【作者】 黄舒；

【导师】 周建忠；

【作者基本信息】 江苏大学 ， 机械制造及其自动化， 2008， 硕士

【摘要】 受控激光喷丸强化的本质是在被处理材料中获得适度的残余应力分布,从而实现特定的强化效果。本课题针对激光喷丸中工艺控制的关键问题——诱发的残余应力的表征进行系统研究,为主动实现对激光喷丸强化后残余应力的优化控制提供依据,主要工作如下:(1)以高能短脉冲激光与材料相互作用诱导高幅冲击波的物理机制为基础,探讨了高幅冲击波加载下金属材料的力学响应以及冲击波诱导残余应力生成的机理,分析了影响残余应力大小和分布的主要因素。探索了激光喷丸强化诱导残余压应力的表征方法,引入残余应力的估算理论模型,分析了残余应力沿层深分布的计算方法。(2)以ABAQUS软件为平台,建立了高应变率条件下激光喷丸过程的有限元分析模型,编制专用的激光喷丸强化分析模块,对激光喷丸诱导的表面动态应力、残余应力各表征值和工艺参数之间的关系以及喷丸后板料表面微观形貌进行了有限元模拟研究,同时预测了单联中心孔疲劳试件喷丸后的残余应力分布,为激光喷丸过程中工艺参数选择和表面质量的有效控制研究提供理论依据。(3)使用六西格玛统计过程控制技术进行激光喷丸强化工艺参数优化研究,利用Minitab软件中的Taguchi设计方法对模拟方案进行试验设计,提取各种激光工艺参数下的残余应力表征值数据进行处理,通过信噪比分析和方差分析确定了各因素对残余应力表征值影响的显著性程度,从中筛选出较优的影响因子水平,在此基础上使用因子设计方法对喷丸后的强化效果进行响应优化设计,确定最佳激光工艺参数组合,为激光喷丸强化过程的参数优化和残余应力控制提供指导。(4)典型材料激光喷丸试验,用X-衍射应力测定仪测量了激光喷丸区材料表面残余应力分布,同时结合电解抛光等工艺测量了沿厚度方向的残余应力分布,测试了喷丸前后材料表面的涂层形貌、冲击坑的形貌、材料显微硬度及表层显微组织的变化,分析了其形成的原因。探讨了激光喷丸区产生的塑性变形与残余应力分布之间的内在联系,表明实验结果与数值模拟及理论分析吻合较好,为受控激光喷丸强化工艺的进一步研究提供了依据。更多还原

【Abstract】 The object of controlled laser shock peening is to get appropriate residual stress distribution in order to achieve specific strengthening effects on the treated materials. In this subject, systematic study is done on the key problem of processing controlling of laser peening, that are characteristics of induced residual stress, which provide reliable basis for optimizing control of residual stress induced by laser shock peening(LSP). The principal works are showed as following:(1) Begin with the study of interaction between laser and materials, the basic process and physical mechanism of laser induced shock waves are analyzed, the mechanical response of metal material under high amplitude shock waves loading and generation mechanism of residual stress induced by shock waves are discussed, the main factors which impact the size and distribution of residual stress are analyzed. Characteristics methods of residual compressive stress distribution induced by laser peening are explored, a theoretical model for estimating residual stress is introduced, and the methods of calculating residual stress distribution along the depth direction are analyzed.(2) Based on ABAQUS software, the finite element models of LSP under high strain ratio condition are established. The special analytic module for LSP is generated. The relationship among LSP induced surface dynamic stress, residual stress characteristics and processing parameters are researched, meanwhile surface micro-topography of sheet metals after laser peening are analyzed, the residual stress distribution in fatigue specimens with center hole are predicted, which provide theoretic basis for optimizing process parameters and effectively controlling surface quality during LSP.(3) Taguchi method of Minitab software is used to carry out experimental design for simulated program, the characteristics of residual stress measured under various laser processing parameters are extracted and treated, the degree of their influencing are determined by the analysis of signal-to-noise ratio and variance, optimal level of influencing factors are screened, then response optimal design of strengthening effects are processed using factor design method based on Taguchi design, optimal processing parameters combination are achieved enventually, which provide great guidance for optimizing the processing parameters and controlling residual stress during LSP.(4) LSP experiments are carried out on typical materials. After measuring residual stress on the surface of the peened areas with X-rays diffraction determinator, the distribution of residual stress along the depth of sheet metals are obtained combining with electrolytic polishing process. Surface coating morphology, shocking shoot morphology, micro-hardness of material and superficial coat microstructure of sheet metals before and after LSP are tested, the creation reasons are analyzed: internal relation between plastic deformation and the distribution of residual stress are discussed. Simulation results agree with experimental results well, which will provide good guidance for further study of controlled LSP.更多还原