CFRP-钢界面粘结性能试验与数值模拟

碳纤维增强聚合物基复合材料（CFRP）与钢板的界面粘结性能为CFRP加固钢结构的关键问题之一。开展了17个CFRP板-钢板单搭接试件的拉伸剪切试验,研究了不同环氧粘结剂与CFRP材料的CFRP-钢界面力学行为和破坏模式;分析了粘结剂类型和CFRP材料对界面粘结滑移本构和界面剪切性能的影响,讨论了其承载力计算方法。结果表明：采用不同的粘结剂或CFRP材料,界面破坏形式和抗剪承载力均差异较大。采用Sika 330、Lica粘结剂的试件为CFRP板或钢板与胶层的界面破坏,采用Araldite粘结剂的试件为CFRP板浅表层离,采用Sika 30粘结剂的试件为胶层内聚破坏,采用SF（Sika S512/80）碳板的试件为CFRP板深层层离;Araldite试件的抗剪承载力为其他试件的1.7~2.9倍。Sika 330、Araldite及Lica试件粘结滑移曲线无明显下降段,属脆性破坏,而Sika 30与SF试件存在缓坡下降段,失效前有一定征兆;SF试件的粘结滑移本构可简化为三折线模型,其余试件则可简化为双线性模型。SF试件抗剪承载力需用Xia-a模型表征,其余试件则可用Xia-b模型表征。基于粘聚力模型对界面力学行为进行了数值模拟,结果表明,粘聚力模型可以较好地模拟界面的非线性力学行为,剥离应力对本单搭接试件的界面粘结强度影响很小。     

重组竹-混凝土界面粘结-滑移本构模型

为研究胶粘剂连接的重组竹-混凝土界面粘结性能及构建粘结-滑移本构模型,对44个重组竹-混凝土粘结试件进行单剪试验,并考虑了粘结长度、重组竹粘结宽度与厚度、混凝土强度及胶层厚度等因素对粘结性能的影响。研究结果表明：在不同影响因素下,试件破坏模式基本相同,均为混凝土表面发生剥离破坏,粘结界面间裂缝从加载端产生并向自由端发展,破坏过程分为弹性阶段、软化阶段和脱粘平台阶段;界面峰值剪应力随重组竹厚度、混凝土强度、胶层厚度增加而增大,随粘结宽度增加而减小。根据试验粘结-滑移曲线,建立了重组竹-混凝土界面粘结-滑移本构模型,与实验结果进行对比,该模型能较好地反映重组竹-混凝土界面剪应力与滑移量间的关系。     

CFRP片材-工程水泥基复合材料-混凝土复合界面单面剪切试验研究

为解决碳纤维增强树脂复合材料(CFRP)片材加固混凝土结构时CFRP片材易过早剥离及工程水泥基复合材料(ECC)加固混凝土结构极限承载力提高不足等问题,采用CFRP片材-ECC-混凝土复合界面,以同时发挥CFRP片材高抗拉强度和ECC多缝开裂及耐久性较好的优势。设计21个单面剪切试件并进行单面剪切试验,研究不同ECC厚度和混凝土/ECC强度对复合界面承载力、应变分布及粘结滑移曲线等影响规律。试验结果表明：设置ECC层的单面剪切试件破坏模式均为CFRP片材和ECC界面间的剥离破坏,有效延缓了CFRP片材的剥离,并可以有效地传递界面剪应力。与无ECC层的试件相比,设置ECC层试件的极限承载力增加了27.3%～59.6%。基于陆新征等提出的极限承载力计算模型,提出了考虑ECC厚度的复合界面单面剪切试件的极限承载力预测模型,计算值与试验值相吻合。采用不同粘结滑移模型对试验数据进行分析,对比结果表明：Ferracuti等提出的模型考虑的影响因素较全面且模型的拟合结果较好。     

