This thesis details an investigation into the properties and applications of shape memory alloy (SMA) composites. SMA-composites are a new material which have the possibility of having a large impact on what the structures as we know today, are constructed with. SMA-composites are adaptive materials which can be used to control the shape and frequencies of vibration of a structure. In order to determine the effectiveness of such a material, research into the functional properties of SMAs and SMA-composites was conducted. As an initial step, the transformation behaviour of constrained SMAs was investigated in order to obtain a better understanding into the recovery stress generation of these wires when embedded into a composite material. It is known that the transformation is based on two types of martensite within the alloy; self accommodating and preferentially oriented martensite. The amounts of each type and how they vary with differing pre-strain were determined through DSC measurements and an explanation for why preferentially oriented martensite is not observed during DSC testing was made. The next step was to investigate the effectiveness of embedding SMA wires into composites and the thermomechanical properties of the SMA wires and the SMA-composites were determined. This was completed using a specially designed tensile testing machine which was capable of having the whole specimen immersed into an oil bath and heated and cooled repeatedly. The stress-strain, strain-temperature, stress-temperature, resistance-strain and cyclic properties of various wires were obtained, giving a better understanding of the behaviour of SMA wires under different test conditions. NiTiCu SMA wires were embedded into kevlar composite materials and the recovery stress generation (stress-temperature), stress-strain, and strain-temperature behaviour was determined. If SMA-composites are to be used as new materials for structural applications, verification that the embedment of pre-strained SMA wires into the material doesn't adversely affect the impact behaviour needs to be carried out. SMA-composite specimens with varying volume fractions of superelastic SMA wires, pre-strain and position through the thickness were made up for impact damage characterisation. These specimens were impacted at three different energy levels. The results showed that by embedding SMA wires into composite materials there is a reasonably low damage accumulation after impact. There is also no adverse impact effect on the structure compared with structures without wires as well as structures with other types of wires such as steel and martensitic SMA wires. The SMA-composites showed good damping and energy absorption capabilities. A novel application of SMA-composites is their use as a SMA patch in order to repair damage in existing cracked metallic structures. An analytical study and finite element modelling showing the closure stresses obtainable for use as patches was made.

This thesis details an investigation into the properties and applications of shape memory alloy (SMA) composites. SMA-composites are a new material which have the possibility of having a large impact on what the structures as we know today, are constructed with. SMA-composites are adaptive materials which can be used to control the shape and frequencies of vibration of a structure. In order to determine the effectiveness of such a material, research into the functional properties of SMAs and SMA-composites was conducted. As an initial step, the transformation behaviour of constrained SMAs was investigated in order to obtain a better understanding into the recovery stress generation of these wires when embedded into a composite material. It is known that the transformation is based on two types of martensite within the alloy; self accommodating and preferentially oriented martensite. The amounts of each type and how they vary with differing pre-strain were determined through DSC measurements and an explanation for why preferentially oriented martensite is not observed during DSC testing was made. The next step was to investigate the effectiveness of embedding SMA wires into composites and the thermomechanical properties of the SMA wires and the SMA-composites were determined. This was completed using a specially designed tensile testing machine which was capable of having the whole specimen immersed into an oil bath and heated and cooled repeatedly. The stress-strain, strain-temperature, stress-temperature, resistance-strain and cyclic properties of various wires were obtained, giving a better understanding of the behaviour of SMA wires under different test conditions. NiTiCu SMA wires were embedded into kevlar composite materials and the recovery stress generation (stress-temperature), stress-strain, and strain-temperature behaviour was determined. If SMA-composites are to be used as new materials for structural applications, verification that the embedment of pre-strained SMA wires into the material doesn't adversely affect the impact behaviour needs to be carried out. SMA-composite specimens with varying volume fractions of superelastic SMA wires, pre-strain and position through the thickness were made up for impact damage characterisation. These specimens were impacted at three different energy levels. The results showed that by embedding SMA wires into composite materials there is a reasonably low damage accumulation after impact. There is also no adverse impact effect on the structure compared with structures without wires as well as structures with other types of wires such as steel and martensitic SMA wires. The SMA-composites showed good damping and energy absorption capabilities. A novel application of SMA-composites is their use as a SMA patch in order to repair damage in existing cracked metallic structures. An analytical study and finite element modelling showing the closure stresses obtainable for use as patches was made.

The demographic change in and the higher incidence of degenerative bone disease have resulted in an increase in the number of patients with osteoporotic bone tissue causing. amongst other issues, implant loosening. Revision surgery to treat and correct the loosenings should be avoided, because of the additional patient stress and high treatment costs. Shape memory alloys (SMA) can help to increase the anchorage stability of implants due to their superelastic behavior. The present study investigates the potential of hybridizing NiTi SMA sheets with additively manufactured Ti6Al4V anchoring structures using laser powder bed fusion (LPBF) technology to functionalize a pedicle screw. Different scanning strategies are evaluated, aiming for minimized warpage of the NiTi SMA sheet. For biomechanical tests, functional samples were manufactured. A good connection between the additively manufactured Ti6Al4V anchoring structures and NiTi SMA substrate could be observed though crack formation occurring at the transition area between the two materials. These cracks do not propagate during biomechanical testing, nor do they lead to flaking structures. In summary, the hybrid manufacturing of a NiTi SMA substrate with additively manufactured Ti6Al4V structures is suitable for medical implants.

