内埋FBG传感器复合材料加筋板的固化过程及准静态压缩监测

将布拉格光纤光栅(fiber Bragg grating,FBG)传感器埋植在纤维增强树脂基复合材料加筋板结构的三角填充区,在线监测复合材料T型加筋板的固化过程与准静态压缩过程.结果表明,埋植FBG传感器的加筋板和未埋值FBG传感器的加筋板,其压缩破坏载荷基本相当.同时,内埋于复合材料加筋板三角填充区的FBG传感器可以有效监测复合材料加筋板固化过程的应变变化,固化后亦可用于实时监测结构中产生的温度和应变变化.在准静态压缩过程中,FBG传感器测得的应变值变化曲线与接触力-压头位移曲线变化趋势基本一致.FBG传感器可在不影响结构性能前提下,准确地响应复合材料加筋板在受载条件下出现的分层、开裂等损伤.     

基于FBG传感技术的复合材料T型加筋板低速冲击损伤监测

针对碳纤维增强树脂复合材料低速冲击损伤的实时监测,设计将布拉格光纤光栅（FBG）传感器埋植在复合材料T型加筋板结构的三角填充区,在线监测复合材料T型加筋板冲击损伤过程。分别将FBG传感器埋植于复合材料层合板内部和复合材料T型加筋板的三角填充区,对比FBG传感器的埋入对复合材料层合板和复合材料T型加筋板力学性能的影响。结果表明,内埋FBG传感器的复合材料层合板试样的拉伸强度比未埋植传感器的层合板试样降低了约5%,但在FBG传感器的破坏应变范围内,FBG传感器可以准确、实时地监测复合材料的应变信号。将FBG传感器埋入复合材料T型加筋板的三角填充区,内埋FBG传感器的T型加筋板样件压缩破坏载荷与未埋植的样件基本一致。通过对比T型加筋板蒙皮上冲击位置、冲击能量对FBG传感器测得的冲击过程持续时间和最大应变值的影响,表明冲击过程持续时间随着冲击能量增大而延长,最大应变值随着冲击距离的增加呈下降趋势,而最大应变值随着冲击能量的增大呈上升趋势。利用FBG传感器测得的应变信号可初步实现对复合材料T型加筋板蒙皮冲击损伤位置及冲击能量的实时监测。      

内埋光纤光栅的复合材料层压板拉伸应变研究

利用内埋在复合材料层间的光纤光栅(Fiber Bragg Grating,FBG)传感器监测复合材料层压板在拉伸过程中的应变变化,并与复合材料层压板试样表面粘贴的应变片测得数据进行对比,同时研究了光纤光栅的埋植位置对复合材料力学性能的影响。探索了FBG传感器在复合材料应变监测中的有效性和可靠性。结果表明:内埋于复合材料层间的FBG传感器可以有效反映复合材料层压板在受到拉伸载荷过程中的应变变化,对比FBG传感器与应变片测得的实验结果,二者所测得的应变变化趋势吻合良好,而且埋植光纤光栅对复合材料层压板的拉伸强度影响较小。     

光纤布拉格光栅监测CF3052/5224复合材料成型过程研究

温度与应变是监测复合材料热压罐固化成型工艺两个最重要的表征参数,利用光纤布拉格光栅传感原理,采用毛细钢管封装的方法,制备了完全屏蔽应变信号的温度传感器,将温度传感器和应变传感器同时埋植在复合材料内部,实现了对热压罐成型全过程的实时监测,获得了复合材料成型过程中的内部温度和应变信息.对复合材料平板件和T型加筋板三角填充区域进行的温度监测结果表明,复合材料内部温度变化较罐内温度有一定滞后,传统成型工艺控制给出的加压点偏早,可能引起复合材料贫胶等缺陷.应变监测结果表明,平板件内部的应变变化主要反应树脂固化过程中的物理化学变化,在T型加筋板三角填充区域,应变监测在自然冷却阶段出现了不同于平板件的应变"回弹"现象,一定程度上反映出该区域在成型过程中容易出现缺陷的原因.     

