Fatigue behaviour of the bond interface between carbon fibre‐reinforced polymer sheets and concrete

Externally bonded carbon fibre‐reinforced polymers (CFRPs) have been applied to retrofit and strengthen civil structures. In this study, four‐point bending beams were manufactured and tested to examine the fatigue behaviour of the CFRP–concrete interface. The results indicated that the specimens exhibited debonding failure in the concrete beneath the adhesive layer under static loading. However, when cyclic loads were imposed on the small beams, debonding failure may occur in the adhesive layer. Moreover, fitting expressions were proposed to predict the shear stress–slip relationship between the CFRP sheets and concrete and the flexural strength of the CFRP‐strengthened beams under static loads, and good agreement with the test data was obtained. Finally, a fatigue life prediction model was also presented to capture the fatigue life of the CFRP–concrete interface under cyclic loads. The calculation results showed that the fatigue strength of the CFRP–concrete bond interface was approximately 65% of the ultimate load capacity.     

Co-Curing of CFRP-Steel Hybrid Joints Using the Vacuum Assisted Resin Infusion Process

This study focuses on the one-step co-curing process of carbon fiber reinforced plastics (CFRP) joined with a steel plate to form a hybrid structure. In this process CFRP laminate and bond to the metal are realized simultaneously by resin infusion, such that the same resin serves for both infusion and adhesion. For comparison, the commonly applied two-step process of adhesive bonding is studied. In this case, the CFRP laminate is fabricated in a first stage through resin infusion of Non Crimp Fabric (NCF) and joined to the steel plate in a further step through adhesive bonding. For this purpose, the commercially available epoxy-based Betamate 1620 is applied. CFRP laminates were fabricated using two different resin systems, namely the epoxy (EP)-based RTM6 and a newly developed fast curing polyurethane (PU) resin. Results show comparable mechanical performance of the PU and EP based CFRP laminates. The strength of the bond of the co-cured samples was in the same order as the samples adhesively bonded with the PU resin and the structural adhesive. The assembly adhesive with higher ductility showed a weaker performance compared to the other tests. It could be shown that the surface roughness had the highest impact on the joint performance under the investigated conditions.     

Wet thermo-mechanical behavior of steel–CFRP joints – An experimental study

The long term durability of CFRP strengthened steel structures is a key parameter for their safe use and effective design. Strengthened members can be subjected to different environmental conditions and loading scenarios during their service life, the effect of which on the failure mechanism of the strengthened member requires fundamental investigations. This paper presents an experimental investigation into the effects of wet thermo-mechanical loading on the bond strength and the failure mode of steel–CFRP single lap joints. A total of thirty four steel–CFRP single lap shear specimens were prepared and exposed to different combinations of wet thermal cycle ranges and sustained loads. The results show that these conditions (wet thermal cycles and sustained loads) have little impact on the bond strength of steel–CFRP lap joint when applied separately. However, when applied simultaneously, the bond strength of the joint is significantly reduced with failure observed at less than 30% of the static strength under temperatures that are well below the glass transition temperature of the adhesive.     

Investigation on the effect of process parameters in atmospheric pressure plasma treatment on carbon fiber reinforced polymer surfaces for bonding

Carbon Fiber Reinforced Polymer (CFRP) is used extensively in aerospace applications. Acceptance of bonded CFRP structures, mainly for aerospace applications, requires a robust surface preparation method with improved process controls to ensure high bond quality. Consistent repeatability is a factor lacking from many surface preparation processes. Atmospheric pressure plasma surface treatment is one of the robust surface preparation processes that have drawn wide attention in recent years. This process is capable of being applied in a production clean room environment that would minimize the risk of contamination and reduce cost. In plasma surface treatment the process parameters are easily controlled, documented providing a repeatable process with a high level of consistency. In this paper, the process parameters for atmospheric pressure plasma surface treatment and their effect on bonding for Out-Of-Autoclave (OOA) CFRP composite panels were fully investigated. A mechanized machine with sensory feedback to plasma treat surfaces was developed to change the process parameters for application on larger panels. By the aid of Design of Experiment (DOE) methodology critical process parameters were identified and a mathematical regression model was developed. The mathematical regression model was used to quantify the effect of process parameters on the bonding strength and the model was optimized to find the optimum settings.     

