Engineering Commons^™

Numerical Modeling And Simulation On Deformation And Failure Behaviors Of Polymeric Materials, Heng Feng

Electronic Thesis and Dissertation Repository

Featured by biocompatibility, high compliance and capacity in sustaining large deformation, dielectric elastomers (DEs) and hydrogels have gained extensive research popularity for their potential applications in the fields of soft robots, biomimetics, tissue engineering, drug delivery, and energy harvesting. The design of such soft and smart material-based devices and structures requires deep understanding and accurate simulation of their constitutive behaviors, which is challenged by their nonlinear material properties due to unique microstructures and multi-physics coupling. Meanwhile, in different application contexts, those structures are also susceptible to different failure modes, imposing further challenges in simulating and predicting their performance. To fulfill …

Microstructure-Informed Modeling Of Hydrogen Diffusion In Zirconium Polycrystals, Alireza Tondro

Electronic Thesis and Dissertation Repository

Zirconium alloys are widely used in the core of various types of nuclear reactors. During service, the hot water coolant reacts with zirconium and releases hydrogen atoms that ingress into the lattice of the metal alloy. With time, hydrogen concentration exceeds its terminal solid solubility limit in zirconium, and a brittle phase known as zirconium hydride forms. This phase severely deteriorates the mechanical properties of zirconium alloys, leading to safety concerns regarding the integrity of nuclear pressure tubes. This thesis uses a crystal plasticity finite element model coupled with diffusion equations to study the effects of localized deformation at the …

Hydration Kinetics, Microstructure, And Mechanical Strength Development Of Cement-Based Composites Incorporating Phase Change Materials, Afshin Marani

Electronic Thesis and Dissertation Repository

The research conducted in this thesis investigates the effects of phase change materials (PCMs) on the hydration kinetics and strength development of cement-based composites using extensive experimental and numerical analyses. Purposefully, the effect of microencapsulated PCMs (MPCMs) on the strength development of cement-based mortars and concretes was evaluated using powerful machine learning models trained with the largest available experimental data. Furthermore, a novel ternary machine learning approach was proposed to optimize the mixture design of mortars and concretes based on the thermos-physical properties of the MPCMs. The results obtained from machine learning simulations suggest the assessment of the effects of …

A Dislocation-Based Crystal Plasticity Model For Hexagonal Close-Packed Polycrystals, Omid Sedaghat

Electronic Thesis and Dissertation Repository

Due to their low neutron absorption cross-section and good corrosion properties, zirconium and its alloys have been widely used as the structural material in the core of nuclear reactors. These alloys are exposed to an intensive neutron flux which may lead to dimensional instabilities and the degradation of the mechanical properties of the alloy over the service time of the reactor. The changes in deformation behavior and mechanical properties can be traced back to the formation, evolution, and interaction of the irradiation-induced microstructural defects, e.g., point defect clusters, dislocation loops, and complex dislocation line networks. However, the materials constitutive models …

Development Of A Wireless Telemetry Load And Displacement Sensor For Orthopaedic Applications, William Anderson

Electronic Thesis and Dissertation Repository

Due to sensor size and supporting circuitry, in vivo load and deformation measurements are currently restricted to applications within larger orthopaedic implants. The objective of this thesis is to repurpose a commercially available low-power, miniature, wireless, telemetric, tire-pressure sensor (FXTH87) to measure load and deformation for future use in biomechanical applications. The capacitive transducer membrane of the FXTH87 was modified, and a relationship was reported between applied compressive deformation and sensor signal value. The sensor package was embedded within a deformable enclosure to illustrate potential applications of the sensor for monitoring load. Finite element analysis was an effective tool to …

Incipient Deformation Of Small Volumes Of Fcc Metals, Mahdi Bagheripoor

Electronic Thesis and Dissertation Repository

In the area of mechanics of materials, the classic theories cannot describe the material behaviour as the volume of deformation or sample size is small enough to be compared with the size scales of the imperfections of the crystal. So, there has been a great deal of interest in investigating the plasticity of micron and nano-sized materials, in the last 20 years. As a Ph.D. research project, the deformation mechanism at small scales of fcc metals is studied based on dislocations behaviour. The effect of main parameters that haven’t been studied in detail, including, crystal orientation, pre-existing faults, grain boundaries, …

Characterization And Computational Modelling For The Garnet Oxide Solid State Electrolyte Ta-Llzo, Colin A. Versnick