光纤Bragg光栅应变传感器在霍普金森压杆上的冲击试验研究

利用复合材料封装光纤Bragg光栅(FBG)设计制作了用于测量高速碰撞或爆炸与冲击作用下混凝土内部动态应变的FBG应变传感器。在霍普金森压杆上对FBG在封装前的裸光栅和封装后的FBG传感器分别进行了高速冲击试验,试验表明：设计的FBG传感器的瞬态响应上升时间小于20μs,具有良好的动态响应特性,可以用于工程中混凝土结构内高速冲击下的动态应变测试     

复合材料基片式光纤光栅传感器的制造与性能

基于光纤光栅传感原理,设计、制造了一种玻璃纤维/环氧树脂复合材料基片式光纤Bragg光栅(FBG)传感器。该传感器采用玻璃纤维/环氧树脂复合材料层合板作为基板,干态玻璃纤维布作为覆盖层,采用真空辅助灌注液态环氧树脂的方法将FBG封装于底部基板与上层玻璃纤维布之间。在制备玻璃纤维/环氧树脂复合材料基板的过程中,分别采用一次性完全固化和预固化的制备工艺。通过对比实验结果发现:当玻璃纤维/环氧树脂复合材料基板采用一次性完全固化成型工艺时,传感器温度响应的线性度和重复性较差,相对重复性误差高达10.90%,线性拟合度仅为0.99871;当玻璃纤维/环氧树脂复合材料基板在光纤光栅封装之前采用预固化成型工艺、在封装完成后整体进行二次固化时,传感器温度响应的相对重复性误差仅为1.87%,线性拟合度为0.99998,应变灵敏度系数为0.05514nm/kg,温度灵敏度系数为0.02357nm/℃,是裸光纤光栅传感器温度灵敏度系数的2.4倍。     

纤维复合材料层合板内埋光纤光栅传感器的保护技术

内埋的光纤Bragg光栅（FBG）传感器的存活率及测试精度是其在线监测纤维增强树脂基复合材料制备和服役状态的重要前提。采用[90₁₁/0₁₁]的碳纤维预浸料铺层方式,在层合板0°和45°方向的典型位置埋入FBG温度和应变传感器,采用模压成型工艺制备复合材料层合板。在异向铺排（光纤光栅方向与碳纤维方向不同）的45°方向光纤光栅传感器内埋于碳纤维预浸料层间的过程中,对其采用4种不同的保护方式。通过对比实验结果发现:当对异向铺排的FBG传感器不采取保护措施时,在加热加压复合材料时光纤光栅容易失活;整层铺设同向预浸料以保护异向铺排的FBG传感器的方式改变了具有特定铺层参数复合材料的力学性能;采用窄长条同向预浸料上下包埋保护FBG传感器的方式增大了应变光栅测量结果的系统误差;采用窄长条同向预浸料上下包埋并在邻近铺层开凹槽的保护方式能明显提高内埋光纤光栅的存活率及测试精度。      

带有铝板复合材料层板固化过程中残余应力演化

本文对两种材料组成的层板的残余应力进行了研究.提出应用有效温差并结合线膨胀系数对带有铝板复合材料层板固化成型过程中残余应力形成进行理论分析,其中残余应力主要考虑温度产生的.采用先进的光纤技术对带有铝板复合材料层板固化成型过程中残余应力进行试验研究,即将光纤布拉格光栅(FBG)分别埋入到复合材料内部及复合材料与铝板之间,监测固化全过程残余应变的演变,并且构件最终变形与理论分析释放残余应力方向一致.     

