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The present research analyses the configuration of jaws to avoid the premature failure of the disc in the Brazilian test. The objective is to depict the loading device configuration that most likely produces results comparable to the Hondros' analytical stress solution. To this end, several numerical analyses have been carried out for different contact angles with the Finite Element Method. It was deduced that the final contact angle plays an important part in the success of the Brazilian test and that the Griffith criterion can be fulfilled if the equivalent stress is calculated. Additionally, the orientation of the forces in the contact between the loading device and the disc has been studied for different friction conditions. According to the numerical results, it was found that a loading arc configuration of 20º shows the best agreement with the probable values given by the analytical stress model when the uncertainty of its magnitudes is taken into account. The study also demonstrates that the friction in the contact between the optimal loading configuration and the disc does not seem to significantly affect the theoretical predictions in the centre of the disc.

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.

This research study presents a new theoretical model to calculate the indirect tensile strength for the Brazilian disk with loading arcs, based on numerical simulations, two-dimensional elasticity theory, and Griffith failure criterion. The new expression incorporates a no uniform contact pressure distribution determined by the results of the simulations with the finite element method. A computational experiment design has been developed to test the accuracy of the predictions made with the proposed model. This study demonstrates that the stresses predicted with the new model are closer to those determined by the finite element models than other theoretical solutions available in the literature. Additionally, a comparative analysis with experimental results obtained by other authors also indicates that the new model provides a more accurate magnitude of the indirect tensile strength.

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