Toshimi Sakuragi

Thermomechanical Properties of Shape-Memory Alloy and Polymer and Their Composites

The shape memory effect and superelasticity appear in shape memory alloy (SMA). The large amount of strain by more than several hundreds percent can be recovered in shape memory polymer (SMP). The shape recovery and shape fixity can be used in SMP elements. These characteristics of shape memory materials (SMMs) can be applied to intelligent elements in various fields. In order to use these characteristics and design the SMM elements properly, it is important to understand the thermomechanical properties of SMAs and SMPs. The deformation behaviors of SMMs differ depending on the thermomechanical loading conditions. The main factors which affect these properties are strain rate, stress rate, temperature, subloop loading, temperature-controlled condition, strain holding condition and cyclic loading. In the present paper, the thermomechanical properties of TiNi shape memory alloy, polyurethane-shape memory polymer and their composite are discussed.

Superelastic Deformation Properties of TiNi Shape Memory Alloy

The characteristics of energy storage and dissipation in TiNi shape memory alloys were investigated experimentally based on the superelastic properties under various thermomechanical loading conditions. The results obtained can be summarized as follows. (1) The recoverable strain energy increases in proportion to the rise in temperature, but the dissipated work per unit volume depends slightly on temperature. In the case of low strain rates, the recoverable strain energy and dissipated work do not depend on both the strain rate and the temperature-controlled condition. (2) In the case of high strain rates, while the recoverable strain energy decreases and the dissipated work increases in proportion to the rise in strain rate under the temperature-controlled condition, the recoverable strain energy increases and the dissipated work decreases under the temperatureuncontrolled condition.

Rotary Driving Characteristics of a Shape-Memory Alloy Thin Strip Element

In order to develop a rotary driving element with a shape-memory alloy (SMA) thin strip, the torsional deformation property, cyclic deformation property and torsional fatigue property of a TiNi SMA thin strip were investigated. The results obtained can be summarized as follows. (1) During twisting the SMA thin strip, the martensitic transformation appears along the edge of the thin strip and develops toward the central part. The rate of increase in the tensile strain of the edge increases gradually with an increase in angle of twist. (2) Torque increases with an increase in angle of twist. The torsional deformation properties change slightly under cyclic torsion. (3) With respect to the fatigue properties, the number of cycles to failure decreases with an increase in the angle of twist. The fatigue life in pulsating torsion is five times longer than that in alternating torsion at the same angle of twist. (4) The two-way rotary movement of an opening and closing door model was demonstrated. Therefore, a rotary driving element with a small and simple mechanism can be developed by using the SMA thin strip.

Torsional Deformation Properties of Shape-Memory Alloy Thin Strip Element

If a shape-memory alloy (SMA) thin strip is applied to the elements subjected to torsion, a rotary driving element with a simple mechanism can be developed. In order to develop the rotary driving elements with the SMA thin strip, the torsion test, the recovery torque test and the torsion fatigue test were carried out for the TiNi SMA thin strip. The basic characteristics of the SMA thin strip for torsion were obtained. Torque increases in proportion to angle of twist and temperature. Recovery torque increases in proportion to angle of twist and temperature. The recoverable strain energy increases in proportion to temperature, but the dissipated work decreases slightly with an increase in temperature. Fatigue life decreases in proportion to amplitude of twisting angle. The fatigue life of the heat-treated material is longer than that of the as-received material. The fatigue limit of amplitude of twisting angle for the heat-treated material is almost the same as that for the as-received material. In order to develop the rotary driving elements, an opening or closing door driven by the SMA thin strip is demonstrated.