Experimental Study Of The Static And Dynamic Mechanical Properties Of The Ni-Ti Shape Memory Alloy

Ni-Ti shape memory alloy (SMA) is a new type of intelligent material, with wide application. Nowadays the research on the mechanical properties of Ni-Ti shape memory alloy is concerned widely. The static and dynamic mechanical properties of SMA are deeply discussed and analyzed in this paper based on previous studies.The mechanical properties of SMA at high strain rate is a hot research area nowadays. At the beginning of this paper, the initial stress of martensitic transformation influenced by the strain rate is investigated, and it shows that the initial stress of martensitic transformation increases with the increasing of strain rate, it is the result of the strain rate strengthen effect. Some different conclusions are gained for the results. The internal temperature of SMA rises when SMA is deformed at the high strain rate, thus leading to the increase of the initial stress of martensitic transformation. At the same time, by comparison with the Ni-Ti SMA under static load, the length along strain of Ni-Ti SMA deformed at high strain rate is relatively small. And when the sample deforms at different high strain rates, the residual strain increases with the increasing of the strain rate, but the deformation recovery rate declines. Repetition impact experiments are also done to present the mechanical properties of the Ni-Ti SMA. The results show that with the increasing of the impact time, not only the initial stress for martensitic transformation increases because of successive strengthen effect, but also the deformation recovery rate increases at the same time.About the static mechanical property of Ni-Ti SMA, the main aim of the job is to study the size effect of the Ni-Ti SMA during the compression process. It is significant to study the size effect for the engineering application, but there is rare research on this aspect. The experiment results show the SMA has a significant size effect in static compression. The main conclusions are as follows. First, during the range of the ratio of height to diameter in this paper, as the ratio increases, the specimen shows harden phenomenon in loading stage and soften phenomenon in unloading stage. Second, parent phase and stress-induced martensitic elasticity modulus also increase. Third, the area surrounded by phase transformation super-elasticity curve increases significantly, it indicates that the capability of energy consumption significantly enhances, that is the capacity of seismatic -resistance and disaster-reduction strengthens obviously when the ratio of height to diameter increases. Also the initial stress for the stress-induced martensitic transformation is piecewise, there exits a certain critical ratio of height to diameter, at which the initial stress for the stress-induced martensitic transformation jumps greatly. When the ratio is lower or higher than the critical value the initial stress for the stress-induced martensitic transformation decreases with the increment of the ratio.