發(fā)布時間：2018-06-15 09:15

  本文選題：脈沖激光 + COMSOL�。� 參考：《江蘇大學(xué)》2017年碩士論文

【摘要】：脈沖激光作用于金屬表面,獲得特定的表面形貌,在工業(yè)領(lǐng)域有廣泛應(yīng)用。特定表面形貌的形成,是光與靶材相互作用復(fù)雜物理過程的作用結(jié)果,該過程與激光脈沖寬度密切相關(guān)。當(dāng)脈沖寬度大于材料的熱弛豫時間(納秒、微秒或者毫秒激光),熱力效應(yīng)在表面形貌形成過程中起關(guān)鍵作用;而當(dāng)脈沖寬度小于材料熱弛豫時間(皮秒或者飛秒激光),靶材中光致熱力效應(yīng)較小,表面形貌形成機制與長脈沖激光迥然不同。本文選擇飛秒激光和百微秒激光為加工源,從實驗和數(shù)值研究兩方面,細致研究了長脈沖與超短脈沖激光與金屬材料作用后,表面形貌的形成結(jié)果、形成機制和相關(guān)規(guī)律。主要工作內(nèi)容如下:(1)基于COMSOL Multiphysics仿真軟件,數(shù)值研究了超短脈沖激光作用金屬表面后的能量分布以及長脈沖激光作用金屬材料表面后溫度場分布;研究了金屬表面形貌以及不同金屬材料對超短脈沖激光在金屬表面能量分布的影響;長脈沖激光作用金屬表面能量分布。數(shù)值研究結(jié)果表明:表面微結(jié)構(gòu)越密集,激光能量會越往微結(jié)構(gòu)尖峰移動;由于長脈沖激光熱效應(yīng)的存在,熱影響區(qū)域大于光斑輻照區(qū)域。(2)進行超短脈沖激光金屬表面微加工實驗,研究了金屬材料、靶材表面粗糙度以及單脈沖激光能量等對表面形貌變化的影響規(guī)律。實驗結(jié)果發(fā)現(xiàn):超短脈沖激光作用后,由于激光和表面波干涉,金屬表面形成共振周期性結(jié)構(gòu);不同金屬材料形成周期性表面結(jié)構(gòu)的難易不同,對激光能量吸收更多的材料更易形成周期性表面結(jié)構(gòu);單脈沖能量大的超短脈沖激光加工形成的表面周期性結(jié)構(gòu)的輪廓更加明顯,但是由于高斯光束使得激光能量分布不均勻,光斑中心的熱效應(yīng)也更加明顯。(3)進行長脈沖激光輻照裂紋金屬表面實驗,研究了輸出功率和離焦量對不同金屬材料表面裂紋彌合的影響。實驗結(jié)果發(fā)現(xiàn):硬度低的材料更易利用微熔凝的方法彌合金屬表面裂紋;當(dāng)輸出功率選擇合適時,可以通過適當(dāng)調(diào)整離焦量,在獲得裂紋修復(fù)結(jié)果的同時改善金屬表面的質(zhì)量。
[Abstract]:Pulsed laser acts on metal surface and obtains specific surface morphology, which is widely used in industrial field. The formation of specific surface morphology is the result of the complex physical process of the interaction between light and target, which is closely related to the laser pulse width. When the pulse width is larger than the thermal relaxation time (nanosecond, microsecond or millisecond laser), the thermal effect plays a key role in the formation of surface morphology. However, when the pulse width is smaller than the thermal relaxation time (picosecond or femtosecond laser), the photoinduced thermal effect in the target is small, and the mechanism of surface morphology formation is very different from that of long pulse laser. In this paper, femtosecond laser and femtosecond laser are selected as the processing source. The formation of surface morphology, formation mechanism and related laws of the surface after the interaction of long pulse and ultrashort pulse laser with metal materials are studied in detail from both experimental and numerical aspects. The main work is as follows: (1) based on COMSOL Multiphysics simulation software, the energy distribution of metal surface and the temperature field distribution after long pulse laser acting on metal surface are numerically studied. The influence of metal surface morphology and different metal materials on the energy distribution of ultrashort pulsed laser on metal surface and the energy distribution on metal surface by long pulse laser were studied. The numerical results show that the denser the surface microstructures, the more the laser energy moves to the peak of the microstructures, due to the existence of long pulse laser thermal effects. The influence of metal materials, target surface roughness and single pulse laser energy on the surface morphology was studied. The experimental results show that the metal surface has resonant periodic structure due to the interference of laser and surface wave after ultrashort pulse laser, and different metal materials are difficult to form periodic surface structure. It is easier to form periodic surface structure for more materials absorbing laser energy, and the surface periodic structure formed by ultrashort pulse laser processing with large monopulse energy is more obvious, but the laser energy distribution is not uniform due to the Gao Si beam. The thermal effect at the center of the spot is also more obvious. (3) the effects of output power and defocus on the crack healing of different metal materials have been studied by long pulse laser irradiation on the metal surface. The experimental results show that it is easier for the materials with low hardness to use the method of micro-melting to close the crack on the metal surface, and when the output power is selected properly, the quality of the metal surface can be improved by adjusting the amount of defocusing properly.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG665

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