EVALUATION OF FLEXURAL STRENGTH, COMPLIANCE, AND VIBRATION CHARACTERISTICS OF FIBER REINFORCED WOOD COMPOSITE MATERIALS USED IN BIKE FRAME FRONT TRIANGLES

Specific material properties are desired for an ideal riding experience in the front triangle of a bike frame. The tubes in an optimal front triangle should be strong and able to dampen vibrations while maintaining relatively high compliance. Strength and compliance increase the impact energy the bike frame can absorb before failure, and vibration damping promotes a smoother riding experience. A common impact that can lead to catastrophic failure of a bike frame is a front tire direct strike that invokes a large bending moment into the downtube of the front triangle. The ability of the tube material in this region to comply while maintaining strength can lead to higher durability of the bike by increasing the impact energy required to break the frame. This study investigates the vibration and strength characteristics of several fiber reinforced wood composite materials through the use of a four-point loading test based on the ASTM C1161-18 standard and an impulse excitation of vibration test following ASTM E1876-15. The composite material samples tested included several common weaves of fiberglass, Kevlar, and carbon fibers. While fiberglass and Kevlar-carbon reinforced wood samples demonstrated the highest vibration damping characteristics, Kevlar-carbon reinforced material was selected for further testing due to its higher flexural strength. Pursuant to these tests, the different strength profiles of common bike frame materials, steel, aluminum, and titanium, were compared to the selected Kevlar-carbon reinforced wood composite material using a tube bending test inspired by loading that the downtube experiences during the ASTM F2711-19 falling mass test. Videos of the tube bending tests were analyzed using Vernier Video Analysis software to gather displacement data, and MATLAB was used for strength, energy, and compliance calculations as well as data representation. The results of the stated tests and analysis concluded that the fiber reinforced wood composite materials showed a higher yield strength, energy absorption, and compliance in the bike frame application compared to aluminum, steel, and titanium materials designed for the same purpose. The bending moment in the wood downtube reinforced with one layer of Kevlar-carbon fiber weave was 15.3% higher than aluminum, 11.9% higher than steel, and 32.9% higher than titanium while demonstrating at least twice the compliance during all of the tube bending tests. Wood reinforced with two and three layers of Kevlar-carbon fiber material demonstrated similar compliance results as well as even higher strength characteristics. Additionally, these fiber reinforced wood composite materials demonstrate desirable vibration damping characteristics.