内埋光纤光栅碳纤维增强复合材料层压板力学性能及拉伸应变监测

将不同数量的光纤光栅埋植于复合材料层压板层间部位,研究了光纤光栅的埋植数量对层压板拉伸和压缩性能的影响及光纤光栅埋入对层压板层间结构的影响。此外,利用埋植在层压板内部的光纤光栅监测了层压板在拉伸过程中的应变变化,并与应变片监测结果进行了对比。试验结果表明,当在复合材料层压板中沿纤维方向埋入光纤光栅时,复合材料0°拉伸强度和模量略有降低。而当光纤光栅垂直于纤维方向埋入复合材料内部时,复合材料的90°拉伸强度和模量略有提高。对于压缩性能而言,由于光纤光栅在压缩过程中发生脆断,在复合材料内部产生损伤源,导致复合材料压缩强度有所降低,但当光纤光栅埋植数量较小时,对压缩模量的影响较小。层间形貌的显微观察结果表明,光纤光栅沿纤维方向埋入复合材料内部,在光纤光栅周围未形成树脂富集区,反之则将出现明显的富树脂区。     

Bragg光栅传感器在复合材料加工与检测中的应用

本文介绍了Bragg光栅传感器的结构和工作原理。将Bragg光栅传感器埋入增强体内,通过VARTM成型制作了复合材料。利用SM130光纤光栅解调器,通过收集光的波长的变化来对复合材料的加工工艺进行了在线监测;对埋入光纤光栅传感器的复合材料进行了拉伸试验,通过波长的变化来计算材料在拉伸过程中的受力变化,并与常规的拉伸试验进行了对比,两者所测得的力是基本一样的,所以证明了通过光纤光栅传感器可以进行复合材料的健康监测,并且可疑对大型复合材料的加工、使用实施在线监控。     

重力效应对VARTM工艺中树脂充模过程的影响

采用真空辅助树脂传递模塑(VARTM)工艺制备了环氧树脂/亚麻纤维复合材料层合板,记录了树脂在不同树脂流动倾角下的充模时间。通过对层合板进行拉伸、弯曲性能测试,研究了树脂流动倾角对复合材料层合板力学性能的影响。结果表明,在VARTM工艺过程中重力效应对树脂充模时间和层合板力学性能有显著影响;充模时间随着树脂流动倾角的增大(从–90°至90°)而增加;复合材料层合板的拉伸强度、拉伸弹性模量、弯曲强度、弯曲弹性模量等均随树脂流动倾角的增大而增大,树脂流动倾角对弯曲强度的影响最大,且对强度的影响高于模量。由于树脂流动倾角影响了树脂与亚麻纤维的结合情况,导致树脂流动倾角为–90°和90°的复合材料层合板在拉伸与弯曲失效时拥有不同的失效形式。     

模压成型过程中的复合材料在模腔内的力学分析

树脂基复合材料在模压成型过程中,在压力作用下,形成可压缩流动.由于每种物料的性质不同,在压缩流动时的取向、相互之间的摩擦系数不同,再加上因受模具几何形状的限制,物料与模具壁之间摩擦阻力不同,导致物料在模具内各方向的流动速度和各轴向应力不同.分析和掌握模压成型过程中树脂基复合材料的应力变化规律,可正确指导树脂基复合材料的生产.     

光纤光栅在先进复合材料固化成型研究中的应用

先进树脂基复合材料被广泛应用于航空航天领域。热压罐成型工艺是复合材料结构件首选成型工艺之一,但存在效率低、成本高等问题,并且在成型过程中产生的固化应变会影响制件成型质量,通过光纤光栅传感器在线监测应变/应力参数对于制定合理工艺规程、提高制件品质具有重要作用。本文详细介绍了热压罐成型中光纤光栅传感器应变和温度交叉敏感解决方案,综述了近年来基于光纤光栅传感器在线监测的复合材料固化成型研究进展。并结合国内外研究现状,对光纤光栅在线监测的应用前景及亟待解决的问题提出了几点思考。     

