Thermo-elastic response of a NiTi SMA at compression solicitation

Nitinol material exhibit properties as shape memory effect and super-elasticity with new important applications in many fields. Two different NiTi materials with shape memory effect (SME) and super-elasticity (SE) were subject of compression with a 4% degree using Instron equipment to simulate an external force. The initial, fully annealed materials and compressed samples were analyze by dilatation behavior point of view using Linseis L75H dilatometer. The purpose of the experiment is to establish the thermal behavior of two materials, with SME and SE, after a compression force action from linear point of view. The shape memory alloy exhibit a shape transformation domain in 80-120 degrees C range. Materials, the one with SME as full cylinder and the SE one as tube were mechanically put together (no shrink forces applied) and compressed in similar conditions. After the compression test the "composite" material was heated from room temperature until 400 degrees C on dilatometer. All samples (initial, compressed and combined) were heated for more cycles until a stabilization of the temperatures transformation domain was observed. The effect of super-elastic material on exhibiting of shape memory effect under temperature variation during the martensitic domain was also observed. Behavior of martensitic transformation domain was analyzed in order to establish the external effects, like temperature and stress, influence of shape memory effect.