碳纤维增强空心玻璃微珠/环氧树脂复合材料的力学性能

制备了纤维长度为1 mm和2 mm的碳纤维增强空心玻璃微珠/环氧树脂复合材料,其纤维质量比分别为0.2%、0.5%、1%和3%。对材料进行三点弯曲实验和压缩实验,研究了纤维长度和纤维质量比对其弯曲强度和弯曲弹性模量、压缩强度和压缩弹性模量等力学性能的影响。结果表明,添加两种长度的碳纤维都能明显提高复合材料的弯曲和压缩力学性能。随着碳纤维质量比的增大复合材料的弯曲强度和压缩强度呈先增大后减小的趋势,当碳纤维的质量比为0.5%时达到最大值,随后则随纤维含量的增大而逐渐降低。当碳纤维的长度为1 mm质量比为0.5%时,复合材料试件的弯曲强度和压缩强度比未添加纤维时分别提高198%和110%。碳纤维的长度为1 mm时纤维含量的变化对复合材料的弯曲强度、压缩强度和压缩弹性模量有较大的影响,但是当纤维长度为2 mm时纤维含量的变化对弯曲强度和压缩强度的影响不大。     

B型套筒修复管道的极限轴向承载力预估方法

含环焊缝缺陷的管道采用B型套筒修复后的极限轴向承载能力至关重要。若依靠试验获得大直径管道修复后的极限轴向承载力,或代价昂贵,或因加载设备的载荷限制而难以实施,文章提出采用品字形焊接板预测其极限轴向承载力的方法。首先,选取两段Φ219 mm的管子对接,模拟环焊缝完全断开的管道。经B型套筒修复后,通过“以压代拉”试验获得极限轴向承载力。同时,进行有限元模拟,试验与模拟结果相差仅2.8%。进而,采用同样的有限元建模方法,获得B型套筒修复Φ1 016 mm管道后的极限轴向承载力。最后,针对Φ1 016 mm管道的B型套筒修复结构,分析其轴对称性及品字形焊接板承受拉伸时的边界效应,开展品字形焊接板拉伸试验。结果表明,品字板法预估值与有限元模拟值仅相差3.1%。综合模拟与试验结果,品字形焊接板可以准确预估B型套筒修复含环焊缝缺陷管道后的极限轴向承载力。     

定向分布碳纤维复合材料介电性能研究

以碳纤维为填充物, 环氧树脂为基体, 制备了碳纤维/环氧树脂介电复合材料. 介绍了两种分布方式对复合材料介电性能的影响, 分别研究了两种分布方式的介电常数随碳纤维含量和长度的变化规律. 在2.6–8.2 GHz频率范围内, 轴向介电常数是径向介电常数的数倍; 实部和虚部都随着碳纤维含量的增加而增大; 碳纤维长度也对介电性能的各向异性影响显著. 双层微波传输带模型可以合理地解释这些规律.     

激光改性纤维对其增强环氧树脂复合材料力学性能的影响

利用激光对玻璃纤维、玄武岩纤维和碳纤维进行表面改性后,以环氧树脂为基体,分别制备三种纤维增强环氧树脂复合材料。利用SEM和万能试验机对表面改性前后的碳纤维形态、力学性能及三种纤维/环氧树脂复合材料的力学性能和断面形貌进行表征,研究了纤维激光表面改性对三种纤维及其增强环氧树脂复合材料力学性能的影响。结果表明:激光表面改性对碳纤维/环氧树脂复合材料的力学性能提升最高,其拉伸强度最大提高了77.06%,冲击强度最大提高了31.25%,玄武岩纤维/环氧树脂复合材料的力学性能提升次之,而玻璃纤维/环氧树脂复合材料的力学性能有所下降。因此,激光进行表面改性适用于碳纤维和玄武岩纤维。     

内拱处含壁厚减薄缺陷弯头的爆破压力研究

为研究壁厚减薄缺陷对弯头爆破压力的影响,在试验验证可靠性的基础上,建立了弯头内拱处含局部壁厚减薄缺陷爆破压力预测的显式非线性有限元模型,采用等效塑性应变失效作为弯头的失效准则,研究了缺陷尺寸对弯头爆破压力的影响。研究结果表明：缺陷深度小于壁厚70%时,缺陷宽度对爆破压力的影响较小,但缺陷深度大于70%时,其影响较大不能忽略;缺陷长度的增加会导致爆破压力的减小,但二者不是线性关系;当缺陷长度小于15°时,爆破压力随缺陷长度增加降低较快,而缺陷长度大于15°时,爆破压力随缺陷长度增加降低趋缓;缺陷相对深度是影响爆破压力的主要因素,爆破压力会随着缺陷相对深度的增加而快速降低。     

