis of the rod. Means are provided for compressively stressing the rod in order to enhance themagnetostrictive response thereof. A laser source and photosensor are associated with a free end of the rod to function as an external cavity laser sensor. A DC magnetic bias is required for the magnetostrictive rod in order to operate in the sensitive range of the magnetostrictive characteristics of the rod. In a portable implementation of the device, the DC bias is provided by means of permanent magnets, preferably rare earth magnets, in order to provide the high bias fields compatible with high sensitivity of the material in a miniaturized portable device

Search for NDE Methods to Characterize Thermal History and Mechanical Properties of Al-Li Alloys

Aluminum-lithium alloys have attracted the interest of the aerospace industry for some time now since the use of such alloys would reduce the weight of an airframe by roughly ten percent. The production of these alloys, however, requires precise thermal and/or thermomechanical treatments to insure required material properties, such as the yield strength and ductility. On-line monitoring of the state of the material thus seems to be desirable for quality control of these materials. This paper presents results of an investigation of fieldable NDE methods capable of providing information on the state of the material. Eddy current measurements were found to be particularly sensitive to Li in solid solution. Furthermore, it appears that hardness measurements are sensitive to the volume fractions, and probably the morphology, of the various precipitates formed. The results obtained so far (see also [1]) as well as by other authors on different aluminum alloys [2–4], this work will continue with additional results to be reported in future publications

Effects of fatigue-induced changes in microstructure and stress on domain structure and magnetic properties of Fe–C alloys

A study of the effects of microstructural changes on domain structure and magnetic properties as a result of fatigue has been made on Fe–C alloys subjected to either cold work, stress-relief annealing, or heat treatment that produced a ferritic/pearlitic structure. The magnetic properties varied with stress cycling depending on the initial condition of the samples. Variations in coercivity in the initial stage of fatigue were closely related to the changes in dislocation structure. In the intermediate stage of fatigue the observed refinement of domain structures was related to the development of dislocation cell structures and formation of slip bands. In the final stage of fatigue the remanence and maximum permeability decreased dramatically, and this rate of decrease was dependent on the crack propagation rate

Nondestructive Methods for the Determination of Mechanical Properties of Materials

The nondestructive determination of mechanical properties of materials is desirable because of the rising cost of both materials and labor as well as safety concerns. In most alloys, changes in thermal and/or mechanical history results in microstructural changes and consequently different mechanical properties. Thermal or mechanical cycles may result from processing or occur in service. Therefore nondestructive detection of microstructure and mechanical properties would prove useful in all phases of metallurgical use. This paper reports on efforts to determine selected mechanical properties of structural materials by nondestructive means such as electrical, acoustic and magnetic techniques as well as hardness. Various thermal and mechanical conditions have been imposed on aluminum, titanium and ferrous alloys to arrive at a wide range of mechanical properties. It is concluded that the intimate knowledge of the microstructure and environmental effects are essential to select the nondestructive method that is most sensitive to property changes