EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Since the first appearance of shape memory alloys in the early 60s, the interest in shape memory applications has been constantly increasing.Shape memory alloys based on Nickel and Titanium provide the best combination of material properties for many commercial applications in the medical and industrial field. One of the first successful applications of NiTi alloys have been clamping sleeves for coupling and fastening.For the functionality of these clamping elements, different effects are used, both the thermal shape memory effect as well as the mechanical shape memory effect. Such elements are usually used for frictional joints. They are detachable and scalable. Also, material similarity is not a requirement. However, the complexity of the shrinkage process and the use of complex clamping element geometries and manufacturing costs may be challenging. This work gives an overview of shape memory alloy basics, particularly the martensitic and austenitic phase transformation characteristics. Also, the extraordinary stress-strain behavior of these alloys is shown. Furthermore, different joining concepts will be evaluated with pointing out the advantages of a NiTi clamping element based on the mechanical shape memory effect. Exemplarily, the influence of sleeve length and application temperature to the pull-off forces will be shown for mechanical shape memory effect clamping sleeves based on a pull-off test. A typical medical device application for this clamping sleeve will be presented in the orthodontics field in terms of a re-adjustable oral device. In addition, new perspectives of these joining principles will be underlined. Advances in manufacturing capabilities for making continuously rolled strips and optimized material properties enable many new possibilities.