【作者】 孙九霄；

【导师】 王继辉；

【作者基本信息】 武汉理工大学 ， 材料学， 2011， 博士

【摘要】 复合材料具有优异的比强度、比刚度、抗疲劳性能和耐久性,已广泛用于飞机的承力结构中。然而,由于厚度方向没有增强体,复合材料对损伤非常敏感。高效的无损检测技术对于复合材料结构损伤检查和持续监测有着重要意义。将光纤光栅传感器(FBG:Fiber Bragg Grating)内置于复合材料结构中,可以实现复合材料结构的实时健康监测,同时具有成本低、不受电磁干扰、能监测结构内部变化等特点,是复合材料结构无损检测技术的重要发展趋势。研究FBG传感器埋入复合材料结构中,对于大飞机的结构健康监测具有非常重要的意义。本文分别对采用手糊成型、真空灌注成型(VIMP:Vaccum infusion molding process)、RTM (Resin transfer molding)成型、热压罐成型等几种不同的复合材料成型工艺时的光纤引出及保护方式进行了研究。利用自制光纤定位装置及模具活块解决了RTM成型工艺非分型面光纤引出问题,研究了系统正压和负压光纤引出时的模具密封问题。针对热压罐成型工艺研究了端面引出和表面引出两种引出方式,解决了光纤引出保护问题。采用光学显微镜及扫描电镜对埋入光纤后的复合材料截面进行观察,分别对埋入光纤后的玻璃纤维/乙烯基酯树脂复合材料、碳纤维/环氧树脂复合材料静态力学性能进行了测试。发现埋入光纤对复合材料拉伸、弯曲性能影响不大,对压缩性能有一定影响。成功地将FBG传感器埋入通过不同成型方式成型的玻璃纤维/乙烯基酯树脂和碳纤维/环氧树脂两种复合材料中。对埋入FBG传感器后的碳纤维/环氧树脂复合材料进行拉伸性能和弯曲性能测试,结果显示FBG传感器可以准确反映材料内部应变的变化趋势。利用埋入FBG传感器对乙烯基酯树脂浇注成型、复合材料VIMP成型、热压罐成型等成型工艺进行了监测。根据乙烯基酯树脂的固化监测结果,确定了乙烯基酯树脂固化时凝胶点及放热峰出现的时间,与拉丝法测定的凝胶时间基本一致。对埋入玻璃纤维/乙烯基酯树脂复合材料的FBG传感器进行了温度灵敏系数和应变灵敏系数的标定,通过监测复合材料VIMP成型时FBG波长及光强的变化,确定了玻璃纤维/乙烯基酯树脂复合材料的凝胶点,并排除温度的影响,得出复合材料固化过程中内部的应变变化历程。将FBG埋入碳纤维/环氧树脂复合材料飞机扰流板缩比件,在高温VIMP工艺下成型,得到了升温、注胶、保温过程中的波长漂移曲线,对成型后的部件进行加载,结果显示存活的FBG可以灵敏的反映复合材料的应力变化。将FBG传感器和热电偶埋入碳纤维/环氧树脂复合材料,采用热压罐工艺成型,得到了整个固化过程的波长漂移曲线,并消除了温度对FBG信号的影响,得到了整个固化过程中复合材料内部应变的变化历程。采用准静态压缩的方法代替低速落锤冲击,并使用FBG传感器进行信号监测,验证了FBG传感器铺设角度、距离冲击点的位置对FBG信号的影响,提出了一种埋入光纤传感器监测复合材料冲击信号的FBG传感器网络布置方法。根据监测信号推导出相同距离不同角度、相同角度不同距离时的波长漂移公式,并对公式进行了验证和修改,为后续研究奠定了理论基础。分别将FBG传感器埋入到玻璃纤维和碳纤维复合材料中,利用自制落锤试验机进行了低速冲击试验,采用低频和高频光纤光栅解调仪对信号进行了监测,结果显示高频光纤光栅解调仪可以有效的监测到冲击信号,低频光纤光栅解调仪监测数据偶然性过大,只能作为参考。对不同能量、相同能量不同距离、相同能量不同层间、累计冲击时埋入复合材料内的FBG信号进行了监测,对冲击发生时的波长变化、冲击前后的波长变化、冲击振动信号进行了研究。采用超声C扫描设备对碳纤维复合材料的分层状况进行了检测。试验结果显示,光纤FBG传感器可以有效的监测复合材料冲击信号,根据信号的变化可以推测出冲击造成的复合材料内部损伤类型及损伤面积大小。最后分别采用ANSYS和LS-DYNA有限元软件对复合材料准静态压缩和低速冲击过程进行了数值模拟。将模拟结果与光纤FBG传感器监测试验结果对比,材料内部应变场的分布及变化趋势与试验结果基本一致。更多还原

