Theses and Dissertations at Montana State University (MSU)
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Item Distributed control of a segmented and shape memory alloy actuated biologically inspired robot(Montana State University - Bozeman, College of Engineering, 2005) Schubert, Oliver John; Chairperson, Graduate Committee: Hongwei GaoToday's robots are limited in mobility, flexibility, and scalability. Their rigid bodies prevent operation in many environments and often restrict movement to a twodimensional space. Most robotic vehicles cannot operate in a confined space or unstructured terrain and are incapable of climbing surfaces a fraction of their size. Their stiff bodies significantly reduce their performance and present a major weakness. The nextgeneration robot must be highly adaptable, flexible and capable of operating in many environments. A possible solution is to create a flexible and scalable segmented snake robot incorporating smart material for actuation. This project, in partnership with The Idaho National Laboratories (INL), plans to implement a snakeeelworm (SEW) design to meet the needs of the nextgeneration robot as a part the Visual Inspection Platform for Exploration and Research (VIPER) project. Snakeeelworm platforms have the dexterity to traverse highly unstructured amphibious and landbased terrain. To create this flexible and scalable structure this work proposes the implementation of Shape Memory Alloy (SMA) as the actuation device under distributed control of several embedded computer modules. This project found that a mechanical prototype can achieve snakelike locomotion while using SMAs under distributed control. A threesegment SMAactuated structure moves in an inchworm motion under a distributed control network consisting of several PowerPC single board computers (SBC).Item Thermomechanical training and characterization of Ni-Ti-Hf and Ni-Ti-Hf-Cu high termperature shape memeory alloys(Montana State University - Bozeman, College of Engineering, 2011) Denowh, Chantz Michael; Chairperson, Graduate Committee: David A. MillerNickel-Titanium (NiTi) is the most commonly used Shape Memory Alloy (SMA) for actuator applications. Typical SMA actuators use changes in temperature to initiate solid to solid phase transformations resulting in macroscopic material deformations; though NiTi is limited to temperature changes below 100°C. This eliminates high temperature applications of NiTi actuators. To expand the design window of SMAs, many high temperature NiTi based SMAs have been developed by adding ternary elements to the NiTi matrix. The additions result in degradation of the shape memory behaviors and their usefulness as actuators is still in question. The purpose of this research is to characterize and train two recently developed high temperature SMAs, NiTi 29.7Hf 20 and NiCu 5Ti 29.7Hf 20, to determine their effectiveness as linear actuators. Shape memory effect (SME) and superelastic tests were used to characterize the materials behavior followed by thermomechanical training at a constant stress. The SME test resulted in no martensite detwinning plateau and a non-linear stress-strain curve implying the simultaneous occurrence of slip and martensite reorientation. The superelastic tests also show an austenitic yield stress above 600 MPa. Thermomechanical training resulted in small amounts of plastic strain growth, and the development of two-way shape memory (TWSM). The TWSM results were fitted using the Bo & Lagoudas model, and is capable of predicting the actuation strains at other stresses. The results support the conclusion that hafnium distorts martensite slip planes, and (Ti,Hf) 2Ni and (Ti,Hf) 3Ni 4 precipitates form during aging and annealing. The distorted slip planes cause slip and martensite reorientation to occur simultaneously. This develops a strong stress field during training within the first few cycles. The stress field develops TWSM, but limits further plastic growth and TWSM development. The precipitate formation increases material strength, as seen in the superelastic loading, but also embrittles the material. Thermomechanical training of an annealed specimen resulted in a brittle failure after several thermal cycles due to the growth of particulate size during annealing. The two alloys are ideally suited for high temperature actuators. TWSM was trained into the material and the transformation temperatures are higher than that of NiTi, but low enough to avoid annealing and problematic creep temperatures.Item Thermomechanical training and characterization of shape memory alloy axial actuators(Montana State University - Bozeman, College of Engineering, 2010) Becker, Marcus Patrick; Chairperson, Graduate Committee: David A. MillerAlthough considerable work has been performed to understand the key mechanisms of Shape Memory Alloy (SMA) behavior, little of this work follows a standard testing protocol, quantifies a conditioning methodology, or develops data appropriate for design of SMA actuators. One major issue that limits the ability of the material from being used directly as an actuator is the large, non-recoverable strains likely to accrue in the material during each training cycle, mechanical or thermal. When mechanical or thermal cycling is performed, a hysteresis curve develops and reaches a steady state strain recovery response. At the point where permanent plastic strain stops growing, or saturates, the SMA has been successfully trained. The focus of this work is oriented toward SMAs in general, but all testing and experimentation was carried out on Nickel-Titanium (NiTi) alloys. The experimentation and testing was performed on a combination of 4 different sizes and 3 different NiTi alloy compositions. Thermomechanical testing was performed to determine critical values to describe the stress-temperature phase space of the materials and parameters to model the applied stress and transformation strain relationship. All material size and alloy combinations were tested in the as-received, or as-machined, and fully annealed state. The results of the training and actuation strain characterization process developed in this work shows that the samples that experienced Transformation Induced Plasticity (TRIP), greater than 2% during the training process and exhibit Two-Way Shape Memory (TWSM) after being fully trained, share a very similar applied stress versus transformation strain curve. This curve is modeled by the Back Stress formulation derived from the Gibbs Free Energy constitutive model by Bo & Lagoudas. The design space created by the Back Stress formulation, recrystallization temperature, and training stress allows SMA materials to be characterized and implemented as stable 1-D actuators. This research formalized a thermomechanical training and characterization method for uniaxial SMA actuators by addressing the interaction between processing, recoverable and non-recoverable deformation. Using various sizes and NiTi alloy combinations, this research develops and evaluates a method to train and characterize a diverse range of SMAs through a set of thermomechanical and physical property measurements.