Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2010. / Hybrid polymeric composites (HPC) are widely used for the design of aerospace, automobile and civil engineering structures. One of the major challenges posed by these materials and structures is their brittle nature. When subjected to impact and dynamic loads, the polymeric composite structures undergo micro cracking. The cracks coalesce, propagate and can lead to catastrophic failure of the material and structures. In this thesis, an intelligent hybrid polymeric composite (IHPC) beam with healing ability was developed and tested. The IHPC beam developed consisted of a 3% prestrained 1mm diameter Ni-Ti shape memory alloy (SMA) wire actuator embedded in the polymeric host matrix. The function of the embedded Ni-Ti shape memory alloy was to enhance intelligence and healing ability to the IHPC beam. Upon electric current resistance heating, the Ni-Ti SMA actuator responds by contracting as a result of detwinned martensite → austenite phase transformation. Contraction of the SMA in the IHPC beam was utilized to stiffen and enhance healing by retarding crack growth and recovery of the strain induced in the loaded IHPC beam. This can result to increase of the flexural stiffness EI (defined as the product of the Young’s Modulus E of the material and the moment of inertia I of the geometry of the beam) and mode I fracture stress intensity factor KIC of the IHPC beam. One (1) mm diameter Ni-Ti SMA wire was used in the experimental work in this thesis. The wire was cut into 35 pieces, 200 mm long each. Ni-Ti SMA wires were heated in the furnace to a temperature of 250ºC for ten (10) hours then were left to cool in the ambient air. The heat treatment was aimed to release any residual stress and to stabilize the austenite start (AS) and austenite finish (Af) transformation temperatures of the Ni-Ti SMA. After heat treatment, the Ni-Ti SMA wires were prestrained by 3% (based on a gauge length of 150mm) on a tensile testing machine. Prestraining of the Ni-Ti SMA wires was aimed to induce detwinned martensite volume fraction in them hence increasing the transformation strain and recovery force of the Ni-Ti SMA actuator. Intelligent hybrid polymeric composite (IHPC) beams and polymeric virgin (PV) beams, all of dimensions 150mmx25mmx10mm were manufactured by casting 60D polyurethane thermosetting epoxy resin in a silicon mould. transformation strain and recovery force of the Ni-Ti SMA actuator.

Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2015. / This dissertation addresses the development and the testing of a simulation tool to be used to predict the behaviour of smart material/structures. Along with the development of the simulation tool, a new form of the model describing the behaviour of shape-memory alloy was developed and implemented. The proposed model was developed based on the existing cosine model, conventionally used in literature, but it uses hyperbolic tangent functions. The hyperbolic tangent function was chosen so as to allow the simulation of any range of temperatures. Experiments were performed to obtain the parameters to be used in the simulation and to validate the numerical results. Two different simulations were performed: a one dimensional FEA analysis with a two dimensional orientation (NiTi SMA wire simulation) and a three dimensional FEA analysis (NiTi SMA plate) [Msomi and Oliver, 2015]. Alongside the FEA analysis, two experiments were performed with the purpose of obtaining the material parameters to be used in FEA analysis and to compare the FEA results to the experimental results. / Airbus Company

Orientador: Jorge Otubo / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-16T22:36:53Z (GMT). No. of bitstreams: 1 Minetto_RobertoTadeu_M.pdf: 5159616 bytes, checksum: a09b62580c76b0c4d2322045c6ba6a3d (MD5) Previous issue date: 2010 / Resumo: Idealmente, as juntas rigidamente fixadas por parafusos deveriam manter as forças de aperto aplicadas em cada parafuso até o final da vida útil e com um mínimo de variação entre os parafusos de um mesmo conjunto. No entanto, ensaios mecânicos comprovam que a dispersão das forças de aperto, nos processos atuais de fixação do cabeçote de cilindros, é muito grande e que a perda de pré-carga pode chegar a 30%. Ou seja, se aplica 100 kN e ter-se-á efetivamente 70 kN de força resultante após algumas horas de utilização. Esta perda é devido à acomodação (relaxamento) dos picos de usinagem da rosca e da face de assentamento da cabeça do parafuso, das deformações plásticas dos componentes envolvidos, do "endireitamento" parafuso, da velocidade do fuso de aperto, etc. Como o sistema de aperto convencional não usa arruela entre o parafuso e o cabeçote, a proposta deste projeto foi estudar o uso da liga Ti-50,67at%Ni com efeito de memória de forma (superelástico) para a utilização na confecção desta arruela. Uma vez montada no conjunto, a arruela estará sujeita a uma carga de compressão, e, devido ao efeito da memória de forma, o componente tenderá a voltar à forma original minimizando ou mesmo eliminando a perda de carga sofrida pelos parafusos usados na montagem / Abstract: Gaskets rigidly attached by bolts should keep the applied forces to each bolt until the end of its life and presenting a small force variation among the bolts of the same set. However, mechanical tests confirms that the bolt forces dispersion, in the current cylinder head fixation process, is large and the pre load loss reach 30 per cent. It means that if we apply 100 kN, we are going to have 70 kN of resultant bolt forces after few hours of running tests. This loss is caused by machining peaks accommodation in the thread contact and bolt head seating, plastic deformation (thermal and mechanical) of the involved components, bolts beating and others important aspects of bolt torque strategy. As the current system does not use flat washers between the bolt head and cylinder head bosses this project purposes to study the use of Ti-50,67at%Ni alloy, with shape memory effect (superelasticity) , for fabricating this washer. When assembled in the set, the washer will suffer a compressive load and because of the shape memory effect, the component will try to return to the original form, minimizing or even eliminating the pre load loss by bolts used to set / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Automobilistica

