-
激光与物质的相互作用主要是靠其热效应,激光切割CFRP过程中,由于材料对激光的透射率极低,激光与物质相互作用主要集中在材料表面,波长为1064nm的激光光源,其波长远小于模型尺寸,这里把激光光源等效为符合高斯分布的面热源[16]:
$ {q_0} = {\left( {\frac{{2P}}{{\pi {R^2}}}} \right)^{ - 2\left[ {{{\left( {\frac{{x - {x_0}}}{R}} \right)}^2} + {{\left( {\frac{{y - {r_0}t}}{R}} \right)}^2}} \right]}} $
(1) 式中, P为激光功率,R为光斑半径,x0为激光光斑横坐标, v0为激光光斑移动速度, t为时间。
激光作用在CFRP上能量扩散满足热传导方程:
$ \rho c\mathit{\boldsymbol{u}} \cdot \nabla T + \nabla \cdot \mathit{\boldsymbol{q}} = Q $
(2) $ \mathit{\boldsymbol{q}} = - \kappa \nabla T $
(3) 式中, ρ为材料密度,c为材料比热容,κ为热导率,u为当模型的各部分在材料框架中移动时由平移运动子节点定义的速度场,q为热流密度矢量,Q为热源, ▽是拉普拉斯算子,▽T表示温度在空间梯度的分布。
激光切割CFRP时满足初始条件为T0=293.15K,相应的边界条件为:
$ - \mathit{\boldsymbol{n}} \cdot \mathit{\boldsymbol{q}} = {q_0} $
(4) $ {q_0} = h\left( {{T_{{\rm{ext}}}} - T} \right) $
(5) (4) 式和(5)式分别为广义向内热通量与对流热通量,n为单位法向矢量,h为材料与外界对流传热系数,Text为外界温度。
由于激光切割碳纤维复合材料是一个很复杂的过程,其中设计的因素较多,为了能够顺利激光切割过程中的温度场分布,对激光切割碳纤维复合材料做了一些假设,比如不考虑材料与夹具之间的热传导,加工过程中不发生氧化反应,不产生内热源,不考虑材料吸收率变化,不考虑热辐射产生的能量损失。
激光切割碳纤维复合材料过程中,对于碳纤维复合材料这种非金属材料,内部没有大量的自由电子,材料内部传热主要靠晶格振动。热量的传递主要靠分子产生的振动波引起相邻分子振动,传播速率很慢,因此高分子材料热导率随温度变化范围较小,由于聚合物的拉伸取向,导致热导率具有各向异性,沿拉伸方向导热率较大,横向方向导热率较小[17]。对于激光波长为1064nm,工作方式为连续激光,CFRP的吸收率为0.8。CFRP的主要参量见表 1。
表 1 Parameters of CFRP material
parameter fiber resin density/(kg·m-3) 1760 1300 thermal conductivity/(W·m-1·K-1) 84(axial),
8.4(radial)0.2 specific heat capacity/(J·kg-1·K-1) 795 1200
激光切割碳纤维复合材料的温度场仿真
Temperature field simulation of laser cut carbon fiber reinforced plastics
-
摘要: 为了揭示激光切割碳纤维复合材料过程中温度场的分布规律、材料对能量的吸收和传递规律以及热影响区的形成机制,采用碳纤维复合材料为研究对象,建立激光切割碳纤维复合材料的多物理场模型,计算仿真了激光切割碳纤维复合材料过程中温度场分布及激光参量对碳纤维复合材料温度和热影响区影响规律,得到了激光切割碳纤维复合材料过程中的3维温度场分布。结果表明,激光切割过程中,碳纤维复合材料表面温度场近似为椭圆形,且碳纤维复合材料中能量的传递和扩散主要沿着碳纤维铺设方向;激光功率20W、光斑半径100μm、切割速率50mm/s的激光沿垂直于碳纤维铺设方向切割时,激光光斑作用处碳纤维温度远低于树脂层温度;随着切割光斑半径和激光功率的增加,碳纤维复合材料中最高温度逐渐增加,热影响区逐渐增大;随着切割速率的增加,碳纤维复合材料中最高温度逐渐减小,热影响区逐渐变小。该研究为了解激光切割碳纤维复合材料过程中的热损伤机理及材料高质高效的加工提供了一定的理论指导。Abstract: In order to reveal the distribution of temperature field, the absorption and transfer of energy, and the formation mechanism of heat affected zone during laser cutting carbon fiber reinforced plastics, the carbon fiber reinforced plastics was chosen as the research object, and the multiphysics model of laser cutting carbon fiber reinforced plastics was established. The temperature field distribution during laser cutting and the influence of laser parameters on carbon fiber reinforced plastics temperature and heat affected zone were calculated. The 3-D temperature field distribution during laser cutting carbon fiber reinforced plastics was then obtained. The results show that the surface temperature field of carbon fiber reinforced plastics is approximately elliptical during laser cutting.The energy transfer and diffusion in carbon fiber reinforced plastics are mainly along the direction of carbon fiber laying. When the laser power is 20W, the spot radius is 100μm, and the laser with a cutting speed of 50mm/s is cut perpendicular to the carbon fiber laying direction, the carbon fiber temperature at the laser spot is much lower than the temperature of the resin layer. With the increase of spot radius and laser power, the maximum temperature in carbon fiber reinforced plastics increases gradually, and the heat affected zone gradually increases. With the increase of cutting speed, the maximum temperature in carbon fiber reinforced plastics gradually decreases, and the heat affected zone gradually becomes smaller. This study provides theoretical guidance for understanding the thermal damage mechanism of laser cutting carbon fiber reinforced plastics and the high quality and efficient processing of materials.
