胶接接头破坏分析

<正>介绍了胶接强度理论(材料力学的四大强度理论和断裂力学的断裂准则)、胶接接头的破坏形式(胶粘剂的内聚破坏、被粘物的内聚破坏、黏附破坏和混合破坏)和表面能定义,并对各种形式的胶接接头破坏进行了能量分析,得出理想胶接接头不存在黏附破坏的结论,并指出理想胶接接头的最薄弱环节。     

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。     

胶接接头无损检测研究进展

介绍了胶接接头无损检测技术近年来的发展情况，对超声波、声、应力波等无损检测技术的发展作了概要的阐述，同时对胶接接头的强度检测进行了分析，认为检测中所选用的强度相关参数，应充分体现胶接接头对应力的响应，这样才可能实现胶接强度的定量检测。     

玻璃钢深井滤水管、井管胶接试验小结

由我厂和河北省水文四队共同协作研制,在北京地区装井的玻璃钢深水井管由25根井管,16根滤水管组成,总长100.75米。它是在现场采用接箍过渡,锥面胶接工艺连成一体的。该深井水管共有40个胶接接头,每个接头的胶接面积为840厘米~2左右。对玻璃钢井管胶接工艺的要求是:胶接施工时,每个接头要求在10～20分钟内快速固化,并能承受1.5吨的总载荷;在装井过程中,不允许发生胶接接头脱落现象,同时保证管间同轴。 根据上述要求,我们认为井管的胶接强度问题不大,快速固化是个关键,因而从快速固化要求着手,选配了五种胶粘剂:914胶-环氧、聚硫橡胶、703固化剂;911胶-环氧、三氟化硼甘油络合物;新911胶-环氧、     

汽车用镀锌板单搭接胶接接头强度影响因素研究

针对不同种类汽车用镀锌板单搭接胶接接头强度的影响因素进行了研究分析.考察了不同腐蚀介质及汽车涂装工艺对汽车板胶接接头性能的影响,并深入研究了其失效机理.研究结果表明:汽车板材料的屈服强度、材料厚度以及胶层厚度等均会对胶接接头的力学性能产生一定的影响;为保证胶接工艺在汽车车身结构中发挥最佳的力学性能,且与电泳工艺段同步,...     

温度变化对复合材料双面搭接接头拉伸强度的影响分析

介绍了复合材料三种连接方式之一——胶接。对双面搭接接头进行了有限元建模,在不同的高温环境下进行拉伸试验,运用相关的失效准则,分析判断复合材料胶接接头的破坏形式,确定温度对破坏形式的影响。通过试验,验证了分析的正确性,对复合材料胶接接头的强度校核及设计改进有重要的指导作用。     

金属胶接接头劈裂破坏的模型分析

对金属胶接接头劈裂强度测试方法和影响劈裂强度的主要因素的作用进行了分析与讨论。本文提出了金属胶接接头劈裂破坏模型，对完善劈裂强度测试方法提出了改进意见．     

复合材料/金属胶接结构研究进展及发展趋势

胶接连接应用日渐广泛,特别是在汽车和航空航天等结构领域。首先分析了复合材料/金属胶接连接方式的特点,重点介绍了接头中的次弯曲效应、异质材料间刚度与热膨胀系数的不匹配特性以及载荷传递特性。然后总结了提高胶接接头强度的研究进展,主要包括增大胶接长度和宽度、选择胶黏剂、表面处理、增加胶瘤和被粘合物形状的设计等方面。最后对胶接接头的发展趋势进行了展望。     

