Research On The Laser Irradiation Effects On Fiber Reinforced Resin Composites Subjected To Tangential Gas Flow

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.