加筋增强泡沫夹芯结构面内压缩与界面断裂性能试验

为解决复合材料泡沫夹芯结构面板局部屈曲与面芯脱粘的突出问题,提出了一种由筋条增强的玻璃纤维增强树脂基复合材料（GFRP）面板与泡沫芯层组合而成的新型夹芯结构。采用真空辅助树脂导入技术制备试验件,通过面内压缩与双悬臂梁试验,对比分析了加筋增强夹芯板与未加筋夹芯板的受力特性、失效模式和面芯粘结性能。面内压缩试验显示,与未加筋夹芯板相比,加筋增强夹芯板的失效模式由面板局部屈曲转化为面板压缩剪切破坏或整体屈曲,在GFRP材料使用量相同的情况下,试件长度为130 mm的加筋增强夹芯板平均失效荷载提高了40.87%,长度为190 mm试件提高了35.63%。双悬臂梁试验显示,加筋增强夹芯板的裂缝在发展过程中受到筋条与面板之间纤维丝搭接约束,改善了界面粘结性能,与未加筋夹芯板相比,其平均能量释放率提高了57.35%。     

复合材料夹层板单向受弯应力分析

基于非线性软质芯材位移模式的高阶剪切变形Zigzag夹层板理论,运用有限元方法分析了木质芯材-玻璃纤维增强聚合物（Glass Fiber Reinforced Polymer,下文缩写为GFRP）面板增强层、木芯材-GFRP竹混合增强层、以及泡沫芯材-GFRP面板增强层三种由真空导入工艺制作的复合材料夹层板;以米塞斯应力屈服准则为依据计算了特征点极限荷载,提出层间应力差作为树脂层的计算依据;考虑到根据本构模型直接由有限元法求得的位移获得的横向剪应力精度较低,采用基于应力平衡方程的最小二乘法计算了夹层板横向剪应力。对比实验和等效截面法的分析结果表明,基于非线性软质芯材位移模式的高阶剪切变形zigzag理论有限元分析法对于硬质和软质芯材复合材料夹层板都是十分有效的、实用的分析方法,适合于精细化分析和设计;等效截面法对于硬质芯材复合材料夹层板具有一定准确性,适合于初步分析和设计。     

格构增强木芯复材板的弯曲性能试验及其理论分析

设计一种新型格构增强木芯复材板,通过四点弯试验研究其抗弯性能.该复材板的面层及腹板为复合材料(FRP),芯材分为泡桐木和南方松两种.保持复材板截面尺寸不变,分别将1、2、3、4块木芯利用真空辅助树脂传递模塑工艺一次成型,从而改变格构腹板数目.此外,以纯木板作为对照试验标的物.结果表明:木芯种类会影响木芯复材板的抗弯性能;不同芯材的最佳格构数目也不同;格构数目增加不会导致复材板刚度产生线性增加.     

GFRP筋与自密实混凝土黏结性能的试验研究

为了研究玻璃纤维增强树脂复合材料(GFRP)筋与自密实混凝土(SCC)的黏结性能,制作了66个GFRP/SCC试件进行中心拉拔试验,研究SCC混凝土保护层厚度、GFRP筋直径和黏结长度以及SCC中添加纤维种类等因素对两者黏结性能的影响,并对试件的破坏形式进行分析。结果表明:试件主要出现了三种破坏形式,即劈裂破坏、拔出破坏、拔出带缝破坏;通过电镜扫描发现SCC浇筑方向对GFRP筋与SCC黏结界面的结构有一定影响,GFRP筋上部界面与SCC黏结更紧密。当SCC保护层厚度由4D增大至7D时,黏结强度提高了约44.05%;当GFRP筋黏结长度由5D增大至15D时,黏结强度降低了约65.43%;当GFRP筋直径由12 mm增大至16 mm时,黏结强度降低了约22.57%;SCC中添加聚丙烯纤维、钢纤维、聚丙烯纤维+钢纤维的试件黏结强度比不添加纤维的试件黏结强度分别提高12.80%、15.16%、15.09%。可以通过适当增加SCC保护层厚度、在SCC中添加纤维等措施来提高GFRP/SCC试件的黏结强度。      

齿板-玻璃纤维混合夹层结构弯曲性能试验

提出了一种齿板-玻璃纤维混合面板和泡沫芯材组成的新型混合夹层结构,齿板通过齿钉与泡沫芯材相连。该结构采用真空导入成型工艺制备,通过三点弯曲试验研究该结构在不同跨度以及不同芯材密度情况下的破坏模式和弯曲性能,并与普通泡沫夹层结构进行对比分析,同时探究了齿板对该结构界面性能的影响。结果表明:在泡沫芯材密度为35kg/m~3、80kg/m~3和150kg/m~3情况下,齿板-玻璃纤维混合泡沫夹层梁弯曲承载能力与普通泡沫夹层梁相比分别提高了168%、211%和258%,其界面剪切强度依次为0.09 MPa、0.21 MPa和0.45 MPa;随着芯材密度和跨度的变化,该结构主要产生芯材剪切和芯材凹陷两种破坏形态,齿板的嵌入有效抑制界面的剪切失效。另外,利用理论公式估算了试件受弯极限承载能力,理论值与实测值吻合较好。     

