Study On Fatigue Resistance Of Exhaust Manifold

The reliability and durability of engine performance are studied.The most important part is the exhaust manifold,which affects the performance of engine.This is because of the worst working environment and the most complex working conditions of the exhaust manifold in all the structural parts of the vehicle.after the combustion of exhaust gas,the temperature is extremely high and the distribution is very uneven.the great temperature difference between the outer wall and the inner wall of the exhaust manifold can lead to thermal stress and thermal deformation of the exhaust manifold.combined with the longterm alternating cycle high temperature load,the exhaust manifold will leak air,increase noise,fatigue failure,and even cause engine failure.The method used in this paper is a combination of theory and simulation to study the thermal fatigue of engine exhaust manifold.The main contents of this paper are the following six steps:(1)According to the research results of literature and practical engineering problems,combined with the basic fatigue strength theory,the possible way and position of exhaust manifold failure of starting engine are judged.According to the judgment results,the secondary structure with little influence on the analysis results is ignored,and the engine exhaust manifold model is established for analysis.(2)The three-dimensional model of engine exhaust manifold is established by using CATIA software,and the engine exhaust manifold is meshed with HYPERMESH software.(3)First,the reasonable CFD grid model of exhaust manifold is established,the turbulence model used in the calculation of this paper is established,and the fluid-solid coupling model of exhaust manifold is established according to the fluid-solid coupling method;then,the boundary condition of exhaust manifold fluid calculation is set;finally,the temperature field simulation calculation of exhaust manifold is carried out based on fluid calculation method and fluid-solid coupling calculation method and heat transfer theory,and the calculation results of temperature field are taken as subsequent analysis.(4)Thermal stress analysis is carried out on the finite element model of engine exhaust manifold using ABAQUS software.based on the results of stress analysis,the thermal stress strain and plastic strain values of exhaust manifold under full load condition are obtained.(5)By introducing the obtained plastic strain range into the low cycle fatigue strain range-life formula(Manson-Coffin formula),the fatigue cycle life of exhaust manifold is obtained.Heat strain values obtained by finite element simulation of thermal stress are brought into the FE-SAFE,and the fatigue life of exhaust manifold is calculated by setting load spectrum.(6)creep fatigue analysis of exhaust manifold considering the high temperature creep properties of metal materials.By reference to the appropriate creep model,the parameters needed for the model are obtained,and the creep deformation is calculated in the ABAQUS,and then the creep-fatigue life is calculated.