Research On Laser Shock Peening On Fretting Fatigue Life

Fretting fatigue damage widly exists in jointing components,it can largely reduce the fatigue life of jointing components.The aim of Anti fretting fatigue damage research is improve the fatigue life jointing components,besides material chosen and structure optimization,it's of great significance to research on surface enhancements or modification.Among the recently advanced surface modification techniques is Laser shock peening(LSP),and it has revealed numerous advantages over the conventional techniques in ordinary fatigue field,but little research was conducted on anti fretting fatigue damage.Therefore,systematical research on the parametric studies of LSP on TC11 material and fretting fatigue life prediction will do great contribution to the theoretical study and engineering applications.The main contents of this thesis are summarized as following:In terms of the fretting fatigue damage problem,laser shock peening on the specimen of fretting fatigue was carried out,then the surface finish condition was valued.Based on the generation of shock waves,processing parameters,and characterization of LSP,laser power density(I0)of 3.2GW/cm2?4.8GW/cm2?6.4GW/cm2 and two different laser shock area plans was carried out on TC11 alloy.The surface finish condition indicate that: laser shock plan 2,laser power density of 4.8GW/cm2 has a better surface finish condition.Based on single clamp fretting fatigue apparatus,fretting fatigue experiments was carried out before and after LSP.The stress situation of apparatus cantilever and fretting fatigue crack initiation was monitored.The fretting fatigue life results,crack initiation site,fretting fatigue surface wear and fatigue fracture was discussed.The fatigue life improvement is biggest when the specimen is surface modificated by power density 4.8GW/cm2,the improvement factor is 3.7.With the increase of laser power density,surface wear is reduced,and the crack initiation site tends to move to the inside of specimen.The mechanical models of different contact pad gripping rigidity apparatuses were developed.By the investigation of the experimental results and numerical analysis,the effect of contact pad gripping rigidity on fretting fatigue damage was discussed.The results indicate that: with decreasing contact pad gripping rigidity,the maximum SWT(Smith-Watson-Topper)fatigue parameter value remains almost the same and tends to have a symmetrical distribution over contact interface.As a result,the relative slip amplitude and fretting wear decrease correspondingly;the smaller contact pad gripping rigidity of the apparatus,the longer fretting fatigue life will be obtained.The main influence of LSP on fretting fatigue was discussed,compressive residual stress was added into the life prediction model and life prediction was made.Finally the influence of compressive residual stress on parameter in the life prediction model was discussed,the results indicate that: compressive residual stress has a big influence on stress-strain state,but it has little influence on relative slip amplitude.