DISPERSION OF FATIGUE TEST RESULTS ON SMALL DIMENSION COMPONENTS
Tahiriny Ghizoni Kafka1; Walter Lindolfo Weingaertner1
1 Universidade Federal de Santa Catarina
doi:10.20906/CPS/COB-2015-1836
Resumo
Mechanical components subjected to cyclic stresses can break with lower loadings than the necessary to rupture in an almost static loading. Besides the loading, the geometry and the surface finish, as well as other factors that influence the properties of the boundary layer, determine the number of cycles and the loading that can be applied to the component. In order to avoid possible failures caused by fatigue, components manufactured in various materials should be subjected to fatigue tests. The tests should mimic the loads representing the loadings in which the components will be used and allow the designer to ensure that they have sufficient resistance to act in their future activities and be able to withstand the loads that will be assigned. These tests are time consuming and its results are quite dispersed, so, for this reason, it is necessary to perform many tests in order to get a reliable result. To reduce the evaluation time of fatigue behaviour of small components, an equipment for rotating bending test with multiple parallel axes, controlled by a single servo-controlled motor was designed and built. To certify the adequate function of the equipment specimens made of AISI 1020, cold drawn steel bars with 8mm in diameter, with a central strangulation were machined with the same machining conditions on a CNC lathe, thus representing the element under evaluation. For the analysis of failures, tests were conducted under different loads, applied in the free extremity at a preset distance from the strangulation, where the test load by a weight is applied. The results show a typical behaviour that has been observed by Wöhler, reducing the number of cycles with increasing load and presenting infinite life for loads below the critical stress. However, it was observed that the dispersion of the results was quite large, which requires a refinement of the test to ensure reliable information to the designer. No dependence of the individual axis of the equipment was observed.
Palavras-chave: Fatigue; Failure; Dispersion; Fatigue test