Quantification of the Effectiveness of Various Adhesives in Holding an SMA Actuator Wire During Joule Heating

Abstract

Shape memory alloy (SMA) actuator wires undergo a large contraction (∼4%) and resistance change (∼7%) in response to a material phase change induced by heating. However, a major impediment to using SMA wires as embedded actuators or sensors in practical applications is the challenge of attaching the small wires to the surrounding structure without adding significant bulk to the system. This work systematically determines the bond strength of different adhesives that could be used to attach small (<100-µm diameter) SMA wires to a structure by exposing the adhesive bond to the thermal and mechanical loading expected during typical embedded SMA applications. Results show that for all adhesives tested, bonding strength is reduced as heating current is increased; however, some two-part epoxies and contact adhesives are still able to maintain 6 MPa of bonding strength to a heated SMA wire. This number can be used to determine how much adhesive is needed to hold different diameter wires for a range of applications.