钢-UHPC组合结构中栓钉剪力键力学性能研究

为深入研究栓钉在超高性能混凝土(ultra-high performance concrete,UHPC)和普通混凝土(normal concrete,NC)中的力学特性及破坏形态,对8个栓钉剪力键试件进行了推出试验,详细探讨了混凝土类型、栓钉直径及长度对栓钉剪力键极限抗剪承载力的影响规律;基于有限元模型,进一步分析栓钉的极限抗拉强度、直径、长径比及混凝土强度对抗剪性能的影响,并详细研究栓钉直径、长度及混凝土强度对栓钉剪应力有效分布长度的影响。结果表明:栓钉根部附近的剪切断裂是主要的破坏形式;与NC试件相比,UHPC试件的抗剪承载力和抗剪刚度更高,但延性较低;栓钉剪应力在根部出现峰值,并沿钉帽方向迅速衰减;栓钉直径对剪应力有效分布长度影响显著。最后,根据试验结果提出了栓钉剪断破坏模式下的荷载-滑移曲线及抗剪承载力计算公式,计算结果与试验结果吻合良好,可为工程设计提供一定的参考价值。     

高温下双搭接钢-CFRP板胶粘界面力学性能试验

高温环境下钢-碳纤维增强聚合物复合材料(CFRP)板的胶粘界面是CFRP粘贴加固钢结构的薄弱环节。为掌握温度对钢-CFRP板胶粘界面力学性能的影响,制作了双搭接接头试件,开展了3种胶粘剂在4种温度下(25℃、55℃、70℃和90℃)的静力拉伸试验。探索了接头试件的破坏模式、荷载-位移关系、CFRP板表面应变分布、界面剪应力分布和粘结-滑移关系等。结果表明:当温度低于55℃时,试件的破坏模式与胶粘剂种类相关性更大,当温度高于70℃时,不同胶粘剂的破坏模式具有相似性,且均出现了CFRP板撕裂。温度对不同胶粘试件的承载力影响存在差异,HJY-4105高韧性环氧树脂结构胶粘剂(HJY胶)试件的承载力随温度的升高而增大,LICA-100A/B 环氧树脂结构胶粘剂(LICA胶)试件的温度稳定性较差,Sikadur-30 CN双组份环氧结构加固碳板胶(SIKA30胶)试件在55℃时承载力最高。随着温度升高,胶粘层的剪切强度、界面剪应力峰值和剪切刚度下降,胶粘剂的延性增加,峰值剪应力不影响试件的抗拉强度。温度对粘结-滑移关系的影响显著,HJY胶随着温度的升高,粘结-滑移本构的延性增加,破坏模式由脆性破坏变为延性破坏。研究表明:合理的耐高温胶应用于钢结构加固,能适应自然高温环境的不利影响。      

基于双剪试验的铝合金板-混凝土界面粘结滑移性能研究

铝合金板具有轻质高强、延展性好、低温脆断敏感性小、耐腐蚀、易于成型等优点,可用于腐蚀及寒冷环境下的混凝土结构加固。该文基于双剪试验下的铝合金板-混凝土界面粘结滑移性能研究,完成了45个构件的双面纯剪试验,分析了混凝土强度等级、铝合金板表面粗糙度、铝合金板粘结长度和粘结宽度对粘结界面破坏机理、剥离承载力以及界面滑移的演化规律。研究表明:加载过程中界面应力从加载端向自由端逐步传递,且随着混凝土强度等级、铝合金板的粘结长度和宽度的增加,试件的剥离承载力也有所提高。但铝合金板的粘结长度存在一个有效粘结长度值,超过该值试件的剥离承载力将不会增加,同时铝合金板表面粗糙度对试件剥离承载力的提高没有实质影响。     

冻融循环对CFRP-烧结粘土砖界面粘结性能影响

为考察冻融循环对碳纤维增强聚合物复合材料(CFRP)-烧结粘土砖界面粘结性能的影响,通过模拟自然冻融环境,在试件经过不同次数的冻融循环后对其进行单面剪切试验。结果表明:在冻融循环作用下,CFRP-烧结粘土砖试件界面粘结性能发生了显著的退化,即随着冻融循环次数的增加,界面承载力和剪应力不断降低;界面剪应力在不同冻融次数下的分布具有相似性,均表现为随着荷载的增加剪应力逐渐由加载端向自由端传递,在传递过程中,有效传递长度变化不显著。在已有界面理论的基础上,根据试验提出了考虑冻融循环时间的界面粘结-滑移模型,通过对比分析,该模型能够很好地反映冻融循环作用下界面粘结性能退化规律。      