Reinforced concrete buildings built prior to the enactment of modern seismic codes are often seismically deficient. These buildings may have inadequate strength and ductility to withstand strong earthquakes. Conventional retrofit techniques for such frame buildings involve adding reinforced concrete shear walls or structural bracing systems to the existing bays. These techniques can be intrusive and result in lengthy down times and expensive structural interventions. An alternative to conventional techniques is the use of high-strength prestressing strands or cables, diagonally placed as tension elements. This technique was researched and used in a limited manner after the 1985 Mexico City Earthquake. It has since been further investigated at the University of Ottawa through experimental and analytical research (Shalouf and Saatcioglu (2006), Carrière (2008), Molaei (2014)). While the use of steel strands as tension bracing elements proves to be an effective technique, the resulting stiffening effects on the frames lead to increased seismic force demands and higher based shear, as well as increased axial forces on the attached columns, potentially generating net tension, foundation uplift and excessive compression. Relatively low elongation characteristics of high-strength cables and slack caused by yielding strands and associated pinching of hysteresis curves reduce potential energy dissipation capacity. The current research aims to improve the previously observed deficiencies of the system. One of the improvements involve the use of shape memory alloys (SMA) in the middle of the cables, which reduce/eliminate residual deformations upon yielding and associated pinching of the hysteresis curves. SMA allows energy dissipation in the system while forcing the structure to recover from its inelastic deformations because of the flag-shape hysteretic characteristics of the material. The feasibility of the cable-SMA assembly as tension brace elements is illustrated through dynamic analyses of selected prototype buildings. The other improvement is the development of progressively engaging, initially loose multiple strands as tension cables. These cables are placed loosely to engage in seismic resistance at pre-determined drift levels, thereby eliminating premature increase in seismic force demands until their participation is required as the frame capacity is reached. Tests of a large-scale reinforced concrete frame, designed following the requirements of the 1965 National Building Code of Canada NRC (1965) as representative of existing older frame buildings in Canada, are conducted under simulated seismic loading to assess the effectiveness of the proposed system. The verification of the concept is extended analytically to prototype buildings and the effectiveness of the system is demonstrated for mid-rise and low-rise frame buildings.

