Investigations into the use of shape memory alloy for biomimetic propulsion of underwater vehicles

The present study investigated the use of electroactive materials to simulate the swimming muscles of scombrids. The anatomy and physiology of natural muscles were reviewed and the physical and kinematic properties associated with the steady swimming of scombrid species were obtained. These were compared to the physical and mechanical properties of electroactive materials. It was found that the nickel-titanium shape memory alloy (Nitinol) was best suited to simulate the powerful swimming motion of the bonito. The properties of SMA were evaluated under identical testing protocols to natural muscles.; An apparatus was designed and constructed to obtain the characteristics of SMA under isotonic, isometric, and dynamic conditions. All the experiments used 150mum diameter wire. The results showed that the functions and mechanism of SMA were different to natural muscles. Under isometric conditions, the force output of SMA was constant beyond 0.5% strain, regardless of input power. Under isotonic conditions, the recovered strain was proportional to the duration and magnitude of the applied voltage. Under dynamic conditions, the optimum power at 1Hz and 2.3% strain cycle was obtained at the lowest input voltage and the longest duration (1.5V, 100ms duration at 110° offset phase). This resulted in a force of 5.2N, 2.0mJ of work and 8% efficiency. It was found that residual heat from previously applied voltage greatly affected the SMA performance under cyclic applications. No definite evidences of elastic strain effect were found from these experiments.; SMA wire arrangements, based on the morphology of the bonito and data from these experiments, were examined to enhance power or stroke. The longitudinal arrangement enhanced the power output while the vertical wire arrangement increased the stroke without significant loss of force output. The use of SMA in biomimetic swimming application is limited to steady swimming due to its physical constraints. However, from a force production perspective, SMA provided ample power to match or exceed the power of natural muscles.