Optimum Discrete Location of Shape Memory Alloy Wire for Enhanced Actuation of Slender Fixed-Free Beam

Shape memory alloy (SMA) wires are capable of exerting large force and undergoing large recoverable strain. These capabilities render them suitable for being used as actuators. SMA wires are either embedded within the structure, as in a composite Choi et.al. [1], or can be placed discretely Chaudhry et.al. [2]. The advantage of discrete actuation is that, depending upon the offset provided between the structure and the wire, the actuating moment can be controlled. More the offset, higher is the actuating moment. But simultaneously the displacement requirement of the SMA wire increases with increasing offset. Depending on the nonlinear force-displacement characteristics of SMA and the flexural stiffness of the structure, there is an optimum value of the offset for which the maximum actuation of the structure can be achieved for a given input. In this paper large deflection of a cantilever beam actuated through SMA wire with varying offset has been analyzed. The results reveal the existence of an optimum offset yielding more than 100% increment in the end deflection in comparison to the minimum offset position. The value of the optimum offset depends on the flexural stiffness of the beam, SMA wire properties and the input actuation level. Experimental results obtained from beams of different stiffness actuated with a particular SMA wire validate the theoretical prediction.