【作者】 李志；

【导师】 胡永祥；

【作者基本信息】 上海交通大学 ， 机械工程（专业学位）， 2016， 硕士

【摘要】 激光喷丸成形工艺是利用激光诱导产生的等离子体冲击力学效应,在金属板料表面及深度方向上产生高幅残余应力场,从而使金属板料产生弯曲变形。该工艺可以有效提高零件的抗疲劳和耐腐蚀性能,因其独特的技术优势在航空航天大型整体壁板成形中具有广阔的应用前景。本文主要论述了基于固有应变理论的激光喷丸成形建模方法,探讨了工艺参数对激光喷丸成形的影响,主要研究内容包括以下几个方面:建立了基于固有应变理论的分层壳单元有限元模型,实现激光喷丸成形弯曲变形量的建模仿真以及仿真效率的提高。通过实验和有限元仿真预测出激光喷丸冲击载荷,基于显式无限大平板模型计算出沿深度方向上固有应变的分布,然后建立隐式弹性壳单元有限元模型。该模型有效地提高了仿真效率,为大型薄壁件的仿真优化提供了可能。揭示了激光喷丸不同方向上的变形差异,研究了喷丸路径和材料性能对变形差异的影响。本文采用不同的扫描方式激光喷丸2024-T3铝合金,来研究扫描路径对激光喷丸变形的影响。同时通过设计不同的实验对2024-T3铝合金进行单次和多次激光喷丸冲击,比较轧制方向和垂直方向上的弯曲变形。结果表明:扫描方式和材料轧制方向对激光喷丸不同方向弯曲变形有明显影响,材料轧制方向上弯曲变形小于垂直方向上的,但是多次喷丸后不同方向上的弯曲变形趋于一致,这可能是材料塑性变形层各向异性减弱造成的。探究了不同工艺参数条件下激光条带喷丸变形规律,实现了对激光条带喷丸变形的预测。通过设计不同的实验方案来研究不同工艺参数条件下条带喷丸变形的情况,分析不同工艺因素对条带喷丸变形的影响,并建立激光条带喷丸有限元模型。结果表明:激光条带喷丸可以抑制条带方向上的弯曲变形,而有限元仿真可以有效预测条带喷丸的变形情况。提出了基于遗传算法优化激光条带喷丸工艺参数的方法,实现了条带喷丸几何参数的优化。将条带宽度和间隔宽度作为设计变量,以仿真曲面与理想曲面位移差值的平方和最小为目标函数,基于遗传算法和数值仿真优化出条带和间隔宽度。该优化方法通过实验证明了其有效性,为抑制激光喷丸球面变形趋势提供了可能。综上所述,本文以激光喷丸成形为研究对象,建立了基于固有应变理论的分层壳单元模型,探究了激光喷丸不同方向变形差异的影响因素和不同工艺参数条件下激光条带喷丸变形规律,基于遗传算法实现了工艺参数优化,为实现激光喷丸精确成形提供了可能,同时增强了激光喷丸成形的可预测性。更多还原

【Abstract】 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.更多还原