A simplified analytical model to simulate constrained recovery mechanisms of SMA rings exhibiting two-way shape memory effect

Shape memory alloys (SMAs) with shape recovery capabilities have been investigated recently at the European Organization for Nuclear Research (CERN) to develop ring-shaped pipe couplers for vacuum applications. SMA couplers exploit the One-Way and Two-Way Shape Memory Effect (OW- and TW-SME) to mount/dismount vacuum pipe, by temperature variations. A phenomenological analytical model based on simplified elastic-plastic axisymmetric theory has been developed and implemented in a commercial software to simulate biaxial constrained recovery mechanisms in thick-walled SMA rings with rectangular cross section. The model is particularly useful to predict the stress field in the SMA coupler as well as the contact pressure developed at the SMA ring/pipe interface during thermal mounting/dismounting operations, knowing their initial geometry and material properties. The predictions of the analytical model have been compared with experimental data and Finite Element (FE) simulations based on a user-defined material routine.