Department of Mechanical and Materials Engineering Graduate Theses

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    The Development of a Head and Neck Support Device for Children with Cerebral Palsy
    (2024-05-17) Cooke, Hannah; Mechanical and Materials Engineering; Li, Qingguo; Davies, Claire
    Children with cerebral palsy, who are classified as levels four and five on the Gross Motor Function Classification System, struggle with posture and sitting upright. This inability to sit upright impacts many aspects of their life such as learning, eating, communicating, and breathing. If a person with cerebral palsy can keep their head upright, there are many benefits that include reduced muscle tone, better upper-extremity functioning, increased comfort, and improved functioning in society. The purpose of this research was to develop a head and neck support device for children with cerebral palsy. A user-centered design approach was taken focusing on a child in Kingston with cerebral palsy. While the device addresses the needs of the research participant, it is still generalizable to other children with cerebral palsy, who experience similar problems. A quality function deployment was performed, to identify the engineering specifications. To gain information about the child’s requirement for self-support, evaluation techniques included a measurement of the range of head motion during cervical flexion and quantification of the force exerted during these movements. A separate testing scenario was created to investigate mechanical fuse options. To design the device, an iterative trial and error process was undertaken. This process involved reflective assessment, which included evaluations using weighted design matrices with the client. The final design was divided into four components: the mounting system, the head support, the connection point, and the chin support. When people with cerebral palsy have better posture, they can make proper eye contact, feel more confident and better engage in conversation. This thesis provides an overview of the developmental process when integrating participatory action research in the creation of a head and neck support device for children with cerebral palsy.
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    Design of a Bone-Implant Micromotion Test for Total Ankle Arthroplasty Tibial Components
    (2024-05-08) Nguyen, Kevin; Mechanical and Materials Engineering; Ploeg, Heidi-Lynn
    Total ankle arthroplasty (TAA) has become a favourable treatment for ankle osteoarthritis (OA). This surgical procedure allows for the preservation of ankle mobility and function, while also reducing the progression of adjacent joint degeneration. Although TAA may show improvements in short- and mid-term clinical outcomes, at the 10-year survivorship, there is a high failure rate associated with aseptic loosening of at least one component (26% to 68%), which is significantly higher than hip and knee arthroplasty. Currently, the newer generation of TAA implants rely on primary and secondary fixation, in which primary fixation is obtained through mechanical fixation immediately post-operative and secondary fixation is achieved through bone ingrowth at the bone-implant interface. To promote bone ingrowth, low micromotion between the bone and implant of 20 µm to 50 µm is required. Due to the lack of standard micromotion tests for TAA tibial components, the current study aimed to develop a mechanical test to measure the maximum micromotion at the bone surrogate-implant interface for TAA tibial components. The proposed mechanical test was able to measure micromotion with linear variable differential transformers (LVDTs) and calculate the maximum micromotion. A statistically significant difference in maximum micromotion was detected when tested with two low density PU foams (10 PCF and 15 PCF). Although, the maximum micromotion (>150 μm) observed was larger than other published studies, the proposed mechanical test can be further improved including implementing finite element analysis or digital image correlation. This thesis gives insights on the importance of a patient’s bone density and how that may dictate the successful fixation of TAA tibial components. By providing testing methods and quantifying micromotion of TAA tibial components with different clinical experiences, orthopaedic surgeons and implant manufacturers will gain insights into operative techniques and implant choices to improve long-term clinical outcomes for TAA.
