Study On Properties Of Magnetically Controlled Shape Memory Alloy And Its Application For Actuators

Magnetically controlled shape memory alloy (MSMA) is a new functional material which is found in recent years. MSMA has characteristics of large deformation rate and high response frequency in the martensite state. It is an important potential material for the next generation of intelligent actuators and sensors. So far, researches on MSMA are mainly concentrated on its properties under the changes of microstructure, temperature and components, while few researches are done on its application. The main contribution of this dissertation is the deep experimental study of an MSMA actuator.At first, the deform principle and the preferred orientation process of MSMA are studied, the microstructure and physical characteristics of the MSMA sample have been analyzed. According to the theory of phase interface friction, the expression of the thermodynamics parameter of MSMA has been deduced. The friction loss on the interface of different samples in the course of the martensite phase transformation has been calculated. The results show that the loss energy in the movement of the phase interface only occupies a little part of the latent heat of phase transformation. The larger the latent heat of phase transformation is, the less the friction loss of phase interface movement will be. By the analysis, just the interface friction during the phase transformation causes the thermal hysteresis of phase transformation.Because the relationships of temperature, magnetic field, pre-press and deformation are nonlinear, it is difficult to analyze quantitavely its characteristics. So an experimental device for study of the MSMA was designed and built. The characteristics of MSMA under different temperature, magnetic field and pre-press were studied. A measurement method for MSMA relative permeability was advanced, too. In addition the method of recovery deformation was discussed and the dynamic variation rules of recovery deform by spring was studied, the nonlinear relationship of magnetic permeability of MSMA has been studied. Neglecting the temperature change, the mathematic model of the system has been established.Although the deformation rate of MSMA is high, it is difficult to realize the linear actuator with large pace. The first reason is that the production cost is high because it needs a mounts of material. The second is that the exciting power is large with the large bulk. By utilizing bionic inchworm principle, a MSMA linear actuator has been developed successfully, the prototype and the control system have been designed, which has been realized bidirectional movement with large pace. Relationships of exciting current, displacement and power frequency are also studied.At last, using permanent magnetic generates bias magnetic field, a differential control strategy was put forward which can decrease exciting power, eliminate temperature influence and improve control precision. The designed of prototype and the analysis of magnetic field have been finished, which verified the feasibility of this method.