胶层尺寸对单搭胶接接头性能的影响研究

针对汽车车身中应用日益广泛的钢板胶接结构,通过试验得到了不同胶层尺寸对胶接接头承载能力的影响规律,建立了钢板单搭接头的三维弹塑性有限元模型,分析了胶层尺寸对胶接接头应力分布的影响.研究结果表明:随着胶层厚度的增加,胶接件的承载能力呈先升后降的趋势,合理的胶层厚度应为0.3-0.5 mm;无论胶层厚度为多少,增加搭接区域胶层的长度或宽度.均会提高胶接件的承载能力.     

旋翼调整片粘接强度分析与影响因素研究

详细分析了旋翼调整片粘接剥离破坏过程和应力分布变化,并研究了粘接宽度和胶层厚度对粘接强度的影响。使用共固化制备相应的粘接试样,通过剥离试验得到接头的破坏模式及载荷-位移曲线。研究结果表明:接头有限元数值分析结果与试验相契合,接头破坏形式为调整片粘接界面的破坏,破坏为从左向右和由边向中逐渐发生失效;粘接强度随胶接宽度的增加而提高,但增长速度逐步变缓,80 mm为较优搭接宽度值;粘接强度受胶层厚度影响较小,增加厚度时粘接强度先缓慢增加后下降。     

CFRP与铝板胶螺混合连接结构拉伸性能研究

基于三维渐进损伤理论,建立了复合材料层合板-铝板双搭接胶接连接、螺栓连接、胶螺混合连接结构拉伸强度预测模型,数值仿真结果与试验高度吻合,验证了所建模型的可行性。在此基础上,探究了搭接宽度、搭接长度、胶层厚度、接触面摩擦系数和螺栓个数等参数对胶螺混合连接结构拉伸性能的影响。结果表明:随着搭接宽度和搭接长度的增加,接头失效载荷先逐渐增加后趋于稳定,最优搭接宽度和搭接长度为30 mm和35 mm;胶层厚度对混合连接结构的拉伸失效载荷基本没有影响;胶螺混合连接结构中螺栓接头和层合板之间、螺栓与孔之间的摩擦系数越大,连接结构的拉伸失效载荷越大;在搭接区域相同的情况下,双钉混合连接结构的拉伸失效载荷比单钉的拉伸失效载荷提高了69%。     

高性能航空KH-CL-RTV-2型硅橡胶胶粘剂的粘接工艺研究

以高性能航空KH-CL-RTV-2型硅橡胶作为胶粘剂,采用单因素试验法着重考察了固化工艺、稀释剂用量、金属基材、单双面喷胶、胶层厚度和填料等因素对胶粘剂粘接强度的影响,从而优选出胶接件的最佳施胶工艺;最后利用硅橡胶黏度-时间曲线对胶接件的固化过程进行了验证和解释。研究结果表明:稀释剂环己烷用量对胶接件的粘接强度无影响;胶接件的最佳施胶工艺是双面喷胶、胶层厚度为0.50 mm、被粘基材为除油打磨处理后的铝合金、固化温度为50℃和固化时间为36 h,此时胶接件的粘接强度(为3.04 MPa)相对较大。     

CRH3型动车组侧窗的粘接结构设计

根据CRH3型高速动车组侧窗的结构,设计了侧窗粘接接头的形式及粘接密封结构;根据胶粘剂厂商提供的数据及粘接工艺,分析设计了侧窗粘接厚度和接缝宽度。研究结果表明:侧窗粘接接头应选择搭接接头,粘接厚度的理论设计值为5～10mm,接缝宽度的理论设计值为10～17mm;将动车组侧窗的受力情况进行模型化,通过理论计算,并引入衰减因子和安全因子,可推算出侧窗粘接用聚氨酯(PU)弹性胶粘剂的剪切强度需超过0.54MPa,而目前国内外PU结构胶的剪切强度均超过此数值。     

冲击载荷作用下胶层厚度对金属双搭接胶接接头应力分布的影响

采用LY12铝合金材料在Ansys12.0软件平台上建立环氧树脂胶粘剂双搭接胶接接头有限元模型进行分析,着重考察了在冲击载荷作用下胶层厚度的改变对胶接接头应力分布的影响。研究结果表明:在一定范围内,随着胶层厚度的增加,胶接接头中最大应力值逐渐下降,而最小应力值开始先下降,在胶层厚度为0.4 mm时最小,之后应力值又继续增大,且最大应力值总是出现在胶层界面的边缘处;在冲击速率为3.4 m/s时,胶接接头在0.4、0.6 mm的胶层中节点的轴向应力S_x、剥离应力S_y、剪切应力S_(xy)、第一主应力S_1、等效应力S_(eqv)随着胶层厚度的增加,波动范围变窄,应力峰值也变小,而胶层厚度为0.2 mm时应力值波动异常剧烈,峰值很大。     

