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。      

Three-dimensionally printed designable joint for carbon fibre reinforced plastics

Three-dimensional (3D) printing of carbon fibre reinforced plastic (CFRP) components shows promise for building light-weight strong components for industry. Many structures require multiple components to be joined to form the completed parts. However, tightening of metal bolts used to join CFRP can damage the composite and the bonding strength of adhesive bonding is variable. Here, we propose a new joint system, based on all-3D printed parts. Snap-in joints and Ajax-pins induce a mechanical joining force at the interface between parts, together with a bearing force. This joint system offers comparable strength to that of adhesive and metal bolt joints, while adding negligible weight to the parts. Furthermore, 3D printing of the surface structures, holes and pins enables unprecedented control over the joint design, enabling strength optimization through the thickness and in-place directions as required. The Snap-in joint system shows great potential for the fabrication of strong light-weight 3D printed structures.     

钢和碳纤维增强材料胶接研究现状

碳纤维增强复合材料(CFRP)由于轻质高强,广泛应用于航空航天和汽车工业领域。金属传统的连接方式如焊接对金属和CFRP的连接有较多限制,所以目前CFRP和钢的连接主要还是胶接和机械连接。本文主要归纳了胶接的作用机理和失效形式及胶-铆混合连接的优点,总结胶接主要工艺参数:胶层厚度、粘结长度及表面处理对接头强度的影响,最后对该领域依然存在的主要问题和未来研究工作提出自己的看法。     

A parametric study on the failure of bonded single-lap joints of carbon composite and aluminum

A parametric study on adhesively bonded carbon composite-to-aluminum single-lap joints was experimentally conducted. FM73m, a high strength adhesive produced by Cytec, was used for bonding. The primary objective of this study is to investigate the effects of various parameters, such as bonding pressure, overlap length, adherend thickness, and material type, on the failure load and failure mode of joints with dissimilar materials. While metal bonded joints generally fail at the adhesive, the final failure mode of all the tested bonded joints with dissimilar materials was delamination of the composite adherend. Bonding strengths of the tested joints were lower than the metal-to-metal bonded joint strength. The specimens bonded under pressure of 4 and 6 atm yielded higher failure loads than under pressure of 3 atm, which is within the range of the manufacturer-recommended bonding pressure. Failure loads of the joint increased slightly at an overlap length larger than 30 mm. Increasing adherend thickness resulted in an increase of the failure load, but was not linearly proportional to the failure load.     

Mixed-mode crack growth in bonded composite joints under standard and impact-fatigue loading

Carbon fibre reinforced polymers (CFRPs) are now well established in many high-performance applications and look set to see increased usage in the future, especially if lower cost manufacturing and solutions to certain technical issues, such as poor out-of-plane strength, can be achieved. A significant question when manufacturing with CFRP is the best joining technique to use, with adhesive bonding and mechanical fastening currently the two most popular methods. It is a common view that mechanical fastening is preferred for thicker sections and adhesive bonding for thinner ones; however, advances in the technology and better understanding of ways to design joints have lead to increasing consideration of adhesive bonding for traditionally mechanically fastened joints. In high-performance applications fatigue loading is likely and in some cases repetitive low-energy impacts, or impact fatigue, can appear in the load spectrum. This article looks at mixed-mode crack growth in epoxy bonded CFRP joints in standard and impact fatigue. It is shown that the back-face strain technique can be used to monitor cracking in lap-strap joints (LSJs) and piezo strain gauges can be used to measure the strain response of impacted samples. It is seen that there is significant variation in the failure modes seen in the samples and that the crack propagation rate is highly dependent on the fracture mode. Furthermore, it is found that the crack propagation rate is higher in impact fatigue than in standard fatigue even when the maximum load is significantly lower.     

