Shape memory alloy (SMA) actuator wires promise substantial size, weight, and potential cost advantages over their solenoid and electric motor counterparts. Designing actuators which fully realize these advantages is hampered by a limited understanding of how interactions between wires and their environment affect cyclic lifetime. For example, many devices use two SMA wires mechanically in parallel but electrically in series. This has practical advantages in simplified electrical routing and thermal lag. However, it complicates modeling in that wires interact both electrically and mechanically.
Here we study the effect of a mismatch in length between two SMA wires in parallel. We perform a series of fatigue experiments to show that mismatch of up to 0.75%, at the chosen set of conditions, has no measurable effect on cycle life. We also perform a series of simulations to show how the mechanical interaction between the two parallel wires tends to suppress, rather than amplify, any impact of length mismatch.
