Production Process and Validation of SMA Actuators Based On R-Phase Transformation

The R-phase transformation is interesting for applications that need a small temperature hysteresis and good dynamic behaviour. These applications are e.g. thermostatic valves.

The aim of this paper is to show the production process and validation of different  R-phase sma actuators, starting with a semi finished product and concluding with a finalized R-phase actuator. The focus of this work is, next to the thermomechanical pretreatment, the experimental validation of the produced actuators.

The first part of this paper shows the production process of sma actuators, based on the R-phase transformation. Here, the thermomechanical pretreatment process of different cold worked NiTi alloys and actuator forms is shown. Important parameters of the thermomechanical pretreatment are being varied in order to achieve different characteristics of the R-phase, e.g. annealing temperature and time.

In the second part of the paper selected actuators will be designed and functional characterized. At first the stroke and the force of the selected actuators will be calculated based on a mathematical model. In the next step, the behaviour of the actuators will be analysed and compared with the results of the previous calculation with regard to the transformation temperature, the width of the temperature hysteresis and their stroke.

In the last part of the paper, different fields of application for R-phase actuators will be identified and an evaluation of feasibility is carried out.