Research About Fatigue And Optimization Design For Gasoline Engine Exhaust Manifold Under Thermo-mechanical Load

Fatigue damage is widespread exist in machinery,aviation,railway,automobile and other fields.According to incomplete statistics,about 50% ~ 90% of the mechanical structure damage belongs to fatigue failure.Fatigue damage is not only one of the common failure form,but also the most harmful failure forms of auto parts.Directly contact with high temperature exhaust gas,and bearing the vibration load generated by engine,the working environment of exhaust manifold is very bad.Frequency response analysis and vibration fatigue analysis based on thermo-mechanical coupling was conducted on a gasoline engine exhaust manifold in order to get the accurate simulation result of the vibration character and fatigue life.The main research work in this paper is as follows.The temperature distribution and flow characteristic was calculated based on twoway FSI in an exhaust manifold.And it's accuracy was verified according to the vehicle thermal equilibrium experiment.Based on the results of the finite element analysis of temperature field,the static strength of exhaust manifold was evaluated according to the stress value and distribution.Then built the thermo-mechanical frequency response analysis model based on the structure analysis model and the thermal boundary from the fluid-structure coupling analysis.Using the temperature distribution and thermal stress distribution as vibrations,the frequency response analysis was carried out to study the influence of thermal load to vibration character and structure stiffness.Evaluated the exhaust manifold's reliability on the basis of vibration fatigue analysis.And comparative study the thermal-mechanical coupling effect on the fatigue analysis.Then determined the optimization design object and goal through the result of thermal-mechanical fatigue analysis.With extending the fatigue life for total goal,increasing natural frequency of 1st/2nd/3rd/6th order for subgoals,the objective function was established based on the exponential weighted method,topology optimization and topography optimization was carried out to get the better design scheme.The optimized exhaust manifold's fatigue life and vibration character is much better than the original design.This optimization method has some certain reference value for the design of exhaust manifold.