On the response of two commercially-important CFRP structures to multiple ice impacts

Carbon-fibre reinforced composites (CFRPs) are likely to feature heavily as structural elements of future aerospace vehicles due to their high stiffness and low densities. However, such components are likely to be subjected to a variety of impact-related events during their in-service lives. One area which has only received limited attention in the literature is that of ice impact on CFRP structures; e.g. hail stone impacts on aerospace components. In this study the response of two aerospace-grade CFRP structures (one woven and one uni-directional lay-up) to multiple ice impacts with cumulative impact energies in the range 72–1215 J was investigated. Six empirical damage categories were identified, ranging from no apparent surface damage (Type 1) to penetration accompanied by complete lay-up disruption (Type 6). Surface damage was found to correlate with changes in recovered panel properties; determined by ultrasonic C-Scan and compression-after-impact strength tests. With both CFRP structures sub-surface disruption and residual compressive strength varied linearly with total impact energy; suggesting that damage in such structures is cumulative in nature. Further, in line with previous studies, the woven structure consistently exhibited lower levels of damage at a given impact energy, even when damage extent was normalised by areal density.     

Temporary bond strength of partly cured epoxy adhesive for anchoring prestressed CFRP strips on concrete

Externally bonded Carbon Fiber Reinforced Polymer (CFRP) strips have been used for strengthening reinforced concrete structures. This paper presents an experimental study on the debonding of externally bonded CFRP strips anchored to a concrete substrate by a commercial epoxy adhesive. The study represents the basis for the characterization of an innovative ‘gradient method’, giving the possibility to anchor prestressed CFRP strips to concrete without the use any mechanical anchorage systems such as plates and bolts. Bond between the two components is achieved by an epoxy adhesive able to carry loads after an accelerated curing process under elevated temperatures. The effect of heating configuration/duration, strip thickness and bond length on the temporary bond resistance have been investigated using prestressed and non-prestressed CFRP-strips. Besides the optimization of the heating elements necessary for the curing process, curing parameters for an optimal temporary bond strength could be determined. Twenty-five minutes of heating and curing at 90 °C was found to be an optimum heating configuration, resulting in better short-term mechanical performances than after conventional curing at room temperature for several days. The main reason is a temporarily softer adhesive which allows the use of the full bond length by reducing shear force peaks.     

基于激光三维雕刻的CFRP多梯层挖补胶接接头加工技术研究

在航空飞行器的碳纤维复合材料(CFRP)结构件损伤修复时,挖补胶接技术是获得高性能的CFRP层合板接头的理想工艺.本文提出一种CFRP层合板的多梯层挖补胶接接头设计策略,设计了挖补胶接接头阴阳膜构建和分层切片激光三维雕刻扫描工艺代码生成算法,探索了CFRP梯层界面的激光烧蚀成型工艺规律和粘结性能改善机理,验证了胶接接头...     

粘结层和预应力对CFRP板加固损伤钢梁抗弯性能的影响

为了对比粘结层和预应力对碳纤维增强聚合物复合材料(CFRP)板加固损伤钢梁抗弯性能的影响,进行了5根H型损伤钢梁的抗弯试验,分析了特征荷载、荷载-挠度曲线、CFRP板应变及其强度利用率的变化。试验结果表明:有粘结和无粘结CFRP板具有相近的加固效果,特征荷载差值小于2%;非预应力CFRP板在正常使用阶段的加固效果很小,而预应力CFRP板加固钢梁的特征荷载比非预应力CFRP板提高了近30%。平截面假定适用于有粘结CFRP板-钢梁复合截面,而不适用于无粘结CFRP板-钢梁复合截面。相比于非预应力CFRP板,对CFRP板施加预应力可以显著提高CFRP板的强度利用率。建立的有限元模型可以较好地预测试件的抗弯性能,增加CFRP板的预应力、厚度和弹性模量可以提高损伤钢梁的抗弯加固效果。      

