Contributions of rider-induced loads to bicycle frame stress

Abstract

Presented in this paper is a new method for design analysis of bicycle frames. The new method relies on measurements of rider induced loading to perform a stress analysis of a bicycle frame. The vehicle for the stress analysis is ANSYS, a commercially available finite element code. Through application of individual measured loads, the method examines the corresponding nodes of maximum stress. Polar plots are developed to illustrate the variation of stress as a function of crank arm angle. Polar plots are also developed for the nodes experiencing the maximum total stress. Such a procedure enables the contribution of individual measured loads to the maximum stress to be ascertained. With this information, not only are the important loads for design analysis identified, but also the structural members of relative high and low stress are determined. Accordingly, these results have application to the detailed design of individual structural members. To illustrate the new method, stress analysis of an aluminum frame is undertaken. The loading data are derived from an earlier study by the authors where significant seat, handlebar, and pedal loads were measured together with absolute pedal position. The loading data simulate that of steady-state cycling over flat terrain at about 9 m/s (20 mile/hr). The node of maximum total stress under steady-state loading is found to be the intersection of the top and seat tubes. Inasmuch as frames typically fail in the area of the bottom bracket (i.e., intersection of down and seat tubes), this result contradicts experience. This contradiction is explained by observing that the alternating stress/mean stress ratio is significantly greater for the bottom bracket area.