Design of mountain bicycle fork inner legs for ASTM fatigue testing

Includes bibliographical references (leaf 51)A successful method for predicting the fatigue life of mountain bicycle suspension fork inner legs for the ASTM fatigue test was developed in this project. An analysis method was created to calculate the stress in legs based on the magnitude of an externally applied load, its reactions in the entire substructure of the fork, as well as any stress concentrations due to variation in the leg's profile geometry. The analysis also calculated the secondary source of stress created due to an interference fit between legs and crown. This analysis was extended to twenty-nine different configurations of legs, and a range of maximum stresses was used as input for fatigue testing. The raw material from which the legs were made was fatigue in isolation tested to failure to create an S-N diagram. The heat treatment of the raw material was varied over a range used in industry to most accurately represent the variation in material conditions of the final product. Statistical data curves were generated to capture the upper and lower bounds of fatigue life variation. Eighty-three documented ASTM fatigue test results were compared to the curves. Successful results where the data was within the curves were yielded for seventy-two out of the eighty-three data points. A Microsoft Excel spreadsheet was created and coded with Visual Basic to encapsulate all of the aforementioned calculations and return a stress analysis and fatigue life prediction for future design