Tool geometry based prediction of critical thrust force while drilling carbon fiber reinforced polymers

Carbon fiber reinforced polymers(CFRPs) are known to be difficult to cut due to the abrasive nature of carbon fibers and the low thermal conductivity of the polymer matrix.Polycrystalline diamond(PCD) drills are commonly employed in CFRP drilling to satisfy hole quality conditions with an acceptable tool life.Drill geometry is known to be influential on the hole quality and productivity of the process.Considering the variety of CFRP laminates and available PCD drills on the market,selecting the suitable drill design and process parameters for the CFRP material being machined is usually performed through trial and error.In this study,machining performances of four different PCD drills are investigated.A mechanistic model of drilling is used to reveal trade-offs in drill designs and it is shown that it can be used to select suitable feed rate for a given CFRP drilling process.     

Failure mode and strength of uni-directional composite single lap bonded joints with different bonding methods

Failure process, mode and strength of unidirectional composite single lap bonded joints were investigated experimentally with respect to bonding methods, that is, co-curing with or without adhesive and secondary bonding. The co-cured joint specimen without adhesive had the highest failure strength. Progressive failures along an adhesive layer occurred in the secondary bonded specimen. In the co-cured specimen with adhesive film, delamination failure occurred and the joint strength was lower than that of secondary bonded specimens. Delamination failure did not occur in the secondary bonded specimen because of early crack growth and progressive failure in the adhesive layer. Therefore, The failure strength of composite bonded joint is not always proportionate to adhesion strength of adhesive due to the weakness of delamination in composite materials. The influences of surface roughness, bondline thickness and fillets in the secondary bonded specimens were also studied.     

纳秒激光调控CFRP复合材料表面润湿性及其对胶接性能的影响

采用纳秒激光对碳纤维增强树脂基(CFRP)复合材料进行表面预处理,调控其表面成分、粗糙度和表面润湿性,然后采用SEM、接触角测量仪、光学轮廓仪、XPS等表征CFRP复合材料的表面微观形貌、接触角、粗糙度和化学成分,并通过拉伸剪切实验评价和分析激光表面处理对CFRP复合材料胶接强度的影响规律和机制.结果表明:优化激光表面...     

铝合金表面特性对其胶接性能影响的研究进展

不同的表面处理方法会导致铝合金表面的表面理化特性发生改变,从而对铝合金板材与胶黏剂的界面结合强度以及胶接接头的耐腐蚀性能有很大的影响。本文从铝合金表面粗糙度、微观织构、表面氧化层和涂层化学特性等方面入手,对铝合金胶接接头的界面强度和耐腐蚀性能影响的研究现状进行了综述。探讨了铝合金胶接研究发展趋势,并认为铝合金表面理化特性的参数化表征以及表面特性与胶接性能的关系模型建立等方面是今后研究的重要方向。     

Hybrid epoxy-silyl modified polymer adhesives for CFRP sheets bonded to a steel substrate

This paper presents an experimental study examining the interfacial behavior between a steel substrate and carbon fiber reinforced polymer (CFRP) sheets bonded with hybrid epoxy-silyl modified polymer (SMP) adhesives. The epoxy adhesive has high modulus and strength characteristics, while the SMP adhesive possesses a low modulus with permanent elastic nature. The hypothesis tested is that a combination of these two distinct materials can alleviate interfacial stresses along the bond line with maintaining adequate strength. Two types of double-lap tension tests are conducted to evaluate the bond-capacity of the epoxy and SMP adhesives and to study the effect of various hybrid bond schemes. Test results show that the specimens bonded with homogeneous epoxy demonstrate abrupt failure, whereas those with SMP exhibit gradual load-softening at failure. The load-carrying capacity and stiffness of the CFRP–steel interface are not influenced by hybrid bond configurations. The degree of CFRP-debonding is, however, affected by the hybrid bond scheme. Stress transfer from the steel substrate to the CFRP is well maintained along the hybrid bond line with significant local deformability of the interface layer. Analytical models report that shear stresses along the CFRP–steel interface are noticeably mitigated at geometric discontinuities and the proposed hybrid bond technique can be used for structure-level application.     

