平纹编织碳纤维增强树脂复合材料离散电导率建模方法

编织碳纤维增强树脂复合材料(CFRP)的电阻抗分布具有各向异性、异质性、几何结构复杂等特点。建立电阻抗分布模型是利用电磁涡流无损检测技术获取编织CFRP缺陷及疲劳损伤信息的关键关节。基于电阻抗张量建模理论,采用多层编织结构CFRP二维平面的分块均化电学特性表征方法,建立编织结构CFRP的简化电阻抗分布模型,从而实现编织结构CFRP电磁特性的精确、快速有限元分析。在有限元仿真基础上,通过设计双空气旋转线圈电磁传感器对平纹编织CFRP进行电磁无损检测,选用阻抗的极坐标图描述被测材料沿不同方向的阻抗变化趋势,通过实验验证有限元建模的正确性。最后利用所提出的建模方法模拟了双空气旋转线圈传感器对平纹编织CFRP的结构缺陷及循环载荷疲劳的检测效果。      

基于激光热激励红外热成像纤维增强聚合物复合材料加固混凝土结构界面损伤无损检测

红外热成像（IRT）检测技术常被用于纤维增强聚合物复合材料（FRP）加固混凝土板的剥离损伤无损检测。但传统热源激励IRT法受加热距离短、热灵敏度低、功耗大等因素影响较大。本文提出了基于光学激发线激光热源的IRT法对FRP加固混凝土的剥离检测方法,该方法通过控制线热束在FRP加固混凝土结构的表面形成移动扫描热激励,通过红外热像仪测量结构中的界面剥离引起的表面局部热分布异常。基于模拟和实验研究结果,证明该方法对FRP加固混凝土结构中界面剥离检测具有如下优势:利用激光扫描热成像技术检测FRP改造混凝土结构中剥离损伤的可行性;实现了FRP加固混凝土结构的远距离、高热灵敏度及低功耗的损伤检测。      

含孔CFRP正交层合板的双轴拉伸力学行为

采用加载臂开槽的中心开孔等厚度十字形试样,实验研究了正交对称铺层碳纤维增强聚合物基复合材料（CFRP）层合板在双轴拉伸载荷作用下的力学行为,分析了3种双轴加载比对其拉伸强度和破坏行为的影响。研究表明:纤维被切断的铺层部分在拉伸作用下容易与其相邻铺层脱粘,导致层合板承载力下降;等双轴加载时,在孔边的被切断纤维与连续纤维间基体在横向拉伸和纵向剪切组合作用下首先开裂;非等双轴加载时,在垂直于快速拉伸方向的铺层中沿孔边应力集中处先出现基体裂纹;随着加载比的增大,快速拉伸方向的细观结构损伤随载荷的增大发展更快,刚度下降更快,破坏时主裂纹的扩展方向更趋于垂直于快速拉伸方向;强度包络线的分析表明快速拉伸方向的拉伸强度随加载比的增大呈缓慢增大的趋势。      

面向CFRP损伤检测的改进L1正则化EIT方法

由于碳纤维复合材料(carbon fiber reinforced polymer, CFRP)具有导电特性,因此可利用电阻抗层析成像(electrical impedance tomography, EIT)技术实现结构损伤检测。考虑EIT电极位置、数量有限以及电场软场特性的影响,其灵敏度矩阵呈现非均匀分布特征,导致场域内不同位置成像效果差别较大。该研究基于传统L1正则化的边缘锐化特性,提出了一种改进L1正则化方法。该方法通过分析损伤重建电导率分布规律,发现其在各邻域梯度分布的特征,并利用此特征保留L1正则化可能滤除的有效数据,在保证重建图像锐利边缘的同时,改善了不均匀灵敏度分布导致的区域成像精度差别。为验证所提出方法的有效性,仿真中设计了不同类型、不同相对位置的损伤模型,并且通过搭建的16电极EIT测试系统对损伤CFRP样品进行测试。仿真和试验结果表明,改进后的L1正则化方法不仅能重建更多位置上的损伤图像,而且不同程度地提高了各类损伤重建图像的精度。     

