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Carbon fiber reinforced plastic (CFRP) composites have extensive value in the aerospace, defense, sporting goods, and high performance automobile industries. These composites have huge benefits including high strength to weight ratios and the ability to tailor their properties. A significant issue with carbon fiber composites is the potential for catastrophic fatigue failure. To better understand this fatigue, there is first a huge push to measure strain accurately and in-situ to monitor carbon fiber composites. In this paper, piezoresistive nickel nanostrand (NiNs) nanocomposites were embedded in between layers of carbon fiber composite for real time, in situ strain monitoring. Several different embedding methods have been investigated. These include the direct embedding of a patch of dry NiNs and the embedding of NiNs-polymer matrix nanocomposite patches which are insulated from the surrounding carbon fiber. Also, two different polymer matrix materials were used in the nanocomposite to compare the piezoresistive signal. These nanocomposites are shown to display repeatable piezoresistivity, thus becoming a strain sensor capable of accurately measuring strain real time and in-situ. This patch has compatible mechanical properties to existing advanced composites and shows good resolution to small strain. This method of strain sensing in carbon fiber composites is more easily implemented and used than other strain measurement methods including fiber Bragg grating and acoustic emissions. To show that these embedded strain gages can be used in a variety of carbon fiber components, two different applications were also pursued.

A nonlinear active vibration absorber to control the vibrations of plates is investigated. The absorber is based on the saturation phenomenon associated with dynamical systems with quadratic nonlinearities and a two-to-one internal resonance. The technique is implemented by coupling a second-order controller with the plate's response through a sensor and an actuator. Energy is exchanged between the primary structure and the controller and, near resonance, the plate's response saturates to a small value. Numerical as well as experimental results are presented for a cantilever rectangular plate. For numerical studies, finite-element methods as well as modal analysis are implemented. The commercially available software ABAQUS is used in the finite-element analysis together with a user-provided subroutine to model the controller. For the experimental studies, the plate is excited using a dynamic shaker. Strain gages are used as sensors, while piezoelectric ceramic patches are used as actuators. The control technique is implemented using a dSPACE digital signal processing board and a modeling software (SIMULINK). Both numerical and experimental results show that the control strategy is very efficient. A numerical study is conducted to optimize the location of the actuators on the structure to maximize its controllability. In this regard, the control gain is maximized for the PZT actuators. Furthermore, a more general method is introduced that is based on a global measure of controllability for linear systems. Finally, the control strategy is made adaptive by incorporating an efficient frequency-measurement technique. This is validated by successfully testing the control strategy for a non-conventional problem, where nonlinear effects hinder the application of the non-adaptive controller. / Ph. D.

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Current progress in mobility assistive devices revolves around traditional actuation methods including electric motors, hydraulics, and pneumatic cylinders to provide assistive joint torques to the user. While these mechanisms are effective at providing the torques needed, they are often bulky, heavy, and suffer from poor alignment with the joints of the user. These drawbacks have created a need for novel technologies that can provide a more compact and compliant form of actuation. Twisted and coiled polymers, under the thermomechanical class of smart material actuators, have emerged as a strong candidate for use as soft actuators in assistive devices due to their low cost, commercial availability, high stroke capacity, and power density. Progress to their development is currently limited by lack of proper standardization in the fabrication process, along with incomplete characterization of its quasi-static mechanical and thermal behaviours and how the performance is influenced by various design considerations. This thesis defined a fabrication process of twisted coiled polymer actuators and evaluated the trends between design considerations and their impacts on the final actuator performance. In this work, a fabrication rig was developed to manufacture consistent and repeatable actuators, while enabling the control of various identified design parameters. Subsequently, a comprehensive experimental evaluation was accomplished which resulted in a better understanding of the relationships between these parameters and the actuator performance including its tensile stroke, force generation, and variable stiffness properties. The results provided a foundation for designers to consider which variables should be controlled during both actuator fabrication and operation, in order to optimize its final performance to meet a set of prescribed requirements.

This dissertation presents innovative research on Shape Memory Alloy (SMA)-actuated active steerable needles to address the limitations of conventional bevel tip needles in needle-based medical procedures such as biopsy, brachytherapy, tissue ablation and drug delivery. The active needle design proposed in this study surpasses the limitations of conventional needles by enabling large tip deflection and active control of deflection during needle insertion, thereby achieving accurate needle placement. A needle prototype was developed, demonstrating substantial 50mm and 39mm tip deflections at a 150mm insertion depth in liver and prostate-mimicking gels, respectively. Finite Element Analysis (FEA) accurately predicted the tip deflection in tissue-mimicking gels, with simulation errors measuring only 16.42% and 12.62% in the liver-mimicking gel and prostate-mimicking gel, respectively, validating the effectiveness of the FEA framework developed in this research for predicting tip deflection in soft tissues. Furthermore, a real-time trajectory tracking control system using a Proportional Integral (PI) controller was designed for the SMA-actuated needle, which resulted in minor root mean square errors (RMSE) of 1.42mm and 1.47mm in the two gels, respectively, highlighting the applicability of the needle design. The capabilities of the active needle, including improved tip deflection and trajectory tracking control, enable it to bypass obstacles, maneuver around critical anatomical structures, and increase the accuracy of needle placement, thus enhancing patient safety and procedure success rates.A bioinspired approach was introduced to enhance the functionality of SMA-actuated needles, drawing inspiration from the mosquito proboscis's unique design and skin-piercing technique. By incorporating an innovative cannula design and applying axial vibration to the SMA-actuated needle, a significant reduction in needle-tissue interaction friction was achieved, which resulted in increased needle tip deflection and improved steering accuracy. Including these bioinspired features led to a remarkable decrease in insertion force by up to 26.24% and an increase in tip deflection by 37.11%. Furthermore, the trajectory tracking error was reduced by 48%, and the control effort decreased by 23.25%, underscoring the benefits of the bioinspired enhancements in improving needle insertion mechanics and control. The findings presented in this dissertation illustrate the potential of SMA-actuated needles and bioinspired features in enhancing needle steering performance during minimally invasive needle-based procedures. Future research will focus on further refining the needle design and control systems, expanding experimental tests to biological tissues, and exploring the application of these advancements on a clinically applicable scale. / Mechanical Engineering

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