Mechanical and Functional Properties of Nickel Titanium Adhesively Bonded Joints

Tuesday, May 21, 2013
OREA Pryamida Hotel
Dr. Marco Alfano , University of Calabria, Arcavacata Rende (CS), Italy
Dr. Luigi Bruno , University of Calabria, Arcavacata Rende (CS), Italy
Dr. Carmine Maletta , University of Calabria, Arcavacata Rende (CS), Italy
Nickel-Titanium shape memory alloys (NiTi) are well known for to their special functional properties, namely shape memory effect (SME) and pseudoelastic effect (PE). Due to these features NiTi alloys are being used in an increasing number of engineering and medical applications, where both PE and SME are exploited for the realization of active and/or tunable devices. However, despite the high scientific and technological interest the use of NiTi alloys is currently limited to high value applications due to the complex material processing and manufacturing with conventional machining processes. Due to these reasons suitable joining techniques should be used to obtain devices and components with complex geometries. From this standpoint, adhesive bonding is a viable alternative to the traditional joining systems for NiTi alloys. Indeed, adhesive bonding is a subject of growing interest in different fields (e.g. automotive, aerospace, biomedical, microelectronics, etc) because of the advantages provided with respect to the traditional joining techniques. For example, it allows to reduce the sources of stress concentration and to extend the fatigue life of the joint.
The focus of this work is the analysis of single lap NiTi/epoxy bonded joints. In particular, a commercial NiTi sheet-metal alloy and a bi-component epoxy adhesive were used for joint fabrication. Both the mechanical and functional properties of the joints were analyzed in terms of strength and shape recovery capabilities. In particular, the measured apparent shear stress was adopted to estimate the strength of the joints. In addition, the thermo-mechanical response of the joints, in terms of thermal and mechanical recovery capabilities have been investigated.Finally, a detailed post-failure analysis of the sample surfaces was carried out using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in order to throw light on the mechanism of adhesion and failure of the joints.