This dissertation demonstrates the design of reversibly self-morphing novel liquid crystalline elastomer (LCE) antennas that can dynamically change electromagnetic performance in response to temperature. This change in performance can be achieved by programming the shape change of stimuli-responsive (i.e., temperature-responsive) LCEs, and using these materials as substrates for reconfigurable antennas. Existing reconfigurable antennas rely on external circuitry such as Micro-Electro-Mechanical-Systems (MEMS) switches, pin diodes, and shape memory alloys (SMAs) to reconfigure their performance. Antennas using MEMS or diodes exhibit low efficiency due to the losses from these components. Also, antennas based on SMAs can change their performance only once as SMAs response to the stimuli and is not reversible. Flexible electronics are capable of morphing from one shape to another using various techniques, such as liquid metals, hydrogels, and shape memory polymers. LCE antennas can reconfigure their electromagnetic performance, (e.g., frequency of operation, polarization, and radiation pattern) and enable passive (i.e., battery-less) temperature sensing and monitoring applications, such as passive radio frequency identification device (RFID) sensing tags. Limited previous work has been performed on shape-changing antenna structures based on LCEs. To date, self-morphing flexible electronics, including antennas, which rely on stimuli-responsive LCEs that reversibly change shape in response to temperature changes, have not been previously explored. Here, LCE antennas will be studied and developed. Also, the metallization of LCEs with different metal conductors and their fabrication process, by either electron beam (E-Beam) evaporation or optical gluing of the metal film will be observed. The LCE material can have a significant impact on sensing applications due to its reversible actuation that can enable a sensor to work repeatedly. This interdisciplinary research (material polymer science and electrical engineering) is expected to contribute to the development of morphing electronics, including sensors, passive antennas, arrays, and frequency selective surfaces (FSS).

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

Shape Memory Alloy is an amazing material, which can “remember” and return to its original shape when heated due to its temperature dependent phase transformation. Shape Memory Alloy wire has significant potential for application in the automobile industry due to its high ratio of energy / weight and silent actuation. However, a dependable method to measure the operating temperature of SMA wire and a reliable heat transfer model to characterize the dynamics of the SMA wire limit its widespread use in the automobile industry. This thesis presents a detailed description of the work performed to develop a reliable method for determining surface temperature of current carrying SMA wires and the development of a heat transfer correlation for natural convection cooling of heated SMA wires. The major findings of the research are as follows: When a spot welded thermocouple measures the temperature of a current carrying SMA wire, there is a “spurious voltage” ΔV added to the thermo electro-motive force (EMF) of the thermocouple as a result of a voltage drop across the two points of contact that the thermocouple wires make with the SMA wire. This leads to an erroneous temperature reading that can be higher or lower than the actual temperature depending on the direction of current flow. When the carrying current is reversed in direction, the “spurious voltage” becomes –ΔV allowing a correct temperature reading to be obtained by averaging the readings based on opposed current flow. A two-step spot welding procedure for attaching thermocouples to SMA wire can eliminate the influence of the “spurious voltage” in the temperature reading. By spot welding the thermocouple wires onto the SMA wire one by one, the thermocouple lead offset is eliminated and the thermocouple provides an accurate point source reading. Infrared thermal imaging can be a good supplement in the experiment to monitor errors in temperature readings from thermocouples. Due to the curvature of the SMA wire, the temperatures of the locations on the SMA wire that are the closest to the infrared camera represent the temperature of the SMA wire. So a line analysis across the SMA wire on the software “ThermaCAM” is required to determine the temperature of the SMA wire by infrared thermal imaging and the highest temperature on the line is the temperature of the SMA wire. A new natural convective heat transfer correlation comprising the inclination angle φ is developed based on experimental results, which can be used to predict the temperature of a SMA wire given its diameter and inclination angle. The comparisons show that the new correlation agrees with existing correlations in a vertical orientation and for small Rayleigh numbers (0.001 < RaD < 0.05) in the horizontal orientation. The correlation developed in this work for horizontal orientation tends to overestimate values of Nusselt numbers as predicted in other correlations when the Rayleigh number is high (0.05 < RaD < 0.6). It is speculated that this overestimation can be attributed to a temperature distortion associated with thermocouple measurement at or near ambient pressure conditions.