光纤光栅监测缠绕复合材料与铝板界面的固化应变

树脂基复合材料经常与金属材料固化在一起使用。用缠绕方法制备了复合材料单向板, 将光纤布拉格光栅(FBG) 埋入复合材料与铝板之间, 监测两种不同的材料在固化过程中界面的性质, 并与复合材料内部的监测结果相比较。监测结果表明, 光纤布拉格光栅准确地监测到了复合材料固化过程的温度历程, 复合材料内部、铝板和复合材料的界面在固化过程中和固化后应变存在着明显的差异。光纤光栅传感器为两种不同材料之间的固化监测提供了工具, 对界面性质的分析提供了新方法。      

光纤布拉格光栅监测复合材料固化

复合材料层合板在固化成型过程中形成的残余应变和应力是影响材料质量的重要因素,它与预浸料铺层在固化工艺过程中产生的应变密切相关。在研究和测试了光纤布拉格光栅应变和温度传感器传感特性的基础上,将二者埋入复合材料预浸料铺层,在热压釜成型工艺过程中监测了材料内部的温度和应变发展历程,由此获得对称正交层合板的宏观残余应变。监测结果表明,单向和对称正交层合板在固化结束后都将产生收缩,对称正交层合板铺层内的残余应变平行于纤维方向为压应变,垂直于纤维方向为拉应变。光纤光栅传感器为复合材料固化监测及层合板残余应力分析提供了一种新的工具,为实现复合材料从制造到服役的全寿命、一体化监测提供了可能。      

布拉格光栅监测不同厚度方向的固化残余应力

复合材料在固化过程中产生的残余应力会严重影响材料的使用和安全。首先在研究和测试了布拉格光栅温度和应力灵敏度的基础上,将3根光栅分别以平行于碳纤维的方向置入预浸料的上、中、下3个位置,以此获得复合材料不同厚度位置的残余应力变化情况。监测结果表明,上、下层光栅监测到的预浸料固化过程几乎完全一致,而在降温时下层的布拉格光栅残余应力则比上层的要大得多,中间层布拉格光栅在固化过程中测得的残余应力最小,但在降温过程中的热残余应力不易释放而导致最后的残余应力也较大。     

Study on the curing process for carbon/epoxy composites to reduce thermal residual stress

In this work, a cure monitoring system using dielectrometry and a fiber Bragg grating (FBG) sensor, was devised to measure the dissipation factor and thermal residual stress of carbon fiber-reinforced epoxy composite materials. Three rapid-cooling points, which were based on the cure initiation point, were chosen as test variables to investigate the effect of cure cycle on process-induced internal strain. The internal strains generated in the composite specimens were measured using embedded FBG sensors. Three-point bending tests were conducted to investigate the effect of thermal residual stress on the flexural strength of the composite specimens.     

基于内埋光纤Bragg光栅传感器的复合材料固化过程监测

为了全面了解复合材料的固化特性,在对碳纤维增强树脂基复合材料固化变形进行数值仿真分析的基础上,将自行设计的光纤Bragg光栅（FBG）传感器埋入复合材料中,实时在线监测复合材料固化过程中温度和应变的演变。预浸料铺层方式为[0₁₁/90₁₁],分别在层合板0°和45°方向的典型位置埋入FBG温度和应变传感器,采用热模压方式固化成型复合材料层合板,并对成型后的层合板进行连续2次降温处理,实时记录固化过程中FBG传感器中心波长的变化。结果表明:在相同的温度条件下,复合材料在第1次降温初始阶段的压应变绝对值明显小于在第2次降温初始阶段的压应变绝对值,表明复合材料在第1次降温过程中仍在进行FBG传感器可检的“后固化”反应;此外,层合板变形的FBG传感器监测数据与有限元模拟结果吻合良好。因此,采用内埋FBG传感器的方法能够实时监测复合材料固化过程,为更全面地分析复合材料固化特性提供了一种可靠有效的方法。      

Monitoring mode II fracture behaviour of composite laminates using embedded fiber-optic sensors

Utilization of embedded Fiber Bragg Grating (FBG) sensors for monitoring mode II fracture behaviour of composite laminate beams containing different delaminations along the thickness-wise direction, by virtue of End-Notch Flexure (ENF) tests, is presented. Non-uniform strain distribution due to the stress concentration at the delamination tip was examined by the way of observing the reflection spectrum from the FBG sensor. The stress concentration in ENF specimens, which are subjected to various applied loads, was analyzed in terms of the shift, shape, bandwidth and intensity of the reflection spectrum. Relationships between the load–displacement graphs and the corresponding reflection spectra under ENF tests were established. In addition, the feasibility and reliability of using the embedded FBG sensors for mode II fracture behaviour monitoring in the composite laminates is discussed.     