无人机机翼用复合材料的胶接与性能研究

为了提升无人机机翼用碳纤维/铝复合材料的胶接强度,采用4因素5水平的正交试验法对超声振动胶接工艺参数进行了优化,并与传统未施加超声振动的胶接接头进行了对比。结果表明,超声振动胶接工艺中对胶接强度影响最大的是振动时间,其次为振动幅值,振动位置的影响最小;正交试验结果表明,碳纤维/铝胶接接头的最佳工艺参数为A3B5C3D5,即振动时间23 s、振动压力0.40 MPa、振动位置30 mm和振动幅值56μm,此时碳纤维/铝胶接接头胶接强度最大。相较于未施加超声振动的胶接接头,正交优化工艺下胶接接头的最大拉伸荷载平均值提高42.13%,胶接强度平均值提高41.59%。     

胶接接头的声技术无损检测

介绍了胶接接头无损检测技术近年来的发展情况,对超声、声-超声、声等无损检测技术的发展作了概要的阐述。同时对胶接接头的强度检测进行了分析,最后指出了制约胶接接头强度无损检测的主要障碍。     

Geometric Factors Impacting Adhesive Lap Joint Strength and Design

Too often adhesive thickness, adherend thickness and other geometric factors are not explicitly considered in adhesive joint design. This study includes experimental and computational research exploring the means of enhancing the engineering design process for adhesive lap joints to include such effects. It clearly demon-strated that both the cleavage stresses and the shear stresses, near the bond termini, play important roles in lap 'shear' joint failure. Finite Element and Fracture Mechanics analyses were used to examine the energy release rate applied to growth of cracks in adhesive lap joints. Lap joints with similar geometries to those analyzed were designed, fabricated and tested. In a separate set of experiments the bond termini were constrained in the direction normal to the uniaxial loading. If the strength of lap shear joints is dominated by the adhesive shear strength, then constraining the lateral motion of the bond termini should have little or no effect on the overall shear strength of the adhesive joint. This work clearly demonstrates that this is not the case. If cleavage stresses are important in lap joints then constraining the bond termini, in a direction normal to the bond area, should have a commensurate effect on the overall strength of the lap joint. None of the ASTM standardized 'lap shear tests' provide any insight into this premise. This paper also presents analyses and experimental results for lap joints to which several methods of lateral constraint were applied near the bond termini. The analytical and numerical methods described and used for explaining and predicting such effects might be a useful adhesive joint design tool.     

Finite Element Analysis of an Adhesive Joint Using the Cohesive Zone Model and Surface Pattern Design of Bonding Surfaces

Adhesive joints have been widely used in the automotive and aerospace fields in order to reduce the weights of products. The strength of adhesive joints, accordingly, needs to be increased and their behaviour should be predicted in order to achieve accurate designs. Studies to improve the strength of adhesive joints via surface treatment methods or by using two adhesives with different mechanical properties have been conducted. Various modeling methods also have been studied to predict the behaviour of adhesive joints. Unfortunately, the relationship between the bonding surface roughness and adhesive joint strength needs to be further clarified in order to be applied in practical design. As analyzing the relationship through a conventional finite element method assuming perfect bonding is challenging, the behaviour of the adhesive joints may be analyzed using a cohesive zone model or interface modeling methods from an integrating released energy point of view.

The strength of adhesive joints can be improved via micro-patterning due to the mechanical interlocking effect. Therefore, in this study, a micro-pattern was fabricated to improve the strength of adhesive joints. Various pattern-sized single leg bending joints and end notched flexure joints were manufactured and experimented upon. In this study, characteristics of each pattern surface were independently classified and modeled with a cohesive zone model. Finite element analyses were then performed and simulation results were compared with experimental results. The numerical results satisfactorily describe the experimental results, and failure loads were predicted with a maximum relative error of 8%. From these results, it may be concluded that the present findings can be applied to practical design and that the failure load can be predicted via a finite element analysis.     