The objective of this study is to reduce the interstory drifts, floor accelerations, and shear forces experienced by masonry houses subject to seismic excitation. Ambient vibration testing was performed on a case study structure in Maip�, Chile, to identify characteristics of the system. Upon creating a multiple degree-of-freedom (MDOF) model of the structure, the effect of implementing several base isolation techniques is assessed. The isolation techniques analyzed include the use of friction pendulum systems (FPS), high-damping rubber bearings (HDRB), two hybrid systems involving HDRB and shape memory alloys (SMA), and precast-prestressed pile (PPP) isolators. The dynamic behavior of each device is numerically modeled using analytical formulations and experimental data through the means of fuzzy inference systems (FIS) and S-functions. A multiobjective genetic algorithm is utilized to optimize the parameters of the FPS and the PPP isolation systems, while a trial-and-error method is employed to optimize characteristic parameters of the other devices. Two cases are studied: one case involves using eight devices in each isolation system and optimizing the parameters of each device, resulting in different isolated periods for each system, while the other case involves using the number of devices and device parameters that result in a 1.0 sec fundamental period of vibration for each baseisolated structure. For both cases, the optimized devices are simulated in the numerical model of the case study structure, which is subjected to a suite of earthquake records. Numerical results for the devices studied indicate significant reductions in responses of the base-isolated structures in comparison with their counterparts in the fixed-base structure. Metrics monitored include base shear, structural shear, interstory drift, and floor acceleration. In particular, the PPP isolation system in the first case reduces the peak base shear, RMS floor acceleration, peak structural shear, peak interstory drift, and peak floor acceleration by at least 88, 87, 95, 95, and 94%, respectively, for all of the Chilean earthquakes considered. The PPP isolation system in the second case (yielding a 1.0 sec period) and the FPS isolation systems in both cases also significantly reduce the response of the base-isolated structure from that of the fixed-base structure.

