Alternate Double-side Laser Peening Of Thin Sections: Experiments&Modelling

Aero-engine compressor blade is a kind of typical thin-wall structure.Laser peening(LP)has been proved to be an efficient surface treatment to resist foreign object damage(FOD)and improve fatigue life of the blades by inducing compressive residual stress.In order to solve the problem of spallation,a method of double-side alternate laser peening was proposed.In this paper,the feasibility of inducing residual compressive stress and eliminating distortion was studied,as well as the modelling and the process optimization.The main research contents include following aspects:The deformation law of double-side alternately laser peened thin sections was studied.2024-T351 thin-walled specimens were designed for single-side and double-side laser peening experiments,and residual stress of all the surfaces was measured.The experiment results indicated that single-side laser peened specimens would bend towards or backwards laser beam as a result of laser intensities,and deflection nearly recovered with double-side alternate laser peening,and compressive residual stress was observed in both treated surfacesDynamic explicit model and eigenstrain model was established for simulation of laser peening on thin-walled sections.The distributed shock pressure was obtained and used for dynamic analysis,and mass damping was applied to the model for efficiency.The results of plastic strain were imported into eigenstrain model for elastic simulation,and the accuracy of the model was verified.The results showed that the application of appropriate mass damping to explicit dynamic model could accelerate the displacement stability without affecting the plastic strain results,and eigenstrain model could accurately and efficiently predict the deformation and residual stress of large-scale laser peening.The influence of laser intensity on the deflection of double-side alternately laser peened thin-walled sections was studied,as well as the recovery mechanism.The deformation process and the effect of plastic strain distribution on deflection was simulated by explicit model.The results indicated that the plastic strain of laser peened thin-walled sections was produced by the interaction of stress wave and the impact deformation.Different plastic strain gradient distributions would cause different bending deflection,and the deflection could be eliminated by laser peening on the other side.The effect of laser scanning sequence was studied,and the scanning strategy was selected to improve the fatigue life.The differences between simultaneous and alternate laser peening were compared by simulation.the effects of the scanning sequences on deformation and residual stress was studied by experiments and simulation.The results showed that double-side alternate laser peening was better in reducing the risk of spallation,but the induced residual stress was less than simultaneous method.In addition,different laser scanning sequences affected deflection and residual stress around leaf edge,and the method of scanning from the inside out parallel to the leaf edge could improve the residual stress near the leaf edge.In conclusion,the laser peening on thin-walled sections was taken as the object of study,and a double-side alternate method was proposed.A dynamic explicit model and an eigenstrain model was established.Deflection and residual stress distribution was studied and laser scanning strategy was optimized further enhance the strengthening effect,to help laser peening of thin-walled sections.