碳纤维增强环氧树脂复合材料与铝板胶螺混合连接接头失效仿真

基于商用有限元软件ABAQUS,建立了碳纤维增强环氧树脂复合材料（CFRP）层合板和铝板双搭接胶螺混合连接接头强度预测模型,并进行了仿真分析,同时与试验结果进行对比,探究了此类混合接头在拉伸载荷工况下的失效形式和承载能力。结果表明,拉伸加载过程中,螺栓通过分担部分载荷加强了胶接连接。混合接头的失效形式先表现为胶层的断裂失效,最终表现为层合板孔边挤压失效。利用模型预测的接头承载能力与试验结果的误差为9.7%,具有较好的吻合性。该分析方法能够为复合材料-金属胶螺混合连接的分析和设计提供一定的参考。      

Failure load evaluation and prediction of hybrid composite double lap joints

Hybrid joints are a combination of adhesive bonding and mechanical fastening and are known to combine the advantages of both joint types. In this paper, we evaluate and compare the strengths of mechanical joints, adhesive joints and hybrid composite joints. We manufactured and tested 10 hybrid joint specimens with different width-to-diameter (w/d) ratios, edge-to-diameter (e/d) ratios and adherend thicknesses. Additionally, the strengths of the hybrid joints were predicted using the Failure Area Index (FAI) method and the damage zone method, and we compared our theoretical predictions with our experimental results. From these data, we were able to predict hybrid joint strengths to within 23.0%.     

碳纤维增强树脂基复合材料层合板胶螺混合连接失效机制

为研究碳纤维增强树脂基复合材料(CFRP)层合板单搭接双螺栓胶螺混合连接失效机制,采用基于断裂能断裂准则的连续渐进退化方式,仿真CFRP层合板刚度退化,采用基于能量的B-K准则仿真胶层的损伤演化,建立胶螺混合连接结构渐进损伤三维有限元模型,有限元模型预测的最大失效载荷与实验结果吻合较好。搭接长度L_a为影响胶螺混合接头刚度和强度的重要几何参数,螺栓的位置不会明显影响接头的刚度,粘结面积越大,强度越大。胶螺混合接头在拉伸载荷作用下,由于二次弯曲效应的影响,螺栓向左倾斜,搭接区域的胶层损伤起始于搭接区域胶层外侧,并由外侧向内部扩展到钉孔附近,当胶层损伤扩展到钉孔附近时,螺栓承载增加,胶层和螺栓共同承载,此时CFRP层合板开始出现损伤;最终,左侧钉孔处的上层合板和右侧钉孔处的下层合板产生分层损伤并发生断裂。      

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.     

Influence of pinning on static strength of co-cured metal-GFRP hybrid single lap joints

This study presents an experimental investigation into the effects of through-thickness pinning reinforcement on the static strength and damage tolerance of hybrid mild steel–glass fibre prepreg co-cured composite single lap joints (SLJ). Stainless steel pins of 0.3 mm in diameter were inserted as mechanical fastening, in addition to adhesive bonding, to form hybrid joints between metal and glass fibre reinforced polymer substrates. Using the hybrid SLJ tensile testing, the failure modes and static strength were experimentally determined for mild steel–glass fibre prepreg co-cured composites. It is revealed that pinning can improve the static failure load via bridging mechanism by as much as 58% depending on the number and location of pins and the presence of clamping due to bent-ends.     

Static strength of a composite butt joint configuration with different attachments

The static failure behaviour of a composite single-strap joint configuration using three different attachments was studied experimentally. The attachments used were: adhesive bonding; mechanical bolting; and bonded-bolted joining. The dimensions of the composite butt joint used were determined based on actual joint configurations in aircraft structures, such that the test results would be beneficial to both the academic exploration and practical engineering application for advanced composite joint design and analysis. A damage evolution process was presented for the bonded-bolted butt joints based on the observed stress versus displacement curves and associated failure modes from all the related butt joints with the three attachments. An approach was then proposed for estimating the ultimate tensile strength in the bonded-bolted joints.     

