Based On The Thermal-fluid-mechanical Coupling Analysis Of Fatigue Life Prediction Of Cylinder Head And Research

Cylinder head is one of the key important parts of the engine, the structure and shape ofthe complex, which and piston jointly define a combustion chamber, to withstand hightemperatures, gas pressure and bolt preload pressure in the work, cylinder head temperatures,cyclical stress and strain occur Changes, prone to fatigue failure. This requires the cylinderhead fatigue life analysis, the cylinder head of a complete analysis should include high-cyclefatigue and low cycle fatigue analysis, the cylinder head of high-cycle fatigue is mainlyproduced an average circulation stress amplitude explosion pressure and thermal loadsgenerated stress caused; low cycle fatigue is mainly due to repeated startup and shutdown ofthe engine to produce cyclic thermal stress caused; thermal stress is generated due to thetemperature of the load, the current account cylinder head temperature, the use ofthermal-fluid-mechanical coupling stress distribution analysis. Cylinder head above thefatigue life prediction, there are two ways: one is the test method, this method, althoughreliable, but costly and tedious work, slow progress; One method is the fatigue life analysismethod, this method is based on material property, combined with the course load selectionmodel to determine the fatigue life analysis of the fatigue life of the structure, this methodmore analytical model, if the cylinder head for fatigue life prediction inappropriate choice ofanalytical models, the results can lead to large errors of its life.To solve these problems, this paper a diesel engine cylinder head for the study, using thewhole field method for solving the cylinder head and coolant direct thermal-fluid couplingcalculation, the cylinder head temperature field. Each node in the cylinder head temperatureand preload, the outbreak of the pressure on the cylinder head coupled thermal-mechanicalcoupling calculation. Studied the cylinder head in mechanical loads and thermal-mechanicalcoupling stress distribution under the stress concentration area to get the cylinder head. Afully transient method for the cylinder head were in mechanical load thermal-mechanicalcoupling under transient dynamic analysis, and the resulting stress and strain time histories ofthe cylinder head as the basis for life prediction load spectrum. Cylinder head for high-cycle fatigue, the effects of a variety of analytical models of its fatigue life prediction life, get onefor the cylinder head life prediction models; for cylinder head start-stop cycle of low cyclefatigue, through standard specimens studied this issue, obtain research cylinder head start-away to stop the cycle of low cycle fatigue life prediction.The main contents of this article:(1) cylinder head thermal-fluid-mechanical interaction analysisWith ANSYS FLUENT flow field analysis software as a tool to calculate the empiricalformula of the cylinder head by thermal load boundary conditions, derived heat transfercoefficient applied in different regions, temperature and coolant outlet boundary conditions.Solving method using the whole field, select the control equation of the cylinder head andcoolant direct thermal-fluid coupling simulation. Studied the coolant flow field, temperaturefield and the cylinder head velocity and temperature distribution of temperature field, andultimately get the cylinder head temperature of each node. The cylinder head temperature ofeach node is mapped to ANSYS structural analysis of the cylinder head combination model inANSYS model of cylinder head combination of mechanical load: preload conditions and theoutbreak of conditions and heat-static calculation of solid coupling conditions. Study thestress distribution of the working conditions of the cylinder head, cylinder head to find theareas of stress concentration and influence of load stress concentration.(2) High Cycle Fatigue Life Prediction Methods cylinder headOn the cylinder head were mechanical and thermal thermal-mechanical coupling oftransient dynamic analysis, the stress-time, strain-time history for the cylinder head of thefatigue life prediction provides a stress spectrum data. DesignLife fatigue analysis softwareusing the cylinder heads high cycle fatigue life prediction. Cylinder head were investigated inmechanical loads and thermal-mechanical coupling selection under the impact of threedifferent damage parameter Pro interface model for the fatigue life of the cylinder head, getone for fatigue life prediction of critical surface of the cylinder head damage parameter model,provide a reliable life prediction models and theoretical basis for the cylinder head designfatigue life.The effects of mechanical, thermal load on the cylinder head surface fire high cyclefatigue life, found after the application of the minimum thermal load fatigue life firepowersurface located at the bridge of the nose, when making life prediction must consider theimpact of thermal loads. (3) Factors affecting the fatigue life of the cylinder headFocused on the effect of surface roughness on the life of the cylinder head. By setting a different surface roughness factor calculated fatigue life of the cylinder head, get a different surface roughness factor on the cylinder head fatigue life curves.(4) Explored through the use of standard specimens for the cylinder head low cycle fatigue life prediction methodBy standard specimen of the cylinder head start-stop cycle low cycle fatigue problems were studied. Life Prediction MethodsN curve of standard specimens lifetime analysis, research cylinder head start-stop the cycle of low cycle fatigue life prediction.