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Bonding composite structures using adhesives offers several advantages over mechanical fastening such as better flow stress, weight saving, improved fatigue resistance and the ability to join dissimilar structures. The hesitation to adopt adhesively bonded composite joints stems from the lack of knowledge regarding damage initiation and propagation mechanisms within the joint. A means of overcoming this hesitation is to continuously monitor damage in the joint. This study proposes a methodology to conduct structural health monitoring (SHM) of an adhesively bonded composite lap joint using acoustic, guided Lamb waves by detecting, locating and predicting the size of damage. Finite element modeling of a joint in both 2D and 3D is used to test the feasibility of the proposed damage triangulation technique. Experimental validation of the methodology is conducted by detecting the presence, location and size of inflicted damage with the use of tuned guided Lamb waves.

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Recently there has been an increased focus on the use of microfluidics for the synthesis of different products. One of the products proposed for synthesis is quantum dots. Microfluidics often uses Polydimethylsiloxane for structure in microfluidic chips, but quantum dots use octadecene in several synthesis steps. The purpose of this work was to create a lab setup capable of anodically bonding 4” diameter wafers, and to characterize the bond formed using the Plaza test chip so that microfluidic devices using glass and silicon as substrates could be created. Two stainless steel electrodes placed on top of a hot plate were attached to a high power voltage supply to perform anodic bonding. A Plaza test mask was created and used to pattern P type silicon wafers. The channels etched were between 300 and 500nm deep and ranged between 1000µm and 50µm. These wafers were then anodically bonded to Corning 7740 glass wafers. Bonding stopped once the entire surface of the wafer was bonded, determined by visual inspection. All bonds were formed at 400°C and the bond strength and toughness between wafers bonded at 400V and 700V was compared. A beam model was used to predict the interfacial fracture toughness, and the stress at the bond was calculated with a parallel spring model. By measuring the crack length of the test structures under a light microscope the load conditions of the beam could be found. It was concluded that the electrostatic forces between the wafers give the best indication of what the bond quality will be. This was seen by the large difference in crack length between samples that were bonded using a thick glass wafer (1 mm) and a thin glass wafer (500µm). The observed crack lengths for the thick glass wafers were between 40 and 60µm. Thin glass wafers had a crack length between 20 and 40µm. The fracture toughness was calculated using the beam model approximation. Fracture toughness of the thin glass wafers was 7MPa m1/2, and of the thick glass wafers was 30 MPa m1/2. The fracture toughness of the thick glass wafers agreed with results found through the use of the double cantilever beam samples in literature. The maximum observed interfacial stress was 70 MPa. Finally, to measure the change in the size of the sodium depletion zone formed during bonding, samples were placed under a scanning electron microscope (SEM). Depletion zones were found to be between 1.1 and 1.4µm for thin glass samples that were bonded at 400 and 700 volts. This difference was not found to have a significant effect on the strength or fracture toughness observed. Thicker glass samples could not have their depletion zone measured due to SEM chuck size.

Yes / In this research work, the transient liquid phase (TLP) bonding process was utilized to fabricate joints using thin (20μm) nickel and copper foils placed between two bonding surfaces to help facilitate joint formation. Two joint configurations were investigated, first, Ti- 6Al-4V/CuNi/Mg-AZ31 and second, Ti-6Al-4V/NiCu/Mg-AZ31. The effect of bonding time on microstructural developments across the joint and the changes in mechanical properties were studied as a function of bonding temperature and pressure. The bonded specimens were examined by metallographic analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD). In both cases, intermetallic phase of CuMg2 and Mg3AlNi2 was observed inside the joint region. The results show that joint shear strengths for the Ti-6Al-4V/CuNi/Mg- AZ31 setup produce joints with shear strength of 57 MPa compared to 27MPa for joints made using the Ti-6Al-4V/NiCu/Mg-AZ31 layer arrangement. / NSERC (Canada)