Analysis of bolted–bonded composite single-lap joints under combined in-plane and transverse loading

A semi-analytical solution method is developed for stress analysis of single-lap hybrid (bolted/bonded) joints of composite laminates under in-plane as well as lateral loading. The laminate and bolt displacements are based on the Mindlin and Timoshenko beam theories, respectively. For the adhesive, the displacement field is expressed in terms of those of laminates by using the shear-lag model. The derivation of the governing equations of equilibrium of the joint is based on the virtual work principle, where the kinematics of each laminate are approximated by local and global functions and the bolt kinematics is assumed in terms of cubic Hermitian polynomials. The capability of the present approach is justified by validation and demonstration problems, including the analysis of bolted and bonded joints and hybrid joints with and without considering a disbond between the adhesive and laminates.     

Fatigue performance of hybrid overlap friction stir welding and adhesive bonding of an Al‐Mg‐Cu alloy

The need for weight reduction and leaner manufacturing and assembly processes in aircraft construction has led to the pursuit of welding technologies. One such technology that has been considered for this application is friction stir welding (FSW). Since it is a solid‐state joining method, it creates high performing joints in a wide range of materials while avoiding overlap lengths and added weight from fasteners, crack stoppers, doublers, etc. However, the adoption of this technology to the assembly of large fuselage shell components is challenging, due to geometric tolerance management requirements. In this paper, a hybrid joining method is proposed for such application, involving FSW and adhesive bonding. Fatigue performance of single lap joints of AA2024‐T3 Al‐Mg‐Cu alloy was assessed and benchmarked against FSW overlap and adhesive bonded joints. Significant strength and ductility increase was achieved through the hybridization of the overlap FSW joints. Fatigue strength of the hybrid joints was also higher than FSW overlap joints, although not as high as adhesive bonded joints.     

屈曲约束支撑钢筋混凝土框架结构干式柔性梁柱节点的试验研究

建议了一种由受弯框架与采用梁柱柔性节点的屈曲约束支撑框架并联组成的装配式混凝土双重抗侧力体系,设计并完成了4个装配式梁柱节点试件和1个现浇节点试件的往复加载试验。研究了混凝土楼板、螺栓孔形式等因素对该柔性节点受力性能和破坏模态的影响,并与现浇试件进行了对比。试验结果表明：混凝土楼板对柔性节点刚度及承载力有很大的影响,在设计时不可忽略;螺栓孔形式在结构位移较小时对节点的受力性能没有影响,但当结构位移较大时会影响节点的破坏模式;与现浇节点相比,装配式柔性节点具有很大的变形能力。     

Effect of loading rate on fracture toughness of bonded joints

Feasibility studies in using adhesive bonding to replace conventional fastening methods have been proved successful. At this stage it is essential to furnish the designer with the data required for such type of fabrication. One of the main factors affecting the bonded joint strength is the loading rate. Therefore, the objective of this study is to investigate the role of loading rate on fracture toughness of bonded joints. Cleavage strength tests were carried out at different loading rates using epoxy resin as an adhesive material and two adherend materials, namely aluminium and brass. Tests were carried out to cover seven different loading rates. The results indicate a significant role of the strain rate on the fracture strength.     

Adhesive bonding for high performance materials

Adhesion as a joining technology assumes greater significance as attempts are made to join newer materials in increasingly exotic combinations and where conventional joining techniques are either less suitable or quite unsatisfactory. This paper describes work directed at the use of adhesives in the fabrication or repair of structures involving modern structural materials.This subject is discussed by reference to research involving fibre reinforced polyether ether ketone (PEEK) and particulate silicon carbide reinforced aluminium alloy as representatives of organic and metal matrix composites respectively.Adhesion is essentially a superficial phenomenon depending as it does upon interactions between the adhesive in its liquid state and the surface of the substrate. The surface preparation of the subject to be bonded is therefore of the greatest importance and this aspect is addressed at length. The success of an adhesive bonding operation is reflected in the strength of the joint generated and in its ability to retain useful joint strength for long periods in the operational environment. These aspects are also considered and in particular the effect of water on the integrity of joints is discussed.Both plasma and corona discharge treatments were found to be effective in the adhesive bonding of the organic matrix material (PEEK) whilst anodising and the use of coupling agents were both found to be useful in the bonding of the metal matrix composite (MMC).The versatility of the adhesion process as a joining technology is highlighted by reference to how the individual problems presented by these very different materials are dealt with.     

