| Most of parts in the mechanical field are characterized with complex surface such as fillet,groove and so on.The curvature of the critical curvature section of these curved structures changes greatly,where fatigue is weak because of stress concentration,and fatigue crack easily occurs under external load.Laser shock processing(LSP)can effectively improve the fatigue life of curved parts.However,the residual stress distribution of curved structure in LSP can’t be predicted based on the trend obtained by flat structure.Therefore,it is of great significance to study the residual stress distribution and fatigue performance of curved structure in LSP.In this paper,the influence of LSP on the residual stress distribution and fatigue performance of TC4-DT titanium alloy fillet parts was studied by means of theoretical analysis,numerical simulation and experimental verification.The main conclusions are as follows:(1)The generation mechanism of shock wave induced by laser shock and its interaction with material are discussed through theoretical analysis,and analyzed the formation mechanism of residual stress field under shock wave.The formation mechanism of residual stress in curved structure in laser shock is discussed,and analyzed the possible relationship between curvature and residual stress.Three geometrical models of concave surface,plane and convex surface were established by ABAQUS to study the geometrical effect of curved structure in laser multi-lap impact.The results show that the residual compressive stress and depth of influence layer between three geometric models have the following relationship: concave>flat>convex.For concave structure,the compressive residual stress decreases with the increase of radius.For convex structure,the compressive residual stress increases with the increase of radius.For fillet structure,the residual stress distribution on the R3 model surface is better than that of the R6 model.(2)Based on ABAQUS,the residual stress distribution law of fillet structure under different laser shock parameters is studied.The results show that the compressive residual stress increases with the increase of peak pressure,but there is a saturation value,while the depth of compressive residual stress layer continues to increase.With the increase of laser pulse width,the compressive residual stress increases on each path,and the depth also increases.The role is not obvious with the increase of shock number,and even reverse effect,and the shock numbers have little effect on residual stress distribution in depth direction.(3)On the basis of simulation,the LSP and fatigue tensile test of TC4-DT titanium alloy R3 and R6 fillet specimens are carried out.The results show that the fatigue life of specimens is obviously increased after LSP,the fatigue gain varies under different conditions,but the fatigue increment of R3 and R6 specimen are almost the same.(4)Through microscopic analysis of the fatigue fractures morphology some results can be found.Compare before with after LSP: in fatigue source area,the fatigue source of non-shock side is located at the tangent of fillet root,but the fatigue source of shock side is shifted to the depth direction.In fatigue stability region,the width of fatigue striation of shock side is significantly smaller than that of non-shock,and indicating that LSP can effectively inhibit the growth of fatigue crack.In final rupture region,the size of dimple in shock side is larger than that of non-shock side.The mechanism to improve the anti-fatigue properties of fillet structures in LSP is studied in the paper.The results show that LSP induced compressive residual stress to reduce the effective stress intensity factor amplitude of crack tip,thereby inhibiting the fatigue crack growth and improving the fatigue life of fillet structures.Fillet radius can affect the fatigue properties of fillet structures through affecting concentrated stress and residual stress distribution. |
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