Effect Of Casting Residual Stress On The FEA Analysis Of Cylinder Head

Casting is a complex metal forming method, which contains a large number of physical and chemical processes. Diesel cylinder head is one of the large-complex castings, its structural reliability directly affects the reliability of the engine. On the one hand, the cylinder head has a character of accurate-shape, high dimensional accuracy, resulting in the difficulty of the casting process; On the other hand, with the degree of enhancement of diesel continues to improve, the mechanical and thermal loads exerting on the cylinder head increased significantly. In the previous analysis of the cylinder head, most of the studies failed to consider the effect of casting residual stress due to lack of software interface.In this thesis, finite element analysis is employed to study the effect of residual stress on the stress distribution and fatigue life of the cylinder head, the main work is as follows:(1) With the help of casting manual, the pouring system is carefully designed. Based on the correct settings of casting and process parameters, the solidification process of the casting was simulated in Pro Cast, and the temperature and stress field of the cylinder head were obtained.(2) The casting residual stress was successfully imported into Abaqus as predefined stress field. Based on the correct setting of material, loads and boundary conditions, an elastic-plastic analysis of the cylinder head was carried out and the temperature and stress field were obtained. By carefully analyzing the result, the critical areas are found and the main load of different area is determined by comparing the role of the explosion pressure and the thermal load. With the presence of the residual stress, stress level in different critical areas may increase or decrease, depending on whether the directions of stress are same or not.(3) The stress state in different critical areas is determined through analyzing the direction and magnitude of six stress components and the three principal stresses in different load cases. The result shows, with the presence of residual stress, the stress loading state of different critical areas remains the same. The single-axial stress state appears on the valve bridge areas and the narrow area between the two exhaust passages. And areas of the injection hole, the water jacket, the transition fillets are areas where shows multi-axial stress states.(4) Based on the life prediction models, the low cycle fatigue life of the cylinder head is predicted. The result shows that the fatigue life is either shorten or prolonged due to the effect of residual stress.