Abstract
In this study, a finite element model of a bicycle crank arm are compared to experimental results. The structural integrity of the crank arm was analyzed in a universal dynamic test bench. The instrumentation used has allowed us to know the fatigue behavior of the component tested. For this, the prototype was instrumented with three rectangular strain gauge rosettes bonded in areas where failure was expected. With the measurements made by strain gauges and the forces registers from the load cell used, it has been possible to determine the state of the stresses for different loads and boundary conditions, which has subsequently been compared with a finite element model. The simulations show a good agreement with the experimental results, when the potential sources of uncertainties are considered in the validation process. This analysis allowed us to improve the original design, reducing its weight by 15%. The study allows us to identify the manufacturing process that requires the best metrological control to avoid premature crank failure. Finally, the numerical fatigue analysis carried out allows us to conclude that the new crank arm can satisfy the structural performance demanded by the international bicycle standard. Additionally, it can be suggested to the standard to include the verification that no permanent deformations have occurred in the crank arm during the fatigue test. It has been observed that, in some cases this bicycle component fulfils the minimum safety requirements, but presents areas with plastic strains, which if not taken into account can increase the risk of injury for the cyclist due to unexpected failure of the component.
Highlights
The cycling industry has experienced a breakthrough in recent years
The structural analysis of the crank arm has been developed in two steps
Procedure to Quantify the Experimental Stress Uncertainty. As it has been explained in the previous section, the final Von Mises stress is not directly measured; instead, it is calculated from other magnitudes, as strains experimented by the strain gauges, Young modulus and Poisson ratio of the material
Summary
The cycling industry has experienced a breakthrough in recent years. The demand for increasingly demanding performance—both in the professional and amateur sector—and the inclusion of the bicycle in the city as a clean, silent, inexpensive and healthy personal transport, are responsible for the technological growth of the industry [1]. According to the European Committee for Standardization [7], the crank arm can be considered appropriate for a professional use if it is able to withstand 100,000 load cycles without failure. Experimental results allow validation of the finite element model, where the potential sources of uncertainty are taken into account. It has been necessary to obtain a metamodel for the same areas analyzed in the real model This allows identification of the sources of uncertainty that affect most of the behavior of the crank arm. According to the simulation results, a crank arm can fulfil the minimum safety a crank arm can fulfil the minimum safety requirements, but present zones with plastic strain.
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