Thermomechanical Behaviour Of Shape Memory Rivet - In Situ Study.


F. M. Braz Fernandesa, E. Camachoa, P.F. Rodriguesa, Norbert Schellb

aCENIMAT / I3N - Departamento Ciência dos Materiais, Universidade Nova de Lisboa / FCT, 2829-516 Caparica, Portugal

bHigh Energy Materials Science, PETRA-III, DESY, Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max Planck-Str. 1,21502, Geesthacht, Germany

A Ti-rich NiTi shape memory alloy (SMA) was used to join two components through shape memory effect (Fig. 1) adapted from the principle presented by a recent patent [1] that opens interesting perspectives in the field of aeronautics. In the concept study and viability of such type of rivet, DSC, dilatometric and in-situ XRD during thermomechanical cycles were performed [2]. In situ XRD study during thermomechanical cycle was conducted in a modified dilatometer DIL-805, Bähr (Fig. 2)) at the HZG beamline (HEMS/P07-EH3, Petra III, DESY, Hamburg) to identify the structural changes following combined thermal and mechanical loading, namely the preferential variants orientation at different steps of the process.

Figure 1 –  (a)Schematic representation of the working principle for the joining method (adapted from [1]). (b) Experimental layout used for the in situ measurements at HEMS (DESY).

Figure 2 – Strain (red curve) and structural evolution (2D contour plot and 3D view) during a thermomechanical cycle comprising (i) heating up to 250ºC (black curve), (ii) 15% compression at room temperature (blue curve) and (iii) two consecutive unconstrained heating/cooling cycles of the material (black curve).