In completion of my undergrad Honors Thesis, I worked with Metrofiets, a boutique cargo bike manufacturer in Portland, Oregon, to explore the feasibility of developing a carbon fiber frame for their dutch style cargo bikes. The primary goals were to assess lightweighting possibilities and better understand the design process for composite products.

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Key objectives for the bike included reducing the frame weight by 30%, increasing stiffness by 10%, matching or exceeding the steel frame’s strength, and maintaining Metrofiets’ distinctive aesthetic. I identified wet layup over 3D-printed cores as a low-cost, practical manufacturing method suitable for creating a functional proof of concept without the significant upfront investment in tooling associated with typical carbon frame manufacturing.

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To support the project, I built an open source 3D printer to create ABS cores for the complex intersections of the frame. Leaning on the strengths of a table saw, straight sections were cut from structural foam as a lighter and faster method. These cores were wrapped in carbon fiber, wetted out with epoxy, and consolidated using vacuum bagging.

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To assess the material properties produced with this method, I fabricated dogbones and tube specimens and conducted mechanical testing on an Instron in accordance with ASTM composite test standards. With these results, I informed a material model to be used in FEA. Seeking smooth distribution of stresses and the target stiffness, I adjusted the CAD geometry and composite layup schedules for a representative section of the frame that included the main tube, bottom bracket, and rear triangle as this is a critical area subjected to dynamic forces from the rider and cargo.

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The transition from simulation to physical parts was a messy but valuable experience, providing a hands-on education in composite layup. I encountered common composite defects, such as bridging and voids, and learned practical techniques to improve composite quality. Carefully following the layup schedule, vacuum bagging the 3D-printed cores and meticulous sanding, brought the prototype to life.

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The completed test piece was finally evaluated for stiffness and failure strength using an instrumented hydraulic press. Results showed exceptional alignment with the targeted 10% increase in stiffness (torsion +2%, vertical bending +12%).

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This project combined real-world constraints, iterative design, and hands-on experimentation, offering insights into the challenges and opportunities of small-scale composite manufacturing. It also solidified my passion for developing products that align with my interests, a principle that continues to guide my work.