碳纤维增强环氧树脂复合材料层合板结构及间隙尺寸对铆接性能的影响

通过对不同纺织结构的碳纤维增强树脂基复合材料（CFRP）层合板与铝合金（AlMg3）异质材料连接结构进行单剪切拉伸研究,分析间隙尺寸对不同纺织结构CFRP层合板与AlMg3连接结构性能的影响。试验结果表明,当CFRP层合板铺层数目相同时,对于纺织结构不同、间隙配合尺寸相同的CFRP-AlMg3单铆钉单剪切连接结构,编织结构碳纤维增强树脂基复合材料（WO-CFRP）层合板所受挤压应力比非编织结构碳纤维增强复合材料（UD-CFRP）层合板所受挤压应力大25%左右;对于纺织结构相同、间隙配合尺寸不同的CFRP-AlMg3单铆钉单剪切连接结构,其各自铆钉所受剪切应力和连接CFRP层合板所受挤压应力相差不大。同时对相同间隙尺寸、不同纺织结构的CFRP-AlMg3单铆钉单剪切连接结构各个阶段挤压应力分析得知：其他条件一定,各个阶段中WO-CFRP的挤压应力比UD-CFRP的挤压应力高20%左右。最后研究间隙尺寸对CFRP-AlMg3单铆钉单剪切连接结构性能的影响,发现铆钉与孔壁间隙尺寸对位移为铆钉直径大小的4%时的CFRP层合板受到的挤压应力影响较大,铆钉与孔壁间隙大小增加0.1 mm,位移为铆钉直径大小的4%时的CFRP层合板受到的挤压应力降低约17%,而对CFRP层合板的初始损伤应力和破坏应力几乎没有影响,对铆钉所受剪切作用力和AlMg3板材所受挤压应力也几乎没有影响。     

基于矩形脉冲涡流传感器的表面缺陷定量评估及成像检测技术研究

本文介绍利用矩形脉冲涡流传感器的自差分特性来提高缺陷检测能力,并最终实现对表面缺陷的成像检测.采用ANSYS软件建立了矩形脉冲涡流传感器的仿真模型,对铝板表面涡流分布进行了仿真分析,结果表明:矩形传感器能够在铝板表面激励出均匀的感应涡流,当有缺陷存在时,提取Z向和Y向感应信号的幅值扫描曲线可以实现对表面缺陷长度和深度的定量.并对仿真结果进行了实验验证,得到了表面缺陷的成像结果.研究结果表明,该矩形脉冲涡流传感器可以很好的实现对表面缺陷的定量评估及成像检测.     

多层结构缺陷检测中的脉冲涡流磁场测量技术

脉冲涡流技术是一种可以对飞机多层结构中缺陷实施有效检测的方法。交变磁场测量技术是一种精确测量表面裂纹的非接触式无损检测方法。提出了脉冲涡流磁场测量（PECFM）技术,并对其进行了理论分析。在设计了相应传感器的基础上,对多层铝板结构中的缺陷进行了检测实验,实验结果与理论分析相一致。实验证明PECFM技术可以有效地实现多层结构中缺陷的识别与定量检测。可以预见,PECFM技术将会在无损检测领域中发挥很大的作用。     

搭接长度和铺层方式对CFRP复合材料层合板胶接结构连接性能和损伤行为的影响

针对不同搭接长度和铺层方式的碳纤维增强树脂（CFRP）复合材料层合板单搭胶接结构进行了拉伸试验,观察了试件的受力过程和失效形态,获得了载荷-位移曲线;同时基于连续损伤力学模型和三维Hashin失效准则模拟了CFRP复合材料层合板的层内损伤形成和演化,并利用内聚力模型来模拟层间及胶层的失效损伤,对CFRP复合材料层合板单搭胶接结构在拉伸作用下的失效强度和损伤机制进行了预测,通过对比验证了该数值方法的有效性;通过数值试验比较不同搭接长度和铺层方式的单搭胶接结构及双搭胶接结构的连接强度和损伤行为,并提出了一种优化的CFRP复合材料层合板胶接结构。结果表明:CFRP复合材料层合板胶接结构的极限失效载荷随着搭接长度的增大逐渐增加并趋于稳定值,且结构的失效形式逐渐从胶层自身剪切失效过渡到邻近胶层的层合板层间分层失效;CFRP复合材料层合板胶接结构的连接强度和损伤行为随着铺层方式的不同而改变,通过对3种铺层方式的对比和分析,得到性能最好的铺层方式是[0₃/90₃]_2S;在搭接长度为5~20 mm时,通过对搭接长度进行优化,得到单搭胶接结构的最优搭接长度是17 mm,双搭胶接结构的最优搭接长度是19.3 mm,与搭接长度为20 mm相比,单搭胶接结构和双搭胶接结构的连接强度分别提高了13.26%和0.43%。      

