Investigation of Transformation Behaviour of Pseudoelastic NiTi Shape Memory Alloys Under Compressive Loading to Assess the Potential Use in Vibration Damping in Milling Operations

Abstract

Abstract Passive vibration isolation is a key element to achieve precise results in milling processes and to increase tool durability. Damping of vibrations near to the cutting edge is considered highly effective as well as hard to implement because of the limited damping properties of conventional materials in the available space. Particularly long projecting tools tend to be unstable with high vibration amplitudes due to their low material damping and high compliance. Problems may also occur in case the damping values are too low. Besides causing substandard goods, it also results in increased risk of tool fracture, which in turn increases production costs. Current approaches to solving these problems are vibration dampers or special damping tools. These systems are often complex, specially adapted and therefore cost-intensive. NiTi based shape memory alloys (SMA) are known to be suitable damping materials for different applications, e.g. dampening of large circular saws or buildings. Their use depends on the capability to convert large amounts of mechanical energy into thermal energy based on the pseudoelastic effect. Especially the material’s pronounced transformation hysteresis results in an useable damping potential. In order to maximize the usable damping effect in machining tools, SMA-based damping elements have to be integrated into the force flow of different machine components in a preloaded compressive stress state. The purpose of this paper is to demonstrate the stress-strain behavior of damping elements under the influence of various heat treatment parameters and high dynamic loading. For this purpose, the Forschungsgemeinschaft Werkzeuge und Werkstoffe e.V. (FGW) carried out tests on various SMA specimens under approximately static compressive loads in order to determine fundamental parameters influencing the damping capacity. In particular, the influences on the transformation hysteresis were investigated. Depending on the results, tests under high dynamic loads will be carried out by the Laboratory for Machine Tools and Production Engineering (WZL) at the RWTH Aachen University in order to be able to assess subsequent use within the machine tool. Therefore, the most promising pretreatment parameters from the preliminary tests were used to manufacture the specimen. The paper presents the methodology, experiments and results of investigations to evaluate the possible use of pseudoelastic NiTi-based shape memory alloys in vibration damping in milling operations.