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

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

Shape xity and shape recovery of polyurethane shape-memory polymer foams

Abstract: The thermomechanical properties of polyurethane shape memory polymer (SMP) foams were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam after compressive deformation at high temperature, stress decreases and the deformed shape is xed. Stress decreases markedly in the region of temperature below the glass transition temperature T g during the cooling process. (2) By heating the shape-xed foam under no load, the original shape is recovered. Strain is recovered markedly at the temperature region in the vicinity of T g . (3) The ratio of shape xity is 100 per cent and that of shape recovery 98 per cent. Neither ratio depends on the number of cycles. (4) Recovery stress increases by heating under constraint of the xed shape. Recovery stress is about 80 per cent of the applied maximum stress. Relaxed stress at high temperature is not recovered

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

Shape memory alloy based 3D printed composite actuators withvariable stiffness and large reversible deformation

Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft poly- mer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufac- turing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators

Thermomechanics of shells undergoing phase transition

International audienceThe resultant, two-dimensional thermomechanics of shells undergoing diffusionless, displacive phase transitions of martensitic type of the shell material is developed. In particular, we extend the resultant surface entropy inequality by introducing two temperature fields on the shell base surface: the referential mean temperature and its deviation, with corresponding dual fields: the referential entropy and its deviation. Additionally, several extra surface fields related to the deviation fields are introduced to assure that the resultant surface entropy inequality be direct implication of the entropy inequality of continuum thermomechanics. The corresponding constitutive equations for thermoelastic and thermoviscoelastic shells of differential type are worked out. Within this formulation of shell thermomechanics, we also derive the thermodynamic continuity condition along the curvilinear phase interface and propose the kinetic equation allowing one to determine position and quasistatic motion of the interface relative to the base surface. The theoretical model is illustrated by two axisymmetric numerical examples of stretching and bending of the circular plate undergoing phase transition within the range of small deformations