Room temperature ionic liquids (ILs) are a unique class of solvents which are characterized by non-volatility, non-flammability, electrochemical stability and high ionic conductivity. These properties are highly desirable for ion-conducting electrolytes, and much work has focused on realizing their application in practical devices. In addition, hydrophilic and ionophilic polymers are generally miscible with ILs. The miscibility of ILs with ion-coordinating polymers makes ILs effective plasticizers for gel polymer electrolytes. Due to their unique properties, ILs present a means to realize the next generation of energy storage technology. In this dissertation, the fundamental interactions between poly(ethylene oxide) (PEO) and a variety of room temperature ILs were investigated. ILs with acidic protons were demonstrated to form a stronger interaction with PEO than ILs without such protons, suggesting that hydrogen bonding plays a dominant role for PEO miscibility with ILs. The hydrogen bonding interaction is selective for the PEO block of a PEO-b-PPO-b-PEO block copolymer (BCP). Therefore, blending these copolymers with the strongly interacting IL 1-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]) induced microphase separation into a well-ordered structure, whereas the neat copolymer is phase mixed. At sufficient quantities, the interaction between [BMI][PF6] and PEO suppresses PEO crystallinity entirely. In addition, the induced microphase separation may prove beneficial for ion conduction. Therefore, microphase separated copolymer/IL blends were investigated as potential gel polymer electrolytes. Cross-linkable block copolymers which microphase separate when blended with [BMI][PF6] were synthesized by modifying PPO-b-PEO-b-PPO copolymers with methacrylate end-groups. Cross-linking these copolymers while swollen with an IL generates ion gels with high ionic conductivities. The copolymer/IL blends vary from a well-ordered, strongly microphase separated state to a poorly ordered and weakly microphase separated state, depending upon the molecular weight. Stronger microphase separation results in higher mechanical strength upon cross-linking. However, this does not greatly affect ion conductivity. Nor is conductivity affected by forming gels from cross-linked PEO homopolymers when compared to BCPs. It was found that BCPs can be beneficial in producing gel electrolytes by allowing sequestration of phase selective cross-linkers away from the conducting block. Cross-linker molecules that are selective for the PPO blocks can be used to increase the mechanical strength of the gels with only a small effect on the conductivity. When cross-linkers that partition to the mixed PEO/IL block are used, the conductivity decreases by nearly a factor of 2. These studies show how ILs interact with PEO and how gel polymer electrolytes can be constructed with the IL [BMI][PF6]. While BCPs cannot directly be used to increase ion conductivity, they do allow for greater mechanical strength without sacrificing conductivity. This suggests many new approaches that may be used to simultaneously achieve high ionic conductivity and mechanical strength in solid and gel polymer electrolytes.

This study provides a test of the market valuation impact of Securities and Exchange Commission (SEC) enforcement actions for foreign firms. I examine the SEC enforcement policy towards foreign firms under its jurisdiction. In contrast to Siegel (2005) who examines earlier years, I find that the SEC's current (post-2002) enforcement intensity is considerable and has increased dramatically by comparison. I construct a novel test using the burgeoning series SEC enforcement events as changes to the legal environment that circumvents the issues associated with firm-level exchange-listing events (e.g. self-selection and simultaneous changes to firm traits). The tests focus on stock returns of foreign firms not targeted by the SEC during event windows surrounding SEC announcements of enforcements against foreign firms. This isolates the effect of a changing enforcement environment. I find that when the SEC takes action against a foreign firm, non-target foreign firms experience positive stock returns. Returns are amplified for firms from weaker home legal environments, suggesting that the returns are due to a perceived increase in SEC scrutiny. Finally, consistent with the market adjusting to the new enforcement regime, the magnitude of non-target firm returns declines with each sequential SEC enforcement action. The overall results provide evidence that SEC oversight plays a significant role in increasing the value of foreign firms, which supports the legal bonding hypothesis discussed in prior literature.

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<p> Mn2P2O7 belongs to the monoclinic space group C2/m. The manganese atoms are six-fold coordinated to oxygen atoms forming distorted octahedra. The bonding in P2O7^4- ion is discussed with reference to values predicted by Cruickshank and Baur.</p> <p> The central oxygen atom in P2O7^4-ion shows enhanced motion, a feature common to all the members of the thortveitite series. By collecting X-ray data at -180°C, an attempt has been made to understand the nature of this enhanced motion.</p> / Thesis / Master of Science (MS)