动车组座椅弹性支撑粘接接头设计

对动车组座椅弹性支撑的粘接接头进行了设计,采用Bigwood法测算出胶层在接头边缘部位承受的极限载荷,通过试验对两种备选胶粘剂老化前后的强度进行了测试并计算其特征参数。研究结果表明:粘接面长度、宽度值至少应大于96 mm时,可以避免应力集中;极限载荷约为5.6 MPa;胶粘剂A特征参数为-3.25 MPa,胶粘剂B为7.75 MPa,胶粘剂B可满足接头要求。     

胶接双悬臂梁极限载荷影响因素分析

为了更加精确地计算风电叶片厚胶层胶接接头的极限承载能力,给出了一种基于虚拟裂纹闭合技术的胶接接头有限元建模方法,研究了粘接胶厚度和铺层结构弯曲刚度对胶接双悬臂梁极限承载能力的影响。首先,给出了基于虚拟裂纹闭合技术的胶接接头极限载荷计算的有限元建模方法;然后,建立了胶接双悬臂梁试验件的有限元模型,并预测了剥离载荷作用下的极限承载能力;最后,基于胶接双悬臂梁的有限元模型,计算了不同粘接胶厚度和铺层刚度下的双悬臂梁极限承载能力。研究结果表明:胶接接头开裂行为可以采用虚拟裂纹闭合法进行模拟,模拟结果与试验结果吻合良好;随着粘接胶厚度的增加,胶接结构承载能力增加;随着铺层结构弯曲刚度的增加,胶接结构极限承载能力增加;基于虚拟裂纹闭合法的胶接接头建模方法,可以用于风电叶片厚胶层胶接接头的失效模拟。     

不同胶厚对硬聚氯乙烯板搭接强度的影响

为验证不同胶层厚度对硬质聚氯乙烯(PVC)板材单搭接接头强度的影响,对不同胶层厚度的单搭接板材件进行拉伸-剪切载荷试验,确认胶层厚度会影响搭接接头的粘接效果,且胶层厚度由0.2 mm增加到2 mm时,搭接件能承受的最大应力由3.59 MPa减小至2.51 MPa;通过有限元仿真得出,当胶层的厚度由0.2 mm增加到2 mm时,搭接件能承受的最大应力由3.32 MPa减小到2.59 MPa;实验与仿真均得出了随着胶层厚度增加,搭接强度变弱的结果。对不同胶层厚度的搭接板材进行仿真,得出最大应力均出现在胶层的边缘位置,因此胶层边缘位置容易先发生破坏;与无胶瘤时相比,胶瘤的存在能减少胶层边缘处的应力集中现象。与无胶瘤的搭接板材件相比,胶瘤存在时的搭接板材件强度提升了20%,胶瘤的存在显著增加了搭接的强度性能。仿真结果与实验结果相比较,误差在10%内,仿真模型有较好的准确度。     

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。     

Effect of protrusion at the ends of bondline in single lap joints under tension and bending

In this work, elasto-plastic stress analysis of single lap joints with and without protrusion in adhesive bondline subjected to tension and bending was carried out using 2D non-linear finite element analysis and confirmed experimentally. AA 2024-T3 aluminum adherends were bonded with SBT 9244 film adhesive. The protrusion was obtained by extending the adhesive film by 2?mm from the overlap length at both overlap ends. Three different adherend thicknesses and overlap lengths for each loading and bondline type were used. The joints with and without protrusion, for comparison, were loaded with the same load for each adherend thickness and overlap length. Finally, it was observed that the protrusion reduces the strength in the joint under tension, while the protrusion increases the strength in the joint under bending.     

Experimental study of adhesively bonded CFRP joints subjected to tensile loads

The tensile performance of adhesively bonded CFRP joints has been investigated experimentally. In this study, overlap length, adherend thickness, adherend width and scarf angle were chosen as design parameters. All load–displacement curves are linear, except that the thicker single-lap joints behave slightly nonlinearity due to the bending effect caused by eccentric loading. The lap shear strength is not directly proportional to overlap length, adherend thickness, adherend width and scarf angle for the brittle adhesive studied in the paper. The major failure mode includes adhesive shear failure and adherend delamination failure, sometimes accompanying with some fiber pull-out. Finally, the lap shear strength of three different lap types with similar bonding area (W=25 mm, L=10 mm, θ=5.71°) and adherend thickness (0.96 mm) was analyzed. It is found that the double-lap joint has the highest ultimate failure load. However, when considering the lap region weight, the scarf-lap joint is the most efficient.     

