Evaluation of Bike Frame Fatigue Behavior

Oxide Cycles, a local bike frame designer, is manufacturing hard-tail mountain bike frames made from 4130 chromoly tubing and low carbon steel tubing. During typical mountain bike conditions, a frame experiences cyclic loading. The magnitude and distribution of stresses within the frame is a result of the following parameters: bike geometry, tubing diameter, tubing wall thickness, welding parameters, and loading conditions. Over time, these cyclic stresses can result in frame failure. A main mechanism for frame failure is associated with fatigue in high stress regions. To evaluate frame fatigue behavior, ASTM F2711-08, Standard Test Methods for Bicycle Frames was followed. Custom fixtures were designed and fabricated to allow for ASTM fatigue testing in an axial load mechanical testing machine. Along with mechanical testing, computer modeling and finite element analysis (FEA) simulations of the frame have been performed. FEA was used to estimate the stress states and strains the frame experiences during testing. An attempt to correlate the finite element analysis model to frame lifetime will be made. The mechanical testing and the FEA results will provide an indication of frame performance, which can be leveraged for design and/or process recommendations