Department of Mechanical and Materials Engineering Graduate Theses
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Item Trabecular Bone Adaptation: An Experimental And Computational Investigation(2025-03-24) Zojaji, Mahsa; Mechanical and Materials Engineering; Ploeg, Heidi-LynnBone mechanical properties are influenced by its complex microstructure which when disrupted, compromises bone function and increases fracture risk. This thesis explored trabecular bone adaptation to mechanical loading using ex vivo experimental and computational approaches. The effects of mesh density, element formulation, and heterogeneous material grouping on human trabecular bone micro finite element (μFE) models were quantified. Finer mesh resolutions (20 μm) yielded more accurate predictions but required higher computational resources. Both voxel- and geometry-based μFE models showed strong correlations (R² ≥ 0.8) with measured apparent elastic modulus, confirming their accuracy in predicting bone mechanics. Geometry-based models provided higher accuracy, while voxel-based models yielded more precise predictions. The ex vivo experiment found high strain magnitude and low strain rate were insufficient to stimulate trabecular bone formation. A custom-made algorithm was developed to simulate trabecular bone surface adaptation in response to mechanical loading and compared against the experiment. Although the predicted change in stiffness did not align with the ex vivo measurements, several valuable insights on structural contributions to trabecular bone adaptation in response to mechanical stimuli were discovered: 1. adaptation was specimen specific; 2. formation and resorption occurred simultaneously throughout the bone core; 3. tissue elastic modulus and thickness changed in a heterogeneous manner; and, 4. peak stress was reduced through bone adaptation. The contributions of this thesis advance the understanding of trabecular bone mechanical behaviour and its adaptation to mechanical loading, offering a promising framework for future applications in bone health research and the development of personalized therapeutic strategies.Item Integrated Packaging and Topology Optimization for Non-Structural Component Assemblies(2025-03-10) Krsikapa, Daniel; Mechanical and Materials Engineering; Kim, Il YongThis thesis proposes new Packaging Optimization (PO) and Integrated Packaging and Topology Optimization (IPTO) methods tailored for electro-mechanical assemblies in the automotive and aerospace industries, addressing key challenges such as mounting requirements, accessibility, part-dependant loading and assemblability. First, a gradient-based PO framework is proposed that accounts for space utilization, component overlap, proximity relationships, and continuous positioning on non-planar mounting surfaces, as well as accessibility from customizable access points. Applied across three case studies, the proposed method achieved feasible, tightly packed layouts under various engineering constraints. Notably, when compared to the established Dynamic Vector Fields (DVF) method in a simplified packing problem, it achieved a 5.3% increase in packing density and a 98.2% reduction in component overlap. Building on this PO method, a novel IPTO approach is proposed that simultaneously optimizes component layouts and supporting structures. Novel procedures were implemented to handle part-dependent loading from non-structural components without modifying finite-element meshes, and an assembly penalty function ensured practical manufacturability by penalizing designs that block component installation. In one academic-level case study, the new method produced a 90.6% lower compliance value than a traditional design benchmark, and for a more complex drone design, it achieved a 41.2% lower compliance value than the respective benchmark. Through these newly formulated engineering parameters, novel PO and IPTO methodologies have emerged, both capable of addressing a variety of industrial design challenges, enabling designers to achieve efficient, high-performance assemblies for electro-mechanical systems.Item Development and Testing of a System to Interpret Emotion for Children With Severe Motor and Communication Impairments (SMCI)(2025-01-30) Vowles, Caryn; Mechanical and Materials Engineering; Davies, ClaireThis research aimed to advance the understanding of emotional expression in children with severe motor and communication impairments (SMCI) by developing and testing an algorithm to interpret psychophysiological signals of emotion. The study had three primary objectives: to create an emotion-detection algorithm, to validate its accuracy with typically developing populations, and to evaluate its applicability for children with SMCI. Despite the pandemicrelated restrictions that prevented direct collaboration with SMCI participants, the research leveraged data from typically developing individuals. Currently, models do not contain representative data or predict for individuals that are non-typical such as children with SMCI. The main limitation of this research was the reliance on data from typically developing populations in the development of the initial model, which limited the application of the model when processing data from children with SMCI. The complexities of emotion assessment in participants with SMCI were further compounded by challenges in communication and the limitations of the Self-Assessment Manikin (SAM) tool, which some children with SMCI struggled to comprehend. Additionally, there appeared to be a tendency to suppress or exaggerate emotions which posed challenges when corroborating scores from the caregiver. This research highlighted the need for an emotion detection device based on physiological signals especially in situations where it is important to know the child’s emotion for their overall wellbeing. The developed algorithm employed a two-phase model, integrating Signal to PAD (Pleasure, Arousal, Dominance) and PAD to Emotion, to decode emotions. Based on data from the typical population, the model confirmed the presence of six basic emotions, including happy, sadness, anger, disgust, and nuanced types of surprise (good and bad) while also highlighting the intricate nature of emotional experiences