Durability design of the crankshaft for marine diesel engines is not easy because a dynamic load acting on the crankshaft is combination of bending moment and torque and its magnitude and direction continuously vary in every time. It is necessary to understand a non-proportional loading of bending moment and torque as well as multi-axial fatigue theory. In a practical point of view, IACS M53 guideline is popularly used and if necessary, additionally simple FE method is applied in order to evaluation the fatigue strength more conservatively. However, a basic assumption to combine bending stress and shear stress in IACS M53 is different from a real stress history of crankshaft. The variation of inertia and pressure force in fatigue analysis of the conrod is generally taken into consideration. Since a weak point of the conrod and effective loading on fatigue damage is different relatively, the fatigue strength of the conrod should be evaluated based on not the load variation but the stress history. The local and global oil film pressure distribution is very important for optimum design of conrod and is resulted from the elasto-hydrodynamic bearing analysis. In this study, the durability design and verification of the crankshaft and conrod was carried out based on the full cycle simulation during one cycle that is an analysis technique to consider the time-varying forces and moments in one cycle. In case of the crankshaft, the radial force and tangential force on the crank pin were calculated and also an alternating torque predicted by the torsional vibration calculation was considered during one cycle. The whole time step was divided by 72 steps and a combined stress in every step was calculated. Fatigue safety was calculated at the crank pin fillet, journal fillet and oil hole and a critical damaged plane at each location was found by the FE analysis using the stress gradient method. In case of analysis for the conrod, the bearing force with more realistic oil film pressure was applied to FE model. Based on the multistep analysis that the assembly procedure is taken into consideration, the effective force and stress of several weak points on fatigue damage were identified and fatigue strength was evaluated.
Full cyclic simulation and fatigue design of conrod and crankshaft for medium-speed diesel engine
2010
9 Seiten, 15 Bilder, 2 Tabellen, 8 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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