复合材料层合板工程常数的光纤光栅测试与分析

复合材料工程常数的精确测试是合理有效开展复合材料结构力学分析与评估的基础。采用埋入式光纤光栅测试技术对复合材料结构应变特征进行测量,可有效获取复合材料的工程常数,如弹性模量、泊松比等。本文将光纤光栅与引伸计、应变片的单向应变测试结果进行了对比,得出不同测试方法下弹性模量的结果,验证了光纤光栅测试方法的可靠性和有效性。进一步通过在复合材料试件内部分别铺设横向及纵向的光纤光栅,对复合材料试件的泊松比进行了测试,并与应变片的测试结果进行了对比。试验结果表明,光纤光栅相对于应变片测试灵敏度更高,测得的泊松比数值更为稳定。     

模具构件相互作用对复合材料固化应变的影响分析

复合材料热压罐固化工艺中,构件的脱模变形是影响成型质量的重要原因。通过热电偶和光纤光栅传感器相结合的方法对复合材料构件在热压罐成型工艺过程中的温度和应变进行了在线监测,研究了模具构件的相互作用导致的应变发展,并分析了树脂固化对模具构件相互作用的影响。结果表明:固化过程初期,应变主要来自构件压实和树脂的流动、凝胶,而后模具构件的相互作用会随树脂固化度的增大而增大,模具与构件之间转变为粘接状态,降温时模具构件的相互作用会使二者发生分离导致构件发生应力释放,并且应力释放会使模具构件的相互作用减弱。     

土木工程自监测纤维复合材料

纤维复合材料(FRP)具有轻质、高强、耐腐蚀、抗疲劳及良好的自传感特性等优点.将FRP与光纤光栅传感技术相结合,即在FRP材料加工过程中埋入光纤光栅传感元件(OFBG)可制成新型自监测复合材料(OFBG-FRP).OFBG-FRP兼有FRP优良的物理力学性能及光纤光栅的智能传感特性.本文主要介绍FRP及OFBG-FRP的传感特性及其在土木工程健康监测中的应用等方面的研究进展.     

PS／OMMT复合材料制备及流动性研究

将聚苯乙烯(PS)树脂与有机蒙脱土(OMMT)进行熔融共混制备PS纳米复合材料.通过X射线衍射仪对复合材料的微观结构进行了分析,采用HAAKE流变仪和熔体流动速率仪研究了复合材料的熔体流动行为.结果表明:将PS与OMMT熔融共混可得到插层的纳米复合材料,OMMT用量较少时,该复合材料具有良好的熔融流动性能,随着OMMT用量增加,复合材料的塑化时间逐渐延长,流动性逐渐下降.熔融复合过程中聚苯乙烯降解.     

基于材料物性参数时变特性的复合材料层合板固化残余应变应力数值模拟

热固性树脂基复合材料层合板成型过程形成的残余应力是影响材料质量的重要因素。针对复合材料固化过程建立了基于复合材料物性参数时变特性的复合材料固化过程的三维多场耦合计算模型。该模型包含经典的热-化学模型、树脂固化动力学模型、残余应力模型;在此基础上将材料物性参数时变特性引入多场耦合计算模型中,模型计算结果通过与文献中实验结果比较,验证所建立的固化模型的可靠性;在此基础上,对AS4/3501-6复合材料层合板的固化残余应变应力进行数值模拟,研究了固化过程中残余应变/应力的变化规律,分析工艺参数对应力应变的影响。通过与光纤光栅应变试验比较,验证其正确性。研究结果表明:模型可以很好地仿真复合材料固化过程;温度、树脂体积分数、铺层角度对层合板应力/应变都有较为显著的影响,为正相关关系,其中树脂的体积分数影响最为显著。     

