Theoretical modeling and experimental study on nanosecond laser machining of Kevlar fiber reinforced plastics
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摘要: 纳秒激光加工在纤维增强树脂基复合材料的加工中应用广泛,但在对温度较敏感的Kevlar纤维增强树脂基复合材料(KFRP)的激光加工中,极易产生不可控的热损伤。针对KFRP的纳秒激光切割,分析激光加工过程中的温度演变过程,根据激光加工烧蚀阈值理论,分析KFRP的烧蚀阈值及烧蚀机制,并基于热传导中的能量守恒定律、质量守恒及动量守恒,分别建立Kevlar纤维和树脂基体热影响区的损伤预测模型。结果表明,KFRP激光加工热影响区存在显著差异,可以通过切削温度变化规律明显区分激光加工不同损伤区域;Kevlar纤维的烧蚀阈值为0.01 J·cm−2,环氧树脂基体的烧蚀阈值为0.005 J·cm−2;切缝宽度、切缝深度、炭化区宽度的理论预测模型与实验结果基本吻合,激光加工工艺参数对热影响区影响显著,其中,激光功率对切缝宽度的影响最大,扫描速度对切缝深度、炭化区宽度的影响最显著,但脉冲宽度和重复频率对热影响区影响较小。
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关键词:
- Kevlar纤维增强树脂复合材料(KFRP) /
- 纳秒激光切削 /
- 烧蚀阈值 /
- 热影响区 /
- 切削温度
Abstract: Nanosecond laser processing is widely used in the processing of fiber-reinforced composites, but it is easy to produce uncontrollable thermal damage in the laser processing of Kevlar fiber reinforced plastics (KFRP), owing to its poor high temperature resistance. During the nanosecond laser cutting of KFRP, the temperature evolution process was analyzed. According to the ablation threshold theory of laser processing, the ablation threshold and the ablation mechanism were analyzed. Based on the conservation law of energy in heat conduction, the conservation of mass and the conservation of momentum, the damage prediction models of the Kevlar fiber and the resin matrix in the heat-affected zone were established, respectively. The results show that there are significant differences in the heat-affected zone of KFRP laser machining, and the different damage zones can be distinguished by the change law of cutting temperature. The ablation threshold of the Kevlar fiber and that of the epoxy resin matrix are 0.01 J·cm−2 and 0.005 J·cm−2, respectively. The theoretical model of the kerf width, the kerf depth and the carbonization zone width is consistent with the experimental result. The heat-affected zone is significantly affected by the laser processing process parameters. Among them, the kerf width is most significantly affected by the laser power, the kerf depth and the width of the carbonization zone are most significantly affected by the scanning speed. But, the heat-affected zone is little affected by the pulse width and the repetition frequency. -
表 1 Kevlar纤维增强树脂基复合材料(KFRP)的特征参数[10, 26]
Table 1. Performance parameters of Kevlar fiber reinforced plastics (KFRP)[10, 26]
Performance parameter Value Density of Kevlar fiber ρ1/(g·mm−3) 1.44×10−6 Density of epoxy matrix ρ2/(g·mm−3) 1.20×10−6 Specific heat capacity of Kevlar fiber
C1/(J·kg−1·℃−1)1398.46 Specific heat capacity of epoxy resin
C2/(J·kg−1·℃−1)1884.00 Environment temperature T0/℃ 25 Melting temperature of epoxy resin Tm/℃ 90 Vaporizer temperature of epoxy resin T2/℃ 425 Carbonization temperature of Kevlar fiber T1/℃ 427 Thermal conductivity of Kevlar fiber
K1/(W·mm−1·℃−1)1.57×10−3 Thermal conductivity of epoxy resin
K2/(W·mm−1·℃−1)2.00×10−4 Energy absorption rate A 0.6 Transition latent heat of epoxy resin Qv2/(J·kg−1) 1×106 Coefficient of overheating in melting ημ 0.01 Density of assisted gas ρg/(kg·m−3) 2.786 Molecular diameter of assisted gas σ/mm 3.75×10−7 Pressure of assisted gas Pg/Pa 2.98×105 Pressure drop coefficient F 0.5 表 2 激光加工工艺参数
Table 2. Laser machining process parameters
Number P/W V/(mm·s−1) f/kHz τ/ns 1 10 3 200 20 2 20 3 200 20 3 30 3 200 20 4 40 3 200 20 5 50 3 200 20 6 30 1 200 20 7 30 2 200 20 8 30 3 200 20 9 30 4 200 20 10 30 5 200 20 11 30 3 350 20 12 30 3 500 20 13 30 3 650 20 14 30 3 200 30 15 30 3 200 60 16 30 3 200 120 Notes: P—Laser power; V—Scanning speed; f—Repetition frequency; τ—Pulse width. -
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