Bending Deformation Of Laser Peen Forming:Experiments And Eigenstrain Modelling

Laser peen forming(LPF)is a process that uses high intensity and short duration laser to induce shock pressure as mechanical loading on the surface of metallic components to make them bend.It effectively extends service life and reliability by improving resistance to fatigue and to stress corrosion cracking.Because of its unique technical advantages,LPF,as a non-contact and tool-free process,has a promising prospect for forming large-scale structure with complex geometry such as plane wing panel and rocket tank sheet.This thesis presented a detailed investigation on modeling based on egienstrain method of laser peen forming and investigated the effects of process parameters and material properties on resulting deformation.Main researches are as follows:Composite shell modeling was built based on egienstrain method.Laser shock pressure was predicted through experiment calibration and simulation.Then the gradient distribution of eigenstrain was determined using an explicit-infinite plate model.And at last an implicit elastic model with composite shell elements was used to predict resulting deformation by incorporating the eigenstrain.The modelling was very effective to improve the simulation efficiency,which made it possible to realize the optimization based on simulation for large-scale thin workpiece.Different deformation in different directions was revealed,and the effects of scanning strategies and mechanical performance on deformation were investigated.Different scanning strategies were adopted in experiments to investigate their effects on aluminum alloy 2024-T3.Meanwhile,experiments with one-layer and multiple-layer scanning were conducted respectively.The results showed that scanning strategies and mechanical performance had a significant influence on the bending deformation.The deformation along rolling direction was smaller than that in transverse direction.However,the deformation in different directions became consistent after multi-layer peening,which might results from that material anisotropy of plastic surface weakened.The deformation characteristic of strip laser peen forming with different process parameters were revealed,and the deformation could be predicted through modelling.Experiments were conducted to investigate the effects of different process parameters such as strip width,interval width and sample size on the resulting deformation.Moreover,a model for laser strip peening was built.The results indicated that laser strip peening could restrain the deformation in the direction of strip.Simulation after parameter calibration was able to effectively predict the deformation of strip peening.An optimization method was proposed based on Genetic Algorithm for strip laser peen forming.The design variables were strip width and interval width.With the Genetic Algorithm,the method was aimed to obtain the minimum quadratic sum of differential value between node displacements of simulation surface and ideal surface.The optimization model was verified to be effective through experiments,which could reduce the dependence on experiments and experience.Besides,it was beneficial for laser peen forming to inhibit the spherical tendency.In conclusion,the modeling and process researches in this thesis make it possible for laser peen forming to obtain the precise deformation.Also,it is an effective and precise approach to predict the deformation in laser peen forming and to reduce the dependence on experiments and experience.