纤维缠绕玻璃钢管道的渗漏判据

本文通过对无矩层合板细观应变的有限元分析,求得层合板的最大应变集中系数。利用细观力学分析结果,建立了无矩层合板的树脂开裂宏观力学判据。利用该判据建立了管道的渗漏判据。并分析了纤维含量、温差、管径对渗漏压力的影响情况。      

碳纤维增强银粉改性树脂复合材料的雷击损伤效应

针对碳纤维增强树脂(CFRP)复合材料中树脂电阻大,在雷电流作用下会产生大量焦耳热造成雷击损伤的短板,探索通过增强基体的导电性来解决这一问题。为实现对CFRP复合材料的改性,在其环氧树脂浆料中加入了以Ag粉为主的导电填料,使改性CFRP复合材料层合板沿厚度方向的电导率提高217.30倍。采用不同峰值的单一雷电流D分量分别对改性及未改性CFRP复合材料层合板试件进行雷击损伤实验,通过损伤区域超声C扫描图像、试件残余温度场和仿真热解损伤的对比,分析基体改性对CFRP复合材料雷击损伤的防护机制。结果表明:通过Ag粉改性能有效提高CFRP复合材料层合板的电导率,且在厚度方向上的改性效果最佳;在峰值电流分别为20 kA、40 kA和60 kA的条件下,改性CFRP复合材料层合板的损伤面积分别下降87.28%、77.82%和88.59%,损伤深度分别增加147.06%、130.65%和119.72%;以损伤体积为最终指标,则Ag粉改性基体能有效降低CFRP复合材料的雷击损伤,其防护机制是通过减少雷电流作用下的高温区域面积和升温幅度来降低热解和爆炸冲击实现。      

Detection of in-plane fiber waviness in cross-ply CFRP laminates using layer selectable eddy current method

This paper presents an eddy current testing method to detect in-plane fiber waviness in cross-ply carbon fiber reinforced plastic (CFRP) laminates. We propose a method which has high sensitivity to presence of in-plane waviness and can select layers to be inspected. The probe was used to detect artificially induced in-plane waviness in cross-ply CFRP laminates. It was observed that obtained signal has extreme value at the edges and vertex of the waviness, which implies the possibility of precise identification of waviness location. Detectability of subsurface waviness was investigated using 20 layer cross-ply laminate with in-plane waviness at different depths. Experimental results showed that in-plane waviness 18 layers away from the surface could be detected. The minimum misalignment angle of the detected waviness was 7.4°. The effectiveness of the probe and physical background of the obtained signals were verified by finite element method analyses.     

Feasibility on fiber orientation detection of unidirectional CFRP composite laminates using one-sided pitch–catch ultrasonic technique

It is important to assess fiber orientation, material properties and part defect because strength and stiffness of composites depend on fiber orientation of CFRP (carbon fiber reinforced plastics). A one-sided pitch–catch setup was used in the detection and evaluation of ultrasonic wave behavior and fiber orientation in the unidirectional CFRP composite laminates. Two Rayleigh wave transducers were joined head-to-head and used in the pitch–catch mode on the surface of the composites. The pitch–catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composite. Especially, one-sided ultrasonic measurement was made with using a Rayleigh wave transducers and the Rayleigh ultrasonic waves were extensively characterized in the CFRP composite laminates. Also, a conventional scanner was used in an immersion tank for extracting fiber orientation information in the unidirectional laminate. Therefore, it is thought that the proposed method is useful to evaluate integrity of CFRP laminates.     

