Characteristics of two-way shape memory TiNi springs driven by electrical current

The electrothermal driving characteristics of the two-way shape memory effect (TWSME) extension TiNi springs, which can extend upon heating and contract upon cooling, were investigated with alternating and direct current. It was found that the response time (the time interval between the start and the end of the springʹs shape change) and the maximum elongation greatly depend on the magnitude of the electrical current. The response time was large for a small electrical current and small for a high one. The maximum elongation increased to a maximum value with increasing current first and then decreased. For practical applications, electrothermal driving working cycles cannot be avoided in repeated use. So the degradation of the TWSME was also investigated by repeated application of the effect. There was a rather strong decay during the first electrothermal cycling. In the latter stage the degradation rate was small.