风电叶片用胶粘剂剪切疲劳性能和蠕变性能分析

简述了胶粘剂在风电叶片中的重要性,风电叶片大多采用环氧胶粘剂。从叶片的设计需求角度,对比测试了国产胶粘剂和进口胶粘剂的玻璃化转变温度、剪切疲劳和蠕变性能,并对两种胶粘剂的粘接断面进行形貌扫描,简单分析得出:进口胶粘剂的粘接断面是比较典型的韧性断裂,国产胶粘剂的粘接断面呈现韧性和脆性结合体;提高胶粘剂的韧性,并不断改良增韧体系和环氧树脂基体的相容性是国产胶粘剂亟待解决的问题。     

表面内嵌FRP筋混凝土粘结-滑移本构关系试验研究

通过对一组表面内嵌FRP筋混凝土试件进行拉拔试验,分析表面内嵌FRP筋混凝土的受力过程和破坏模式;研究FRP筋直径、粘结长度和FRP筋类型等因素对粘结滑移性能的影响。结果表明,试件的破坏模式表现为FRP筋与结构胶界面破坏、结构胶与混凝土界面剥离、FRP筋被拉断和结构胶劈裂四种破坏模式;内嵌BFRP筋试件的粘结应力随粘结长度的增长而增大,而内嵌GFRP筋试件的粘结应力随粘结长度的增长而减小。因FRP筋泊松比的降低和剪切滞后效应,试件的粘结应力随着FRP筋直径的增大而减小。同时,对试验结果进行处理分析,建立了一种适用于表面内嵌FRP筋混凝土粘结-滑移本构关系模型,并给出模型特征点的数学表达式,将拟合曲线与试验曲线进行对比分析。结果表明,该本构关系能够较为准确地模拟表面内嵌FRP筋混凝土的粘结滑移性能。     

振动注塑PP/CaCO3的拉伸蠕变研究

采用自制的机械振动注塑机,在不同振动频率和振动压力下成型PP/CaCO3试样.考察了试样的拉伸蠕变.结果表明,当振动压力一定时,PP/CaCO3的拉伸应变随着振动频率的增加先增大后减小,当振动频率为15 Hz时达最大;而当振动频率一定时,材料的拉伸应变随着振动压力的增大而减小.通过对不同成型条件下注塑的PP/CaCO3材料进行了短时拉伸实验和动态力学性能测试,从材料柔性和刚性分析其蠕变原因.     

PE100管及其热熔接头的蠕变裂纹扩展行为

聚乙烯(PE)管性能优异,广泛应用于城市水及燃气供应系统。PE管的主要破坏形式是长期静压载荷下的慢速裂纹扩展失效。在蠕变条件下,采用光滑试样和裂纹圆棒试样对PE100管及其热熔接头进行了测试,得到了基于蠕变断裂参数C*的蠕变裂纹扩展动力学关系式。利用扫描电子显微镜(SEM)分析了裂纹圆棒试样的断面形貌,对比分析结果发现,蠕变裂纹扩展失效模式对应的最大应力为15.05 MPa,热熔接头熔合面分布有约11个/mm^2、直径范围为1~5μm的微气孔,热熔接头断裂微纤平均长度比母材约小20%~45%。当热熔对接时,熔合面存在的微气孔以及系带分子的浅渗透是导致PE100热熔接头蠕变裂纹扩展抗力降低的主要原因。     

均苯四甲酸酐固化聚丁二烯环氧树脂胶粘剂的研究

采用均苯四甲酸酐(PMDA)固化聚丁二烯环氧树脂(ELPB),制备了ELPB/PMDA耐高温胶粘剂,并使用傅里叶红外光谱仪(FT-IR)、热重分析仪(TGA)、拉力机和数码显微镜对固化产物的性能进行了表征。实验结果表明,在200℃固化2h的条件下,PMDA可以对ELPB成功地固化;固化后的胶粘剂具有良好的耐热性能,其失重3%时的分解温度为300℃;该胶粘剂对铝/铝合金的粘接强度达到15MPa;剪切破坏是以内聚破坏为主的混合破坏,表明该胶粘剂对金属有较好的粘接性能。     