单螺栓修复对含冲击损伤碳纤维/环氧树脂复合材料层合板压缩承载能力的影响

开展了单钉修复对含冲击损伤碳纤维/环氧树脂复合材料层合板压缩承载能力影响的试验研究。测试了三种不同能量冲击后碳纤维/环氧树脂复合材料层合板的压缩承载能力及失效模式,测定了单螺栓对碳纤维/环氧树脂复合材料层合板压缩承载能力的修复效率,并借助数字图像相关技术(DIC)表征手段揭示了单螺栓修复对含冲击损伤结构失效行为的影响。结果表明:冲击后碳纤维/环氧树脂复合材料层合板的压缩承载能力随着冲击能量的增加而降低,冲击损伤破坏了碳纤维/环氧树脂复合材料层合板结构的对称性,并导致结构在加载初期呈非对称的局部屈曲变形特征,局部屈曲诱发并加剧分层损伤扩展;单螺栓修复能有效恢复结构的整体对称性,在一定程度上抑制含冲击损伤碳纤维/环氧树脂复合材料层合板的局部屈曲,达到可观的修复效率。该研究为复合材料紧固件修理方案的制订及修理损伤容限的定义提供一定的指导意义。      

气相处理对碳纤维表面及其复合材料性能的影响

本文对气相表面处理碳纤维的新工艺进行了系统研究。处理后的碳纤维强度、模量不下降,且其表面能、表面化学官能团含量明显增加;表面微晶结构变小,与环氧树脂复合后,层间剪切强度(LLSS)提高47%左右。本文还对复合材料断口的形态结构进行了分析,说明这种表面处理方法能有效改善碳纤维增强环氧树脂复合材料(CFRP)的界面粘结。     

碳纤维复合材料构件高效加工对策

近20年来，碳纤维增强复合材料研究与应用受到世界各国的普遍重视，本文以碳纤维增强／树脂基复合材料为研究对象，讨论了轴向力对缺陷的影响规律结论如下：纤维方向对缺陷形成有重要的影响，轴向力增大分层与撕裂缺陷相应增大：以磨代钻加工工艺、新型PCD刀具和螺旋面钻头对于提高碳纤维复合材料钻孔质量都有很大提高。     

碳纤维改性环氧树脂基复合材料的制备及性能研究

以环氧树脂E51为基础材料,碳纤维为增强材料,制备出了不同碳纤维掺杂量(0,3%,6%,9%(质量分数))的改性环氧树脂基复合材料,研究了碳纤维掺杂量对环氧树脂基复合材料力学性能、微观形貌、热稳定性和导热性能的影响。结果表明,适量碳纤维的掺杂提高了环氧树脂基复合材料的力学性能、热稳定性和导热性能。随着碳纤维掺杂量的增加,改性环氧树脂基复合材料的拉伸强度、断裂延伸率、弯曲强度和弯曲模量均先增大后降低,当碳纤维的掺杂量为6%时,复合材料的拉伸强度、断裂延伸率、弯曲强度和弯曲模量均达到了最大值,分别为48.5 MPa, 1.86%,85.6 MPa和3.09 GPa。随着碳纤维掺杂量的增加,复合材料的分解温度和残留量先升高后降低,当碳纤维的掺杂量为6%时,复合材料的分解温度和残留量达到最大,分别为453.7℃和4.9%。复合材料的导热系数随碳纤维掺杂量的增加而增大,当碳纤维的掺杂量<6%时,导热系数增长速率较快。综合分析可知,碳纤维的最佳掺杂量为6%。     