γ辐照对GFRP拉-拉疲劳性能的影响

玻璃纤维增强树脂基复合材料(Glass Fiber Reinforced Plastic,GFRP)由于其良好的电绝缘性和力学性能,被作为北京正负电子对撞机束流管支撑法兰的制作材料。北京电子对撞机运行时,将对束流管及其支撑法兰产生大量γ和中子辐射。研究发现,玻璃纤维增强环氧树脂基复合材料长期处于γ辐射环境中,其力学性能会发生变迁。本文对由20kGy、100kGy、200kGy剂量γ辐照前后的GFRP试件进行拉-拉疲劳实验研究,发现γ辐照对低周疲劳阶段的疲劳寿命影响较为明显,而对于高周疲劳阶段疲劳寿命影响不大。基于Hwang和Han提出的假设,建立了拉-拉疲劳双参数疲劳寿命模型,并验证该疲劳寿命模型的准确性。利用扫描电镜对试件进行观察,发现辐照后环氧树脂基体出现碎片,环氧树脂与增强玻璃纤维的黏结界面受到破坏,但辐照对玻璃纤维影响程度较小。红外光谱图显示环氧树脂在辐照过程中降解反应较交联反应占优势。     

泡沫夹芯结构复合材料VARI工艺模拟仿真技术研究

采用模拟仿真软件对聚氯乙烯泡沫夹芯结构复合材料矩形平板成型工艺进行了模拟分析.考察了芯材厚度、芯材的开槽方式及开槽尺寸等对树脂充模过程的影响,确定了适于工程应用的开槽方式及尺寸.     

CFRP@GFRP混杂复合材料杆体在水浸泡环境下的性能演化

碳纤维增强树脂复合材料(CFRP)@玻璃纤维增强树脂复合材料(GFRP)混杂复合材料杆体发挥碳纤维的高力学、疲劳性能与玻璃纤维的低成本、高变形能力等优势,在桥梁与海洋工程中具有巨大应用潜力,如跨海大桥斜拉索。针对CFRP@GFRP混杂复合材料杆体在服役环境下长期性能演化,本文采用加速试验方法研究蒸馏水环境下CFRP@GFRP混杂复合材料杆体的水吸收及界面剪切性能长期演化规律。研究结果表明:混杂复合材料杆体皮、芯层及杆体吸水行为符合Fick定律,GFRP皮层扩散系数最大,CFRP芯层次之,混杂复合材料杆体由于在皮/芯界面层形成吸水屏障而扩散系数最小。浸泡在蒸馏水环境下芯层、皮/芯界面及皮层界面剪切强度下降,这是由于浸泡过程中水分子通过氢键形式与树脂基体结合形成结合水,导致树脂基体发生水解和塑化及纤维/树脂界面脱黏。基于Arrhenius加速理论建立了混杂复合材料杆体在三座典型桥梁服役环境下的界面剪切强度预测模型。      

湿热环境下泡沫复合材料夹芯板的Ⅱ型界面剥离

本文通过端部切口弯曲试验(ENF)对湿热老化后泡沫复合材料夹芯板Ⅱ型界面剥离进行研究。测定了湿热老化前后玻璃纤维增强复合材料面板、聚氨酯泡沫芯材的抗压强度和压缩模量。结果表明,由于后固化作用,GFRP面板抗压强度、压缩模量先增大后减小;聚氨酯泡沫芯材的抗压强度、压缩模量先减小后趋于稳定。Ⅱ型临界能量释放率(Gc)随着老化时间的增加呈现下降趋势。湿热老化90天后,Gc下降26.68%。     

波纹腹板增强泡沫夹芯复合材料结构准静态压缩吸能特性

随着车船运输量与日俱增,由此引发的车船撞击结构物的事故频发,造成严重的生命财产损失与结构破坏,亟需为桥梁等结构物设置防护吸能装置。该文提出了一种新型波纹腹板增强泡沫夹芯复合材料吸能结构。该复合结构以聚氨酯泡沫为芯材,玻璃纤维增强复合材料(Glass fiber reinforced polymer,简称GFRP)为面板,在波纹型泡沫的间隙铺设双轴向玻璃纤维布,利用真空导入工艺成型。通过波纹腹板增强泡沫夹芯复合材料结构的准静态压缩试验,研究了波纹腹板与面板壁厚以及波长对夹芯结构破坏模式、承载能力以及吸能特性的影响。试验结果表明：腹板壁厚较大、波长较短的试件吸能效果最优。此外,对试验工况进行了有限元数值模拟,分析了腹板壁厚与泡沫密度因素对试件承载力的影响,为其在防撞领域的应用提供一定依据。     