激光表面处理提高铝合金胶接接头强度的研究

粘接作为重要的汽车轻量化连接技术之一,胶接接头的强度和性能是我们关注的重点,胶接接头的强度和性能完全取决于胶粘剂接触的表面类型,因此在粘接之前对基材表面进行一定处理是粘接工艺中最重要的环节之一。金属的表面处理包括溶剂擦拭、机械打磨、化学清洗和酸蚀。激光表面处理是一种新型绿色环保的表面处理工艺,它可以高速有效的清洁材料表面附着物,并且改变材料表面微观结构及材料表面自由能及浸润性。从而提高粘接接头十字拉伸强度、单搭接拉伸剪切强度和接头耐水性能。通过激光处理,所有接头的破坏形式由界面破坏转为内聚破坏。对铝合金环氧结构胶2098G胶接接头而言,十字拉伸强度、剪切强度和水浴剪切强度,激光处理后比溶剂擦拭分别提高了17.8%,133.8%,88.1%。对铝合金聚氨酯结构胶TS6015胶接接头而言,十字拉伸强度、剪切强度和水浴剪切强度,激光处理后比溶剂擦拭分别提高了698%,225%,223%。激光表面处理有效的使铝合金胶接接头的强度达到胶的本体强度的94%~100%,是铝合金粘接的有效表面处理方法。     

缓凝型环氧树脂建筑结构胶的制备与性能研究

以高活性酚醛胺(T-31)为主固化剂、聚酰胺树脂(PA)为辅助固化剂及增韧改性组分、气相白炭黑为触变改性组分,以水泥、超细石英砂及石棉纤维为增稠及增强改性组分,制备了高温施工适用期较长、触变性较好、强度较高及韧性较佳的EP(环氧树脂)建筑结构胶。研究结果表明:该结构胶的适用期为75min,并且垂直施工无流淌现象;该结构胶的1d压缩强度为60MPa、14d压缩强度为80MPa、14d拉伸强度为35MPa、14d剪切强度为17MPa且其与混凝土界面的正拉粘接强度为6.0MPa(界面破坏形式为混凝土内聚破坏),完全满足GB50728—2011标准中的指标要求。     

将动态应力和静态应力相结合研究环氧胶粘剂的热─力学性能

本文研究了动态应力和静态应力在加对环氧胶粘剂力学和热学性能的影响．在玻璃化温度范围内把剪切蠕变和扭力摆动同时作用于胶接接头，会使接头的剪切强度增大，胶粘剂的玻璃化转变温度升高．在接近胶粘剂的玻璃化转变温度Ｔｇ时施加相同的负载应力．对上面提到的胶接接头性能会产生相反的作用．本文研究中所选用的整个温度范围内，对各种环氧组成物，胶粘剂从玻璃态到高弹态转变宽度的增加均是由动态度力在加作用产生的．我们认为进行应力实验时，聚合物网络变硬而使玻璃化转变加宽．发现在温度低于Ｔｇ，试验前空动态应力和静态应力且加支配作用的试样的第一次ＤＳＣ扫描吸热线的面积和接头强度是线性关系，观测的结果与文献数据相一致，树脂的玻璃化转变温度（由ＤＳＣ扫描图上第一峰测得）和接头的剪切强度呈线性关系．由实验观测的结果和一些有关文献可知，要想提高胶接强度又改变胶粘剂的耐热性，主要采取使用状链小范围内取向以及增子内网络强极性点间的相互作用等物理方法．文中讨论了应力叠加会有改变化学交联的可能性，但未见有这种变化发生．     

风电叶片用环氧结构胶疲劳性能研究

采用拉拉单向剪切疲劳测试评价了叶片用环氧结构胶的疲劳性能,根据ISO 9664:1995,设定平均应力τm=0.35τR,频率为30Hz,振幅为2.0≤τa≤3.0MPa,测试环氧结构胶疲劳次数,得到S-N曲线并计算疲劳极限,研究胶层厚度、增韧剂及试样破坏形式等因素对疲劳性能的影响。本研究证明叶片用环氧结构胶疲劳性能指标对叶片设计和使用具有重要价值。     

热力耦合作用下浇注式沥青混凝土三轴蠕变特性研究

为了深入研究浇注式沥青混凝土沥青混合料在温度、应力耦合作用下的三轴蠕变特性,采用MTS815试验机开展了不同温度、不同应力水平和不同围压条件下的三轴蠕变试验,获取了相应的蠕变曲线,并将改进的Burgers模型推广到三维形式,用来描述浇注式沥青混凝土的蠕变本构关系。研究结果表明：浇注式沥青混凝土蠕变曲线的第一阶段不明显,这反映出其内部空隙率较低;蠕变变形值随温度升高和偏应力水平增大而明显增大,这反映出高温重载共同作用是浇注式沥青混凝土路面出现车辙的决定性因素;蠕变变形随围压增大略有减小,围压对蠕变变形有抑制作用,三轴蠕变试验获得的蠕变规律较之单轴蠕变试验更能反映实际受力过程中的变形规律,三维的改进Burgers模型能够准确反映热力耦合作用下浇注式沥青混凝土的蠕变特性。     

