The Research On Fretting Fatigue Life Prediction Method Of Diesel Engine Aluminum Alloy Block Fastening Surface

In the diesel engine working process,the block will be subjected to the bolt pretension force and cylinder cycle load,and it leads to the reciprocating sliding of small displacement on the fastening surface of the main bearing cap,which named fretting.Under the action of fretting,block fastening structures are easy to suffer from fretting,which causes the body crack and then failure.In response to this phenomenon,the experimental research,simulation and theoretical research are combined to study generation characteristics and failure mechanism of block's fretting crack,and the method of evaluating block's fretting fatigue life is obtained.The main work and conclusion contents:(1)Carrying out fretting fatigue experiment under six conditions,the experimental results show that specimen failures near the edge of the specimen contact,fretting fatigue lifetime decreases with the increase of axial load,fretting area could be divided into sliding zone,mixed zone and clear adhesive zone,fretting crack is more likely to occur in mixed zone.(2)Taking the bridge/specimen structure as the research object and establishing fretting fatigue simulation finite element model.Comparing and analyzing the calculation results of 2D and 3D finite element models,and the results show that the error of the two models is within 5%.Analyzing the fretting features of models by eleven multi-axial fatigue parameters,and fitting out of the fretting fatigue life prediction model which based on Farris model.Compared with the experimental data,the predicted results of Ruiz model are closer to the experimental data.(3)Based on thermodynamics of irreversible process and convex function derived from damage mechanics,the damage kinetic constitutive equations are obtained,and fretting damage model is obtained based on dual dissipation potential function.Then,introducing the KBM parameters which based on strain to non-linear continuum damage model proposed by Chaboche.Using the KBM parameter substitute cyclic strain amplitude to characterize of constitutive relation under the condition of fretting.Finally a new fretting fatigue life prediction method is proposed in conjunction with experimental data.(4)3D model and finite element model of diesel engine block fastening surface composite structure are build,and the characteristic parameters such as the stress on the contact surface are analyzed quantitatively.The influence of friction coefficient on the relative slip and friction work is studied as well.The eveluation model is applied to the study of block's fretting,and the fretting fatigue life is predicted.The results show that Ruiz model,dissipation potential function model based on thermodynamics and NLCD model are suitable for evaluting the fretting fatigue life of diesel engine block.