VARI成型泡沫夹芯壁板结构界面性能

针对真空辅助成型工艺(VARI)制备的泡沫夹芯壁板面-芯界面粘接强度较低的问题, 提出铺放本体树脂胶膜和对芯材进行打孔两种解决方案。通过无损检测、三点弯曲力学性能测试、计算机模拟树脂充模流动以及微观界面结构观察, 探究两种方案的可行性及改善效果, 分析了胶膜的有无和厚度、打孔工艺参数对界面性能的影响。结果表明, 在不加入胶膜时界面强度最高, 胶膜厚度在0.5 mm时, 无损检测显示的界面缺陷最少, 胶膜厚度达到2 mm后界面质量下降; 合理设计芯材的打孔行、间距可以促进树脂充模流动, 形成质量好的连续界面, 同时还能提高结构刚度。     

A procedure to embed fibre Bragg grating strain sensors into GFRP sandwich structures

Embedding FBG strain sensors within a GFRP sandwich composite material allows early detection of internal defects. However, the sensors need to survive the manufacturing process to provide this capability. Vacuum infusion is commonly used to manufacture GFRP sandwich composite materials but, it needs to be modified to accommodate the embedding process. A stage by stage procedure is demonstrated here to embed FBG strain sensors between the skin–core interface of a GFRP sandwich beam specimen using the vacuum infusion method. Practical issues relating to sensor placement, fibre alignment, specimen lay-up and resin infusion are discussed. Also, the post cure effects of the resin on the FBG strain sensors are investigated. Static and dynamic load analyses are then performed to verify the repeatability and accuracy of the FBG strain sensors.     

Enhancing the resistance of composite sandwich panels to localized forces for civil infrastructure and transportation applications

This paper presents the details of an experimental and numerical study that was conducted to evaluate different methods of increasing the punching resistance of glass fiber reinforced polymer (GFRP) composite sandwich panels with balsa wood cores. A total of four large-scale panels were subjected to concentrated loads in a two-way bending configuration. Different techniques of locally stiffening the panels were investigated including bonding a steel coupling plate to the loaded surface of the panels and embedding steel tubes within the panel core. The experimental program was supplemented by a finite element study to evaluate the location, magnitude, and extent of stress concentrations in the panels. The experimental program demonstrated that the failure modes of the stiffened panels shifted from local punching to delamination of the loaded GFRP skin which initiated at the discontinuities of the panel stiffness. The finite element analysis indicated that the delamination failure was due to stress concentrations which formed at these critical locations. The local stiffening of the panel approximately tripled the concentrated load carrying capacity of the panels. The research findings suggest that, through careful design and detailing, composite sandwich panels can be used to resist large-magnitude concentrated loads such as those found in civil infrastructure and heavy freight transportation applications.     

Time-Variant Simulation of Multi-Material Thermal Pultrusion

Pultrusion being the viable and economical process for producing constant cross-section composite products, many variants of it are being tried out. This paper embarks on the pultrusion with multi-materials; typically of polymer foam/glass fibre reinforced polymer (GFRP) sandwich panels. Unlike conventional composites pultrusion, this process with more than two material phases, one of them dry, poses a challenge in simulating the thermal co-curing within the die. In this paper, the formulation and development of three-dimensional, finite element/nodal control volume (FE/NCV) approach for such multi-material pultrusion is presented. The numerical features for handling the dry-wet material interfaces, material shrinkage, variations in pull speed and die heating, and foam-to-skin thickness ratio are discussed. Implementation of the FE/NCV procedure and its application in analyzing pultrusion of polymer foam/GFRP sandwich panels with multi-heater environment are presented.     

