Experimental Study On Several Multi-Field Coupled Behavior Of Ferromagnetic Materials

Ferromagnetic materials have an immeasurable applied prospect in the field of aerospace industry, microelectromechanical system (MEMS), ultrasonic generating system, etc, and occupy an important place in the novel smart materials, due to their outstanding advantages of magnetic sensitivity and easy machining. However, the nonlinear coupled behavior of ferromagnetic materials under various working conditions such as magnetic field, stress and environment temperature is quite complex, which is critical to the safety and the efficiency of the device. In this dissertation, the experimental study on the crucial material properties, especially the mechanical properties for three kind of ferromagnetic materials, i.e. super-low carbon cast steel, giant magnetostrictive alloys, iron-nickel alloys is carried out with engineering demand taken into account. Furthermore, the static and dynamic behavior of the giant magentostrictive rods under coupled operation conditions is mainly studied.The heat transfer process in the giant magnetostrictive alloys, iron-nickel alloys and super-low carbon cast steel subjected to an applied non-uniform AC or DC electric field is studied by experiment, and it can be find that the effect of non-uniform electric field on the heat conduction is relevant to thermal conductivity of materials. The larger thermal conductivity is the more the material is sensitive to electric field. Then the influence of magnetic field and thermal conductivity on the rate of heat transfer is further discussed; Based on the design of the smart temperature control system, a new mechanical-magnetic-thermal coupled testing system is developed by combining with the existing mechanical-magnetic coupled testing system. With aid of this new system, the static and dynamic magnetoelastic response of giant magnetostrictive alloy rods under magnetic-elastic-thermal coupled operation conditions is firstly measured. The change of Young's modulus for magnetostrictive rods with magnetic field, pre-stress (i.e.ΔE effect) as well as environment temperature is revealed, and the factors influencing the minimum of Young's modulus, i.e. the point for safety working, are also analyzed. Then a set of empirical formula for Young's modulus which is convenient to be used in engineering applications are given with the effect of magnetic-elastic-thermal coupling considered. On the other hand, the changes of both the slopes and area of the minor magnetostriction loops of giant magnetostrictive alloy rods with magnetic excitation (bias and AC amplitude), frequency, pre-stress and environment temperature are investigated. A "drift" with bias field is observed in the high-order natural frequency during the dynamic response process of giant magnetostrictive alloy rods. Furthermore, the "hysteresis" between magnetic excitation and output strain is investigated in detail. The relations between the "hysteresis" and pre-stress, between the "hysteresis" and magnetic excitation frequency, as well as between the "hysteresis" and environment temperature are further discussed, and then the parameters of magnetic excitation frequency minimizing the "hysteresis" are given; For giant magnetostrictive films which have been widely used in MEMS such as micro-valve and micro linear motor, a method of choosing optimal temperature and time during heat treatment process which can dramatically enhance magnetostrictive performance of giant magnetostictive films under low magnetic field is proposed; For iron-nickel alloys which often used in magnetic protection system for shielding the surrounding magnetic field of the magnetic sensitive devices in the feeder system outside Tokamak fusion test reactor, a set of methods for promoting the permeability of iron-nickel alloys as well as significantly improving shielding efficiency are proposed. Moreover, a design for magnetic shielding enclosure is given and the shielding enclosures which satisfy the shielding demand are manufactured.