Presented is a model for predicting SMA-induced deformations in an unsymmetric cross ply laminate. A previously developed theory is used to predict the room-temperature shape of the cross-ply laminate by minimizing its total potential energy. Then, using the principle of virtual work, equations relating the shape of the laminate to a force applied on supports fastened to the laminate are derived. Induced strains and displacements are predicted as a function of the applied force. Experiments where the force is generated by known weights are conducted. Good correlations are established between the experimental results and the predictions. The developed theory is able to predict with good accuracy the shape, strains and, displacements of an unsymmetric cross-ply laminate to the force applied on the laminate. This theory is then used to develop a model relating the laminate response to forces produced by a SMA actuator, the actuator being a SMA wire. To describe the mechanics of the SMA actuator, constitutive equations derived by other researchers are used. These constitutive equations relate the temperature of the wire to forces generated in it. Experiments where a SMA wire is used as an actuator are conducted. These experiments consist of resistively heating a SMA wire attached to supports fastened to the laminate. During these experiments, laminate deformations are measured as a function of the applied voltage. Comparisons with the temperature-based constitutive model predictions are not made since the relation between the applied voltage and the SMA temperature is very difficult to establish. However, the experiments show that a SMA used in conjunction with cross-ply unsymmetric laminates can induce very large changes in the laminate shapes. Thus, the concept of using a SMA actuator to control the shape of cross-ply unsymmetric laminates is validated. / Master of Science

A heightened interest in intelligent material systems has occurred in recent years due to their remarkable adaptive abilities. Intelligent materials systems, which contain sensors and actuators coupled by means of active control, frequently utilize composite materials as the skeletal structure. In order for composite materials to be utilized in intelligent material systems to their utmost capability, many material properties, including the interfacial shear strength between the embedded sensor or actuator and the matrix must be thoroughly understood.. Investigations were performed in order to examine the effects of different variables on the interfacial characteristics between a nitinol fiber and a composite matrix. First, rough, clean fiber surfaces were found to provide the best adhesion to the matrix due to the mechanical interaction of the matrix with the rough surface finish. Second, it was determined that the interfacial shear strength is not dependent upon embedded fiber length. Third, a very small diameter fiber will break before pulling out of the matrix, but overall, large fibers have a greater interfacial strength. Fourth, it was found that the initial prestrain on the fiber during processing had no effect on the interfacial shear strength of the fiber to the matrix. Fifth, it was determined that fatigue does not degrade the shear strength of any of the different initial pres trains. Finally, it was found that a coating that does not adhere well to the fiber neither macroscopically degrades nor enhances interfacial strength. / Master of Science

Shape memory alloy (SMA) materials such as nitinol have unique properties associated with the shape recovery effect and the material’s phase changes that have been used in a variety of actuator and sensing applications. By embedding SMA elements into host composite materials, control or modification of the SMA hybrid composite’s structural properties can be accomplished in-service, thereby increasing the hybrid composite’s structural functionality. Previous studies addressed increasing composite materials’ functionality by enabling in-service control of their dynamic response. Utilizing the SMA’s substantial recovery stress and capacity to dissipate strain energy to increase the hybrid composite’s static functionality is addressed herein. Specific applications for SMA hybrid composites include improving composite material’s impact damage resistance and composite cylinder stress and deflection control. In stress and deflection control of cylindrical structures, SMA actuators are placed within the composite cylinder to form an active compound cylinder. The active SMA elements can significantly reduce the internal pressure-induced radial dilation and creep so that under severe loading, piston to cylinder tolerances may be maintained. Similar to a conventional metallic compound cylinder, the active compound cylinder also reduces peak cylinder hoop stresses. Hybridizing composites with nitinol improves their impact resistance because of nitinol’s tremendous capacity to absorb impact strain energy through the stress-induced martensitic phase transformation. The amount of impact damage is reduced and the material’s resistance to impact perforation at various velocities is improved. The experimental response of nitinol hybrid composites and the associated mechanics are presented. The unique toughness and resistance to permanent deformation that is a result of the stress-induced martensitic phase transformation enables the nitinol to absorb on the order of 4 times the strain energy of high alloy steel and 16 times that of many graphite/epoxy composites. In most static applications where SMA elements are used for reinforcement, maintaining the integrity of the interface between the SMA elements and the host polymeric matrix composite material is critical to operation. The relationship between preparation of SMA elements for hybrid composite fabrication and interfacial bond strength is presented to address this issue. The mechanics of interfacial shear failure between SMA element and composite is also presented. / Ph. D.