Numerical study of the effect of carbon fiber/epoxy resin adhesive thickness on the creep behaviour of carbon steel plate joints

Nowadays, the use of adhesive and adhesively bonded joints have been considerably appreciated in the industry due to the dramatic reduction in bonding strength, reduced stress concentration, rust prevention, uniform bonding of the bonding surface and a significant reduction in costs compared to other types of permanent joints such as welding. In this study, the effect of adhesive thickness on creep behaviour of a single lap adhesive joint with the aid of Abaqus FEM software is investigated. It should be noted that the two-layer and two-dimensional models are considered, in which their adhesive layer is made of a reinforced epoxy resin with 0.5% carbon fiber and the adherend layers are made of carbon steel plates, which is affected by tensile forces. Since the main purpose of this paper is to study the effect of adhesive thickness on the adhesive joints behaviour, the effects of the distribution of shear stress, effective stress and creep strain were studied in different thicknesses of the adhesive layer. The results show that by increasing the thickness, the stress and the creep strain decrease, and over time, the stress decreases and the creep behaviour of adhesives increases.     

Rheological modeling and finite element simulation of epoxy adhesive creep in FRP-strengthened RC beams

We have shown that a significant creep occurs at the concrete–fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete–FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete–FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained.     

Photoelastic Stress Analysis of Bonded Lap Shear Joints Having Thermoplastic Adherends

The effects of substrate stiffness and modulus on joint strength and stress distribution were investigated for a series of nylon substrates bonded with an epoxy adhesive. Substrate stiffness and modulus were controlled by the level of glass filler in the resin. Single lap shear samples having both identical (“self-bonded”) and dissimilar (“cross-bonded”) substrates were investigated. For the self-bonded samples, lap shear strength was found to increase with increasing substrate modulus and stiffness. The strengths of the cross-bonded samples were intermediate to the strengths of the corresponding self-bonded samples. Photoelastic techniques were used to observe stress patterns in the lap joints during testing. One type of stress pattern was observed for all self-bonded samples regardless of substrate stiffness. Two patterns, one for the stiff substrate and one for the more flexible substrate, were observed for cross-bonded samples. The photoelastic analysis agreed qualitatively with predictions of stress distributions based on linear elastic and linear elastic/perfectly plastic theoretical models.     

Effects of primer and annealing treatments on the shear strength between anodized Ti6Al4V and epoxy

The effects of primer and annealing treatments on the shear strength between anodized Ti6Al4V and epoxy were investigated. Primer coating improved the shear strength between anodized Ti alloy and epoxy by up to 81.3% using concurrent curing compared with that of control specimens. After annealing of anodized Ti alloy and applying primer, the shear strength of the specimen was further increased by 6.4% due to the formation of stable TiO₂ transferred from TiO in the anodization process. SEM analysis revealed the specimen without primer and annealing treatments showed adhesive failure between epoxy–alloy interface and discontinuous cohesive failure of epoxy. Primer coating initiated a new interfacial failure mode between the oxide layer and alloy due to the improved bonding strength between epoxy and oxide layer. In addition, annealing and primer treatments generated large tracts of epoxy continuous cohesive failure, showing good agreement with its higher shear strength and work of fracture.     

低模量硫化硅橡胶粘接研究

采用sol—gel工艺自制的SiO2补强增韧环氧树脂作为胶粘剂,对低模量硫化硅橡胶与金属或复合材料进行粘接试验,分析胶粘剂中SiO2理论含量及粘接工艺对粘接性能的影响,并把硫化硅橡胶放在改性环氧树脂中进行溶张试验,探索胶粘剂对硅橡胶的粘接机理、结果表明,随着SiO2先驱体-有机硅烷含量的增加,硅橡胶的溶胀程度提高改性环氧树脂胶粘刺能浸入硅橡胶的表层,对硅橡胶具有良好的亲和力。用该胶粘剂对硅橡胶与金属或复合材料进行粘接时,取得了良好的粘接效果。     

