Abstract
The shape memory alloys are special materials which can remember their shape. This phenomenon is known to arise from reversible transformation between two solid phases, martensite and austenite. Some shape memory alloys like NiTi-nol present high damping properties. They are able to dissipate the energy of a mechanical system, resulting from the energy conversion during the phase change processes. This paper focuses on the damping proprieties of pseudo-elastic NiTi wires. In the first part results of tested wires with 0,1 to 0,5mm maximum diameter are shown. The influence of the testing speed is classified as follows: ‘slowspeed’and ‘high speed’defines the slowest and the highest speed which can be realized with the adapted testing machine and varies between 0,1mm/s and 20mm/s. The temperature range of the specimenswas defined from -20°C to +25°C. In this test method it could be shown that with increasing testingspeed for a given specimen the reversible plateau area decreases. In the second part of this paper a new testing machine is presented, which is able to realize test speeds up to 6000 mm/s. This speed can be achieved when the drop weight will contact a bottom plate and the impact is transferredto the sample. Because the weight is dropped the stroke for the sample is measured in two points. The force of this impact will be parallel measured and if the sample will be electrically activated during this test it is also possible to record the electrical tension. The maximum length of the sample is 1m. With this new machine it is able to test pseudo-elastic wires as well as actuatorwires when they are electrically activated. To enlarge the application range for the shape memory alloys it is necessary to study their behavior in the dynamic area. With the new testing facility it is expected to test the damping proprieties of SMA wires. In that case, these results can be followed in finding new applications for shape memory alloys especially in the automotive industry.
Keywords: shape memory alloy, dynamic area, dynamic testing plant