碳纤维网络增强环氧树脂基复合材料的制备与表征

为提高碳纤维/环氧树脂复合材料的刚性和热尺寸稳定性,首先利用短切碳纤维制备了碳纤维网络增强体(CFNR),并将其与环氧树脂复合制备了CFNR/环氧树脂新型复合材料。然后,分别利用扫描电镜和热机械分析仪对CFNR/环氧树脂复合材料的微观结构和热力学性能进行了表征。结果表明:CFNR/环氧树脂复合材料中有明显的网络节点,即碳质粘结点;CFNR/环氧树脂复合材料具有较好的导电性、较高的刚性和较低的热膨胀性,其弹性模量分别为常规短切碳纤维/环氧树脂复合材料及纯环氧树脂的3倍和6倍,平均热膨胀系数(60~200℃)分别为常规短切碳纤维/环氧树脂复合材料的1/15及纯环氧树脂的1/40;随着温度升高,CFNR/环氧树脂复合材料、常规短切碳纤维/环氧树脂复合材料及纯环氧树脂的弹性模量均因环氧树脂变软而降低,当温度高于80℃时,CFNR/环氧树脂复合材料的弹性模量分别约为常规短切碳纤维/环氧树脂复合材料的7倍和纯环氧树脂的近70倍。研究结论可以为开发高刚性、低膨胀聚合物基复合材料提供实验依据和理论指导。     

XFEM fracture analysis of cracked pipeline with and without FRP composite repairs

Abstract

The effect of fiber reinforced polymer composite (FRPC) repair on crack propagation in thin-walled steel pipes is examined. The extended finite element method is used in this study to simulate a pressurized cylindrical pipe with longitudinal crack in two conditions: the original cracked pipe and the pipe repaired with a composite patch. Carbon/epoxy or E-glass/epoxy FRP in two different fiber orientations are assumed for cracked pipe repair. Performance of four types of FRP repair systems are investigated by CTOA, COD and COA fracture criteria for both the pipe integrity assessment and the potential age of leak before break criterion.     

Finite-Element Analysis of Crack Arrest Properties of Fiber Reinforced Composites Application in Semi-Elliptical Cracked Pipelines

In nowadays, repair method using fiber reinforced composites as the mainstream pipe repair technology, it can provide security for X100 high-grade steel energy long-distance pipelines in engineering. In this paper, analysis of cracked X100 high-grade steel pipe was conducted, simulation analysis was made on structure of pipes and crack arresters (CAs) to obtain the J-integral value in virtue of ANSYS Workbench finite element software and evaluation on crack arrest effects was done through measured elastic-plastic fracture mechanics parameter J-integral and the crack arrest coefficient K, in a bid to summarize effect laws of composite CAs and size of pipes and cracks for repairing CAs. The results indicate that the K value is correlated with laying angle λ, laying length L₂/D₁, laying thickness T₁/T₂of CAs, crack depth c/T₁ and crack length a/c, and calculate recommended parameters for repairing fiber reinforced composite CAs in terms of two different crack forms.     

原位聚合碳纤维增强聚甲基丙烯酸甲酯基复合材料损伤与修复研究

基于热塑性复合材料易修复的特性,开展了碳纤维增强聚甲基丙烯酸甲酯(PMMA)基复合材料修复技术研究。研究了工艺温度、压力和时间对复合材料力学性能的影响规律。结果表明：在200℃、0.75 MPa压力下保持10 min可以获得优化的复合材料力学性能。引入低速冲击损伤,使用热压修复工艺修复碳纤维增强PMMA基复合材料的损伤。通过X射线断层扫描测试、超声波无损检测技术和断面摄像方法评估了此复合材料的损伤行为和修复效果。结果表明：低速冲击对碳纤维增强PMMA基复合材料的损伤分为低变形量区域的纵向开裂与分层和高变形量区域的纤维断裂与基体失效的混合模式。碳纤维增强PMMA基复合材料损伤试样经过热压修复后,损伤外形恢复良好,损伤区域大小显著减少,内部的开裂和分层等损伤恢复良好,复合材料压缩强度从140 MPa恢复至263 MPa,达到未损伤复合材料压缩性能(307 MPa)的85.7%。     

Pavement repair strategy and construction technology for Bangabadhu multipurpose bridge

In this communication, the pavement repair strategy for the Bangabadhu multipurpose bridge has been optimized. The former design of the repair strategy includes six parts of repairing cracks with epoxy adhesive, 1.4 mm thick carbon fiber reinforced polymer (carbon fiber reinforced polymer), 5 mm thick thermal insulation, 6–12 mm surface material non‐shrink mortar grout, 5 mm thick waterproofing membrane, and 50 mm thick mastic asphalt. The optimized repair proposal includes five parts of repairing cracks with epoxy adhesive, 1.4 mm thick carbon fiber reinforced polymer, 4–10 mm thick epoxy resin motar grout, 5 mm thick epoxy asphalt waterproofing adhesive coat, and 50 mm thick stone mastic asphalt. In addition, the requirements for the materials selection and specific technology for the construction processes has also been provided.     

