Methodology Development for Fatigue Analysis of Crankcase Mounting for Stress Member Type Motorcycle Frame Subjected to Vehicle Dynamic loads

This paper depict the difference in the endurance factor of safety with usage of static and quasi static FE analysis and corrective measures take to solve the problem. The importance of the dynamic loading and subsequent effect of it on the multi axial fatigue analysis. Considering the modern trend prevailing among the vehicle manufacturers and specifically talking about two wheeler industry, it is clear that while the engine remains the same but the frame is changed to cater the market with new models to cut down on the development time. Initially the crankcase was designed for a double cradle frame where the crankcase was mounted on the frame. Later, the frame design was changed to single cradle where engine acts as a stress member link. This kind of arrangement makes the crankcase mountings participate in the chassis loads. Therefore, the crankcase mounting experiences road loads when the vehicle encounter the road irregularities.

Earlier the design was verified by static simulation, where the maximum force and the moment were applied for FEA analysis, the results of which couldn’t capture the fluctuation in the load and resulting in greater FOS. The quasi static analysis generated cyclic stress files which was used to determine the endurance factor of safety. The results showed very low factor of safety and thus, the existing crankcase mounting could not be used for the stress member proposal. The mounting were required to be modified to increase the endurance factor of safety. The mounting were brought closer to the crankcase and were reinforced with ribs. This helped us to use same crankcase for different type of frames.