Analysis of the nonlinear creep behavior of concrete/FRP-bonded assemblies

This paper investigates the creep behavior of adhesively bonded concrete/fiber-reinforced polymer (FRP) joints, through experimental and modeling approaches. The first part proposes a methodology for predicting the long-term creep response of the bulk epoxy adhesive; such a procedure consists of (1) performing short-term tensile creep experiments at various temperatures and stress levels, (2) building the creep compliance master curves according to the time–temperature superposition principle in order to assess the long-term evolution for each stress level, and (3) developing a rheological model whose parameters are identified by fitting the previous master curves. In our case, it was found that master curves (and, consequently, parameters of the rheological model) are dependent on the applied stress level, highlighting the nonlinear creep behavior of the bulk epoxy adhesive. Therefore, evolution laws of the model parameters were established to account for this stress dependence. The second part focuses on the creep response of the concrete/FRP assembly in the framework of a double lap joint shear test configuration. Experiments showed that creep of the adhesive layer leads to a progressive evolution of the strain profile along the lap joint, after only one month of sustained load at 30% of the ultimate strength. Besides, a finite element approach involving the abovementioned rheological model was used to predict the nonlinear creep behavior of the bonded assembly. It confirmed that creep modifies the stress distribution along the lap joint, especially the stress value at the loaded end, and leads to a slight increase in the effective load transfer length. This result is of paramount interest since the transfer length is a key parameter in the design of FRP-bonded strengthening systems. Moreover, instantaneous and long-term calculated strain profiles were found in fair agreement with experimental data, validating the modeling approach.     

一种低蠕变单组分应变胶的研制

为便于在应变计贴片量少的场合下使用,根据对应变计贴片胶（以下简称应变胶）的性能要求,研制了一种单组分应变胶,其蠕变小,粘接强度高,粘贴工艺简单,贮存期长,完全达到粘贴应变计的使用要求。介绍了应变胶的制备原理、配方和制备工艺。讨论了双酚A型环氧树脂相对分子质量、F-44酚醛环氧树脂用量、聚乙烯醇缩醛用量、固化剂用量、固化条件等因素对粘贴后应变计蠕变和剪切强度等性能的影响。将该单组分应变胶与国内某种双组分应变胶进行了性能对比测试,结果表明,该单组分应变胶具有良好的低蠕变特性。     

Photoelastic Stress Analysis of Bonded Lap Shear Joints Having Thermoplastic Adherends

The effects of substrate stiffness and modulus on joint strength and stress distribution were investigated for a series of nylon substrates bonded with an epoxy adhesive. Substrate stiffness and modulus were controlled by the level of glass filler in the resin. Single lap shear samples having both identical (“self-bonded”) and dissimilar (“cross-bonded”) substrates were investigated. For the self-bonded samples, lap shear strength was found to increase with increasing substrate modulus and stiffness. The strengths of the cross-bonded samples were intermediate to the strengths of the corresponding self-bonded samples. Photoelastic techniques were used to observe stress patterns in the lap joints during testing. One type of stress pattern was observed for all self-bonded samples regardless of substrate stiffness. Two patterns, one for the stiff substrate and one for the more flexible substrate, were observed for cross-bonded samples. The photoelastic analysis agreed qualitatively with predictions of stress distributions based on linear elastic and linear elastic/perfectly plastic theoretical models.     

Shear creep behaviour of elastomeric adhesives

The shear creep behaviour of elastomeric adhesives has been investigated at various temperatures, loading stresses and adhesive thicknesses. Three adhesive types were included in the study: two polysulphides, one silicone and one polyurethane elastomer. The creep compliance of the two polysulphide adhesives could be described by an Arrhenius-type relationship incorporating time, temperature and stress. The silicone and polyurethane adhesives, on the other hand, showed an initial creep response followed by a long period of zero creep over the ranges of temperature and load studied.     

Comparison of fracture behavior between acrylic and epoxy adhesives

An experimental study was conducted on the strength of adhesively bonded steel joints, prepared epoxy and acrylic adhesives. At first, to obtain strength characteristics of these adhesives under uniform stress distributions in the adhesive layer, tensile tests for butt, scarf and torsional test for butt joints with thin-wall tube were conducted. Based on the above strength data, the fracture envelope in the normal stress-shear stress plane for the acrylic adhesive was compared with that for the epoxy adhesive. Furthermore, for the epoxy and acrylic adhesives, the effect of stress triaxiality parameter on the failure stress was also investigated. From those comparison, it was found that the effect of stress tri-axiality in the adhesive layer on the joint strength with the epoxy adhesive differed from that with the acrylic adhesive. Fracture toughness tests were then conducted under mode l loading using double cantilever beam (DCB) specimens with the epoxy and acrylic adhesives. The results of the fracture toughness tests revealed continuous crack propagation for the acrylic adhesive, whereas stick-slip type propagation for the epoxy one. Finally, lap shear tests were conducted using lap joints bonded by the epoxy and acrylic adhesives with several lap lengths. The results of the lap shear tests indicated that the shear strength with the epoxy adhesive rapidly decreases with increasing lap length, whereas the shear strength with the acrylic adhesive decreases gently with increasing the lap length.