DEVELOPMENT OF A TESTING INSTALLATION FOR SHAPE-MEMORY-ALLOYS

Abstract

Recent development trends within the industry have revealed an increased interest in intelligent materials. They can offer the functions a shifter or an actuator do, but without using complicated electronics, an important issue with regard to the cost-reduction strategies of the past years. Usually, shape-memory alloys are metallic materials in form of wires, plates or bars. They are characterized by the shape-memory effect which is a reversible thermo-elastic martensitic transformation with two thermal phases: the high-temperature phase (also called the austenitic-phase) and the low-temperature phase (also called martensitic phase). In order to use shape-memory alloys in various applications the exact performances of the material has to be known. This is extremely important especially within the automotive industry where strict quality procedures and regulations are applied. It is maybe of interest to mention that an intended area of application is within the vehicle’s safety systems. In order to be able to deliver performance certificates for each tested sample, the Materials Department of the Technical University of Konstanz has managed to develop within the framework of a research project an installation dedicated for testing shape memory materials. The system is primarily designed to determine very precisely the temperatures of the two transformation phases under mechanical strain as well as to "train" the metal sample. The training (a cyclic thermal and mechanical load) induces in the material a certain shapememory behavior. The testing rig consists of a mechanical tensile strength machine, a thermal installation and a training installation. The most innovative part is the thermal installation which cools down and heats up the metallic samples by using the peltier-effect. The developed testing rig can provide suppliers or manufacturers who intend to use intelligent materials in their products accurate idata about the performances and quality of the shape memory alloys.