Chemical functionalization of composite surfaces for improved structural bonded repairs

In terms of lightweight design, aerodynamics and structural integrity, bonded repairs represent the preferred approach for repairing composite structures in aircraft applications. In this work the influence of crucial surface parameters including roughness, polarity and chemical composition on the performance of bonded repairs is studied. Besides mechanical and physical interactions, the study aims at the surface modification of carbon-fiber reinforced polymers (CFRP) to tailor chemical interactions with the adhesive. Reactive epoxy and mercapto derivatives are attached onto the CFRP surface by a 2-step functionalization route to ensure optimized adhesion and covalent bonding to epoxy-based adhesives. The performance of bonded coupon joints is determined by single lap shear tests (tensile-shear loading) and fracture mechanical tests (mode I loading). The results give evidence that chemical interactions play a key role in the quality of bonded repair systems. By controlling the chemical surface properties improved bond strength, homogenous crack growth and cohesive failure patterns are achieved.     

基于电阻信号的CFRP纤维断裂识别实验及理论模型

碳纤维是决定CFRP复合材料性能的主要因素之一,因此为保证复合材料结构的健康状态、识别纤维的损伤与断裂就显得至为关键。文中通过加载电流并采集电阻信号的方式来识别CFRP复合材料中碳纤维的健康状态,通过实验和理论分析的方法进行了深入研究。实验针对2种不同铺层的试件进行测量:单向层合板[0]8和正交层合板[0/90]4。对试件端部进行了粘接铜箔处理以使试件稳定导电,使用KEITULEY2700数据采集仪测量试件电阻。实验内容包括静态电阻测量、拉伸受力状态下材料的电阻特性分析,并建立和推导了电阻-应变理论分析模型,进行了通电疲劳实验。研究结果表明,碳纤维的铺层角度对CFRP结构电阻有较大影响,[0]8铺层材料电导率和破坏强度约为[0/90]4铺层材料的2倍;CFRP材料受外载荷作用时,损伤程度与其电阻变化有对应的关系,其电阻信号变化可以作为反映材料损伤情况和识别纤维断裂的主要参数;实验结果与所建立的电阻-应变模型拟合结果吻合较好。文中研究的CFRP纤维断裂识别和航空复合材料结构健康监控及实时监测具有重要的意义。     

基于遗传算法的碳纤维增强树脂复合材料层合板单搭胶接结构的多目标优化

基于遗传算法对碳纤维增强树脂复合材料(CFRP)层合板单搭胶接结构进行了多目标优化,以提高其结构性能.首先,通过三维Hashin准则和三角形内聚力模型建立三维有限元模型来预测CFRP层内损伤过程、层间失效和胶层损伤过程,并通过试验验证其有效性.其次,利用拉丁超立方抽样(LHS)方法和二次多项式响应面法(RSM),基于搭...     

氧气等离子体处理对CFRP表面特性及胶接界面力学性能的影响EI北大核心CSCD

为改善碳纤维增强复合材料(CFRP)胶接界面力学性能,采用低温氧气等离子体处理设备对CFRP进行表面处理。利用接触角测量仪、扫描电子显微镜(SEM)、原子力显微镜(AFM)、X射线光电子能谱(XPS)对CFRP表面润湿性、表面能、表面形貌、表面化学组分等进行表征,通过双悬臂梁实验(DCB)对CFRP胶接界面力学性能进行研究。结果表明:随氧气等离子体处理时间从0 s增加至30 s,表面水接触角从97°降至29°,CFRP表面润湿性达到最佳,极性分量占比显著增多;随处理时间的增加,CFRP表面粗糙度和最大高低差降低,形成较多谷峰分布的纳米级沟壑,基体表面积增大;同时,表面C—O和C■O等含氧极性官能团含量明显增加,C—C/C—H和Si—C官能团含量减少,表面污染物得到有效清除和转化;与未处理相比,经氧气等离子体处理20 s后,CFRP胶接界面最大剥离载荷和Ⅰ型断裂韧度分别提高了1.01倍(62.73 N)和1.92倍(649.21 J/m 2)。研究发现,氧气等离子体处理可以显著改善CFRP表面物理化学特性,有利于CFRP与胶黏剂更好的黏结,提高胶接界面剥离强度与韧性。     

