Influence of Ultrasonic-Shot Peening on Bending Fatigue of TiNi Shape Memory Alloy

The fatigue property of shape memory alloy (SMA) is one of the most important subjects in view of evaluating functional characteristics of SMA elements. In the present study，ultrasonic shot peening (USP) was applied to induce compressive residual stress on the surface layer of TiNi SMA tape and the influence of USP on the bending fatigue life was investigated. The fatigue life of USP-treated tape is longer than that of the as-received tape. The fatigui life of the tape USP-treated with high coverage is longer than that with low coverage. The fatigue life of the USP-treated tape increases in proportion to the hardness on the surface of the tape

Evaluation of Precision-Cast TiNi Shape Memory Alloy Brain Spatula

In order to develop a brain spatula made of a shape memory alloy (SMA)， this paper discusses the bending characteristics of a new brain spatula precision-cast in a TiNi SMA. Based on the yield stress and the modulus of elasticity of the copper and the TiNi SMAs， the bending deformation properties of the SMA-brain spatula were estimated by assuming the condition to use the brain spatula as the bending of the strip cantilever. With respect to the SMA-brain spatula for the same length and width as the existing copper one， if the thickness of the conventional rolled-SMA spatula is 1.3 times as large as that of the existing copper-brain spatula，the SMA spatula can hold the same bending rigidity and can be bent by a smaller force than the existing copper one. If the thickness of the new cast-SMA spatula is 1. 2 times as large as that of the existing-copper spatula， the SMA spatula can hold the same bending rigidity and can be bent by the same force as the existing copper one

Bending Fatigue Property in Nitrogen Ion-Implanted TiNi Shape Memory Alloy Tape

A shape memory alloy (SMA) is expected to be applied as intelligent or smart material since it shows the functional characteristics of the shape memory effect and superelasticity. Most SMA elements，with these characteristics， perform cyclic motions. In these cases，the fatigue property of SMA is one of the most important subjects in view of evaluating functional characteristics of SMA elements. the fatigue properties are complex since they depend on stress，strain，temperature and their hysteresis. If SMA is implanted by high energy ions，the thermomechanical properties of the material may change，resulting in long fatigue life. In the present study， the nitrogen ion implantation was applied to modify the surface of a TiNi SMA tape and the influence of implantation treatment on the bending fatigue properties was investigated

TiNi SHAPE MEMORY ALLOY TENSION AT VARIOUS TEMPERATURES - INFRARED IMAGING OF SHAPE MEMORY EFFECT AND PSEUDOELASTICITY

The mechanical characteristics and the infrared imaging of stress-induced martensite transformation developing in TiNi shape memory alloy (SMA) subjected to tension in various conditions with respect to the SMA austenite finish parameter have been presented. Based on the mechanical curves and their related temperature changes it was found that onset of the martensitic transformation appears at the end of the elastic part of the stress-strain curve, since the temperature starts to increase before the knee in the curve. The uniform temperature distribution observed on the specimen surface at this stage confirms that the initial martensite transformation is macroscopi-cally homogeneous. For the shape memory effect behavior the uniform temperature distribution on the specimen surface was observed during the complete process of the SMA loading which means that the transformation process is macroscopically homogeneous. For the shape memory alloy pseudoelasticity behavior bands of higher temperature have been recorded during the specimen loading and bands of lower temperature during its unloading, manifesting localized Luders-like deformation, caused by the transformation process. As the transformation advances, the higher temperature changes have been recorded. Taking advantages from the infrared technique a new results concerning nucleation and development of the martensite forward and reverse transformation have been obtained. Finally, some examples of the SMA new applications due to the SMA shape memory effect have been presented and discussed

Shape recovery and irrecoverable strain control in polyurethane shape-memory polymer

In shape-memory polymers, large strain can be fixed at a low temperature and thereafter recovered at a high temperature. If the shape-memory polymer is held at a high temperature for a long time, the irrecoverable strain can attain a new intermediate shape between the shape under the maximum stress and the primary shape. Irrecoverable strain control can be applied to the fabrication of a shape-memory polymer element with a complex shape in a simple method. In the present study, the influence of the strain-holding conditions on the shape recovery and the irrecoverable strain control in polyurethane shape-memory polymer is investigated by tension test of a film and three-point bending test of a sheet. The higher the shape-holding temperature and the longer the shape-holding time, the higher the irrecoverable strain rate. The equation that expresses the characteristics of the irrecoverable strain control is formulated

Transformation-Induced Creep and Creep Recovery of Shape Memory Alloy

If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection of shape memory alloy elements can change under constant stress. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the shape memory alloy. During loading under constant stress rate, temperature increases due to the stress-induced martensitic transformation. If stress is held constant during the martensitic transformation stage in the loading process, temperature decreases and the condition for the progress of the martensitic transformation is satisfied, resulting in the transformation-induced creep deformation. If stress is held constant during the reverse transformation stage in the unloading process, creep recovery appears due to the reverse transformation. The details for these thermomechanical properties are investigated experimentally for TiNi shape memory alloy, which is most widely used in practical applications. The volume fraction of the martensitic phase increases in proportion to an increase in creep strain