Les alliages Cu-Al-Ni sont les seuls à posséder une température de transformation allant jusque 200°C. Ceci leur confère un avantage par rapport aux alliages Cu-Al-Zn ou Ti-Ni dont les températures de transformation ne dépassent pas 100°C.<p><p>Néanmoins, un chauffage temporaire au dessus de 200°C peut provoquer une perte de l’effet mémoire des alliages Cu-Al-Ni.<p><p>Nous avons étudié trois alliages aves des teneurs en nickel comprises entre 3 % et 5 %.<p><p>L’objectif de notre étude est double :<p><p>• Étudier la cinétique des transformations structurales au cours d’un vieillissement en phase β dans le domaine de températures 200°C-350°C ;<p><p>• Quantifier la perte de l’effet mémoire au cours du vieillissement afin de déterminer les possibilités d’utilisation de ces alliages au dessus de 200°C.<p><p>La caractérisation structurale a été effectuée par microscope optique, diffraction des rayons X, microscopie électronique à balayage et microscopie électronique en transmission. <p><p>Les caractéristiques de la transformation martensitique ont été déterminées par analyse thermomécanique (TMA), par calorimétrie différentielle à balayage (DSC) et par des mesures de résistivité électrique. <p><p>La perte de l’effet mémoire simple sens a été quantifiée à partir des courbes de transformations obtenues par analyse thermomécanique(TMA) sur des échantillons comprimés.<p><p>Les résultats principaux sont :<p><p>&61636; Au dessus de 300°C, la précipitation de la phase d’équilibre у&8322; se produit au cours du vieillissement. Elle entraîne une augmentation de la température Mѕ.<p><p>Nous avons montré que cette augmentation de Ms peut être reliée à la fraction transformée par une loi de puissance.<p><p>&61636; Il n’y a pas de relation directe, en revanche, entre la perte de l’effet mémoire et la fraction transformée. Cela indique que le nombre et la taille des précipités ont une influence sur la perte de l’effet mémoire.<p><p>&61636; Pour un vieillissement de 256 minutes à 275°C, la perte de l’effet mémoire est inférieure à 15%. Par contre, au dessus de 300°C, la perte de l’effet mémoire est très rapide.<p><p>Nous pouvons donc considérer que 275°C est une température limite à ne pas dépasser pour ces alliages.<p><p><p><p><p><p><p>ABSTRACT<p><p>The shape memory alloys Cu-Al-Ni are the only ones to have a transformation temperature of up to 200°C. This gives them an advantage compared to shape memory alloys Cu-Zn-Al or Ti-Ni whose transformation temperatures do not exceed 100 ° C.<p><p>However, a temporary heating above 200 ° C can cause a loss of memory effect alloys Cu-Al-Ni.<p><p>We studied three alloys with nickel content between 3% and 5%.<p><p>The aim of our study is twofold:<p><p>• Studying the kinetics of structural changes during aging in β phase in the temperature range 200 °C-350 °C.<p><p>• Quantifying the loss of memory effect with aging in order to determine the potential use of these alloys above 200°C.<p><p>The structural characterization was carried out by optical microscope, XR-ray diffraction, scanning electron microscopy and transmission electron microscopy.<p><p>The characteristics of the martensitic transformation were determined by thermomechanical analysis (TMA), differential scanning calorimetry (DSC) and by measuring the electrical resistivity.<p><p>The loss of one way shape memory was quantified from the curves obtained by thermomechanical analysis (TMA) on compressed samples.<p><p>The main results are:<p><p>&61636; Above 300 ° C, the precipitation of equilibrium phase γ2 occurs during aging. It causes an increase in temperature Mѕ.<p><p>We showed that this increase of Ms may be related to the fraction transformed by a power law.<p><p>&61636; There is no direct relationship between the loss of memory effect and the fraction transformed. This indicates that the number and size of the precipitates have an influence on the loss of memory effect.