Influence of the properties of externally bonded CFRP on the shear behavior of concrete/composite adhesive joints

This paper concerns the strengthening of concrete structures with externally bonded composite reinforcement, and focuses mainly on the influence of the FRP characteristics on the mechanical behavior of the composite to concrete interface. An experimental investigation was conducted, based on the characterization of such bonded assemblies and using a double lap joint shear test. Twelve different series of specimens were studied in order to evaluate the influence of various parameters related to the FRP material (i.e. the use of carbon or aramid and of fiber reinforced systems, the type of manufacturing process, the values of the Young modulus, the thickness of the FRP and the bonded length) as well as several parameters related to the adhesive joint (i.e. the lap joint thickness, the curing conditions and the elastic modulus of the epoxy adhesive). Analyses of the strain and shear stress distributions along the lap joints emphasized significant effects of the FRP properties and epoxy curing conditions on the interfacial strength. In addition, a bond strength model is proposed in the last part of the study.     

超声强化氨基化多壁碳纳米管改性环氧黏接接头性能研究

目的 探究超声处理对氨基化多壁碳纳米管(MWCNTs–NH₂)改性环氧黏接接头黏接性能和热稳定性的影响,为强化MWCNTs–NH₂改性环氧胶黏剂与铝合金的黏接提供参考。方法 通过机械搅拌与声波破碎的方法将质量分数为0.75%的MWCNTs–NH₂添加到环氧胶黏剂基体中,使用MWCNTs–NH₂改性环氧胶黏剂制备铝合金黏接接头,基于超声辅助黏接工艺在铝合金黏接过程中进行超声处理。通过傅里叶变换红外光谱仪(FTIR)分析MWCNTs–NH₂改性环氧胶黏剂基体官能团的变化情况。采用单搭接剪切强度试验测定黏接接头的拉伸剪切强度。通过扫描电子显微镜(Scanning Electron Microscope,SEM)观察黏接接头拉伸失效断面以及铝合金与胶黏剂间的黏接界面。通过热失重分析仪(TGA)测试并记录胶黏剂试样质量随温度变化的曲线。结果 经超声处理后,MWCNTs–NH₂与树脂基体间的化学反应增强。与纯环氧黏接接头相比,超声处理后的MWCNTs–NH_2...     

Behavior of RC T-section beams strengthened with CFRP strips,subjected to cyclic load

This paper presents results of an experimental investigation on T-section reinforced concrete (RC) beams strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) strips. Specimens, one of which was the control specimen and the remaining six were the shear deficient test specimens, were tested under cyclic load to investigate the effect of CFRP strips on behavior and strength. Five shear deficient specimens were strengthened with side bonded and U-jacketed CFRP strips, and remaining one tested with its virgin condition without strengthening. The type and arrangement of CFRP strips and the anchorage used to fasten the strips to the concrete are the variables of this experimental work. The main objective was to analyze the behavior and failure modes of T-section RC beams strengthened in shear with externally bonded CFRP strips. According to test results premature debonding was the dominant failure mode of externally strengthened RC beams so the effect of anchorage usage on behavior and strength was also investigated. To verify the reliability of shear design equations and guidelines, experimental results were compared with all common guidelines and published design equations. This comparison and validation of guidelines is one of the main objectives of this work. The test results confirmed that all CFRP arrangements differ from CFRP strip width and arrangement, improved the strength and behavior of the specimens in different level significantly.