Novel test method for accurate characterization of intralaminar fracture toughness in CFRP laminates

A novel initial crack insertion method, “intralaminar film insertion method”, was proposed to investigate the fracture toughness of unidirectional carbon fiber reinforced plastic (CFRP) laminates when the crack propagates inside the ply and not in the interlayer resin-rich area. Here, a release film was inserted inside a single lamina during the resin impregnation process of prepreg manufacturing. Mode I intralaminar fracture toughness tests were carried out for conventional CFRP laminates and interlayer toughened CFRP laminates. For comparison, two conventional methods were used to introduce initial cracks. One is the “interlaminar film method”, where a release film is inserted between two prepreg plies during the lay-up process. The other is the “machined slit method”, where a slit notch is machined in parallel to the layer of CFRP laminates. It was demonstrated that the proposed “intralaminar film method” can correctly evaluate the intralaminar fracture toughness of both conventional CFRP laminate and interlayer toughened CFRP laminate from the initial value to the propagation value. For this range, it was also found that the intralaminar fracture toughness of interlayer toughened CFRP laminate was the same as that of conventional CFRP laminate. Thus, the intralaminar fracture toughness was not influenced by interlayer toughening.     

碳纤维/环氧树脂复合材料-铝合金层合板深拉成型特性

碳纤维增强树脂复合材料（Carbon fiber reinforced plastic,CFRP）因其轻质高强的特点,越来越多地应用到汽车轻量化设计和制造中。为研究CFRP板件及CFRP-Al层合板深拉成型影响因素,加速CFRP零部件产业化进程,本文通过DSC测试分析了CFRP预浸料的固化放热过程,以此为依据,用热压罐制备了不同后固化温度下成型的CFRP板材及单向、编织两种预浸带铺层的CFRP-Al层合板,用Inspekt table 100材料试验机对上述两种板材分别做了深拉试验。考虑到提高制备效率,用打磨、打磨+涂覆硅烷偶联剂、阳极氧化+涂覆硅烷偶联剂三种方式对铝合金板进行表面处理,不经热压罐固化成型,直接和正交对称铺层的单向预浸带一起在Inspekt table 100材料试验机的环境箱中混合温深拉,固化成形。并通过金相显微镜、SEM进行显微组织观察,验证后固化温度、深拉环境温度、预浸带的种类对CFRP板材及CFRP-Al层合板深拉成型性能的影响及铝合金板表面处理方式对CFRP叠层预浸带、铝合金板材混合温深拉成型性能的影响。结果表明,适当降低后固化温度、提高深拉环境温度有利于板材二次深拉成型。编织预浸带较单向预浸带能更好地承受压力,深拉成型质量更优。阳极氧化+涂覆硅烷偶联剂的表面处理方式一方面能在铝合金板材表面形成致密、均匀的微孔,另一方面硅烷偶联剂能很好地促进铝合金板材和CFRP的界面结合,有利于深拉成型。      

基于纤维束/环氧树脂复合材料试验的单向层合板横向拉伸强度预测方法

实验研究表明,纤维束/环氧树脂复合材料试件的横向拉伸强度与工程上常用的单向层合板横向拉伸强度在趋势上具有很好的相关性,但是数值上存在一定差距。本文使用两种碳纤维和两种环氧树脂制备了三种纤维束/环氧树脂复合材料和单向层合板,并分别测量了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度,以及环氧基体的拉伸强度。在实验基础上,应用Griffith断裂强度理论建立了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度的关系模型,通过两种复合材料实验的结果拟合了该模型中的参数。利用第三种复合材料实验进行校验,发现该模型预测的单向层合板横向拉伸强度与实测强度之间达到很好的一致性,相对偏差为9%。采用本文提出的方法,可以用较为简单的纤维束/环氧树脂复合材料和环氧基体拉伸试验预测单向层合板的横向拉伸强度。     