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    The Role of the Trunk in the Stability and Energetics of Locomotion
    (2024-05-07) Best, Aaron Nicholas; Mechanical and Materials Engineering; Wu, Amy
    Human bipedal walking can be both stable and energetically efficient in complex envi ronments. Previous research in the field has primarily addressed how the lower limbs are controlled to ensure this stability and efficiency. However, little is known about how the trunk contributes towards gait stability and energetic efficiency. To address this gap, I proposed four novel studies that investigated the role of trunk in human gait. In the first study, I demonstrated that the trunk plays a more important role in stability during very slow walking compared to walking at the typical speeds of healthy humans. The second study investigated how the trunk is utilized to maintain stability in winter weather conditions in Canada, finding that there was no alteration to the use of the trunk in the winter. To investigate if the trunk compensated for restrictions to other stability strategies, the third study involved walking with restric tions while perturbations were applied. These experiments revealed that there was no additional contribution of the control of the trunk to maintaining stability when other strategies are restricted. The final study investigated how trunk angle affects the mechanics and energetic cost of gait during sloped walking. I found that the pre ferred trunk flexion coincides with minimum metabolic cost, and increased hip work with greater trunk flexion also leads to decreased work at the knee and angle. The results overall lead to the conclusion that the trunk is narrowly used to maintain sta bility but still offers work trade-offs that can reduce energy expenditures. These four studies served to improve the scientific understanding of how the trunk is controlled in order to maintain stability and energetic efficiency during walking.
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    Topology Optimization for Weldment Structures Using Bezier Curve-Based Cold-Formed Members
    (2024-05-07) Morris, Zane; Mechanical and Materials Engineering; Kim, Il Yong
    In an effort to reduce both greenhouse gas emissions and vehicle cost of ownership, the heavy equipment and vehicle design industries are undergoing a large migration from diesel to electric power systems. The battery technology on which electric vehicles are reliant is so far unable to match the operational ranges of combustion engine vehicles, due both to its increased weight and reduced energy density. Therefore, utilizing structural optimization (SO) to design lightweight chassis and manipulator systems is an important step to take in increasing the adoption of these electric systems. Heavy equipment relies on the weldment design paradigm; systems are fabricated via the welding of a series of structural members like plate and hollow structural sections. Current SO efforts in this field generate topology by determining the optimal layout of these structural members or primitives and their connectivity. The resulting structures contain multiple curved load paths. These efforts, however, disregard curvature as an attribute that can be assigned to a structural member itself; primitives used in these works are often limited to straight sections. This is despite the recent noting by purveyors of the industry that using curved members via forming technology can offer both cost savings and reduction of structural degradations caused by excessive welding. To address these shortcomings of existing literature, this work aims to provide a weldment topology optimization tool with three novel advantages. First, the capability of cold-work (CW) technology to generate continuously variable curvature is unlocked via the construction of a Bezier curve-based structural member. Second, the effects that CW has on member material properties are controlled via the implementation of a CW bending strain constraint. This ensures the feasibility of fabrication of the optimal design via cold-working, and allows weldments using CW members to be validated via linear static analysis. Third, material costs associated with the CW manufacturing process are utilized to construct a constraint, able to achieve significant cost savings per member. Academic case studies demonstrate the effectiveness and capability of each feature, which together enhance manufacturing and cost considerations in SO as a whole.
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    Persistence of vortical structures in dense suspensions and shear-thinning fluids: Characterization of vortex formation and evolution
    (2024-04-30) Barnes, Moira; Mechanical and Materials Engineering; Rival, David
    The following thesis explores the formation and evolution of coherent vortical structures formed in dense suspensions and fluids with strong non-Newtonian shear-thinning behaviour. The work is motivated by the inherent complexity of cardiovascular flows, as blood is a dense suspension and a shear-thinning fluid. Flows typical of the human circulatory system exhibit a high degree of unsteadiness where the formation of coherent vortical structures occurs within confinement. This problem is studied experimentally using analogous fluids and flow configurations; examining first the effect of solid volume fraction on vortex-ring formation in dense suspensions and second, the effect of shear-thinning strength on vortex-ring formation and small-scale structure coalescence in pulsatile and steady flows. To enable these experiments, a Lagrangian ultrasound-based imaging technique was further developed, allowing path-dependent parameters such as entrainment in dense suspensions of up to 40\% volume fraction to be measured directly. Across the varied composition and parameterization of the different fluids and configurations studied, unifying observations are found, namely that unsteady large-scale roll-up of coherent vortical structures appears to generally persist with increasing volume fraction or shear-thinning strength in the early stages of formation. The findings presented in this thesis contribute to a deeper comprehension of how real blood properties influence vortex formation, particularly akin to those observed in the human heart. This knowledge helps inform indicators of cardiovascular health and aids in the design of heart valve replacements.