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

Ο θερμομηχανικός χαρακτηρισμός του κράματος NiTi και η ενσωμάτωση του σε πολυμερική μήτρα με στόχο τη γέννηση εσωτερικών μηχανικών τάσεων όταν υπάρξει θερμική διέγερση, είναι επιγραμματικά ο σκοπός της παρούσας εργασίας. Το ‘ευφυές’ σύστημα που μελετάται στην εργασία αυτή αποτελείται από εποξειδική ρητίνη, ενισχυμένη με ίνες Kevlar 29 και ενσωματωμένα σύρματα Νικελίου-Τιτανίου. Στο πρώτο πειραματικό μέρος, περιλαμβάνεται η μελέτη και ο θερμομηχανικός χαρακτηρισμός του υλικού. Χρησιμοποιήθηκαν σύρματα NiTi διαμέτρου 0.3mm, αλλά και ράβδοι για τη διεξαγωγή κάποιων συγκεκριμένων πειραμάτων. Οι πειραματικές τεχνικές περιλαμβάνουν μηχανικά πειράματα εφελκυσμού σε σερβοϋδραυλικό πλαίσιο δοκιμών, ηλεκτρονιακή μικροσκοπία σάρωσης (SEM), οπτική μικροσκοπία, χρήση θερμοκάμερας υπερύθρου ακτινοβολίας, διαφορική θερμιδομετρία σάρωσης (DSC), δυναμική μηχανική ανάλυση (DMA), μέτρηση ηλεκτρικών ιδιοτήτων καθώς και ένα πρωτοποριακό σύστημα χαρακτηρισμού υλικών (σύστημα THERMIS), που αναπτύχθηκε στο εργαστήριο. Το δεύτερο τμήμα, περιλαμβάνει τη μελέτη του υβριδικού σύνθετου υλικού. Η παρασκευή του πραγματοποιείται σε αυτόκλειστο φούρνο (autoclave) και για την ενεργοποίηση του και την καταγραφή των παραμέτρων κατά τη λειτουργία του, χρησιμοποιείται το σύστημα THERMIS. Για να επιτευχθεί η σύγκριση μεταξύ της συμπεριφοράς του κράματος όταν αυτό ενεργοποιείται με και χωρίς την πολυμερική μήτρα να το περιβάλει, έχουν επιλεγεί δύο τύποι πειραμάτων: συνεχής ενεργοποίηση για μεγάλο χρονικό διάστημα (χαλάρωση τάσης ενεργοποίησης - activation stress relaxation) και κυκλική ενεργοποίηση-απενεργοποίηση για μεγάλο αριθμό επαναλήψεων (λειτουργική κόπωση – transformation fatigue). Τα πειράματα της λειτουργικής κόπωσης στα σύρματα, έδειξαν ότι η αρχική αναπτυσσόμενη τάση, μειώνεται εκθετικά, συναρτήσει των κύκλων ενεργοποίησης. Σύμφωνα με τα αποτελέσματα, η κοπωτική συμπεριφορά του σύρματος, δεν εξαρτάται από τη διάρκεια του χρόνου θέρμανσης ανά κύκλο, αλλά από τον αριθμό των κρυσταλλογραφικών μετασχηματισμών μεταξύ οστενιτικής - μαρτενσιτικής φάσης και αντίστροφα. Ο ρυθμός υποβάθμισης της ικανότητας του κράματος να ασκεί μηχανική τάση, είναι πολύ έντονος κατά τη διάρκεια των πρώτων εκατοντάδων κύκλων και μειώνεται όσο το φαινόμενο εξελίσσεται. Στα σύνθετα υλικά, όπως και στην περίπτωση των συρμάτων SMA, η υποβάθμιση της λειτουργικής ικανότητας των υβριδικών συνθέτων, φαίνεται ότι δεν εξαρτάται από το χρόνο της θέρμανσης ανά κύκλο, αλλά μόνο από το πλήθος των κρυσταλλογραφικών εναλλαγών. Στα πειράματα χαλάρωσης τάσης, η αρχική τάση των συρμάτων ήταν γύρω στα 500MPa και σύμφωνα με τα πειραματικά αποτελέσματα, με την πάροδο του χρόνου και υπό την επίδραση της θερμοκρασίας, λαμβάνει χώρα εκθετική μείωση του μεγέθους της. Το επίπεδο της θερμοκρασίας λειτουργίας, επηρεάζει δραματικά την υποβάθμιση της μηχανικής αναπτυσσόμενης τάσης, της οποίας ο ρυθμός είναι ιδιαίτερα αυξημένος κατά τις πρώτες ώρες λειτουργιάς του υλικού. Ποιοτικά, το ίδιο φαινόμενο συμβαίνει και στην περίπτωση της χαλάρωσης τάσης ενεργοποίησης των υβριδικών συνθέτων, με τη διαφορά ότι η υποβάθμιση είναι σαφώς πιο έντονη. Προτείνεται τέλος, η μελέτη της υποβάθμισης της ικανότητας των ενεργοποιητών, με βάση στατιστικά εργαλεία και μεθόδους, κατά αναλογία με άλλα κοπωτικά φαινόμενα στη φύση (κυρίως στη μηχανική), εφόσον ουσιαστικά πρόκειται για ακολουθία δράσεων που τελικά οδηγούν στην απώλεια της ικανότητας των υλικών μας να ασκούν τάση. Συνηγορεί εξάλλου σε αυτό και η μορφή των πειραματικών καμπυλών, που παρουσιάζουν μεγάλη ομοιότητα με τις αντίστοιχες καμπύλες S/N, στη μηχανική κόπωση των υλικών. / The present work, aims to the thermo-mechanical characterization of the NiTi Shape Memory Alloy and the characterization of ‘smart’ hybrid composites with embedded SMAs, under thermal activation. The composite structure that is being investigated consists of an epoxy resin matrix, Kevlar 29 fibers and NiTi SMA wires. The first experimental section deals with the thermo mechanical characterization of the Shape Memory Alloy. 0.3 mm in diameter wires were used. The experimental techniques, include mechanical tests using a servo-hydraulic testing apparatus, scanning electron microscopy (SEM), optical microscopy, thermal IR camera imaging, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), electrical measurements and a novel thermo mechanical characterization system (Thermis), which was tailor made according to the needs of this project. The second experimental section deals with the characterization of the composite material, which was developed using a special purpose furnace (autoclave) and was tested on the Thermis system. In order to compare the functionality of the SMA either in free condition or embedded in a polymer matrix, two experiments were chosen: continuous activation for a long time (activation stress relaxation) and recurrent thermal activation (transformation fatigue). The transformation fatigue experiments showed that the initially developed mechanical stress, reduces exponentially, according to the number of the crystalline transformations. The functional fatigue life of the alloy, does not depend on the heating time per cycle, but is strongly correlated to the number of the recurrent transformation between martensite and austenite. The stress reduction rate is increased during the first cycles and reduces as the phenomenon develops. As it concerns the composite materials, like the SMA wire case, the reduction of the stress generation capability, is not affected by the heating time per cycle, and is only related to the number of the crystalline transformations. During the stress relaxation experiments, the initial developed stress of the wires was about 500 MPa and according to the experimental results, as time passes and under the influence of the thermal field, the stress reduces exponentially. The temperature level strongly affects the reduction phenomenon and the reduction rate is very high during the first hours of the experiment. The same behavior is observed not only at the SMA wires but also at the composites, as well, noting that reduction in the later case is much more intense. At the end, the study of the fatigue and relaxation phenomena, using a statistical approach, is suggested, like many other fatigue cases in nature (especially in mechanics). The fatigue curves presented here resemble to the S/N curves that can derived from the case of mechanical fatigue of other structural materials, like steel or CFR composites.