Development of an anti-loosening fastener and comparing its performance with different other threaded fasteners

Threaded fasteners are widely used for temporary joining of different components that require occasional disassembling. However, threaded fasteners may have the problem of loosening under vibrating conditions, which may lead to decreasing clamping force and, thereby, a system failure. In the present experimental investigation, anti-loosening ability of various fastening elements, such as conventional nut, nylock nut, flat washer, spring washer, inside and outside serrated washer, is tested with a conventional M16 high-tension steel bolt. A hybrid double nut is used to clamp the plates in which a conventional nut is used to tighten first, and one nylock nut is then placed at the outer side for further tightening. An adhesive-bonded nut is also tested, where an adhesive is placed between bolt and nut threads. All these fasteners are tested in terms of their loosening characteristics. Accelerated vibrating conditions are used for the test on an indigenously made test rig. A split bolt with taper pin is introduced for the first time to reduce loosening of fasteners. The split bolt with taper pin shows considerably good anti-loosening property compared with other threaded fasteners tested in this work.     

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...     

Experimental characterization of hybrid composite-to-metal bolted joints under flexural loading

Presented is an investigation of the structural performance of hybrid composite-to-metal bolted joints loaded in flexure. The main goal was to develop a watertight, hybrid connection to resist bending loads. The effect of bolt type, doubler plate geometry and foam inserts was studied. Fourteen different joint configurations were tested including standard bolted joints and bolted joints with doubler plates. The performance of connections loaded cyclically in flexure was assessed by comparing: (1) the initial damage and failure loads; (2) the types of failure modes; and (3) the joint initial rotational stiffness. Instability in the hysteresis loops, where the load drops in subsequent cycles, is used as an indication of damage. A joint using a short doubler plate, a foam insert, and a single row of bolts, was found to be at least 33% stronger and 29% stiffer when compared to a standard bolted joint with two rows of the same diameter bolts. Use of doubler plates and foam inserts in a bolted joint resulted in higher strength and stiffness and can effectively mitigate joint opening, which improves the ability to seal the joint and maintain watertight integrity.     

服役低温老化对铝合金-玄武岩纤维增强树脂复合材料粘接接头力学性能的影响及失效预测

为了给铝合金-玄武岩纤维增强树脂(BFRP)复合材料粘接结构在汽车工业中的应用提供参考和指导,加工了铝合金-BFRP复合材料粘接接头。结合汽车服役中的温度区间,选取?10℃和?40℃的低温老化环境,对接头进行0、10、20、30天的老化。对老化后的粘接接头进行准静态拉伸试验和剪切试验,得到不同老化时间下铝合金-BFRP粘接接头的准静态失效强度。结合DSC和FTIR分析低温老化对BFRP复合材料的影响,并对粘接接头的失效断面进行宏观分析和SEM分析。结果表明:在低温老化环境中,胶粘剂与BFRP复合材料的化学性质受低温老化作用影响不大,BFRP中的官能团与玻璃化转变温度(T_g)没有发生明显的变化,接头的失效强度和失效模式主要受胶粘剂与粘接基材的热应力影响。对于拉伸接头,随着低温老化时间的增加,BFRP复合材料纤维与树脂基体间的结合力降低,铝合金-BFRP复合材料接头的失效断面中纤维撕裂的比例逐渐减少,拉伸接头失效强度逐渐下降。老化后剪切接头仍为内聚失效,BFRP复合材料的低温老化对铝合金-BFRP复合材料剪切接头的失效强度几乎没有影响,剪切接头失效强度的下降主要是胶粘剂与粘接基材热膨胀系数不一致引起的热应力的影响。采用二次应力准则公式对?10℃和?40℃低温环境下,拉应力、剪应力值随老化时间的变化规律进行了拟合,在此失效准则的基础上,根据响应面原理,建立接头失效强度随老化时间变化的三维曲面,为粘接技术在车身结构中的工程应用提供参考。