Manufacturing of Adaptive Graphite/Epoxy Structures with Embedded Nitinol Wires

Shape memory alloy (SMA) composites are a class of smart materials in which embedded nitinol wires are used as actuators. Previous research in SMA composites has been limited to wires using one-way shape memory behavior. The objective of this paper is to assess the feasibility of using two-way shape memory (TWSM) training of nitinol, a nickel-titanium SMA, wires for their use as embedded actuators in SMA composites and to investigate the effects of processing conditions on SMA composite quality and actuation ability. Training of the TWSM behavior in nitinol was investigated for a range of initial strains and training cycles. In each case, over 50% of the initial strain can be recovered after training and trained response is generally stable after about 30 training cycles. SMA composite specimens were manufactured using either hot press or autoclave methods and several different types of cure cycles. Voids were found to congregate near the embedded wire surface and can typically be as high as 10% in these regions. Using a staged-cure cycle, the average void content was reduced to 1.3-1.5%. The effect of the composite cure cycle was found to have no significant effect on trained nitinol wire behavior. Finally, the structural behavior of an SMA composite beam was investigated by actuating wires through electrical resistance heating. The tip deflection of a cantilevered beam was found to be primarily composed of SMA transformational effects, however, some localized heating was evident.