CFRP-火灾后混凝土界面快速剥离试验

该文完成了72个快速荷载下CFRP加固火灾后混凝土试件单面剪切试验,基于Dai模型对界面应变分布进行拟合,并探讨了混凝土强度、应变率和过火温度三种因素对界面剪切黏结强度、应变分布、黏结剪应力、界面黏结滑移关系和界面断裂能等黏结性能参数的影响。试验表明:界面剪切黏结强度、峰值剪应力和界面断裂能随着混凝土强度和应变率的提高而提高,但随着过火温度的升高而下降,在500℃以后下降尤为显著,过火温度为700℃的试件界面平均峰值剪应力相比于常温试件下降33.0%,界面断裂能下降83.8%;有效粘结长度随着混凝土强度和应变率的提高略有减小,但随着过火温度的升高而显著增大。常温试件的有效粘结长度在70 mm～90 mm之间,而过火温度为700℃的试件有效粘结长度达165 mm左右。     

锈蚀对钢板表面特性及CFRP板-锈蚀钢板界面黏结性能的影响

为研究锈蚀对钢板表面特性及碳纤维增强树脂复合材料(CFRP)板-锈蚀钢板界面黏结性能的影响,开展了6批次锈蚀钢板表面特性测试及22个CFRP板-锈蚀钢板双搭接试件的拉伸试验,揭示了锈蚀对钢板表面形貌与粗糙度、表观接触角与表面自由能以及CFRP板-钢板黏结界面破坏模式、有效黏结长度、极限荷载的影响.研究结果表明:随着腐蚀...     

带栓钉波形钢板混凝土组合构件粘结滑移性能与承载力试验研究

通过11个带栓钉的波形钢板混凝土组合构件在单调荷载下的推出试验和1个自然粘结构件的对比试验,研究带栓钉波形钢板混凝土组合构件的破坏形态、裂缝模式、荷载-滑移特性、波形钢板应变分布和承载力等。结果表明:带栓钉波形钢板混凝土组合试件的破坏形态以混凝土劈裂为主。试件的荷载-滑移曲线由上升阶段、下降阶段、残余阶段三个部分组成。由于混凝土和栓钉的组合作用,波形钢板自由端存在受拉区,产生过零点现象。带栓钉波形钢板混凝土组合试件的抗剪承载力随栓钉直径、数量的增长呈线性增长,而在一定条件下,栓钉长度、钢板厚度对抗剪承载力影响不大,另外在200 mm范围内适当增大栓钉间距对抗剪承载力也有提高。基于试验结果和力的扩散原则,分别提出了考虑栓钉影响的波形钢板混凝土界面粘结滑移本构模型以及带栓钉的波形钢板混凝土推出试件的承载力计算公式,所提模型与试验结果吻合良好,承载力公式计算结果与试验结果总体相符且偏于安全。     

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%。      

CFRP加固混凝土梁各受力阶段的剥离机理

粘贴碳纤维片加固混凝土梁的试验数据和破坏模式表明,在锚固措施可靠的情况下,界面粘贴失效或基面混凝土剥离是加固混凝土梁的主要早期破坏形态。为研究混凝土梁不同受力阶段对界面粘结失效或混凝土剥离的影响程度,针对实际加固工程中常见的混凝土梁损伤状况并结合室内试验结果,分别研究了粘贴碳纤维片加固完整梁及不同开裂程度梁在不同受力阶段中的界面应力分布与剥离机理,指出了加固梁的开裂或裂缝扩展是导致界面或粘贴基面混凝土剥离的主要原因。最后,结合实际混凝土梁的损伤特点,提出了加固设计施工过程中的注意事项及应采取的技术措施。     

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.     

