航空复合材料及其基体树脂的太赫兹光谱特性研究

Terahertz Time-Domain Spectroscopic Study of Aircraft Composite and Matrix Resins

现如今各类航空复合材料大量应用在航空飞机制造领域,而不同基体树脂的复合材料具有不同的性能优势,其物理性能关系到复合材料的设计、使用与检测。为研究不同种类的航空玻璃纤维复合材料及其基体树脂在太赫兹频段的光谱特性与介电性能,利用太赫兹时域光谱技术(THz-TDS)在0.2~1.0THz频段内研究了3类不同航空玻璃纤维复合材料及其基体树脂:环氧树脂3238A/玻璃纤维EW180A,氰酸酯树脂9915/玻璃纤维QW120A,双马来酰亚胺树脂QY8911/玻璃纤维ZW100A的光谱吸收和介电色散特性,计算得到了不同航空复合材料及其基体树脂的折射率n、吸收系数α、介电常数实部ε′和介电常数虚部ε″,并结合改性添加剂进行了基体树脂的对比分析,以及结合增强体玻璃纤维进行了复合材料的对比分析,在此基础上,使用Debye模型对树脂体系中偶极子的弛豫过程进行了理论计算,并对实验结果进行了拟合分析。研究表明,对于ε″和α,均以QW120A/9915<ZW100A/QY8911<EW180A/3238A和9915<QY8911<3238A的顺序增大,这是由于在树脂体系中含有的极性官能团和分子越多,偶极子取向极化引起的弛豫运动则会越剧烈,介电耗损就越大;随着交变电场频率的增加,偶极子因弛豫运动落后于电场的变化,需要更多的能量克服材料内粘滞阻力,引起介电耗损增大,导致ε″和α随之增大,并且均未有明显的吸收峰;由于树脂体系中分子链结构和极性基团的含量不同,对于各类复合材料和浇注料,氰酸酯树脂的ε′和n均最小,介电性能最好也最稳定,双马来酰亚胺树脂和环氧树脂介电性能次之,稳定性稍差,顺序为QW120A/9915>ZW100A/QY8911>EW180A/3238A和9915>QY8911>3238A;在聚合物树脂内部,偶极子的极化行为由于弛豫运动而受阻尼影响,滞后于交变电场的周期性变化,导致取向极化的程度相对减弱,ε′和n呈现反常的色散现象,即ε′和n随频率的增大而降低,而对于复合材料,玻璃纤维作为无机非金属材料弱化了聚合物树脂中极化行为的影响,均未出现反常色散现象;由于混合型树脂体系中不同极性的基团发生极化响应的机制不同,导致实际介电耗损高于拟合结果,而ε′和n并不受影响,因而在使用Debye方程进行拟合时,ε″和α的拟合结果稍有误差。首次报道了不同航空复合材料及其基体树脂在太赫兹频段的介电性能差异、光谱特性及其规律,给出了环氧、氰酸酯和双马来酰亚胺三种不同航空树脂及其玻璃纤维复合材料在太赫兹频段的基础参数,为太赫兹频段下固体电介质材料透波性能的研究补充了新的内容,为航空复合材料的太赫兹无损检测提供了重要参考,并且对航空复合材料性能改进、吸波复合材料、光电半导体材料、太赫兹超材料和高性能雷达罩等研究具有重要意义。

Nowadays,many kinds of advanced composite havebeen applied in manufacture of aircraft.And composites with different matrix resin have different performance superiorities,its physical properties influencethe design,employment and detection of composites.The purpose of this study was to investigate the spectral characteristics and dielectric properties of aircraft glass fiber composites and matrix resins in the terahertz(THz)frequency range.Terahertz time-domain spectroscopy was employed to examine the spectral absorption and dielectric dispersion characteristics of three major types,namely,epoxy resins 3238A/glass fiber EW180A,cyanate ester(CE)resin 9915/glass fiber QW120A,and bismaleimide(BMI)resins QY8911/glass fiber ZW100A,in the 0.2~1.0 THz frequency range.The refractive index n,the absorption coefficientαand the real partε′and imaginary partε″of the dielectric constant of each composite and resin were calculated.Additionally,the influence of added modifying groups in resins was analyzed and the property of composites with glass fiber was compared.On this basis,the relaxation process ofthe dipoles in each resin system was theoretically calculated and fitting analyzed using the Debye model.The results showed the following points.The sequenceofε″andαis QW120A/9915<ZW100A/QY8911<EW180A/3238A and 9915<QY8911<3238A.The reason is that,for a resin system,the more polar functionalgroups and molecules it has,the higher its polarity is,the more intense the relaxation motions caused by the orientation polarization of the dipoles,the greater the energy loss is.With the increasing frequency of the alternating electric field,the change of dipoles lags behind the change in the electric field,the relaxation also becomes more prominent,and more energy is required to overcome the viscous resistance inside the material.Consequently,the dielectric lossincreased,resulting in an increase inε″andα.In addition,no significant absorption peaks appeared for any of the composites and resins.Because of the difference in molecular chain structure and content of polar groups,the CE resin had the lowestε′and n,and exhibited the highest and moststable dielectric performance,followed by the BMI resins,whereas the epoxy resins exhibited fluctuating and slightly less stable dielectric performance.Andthe sequence ofε′and n is QW120A/9915>ZW100A/QY8911>EW180A/3238Aand 9915>QY8911>3238A.In polymers,due to their relaxation motions,the polarization behavior of the dipoles was affected by damping,resulting in a relativedecrease in the extent of orientation polarization.ε′and n eachexhibited an abnormal dispersion,i.e.,ε′and n decreased with increasing frequency.However,the influence of polarization behavior is weakened bythe glass fiber of composites,which don’t exhibit an abnormal dispersion.Dueto the difference in the mechanism of polarization response between groups differing in polarity in the mixed resin systems,the fitting of the data ofε′and n using the Debye equation had good results,whereas there was anerror between the fitted and measured values ofε″andα.This study reports,for the first time,the difference in dielectric properties between various types of composites and matrix resins,and their spectral characteristicsand patterns in the THz frequency range.Additionally,it gives the basic parameters of five aircraft glass fiber composites with epoxy,CE and BMI resins in the THz frequency range,adds new content to the research on solid dielectric materials in the THz frequency range,and provides an important reference for THz nondestructive testing of aeronautical composites and improving the performance of aeronautical composites and matrix resins as well as technologies currently inrapid development,such as THz and wave-absorbing materials,opto-semiconductors and high-performance radomes.