Thermomechanical Behaviour Of Shape Memory Rivet - In Situ Study

A Ti-rich NiTi shape memory alloy (SMA) was used to join two components through shape memory effect (SME). A recent patent in the field of aeronautics opens interesting perspectives for this kind of joining processes. In the concept study and viability of a rivet with SME, DSC, dilatometric and in-situ XRD during thermomechanical cycles were performed. In situ XRD study during thermomechanical cycle was conducted in a modified dilatometer DIL-805 (Bähr) at the HZG beamline (HEMS/P07-EH3, Petra III, DESY, Hamburg). The force exerted by SME is directly related to the initial texture of the material and the reorientation of the crystallographic variants. The maximum recovery reached by SME was 4.2%. The thermal hysteresis increases after the deformation of the samples. For the proof of concept, a sample of 5x5.5x5.5 mm3 was used, where pull-out tests were performed to simulate the separation of 2 sheets of metal, reaching up a maximum force of 340 N. Also, the actuation force by SME promoted a localized strain-hardening of the joined material, hence improving the contact interface between rivet and joined components.