激光诱导冲击波在层状介质中传输规律及其应用研究

发布时间：2018-02-04 02:37

  本文关键词： 激光冲击 层状介质 界面 阻抗匹配 强化 表面微制造　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：激光冲击被广泛用于均质材料表面强化或成形,但很少用于层状介质的加工制造。这是因为,在层状介质界面处冲击波会发生透射、反射、拉压性质突变等,这使得激光诱导冲击波在此类介质中传输过程复杂,可控性不好。但是,前人研究结果表明,高幅冲击波能够强化材料表面,甚至层状介质的界面。此外,合理设计层状介质,可实现冲击波传输主动控制,获得调制冲击波,进而,不仅能够实现材料改性,还能够控制材料塑性流动方式,实现表面微造型。本文基于层状介质中激光诱导冲击波的调制理论,对激光冲击强化层状介质和金属表面激光冲击毛化进行了系统的实验和仿真研究。主要工作和结论如下:(1)层状介质中冲击波传输理论。基于Abaqus有限元仿真软件,建立层状介质物理模型,系统仿真冲击波在层状介质内的传输过程,研究应力波在膜基结构中的传输规律:若冲击波从较高阻抗介质传输到较低阻抗介质,冲击波振幅会在介质界面处发生突然衰减,反射波与入射波互相作用,导致拉应力产生。若冲击波从较低阻抗介质传输至较高阻抗介质,冲击波幅值会在介质界面处放大,同时反射波会与入射冲击波相互作用从而形成压应力。对于双金属复合材料,膜层的残余应力分布与单层材料一致,当从膜层传输至基体时,由于阻抗匹配的不同,残余应力的分布趋势也有所不同。(2)激光冲击强化铜铝层状复合材料研究。通过实验和仿真,研究激光参数和界面处材料声阻抗匹配度对界面性能和材料综合性能的影响。结果发现:当激光冲击高阻抗膜层-低阻抗基体时,膜层能够得到强化,如果膜层足够薄,基体也能够得到强化。当激光冲击低阻抗膜层-高阻抗基体材料时,不仅膜层材料能够被强化,基体被强化的可能性也变大。(3)铜靶材表面激光冲击毛化研究。主动设计制造空穴映射层,利用空穴映射层对入射宽幅冲击波进行空间调制,获得幅值具有一定空间分布的透射冲击波,在靶材表面获得微凸起。结果表明:当能量低于某一阈值时,凸起高度是随能量增加而变大;当能量大于这一阈值后,过大的激光能量会使微凸起的顶端产生次级微凹陷,从而形成火山口形貌,降低了凸起总高度;映射层声阻抗与基体、约束层之间的声阻抗匹配度越高,越有利于凸起的产生;空穴间距的减小会影响凸起之间材料流动,由圆形凸起逐渐过渡为四周有圆角的方形凸起;微凸起部位以及微凸起之间的材料硬度均显著高于基体硬度,说明激光冲击毛化技术具有表面微造型和表面强化的复合效果。
[Abstract]:Laser shock is widely used in the surface strengthening or forming of homogeneous materials, but rarely used in the fabrication of layered media. This is because the shock wave at the interface of the layered medium will be transmitted, reflected, and the properties of tension and compression sudden change. This makes the propagation process of laser-induced shock wave in this kind of medium complex and uncontrollable. However, previous studies show that the high amplitude shock wave can strengthen the interface of the material surface and even the layered medium. Reasonable design of layered medium can realize active control of shock wave transmission and obtain modulated shock wave, which can not only realize material modification, but also control material plastic flow mode. This paper is based on the modulation theory of laser-induced shock wave in layered medium. A systematic experimental and simulation study on laser shock texturing of layered medium and metal surface strengthened by laser shock has been carried out. The main work and conclusions are as follows: 1). Theory of shock wave propagation in layered media. Based on Abaqus finite element simulation software. The physical model of layered medium is established and the propagation process of shock wave in layered medium is simulated systematically. The transmission law of stress wave in film based structure is studied: if the shock wave is transmitted from high impedance medium to low impedance medium. The amplitude of shock wave will suddenly attenuate at the interface of the medium, and the reflected wave will interact with the incident wave, resulting in tensile stress. If the shock wave propagates from the lower impedance medium to the higher impedance medium. The shock wave amplitude will be amplified at the interface of the medium, and the reflection wave will interact with the incident shock wave to form the compressive stress. For bimetallic composites, the residual stress distribution of the film is consistent with that of the monolayer material. When transferring from film to matrix, the distribution trend of residual stress is different due to the different impedance matching. The effects of laser parameters and material acoustic impedance matching degree on the interface properties and material properties were studied. The results show that the film can be strengthened when the laser strikes the high impedance film and the low impedance substrate. If the film is thin enough, the substrate can be strengthened. Not only the film material can be strengthened when the laser strikes the low impedance film layer-high impedance substrate material. The possibility of strengthening the matrix is also increased. 3) the surface of copper target is studied by laser shock. The hole mapping layer is designed and manufactured and the incident wide shock wave is modulated by the hole mapping layer. When the energy is below a certain threshold, the height of the bulge increases with the increase of energy. When the energy is larger than this threshold, the laser energy will make the top of the microbulge produce secondary microdepression, thus forming the crater morphology and reducing the total height of the protuberance. The higher the matching degree between the acoustic impedance of the mapping layer and the matrix, the more favorable the protuberance is. The decrease of the gap between the holes will affect the material flow between the protuberances and gradually transition from the circular protuberances to the square bulges with round corners. The hardness of the materials at and between the micro-protrusions is significantly higher than that of the matrix, which indicates that the laser impact texturing technology has the composite effect of surface micro-molding and surface strengthening.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665
，

本文编号：1489072