Characteristics Of Shape Memory Alloy Research Articles

Three-dimensional model for solids undergoing stress-induced phase transformations

A phenomenological model describing the mechanical behavior of polycrystalline solids undergoing stress-induced phase transformations is presented in the setting of three-dimensional (3-D) media. The model, which is developed within the framework of Generalized Standard Materials, has been built on a few basic assumptions, namely an admissibility condition for thermodynamic forces and a locking constraint for phase transformations. The macroscopic kinematic consequences of stress-induced phase transformations are described by a tensor named transformation strain. Numerical integrations of the resulting set of equations show that many features of shape memory alloys obtained by certain authors for CuAlZnMn alloys under non-proportional loadings can be qualitatively described by the present model.

The Effect of Stress Ageing on the Properties of Shape Memory Alloys

The performance characteristics of shape memory alloys operating in an overtemperature shut-off valve at a temperature of 95 o C for up to 2000 hours are presented. Alloys of NiTi, Cu-Al-Ni and Cu-Zn-Al have been characterized under these ageing conditions. The effect of altering the processing parameters, viz solution treatment temperature, quenching technique and training procedure were examined. All alloys show degradation of the memory behaviour but results are presented which demonstrate that improvements in degradation can arise by altering the solution treatment temperature and training procedure

A multi-dimensional constitutive model for shape memory alloys

This paper presents a multi-dimensional thermomechanical constitutive model for shape memory alloys (SMAs). This constitutive relation is based upon a combination of both micromechanics and macromechanics. The martensite fraction is introduced as a variable in this model to reflect the martensitic transformation that determines the unique characteristics of shape memory alloys. This constitutive relation can be used to study the complex behavior associated with 2-D and 3-D SMA structures. A simple example using this constitutive model is also presented, which reveals a new and interesting phenomenon of 3-D SMA structures.

Mechanical characteristics of the shape memory alloy driver focusing on quick replacement technology for fusion devices

Mechanical characteristics of shape memory alloy (SMA) driver have been studied. The SMA changes from a deformed form to its original form by a phase transformation from a martensite structure to an austenite structure with rising temperature. This large recovery force is used for a compact driving mechanism. The material of SMA used in this experiment is TiNi (50 at%) alloy. The recovery force is formularized to fit well to experimental curves. The shapes of SMA driver are a cylindrical tube, a ring and a pipe type. The cylindrical tube type is able to be used as the coupler for connection between the core elements with vacuum tight. The ring and a pipe type are able to be used as the driver of retainer of the large compact gate valve.

The Dynamics of Helical Shape Memory Actuators

This paper presents an experimental and theoretical study of the dynamic and thermal characteristics of SHAPE MEMORY ALLOY (SMA) actuators. The actua tors are made of a NIckel-TItanium (NITINOL) wires formed in the shape of helical coils that are capable of generating large deflections when subjected to low voltage excitations. The deflections produced are accompanied by significant forces resulting from the unique phase transformation of the NITINOL alloy as it is heated past its transition temperature.