Finite Element Analysis And Design Optimization Of Ductile Iron Crankshaft Undercut Slot

Crankshaft is the heart of the diesel engine and the working reliability of a diesel engine depends on the reliability of the crankshaft to a certain extent. Most of the time, the breakdown of the crankshaft will lead to destroy the whole diesel engine. Most of the breakdown forms of the crankshaft are caused by bend fatigue and torsion fatigue and the critical factor is bend fatigue breakdown. To make sure the reliability of the crankshaft, we must try to improve the quality of material and its structural dimension. Ductile iron crankshaft has good friction durability and efficiency. Recycled steel is good material for producing ductile iron crankshaft. Round angle by rolling processs is employed to compensate the stess at the corner where breakup is easly taken place and conquer the disadvantage of strength deficiency, thus the reliability of crankshaft can be improved. In general, undercut technology is used to adapt the rolling precess requirement.But, undercut technology may deteriorate the stresss concentration. In order to improve the situation, for a crank throw of a given ductile iron crankshaft, finite element analysis is conducted. The analysis result is optimized and related fatigue calculation is carried out. A compare between calculation and test results is performed and compared results show that conculation result is reliable. Therefore a good undercut structure is found and the reliability of crankshaft is improved.During the finite analysis, a CAD software PRO/E is used to import the cranksaft model into HyperMesh and mesh is created. At the round corner, mesh is refined to ensure a good mesh quality and calculation requirement. There are 145481 nodes and 131730 elements in this crankshaft model. For the processs of constraints, a new method rather than conventional method force directly exerting on the connecting-rod journal is used. In the new method, simplified connecting-rod and bearing carrier are added into the model. Contacting analysis is used to simulate the force transmission between the cranksaft and bearing shell, thus the calculation result can be closed to the truth that force exerting on the connecting-rod. According to the analysis result by Ansys, the result is optimized. According to the contrast of fatigue calculation and test results, the new method is proved to be reasonable.After analysis and test, we can conclude that undercut crank, stress concentration can be decreased by undercut a groove on the crank arm by 0.3mm and transition roundness by 3.0.