-
表 1 Parameters of CFRP material
parameter fiber resin density/(kg·m-3) 1760 1300 thermal conductivity/(W·m-1·K-1) 84(axial),
8.4(radial)0.2 specific heat capacity/(J·kg-1·K-1) 795 1200 -
[1] TANG S, HU C. Design, preparation and properties of carbon fiber reinforced ultra-high temperature ceramic composites for aerospace applications:A review[J]. Journal of Materials Science & Technology, 2017, 33(2): 3-16. [2] TAN X H, SHAN J G, TANG L, et al. Study on laser surfi-sculpt of GMW2 autobody sheet steel for carbon fiber reinforced polymer/steel dissimilar joint[J]. Chinese Journal of Lasers, 2015, 42(3): 0303002(in Chinese). doi: 10.3788/CJL201542.0303002 [3] JIANG Y, CHEN G Y, ZHOU C, et al. Research of carbon fiber reinforced plastic cut by picosecond laser [J]. Laser Technology, 2017, 41(6): 821-825(in Chinese). [4] JIANG Sh Sh, CAI J X, JIN G Y, et al. Research of damage morphology of carbon fiber epoxy resin irradiated by millisecond/nanosecond pulsed laser[J]. Laser Technology, 2018, 42(6): 775-779(in Chinese). [5] JIA Z, SU Y, NIU B, et al. Deterioration of polycrystalline diamond tools in milling of carbon-fiber-reinforced plastic[J]. Journal of Composite Materials, 2016, 19(2):201-210. [6] WANG F J, CHENG D, ZHAO M, et al. Influence of cooling air direction on tool wear and hole quality in CFRP drilling[J]. Acta Materiae Compositae Sinica, 2019, 36(2): 410-417(in Chinese). [7] STAEHR R, BLUERNEL S, JAESCHKE P, et al. Laser cutting of composites—Two approaches toward an industrial establishment[J]. Journal of Laser Applications, 2016, 28(2): 192-203. [8] CHEN Y, GE E D, FU Y C, et al. Review and prospect of drilling technologies for carbon fiber reinforced polymer[J]. Acta Materiae Compositae Sinica, 2015, 32(2): 301-316(in Chinese). [9] SALAMA A, LI L, MATIVENGA P, et al. High-power picosecond laser drilling/machining of carbon fibre-reinforced polymer (CFRP) composites[J]. Applied Physics, 2016, A122(2): 73-81. [10] MUCHA P, BERGER P, WEBER R, et al. Calibrated heat flow model for the determination of different heat-affected zones in single-pass laser-cut CFRP using a CW CO2 laser[J]. Applied Physics, 2015, A118(4): 1509-1516. [11] NEGARESTANI R, SUNDAR M, SHEIKH M A, et al. Numerical simulation of laser machining of carbon-fibre-reinforced composites [J]. Journal of Engineering Manufacture, 2010, 224(7): 1017-1027. doi: 10.1243/09544054JEM1662 [12] OHKUBO T, TSUKAMOTO M, SATO Y. Numerical simulation of combustion effects during laser processing of carbon fiber reinforced plastics[J]. Applied Physics, 2016, A122(3): 196-203. [13] LI Z K, LU D, WANG Q, et al. Numerical simulation of the orthogonal cutting of carbon fiber reinforced composite material[J]. Advanced Materials Research, 2014, 29(9): 1246-1250. [14] YU D Y, WANG X Y. Temperature field simulation of single-layer carbon fiber reinforced plastics in multi-directional laser cutting[J]. Laser & Optoelectronics Progress, 2017, 54(11): 111409(in Chinese). [15] ZHANG Ch, YUAN G F, CONG Q D, et al.Analysis and prediction on laser cutting of CFRP[J]. Laser & Infrared, 2018, 48(7): 821-826(in Chinese). [16] LI H J. Temperature field analysis of single-layer HfO2 film induced by long-pulse laser[J]. Journal of Applied Optics, 2014, 35(5): 912-916(in Chinese). [17] YAN X D.Simulation analysis of movable laser etching of resin matrix composite[D]. Lanzhou: Lanzhou University of Technology, 2017: 12-62(in Chinese).