Takashi Hachisuka

Influence of strain rate on superelastic properties of TiNi shape memory alloy

The influence of strain rate on the superelastic properties of TiNi shape memory alloy was investigated. In the case of strain rate higher than 10%/min, the martensitic transformation stress and the dissipated work increased with an increase in strain rate but the reverse transformation stress and the strain energy decreased. In the case of strain rate lower than 2%/min, these characteristic values associated with the martensitic transformation did not depend on strain rate.

Rotating-bending fatigue of a TiNi shape-memory alloy wire

The rotating-bending fatigue of a TiNi shape-memory alloy wire was investigated. The influence of air and water atmospheres, temperature, strain amplitude and rotational speed on the fatigue life was discussed. In the case of the strain amplitude due to the rhombohedral-phase transformation, the fatigue life lengthened above 107 cycles. In the case of the strain amplitude due to the martensitic transformation, the fatigue life in air was shorter than that in water.

Thermomechanical properties due to martensitic and R-phase transformations of TiNi shape memory alloy subjected to cyclic loadings

The thermomechanical properties of the shape memory effect and superelasticity due to the martensitic transformation and the R-phase transformation of a TiNi shape memory alloy were investigated experimentally. The transformation line, recovery stress and fatigue property due to both transformations were discussed for cyclic deformation. The thermomechanical properties due to the R-phase transformation were excellent for deformation with high cycles.

Deformation Properties of TiNi Shape Memory Alloy Subjected to Variations in Strain and Temperature.

The subloop behavior of TiNi shape memory alloy subjected to variations in strain and temperature was investigated experimentally through various kinds of loading-unloading and heating-cooling processes. The results are summarized as follows. (1) During the thermomechanical cycling, the martensitic transformation (MT) stress decreases but the MT temperature increases with increasing the number of cycles. In the case of variations in strain and temperature during the loading-unloading and heating-cooling processes, if strain is in the MT region, the MT stress and the MT temperature are almost constant not depending on strain. (2) If the material is used after the mechanical training of 20 cycles in practical applications, the MT stress and the MT temperature can be treated as almost constant.

Cyclic deformation properties of TiNi shape memory alloy under thermomechanical loading

The thermomechanical properties of shape memory effect and superelasticity due to the martensitic transformation and the R-phase transformation of TiNi shape memory alloy were investigated experimentally. The transformation stress, transformation line and fatigue property due to both transformations were discussed for cyclic deformation. The thermomechanical properties due to the R-phase transformation were excellent for deformation with high cycles.