Papers by Author: Hisaaki Tobushi

Abstract: The SMC belt composed of two kinds of SMAs and SMP was fabricated and the three-way movement and recovery force in bending were investigated. The results obtained can be summarized as follows. (1) The three-way bending movement was achived during heating and cooling based on the characteristics of the SMA tapes and the SMP sheet. (2) The recovery force increased during heating and decreased during cooling. The recovery force was evaluated by the proposed simple model.

Abstract: The torsional deformation properties of a TiNi shape-memory alloy thin strip were investigated. The results are summarized as follows. (1) The martensitic transformation starts at the edge of the thin strip. (2) The fatigue life in pulsating torsion is longer than that in alternating torsion. (3) A simple rotary driving element can be developed by using SMA-thin strip torsion.

Abstract: In order to develop a brain spatula or a brain retractor made of a shape memory alloy (SMA), the bending characteristics of the brain spatula of TiNi SMA made by the precision casting were discussed based on the tensile deformation properties of the existing copper and the TiNi rolled-SMA. The fatigue properties of both materials were also investigated by the plane-bending fatigue test. The results obtained can be summarized as follows. (1) The modulus of elasticity and the yield stress for the cast and rolled SMAs are lower than those for the copper. Therefore, the conventional rolled-SMA spatula and the new cast-SMA spatula can be bent easily compared to the existing copper-brain spatula. (2) With respect to the alternating- and pulsating-plane bending fatigue, the fatigue life of both the copper and the SMAs in the region of low-cycle fatigue is expressed by a power function of the maximum bending strain. The fatigue life of the conventional rolled SMA and the new cast SMA is longer than that of the existing copper. The fatigue life of the new cast and rolled SMAs in the pulsating-plane bending is longer than that in the alternating-plane bending. (3) The fatigue life of the rolled-SMA and the cast SMA for alternating- and pulsating-plane bendings can be expressed by the unified relationship with a power function of the dissipated work.

Abstract: The shape memory composite (SMC) with shape memory alloy (SMA) and shape memory polymer (SMP) was fabricated, and the two-way bending deformation and recovery force were investigated. The results obtained can be summarized as follows. (1) Two kinds of SMA tapes which show the shape memory effect and superelasticity were heat-treated to memorize the round shape, respectively. The shape-memorized round SMA tapes were sandwiched between the SMP sheets, and the SMC belt was fabricated. (2) The two-way bending deformation with an angle of 56 degrees is observed during heating and cooling. (3) If the SMC belt is heated and cooled by keeping the form, recovery force increases during heating and decreases during cooling.

Abstract: The shape-memory composite belt with a TiNi-SMA wire fiber and a polyurethane-SMP sheet matrix was fabricated. The bending actuation characteristics of the belt were investigated by the thermomechanical tests. Residual deflection obtained by cooling under constant maximum deflection is close to the maximum deflection. The residual deflection disappears by heating under no load. Both the rates of shape fixity and shape recovery are close to 100%. Recovery force which appears by heating under constant residual deflection is 93-94% of the maximum force. The model of bending-spring constant of the shape-memory composite belt is proposed and evaluated based on the experimental data.

Abstract: If a shape-memory alloy (SMA) thin strip is applied as an element subjected to torsion, a rotary driving element with a simple mechanism can be developed. The torsion tests were carried out for the SMA thin strip. Torque and recovery torque, both increase in proportion to the angle of twist and temperature. The recoverable strain energy increases in proportion to temperature. The dissipated work decreases slightly with an increase in temperature. A means of opening and closing a door with an element driven by an SMA thin strip is demonstrated.

Abstract: The influence of the strain-holding conditions on shape recovery and secondary-shape forming was investigated. The results obtained are summarized as follows. (1) If strain is held at holding temperature Th = Tg+20K in a short time, irrecoverable strain starts to appear at the holding time th= 0.5h and strain is not recovered at all at th=8h. In the case of Th = Tg+10K, irrecoverable strain appears in a short holding time if holding strain is large and the rate of secondary-shape forming S is 42% at th=8h. (2) If strain of 50% is held at Th = Tg+10K in a long time, strain becomes not to be recovered and S is 93% at th =12h. In the case of Th = Tg, the increasing rate of S increases if th is longer than 40h. If Th is lower than Tg-10K for th= 72h, strain is recovered perfectly by heating and secondary-shape forming does not appear.

Abstract: 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.

Abstract: In this study, we performed the bending fatigue test and investigated the influence of strain ratio on fatigue life in TiNi shape memory thin wire. The pulsating plane bending, alternating plane bending and rotating bending fatigue tests were carried. Additionally, we carried out the observation of the fatigue fracture surface by a scanning electron microscope. The behavior of fatigue crack was investigated. The results obtained are summarized as follows. (1) The martensitic transformation (MT) stress of the superelastic thin wire (SE-NT) is higher than that of the SMA thin wire (SME-NT) and the fatigue life of SE-NT is shorter than that of SME-NT. Maximum bending strain at the fatigue limit is the MT starting strain. (2) The low-cycle fatigue life curve in plane bending for SE-NT is expressed by a power function of maximum strain εmax and the number of cycles to failure Nf. The smaller the strain ratio for the same εmax, the shorter the fatigue life. (3) In both the rotating bending and the plane bending, fatigue cracks nucleate on the surface of the wire and one fatigue crack grows preferentially. The region in which fatigue crack propagated is fan-shaped.

Abstract: The shape-memory composite belt with a TiNi-SMA wire fiber and a polyurethane-SMP sheet matrix was fabricated. The bending actuation characteristics of the belt were investigated by the thermomechanical tests. The results obtained can be summarized as follows. (1) Residual deflection close to the maximum deflection is obtained by cooling under constant maximum deflection. The residual deflection disappears by heating under no load. Both the rate of shape fixity and the rate of shape recovery are close to 100%. (2) Recovery force appears by heating under constant residual deflection. The recovery force is 93-94% of the maximum force. The development of high functionality of shape-memory composite elements is expected by various combinations of SMAs and SMPs.