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M. Tech. Metallurgical Engineering. / StudIes the tribocorrosion behaviour of copper-nickel-titanium shape memory composite reinforced by zirconia,synthesized through powder metallurgy process. The research aims to achieve the following objectives: 1. Study the tribocorrosion mechanisms of the composites in NaCl solution (typical human body fluid). 2. Investigate the tribocorrosion mechanisms of the composites in other environments typical of some engineering applications.The proposed study on incorporating zirconia into the matrix NiTiCu through powder metallurgical process and investigations of the phenomenon of joint wear-corrosion synergism occurring in sodium chloride considered typical of human body system and sulphuric acid environment typical of wide range engineering applications is therefore very novel. It is therefore aimed that information on the tribocorrosion behaviour of NiTiCu as well as with zirconia incorporation will form basis for typical compositional formulation approaches for improved bio-tribocorrosion improvement in biomedical applications and actuators used in other engineering applications.

Previous experimental observations have shown that the pseudoelastic response of NiTi shape memory alloys (SMA) is localized in nature and proceeds through nucleation and propagation of localized deformation bands. It has also been observed that the mechanical response of SMAs is strongly affected by loading rate and cyclic degradation. These behaviors significantly limit the accurate modeling of SMA elements used in various devices and applications. The aim of this work is to provide engineers with a constitutive model that can accurately describe the dynamic, unstable pseudoelastic response of SMAs, including their cyclic response, and facilitate the reliable design of SMA elements. A 1-D phenomenological model is developed to simulate the localized phase transformations in NiTi wires during both loading and unloading. In this model, it is assumed that the untransformed particles located close to the transformed regions are less stable than those further away from the transformed regions. By consideration of the thermomechanical coupling among the stress, temperature, and latent heat of transformation, the analysis can account for strain-rate effects. Inspired by the deformation theory of plasticity, the 1-D model is extended to a 3-D macromechanical model of localized unstable pseudoelasticity. An important feature of this model is the reorientation of the transformation strain tensor with changes in stress tensor. Unlike previous modeling efforts, the present model can also capture the propagation of localized deformation during unloading. The constitutive model is implemented within a 2-D finite element framework to allow numerical investigation of the effect of strain rate and boundary conditions on the overall mechanical response and evolution of localized transformation bands in NiTi strips. The model successfully captures the features of the transformation front morphology, and pseudoelastic response of NiTi strip samples observed in previous experiments. The 1-D and 3-D constitutive models are further extended to include the plastic deformation and degradation of material properties as a result of cyclic loading.

Shape Memory Alloy is an amazing material, which can “remember” and return to its original shape when heated due to its temperature dependent phase transformation. Shape Memory Alloy wire has significant potential for application in the automobile industry due to its high ratio of energy / weight and silent actuation. However, a dependable method to measure the operating temperature of SMA wire and a reliable heat transfer model to characterize the dynamics of the SMA wire limit its widespread use in the automobile industry. This thesis presents a detailed description of the work performed to develop a reliable method for determining surface temperature of current carrying SMA wires and the development of a heat transfer correlation for natural convection cooling of heated SMA wires. The major findings of the research are as follows: When a spot welded thermocouple measures the temperature of a current carrying SMA wire, there is a “spurious voltage” ΔV added to the thermo electro-motive force (EMF) of the thermocouple as a result of a voltage drop across the two points of contact that the thermocouple wires make with the SMA wire. This leads to an erroneous temperature reading that can be higher or lower than the actual temperature depending on the direction of current flow. When the carrying current is reversed in direction, the “spurious voltage” becomes –ΔV allowing a correct temperature reading to be obtained by averaging the readings based on opposed current flow. A two-step spot welding procedure for attaching thermocouples to SMA wire can eliminate the influence of the “spurious voltage” in the temperature reading. By spot welding the thermocouple wires onto the SMA wire one by one, the thermocouple lead offset is eliminated and the thermocouple provides an accurate point source reading. Infrared thermal imaging can be a good supplement in the experiment to monitor errors in temperature readings from thermocouples. Due to the curvature of the SMA wire, the temperatures of the locations on the SMA wire that are the closest to the infrared camera represent the temperature of the SMA wire. So a line analysis across the SMA wire on the software “ThermaCAM” is required to determine the temperature of the SMA wire by infrared thermal imaging and the highest temperature on the line is the temperature of the SMA wire. A new natural convective heat transfer correlation comprising the inclination angle φ is developed based on experimental results, which can be used to predict the temperature of a SMA wire given its diameter and inclination angle. The comparisons show that the new correlation agrees with existing correlations in a vertical orientation and for small Rayleigh numbers (0.001 < RaD < 0.05) in the horizontal orientation. The correlation developed in this work for horizontal orientation tends to overestimate values of Nusselt numbers as predicted in other correlations when the Rayleigh number is high (0.05 < RaD < 0.6). It is speculated that this overestimation can be attributed to a temperature distortion associated with thermocouple measurement at or near ambient pressure conditions.