發(fā)布時(shí)間：2018-02-04 02:37

  本文關(guān)鍵詞： 激光沖擊 層狀介質(zhì) 界面 阻抗匹配 強(qiáng)化 表面微制造　出處：《江蘇大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：激光沖擊被廣泛用于均質(zhì)材料表面強(qiáng)化或成形,但很少用于層狀介質(zhì)的加工制造。這是因?yàn)?在層狀介質(zhì)界面處沖擊波會(huì)發(fā)生透射、反射、拉壓性質(zhì)突變等,這使得激光誘導(dǎo)沖擊波在此類介質(zhì)中傳輸過程復(fù)雜,可控性不好。但是,前人研究結(jié)果表明,高幅沖擊波能夠強(qiáng)化材料表面,甚至層狀介質(zhì)的界面。此外,合理設(shè)計(jì)層狀介質(zhì),可實(shí)現(xiàn)沖擊波傳輸主動(dòng)控制,獲得調(diào)制沖擊波,進(jìn)而,不僅能夠?qū)崿F(xiàn)材料改性,還能夠控制材料塑性流動(dòng)方式,實(shí)現(xiàn)表面微造型。本文基于層狀介質(zhì)中激光誘導(dǎo)沖擊波的調(diào)制理論,對(duì)激光沖擊強(qiáng)化層狀介質(zhì)和金屬表面激光沖擊毛化進(jìn)行了系統(tǒng)的實(shí)驗(yàn)和仿真研究。主要工作和結(jié)論如下:(1)層狀介質(zhì)中沖擊波傳輸理論�；贏baqus有限元仿真軟件,建立層狀介質(zhì)物理模型,系統(tǒng)仿真沖擊波在層狀介質(zhì)內(nèi)的傳輸過程,研究應(yīng)力波在膜基結(jié)構(gòu)中的傳輸規(guī)律:若沖擊波從較高阻抗介質(zhì)傳輸?shù)捷^低阻抗介質(zhì),沖擊波振幅會(huì)在介質(zhì)界面處發(fā)生突然衰減,反射波與入射波互相作用,導(dǎo)致拉應(yīng)力產(chǎn)生。若沖擊波從較低阻抗介質(zhì)傳輸至較高阻抗介質(zhì),沖擊波幅值會(huì)在介質(zhì)界面處放大,同時(shí)反射波會(huì)與入射沖擊波相互作用從而形成壓應(yīng)力。對(duì)于雙金屬?gòu)?fù)合材料,膜層的殘余應(yīng)力分布與單層材料一致,當(dāng)從膜層傳輸至基體時(shí),由于阻抗匹配的不同,殘余應(yīng)力的分布趨勢(shì)也有所不同。(2)激光沖擊強(qiáng)化銅鋁層狀復(fù)合材料研究。通過實(shí)驗(yàn)和仿真,研究激光參數(shù)和界面處材料聲阻抗匹配度對(duì)界面性能和材料綜合性能的影響。結(jié)果發(fā)現(xiàn):當(dāng)激光沖擊高阻抗膜層-低阻抗基體時(shí),膜層能夠得到強(qiáng)化,如果膜層足夠薄,基體也能夠得到強(qiáng)化。當(dāng)激光沖擊低阻抗膜層-高阻抗基體材料時(shí),不僅膜層材料能夠被強(qiáng)化,基體被強(qiáng)化的可能性也變大。(3)銅靶材表面激光沖擊毛化研究。主動(dòng)設(shè)計(jì)制造空穴映射層,利用空穴映射層對(duì)入射寬幅沖擊波進(jìn)行空間調(diào)制,獲得幅值具有一定空間分布的透射沖擊波,在靶材表面獲得微凸起。結(jié)果表明:當(dāng)能量低于某一閾值時(shí),凸起高度是隨能量增加而變大;當(dāng)能量大于這一閾值后,過大的激光能量會(huì)使微凸起的頂端產(chǎn)生次級(jí)微凹陷,從而形成火山口形貌,降低了凸起總高度;映射層聲阻抗與基體、約束層之間的聲阻抗匹配度越高,越有利于凸起的產(chǎn)生;空穴間距的減小會(huì)影響凸起之間材料流動(dòng),由圓形凸起逐漸過渡為四周有圓角的方形凸起;微凸起部位以及微凸起之間的材料硬度均顯著高于基體硬度,說明激光沖擊毛化技術(shù)具有表面微造型和表面強(qiáng)化的復(fù)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.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG665
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本文編號(hào)：1489072