Electronic Thesis and Dissertation Repository

The all-solid-state-battery (ASSB) serves as a promising candidate for next generation lithium ion batteries for significant improvements in battery safety, capacity, and longevity. Of the material candidates researched to replace the conventionally used liquid electrolyte, the garnet oxide Ta-LLZO (Li_6.4La₃Zr_1.4Ta_0.6O₁₂) has received much attention thanks to its high chemical and electrochemical stability, and ionic conductivity which rivals that of liquid electrolytes. While much investigation has taken place regarding the electrochemical performance of Ta-LLZO, much less is known about the micromechanics, including microstructural characterization, stress and strain development, and material failure …

Effect Of The Nonlinear Material Viscosity On The Performance Of Dielectric Elastomer Transducers, Yuanping Li

Electronic Thesis and Dissertation Repository

As a typical type of soft electroactive materials, dielectric elastomers (DEs) are capable of producing large voltage-induced deformation, which makes them desirable materials for a variety of applications in transduction technology, including tunable oscillators, resonators, biomimetics and energy harvesters. The dynamic and energy harvesting performance of such DE-based devices is strongly affected not only by multiple failure modes such as electrical breakdown, electromechanical instability, loss-of-tension and fatigue, but also by their material viscoelasticity. Moreover, as suggested by experiments and theoretical studies, DEs possess nonlinear relaxation processes, which makes modeling of the performance of DE-based devices more challenging.

In this thesis, …

Advances In Design Methodology In Swelling Shale Rock In Southern Ontario, Thomas R.A. Lardner

Electronic Thesis and Dissertation Repository

As infrastructure requirements increase in southern Ontario, excavations within swelling rock formations will become more frequent and larger. The objective of this study is to advance design capability for structures in swelling rock through three aspects: i) developing a practical swelling model for design engineers, ii) investigate two crushable/compressible materials for the mitigation of swelling rock effects, and iii) observe and analyze the behaviour of swelling rock to current excavation techniques.

A swelling rock constitutive model has been developed. The swelling parameters include the horizontal and vertical free swell potential, threshold stress, and critical stress as well as a “pseudo-Poisson’s …

Electrospun Collagen Fibers For Tissue Regeneration Applications, Ying Li

Electronic Thesis and Dissertation Repository

Tissue engineering aims to regenerate damaged and deceased tissue by combining cells with scaffold made from an appropriate biomaterial and providing a conducive environment to guide cell growth and the formation or regeneration of new tissue or organ. While collagen, an important material of the extracellular matrix (ECM), is a natural choice as a scaffold biomaterial, the conducive environment can only be created by having the ability to control the geometry, organization, structural and mechanical properties of the scaffold. Moreover, degradability and degradation rate control of the scaffold has to be taken into consideration too. In this work, we aim …

Effect Of Material Viscoelasticity On Frequency Tuning Of Dielectric Elastomer Membrane Resonators, Liyang Tian

Electronic Thesis and Dissertation Repository

Dielectric elastomers (DEs) capable of large voltage-induced deformation show promise for applications such as resonators and oscillators. However, the dynamic performance of such vibrational devices is not only strongly affected by the nonlinear electromechanical coupling and material hyperelasticity, but also significantly by the material viscoelasticity. The material viscoelasticity of DEs originates from the highly mobile polymer chains that constitute the polymer networks of the DE. Moreover, due to the multiple viscous polymer subnetworks, DEs possess multiple relaxation processes. Therefore, in order to predict the dynamic performance of DE-based devices, a theoretical model that accounts for the multiple relaxation processes is …

Mechanical Characterization And Shear Test Comparison For Continuous-Fiber Polymer Composites, Matthew Crossan

Electronic Thesis and Dissertation Repository

As fiber-reinforced composites continue to be used in a wide-range of high performance structures, more detailed understanding and accurate prediction of stress-strain behaviour is necessary to improving designs and reducing costs. This thesis compares the experimental behaviour of a continuous fiber polymer composite of carbon fiber and epoxy resin using Digital Image Correlation to analytical and theoretical predictions. Furthermore, an in-depth analysis of shear testing methods reveals the advantages and limitations of different testing standards. Finally, the limitations of the Iosipescu Shear test (ASTM 5379) fixture to break high-strain-to-failure composites in comparison to the V-notched Rail Shear Fixture (ASTM 7078) …

Process-Structure-Property Relationships For High Pressure Die-Cast Magnesium Alloys, Pouya Sharifi

Electronic Thesis and Dissertation Repository

The primary goal of this study was to conduct experiments and simulation modeling to determine the relevant filling and solidification process parameters that influence microstructural features of the high-pressure die-cast magnesium alloy AM60. This work continues from the previous research that has been carried out by Dr. Jeff Wood’s research group over the last sixteen years.

