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The research described herein accomplished the goals of off-road bicycle load quantification and fatigue life prediction. A fully-instrumented test bicycle was equipped with dynamometers at the pedals, handlebars, and hubs to measure all in-plane structural loads acting through points of contact between the bicycle and both the rider and the ground. A portable data acquisition system carried by the standing rider allowed, for the first time, this loading information to be collected during extended off-road testing. In all, seven experienced riders rode a downhill trail test section with the test bicycle in both front-suspension and full-suspension configurations.
The load histories were used to quantitatively describe the load components through the computation of means, standard deviations, amplitude probability density functions, and power spectral density functions. For the standing position, the coefficients of determination for the load components normal to the ground were greater than 1.35 for handlebar forces and 0.3 and 0.5-0.6 for the pedal and hub forces respectively. Thus the relative contribution of the dynamic loading was much greater than the static loading at the handlebars but less so at the pedals and hubs. As indicated by the rainflow count, high amplitude loading was developed approaching 3 and 5 times the weight of the test subjects at the front and rear wheels respectively. The power spectral densities showed that energy was concentrated in the band 0–50 Hz.
To illustrate the usefulness of the loading data, the load history at the pedal was used to determine the corresponding stresses at the pedal spindle hot-spot location. To predict the fatigue life, the resulting stress cycles were processed by use of a rainflow counting algorithm. Cumulative damage was quantified through Miner's linear damage rule used in conjunction with the nominal S-N method. The stress cycles were also used to develop a fatigue testing protocol for verifying analytical predictions of fatigue life.
dynamometers, off-road bicycle, structural components, fatigue failure, high cycle
Research assistant, University of California, Davis,
Professor, University of California, Davis,