【Abstract】 The composite material has excellent specific strength and specific stiffness, fatigue resistance and durability, has been widely used in load-bearing structure of aircrafts. However, along the thickness direction, there is no reinforcement existed in composite materials, which are very sensitive to injury. Efficient nondestructive testing technology is very important for composite structure damage inspection and continuous monitoring. The optical fiber grating sensor (FBGs) is embedded into the composite material structure, can achieve real-time health monitoring of composite structure, FBGs shows the advantages of low cost, no electromagnetic interference and monitor the internal structure, which is an important trend of a composite structure nondestructive testing technology.The study of FBG sensor embedded in the composite material structures is very important for health monitoring in aircraft structures.Several different composite molding technologies such as hand lay-up, vacuum infusion molding (VIMP), RTM (Resin transfer molding) molding, autoclave molding were used to study the output and protection of optical fiber in this paper.The problem of fiber extraction in the non-parting surface of RTM molding was solved by using optical fiber positioning device and mold loose piece, mold sealing problems was also studied during this system was under positive and negative pressure respectively.In view of autoclave moulding technology, we studied two kinds of eduction mode,end extraction and surface enduction, solved the problem of fiber protection.on After optical fibers were embedded in composites, the cross-section were observed through optical microscope and scanning electron microscope, static mechanics performance of vinyl/glass fiber, epoxy/carbon fiber composite materials were tested respectively which were both embedded by optical fibers.We found that a single optical fiber was embedded in the two composite, their static mechanical properties hadn’t been effected a lot. FBG sensor was successfully embedded in this two composite materials -glass fiber/vinyl and carbon fiber/epoxy resin.After FBG sensor was embedded in carbon fiber/epoxy composite material, tensile and bending properties were tested, results showed that the FBG sensor could accurately reflect the changing trend of material internal stress.The use of embedded FBG sensors for vinyl resin curing, composite materials VIMP curing, autoclave curing, molding process was monitored. According to vinyl resin cure monitoring results, the gel point when the vinyl resin curing and when the exothermic peak occurs were determined, and basically corresponding to the results of Roberts Law. The calibration for temperature sensitivity and strain sensitivity coefficient of vinyl resin/glass fiber composite materials with FBG sensor embedded in, by monitoring FBG wavelength and light intensity changes during molding composite materials VIMP, the gel point of the material was determinded, and the influence of temperature was excluded, composite curing process changes within the course of the strain was achieved as well. FBG was embedded in the carbon fiber/epoxy composite aircraft spoiler subscale pieces, under the VIMP molding process at high temperatures, wavelength drift curve in the process of heating up, plastic injection, heat could be obtained, applied the load after forming the parts, the results showed that the survival response of the FBG can be sensitive to stress changes of the composite. FBG sensors and thermocouples were embedded in the carbon fiber/epoxy composites, using autoclave molding process, the wavelength shift curve of the curing process was obtained, the effects of temperature on the FBG signal was edcluded, and the material changes in the course of the internal strain during the whole curing process were obtained.Low-speed compression drop hammer impact was replaced by Quasi-static compression methods, and using FBG sensors monitoring signal, it was verified that the laying of fiber angle, the distance from the impact point on the FBG signals, presented a buried fiber optic sensors to monitor the impact of the FBG sensor network signal layout. According to the monitoring signal is derived from the different angles in the same distance, the same point in different angels from the wavelength shift, verified and modified the formula to establish a theoretical basis for the follow-up study.The FBG sensor is embedded in the glass fiber and carbon fiber composite materials, using the self-made drop test machine for the low speed impact test, using a low frequency and high frequency fiber Bragg grating demodulation instrument for signals were monitored, the results showed that the impact signal could be effectively monitored by a high frequency fiber Bragg grating demodulation instrument,while monitoring datas were great chance by a low frequency fiber Bragg grating demodulation instrument, for reference only. We monitored composite material within the FBG signals of different energy, the same energy of different distance, the same energy between different layers during cumulative impact, wavelength changes and the signal of the vibration during the impact, tchange of the wavelength before and after the impact was studied. Carbon fibre composite material stratification status was detected by ultrasonic C scanning device. The test results showed that the composite material impact signal could be monitored effectively through the FBG optical fiber sensor, internal damage types and damage area of composite which caused by the impact could also be conjectured according to the signal.Finally, composites under quasi-static compression and low-velocity impact process were simulated through ANSYS and LS-DYNA finite element software. The simulation results were compared with the FBG optical fiber sensor monitoring test results, the material of the inner strain variation and the test results were essentially consistent.更多还原