Evaluation of fatigue behavior on repaired carbon fiber/epoxy composites

The continuous use of structural polymer composites in aeronautical industry has required the development of repairing techniques of damages found in different types of laminates. The most usually adopted procedure to investigate the repair of composite laminates has been by repairing damages simulated in laminated composite specimens. This work shows the influence of structural repair technique on mechanical properties of a typical carbon fiber/epoxy laminate used in aerospace industry. When analyzed by tensile test, the laminates with and without repair present tensile strength values of 670 and 892 MPa, respectively, and tensile modulus of 53.0 and 67.2 GPa, respectively. By this result, it is possible to observe a decrease of the measured mechanical properties of the repaired composites. When submitted to fatigue test, it is observed that in loads higher than 250 MPa, this laminate presents a low life cycle (lower than 400,000 cycles). The fatigue performance of both laminates is comparable, but the non-repaired laminate presented higher tensile and fatigue resistance when compared with the repaired laminate.     

A study on low velocity impact damage evaluation and repair technique of small aircraft composite structure

Composite structures are very prone to damage at fairly modest levels of impact energy due to foreign object damages. A repair technique using external patch is recognized as an effective method to recover the damaged structures during service life. This work is focusing on the impact damage evaluation and the external patch repair techniques of the aircraft composite structure. The impact damages of composite laminates of the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate are simulated by the drop-weight type impact test equipment. The damaged specimens are repaired using the external patch repair method after removing the damaged area. The compressive strength test and analysis results of the repaired impact damaged specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, the strength recovery capability after repairing is investigated.     

A scientific evaluation of the approximate 2D theories for composite repairs to cracked metallic components

In this paper, we show how the published literature reveals that the approximate two-dimensional solution for the stress intensity factor associated with cracked panel repaired using an externally bonded composite repair is inconsistent with experimental data, and that for short to mid-size cracks the fibre bridging effect is often a second-order effect. The result of this finding is that prediction of the effect of a composite repair on the structural integrity of cracked components repaired by an externally bonded composite repair is dramatically simplified. We also show why structures repaired using Glare patches have a fatigue performance that is superior to structures repaired using boron epoxy or carbon fibre patches.     

Assessment of failure pressure of a GFRP composite repair system for wall loss defect in metallic pipelines

The present paper is concerned with the failure pressure assessment of a newly developed GFRP matrix laminated composite repair of metallic pipelines with 80 % wall loss defect. The main motivation is to validate the experimental failure pressure with the theoretical one. Wall loss defects were manufactured into the tube specimen and the performance of the repaired pipe was assessed by hydrostatic tests as per ISO/TS 24817 standard. Results reveal that the theoretical failure pressure as per ISO/TS 24817 standard is found to be conservative. A wide range of failure pressure values was obtained using different criteria. Only RSTRENG 0.85* modified criterion provides a closer value towards the experimental one. However, the criterion selection for damage factor and flow stress condition is an open question as it gives dispersed values of failure pressure. The prediction of the failure pressure must be accurate without being overly conservative. Plastic deformation of the tube occurs towards the end of the tube, consequently, it is necessary to account for this behavior in failure pressure analysis for an accurate prediction. The application of loading‐unloading cycles before the failure burst test should be also accounted in order to predict the failure pressure.     

Strengthening steel bridge sections using CFRP laminates

This paper presents results from an experimental investigation to determine the feasibility of using carbon fiber reinforced polymer (CFRP) epoxy laminates to repair steel composite bridge members. Six specimens, each consisting of a 6.1 m long W8×24 wide flange A36 steel beam acting compositely with a 0.114 m thick by 0.71 m wide reinforced concrete slab, were first loaded past yield of the tension flange to simulate severe service distress. The damaged specimens were then repaired using 3.65 m lengths of 2 or 5 mm thick CFRP laminates bonded to the tension flange and tested to failure. The results indicated significant ultimate strength gains but more modest improvement in the elastic response. Non-linear finite element analyses were in good agreement with the experimental results. The study suggests that it is feasible to strengthen steel composite members using CFRP laminates.