Evaluation of sandwich panels with various polyurethane foam-cores and ribs

The objective of this study was to evaluate three potential core alternatives for glass fiber reinforced polymer (GFRP) foam-core sandwich panels. The proposed system could reduce the initial production costs and the manufacturing difficulties while improving the system performance. Three different polyurethane foam configurations were considered for the inner core, and the most suitable system was recommended for further prototyping. These configurations consisted of high-density polyurethane foam (Type 1), a bidirectional gridwork of thin, interconnecting, GFRP webs that is in-filled with low-density polyurethane foam (Type 2), and trapezoidal-shaped, low-density polyurethane foam utilizing GFRP web layers (Type 3). The facings of the three cores consisted of three plies of bidirectional E-glass woven fabric within a compatible polyurethane resin. Several types of small-scale experimental investigations were conducted. The results from this study indicated that the Types 1 and 2 cores were very weak and flexible making their implementation in bridge deck panels less practical. The Type 3 core possessed a higher strength and stiffness than the other two types. Therefore, this type is recommended for the proposed sandwich system to serve as a candidate for further development. Additionally, a finite element model (FEM) was developed using software package ABAQUS for the Type 3 system to further investigate its structural behavior. This model was successfully compared to experimental data indicating its suitability for parametric analysis of panels and their design.     

一种新型自粘接预浸料-Nomex蜂窝板面-芯结合强度关键影响因素试验研究

以Nomex蜂窝和新型自粘接预浸料作为试验材料, 通过采用均压板的共固化工艺制备蜂窝夹层板。采用滚筒剥离方法测试其面-芯结合性能, 采用电子显微镜等方法观察其蒙皮-蜂窝粘接面、剥离后蒙皮表面结构及蜂窝壁端面的微观形态, 并测试了蜂窝壁厚度与蜂窝壁浸渍的树脂成分。结合以上测试结果研究了在采用均压板的制备过程中工艺参数和蜂窝特征对蜂窝夹层板面-芯结合强度的影响规律, 并考察了蜂窝夹层板的粘接形式。结果表明: 在采用均压板模具的共固化工艺中, 一定的升温速率范围内, 蜂窝板的面-芯结合强度随着升温速率的减小而增大; 而加压时机对蜂窝板的面-芯结合强度的大小没有明显的影响; 蜂窝壁端面越粗糙、蜂窝壁树脂层厚度越小, 夹层板的面-芯结合强度越好。     

Effects of core machining configuration on the debonding toughness of foam core sandwich panels

Core machining is often applied to improve the formativeness of foam core and the manufacturing effectiveness of sandwich panels. This paper investigates the effects of core machining configuration on the interfacial debonding toughness of foam core sandwich panels fabricated by vacuum-assisted resin transfer molding process. Several machining configurations are conducted to foam core, and skin–core debonding toughness of fabricated sandwich panels is evaluated using double-cantilever-beam tests. The sandwich panels with core cuts exhibited higher apparent fracture toughness than the panels without core cut, specifically in the case of perforated core. The relationship between core machining configuration and measured fracture toughness is discussed based on the experimental observations and the numerical analyses of energy release rates.     

碳纳米管-玻璃纤维/环氧层板双真空灌注工艺及性能

针对碳纳米管(CNT)-玻璃纤维/环氧树脂体系, 采用传统的真空灌注工艺(VARIM)和双真空灌注工艺(DVARIM)制备复合材料层板, 分析了不同工艺方法下层板缺陷状况, 测试了层板的弯曲性能和层间剪切性能, 并结合树脂性能和纤维/树脂界面粘结状况观察, 探讨了DVARIM对CNT分布的影响及碳管的增强机制。结果表明: 与传统的VARIM相比, DVARIM能增加纤维的间距, 提高树脂对纤维的浸润能力, 减小纤维束内的孔隙缺陷; 添加质量分数为0.05％的酸化CNT后层板性能提高, 而且采用DVARIM性能提高更明显; 不同灌注工艺对CNT的分布产生影响, 从而改变了CNT对纤维/树脂界面粘接的影响, 同时这种影响与织物结构的紧密程度有关。      

考虑界面效应的GFRP复合材料蠕变模型

建立了包含界面的玻璃纤维增强树脂复合材料(GFRP)蠕变混合率单胞模型,对GFRP的蠕变性能进行分析;并与GFRP在应力水平为初始弯曲强度的20%所对应的载荷下的弯曲蠕变实验结果进行对比。分析了界面模量、界面厚度、纤维连续性与形态以及位向等因素对复合材料蠕变性能的影响。结果表明:相较于不考虑界面效应的混合率模型,本模型具有更高的准确性,与实验结果更为吻合;界面模量反应了纤维与基体的结合程度,对复合材料的蠕变性能产生影响,其蠕变柔量随着界面模量的增大而减小;界面厚度的增大会导致复合材料的蠕变柔量略微增大;相较于连续纤维增强树脂复合材料,短切纤维毡增强树脂复合材料的蠕变性能更易受到界面效应的影响;纤维方向对复合材料蠕变性能有显著影响,随着纤维方向角的增大,复合材料蠕变柔量增大,但当纤维方向角达到60°后,纤维已基本失去载荷传递和增强能力,复合材料蠕变柔量不再继续随着纤维方向角的增大而增大。