NiTi based shape memory alloys (SMA) cover most of the commercially produced shape memory devices and components. The reversible martensitic transformation between the phases B2 (austenite) and B19′ (martensite) is responsible for the shape memory effect in these alloys. The amount of strain which can be regained after a permanent deformation through thermal activation, known as the recoverable strain, is a strong function of crystallographic texture and microstructure. Texture influences the activation of a specific martensite variant during stress induced martensitic (SIM) transformation and also the re-orientation of twinned variants during further deformation. The variant selection decides the amount of recoverable strain. Since the NiTi based shape memory alloys inevitably undergo thermo-mechanical processing in the course of component design, the consequent evolution of texture and microstructure regulate the shape memory behavior. The present thesis is aimed to address this issue in some NiTi alloys that are technologically important for different applications, namely a binary Ni-rich NiTi alloy, a copper containing NiTi alloy and a hafnium containing NiTi alloy. The Ni rich NiTi alloy displays pseudoelastic behavior that can be used for couplings, the NiTiCu alloy provides a controlled thermal hysteresis suitable for actuator applications and the NiTiHf alloy can be used for high temperature applications. The first Chapter of the thesis provides a detailed overview of the existing knowledge related to evolution of microstructure and texture during processing, the transformation texture and its role on the shape memory behavior in NiTi alloys. The second chapter includes the experimental procedure followed to generate different textures, namely unidirectional and cross rolling with and without a subsequent annealing and also the details of the techniques used to characterize the structure, microstructure, texture and mechanical properties. The evolution of texture during thermo-mechanical processing of a Ni rich NiTi alloy and its impact on shape memory behavior is addressed in Chapter 3. The two modes of rolling employed at higher temperature led to the formation of different textures. The texture of unidirectionally rolled samples was characterized by a strong <111>||ND fiber, while a strong Goss {100}<110> component along with <111>||ND fiber was observed in the texture of the cross rolled samples. Annealing of the unidirectionally rolled samples generated a strong <100>||ND fiber, and a weak <111>||ND fiber was observed for the cross rolled samples. Microtexture analyses indicated that dynamically recrystallized grains had significantly different texture compared to the statically annealed material. One of the salient features of this study is the analysis of different twin boundaries with coincident site lattice (CSL) relations that has been observed in the hot rolled material. The origin of these twins has been attributed to deformation. The evolution of twin boundaries with CSL relation has strong influence on texture formation. A few of the important texture components have been found to have CSL relation amongst them. The origin of different texture components were found using intra-grain misorientation parameters. In-situ transformation studies in a scanning electron microscope have confirmed the formation of different types of twins at very low amount of strain in the Ni rich NiTi alloy. A Schmid factor based criterion was used to identify the activation of a particular variant. Trace analysis of the surface relief due to SIM transformation was utilized to confirm the theoretically predicted variant. Schmid criterion has been found to be valid in all the cases. Modulus variation with temperature and strain was studied using dynamical mechanical analysis. Microstructural changes during thermal and thermo-mechanical cycling revealed higher orientation gradient along grain boundaries compared to grain interior. The compatibility condition at the grain boundaries were attributed to higher misorientation development. Misorientation development during cycling loading process is also found to be a strong function of texture. Processing condition and texture has a strong influence on the recoverable strain. Particularly, the strength of <111>||ND fiber is influential in deciding the recoverable strain. Study of microstructure and texture evolution in the TiNiCu SMA and subsequent study on its impact on recoverable strain is presented in Chapter 4. Convincing evidences for the mechanisms operating during different dynamic restoration processes have been presented through microstructural investigation. Texture analysis of the austenite phase showed the formation of <111>||ND fiber. Despite the weakening of texture at larger strain, strength of certain deformation texture components like S {123}<634> and Cu {112}<111> increased, which suggested that texture evolution in TiNiCu alloy deviates from the texture of binary NiTi at large strains. Transformation texture analysis was carried out through electron back scattered diffraction technique, using an in-situ heating stage. The analysis of the results showed predominant activation of <011> type II as well as {11 1 } type I twins. A comparison of martensite and austenite pole figures indicated strong variant selection during phase transformation. Like the binary NiTi alloy, cross rolling of TiNiCu alloy also showed ample changes in the texture of martensite phase through the formation of different texture components. Annealing of both unidirectionally and cross rolled samples led to the weakening of texture. The change in volume fraction of Ti2NiCu precipitates, resulting from different processing conditions, influenced the transformation temperature. In this case also, texture and large intra-grain misorientation governed the recoverable strain. Chapter 5 is dedicated to the study of high temperature NiTiHf alloy. X-ray diffraction and differential scanning calorimetric studies confirmed a two step martensitic transformation, a B19` monoclinic and rhombohedral R-phase martensite in the studied alloy (Ni49.4Ti38.6Hf12). Microstructural investigations showed the formation of dendritic (Ti,Hf)2Ni precipitates along the grain boundary. Evolution of R-phase martensite was always observed along with (Ti,Hf)2Ni precipitates, irrespective of the processing condition. Dissolution of (Ti,Hf)2Ni precipitates by solution treatment suppressed the R phase formation. Strong texture of R-phase martensite confirmed variant selection during martensitic transformation. On the contrary, texture of B19` martensite was always weak, suggesting no preference for variant selection. Rolled material with a relatively strong texture exhibited higher recoverable strain compared to annealed material. Finally, all the significant outcomes of the present investigation are summarized in Chapter 6. Based on the conclusions, suggestions for future work have been mentioned.

Ο στόχος αυτής της εργασίας είναι να αποκτήσουμε μία βασική γνώση όλων των διαφορετικών σχεδιαστικών παραμέτρων που πρέπει να εξεταστούν για να είναι εφικτή η κατασκευή και ο έλεγχος ενός πολυαρθρωτού εργαλείου. Επιπλέον, όλες οι αναλυτικές μέθοδοι ελέγχου που βασίζονται στις ιδιαιτερότητες των SMA παρουσιάζονται λεπτομερώς, ώστε να παραχθεί μία ικανοποιητική λύση βασιζόμενη στις μεταβολές κατάστασης των κραμάτων και του συγκεκριμένου βραχίονα. Με άλλα λόγια, μία πλήρης γνώση του πώς σχεδιάζουμε, κατασκευάζουμε, προσομοιώνουμε, ελέγχουμε και απεικονίζουμε ένα λειτουργικό μικροσκοπικό πολυαρθρωτό βραχίονα, με τένοντες βασισμένους σε SMA για ελάχιστα επεμβατική χειρουργική είναι ο στόχος της παρούσας εργασίας. / The purpose of this work is to acquire a fundamental knowledge of all the different design parameters, which must be evaluated in order to be able to fabricate and control a multi-DOF manipulator. Moreover, all the analytical control techniques based on the particularities of the shape memory alloys will be shown in details, in order to provide an efficient solution based on the variations of the alloys and the specific manipulator. In other words, the knowhow of building, evaluating, controlling and displaying a functional tiny multi- DOF SMA-based manipulator for minimally invasive surgery is the purpose of this work.