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" Actuation Training and Its Effects on Actuation Fatigue of Nitinol Shape Memory Wires "
Rocco, Pete A.
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Latin Dissertation
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| Language of Document
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English
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| Record Number
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1107857
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| Doc. No
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TLpq2457979515
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| Main Entry
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Rocco, Pete A.
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| Title & Author
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Actuation Training and Its Effects on Actuation Fatigue of Nitinol Shape Memory Wires\ Rocco, Pete A.
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| College
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The University of Toledo
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| Date
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2019
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| student score
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2019
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| Degree
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M.S.
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| Page No
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65
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| Abstract
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Shape memory alloys (SMAs) possess unique properties which make them a great candidate in many applications. Nitinol is the most famous SMA that have been used widely in aerospace, biomedical, civil, and automotive industries. Shape Memory Effect (SME) is the feature that allows Nitinol to recover large amount of deformation by heating it up above its transformation temperature. In addition to SME, high actuation energy density of the SMAs qualified them to be used as a compact and lightweight actuator in many applications. Generally, actuators undergo repetitive loading-unloading conditions. In case of wire actuators, Nitinol wires can be deformed by the actual loads and then will recover to their original shape by heating them up and this process is repeatable. Heating and cooling the actuators for specific number of cycles under specific level of load prior to the actual application is called training. Training has been used to stabilize the strain recovery of SME NiTi actuators. However, training could also affect the actuation fatigue life and need to be more investigated. In this study in order to evaluate the actuation fatigue life as well as the effect of the training on the fatigue life of the Nitinol wire actuators a setup was built. In this setup, the Nitinol wires were loaded at a constant load, and then were heated up via Joule heating to lift the weights. Then the wires were cooled down to become deactivated and then the cycles continued. The number of cycles to failure, as well the mechanical response, for different types of loading were recorded. The fracture surface of the samples was analyzed using SEM. The results showed that the actuation fatigue life of Nitinol wires decreased linearly in logarithmic scale by increasing the actuation load. Experimenting the trained Nitinol wires showed that the training has the capacity to increase the actuation fatigue life of the Nitinol wires by a factor of 2. However, the effect of training strongly depends on the level of load used for the training procedure and the actuation load in the main application. Evaluating the fracture surfaces revealed that the fracture mechanism in trained samples is different from the ones in not-trained samples. Trained samples showed a more ductile fracture mechanism, while the virgin samples showed a relatively brittle fracture type.
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| Subject
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Mechanical engineering
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