Research On Laser Shock Peening Of TC4 Thin Plate And Its Effect On Foreign Object Damage Performance

Foreign object damage(FOD)usually occurs during take-off and landing of aircraft.FOD causes significant damage to compressor blades in areo-engines and even severely weakens its high cycle fatigue performance.Laser shock peening(LSP)has been proposed as an advanced surface strengthening technology,to extend fatigue life of blades.Residual compressive stresses induced by LSP can alleviate the stress concentration caused by FOD effectively.Meanwhile,the hardened layer and grain refined layer formed on the surface of the material through LSP effectively inhibit fatigue crack growth and then prolong the fatigue life of the blade material subjected to FOD.In this study,TC4 titanium alloy was taken as the research object,which is usually used for manufacturing airplane fan/compressor blade.The strengthening effects of LSP on the high cycle fatigue performance of damaged blade was investigated by using experimental and simulation methods in the present work.The main results and conclusions are as follows:(1)The effects of multiple LSP on the surface roughness,micro-hardness and residual stress distribution was investigated.The results showed that LSP has little effect on the surface roughness when comparing with the traditional surface strengthening technique.The micro-hardness increased with the increase of impact times.The micro-hardness reached maximum and tended to be saturate after three impacts.The LSP strategies had a great influence on the distribution of residual stress in the material.The depth of residual compressive stress was about 1000?m after the single-sided LSP,while the residual stress distribution induced by the double-sided interval impact showed obvious asymmetry.Furthermore,the residual compressive stress of the first-strengthened surface was lower than the post-strengthened surface.(2)The effect of LSP on the microstructure of TC4 titanium alloy was studied and the relationship between microstructure and macroscopic mechanical properties was analyzed.The results showed that the main grain refinement mechanisms were dislocation slip and twinning intersection mechanism.The grain size in the processed surface reached nanoscale after multiple LSP.The gradient distribution of macroscopic mechanical properties of the material was dominated by the variation of microstructure along the depth direction.(3)The characteristics of typical FOD morphology were characterized,and the high fatigue properties of the samples before and after LSP were tested.The results showed that the typical damage morphology is plastic deformation,tearing,material loss,small gap and micro-crack.The notch has obvious effect on the high fatigue performance of the specimen.After single laser shock,fatigue strength could be improved by 20.5%.(4)The LSP process and FOD process were simulated by ABAQUS.The results showed that Johnson-Cook(J-C)model could be applied to simulate the dynamic process under ultra-high strain rate deformation.The residual stress field induced by the simultaneously double-side LSP showed a better symmetry with M-type distribution than that of the interval double-side LSP.The residual compressive stress exists in the plane region while a comparatively high tensile residual stress exists on the top surface and at the bottom of the notched specimen.Meanwhile,the residual compressive stress induced by LSP could effectively balance the tensile stress caused by FOD effectively,which may improve the fatigue performance of the damaged specimens.