<p><p>& / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Thomas Kin Fong Lei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 64-66). / Abstracts in English and Chinese. / LIST OF FIGURES --- p.IV / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Model-based Control of SMA Wires --- p.3 / Chapter 2.1 --- Model Identification of SMA Wires --- p.3 / Chapter 2.1.1 --- Temperature-Current Relationship --- p.3 / Chapter 2.1.2 --- Stress-Strain Relationship --- p.5 / Chapter 2.1.3 --- Martensite Fraction-Temperature Relationship --- p.8 / Chapter 2.2 --- Model-based Position Control of Two Linking SMA Wires --- p.9 / Chapter 2.3 --- Summary --- p.12 / Chapter 3 --- Neural-fuzzy-based Control of SMA Wires --- p.13 / Chapter 3.1 --- Adaptive Neuro-fuzzy Inference System (ANFIS) --- p.13 / Chapter 3.1.1 --- ANFIS Architecture --- p.13 / Chapter 3.1.2 --- Hybrid Learning Algorithm --- p.16 / Chapter 3.2 --- Generalized Neural Network (GNN) --- p.20 / Chapter 3.2.1 --- GNN Architecture --- p.20 / Chapter 3.2.2 --- Approximation of the GNN --- p.22 / Chapter 3.2.3 --- Backpropagation Training Algorithm --- p.24 / Chapter 3.2.4 --- Complexity Reduction of the GNN --- p.25 / Chapter 3.2.5 --- Error Bound of In-exact Reduction of the GNN --- p.29 / Chapter 3.3 --- Neural-fuzzy-based Position Control of Four Linking SMA Wires --- p.32 / Chapter 3.3.1 --- ANFIS-based Position Control of Four Linking SMA Wires --- p.32 / Chapter 3.3.2 --- GNN-based Position Control of Four Linking SMA Wires --- p.35 / Chapter 3.3.3 --- Performance Comparison of ANFIS and GNN Algorithms --- p.37 / Chapter 3.4 --- Summary --- p.39 / Chapter 4 --- SMA Actuated Artificial Face --- p.40 / Chapter 4.1 --- Muscles of the Human Face --- p.40 / Chapter 4.2 --- The Software Part: facial model --- p.41 / Chapter 4.3 --- The Hardware Part: artificial face and peripheral interface --- p.43 / Chapter 4.3.1 --- SMA Actuated Artificial Face --- p.43 / Chapter 4.3.2 --- Peripheral Interface --- p.45 / Chapter 4.4 --- Position Control on the Artificial Face --- p.47 / Chapter 4.4.1 --- Model-based Position Control on Artificial Face --- p.48 / Chapter 4.4.2 --- Neural-fuzzy-based Position Control on Artificial Face --- p.49 / Chapter 4.4.3 --- Comparison of the Model-based and Reduced GNN Control of Artificial Face --- p.49 / Chapter 4.5 --- Experimental Result --- p.50 / Chapter 5 --- Conclusion --- p.52 / Appendix1 --- p.53 / Appendix2 --- p.55 / Appendix3 --- p.56 / Appendix4 --- p.58 / Bibliography --- p.64

Shape memory alloys (SMA) offer several advantages over traditional electro-mechanical devices, including: smooth, silent, clean operation; linear actuation; high power/weight ratio; scalability; and reduced part counts. These unique characteristics make them an attractive option when developing actuators, particularly at the meso- and micro-scales. However, SMAs do not typically display cyclic actuation and, therefore, require some reset force or bias mechanism in order to achieve this behaviour. Additionally, the micro-assembly of SMA material with a reset mechanism becomes increasingly difficult as the dimensions of actuators are scaled down. Therefore, actuators have been developed in which the actuation and reset mechanism are fabricated from a single piece of material. These actuators are referred to as monolithic actuators. Monolithic actuators are fabricated from a single piece of SMA material in which local annealing is used to selectively impart the shape memory effect (SME), while the remainder of the material acts as the bias mechanism. This work proposes an extension to monolithic actuators that locally varies the material composition of the monolithic component to exhibit different mechanical properties in select regions. This eliminates the need for local annealing by introducing regions of material unaffected by the annealing process. Additionally, incorporating regions of superelastic material to act as the bias mechanism greatly increases the actuator’s range of motion. These actuators are referred to as hybrid monolithic actuators. The creation of hybrid monolithic SMA actuators requires the development of both a fabrication technique and design tool. Varying the composition locally is accomplished by utilizing powder metallurgy fabrication techniques, specifically tape casting. Tapes of different compositions are cut, stacked, and sintered resulting in a monolithic component with mechanical properties that vary spatially. Tape casting NiTi from elemental powders is studied in this work, and tape recipes and sintering profiles are developed. In order to model the SMA behaviour of complex geometries, a finite element implementation of an existing lumped-element SMA model is developed. This model is used to design and simulate a prototype hybrid monolithic actuator. The prototype is fabricated and its performance used to illustrate the advantages of hybrid design over typical monolithic actuators.