Influence of alcohol pre‐infusion on the quality of VARTM composites

In the vacuum assisted resin transfer molding (VARTM) process, part‐to‐part variations such as the uncertainty in the permeability and race tracking phenomenon make it difficult to achieve consistent mold filling and ensure part quality of composites. Alcohol pre‐infusion was presented in this study as a novel real‐time monitoring and control approach for the flow process in the VARTM process, alcohol test fluid is infused before the actual resin infusion to locate the potential dry spots without using the large quantity of sensors. Then corresponding process control strategy is designed, such as opening the auxiliary gate at specific moment on those predicted dry spot locations to compensate flow defects. Moreover, alcohol can be easily removed by heat without changing the local permeability. The influence of alcohol pre‐infusion on the quality of VARTM composites were investigated in this study. The mechanical tests were conducted to verify that the alcohol pre‐infusion approach has no significant effect on composite properties because alcohol can be removed from fiber by heat and air flow. Specifically, DMA, TGA, and FTIR spectrum proved that negligible difference existed on the resin–fiber interface between the composites with or without alcohol pre‐infusion. Finally, the microscopy results revealed a similar failure path in a resin matrix. TMA results also demonstrated similar dimension stability. This alcohol pre‐infusion approach was effective when compared with computer simulation and could eliminate the occurrence of dry spots and voids without using sensors or data‐acquisition system. The control schemes were shown in a case study to be capable of compensating the flow defects and achieving desired fill patterns in the face of permeability uncertainty. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

VARTM工艺用乙烯基酯树脂基体配方及性能研究

以溴化改性乙烯基酯树脂、氨基甲酸酯改性乙烯基酯树脂为混合基体,以E-玻璃纤维(GF)为增强材料,通过真空辅助树脂传递模塑(VARTM)工艺制备乙烯基酯树脂/GF复合材料,对其力学性能和阻燃性能进行了研究.结果表明,在两种树脂质量比为1:1时该复合材料的拉伸强度与弯曲强度达到最大值,且综合性能最优.氧指数随溴化改性乙烯基...     

Effect of advancement on epoxy prepreg processing—a dielectric analysis

With the relatively recent trend toward adaptive process control during processing of structural composites, there is need for an understanding of the nature of variations during cure that are encountered. Part-to-part variations can arise because of differences in thermal exposure arising from part placement or part thickness, or from chemical differences due to formulation or advancement. Microdielectric sensors are particularly well suited for monitoring thermoset cures from initial point of flow, through the liquid region, and on into the solid state. In this study, microdielectric sensors are used to systematically study the influence of resin advancement on cure behavior. Relationships between advancement and critical cure phenomena such as flow temperature, point of viscosity minimum, and reaction end point are discussed.     

基于FBG传感器的CF/GF混杂复合材料界面变形研究

利用FBG传感器对采用真空导入模塑工艺制作的CF/GF(Carbon Fiber/Glass Fiber)混杂复合材料在固化成型过程中以及成型后的界面性能进行了检测,此外,为了对比研究混杂复合材料的性能,还检测了CF/CF层和GF/GF层在成型和成型后的应变变化。结果显示:GF/GF、GF/CF和CF/CF复合材料的应变与温度之间存在良好的线性关系,且热膨胀系数的大小顺序为GF/GF层GF/CF层CF/CF层;FBG传感器监测CF/GF混杂复合材料热膨胀系数的转折温度与基体树脂的T_g值(79.09℃)相吻合;CF/GF混杂复合材料在20~120℃范围内升温、降温过程中未发生界面破坏。     

非织造工艺对天然纤维增强体树脂流动性能的影响

纤维增强体的树脂流动性能是影响树脂传递模塑工艺设计及其复合材料质量的一个重要因素。本文利用单向法测试真空辅助传递模塑工艺中非织造工艺对亚麻纤维增强体对树脂流动性能的影响。结果表明,相同压力条件下,由平行铺网工艺制作的纤维增强体比交叉铺网工艺增强体树脂渗透率低,流动各项异性大;随着层数的增加及压力的增大,两种铺网工艺增强体的树脂渗透率降低,压力的变化对流动各向异性影响不大。     