and the pivotal role of dominance in emotion perception. The model was tested using the DEAP dataset available online and the BDAT lab dataset that includes participants with SMCI. The model was accurate 21% of the time when selecting P, A, D scores on a nine point scale. However, the model was only successful in correctly predicting emotions in four cases of a potential 300 trials collected with the population of children with SMCI. The research contributes valuable insights into emotion detection in underrepresented populations, emphasizing the need for more nuanced models to capture the complexity of emotional experiences. Future research should focus on long-term studies involving participants with SMCI in natural settings and explore advanced technologies like ECG enabled smartwatches. Investigating alternative modeling techniques, such as neural networks, could also enhance the accuracy of emotion detection.Item Preferential Intergranular Oxidation and Stress Corrosion Cracking of Alloy X-750 in CO-CO2 Gas Mixtures(2025-01-30) Yaedu, Adriano Eidi; Mechanical and Materials Engineering; Persaud, SurajThe mechanical integrity of garter spring spacers used in CANada Deuterium Uranium (CANDU®) reactors are important to the integrity of pressure tubes that house fuel bundles. Brittle intergranular fracture was observed on Alloy X-750 ex-service spacers, instigating materials research to identify the responsible mechanisms. Alloy X-750 is a precipitation-hardened variant of Alloy 600 (72Ni-16Cr-9Fe) with the addition of Al and Ti, resulting in the formation of ’ precipitates, providing high strength. Alloy 600 and X-750 are susceptible to primary water stress corrosion cracking (PWSCC) in both pressurized water reactors (PWR) and boiling water reactors (BWR). Currently, preferential intergranular oxidation (PIO) is the most accepted mechanism for PWSCC, where the primary water environment (~300 °C hydrogenated water) enables selective oxidation of alloying elements, notably Cr, while Ni remains metallic. While spacers normally reside in a dry oxidizing mixture of CO2 and O2 within the annular gas system (AGS), extreme off-chemistry reducing conditions are being considered, which could promote PIO and embrittlement. In this project, PIO of Alloy X-750 was studied in 480 °C CO-CO2 reducing environments, in scenarios well away from the AGS but useful for establishing boundary conditions. Aged and annealed samples of Alloy X-750 were exposed to reducing CO-CO2 mixtures with the oxygen partial pressure ranging from 500× to 100,000× below the NiO oxygen dissociation pressure. Internal and intergranular oxidation were observed under all conditions, similar to Alloy 600 when exposed to 480 °C H2-steam in reducing thermodynamic conditions. Further nanoscale analysis of the samples tested at 500× and 5000× revealed that Al and Ti oxides lead PIO, while intergranular carbides hindered intergranular oxidation. Pre-notched samples tested in the 500× condition at 480 °C and with a stress intensity of 29.1 MPa×m0.5 resulted in fracture with characteristics analogous to PWSCC and internal oxidation: intergranular cracking driven by PIO with Ni nodules covering the fracture surface. In conclusion, Alloy X-750 spacers can undergo PIO in CO-CO2 gaseous environments via a PWSCC-like mechanism; however, this is conditional on the absence of O2 and maintaining a reducing environment for an extended period of time, both of which are unlikely in the AGS.Item Modeling Zirconium Under Neutron Irradiation: Interatomic Potentials, Displacement Cascades, and Electron-Ion Coupling(2025-01-28) Ghorbani, Amir; Mechanical and Materials Engineering; Béland, Laurent Karim; Tamm, ArturThis thesis presents a comprehensive atomistic computational study on the effects of neutron irradiation on Zr, a material extensively used in CANada Deuterium Uranium (CANDU) reactors. Our goal is to improve the understanding of microstructural changes under irradiation, focusing on displacement cascades that produce defects. Point defects and their clusters influence the mechanical properties, dimensional stability, and service life of components in reactor environments. The key contributions are: 1. Reparameterization of Interatomic Potentials: Three embedded atom method (EAM) potentials were reparameterized to improve simulation accuracy. Using density functional theory (DFT) calculations, the two-body and embedding energy functions were refitted to better describe atomic interactions at short distances. The modified potentials maintained similar near-equilibrium properties such as defect formation energies and elastic constants but significantly improved threshold displacement energies (TDEs), particularly for [0001] direction. 2. Simulation of Displacement Cascades: Large-scale molecular dynamics (MD) simulations modeled high-energy collision cascades in hexagonal close-packed (HCP) α-Zr. The study examined defect generation, damage morphology and diffusion behaviour. For this purpose, a novel post-processing technique was developed. Self-interstitial atom (SIA) clusters displayed greater anisotropy than equilibrium clusters. 1D and 2D diffusion modes were observed. Findings were integrated into a rate-theory model that predicted radiation-induced growth strains. 3. Effect of Electron Stopping: MD simulations that incorporate ion-electron coupling were conducted using a calibrated version of the unified two-temperature model (UTTM). This approach allowed for a more accurate assessment of electronic effects on primary damage production in Zr, representing the first application of the UTTM to neutron irradiation in Zr. The results suggested that the electronic stopping and the assisted recovery altered the damage production. This thesis advances the atomic-scale understanding of radiation-induced damage in Zr. The reparameterized EAM potentials enhance the fidelity of future MD simulations. The insights into the anisotropy of defect diffusion and its role in radiationinduced growth, along with the novel UTTM-based simulations, contribute significantly to the field. These findings provide a stronger foundation for ongoing experimental, operational, and regulatory efforts to maintain the safety and performance of nuclear reactors.