High performance shape memory effect mini device realized by femtosecond laser cutting

After the discovery of the High-Performance Shape Memory Effect (HP SME) [1] the heating/cooling cycling of the stress induced martensite (SIM) opens to manufacturing of a new class of shape memory alloy (SMA) smart actuators with extremely high recovery stresses values (up to 1 GPa). Basically, when the martensite is stress induced, from austenitic state, the material itself becomes an actuator that can be activated by heating/cooling cycles. Again, if the "SIM is localized" into an austenite matrix, you have a "localized actuator" that can generate a force to the entire device. The latter condition opens new perspectives in the field of meso and micro scale smart actuators. In this work a commercial superelastic NiTinol thin sheet was used for realizing a diamond-like HP SME element. The diamond-like shape was chosen for assuring localization of SIM in certain parts of the material. Femtosecond wave laser source was used for vaporization cutting of the samples (with truss about 100 microns wide). Stress-strain properties were measured in the 20-100 °C range and thermal loops under constant load of the HPSME diamond actuators were performed. Fatigue tests of actuators under HP SME confirm lifetime performances according to the traditional superelastic material ones. Finally, a numerical investigation was performed to predict the diamond-like response under operating HP SME, observed experimentally, and to analyze the behavior under different loading conditions and geometries for an optimal design.