【作者】 陈敏孙；

【导师】 刘泽金； 江厚满；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2012， 博士

【摘要】 切向气流作用下，连续波激光对纤维增强树脂基复合材料的辐照效应研究目前还不够深入。本文对该问题开展实验、理论和数值模拟研究，将空气气流、氮气气流和无气流状态下的辐照效应进行比较，以分析空气气流的作用。主要开展了以下几个方面的工作：1.建立了连续波激光辐照下树脂基复合材料热响应的三维模型。针对激光光斑相对于样品厚度比较大的情形，提出了热分解气体一维流动假设，从而在不引入力学量的前提下，在三维热响应模型中考虑了热分解气体的流动。给出了有表面切向气流、有热分解气体流出边界以及边界上固体材料可能发生相变烧蚀或氧化烧蚀情况下的边界条件，在氧化烧蚀模型中基于稳态扩散图像，描述了热分解气体流出导致的边界层对O2的屏蔽作用。对模型中相关参数的计算方法进行了推导，并对玻璃纤维增强E-51环氧树脂复合材料进行了热分析，确定了该材料的热分解动力学参数和E-51固化体的热分解热。2.利用改进的光滑粒子流体动力学方法实现了三维热响应模型的求解。利用FORTRAN语言编制了程序，设计了两个算例，对程序功能进行了考证。为提高计算效率，缩短程序的运行时间，在MPI并行编程环境下成功地实现了串行编码的并行化。3.开展了表面有切向空气气流、氮气气流和无气流时，连续波激光对碳纤维增强树脂基复合材料样品和玻璃纤维增强树脂基复合材料样品辐照效应的实验研究。综合对损伤形貌、质量损失、烧蚀率、温度曲线、光电探测器电压信号和辐照后样品反射率的分析，对入射功率密度在100~600W/cm2范围内、气流速度在0.1~0.8Ma范围内、976nm激光辐照下两种样品的热响应形成如下结论：当样品发生剧烈热分解时，随热分解气体流出边界的固体颗粒对入射激光有屏蔽作用。切向气流一方面可以减弱这种屏蔽作用，有利于辐照区的烧蚀；另一方面对样品有冷却作用，不利于烧蚀。相比于氮气流，空气流有助于产物的燃烧，对下游附近区域产生明显的加热作用。三种气流状态下，两种样品的质量损失均随入射激光功率密度单调增加。在入射激光功率密度相等、吹空气流时，两种样品的质量损失均随气流速度的增大先增加后减小。三种气流状态下，碳纤维样品的烧蚀率随功率密度逐渐下降；玻璃纤维样品的烧蚀率则随功率密度逐渐上升趋于饱和。4.对三种气流状态下两种样品在连续波激光辐照下的热响应进行了数值模拟。根据样品热分析获得的几个特征温度，描述了表面反射率和吸收系数的变化，描述了无气流时热分解气体带出的固体颗粒对入射激光的屏蔽系数的变化；将喷出的热分解产物对下游附近区域的加热作用等效为对下游区域气流静温的提高。对碳纤维样品，将不同辐照条件下三个热电偶测点位置处温度历史的数值模拟结果同实验结果进行了比较，考察了质量损失随气流速度和激光功率密度的变化趋势，并同实验结果进行了比较。对玻璃纤维样品，计算了不同辐照条件下的平台持续时间和峰值时刻，考察了这两个时间随激光功率密度的变化，并同实验结果进行了比较。总体而言，上述各量的数值模拟结果与实验结果是符合的，表明本文建立的树脂基复合材料在激光辐照下的三维热响应模型是合理的，相关物性参数取值的合理性也得到了初步验证。更多还原

