Browsing by Author "Abdurhman Suleiman"

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    Analyzing the Effect of Multiaxial Stresses on the Structural Integrity of Composite Bogie Frames
    (Addis Ababa University, 2025-11) Abdurhman Suleiman; Mulugeta Habtemariam (Ph.D.)
    The increasing global demand for sustainable and efficient transportation has driven interest in replacing traditional steel railway components with advanced composite materials like Basalt Fiber-Reinforced Polymer (BFRP) due to their high strength-to-weight ratio, corrosion resistance, and cost-effectiveness. However, a comprehensive understanding of BFRP behavior under complex multiaxial stress conditions, typical of operational railway environments, remains limited, hindering confident application in critical components such as bogie frames. This research aimed to analyze the structural and fatigue behavior of a Y25 railway bogie frame made from BFRP, specifically focusing on developing a multiscale material model using DIGIMAT and ABAQUS, analyzing stress distribution under operational multiaxial load cases, predicting and comparing fatigue life with S355 steel, assessing failure behavior using the Hashin Failure Criterion, and evaluating strength-to-weight performance. The study employed a simulation based approach, selecting a 60% fiber volume fraction plain weave BFRP laminate, generating its homogenized properties, applying manual geometry modifications to an original steel bogie frame, and performing structural simulations in ABAQUS under EN 13749-defined multiaxial loading conditions, with fatigue life predicted using FE-SAFE and damage onset assessed via Hashin-based failure analysis. Results demonstrated a significant 75% weight reduction from 892 kg to 223 kg for the BFRP frame. Under multiaxial loading, the BFRP bogie maintained sufficient stiffness with stresses remaining within allowable limits, while fatigue life prediction showed a remarkable improvement: for example, in Case 2 the steel bogie frame failed at 594,292 cycles, whereas the BFRP frame exceeded 50 million cycles. Similarly, across all load cases, steel fatigue life ranged between 0.59–9.97 million cycles, while the BFRP consistently survived beyond 50 million cycles, confirming its superior durability. Hashin failure analysis also showed delayed damage onset in BFRP compared to steel, highlighting the material’s ability to withstand operational stresses without premature failure.
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    Static Analysis of Auxetic Femur Stem for Total Hip Arthroplasty (THA) Application Using Angle Optimization
    (Addis Ababa University, 2024-06) Abdurhman Suleiman; Araya Abera (PhD)
    Total hip arthroplasty (THA) is the preferred treatment for severe hip diseases, but the durability of hip prostheses is compromised by stress shielding, leading to bone resorption and implant failure. This study aims to optimize femur stems using auxetic materials, which exhibit a negative Poisson's ratio, potentially providing better stiffness matching with the femur and reducing stress shielding, thereby enhancing implant performance and patient outcomes. The study systematically optimized an auxetic femur stem for hip arthroplasty by collecting patient-specific data from Samaritan Surgical Center, performing finite element analysis using SolidWorks and ANSYS, and comparing the optimized design to Zimmer's femur stem under realistic loading conditions. This comprehensive methodology included simulations of activities like walking and stair climbing, supported by statistical evaluations to ensure robust conclusions on stress shielding and biomechanical performance. The optimized femur stem, incorporating a 3D Star Honeycomb structure and Zimmer's Titanium Alloy, significantly reduced stress shielding in realistic loading conditions, achieving reductions of up to 38.16%. This innovative design aligns biomechanical behavior closely with intact bone, outperforming conventional femur stem designs in reducing stress concentrations and facilitating bone ingrowth. This study demonstrates that incorporating a 3D star honeycomb auxetic structure into femur stem design significantly reduces stress shielding and improves biomechanical performance under realistic loading conditions compared to Zimmer's femur stem. These findings highlight the potential for innovative implant designs to enhance stability and patient outcomes in hip arthroplasty.