The determination of dynamic strength of single lap joints using the split Hopkinson pressure bar

The current investigation focuses on the determination of the strength of adhesive-bonded single lap joints under impact with the use of a split Hopkinson pressure bar (Kolsky bar). For this, experiments were conducted at different loading rates, for identical metallic adherends bonded by a two-part epoxy adhesive. Four different types of specimens were adopted, all with a given adhesive thickness. The length of overlap and the width of the adherends were varied resulting in four different areas of overlap. It was found that the average strength, as calculated from the readings obtained from a Kolsky bar, increases with decrease of overlap area. An elastodynamic model for the shear strain of the adhesive-bonded single lap joint was developed to investigate this drastic effect of overlap area on the average strength of the joint. The mathematical model was found to be dependent on both the material properties of the adherend and adhesive, as well as the structural properties of the joint, viz. the width and the thickness of the adhesive layer. A combined experimental-numerical technique was used to predict the strain distribution over the length of the bond in the adhesive. It was found that the edges of the adhesive were subjected to maximum strain, while a large part of the adhesive was found to exhibit zero shear strain. The effect of the lap length and the width was studied individually. The cumulative effect of averaging the strain over the entire overlap area, was decreased shear strain for an increased overlap area. The Kolsky bar was identified to give conservative values of the shear strength of an adhesive bonded lap joint under high rates of loading.     

Analysis of tubular adhesive joints with a functionally modulus graded bondline subjected to axial loads

The strength and lifetime of adhesively bonded joints can be significantly improved by reducing the stress concentration at the ends of overlap and distributing the stresses uniformly over the entire bondline. The ideal way of achieving this is by employing a modulus graded bondline adhesive. This study presents a theoretical framework for the stress analysis of adhesively bonded tubular lap joint based on a variational principle which minimizes the complementary energy of the bonded system. The joint consists of similar or dissimilar adherends and a functionally modulus graded bondline (FMGB) adhesive. The varying modulus of the adhesive along the bondlength is expressed by suitable functions which are smooth and continuous. The axisymmetric elastic analysis reveals that the peel and shear stress peaks in the FMGB are much smaller and the stress distribution is more uniform along its length than those of mono-modulus bondline (MMB) adhesive joints under the same axial tensile load. A parametric evaluation has been conducted by varying the material and geometric properties of the joint in order to study their effect on stress distribution in the bondline. Furthermore, the results suggest that the peel and shear strengths can be optimized by spatially controlling the modulus of the adhesive.     

Photoelastic Determination of Flaw Size and Distribution Effects on Adhesively Bonded Lap Joints

It is well known that the load carrying capacity of adhesively bonded lap joints can be influenced by the presence of flaw-like defects which are often created during its bonding process. To design an effective adhesive joint containing possible bonding defects, adequate knowledge and understanding of the shear stress distribution along the entire lap joint are necessary.

This paper describes an investigation into the effects of internal adhesive flaw size and distribution on the fracture behaviour of adhesively bonded lap joints. Photoelasticity is used to gain a quantitative understanding of the localized shear stress concentrations due to the presence of the internal flaws along the bonding layer. It is observed that a 20% increase in the maximum shear stress may be induced when an isolated central flaw of S. O mm was extended to 37.5 mm representing a flaw size of 75% of the lap length. For the presence of multiple flaws along the bonding line, there is no significant effect of the flaw separation distance on the maximum shear stresses. There is, however, a marked increase in the maximum shear stress up to about 45% when a flaw size is increased from 2.5 mm to 7.5 mm.     

Investigation of accumulated laser fluence and bondline thickness effects on adhesive joint performance of CFRP composites

In the present study, both the effects of accumulated laser fluence as surface treatment and bondline thickness on adhesive bonding of carbon fiber reinforced polymer (CFRP) composite materials were investigated. Proper CFRP composite surfaces for adhesive bonding were obtained by a laser treatment process using pulsed CO₂ laser. Laser treatments were obtained with different accumulated laser fluences and then surfaces were analyzed with roughness and contact angle measurements. Adhesive bonding was performed with various bondline thicknesses ranged between 30–500 µm using two component structural epoxy based paste adhesive (Loctite Hysol ® EA 9396^TM). Adhesive bonding strength of bonded samples was determined with single lap shear tests. It is worthy to note that if the accumulated laser fluence which has significant effect on shear strength does not optimize, it causes ineffective adhesion.     

