Customized SMA fasteners for industrial applications

One of the first Shape Memory Alloy products on the market were Cryofit couplings for tube connections in fighter jets. Soon, the necessary handling of pre-strained sleeves in liquid nitrogen gave rise to a new alloy system, NiTiNb, which made it possible to have fittings without the “Cryo”. Since their introduction in the 1970s, little has changed for the alloy system, while new fields of applications can be identified even today. In many areas, connections are made using screws, nuts, bolts or similar components to join a wide variety of materials. A factor in choosing the fastener is the shape and properties of the elements to be joined.

One application example of SMA fasteners are sleeves for a force-fitting connection. The preload can be specifically adjusted through appropriate manufacturing and training. In addition, the sleeve can be mechanically machined after activation. This makes it possible to provide the joining element with a thread in order to generate a screw connection for a brittle ceramic part with a metal partner, creating a two-component connection. Or, for example, the connection between screw and nut can be replaced by a bolt and an SMA sleeve. There is no need to cut a special thread to create a preload, instead the sleeve is shrunk onto the bolt by the shape memory effect.

In this work, we present our results on the functionality and application of customized SMA fasteners for industrial applications.