【作者】 于水生；

【导师】 张永康； 姚红兵；

【作者基本信息】 江苏大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 激光冲击处理(LSP:Laser Shock Processing)作为一种新型的表面强化技术,得到越来越广泛的研究。镁合金是航空航天、交通工具等行业中越来越重要的材料。因此对镁合金进行激光冲击处理的研究,对提高其性能,增加镁合金构件的服役时间等具有重要意义。本文从激光冲击处理的机理出发,介绍了激光冲击处理过程中冲击波的形成和残余应力的产生。采用有限元分析和试验相结合的方法研究了激光冲击波峰值压力在镁合金中的衰减,并利用试验方法讨论了约束层以及激光功率密度对冲击波峰压的影响。论文的主要研究内容如下:对镁合金中激光冲击波峰值压力的衰减进行了研究。一方面运用有限元模拟的方法,通过讨论建模过程中的几个关键问题,模拟冲击波在镁合金靶材中的传播,得到了冲击波在镁合金中的平均传播速度以及冲击波峰压的衰减规律;另一方面,利用PVDF压电传感器对镁合金中的冲击波进行测量,首次得到镁合金中的冲击波波形,并且分析得出冲击波在靶材中的平均传播速度以及冲击波峰压的衰减规律。将试验结果与模拟所得的结果进行了比较,两者较好吻合。研究结果表明:冲击波在镁合金中的平均传播速度与应力波中纵波的传播速度基本一致;在镁合金靶材内部,冲击波峰压呈指数衰减规律。以试验为手段,主要讨论了约束层以及激光功率密度对冲击波峰值压力的影响。首先分别对约束模型以及非约束模型进行讨论,得出约束层对冲击处理效果的影响;并对不同的激光功率密度进行试验研究,最终得出激光功率密度与峰值压力的关系曲线。结果表明:约束模式下,冲击波峰值压力是无约束层时的8倍左右,而且脉冲的持续时间也有显著提高;在一定范围内,随着激光功率密度的增加,冲击波的峰值压力也随之增大。更多还原

【Abstract】 Laser shock processing (LSP) is a new surface hardening technology. It has been widely used for the research of material’s surface modification. Magnesium alloy is an important material in aerospace, automotive etc. So it is meaningful to study LSP on magnesium alloy. This study can be helpful to improve the property and fatigue life of magnesium alloy.In the present work, based on the mechanism of LSP, the induced Shockwave during LSP and the generation of residual stress was discussed. The finite element model was used to study the attenuation law of the peak pressure of stress wave, and the results were compared with the experimental results. Also, the effect of overlay and laser power density on the peak pressure of the Shockwave was studied by experimental method. The main research contents in this paper are listed as follows:The attenuation of the Shockwave in magnesium alloy was investigated by FEM (Finite Element Method) simulation and experiment. First, through describing some key problems in the model construction, the finite element models were used to simulate the attenuation of the Shockwave in the magnesium alloy, and the average propagation velocity and the peak pressure of the Shockwave were obtained. Second, the relative pressures of the shock waves were measured by PVDF gauge. The attenuation law of laser shock wave was obtained by measuring the intensity pressures on the rear surface of the target for different thickness the shock waves had passed each time. Then the experimental results were compared with the simulation results and they agree well. The results show that the average velocity of the shock wave attenuation in magnesium alloy is in good agreement with the propagation velocity of stress longitudinal wave; the law of the shock wave attenuation is exponential.In order to study the effect of overlay and laser power density on shockwave, the laser-induced Shockwave was measured by a PVDF gauge and a digital oscillograph. Based on the piezoelectric waves measured in the overlay geometry and the direct ablation regime, the pressure waves were obtained and compared; the pressure waves acquired in the different laser power density conditions were also compared and analyzed and obtained the curve about the peak pressure as a function of laser power density. The research results showed that the peak pressure of laser Shockwave in the overlay geometry was about as eight times as it was in the direct ablation regime, and the duration time of the pulse was extended obviously. Below the dielectric breakdown threshold of the transparent overlay, the peak pressure of laser Shockwave was improved with the increase of the laser power density.更多还原