Shape memory alloys (SMA) offer several advantages over traditional electro-mechanical devices, including: smooth, silent, clean operation; linear actuation; high power/weight ratio; scalability; and reduced part counts. These unique characteristics make them an attractive option when developing actuators, particularly at the meso- and micro-scales. However, SMAs do not typically display cyclic actuation and, therefore, require some reset force or bias mechanism in order to achieve this behaviour. Additionally, the micro-assembly of SMA material with a reset mechanism becomes increasingly difficult as the dimensions of actuators are scaled down. Therefore, actuators have been developed in which the actuation and reset mechanism are fabricated from a single piece of material. These actuators are referred to as monolithic actuators. Monolithic actuators are fabricated from a single piece of SMA material in which local annealing is used to selectively impart the shape memory effect (SME), while the remainder of the material acts as the bias mechanism. This work proposes an extension to monolithic actuators that locally varies the material composition of the monolithic component to exhibit different mechanical properties in select regions. This eliminates the need for local annealing by introducing regions of material unaffected by the annealing process. Additionally, incorporating regions of superelastic material to act as the bias mechanism greatly increases the actuator’s range of motion. These actuators are referred to as hybrid monolithic actuators. The creation of hybrid monolithic SMA actuators requires the development of both a fabrication technique and design tool. Varying the composition locally is accomplished by utilizing powder metallurgy fabrication techniques, specifically tape casting. Tapes of different compositions are cut, stacked, and sintered resulting in a monolithic component with mechanical properties that vary spatially. Tape casting NiTi from elemental powders is studied in this work, and tape recipes and sintering profiles are developed. In order to model the SMA behaviour of complex geometries, a finite element implementation of an existing lumped-element SMA model is developed. This model is used to design and simulate a prototype hybrid monolithic actuator. The prototype is fabricated and its performance used to illustrate the advantages of hybrid design over typical monolithic actuators.

The exciting thermomechanical properties of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic capabilities. Until recently, the performance capabilities of nickel-titanium devices have been inhibited by the retention of only one thermomechanical characteristic. However, laser processing technology promises to deliver enhanced material offerings which are capable of multiple functional responses. Presented in this thesis, is an investigation of the effects of laser processing on the thermomechanical behaviour of nickel-titanium shape memory alloys. In the context of this work, laser processing refers to removal of alloy constituents, as in the case of laser ablation, or alternatively, addition of elements through laser alloying. The effects of laser ablation on the composition, crystallography and phase transformation temperatures of a nickel-titanium strip have been studied. Application of laser energy was shown to ablate nickel constituents, induce an austenite-martensite phase change and cause an increase in phase transformation onset temperatures, which correlated well with reported findings. Laser processing of a nickel-titanium wire was shown to locally embed an additional thermomechanical response which manifested as unique shape memory and pseudoelastic properties. Localized alloying of ternary species via laser processing of nickel-titanium strip was investigated. Synthesis of a ternary shape memory intermetallic within the laser processing region was achieved through melting of copper foils. Results from thermoanalytical testing indicated that the ternary compound possessed a higher phase transformation temperature and reduced transformation hysteresis in comparison to the reference alloy. Indentation testing was used to demonstrate the augmented thermomechanical characteristics of the laser processed shape memory alloy. In order to demonstrate the enhanced functionality of laser processed nickel-titanium shape memory alloys, a self-positioning nickel-titanium microgripper was fabricated. The microgripper was designed to actuate through four different positions, corresponding to activation of three embedded shape memory characteristics. Thermoanalytical and tensile testing instrumentations were used to characterize the thermomechanical performance of the laser processed nickel-titanium microgripper. Results indicated that each of the laser processed microgripper components possessed unique mechanical and shape memory recovery properties.

