High performance shape memory effect (HP-SME) for new shape memory devices: A diamond-like actuator

Recently, a novel approach was proposed for using shape memory alloys (SMAs) as actuators at higher stress level and temperatures than those conventionally used. This approach is based on a phenomenon named high-performance shape memory effect (HP-SME). It consists in the thermal cycling of stress-induced martensite, so it is suitable for those SMAs that show austenitic phase at room temperature for enabling the development of new shape memory actuators operating at higher working load and temperatures. In this work, a Ni-rich NiTi alloy was selected and a diamond-like geometry device designed, laser machined and tested. Diamond like geometry allowed achieving high displacement recovery and the HP-SME loop increased the working stress level. At room temperature, the austenitic NiTi diamond was axially loaded to induce martensitic state in some specific zone of the element. Then, it was subjected to thermal cycling under a constant load (0.7 N). The SMA element was able to recover a stroke 0.7. mm (about 30% linear elongation) cyclically.