ENIDH - EMM - Engenharia de Máquinas Marítimas
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Browsing ENIDH - EMM - Engenharia de Máquinas Marítimas by Author "Anes, V."
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- Crankshaft failure analysis of a boxer diesel motorPublication . Fonte, M.; Anes, V.; Duarte, P.; Reis, L.; Freitas, M.This paper reports a failure mode analysis of a boxer diesel engine crankshaft. Crankshafts are components which experiment severe and complex dynamic loadings due to rotating bending combined with torsion on main journals and alternating bending on crankpins. High level stresses appear on critical areas like web fillets, as well as the effect of centrifugal forces and vibrations. Since the fatigue fracture near the crankpin-web fillet regions is one of the primary failure mechanisms of automotive crankshafts, designers and researchers have done the best for improving its fatigue strength. The present failure has occurred at approximately 2000 manufactured engines, and after about 95,000 km in service. The aim of this work is to investigate the damage root cause and understand the mechanism which led to the catastrophic failure. Recommendations for improving the engine design are also presented.
- New approach for analysis of complex multiaxial loading pathsPublication . Anes, V.; Reis, L.; Li, B.; Fonte, M.; Freitas, M.Experimentally, it has been proven that the stress level needed to cause fatigue failure in pure shear is less than the axial one. This fact has led to consider a stress scale factor between shear and axial stress in order to reduce different applied stresses to the same shear stress space or principal stress space to facilitate the yielding analysis or fatigue damage evaluations. In this way most of multiaxial fatigue models use a stress scale factor to consider the fatigue damage contributions from the axial and shear stress components regarding the material strength degradation. Much efforts were made to quantify the effective shear and axial stress amplitudes under a three-dimensional stress state, however, the combined damage resulted from those amplitudes have been reduced to a constant value. In some cases, the approaches used proved to be inadequate, leading to compute the same equivalent stress for different loading paths with different fatigue lives. In this work it is performed a series of multiaxial fatigue tests on a high-strength steel in order to determine the multiaxial fatigue strength under proportional and non-proportional loading conditions. A stress scale factor function was mapped based on the experimental results using as arguments, the axial stress amplitude and the stress amplitude ratio, which has proven to be sensitive to the loading path nature. Using the stress scale factor surface an equivalent shear stress was defined and it was used in the fatigue life correlation. Results indicate that the stress scale factor (ssf) is not a constant value and it is strongly dependent on stress amplitude level and loading path shape. The equivalent stress was successfully applied to proportional and non-proportional loading paths with satisfactory results.