Fundamental Resarch on Impact Energy absorbing Actuators of Shape Memory Alloys

本文利用形状记忆合金（SMA）的形状记忆效应和超弹性，研究了三种形状记忆合金（SMA）的冲击吸能驱动器：温度敏感型SMA、磁性SMA（Ni2MnGa）和应力敏感型SMA（FeNiSi）。在传感器预测汽车碰撞时，利用形状记忆合金（SMA）的形状记忆效应和超弹性，对SMA致动器施加磁场，以吸收碰撞能量。首先，本文从理论和实验两方面研究了SMA材料的碰撞响应、磁场产生方式以及温度对SMA致动器碰撞响应的影响。其次，提出了冲击能量吸收执行器的概念。为了提高响应速度，除了温度之外，还使用磁场和应力来诱导SMA中的相变。因此，传统形状记忆合金无法实现的冲击能量吸收驱动器成为可能。本研究的最后，对磁性形状记忆合金和应力敏感形状记忆合金的静态特性进行了研究。静态特性包括磁性形状记忆合金相变临界磁场强度与温度的关系，应力敏感形状记忆合金相变临界应力与温度的关系。实验中通过电容器施加大电流，使SMA驱动器的响应时间缩短到10ms左右。

In this research, impact energy absorbing actuators of shape memory alloys (SMA) was studied by using both the shape memory effect and superelasticity of SMA.Three types of SMAs, temperature-sensitive SMA, magnetic SMA (Ni2MnGa) and stress-sensitive SMA (FeNiSi), were used. When collision of cars is predicted by sensors, magnetic field is applied to the SMA actuators so that the collision energy can be absorbed by the shape memory effect and superelasticity of SMA actuators.First, the relationship between impact force and absorbed energy, impact response of SMA material, the method of magnetic field generation and influence of temperature are clarified theoretically and experimentally in this research. Next the concept of impact energy absorbing actuator was proposed. In order to increase the response speed, magnetic field and stress were also used to induce phase transition in SMAs in addition to temperature. Hence, the possibility of impact energy absorbing SMA actuators, which were impossible for traditional SMAs, has been shown.In the last of this research project, the static characteristics of magnetic SMA and stress-sensitive SMA were investigated. The static characteristics include the relationship between the critical magnetic field strength and temperature for phase transition of magnetic SMA, and the relationship between critical stress and temperature of stress-sensitive SMA.Based on the static characteristics, impact response test was performed. By applying large electric current with capacitors, the response time of SMA actuators was decreased to about 10ms in the experiment.