Metallographic and spherical microindentation were used to analyze the influence of microstructural features on the flow stress for both skin (finer grain sizes) and core (larger grain sizes) of high pressure die castings (HPDC), as well as different regions of gravity cast stepped-plate. It …

Study On The Mechanical Behavior Of Directly Compounded Long Glass Fiber Reinforced Polyamide 6 Composites, Yuchao Liu

Electronic Thesis and Dissertation Repository

With great lightweight potential, high performance-to-cost ratio and mass productivity, direct-compounded long fiber thermoplastics (D-LFT) have drawn great attention from the automotive industry. With better mechanical properties and higher service temperature, polyamide 6 (PA6) was used to replace polypropylene (PP) which is almost the exclusively used matrix for the D-LFT process currently. The investigation was performed on this new material with a focus on the effect of fiber content, processing parameters, temperature and tailored reinforcement on mechanical behavior. The results show that the mechanical properties of this new material are sensitive to the variation of fiber content and service temperature …

Electromechanical Coupling Behavior Of Dielectric Elastomer Transducers, Jianyou Zhou

Electronic Thesis and Dissertation Repository

Dielectric elastomer transducers with large deformation, high energy output, light weight and low cost have been drawing great interest from both the research and industry communities, and shown potential for versatile applications in biomimetics, dynamics, robotics and energy harvesting. However, in addition to multiple failure modes such as electrical breakdown, electromechanical instability, loss-of-tension and fatigue, the performance of dielectric elastomer transducers are also strongly influenced by the hyperelastic and viscoelastic properties of the material. Also, the interplay among these material properties and the failure modes is rather difficult to predict. Therefore, in order to provide guidelines for the optimal design …

Size-Dependent Electroelastic Properties Of Piezoelectric Nanoplates, Zhengrong Zhang

Electronic Thesis and Dissertation Repository

With the development of nanotechnology, piezoelectric nanostructures have attracted a surge of interests in research communities for the potential applications as transistors, sensors, actuators, resonators and energy harvesters in nanoelectromechanical systems (NEMS) due to their high electromechanical coupling and unique features at the nano-scale. Piezoelectric nanomaterials have been characterized to possess size-dependent electromechanical coupling properties from both experimental and theoretical perspectives. Therefore it is of great importance to investigate the physical mechanisms of these distinct nano-scale structure features in order to fulfill the design and application of those piezoelectricity-based nanodevices.

Due to large surface to volume ratio and manifest strain …

Mechanistic Failure Criterion For Unidirectional And Random Fibre Polymer Composites, Jamaloddin Jamali

Electronic Thesis and Dissertation Repository

Polymer composite design in energy absorbing components requires a failure criterion that can predict the energy involved in its fracture under different modes of loading. Present mixed mode criteria are mainly empirical or semi-empirical, and are only suitable for a small range of composite types.

The purpose of this study was to develop a mechanistic failure criterion that is applicable to a wide range of polymer composites. An energy based mechanistic failure criterion is proposed to characterize the toughness of unidirectional (UD) and randomly oriented short fibre composites (random fibre composites).

In UD and random composites, the criterion predicts the …

Continuum Modeling On Size-Dependent Properties Of Piezoelectric Nanostructures, Zhi Yan

Electronic Thesis and Dissertation Repository

Piezoelectric beam- and plate-based nanostructures hold a promise for device applications in the nanoelectromechanical systems (NEMS) due to their superior mechanical and electromechanical coupling properties. “Small is different”, nanostructured piezoelectric materials exhibit size-dependent properties, which are different from their bulk counterparts. For predicting the unique physical and mechanical properties of these novel nanostructures, continuum mechanics modeling has been regarded as an efficient tool. However, the conventional continuum models fail to capture the size effects of nanostructures and thus are not directly applicable at the nanoscale. Therefore, it is necessary to develop modified continuum models for piezoelectric nanostructures by incorporating the …

Vibration And Buckling Of Carbon Nanotube, Graphene, And Nanowire, Mohammad Hadi Mahdavi

Electronic Thesis and Dissertation Repository

Nanostructured materials with superior physical properties hold promise for the development of novel nanodevices. Full potential applications of such advanced materials require accurate characterization of their physical properties, which in turn necessitates the development of computer-based simulations along with novel experimental techniques. Since controlled experiments are difficult for nanoscale materials and atomic studies are computationally expensive, continuum mechanics-based simulations of nanomaterials and nanostructures have become the focal points of computational nano-science and materials modelling.

In this study, emphasis is given to predicting the mechanical behaviour of carbon nanotube (CNT), graphene, nanowire (NW), and nanowire encapsulated in carbon nanotube (NW@CNT), which …