Fatigue life analysis of steel bicycle frame according to ISO 4210

Abstract

The study estimates the fatigue life of a bicycle frame after fatigue failure due to the operational loads. Mechanical properties were determined for a tubular frame made of 25CrMo4 steel. High-cycle fatigue tests were carried out for mini-specimens taken from the location of fatigue failure (joint material) and the base material. The experimental data were compared using a normal distribution for the S-N area and an analysis of the slopes for linear regressions for two data populations. The bicycle frame was evaluated using a fatigue strength approach and nominal stress values. The conditions of the analysis conformed to the safety requirements laid down in the international ISO 4210 standard. The stress was calculated using a finite element model consisting of the surface elements. The highest stress points were selected to compare different fatigue evaluations. The FEA and material data results were compared using a probabilistic Weibull model (P-S-N curve). A mean stress effect was allowed for using the Walker model. The highly stressed volume model and weakest link theory model were used to analyse the size effect. The fatigue life was estimated for the maximum stress determined using FEA. The maximum stress point corresponds to the fatigue failure location on the bicycle frame. The fatigue life at 10% failure probability is below the value recommended in accordance with ISO 4210. A key factor affecting the results is the operating conditions, including the angle of force applied to the bicycle pedals.