Browsing by Author "Li, B."
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- 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.
- Welding assessment of a damaged crane pedestal of a container shipPublication . Fonte, M.; Freitas, M.M.; Li, B.; Duarte, P.; Reis, L.A structural integrity assessment of a damaged crane pedestal/column of a container ship is presented. Crane cabins and pedestal/columns are subjected to fatigue coupled with sudden overloads during cargo operations and corrosion effects due to sea environment. Significant number of surface cracks was detected around the pedestal/column, at inner and outside of the crane foundation, close to the main weld seam and, in consequence, the ship-owner ordered a survey. The main weld seam and the sites where cracks were found are evaluated in the present study. For the purpose, the sample material (hot rolled steel plate and upper ring) of the pedestal was provided by the shipyard and macro and micrographics were observed. Results did not show any cracks, although they have been found by the NDT technical services of the shipyard which have decided to remove them by the grinding process. The weld seam did not also show relevant defects, whereby the replacing of the pedestal/column by a new one would not had been necessary. Regardless of some occasional overloads, the surface cracks found on the pedestal/column could be a consequence of the normal operation conditions of the crane during the last 5 years and also due to poor maintenance.