Glass/epoxy composites and aluminium alloy joint using Kevlar® intermediate layer and nanoclay-reinforced epoxy adhesive

Adhesive lap joint between glass fibre/epoxy composites and aluminium alloy (2014 T4) was prepared by an in situ moulding process using a matched die mould. The surface of aluminium alloy was treated with chromic acid before adhesive bonding. Lap shear strength and fatigue life were evaluated in tensile mode and tension–compression mode (at 40% of lap shear load of adhesive joint), respectively. Knurling on the surface of aluminium alloy improved the lap shear strength of the adhesive joint but did not influence the fatigue life of the same. Lap shear strength and fatigue life of adhesive joint made with neat epoxy adhesive and reinforcement of an intermediate layer of Kevlar^® between glass/epoxy composite and aluminium alloy were observed to be 0.44?kg/mm² and 3.6?×?10⁵ cycles, respectively. In another case, lap shear strength and fatigue life of similar type of adhesive joint made from nanoclay (Cloisite 30B)-reinforced epoxy adhesive and without reinforcement of an intermediate layer of Kevlar^® were observed to be 0.38?kg/mm² and 2.3?×?10⁵ cycles, respectively. Whereas, lap shear strength and fatigue life of adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® were 0.48?kg/mm² and 3.9?×?10⁵ cycles, respectively. Therefore, adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar^® was the best.     

Behaviour of Bi-adhesive Joints

The use of relatively low modulus adhesive at the ends of overlap in a bi-adhesive bondline of a bonded joint can reduce the stress concentration significantly and, therefore, potentially lead to higher strength of the joint. This study presents the two-dimensional and three-dimensional nonlinear (geometric and material) finite element analyses of adhesively bonded single lap joints having modulus-graded bondline under monotonic loading conditions. The adhesives were modelled as an elasto-plastic multi-linear material, while the substrates were regarded as both linear elastic and bi-linear elasto-plastic material. The computational simulations have been performed to investigate the bondline behaviour by studying the stress and strain distributions both at the mid-plane as well as at the interface of the bondline. It has been observed that the static strength is higher for joints with bi-adhesive bondlines compared to those with single adhesives in bondline. Higher joint strength has also been observed for optimum bi-adhesive bondline ratio through parametric studies. Effects of load level, and bondline thickness on stress distribution in the bi-adhesive bondline have also been studied. 3D analysis results reveal the existence of complex multi-axial stress/strain state at the ends of the overlap in the bondline which cannot be observed in 2D plane strain analysis. About 1/3rd of the width of the joint from the free edge in the width direction has 3D stress state, especially in the compliant adhesive of the bondline. Magnitudes of longitudinal and lateral stress/strain components are comparable to peel stress/strain components. It has also been analytically shown that the in-plane global stiffness of the joint remains unaffected by modulus gradation of the bondline adhesive.     

Effects of Different Curvature Patches on the Strength of Double-Strap Adhesive Joints

In general, the damage in adhesively bonded joints initiates from and propagates through the ends of the overlap area due to high stress concentration in that area. The reduction of these stress concentrations results in an increase in the strength of the joints. For this reason, the rounding of the overlap region before bonding and then applying compression during the bonding process will exert compressive residual stresses on the adhesive layer in the overlap end regions. It is known that the residual stresses formed in this process increase the failure strength of the joint and hence delay the initiation of the damage.

In this study, the effects of overlap length (L = 50,75, and 100 mm), patch thickness (h = 1.6, 3.2, and 5 mm) and patch materials (AA2024 aluminum alloy, AISI 304 steel, AISI 1040 steel) on bond strength were experimentally investigated for adhesively bonded double-strap joint (DSJ) and curvature double-strap joint (CDSJ) subjected totensile loading. The experimental study showed that the overlap length, patch thickness and patch materials have considerable influence on the failure strength and displacement capacity of the joints.     

Effect of material,geometry, surface treatment and environment on the shear strength of single lap joints

The single lap joint is the most studied type of adhesive joint in the literature. However, the joint strength prediction of such joints is still a controversial issue as it involves a lot of factors that are difficult to quantify such as the overlap length, the yielding of the adherend, the plasticity of the adhesive and the bondline thickness. The most complicated case is that where the adhesive is brittle and the overlap long. In any case, there is still a problem that is even more difficult to take into account which is the durability. There is a lack of experimental data and design criteria when the joint is subjected to high, low or variable temperature and/or humidity. The objective of this work is to carry out and quantify the various variables affecting the strength of single lap joints in long term, especially the effect of the surface preparation. The Taguchi method is used to decrease the number of experimental tests. The effect of material, geometry, surface treatment and environment is studied and it is shown that the main effect is that of the overlap length.In order to quantify the influence of the adhesive (toughness and thickness), the adherend (yield strength and thickness), the overlap, the test speed, the surface preparation and durability on the lap shear strength, the experimental design technique of Taguchi was used in the present study. An experimental matrix of 18 tests was designed and each test was repeated three times. The influence of the eight previously-mentioned variables could be assessed using the statistical software Statview^®. In this paper a simple predictive equation is proposed for the design of single lap joints.