A Study on the Diesel Engine Crankshaft Fatigue Performance Optimization

This paper summarizes an investigation of the effect of crankshaft fillet rolling load, undercut radius and web thickness on crankshaft fatigue performance. For this purpose crankshafts from two types of micro-alloyed steels were tested at different combinations of geometry and rolling load conditions. Fatigue rig specimens were prepared and subjected to completely reversed constant amplitude cyclic loads on a resonance type of fatigue testing machine. Results were evaluated as load versus number of cycles curves. An optimum design condition within the investigated design range was selected. Fatigue endurance limit for two conditions was obtained by the application of staircase test method.

Following the resonance bending fatigue test, finite element analysis were carried out in order to calculate the corrected endurance strengths from the test data. These corrected endurance strengths of the crankshaft, where effect of rolling, geometry and surface properties are included, were used as input for further fatigue analysis. Engine dynamic simulation is done to demonstrate the dynamic sectional forces and vibrations, and to determine the critical webs. Safety factor calculations were done in FEMFAT, where corrected endurance strengths and dynamical vibrations exported from engine dynamic simulations are used. Fatigue analysis was performed for M1 and M2 crankshafts, and for single mass flywheel and dual mass flywheel configurations.