Composite magnetostrictive materials for advanced automotive magnetomechanical sensors

In this paper we present the development of a composite magnetostrictive material for automotive applications. The material is based on cobaltferrite,CoO⋅Fe2O3, and contains a small fraction of metallic matrix phase that serves both as a liquid-phasesintering aid during processing and enhances the mechanical properties over those of a simple sinteredferrite ceramic. In addition the metal matrix makes it possible to braze the material, making the assembly of a sensor relatively simple. The material exhibits good sensitivity and should have high corrosion resistance, while at the same time it is low in cost

Detection of Fatigue Crack Propagation in Steel Using Magnetic Measurements

For structural components which are exposed to cyclic stresses, fatigue damage could lead to a catastrophic failure. In nuclear pressure vessel systems where A533B steel is widely used as structural material, cyclic thermal expansions often create a low-cycle fatigue condition. The evaluation of fatigue damage therefore is critically important and nondestructive evaluation of fatigue damage is highly desirable from the viewpoint of both safer and longer operation lifetime

Changes in Magnetization and in Dislocation Arrangements in Cyclically Deformed Iron and Nickel

There are a lot of experimental results concerning the effect of stress, elastic and plastic deformation and dislocation structure on the magnetic properties of ferromagnetic material. Atherton et al. measured stress induced changes in the magnetization of steel pipesl. Schroeder et al. studied domain arrangement in plastically deformed iron single crystals2. Hayashi et al. found that the application of an oscillating magnetic field during tensile testing reduced the flow stress of nickel3. Jiles and Atherton4,5D reported changes in magnetization during one stress cycle as a function of an external magnetic field. They have also reported a theory that describes ferromagnetic hysteresis and the effect of stress on magnetization. This theory is based on the Langevins theory of paramagnetism. Jiles and Atherton4 have experimentally shown that the modified Langevins equation gives the change in magnetization as a function of the applied magnetic field

Nondestructive Evaluation of Fatigue Damage Using Magnetic Measurement Techniques

Fatigue is responsible for most of the mechanically-induced service failures of structural components encountered in industry. Therefore there is a pressing need for the development of nondestructive evaluation (NDE) methods to detect the development of fatigue damage, to monitor its progress and to predict impending failure of components as they come close to the end of their fatigue lives. Magnetic measurements offer promising techniques for these purposes, since the magnetic properties of ferromagnetic materials are sensitive to the microstructural changes caused by fatigue damage [1].</p

Surface Barkhausen Noise Investigations of Stress and Leakage Flux Signals in Line Pipe

Pipelines are subjected to a number of different sources of stress. The principal in-service stress component is due to line pressure, with operating stresses commonly about 60% of the yield strength. Pipelines may also be subjected to considerable bending stresses, particularly when constructed on unstable terrain such as permafrost. Residual stresses may also be present, generally resulting from processing or welding, but more seriously as a consequence of mechanical damage. Anomalously high stress levels, whether residual or applied, may lead to pipeline failure; as a result serious efforts are being made to develop on-line stress detection methods. It is well established that stress is a major factor affecting magnetic properties of ferromagnetic materials, however the effects are complex and have only recently begun to be understood [1,2]. Because of the strong influence of stress on magnetic properties, magnetic NDE techniques are being considered as potential methods for the detection of stress

Evaluation of Residual Stress in 300m Steels Using Magnetization, Barkhausen Effect and X-Ray Diffraction Techniques

This investigation was undertaken to compare the techniques of x-ray diffraction, Barkhausen effect and magnetization measurement as methods of nondestructive evaluation of stress in shot peened 300M steel. In particular we were concerned with the estimation of the level of prevailing applied stress and the compressive overload (plastic deformation) which the samples had been subjected to. The 300M steel used in this study is a constructional material for the landing gears of aircraft, and as these components will eventually experience fatigue failure if not replaced, it was of interest to develop NDE techniques for the assessment of the mechanical condition of landing gears of in-service aircraft