亚音速切向气流下连续激光对玻璃纤维增强树脂基复合材料的穿孔效应

Perforation Effect of Continuous Laser on Glass Fiber Reinforced Polymer Matrix Composites Under Subsonic Tangential Airflow

采用波长为1070 nm的连续激光对亚音速切向空气流下玻璃纤维增强树脂基复合材料(GFRP)的穿孔效应进行了研究。通过实验研究了功率密度(848~1556 W/cm^(2))和切向气流流速(0~1个马赫数)对穿孔形貌、穿孔点温度和穿孔时间的影响。结果表明:切向气流流速为0.5个马赫数(Ma)时靶材穿孔时间随功率密度的增加而减小,最大减小了46%;功率密度为848 W/cm^(2)时穿孔时间随气流流速的增加呈先减小后增加的规律,与无气流(0 Ma)时相比,最大仅减小8%。激光功率密度的增加加速了热解气体的产生,使得孔隙压力升高,促进了靶材的剥蚀。切向空气流对作用过程的影响主要包括:降低树脂基体热解所产生的残炭含量,进而改变靶材吸收方式;产生切向剪切力,加速靶材的力学剥蚀;加速对流换热,降低靶材表面温度。当切向气流速度较小(≤0.4 Ma)时,切向气流的作用主要是促进树脂热解,降低残炭含量,转变靶材吸收方式;当切向空气流速较大(0.8~1.0 Ma)时,气流的冷却作用表现得较为明显。

Objective Glass fiber reinforced polymer(GFRP)with excellent wave-transparent properties are the preferred choice for optoelectronic devices and microwave dielectric materials owing to their high strength,light weight,and excellent electrical properties.Traditional cutting techniques for processing GFRP have problems such as severe tool wear,low efficiency,and low accuracy.The application of laser processing can solve these problems and has broader application prospects.However,some problems remain in the processing of reduced materials by a single laser beam,such as the shielding of the subsequent laser by the pyrolysis gas,transformation of the target absorption mode due to incomplete pyrolysis of the residual carbon,and irregularity of the ablation morphology.The laser processing assisted by tangential air flow can solve these problems and improve the efficiency of material processing.In this study,a detailed investigation on the target perforation time,ablation morphology,and temperature distribution on the ablation surface under different power densities and tangential air flow was carried out.These results are helpful for improving the processing efficiency and profile of GFRP.Methods A fiber laser(wavelength of 1070 nm)with a maximum output power of 20 kW was used to interact with the GFRP in a relatively confined metal target chamber.Tangential air flow was provided by an air compressor and flowed out through a nozzle,and the air flow rate was measured using the Pitot tube method.A manometer was used to measure the pressure of the tangential air flow output from the nozzle;therefore,the stability of the air flow was monitored.The range of air flow rate used in the experiment was0-1.0 Ma.The temperature evolution from the front and rear surfaces of the target was recorded using an infrared thermometer imager.The temperature data of the perforation point was extracted to draw a temperature change curve with time,and the perforation time was obtained from the falling edge of the temperature curve.Results and Discussions The perforation effects of GFRP are investigated at different laser power densities(848-1556 W/cm^(2))and tangential air flow velocities(0-1.0 Ma).It is found that the effect of increasing the laser power density on the ablation rate of GFRP is more significant than that of varying the tangential air flow rate(Figs.4 and 8).With an increase in the tangential air flow rate,the perforation time shows a decreasing trend and then a slow increase(Fig.8).This behavior is related to three effects caused by the tangential air flow:reducing the surface residual carbon content to promote the bulk absorption of the target(Fig.5),enhancing the heat convection on the target surface to accelerate the cooling(Fig.7),and providing tangential shear force to produce a mechanical erosion effect.Conclusions The perforation effect of GFRP at different laser power densities(848-1556 W/cm^(2))and tangential air flow rates(0-1.0 Ma)is investigated using a continuous laser with a wavelength of 1070 nm.The experimental results show that the perforation time decreases with increasing power density.A large amount of pyrolysis gas is generated in a shorter time period at higher power densities,which further results in a higher pore pressure and promotes the exfoliation process of the target.The effects of tangential air flow on the GFRP perforation process include reducing the surface residual carbon content to promote the bulk absorption process of the target,enhancing the cooling effect on the target surface,and providing a tangential shear force to produce a mechanical erosion effect.The three effects caused by tangential air flow have an obvious competitive relationship in the perforation process of the target.For the laser power density of 848 W/cm^(2),when the tangential air flow rate is≤0.4 Ma,the effect of tangential air flow is mainly used to promote resin pyrolysis,reduce the residual carbon content,and change the target absorption mode.Hence,the target perforation time decreases with an increase in the air flow rate.When the tangential air flow rate is in the range of 0.8-1.0 Ma,the cooling effect is more obvious.Therefore,the perforation time of the target material increases slowly with an increase in the air flow rate.In addition,compared with the tangential air flow rate,the effect of the power density on the perforation time of the GFRP is more significant.