Un réseau acrylate amorphe a été fabriqué au laboratoire. Une caractérisation de ses propriétés mécaniques par des essais quasi-statiques et cycliques en traction uniaxiale à différentes températures a été effectuée. Puis, des essais qualifiant et quantifiant la propriété de mémoire de forme de ce matériau ont été menés en appliquant des cycles thermomécaniques de traction uniaxiale. Durant cette étude expérimentale, plusieurs paramètres d'essais ont été variés afin d'estimer leur influence sur la propriété de mémoire de forme. Enfin, afin d'étendre les applications mémoire de forme des réseaux polymères, deux études supplémentaires ont été conduites. La première vise à la réutilisation du matériau pour des applications mémoire de forme. La seconde étude vise à renforcer le matériau obtenant un matériau composite pour améliorer sa propriété de retour de forme sous contrainte (en retour de ‘'force'').Afin d'améliorer la conception d'applications des polymères à mémoire de forme, un modèle grandes déformations, combinant les propriétés viscoélastiques et l'équivalence temps--température du matériau, a été choisi pour prédire le comportement et la mémoire de forme du réseau acrylate et ses composites. Le modèle existant dans les librairies matériaux du code éléments finis Abaqus permet de simuler numériquement les cycles thermomécaniques appliqués expérimentalement de manière exacte. Les résultats issus des simulations ont montré une bonne représentation des mesures expérimentales, reproduisant les effets des paramètres du cycle de mémoire observés expérimentalement. Une analyse des paramètres du modèle est proposée mettant en évidence la sensibilité de la propriété de mémoire de forme aux propriétés d'équivalence temps-température mesurées expérimentalement. / A chemically crosslinked amorphous acrylate network has been prepared in the laboratory. Its mechanical properties were characterized by quasi-static and cyclic uniaxial tensile tests, while varying the temperature. The shape memory property of the polymer was recognized by the application of specific thermomechanical cycles in uniaxial tension (free-length and constrained-length recovery). During the experimental study, the thermomechanical cycle parameters were varied in order to study their influence on the shape memory behavior. Two additional studies were included to improve the potential applications of shape memory polymers. The first study targeted the use of the material shape memory property for subsequent shape memory cycles. The second study aimed at improving the material shape memory properties during fixed length heating (constrained-length recovery) by adding fillers .In order to improve the shape memory polymers application design, a large strain model, combining the material viscoleasticity and its time-temperature superposition property, was chosen to predict the shape memory behavior of the material. The model features, existing in the material behavior libraries of the finite element code Abaqus, allowed simulating numerically the experimental thermomechanical shape memory cycles. Results of the simulations showed good agreements when compared with the experimental results, reproducing the shape memory cycles influence to loading parameters. A parameter sensitivity analysis revealed the shape memory property dependence on the time-temperature superposition.

Shape memory alloys (SMAs) are materials that show reversible, thermo-elastic, diffusionless, displacive (solid to solid) phase transformation, due to the application of temperature and/ or stress (/strain). Among different SMAs, NiTi is a popular one. NiTi shows reversible phase transformation, the shape memory effect (SME), where irreversible deformations are recovered upon heating, and superelasticity (SE), where large strains imposed at high enough temperatures are fully recovered. Phase transformation process in NiTi SMA is a very complex process that involves the competition between developed internal strain and phonon dispersion instability. In NiTi SMA, phase transformation occurs over a wide range of temperature and/ or stress (strain) which involves, evolution of different crystalline phases (cubic austenite i.e. B2, different monoclinic variant of martensite i.e. B19', and orthorhombic B19 or BCO structures). Further, it is observed from experimental and computational studies that the evolution kinetics and growth rate of different phases in NiTi SMA vary significantly over a wide spectrum of spatio-temporal scales, especially with length scales. At nano-meter length scale, phase transformation temperatures, critical transformation stress (or strain) and phase fraction evolution change significantly with sample or simulation cell size and grain size. Even, below a critical length scale, the phase transformation process stops. All these aspects make NiTi SMA very interesting to the science and engineering research community and in this context, the present focuses on the following aspects. At first this study address the stability, evolution and growth kinetics of different phases (B2 and variants of B19'), at different length scales, starting from the atomic level and ending at the continuum macroscopic level. The effects of simulation cell size, grain size, and presence of free surface and grain boundary on the phase transformation process (transformation temperature, phase fraction evolution kinetics due to temperature) are also demonstrated herein. Next, to couple and transfer the statistical information of length scale dependent phase transformation process, multiscale/ multiphysics methods are used. Here, the computational difficulty from the fact that the representative governing equations (i.e. different sub-methods such as molecular dynamics simulations, phase field simulations and continuum level constitutive/ material models) are only valid or can be implemented over a range of spatiotemporal scales. Therefore, in the present study, a wavelet based multiscale coupling method is used, where simulation results (phase fraction evolution kinetics) from different sub-methods are linked via concurrent multiscale coupling fashion. Finally, these multiscale/ multiphysics simulation results are used to develop/ modify the macro/ continuum scale thermo-mechanical constitutive relations for NiTi SMA. Finally, the improved material model is used to model new devices, such as thermal diodes and smart dampers.

