Research On Fatigue Life Prediction Of Vermicular Iron Cylinder Head

As the demand and high specific power for high torque continue to grow, the fatigue of cylinder heads has been more and more serious due to the complexity of geometry and load conditions. And the fatigue life of cylinder heads has great influence on the reliable of diesel engines. After the loads of cylinder heads are being analyzed, the stress conditions of cylinder heads under different loads have been investigated. Then the life models are obtained through the alternative test specimens’ low cycle fatigue experiments and FEM. At last, the fatigue life of a vermicular iron cylinder head is predicted. The fatigue life prediction method is useful for the cylinder head anti-fatigue designing.The vermicular iron cylinder head is used in this paper. It shows that the thermal load is the main factor in areas of firing deck and the narrow area between the two exhaust passages. And the fatigue type is low cycle fatigue.A method is proposed to distinguish the stress state of different areas. By analyzing the values and directions of the principle stresses at the same time, the stress state can be determined.The valve bridge alternative test specimens are designed. And the material tests are carried out to gain the basic properties. Based on the low cycle fatigue experiments of these alternative specimens, the uniaxial fatigue life prediction model for cylinder heads is gained. And it is revised at the condition of asymmetric load.Based on the new life prediction models, the low cycle fatigue life of a vermicular iron cylinder head is predicted, which provides suggestions for the structure design. Specially fatigue life of the valve bridge areas and the narrow area between the two exhaust passages is predicted and analysed.