Issue 31

M. Merlin et alii, Frattura ed Integrità Strutturale, 31 (2015) 127-137; DOI: 10.3221/IGF-ESIS.31.10 135 Figure 6 : SEM micrographs of the PE/wire interfaces after the strain recovery tests for wires pre-strained at 4%. (a) A and (b) AB samples, respectively; (c) wire functionalised with the silane coupling agent. C ONCLUSIONS ased on the results obtained regarding improved adhesion of NiTi wires embedded in PolyEster (PE) and VinylEster (VE) resins, the following conclusions can be drawn:  Pull-out tests prove the better adhesion between the NiTi wires and the PE resin. The highest interfacial adhesion is obtained by the functionalisation of the surfaces of the wires with a silane coupling agent.  The physical adhesion between the PE resin and both untreated and chemical etched wires is confirmed. In particular, it is demonstrated by electron microscopy analysis that the adhesion is a result of mechanical interactions due to the increased roughness of the native oxide caused by the chemical etching treatments. Conversely, for the functionalised wires chemical adhesion is promoted by the chemical binding of the silane to the resin. Cohesion is also enhanced by the good wettability between the polymeric matrix and the surface of the actuator.  The strain recovery tests indicate early debonding of the wires pre-strained at 5% and 6% for all the PE/wire interfaces considered. In the case of wires pre-strained at 4%, radial shear cracks on the resin surface are observed by SEM for wires both functionalised and etched in a 5%HNO3 + 15%HF water solution. The thermal mismatch between the embedded SMA wire and the surrounding matrix produces high tensile stress at the end of the bonded region that can lead to the matrix cracking in the radial direction. R EFERENCES [1] Otsuka, K., Wayman, C.M., Shape Memory Materials, Cambridge University Press, Cambridge, (1998). [2] Lagoudas, D.C., Tadjbakhsh, I.G., Active flexible rods with embedded SMA fibers, Smart Mater. Struct., 1 (1992) 162-167. B