Shape memory alloys: Property characterization, control development and innovative applications

In recent years, shape memory alloys (SMAs), Nickel-Titanium alloys (Nitinol) in particular, have found increasingly applications, attributed to their unique properties. However, the full potential of SMAs is yet to be demonstrated. This dissertation addresses several Nitinol SMA research topics, including the characterization of the electrical resistance and the damping capacity, the design of a robust controller and its stability proof, and innovative applications that will greatly help to exploit the full potential of SMAs.;The relationship between the electrical resistance (ER) change and the strain of an SMA during a transformation is deterministic, repeatable, yet hysteretic, and this relationship can be used to eliminate the need of a position sensor for some applications. To further understand and utilize this ER/strain relationship, a series of experiments are conducted on a spring biased SMA wire actuator. Based on the testing results, the ER/strain relationship is modeled by neural networks and the curve-fitting technique, and is used in two applications: one for measurement only, and the other for a closed-loop control of the SMA actuator using the ER feedback. A novel analytical model of the ER of an SMA is also developed.;The existing method using superelastic SMAs for vibration control provides damping and self-restoring. However it does not fully take advantage of the large damping capacity of the martensite SMAs. An approach to use the martensite-austenite co-existing (MAC) SMAs is proposed in this dissertation, in order to fully exploit both the large damping of the martensite and the self-restoring of the austenite. To evaluate the effectiveness of the MAC SMAs, a new measurement approach is developed in this dissertation. Moreover, the vibration reduction devices based on the MAC SMA is also developed and used to control a frame model.;It is a challenge to control an SMA actuator precisely, due to the hysteresis of the phase transformation. A sliding mode based robust controller has been developed to control an SMA wire actuator. This dissertation presents the stability proof of the controller based on the Lyapunov's direct method.;To further demonstrate the potential of SMAs, an innovative design of the SMA actuated adaptive exhaust nozzle is proposed in this dissertation. The feasibility and effectiveness of the proposed exhaust nozzle is demonstrated by the testing of a prototype exhaust nozzle model. Also, a feedback controller is designed and implemented to precisely control the nozzle.;Another innovative device based on SMAs is related to a blowout preventor for offshore oil exploration. The conventional hydraulic actuators used in the blowout preventor (BOP) cannot meet the response time requirement as an oil drilling moves to deep water. This fact motivates the research to use SMA actuators in the BOP. Through the research, a prototype of the SMA actuated BOP is developed and fabricated. The prototype features a compact actuation mechanism and an autonomous battery power system. Experiments on the prototype are conducted to evaluate its effectiveness, and testing results show that the SMA actuator can close the BOP's ram much faster than hydraulic actuators.