In situ monitoring of the strain evolution and curing reaction of composite laminates to reduce the thermal residual stress using FBG sensor and dielectrometry

Generally, a large, thermal residual stress is generated during the curing process for composite laminates due to differences in the coefficients of thermal expansion of the respective layers. The thermal residual stress during fabrication greatly decreases the fatigue life and dimensional accuracy of the composite structures. In the present study, through a fiber bragg grating (FBG) sensor and dielectrometry in an autoclave, the strain evolution and curing reaction in composite laminates with a stacking sequence of [0₅/90₅]_S were monitored simultaneously during a conventional cure cycle and a modified cure cycle to reduce the thermal residual stress. From the study, it was verified that about 50% of the thermal residual stress during fabrication could be reduced in a composite laminate by adjusting the cure cycle; this improved the static strength and fatigue life by 16% and up to 614%, respectively, for a peak ratio of 0.9.     

Chirped fiber-Bragg grating as self-temperature referenced strain sensor in nonisothermal thermoset processing

A partially embedded chirped fiber-Bragg grating (FBG) has been used to monitor the strain build up during nonisothermal curing of a model thermoset resin. The particular feature of the spectrum of a linearly chirped and strongly apodized FBG to encode position along the sensor has been used to simultaneously measure temperature and strain during the cure cycle of an epoxy-based polymer. In particular, the embedded part of the grating allows the monitoring of temperature and processing strain while the rest of the sensor is sensible to temperature variation only. A new self-temperature referenced sensor system has been successfully tested in an operative condition where usually thermomechanical loading are simultaneously active. The onset and progression of gelification, as well as the residual processing strain, have been experimentally measured.     

Monitoring LCM Process by FBG Sensor Under Birefringence

Abstract: Optical fibre Bragg gratings (FBG) provide accurate and non‐intrusive strain and temperature local measurements. FBG sensors can be embedded into fibrous preforms to monitor the flow and the cure of the resin and deliver real‐time information on the ongoing process. The paper concentrates on the utilisation of the strain‐induced birefringence of the FBG to derive information on the effective stress–strain state of the composite at the end of the process cycle (Vacher 2004, Optical fiber sensors to monitor the processing and the mechanical characterization of composites. PhD thesis). During the cooling phase, the reflection spectrum from the FBG splits into two peaks because of the birefringence of the glass fibre owing to the residual stress. The paper shows that this effect can be utilised to estimate the residual stress and strain in composites manufactured by Liquid Composite Moulding technologies. The birefringence effect arising from the cooling of a [0₆,90₃]_S CFRP laminate is first characterised, and then the determination of the strains along the principal axes inside the laminate is completed by modelling the local stress–strain state because of the interaction of the optical fibre and its environment within the framework of orthotropic thermo‐elasticity and the Classical Laminated Plate Theory.     

基于长信号谱自相关的光纤光栅传感解调方法

针对光纤光栅传感领域波长高精度探测和传感复用光栅数量增多的需要,提出一种基于长信号相关谱的新型光纤光栅数字解调技术.该技术在可调谐滤波法的基础上,通过传感光栅与调制光栅反射谱卷积后的信号,即光电探测器的光强时间信号,进行自相关分析以实现对波长漂移的测量以及对传感光栅反射谱形状的识别,增强系统的复用能力,提高了性价比.模拟仿真表明,光纤光栅长信号相关数字解调方法可以准确测量光纤光栅波长的漂移,能更好实现传感复用.等强度悬臂梁实验验证该解调方法能实现光栅应变的高精度测量,优于传统的应变片测试.