CFRP复杂几何结构区相控阵超声检测建模与声传播规律

为厘清碳纤维增强树脂基复合材料(Carbon fiber reinforced plastics,CFRP)复杂几何构件相控阵超声检测中声传播规律,围绕CFRP材料R区开展了弹性特性表征、有限元建模、声场计算及实验验证工作。基于超声液浸背反射法和模拟退火算法求解了CFRP单向板刚度矩阵反问题,并借助Bond变换实现了R区弹性特性的定量描述。结合微观组织分析等获取材料、几何特征,建立了虑及曲面形状、叠层、弹性各向异性的R区相控阵超声检测有限元模型,计算了R区相控阵超声检测A、B扫描信号,发现存在结构噪声和缺陷伪像。在此基础上研究CFRP材料R区瞬态声场并与CFRP平板、弹性各向同性R区和0°单向板R区情况对比,阐明了结构噪声和缺陷伪像的形成机制:弹性各向异性叠层结构导致倾斜入射的超声波发生反射和折射,与沿肋板传播的快速波混叠在R区形成结构噪声,同时多向板R区两侧肋板反射导致缺陷伪像,即材料弹性各向异性与构件曲面叠层结构耦合共同影响缺陷的精准辨识。      

X-ray computed tomography used to measure fiber orientation in CFRP laminates

This paper explains a new method to measure the fiber orientation in carbon fiber reinforced plastics (CFRP) laminates from X-ray CT images. In the method, the fiber orientation is analyzed by the application of digital image correlation (DIC) method to the acquired tomographic images. Using DIC, the brightness pattern, which results from the radiodensity difference between fiber and resin, is compared between two different planes in the thickness direction. Then, the three-dimensional displacement of the brightness pattern, which indicates the fiber orientation, can be measured. This study applied the proposed method to a quasi-isotropic CFRP laminate. After X-ray CT imaging, the sample was sectioned and polished. The fiber orientation was then measured experimentally using microscopy. The fiber orientation calculated using the proposed method agrees very well with the experimentally measured one. After demonstrating the validity of the proposed method, we applied it to a plain woven CFRP laminate. Results revealed that an invalid fiber orientation might be calculated for fibers parallel to the plane of the CT image, or for the fiber orientation of the pattern around the outer edge of CT images.     

Evaluation of impact damage mechanism of multi-axial stitched CFRP laminate

This study focuses on multi-axial stitched fabric, which is a thick, high performance reinforcement for large-scale composite structures. The effects of impact damage on multi-axial stitched CFRP laminates molded by vacuum-assisted resin transfer molding (VARTM) method were evaluated. Impact damage within material was evaluated by ultrasonic scanning device and optical cross-sectional observations. Probed images obtained by both non-destructive and destructive methods were compared, and internal damage distributions of multi-axial stitched CFRP laminates were clarified. In addition, residual compressive strength and fatigue property of impact-damaged CFRP laminates were evaluated by in situ damage growth monitoring using the thermo-elastic stress analyzer (TESA). Three-dimensional damage distribution of impacted CFRP laminate was obtained from ultrasonic C-scan images and cross-sectional photographs. Damage progress behavior was observed on a destructive and non-destructive basis by post-impact fatigue (PIF) test.     

Microscopic damage behavior in carbon fiber reinforced plastic laminates for a high accuracy antenna in a satellite under cyclic thermal loading

For a high accuracy antenna in next radio astronomy satellite, a candidate material is carbon fiber reinforced plastics (CFRP), because negative longitudinal coefficient of thermal expansion (CTE) for unidirectional CFRP enables a laminate with 0 CTE through appropriate laminate design. This enables high structural accuracy under large temperature fluctuation like space. On the other hand, when the laminate is subjected to thermal cycles, cyclic thermal stress occurs and causes microscopic damages. In this study, we characterized damage progress in CFRP laminates and resultant variation in mechanical properties under cyclic thermal loading. Three types of matrices, such as polycyanate ester, polyimide and epoxy resin were used to prepare CFRP laminates. Specimens were subjected to thermal cycles from ?197°C to 120°C. The test was periodically stopped for surface observation and flexural loading. Transverse cracks in 90° plies accumulated with thermal cycles, whereas flexural modulus remained constant. We also numerically evaluated temperature gradient and resultant thermal stress distribution during cooling by finite element analysis. The result indicates higher transverse stress appeared in the surface of the specimen and saturated to constant value which corresponded with the value calculated based on classical lamination theory.