Study On Strengthening And Deformation Of Thin-walled Components Under Flattened Beam Multiple Laser Shock Processing

Laser shock processing(LSP)is a novel surface modification technology,which has the widespread application value in strengthening of aeronautical intergrally blade rotor,laser shock calibration of aeronautical casing,laser shock forming of aircraft panel,automobile manufacturing,shipbuilding,etc.Thin-walled components have been widely used in aero-engine and space-engine with its main characteristic of light weight,high specfic strength.However,it will occur appreciable macroscopic deformation in LSP due to low rigidity of thin-walled components.How realizes the coordination control of the shape and performance is urgently solved in the LSP of thin-walled components.Supported by XXX Project of AECC Hunan Power Machineries Institute(608),Joint Funds of Liaoning Province and National Natural Science Foundation of China(U1608259)and National Key Research and Development Program of China(2016YFB1102601),in this research,the GH4169 superalloy thin-walled components are regarded as the study subject.The strengthening and deformation of GH4169 superalloy thin-walled components by multiple flattened beam laser shock were investigated.Some important conclusions and innovative achievements of this work were listed as follows:(1)The theoretical model of loading under three-dimensional flattened beam laser shock wave was established.A modified explicit finite element analysis method was used to investigate the effects of the overlapping percentage,the number of impacts on the residual stress distribution.The method can greatly save the amount of computational work.The numerical simulation of residual stress relaxation of LSP GH4169 superalloy under cyclic loading was developed.It was applied to revealing the influences of the maximum load,the stress ratios on the residual stress relaxation.(2)The discretized formula for surface roughness was proposed.The numerical model was used to predict the surface roughness by applying the computed results as inputs to analytical equations.The surface node data obtained from ABAQUS were imported to get the mean line through MATLAB software.Having defined the position of mean line,the data were chosen to calculate the surface roughness by the discretized formula.A parametric study was conducted in order to predict the effects of laser energy,number of impacts,and thickness of target on surface roughness and surface deformation.(3)LSP experiments were performed to investigate the effects of different protective coating,laser energy,number of impacts,thickness of target on the microhardness,surface topography,surface roughness,surface residual stress of GH4169 superalloy thin-walled components by LSP.The effects of LSP on surface integrity of TC6 titanium alloy and 6061-T6 aluminum alloy were analysised.The GH4169 superalloy thin-walled components were treated by single-sided and double-sided LSP.One of them was kept thermal insulation for 1 hour under the constant temperature of 600oC.The residual stress was measured and the tensile test of GH4169 superalloy were carried out.The tensile mechanical properties of different specimens were calculated based on experimental data and the fracture morphology of tensile specimens was analyzed.(4)The effects of different process parameters(laser shock energy,thickness of thin-walled components,materials)on the deformation mode and surface residual stress were analyzed.Numerical simulation is developed to get the plastic strain distribution of the thin-walled components to assist understanding distortion generation.A method was proposed to determine the curvature radius of bending deformation of thin-walled components under LSP.Based on the theoretical model of curvature radius of bending deformation,discrete data obtained from the numerical simulations were fitted to get averaged plastic strain distribution by MATLAB,the curvature radius was calculated at last.The calculation method was verified by experiments.(5)The thickness of engine blade is thin and non-uniformity,the numerical simulation of laser variable pulse width shock processing was presented.The position of LSP of Aero engine turbine disc was determined according to fracture failure.LSP of oblique impact and different pulse widths was performed because of the complexity of turbine disc mortise structure.The feasibility of variable pulse width and oblique impact was analyzed by using finite element analysis software ABAQUS.The Experiment of LSP of Aero engine turbine disc was performed.The surface residual stress,surface morphology and surface roughness were analyzed after LSP,it has a guiding significance to further realize the industrial application of LSP of thin-walled blade and Aero engine turbine disc.