Study On Surface Quality And Mechanical Properties Of Copper Target Strengthened By Laser Shock

High energy pulse laser can produce intensive shock wave in the constraint model,which has important industrial applications in aerospace,automobile manufacturing,engine blade strengthening and other fields including laser shock processing(LSP),laser shock forming and others,among which the laser shock processing is the most important applied field in the laser shockwave.It can introduce sharp and deep residual stress layer to the surface of the shocked material.The existence of the residual stress will enhance the fatigue life of the work piece surface by a large margin.However,in order to cover larger area when radiating the material surface,the laser spots need the application of overlap.When lapping the laser spots,it will produce plastic deformation in the working area,leaving micrometer pit and enlarging roughness of the surface.Nevertheless,one of the critical factor for influencing the fatigue life of parts is the quality of material surface,mainly involving surface topography and surface roughness.This thesis aims to carry out researches on the surface quality and material property after laser shock processing.Besides,through the application of the finite element simulation software,the thesis conducts numerical calculation and results analysis on the dynamic process of the plastic deformation and the changes of the residual stress field.The main content and conclusions are as follows: ·The research choose the T2 red cooper as the targeted material for laser shock processing experiment.Besides,it choose aluminum foil tape?black tape?annealing aluminum foil and unannealed aluminum foil as the absorbed layer and water as the restraint layer,researching on the deformation of the cooper surface after laser shock processing on it with different absorbed material.After the laser shock processing,there appear micro defects when choosing aluminum foil tape as the absorbed layer.Almost no changes when choosing black tape and the surface quality is relatively high in the shocking area.When choosing annealing aluminum foil as the absorbed layer,there appear foil on the surface of the targeted material due to excessive ablation.When it comes to unannealed aluminum foil,it will destroy the material surface,so it cannot be used as absorbed layer.(1)Spots overlap rate has an important influence on the effect of the laser shock processing.In the experiment,the research choose three different overlap rates such 30%,40% and 50% to conduct laser shock processing.The results show that with the improvement of the overlap rate,the materials with high roughness after processing significantly decrease with good service quality.Besides,those with low roughness after processing increase with bad service quality.(2)Different ways of laser processing will also have impact on the effect of the laser shock processing with same laser energy.In the laser shock processing experiment,the research design three different processing ways,respectively exploring their effects on the changes of the material property.After detection of the hardness in deep direction of the processing area,the results show thatcompared with one time laser energy injection,the way of two-time injection will significantly improve the hardness.(3)By using the Abaqus software,the author makes a numerical calculation of the dynamic process laser shock processing.It analyzes the residual stress fields' forming process,the influences of different processing methods on residual stress and the influences of different processing methods on material surface quality.The results manifest stagger laser processing methods will improve the residual stress and surface roughness of the material.Therefore,to better control the residual stress and surface quality,it's critical to choose processing methods.