复合材料K/T型接头真空辅助成型工艺树脂流动研究

城市的现代化进程促进了大跨度结构的应用,用于结构间的连接接头需要具有良好的力学、耐疲劳和耐腐蚀性能。先进复合材料以优异的性能成为理想的接头材料,但高昂的制造成本限制了其应用。对基于真空辅助成型(VARTM)工艺制造K/T型接头时的树脂流动过程进行了研究,通过考察四种可能树脂注模方式所需注模时间及流动前锋的信息确定合理的工艺方式;并将模拟结果与相应试验结果对比分析,两者表现出良好的一致性。采用复合材料接头一体化制造模具制造出K/T型接头,并组装了典型复合材料桁架结构。试验结果表明,模拟所得注模方式可实现复合材料K/T型接头的低成本工艺制造,避免了由传统试错法确定注模方式带来的高成本。     

Assessment of thermoset cure‐induced strains by fiber bragg grating sensor

Composites based on thermosetting resin and reinforcement fibers present generally unwanted residual internal stresses inherent to their elaboration process. In this article, different curing experiments of thermosets (isothermal and anisothermal) were monitored using optical fiber Bragg grating (FBG) sensors and thermocouples, to assess the cure‐induced strains. A thermokinetic model evaluates the degree of conversion of the resin. At the onset of stress transfer to the optical fiber, the degree of conversion ranges between 0.63 and 0.68. During curing, the FBG deforms under chemical shrinkage with an amplitude widely lower than the expected chemical strain, showing that the FBG signal is not directly related to the actual chemical shrinkage. However, once the resin is cured, the FBG sensor provides directly the coefficient of thermal expansion of the resin, as function of temperature and degree of conversion, reached in the different experiments. POLYM. ENG. SCI., 54:1585–1594, 2014. © 2013 Society of Plastics Engineers     

Use of a simple,inexpensive pressure sensor to measure hydrostatic resin pressure during processing of composite laminates

A simple and cheap method of measuring the resin pressure within a composite laminate during processing is presented. The method consists of using a small diameter, long needle filled with inert fluid and connected to an external pressure sensor, to measure the resin pressure at a point inside a composite laminate. This method can be used to investigate resin flow, laminate compaction, the control of voids, and in several composite material processing methods such as autoclave processing, hot press curing and resin transfer molding. The sensors are suitable for research and development or troubleshooting, but not for production. Sensor assemblies were developed and tested to show that their response is reproducible, linear and stable with temperature and time. Resin pressure profiles for two AS4/3501-6 laminates were generated and compared. The experimental results were also compared to the resin flow simulation of a general processing model for composites, COMPRO. It is shown that the resin profile in the laminate is influenced by the presence of the bleeder cloth and the vacuum bag pressure. A significant pressure drop corresponded to the point of minimum viscosity of the resin. Finally, the resin pressure was stabilized when the resin reached gelation.     

Strain Profile Measurement for Structural Health Monitoring of Woven Carbon-fiber Reinforced Polymer Composite Bonded joints by Fiber Optic Sensing Using an Optical Backscatter Reflectometer

In order to monitor crack initiation and propagation under static and fatigue loading in adhesively bonded joints, strain profile measurement such as backface strain (BFS) is a very efficient technique. In single lap (SL) joints, crack initiation and propagation in the glue line can be monitored by detecting the negative peak of the strain profile. Therefore, the accuracy of the monitoring system greatly depends on detecting the strain profile correctly and accurately. Previously, an array of electrical strain gages as well as fiber Bragg grating (FBG) sensors had been used successfully to capture the profile of BFS of a SL joint by applying sensors on the backface of an adherend, near the overlap zone. In this work, the backface technique is improved by replacing an array of strain sensors by an ordinary optical fiber (without FBG sensors) connected to an optical backscatter reflectometer. The great advantage of this system over the more conventional arrays of FBG is that the entire length of the fiber can be used for sensing strains, and hence it provides a better spatial resolution. The experimental results are compared with finite element analyses, which were further validated by two-dimensional digital image correlation measurements.