The exciting thermomechanical properties of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic capabilities. Until recently, the performance capabilities of nickel-titanium devices have been inhibited by the retention of only one thermomechanical characteristic. However, laser processing technology promises to deliver enhanced material offerings which are capable of multiple functional responses. Presented in this thesis, is an investigation of the effects of laser processing on the thermomechanical behaviour of nickel-titanium shape memory alloys. In the context of this work, laser processing refers to removal of alloy constituents, as in the case of laser ablation, or alternatively, addition of elements through laser alloying. The effects of laser ablation on the composition, crystallography and phase transformation temperatures of a nickel-titanium strip have been studied. Application of laser energy was shown to ablate nickel constituents, induce an austenite-martensite phase change and cause an increase in phase transformation onset temperatures, which correlated well with reported findings. Laser processing of a nickel-titanium wire was shown to locally embed an additional thermomechanical response which manifested as unique shape memory and pseudoelastic properties. Localized alloying of ternary species via laser processing of nickel-titanium strip was investigated. Synthesis of a ternary shape memory intermetallic within the laser processing region was achieved through melting of copper foils. Results from thermoanalytical testing indicated that the ternary compound possessed a higher phase transformation temperature and reduced transformation hysteresis in comparison to the reference alloy. Indentation testing was used to demonstrate the augmented thermomechanical characteristics of the laser processed shape memory alloy. In order to demonstrate the enhanced functionality of laser processed nickel-titanium shape memory alloys, a self-positioning nickel-titanium microgripper was fabricated. The microgripper was designed to actuate through four different positions, corresponding to activation of three embedded shape memory characteristics. Thermoanalytical and tensile testing instrumentations were used to characterize the thermomechanical performance of the laser processed nickel-titanium microgripper. Results indicated that each of the laser processed microgripper components possessed unique mechanical and shape memory recovery properties.

TiNiPd high-temperature shape memory alloys (HTSMAs) have attracted considerable attention as potential solid-state actuators capable of operating at temperatures up to 500 °C, exhibiting excellent corrosion resistance, adequate ductility levels and significant strain recovery under both constrained and unconstrained thermomechanical conditions. During operation, these actuators may be subjected to multiple cycles and from an application point of view, the functional stability, i.e. conservation of original actuator dimensions and transformation temperatures during repeated employment, is of considerable importance. This study addresses the issue of functional stability in a model HTSMA, Ti50.5Ni24.5Pd25, for its use as a compact solid-state actuator. Since the primary reason for functional instability is the creation of lattice defects (dislocations, vacancies, etc.) during repeated transformation cycles, several methods were successfully undertaken to improve the functional stability through inhibiting the generation of these defects. Solid-solution strengthening through Sc microalloying and thermomechanical treatments via severe plastic deformation were the two approaches used to strengthen the HTSMA against defect generation. Thermal cycling the HTSMA under stress was the third method to voluntarily introduce defects into the microstructure such that further defect generation during application would be impeded. Overall, severe plastic deformation was found to be more efficient than other strengthening methods in improving the functional stability of TiNiPd HTSMA, yet it brought about disadvantages such as reduction in transformation strain and transformation temperatures. While functional instability is due to the creation of lattice defects, the generation of these defects is mainly controlled by the crystallographic incompatibility between martensitically transforming phases and the strength levels for plastic deformation. It was shown that TiNiPd HTSMAs, which exhibited martensitic transformation from a cubic (B2) to orthorhombic (B19) symmetry, illustrated better compatibility and thus better functional stability levels compared to TiNi SMAs, which had a B2 to monoclinic (B19’) transition. Although crystallographic incompatibility seems to be the governing factor for the functional stability of the TiNiPd HTSMA, the strength differential between the onset of plastic deformation and local constraint due to the martensitic transformation was also found to be an influential factor determining the overall stable behavior. Functional stability was also investigated for the two-way shape memory effect (TWSME) in TiNiPd HTSMAs. Better strength and compatibility levels compared to TiNi SMAs were also reflected in the TWSME characteristics in the form of enhanced stability under stress-free thermal cycling. The stability during constrained thermal cycling was not as good and TWSME degraded rapidly while doing work against an opposing stress. Nevertheless, work output levels were much higher as compared to those obtained from conventional TiNi and Cu-based SMAs.