【Abstract】 In the presence of a tangential gas flow, researches on continuous-wave laserirradiance effects on fiber reinforced resin composite are not in-depth enough. In thispaper, experimental, theoretical and simulated studies on this problem are performed.The influence of airflow on laser irradiance effects are analyzed by comparing the laserirradiance effects on fiber reinforced resin composite subjected to tangential airflow,tangential nitrogen gas flow and no gas flow. The contents of this dissertation are givenas follows:1. A three-dimensional thermal response model of resin composite materialssubjected to combined laser and tangential airflow loading is derived. The motion ofpyrolysis gas is assumed to be one-dimensional, for the case that the laser spot issignificantly larger than the thickness of the sample. According to the above assumption,the flow of pyrolysis gas can be considered at the three-dimensional model withoutintroducing any mechanical quantities. The effects of the tangential gas flow, theoutflow of pyrolysis gas and the ablation（including phase change ablation or oxidationablation）of the surface material are included in the surface boundary conditions. Theinfluence of the degassing on the diffusion of the oxygen to the target surface is studied,basing on the steady state diffusion model in the oxidation ablation model. Formulas forcomputing the parameters included in the thermal response model are derived. Thethermogravimetric analysis (TGA) of the glass fiber reinforced E-51resin composite isconducted. The thermal decomposition kinetics parameters of this material and thethermal decomposition heat of E-51resin are determined.2. The three-dimensional thermal response model is calculated numerically byuse of the modified smooth particle hydrodynamics (MSPH) method which is codedwith FORTRAN. The function of this program is validated by two cases. In order toimprove the computation efficiency and shorten the run time of the program, theparallelization of the serial number coding is achieved successfully with the MessagePassing Interface (MPI).3. The irradiation effects of continuous-wave laser on carbon fiber reinforcedresin composite and glass fiber reinforced resin composite are studied experimentally,with tangential airflow and tangential nitrogen gas flow and no gas flow on the targetsurface, respectively. Based on the analysis of the damage morphology, mass loss,ablation rate, temperature history, voltage of photoelectric detector and index ofreflection, the thermal response of two kinds of targets irradiated by laser with awavelength of976nm and a power density in the range of100~600W/cm2, and with agas flow whose velocity is in the range of0.1~0.8Ma can be concluded as follows:when the pyrolysis happens severely, the solid particles, which are flowing out of the interface with the pyrolysis gas, will shield the incident laser. The tangential gas flow,on one hand, can weaken the shield effect of the solid particles outflow the interface,which is helpful to the ablation in the irradiated area. On the other hand, the tangentialgas flow can cool the target, which is adverse to the ablation. Comparing with thenitrogen gas flow, air flow is of advantage to the combustion of the production, whichcan heat the downstream area obviously. Under three different gas flow statuses, themass lose of the two targets increases with the increasing incident power density. Withair flow and a constant incident power density, the mass lose of the two targets increasesfirst and then decreases with the increasing velocity of gas flow. Under three differentgas flow statuses, the ablation rate of carbon fiber target decreases with the increasingincident power density, but the ablation rate of glass fiber target increases up to asaturation value with the increasing incident power density.4. The thermal responses of two targets irradiated by continuous-wave laser in thepresence of three gas flow statuses are simulated numerically. According to thecharacteristic temperatures obtained by the thermogravimetric analysis of targets, thevariations of the reflectance and the absorbtance of targets are described. The variationsof the shielding coefficients of the solid particles carried by pyrolysis gas without gasflow are also described. The heating effect of the pyrolysis products on the downstreamarea is equivalent to the increasing of the static temperature. For carbon fiber targets, thenumerical results of the temperature history at three measuring points measured bythermal couples under different irradiation conditions are compared with experimentalresults. The variation trend of the mass loss with the velocity of gas and laser irradianceis investigated, and then compared with the experimental results. For glass fiber targets,the plateau durations and the peak times in different irradiation conditions are computed,and also compared with the corresponding experimental results. Generally speaking, thecoincidence of the numerical results with the experiments results validates thethree-dimensional thermal response model of resin composite materials irradiated bylaser and the values of the corresponding parameters of properties of matter are checkedto be chosenappropriately.更多还原