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Characteristics and Experiment Study on Residual Stress Induced by Controlled Laser Peening

Author: HuangShu
Tutor: ZhouJianZhong
School: Jiangsu University
Course: Mechanical Manufacturing and Automation
Keywords: Controlled laser peening Residual stress Characteristics Statistical Optimization Taguchi design
CLC: TN249
Type: Master's thesis
Year: 2008
Downloads: 77
Quote: 1
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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.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Laser applications
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