# Application of Virtual Reality for Learning the Material Properties of Shape Memory Alloys
## 1 Introduction  
Shape-memory alloy (SMA), also known as memory metal or smart metal, is an alloy which can fully eliminate the deformation at a lower temperature and restore its original shape when heated. In addition to the shape memory property, SMAs are lightweight and resistant to most chemicals. Some SMAs have the features of super elasticity, damping capacity, and biological compatibility, so they are widely applied in aviation, robotics, and biomedical industries. The SMA products in real life include: self-adjusting dental braces, optical frames, vascular stents, and so on. SMAs can effectively save the cost of repeated shape adjustment and extend the lifetime of a product. The shape memory property was first discovered by [PERSON] and [PERSON] [1] in Au-Cd alloy at the University of Illinois in 1951. A similar property had also been found by [PERSON], [PERSON], and [PERSON] [2]in Ni-Ti alloy at the U.S. Naval Ordrance Laboratory in 1963. Since then, SMAs began to receive the attention of researchers in materials science and related industries. The applications of SMAs grew extensively by the successive finding of the shape memory properties in other alloys, such as Cu-Al-Ni, Fe-Mn-Si, and Cu-Zn-Al [3; 4; 5]. More recent applications of SMAs include space antennas, military aircrafts, civil engineering, and medical treatment [6; 7; 8; 9]. The transition temperature for the transformation of an SMA's material structure can vary with its crystal size, applied stress, thermal cycling times, and other factors [10], among which the proportion of the alloy ingredients has the major influence. Therefore, the applications of the SMA can be determined by controlling the proportion of its ingredients. In addition, the smelling during the manufacture of an SMA can be affected by its constituent elements. Some alloys can be directly smelted in the air, but others may react with oxygen to affect their properties. Taking the Ni-Ti alloy as an example, it must be hot rolled at 800-900 \({}^{\circ}\)C by high-frequency vacuum induction melting, then forged at 700-850 \({}^{\circ}\)C and finally crushed into the sheet or thread shape by processing in a cold room. This process can cause hardening, which is not favorable for many applications. Thus, an annealing process is often required to eliminate the hardening effect. A simplified SMA manufacturing process proposed by [PERSON], [PERSON], and [PERSON] [11] is shown in Figure 1. To create the shape memory property, the SMA is fixed to the designated shape after the annealing process, then heated to about 400-500 \({}^{\circ}\)C while maintaining the shape and finally cooled down. If there is any deformation caused by external force at room temperature, the SMA will return to the memorized shape by simply heating it to the transition temperature. SMAs are an important research field in materials science and engineering. Observing the shaping and restoration processes of an SMA is essential for understanding its basic properties and applications. Supported by the Ministry of Science and Technology (MOST), Taiwan, the objective of this study is to develop a teaching module for the students in the Department of Materials Science and Engineering of a university in North Taiwan to understand the material properties of SMA, conduct the SMA shaping experiment, and become familiar with its real-life applications. The teaching module can also be applied to support the materials science curriculum of other universities in Taiwan. However, it is time-consuming and costly to conduct real shaping experiments using SMA materials, and the waste materials must be disposed of properly to avoid environmental pollution. Additionally, the transformation of crystal structures must be observed using special equipment, such as the transmission electron microscope (TEM) [12] (Figure 2), which is an expensive apparatus and only a few researchers can use it to conduct experiments.