Ultimate behaviour of adhesively bonded FRP lap joints

This paper deals with a numerical investigation on double-lap and symmetrical single-lap joints subjected to shear/bending moment and axial force. The analysis has been developed using the theoretical model proposed by the author in [Ascione F. Mechanical behaviour of FRP adhesive joints: a theoretical model; 2007].The mechanical behavior of the adhesive is modeled through two sets of independent interfacial springs capable of characterizing the normal and transversal interactions, respectively. The adherents are modeled following the hypotheses of the beam technical theory. The mathematical model is based on two fundamental hypotheses: the possibility to separate the shear-flexure problem from the extensional one; the total fracture energy is additionally broken down in a term relative to mode I of fracture (opening) and in a term relative to mode II of fracture (sliding).Five dimensionless parameters which influence the design problem of the joints are identified. Several examples of the ultimate domains of the interface between the adherents are also presented as well as comparisons with some results reported in literature.     

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.     

Prediction of debonding strength of tensile hybrid bonded joints using fracture mechanics

In order to improve the debonding strength of double shear lap (DSL) joints between aluminum plates and carbon fiber reinforced plastic (CFRP) plates, a hybrid bonded fiber reinforced plastics (HB-FRP) technique was proposed in this paper. Debonding strength of the HB-FRP was tested and investigated analytically and numerically. Fracture failure of the aluminum-adhesive interface was identified as the dominant failure mode of the joint. Compared with normal bond joints, the debonding strength of HB-FRP joints can be increased by 71% in experiments. The strain energy release rate (SERR) criterion based on linear elastic fracture mechanics (LEFM) was adopted to estimate the debonding strength of bond joints. Good agreement among theoretical predictions, numerical simulations and experimental data were achieved.     

胶膜连接碳纤维增强树脂复合材料板-钢搭接接头室温条件的力学性能试验

针对碳纤维增强树脂（CFRP）复合材料板-钢搭接接头连接的糊状胶黏剂粘层厚一致性控制较难、铅垂向成形可能不易等问题,将糊状胶黏剂换成胶膜,制作了胶膜连接的五种粘结长度共15个CFRP板-钢双搭接接头试件,并对该胶膜连接的CFRP板-钢搭接接头进行了室温条件下的破环模式、有效粘结长度、传力规律、粘结-滑移本构、承载力等的试验研究。结果表明:所用胶膜的连接强度略高于CFRP板层间强度（即碳纤维与树脂基体的黏聚强度）;室温下,所用胶膜连接的CFRP板-钢搭接接头有效粘结长度约为80 mm;加载初期,剪应力最大值位于接头钢板端;继续加载,其位置向接头CFRP板端移动;加载末期,其位置位于距接头钢板端20 mm （粘结长度不超过80 mm时）或者50 mm （粘结长度不小于120 mm时）处;胶膜连接的CFRP板-钢搭接接头界面粘结-滑移模型为近似梯形,不同于胶黏剂连接的CFRP板-钢搭接接头的近似三角形,胶膜连接接头的延性大为提升;所用胶膜连接接头界面峰值剪应力、断裂能、界面刚度等代表值（可视为准平均值）分别为四种典型商品胶黏剂连接接头的1.2~3.0倍、1.6~5.7倍和5.4~7.5倍;在粘结长度不小于有效粘结长度条件下,所用胶膜连接接头的抗拉承载力代表值为四种典型商品胶黏剂连接接头的1.25~2.39倍;胶膜连接接头的抗拉承载力、最大位移的变异系数与糊状胶黏剂连接接头相差不大。      

Mechanical characterization of steel/CFRP double strap joints at elevated temperatures

This paper examines the mechanical performance of steel/CFRP adhesively-bonded double strap joints at elevated temperatures around the glass transition temperature (T_g, 42 °C) of the adhesive. A series of joints with different bond lengths were tested to failure at temperatures between 20 °C and 60 °C. It was found that the joint failure mode changed from adherend failure to debonding failure as the temperature approached T_g. In addition, the ultimate load and joint stiffness decreased significantly at temperatures near to and greater than T_g, while the effective bond length increased with temperature. Based on the ultimate load prediction model developed by Hart-Smith for double lap joints and kinetic modelling of the mechanical degradation of the adhesive, a mechanism-based model is proposed to describe the change of effective bond length, stiffness and strength degradation for steel/CFRP double strap joints at elevated temperatures. The modelling results were validated by the corresponding experimental measurements.