Multiaxial Fatigue Life Analysis On The Key Parts Of Diesel Engine Cylinder Block

Vehicle engine is the heart of automobile. Engine cylinder block is the frame of thewhole engine, remaining parts of the engine are mounted on the cylinder block either directlyor indirectly. Cylinder block works hard under complex loads. To some extent, the life of thecylinder block determines the fatigue life of the engine. It is significant to research on thefatigue life of the cylinder block. In this paper, inline engine cylinder block and V typecylinder block are used to give a research on the fatigue life simulation. The key parts andtheir stress-strain State，the fatigue life and the possible parts to produce the fatigue crack areacquired. A multiaxial fatigue life simulation method for the engine cylinder block isobtained.This paper discusses the development of the fatigue simulation and the multiaxial fatiguetheory. Also analysis the mechanism, classification, influence factor of the fatigue, and give acriterion to judge the multiaxial stress state.Based on the principle of critical plane method, six critical plane models namely normalstrain model, shear strain model, KBM model, FS model, SWT model and WB model arestudyed. Calculation programs of the six critical plane models are compiled, which can givethe position of the critical plane and the value of damage parameters on it. Thin-walledtubular specimen is used to investigate the impact of the six multiaxial fatigue predictionmodels on the multiaxial proportional stress state and non-proportional stress state. Thencompare the simulation results with the test results. The results show that KBM model issuitable for structure life prediction under multiaxial proportional stress state. And WB modelis suitable for structure life prediction under multiaxial non-proportional stress state.The transient finite element analysis models of the inline engine cylinder block and V type cylinder block are established. The effects of the grid size and load step setting on thetransient finite element analysis results of the engine cylinder block are researched, which areused to ensure the suitable meshing principle and load step setting principle for the enginecylinder block. Then based on the transient finite element analysis of the inline enginecylinder block and V type cylinder block, the key parts and their relevant stress-strain Stateare obtained. Judge the multiaxial stress state on the key parts of the cylinder block. Theresults shows: for the inline engine cylinder block, the upper surface near bolt hole and thecylinder head bolt partner are under multiaxial proportional stress state, and the body acrossclapboard is under multiaxial non-proportional stress state; for the V type cylinder block, theupper surface near bolt hole, cylinder surface near pass water hole, and the body acrossclapboard are all under multiaxial non-proportional stress state.Put the simulation results in the correct model calculate programs, get the position of thecritical plane and the maximum values of damage parameters on it. Then use thecorresponding critical plane model to calculate the fatigue life. The parameters of the fatiguelife prediction models likes’f, b and k can be calculated by the general slope method. Fatiguesimulation results of the inline engine cylinder block and the V type cylinder block areanalyzed, and the results show that: for the inline engine cylinder block, the most possiblepart to produce the fatigue crack is the cylinder head bolt partner,the second is the uppersurface near bolt hole,and the body across clapboard is relatively difficult to produce thefatigue crack;for the V type cylinder block,the most possible part to produce the fatigue crackis the upper surface near bolt hole,the second is cylinder surface near pass water hole,and thebody across clapboard is relatively difficult to produce the fatigue crack.