Research On Correlation Of Cylinder Fatigue Test Based On Finite Element Method

The engine develops in the direction of high power density, low fuel consumption, low emissions and high reliability due to the influences of environmental and economic factors, so the explosion pressure, thermal load and stress level of the engine increase, which put forward a test to the reliability of the engine components. Cylinder head is one of the diesel engine components which are most prone to failure. Fatigue test is one of assessments to evaluate the fatigue of diesel cylinder. Compared with fatigue bench test, the load transfers, constrains and other factors of fatigue platform test are different, resulting in the difference of test results. Finding the factors which causes the differences through experiments is a hard task, so the numerical simulation becomes a considerable way to solve the problem.In this paper, a diesel engine cylinder head is taken as an example. By finite element method, the stress of cylinder heads among bench test and platform test are calculated in different working conditions, and on the basis of the stress results, the fatigue safety coefficients of intake and exhaust channel bridges of the nose radius are estimated as well.When calculating the thermal stress of the cylinder head in bench fatigue test, projecting thermal boundary conditions of similar model is used to acquire the temperature field quickly and accurately. The thermal boundary of firedeck is adjusted referred to the experimental measurement results of hardness plug, after which the calibration error can be controlled smaller than 5%. Then the thermal results provides thermal load to calculate the thermal and mechanical coupling stress of cylinder head.Considering the stiffness of different parts of the cylinder head, extract the stress and displacement under different conditions and analysis the cause of the differences between fatigue results. By comparing the differences (length and direction) between the maximum principal in different working conditions, explore the relationship of maximum principal stress and the fatigue damage.Calculation results shows that, for the rounded corners of the intakeport of the nose area in cold condition, the platform test can be able to accord with the bench test very well, the stiffness and constraint of the platform make the results more dangerous than the bench test in cool working conditions. While compared to hot working condition of bench test, it performs not so well. When thermal stress acts on cylinder head, the directions of maximum principal stress deviate from the tangent direction of fillets, which may enhance the anti-fatigue performance. This should be considered when estimate the fatigue life. After increasing the radius of fillets, the fatigue safety factors of fillets in all working conditions increase as well, and even in the worst working condition, the anti fatigue performance can meet the requirements, which provides a reference for the improvement of cylinder head.