This work deals with the modelling of shape-memory alloys, in particular with the steady-state model of martensitic thin films. After the introductory motivation the crystallographic structure of the materials is described followed by the introduction of the link between the lattice and continuum model. The next parts of the work focus on the possible solutions of the given 3D variational problem (quasiconvexification, Young measures) and on derivation of thin film theories with the aid of different tools (regularization,-convergence). The last part takes over an approximation of an obtained model and sketches numerical experiments on a Ni-Mn-Ga alloy.

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Squat reinforced concrete shear walls are stiff structural elements incorporated in buildings and other structures and are capable of resisting large seismic demands. However, when not properly designed, they are prone to shear-related brittle failure. To improve the seismic behaviour of these structural elements, a retrofitting bracing system incorporating superelastic Shape Memory Alloys (SMAs) was developed. Superelastic Shape Memory Alloys (SMAs) are smart materials with the ability to sustain and recover large pseudo-plastic deformations while dissipating energy. The SMA bracing system consists of tension-only SMA links coupled with rigid steel elements. The SMA links were designed to sustain and recover the elongation experienced by the bracing system, while the steel elements were designed to sustain negligible elastic elongations. The SMA bracing system was installed on third-scale, 2000 mm × 2000 mm, shear walls, which were tested to failure under incremental reverse cyclic loading. The experimental results demonstrated that the tension-only SMA braces improve the seismic response of squat reinforced concrete walls. The retrofitted walls experienced higher strength, greater energy dissipation, and less permanent deformation. The re-centering properties of the SMA contributed to the reduction of pinching in the hysteretic response due mainly to the clamping action of the SMA bracings while recovering their original length. The walls were numerically simulated with the nonlinear finite element program VecTor2. The numerical simulations accurately captured the hysteretic response of both the original and the retrofitted walls. A parametric study was conducted to assess the effect of axial loading and size of the SMA braces.

Les Transformation Martensitiques (TM) sont des transitions du premier ordre entre des phases cristallines qui caractérisent une classe intéressante de matériaux intelligents, les Alliages à Mémoire de Forme (AMF). Ces alliages métalliques furent découverts dans les années 1930 environ. Ils sont surtout intéressants car ils combinent deux effets particuliers : l'effet de mémoire de forme et la pseudo-élasticité. L'effet mémoire de forme consiste à mémoriser une configuration particulière et la retrouver après des cycles thermiques ou mécaniques. La Pseudo-Elasticité consiste à rejoindre des niveaux de déformation très grands qui sont, en général, plus typiques du caoutchouc que des métaux. Dans cette thèse, nous avons traité la caractérisation des transformations martensitiques en analysant des points de vue différents. La compréhension du fonctionnement des AMFs est fondamentale pour plusieurs types d'applications industrielles. Elle constitue encore un domaine de recherche très ouvert. (...) / This thesis deals with the characterization of Martensitic Transformations (MT) that are first order phase transitions among different solid states with different crystalline structures. These transitions are at the basis of the behavior of a class of smart materials, called Shape Memory Alloys (SMA). This work combines an experimental study of a mechanically-induced martensitic transformation in a Cu-Al-Be single crystal and a macroscopic model for the reproduction of permanent effects in cyclic temperature-induced and stress-induced transitions. From the experimental point of view, the novelties are in the device that has been built and used for the test and in the full-field measurement technique at the basis of the data treatment. The especially designed gravity-based device allows for a uni-axial and uni-directional tensile test with slow loading rates. Simultaneously, the full-field measurement technique, known as grid method, provides high-resolution two-dimensional strain maps during all the transformation. With all the data collected during the test, we characterize for the first time the two-dimensional strain intermittency in a number of ways, showing heavy-tailed distributions for the strain avalanching over almost six decades of magnitude. In parallel, we develop a macroscopic mathematical model for the description of fatigue and permanent effects in several kinds of martensitic transformations. We show an easy way to calibrate the model parameters in the simple one-dimensional case. Moreover, we compare the numerical results with experimental data for different tests and specimens and obtain a good qualitative agreement.