Optimum Silane Treatment for the Adhesively Bonded Aluminum Adherends at the Cryogenic Temperature

Aluminum adherends for the adhesive joints at cryogenic application such as LNG (Liquefied Natural Gas) containment tanks were silane treated to improve bond strength of the aluminum joints. The bond strengths of the single-lap joints composed of aluminum adherends and epoxy adhesive were measured with respect to the condition of the silane solution and surface roughness obtained with grit blast. The chemical composition of the silane treated aluminum surface was analyzed by XPS (X-ray photoelectron spectroscopy). Also, contact angles of appropriate liquids on the silane treated aluminum surface were measured with respect to treatment conditions. From the experiments, the optimum treatment conditions for the aluminum adherends were obtained for the adhesive joints at the cryogenic temperature.     

Numerical Study of Adhesive Single-Lap Joints with Composite Adherends Subjected to Combined Tension–Torsion Loads

The present investigation focuses on modifying the strength of single-lap adhesively bonded joints under tension–torsion loading with the use of three-dimensional finite element (FE) modeling. A single-lap adhesively bonded joint is reinforced by fibers and analyzed by means of ABAQUS-6.9.1 FE code. The adherends are considered to be made of orthotropic materials, while the adhesive is neat resin or reinforced by various types of fibers. The carbon and glass unidirectional fibers are used for adhesive reinforcement. In the FE modeling, the behavior of all the members is assumed to be linear elastic. The ultimate bond strength is increased as the fiber volume fraction in the adhesive is increased. By changing the properties and the behavior of the adhesive from neat resin (isotropic) to fiber composite adhesive (orthotropic) and with various fiber volume fractions and by changing the orientation of the fibers in the adhesive region with respect to the global axes, the bond strength in tension–torsion loadings are changed. Also, the excessive adhesive layer is modeled and its effect on the joint strength is investigated.     

Numerical study of lap joints with composite adhesives and composite adherends subjected to in-plane and transverse loads

In this paper, single lap joints for joining fibre composites were modeled and a three-dimensional finite element method was used to study the joint strength under in-plane tensile and out-of-plane loadings. The behaviour of all the members was assumed to be linear elastic. The adherends were considered to be orthotropic materials while the adhesive could be neat resin or reinforced one. The largest values of shear and peel stresses occurred near the ends of the adhesive region, as expected. The values and the rate of variation in peel stress was more than that of shear stress. By changing the properties and behaviour of adhesive from neat epoxy (isotropic) to fibre composite adhesive (orthotropic) and with various fibre volume fractions of glass fibre, the ultimate bond strength increased as the fibre volume fraction increased, in both tensile and transverse loadings. Also, changing the orientation of fibres in the adhesive region with respect to the global axes influenced the bond strength.     

Ultrasonic testing for bond efficiency of carbon steel to stainless steel adhesive joints

Structural adhesive joints between carbon steel and stainless steel were made and evaluated. Various combinations of a two-component epoxy adhesive were used and diverse polymerization cycles were employed to obtain joints of different mechanical strengths. Two ultrasonic procedures were used: ultrasonic scanning with a focused beam to ascertain the quality and the uniformity of the joints; and ultrasonic spectrum analysis to evaluate bond strength. The influence on adhesion of surface calamine of the carbon steel was also investigated: bond strengths were comparable with those attained with ground carbon steel adherends. Adding lubricating oil to the adhesive was found to increase the mechanical properties of the joints.     

A reinforcing technique for the adhesive bonded composite joints using metallic wires

One of the strengthening methods of composite connection is the employment of reinforcing elements in the adhesive layer. Using of additional elements in the adhesive layer make uniform stress distribution and improves the strength and toughness of the connection. In this paper, metal wires were used to reinforce the adhesive joints of composites. The effects of the number of wires, wire diameter, wire stiffness, angle of wire and the adhesive type on the strength of the adhesive reinforced bonded composite joints were investigated experimentally and numerically. A finite element model was developed to study the stress distribution in the reinforced adhesive joints. The numerical results showed a good agreement with the experimental observation. It was found that increasing the number of wires and wire diameter, choosing a stiffer material for the wire and increasing the wire angle, uniform the stress distribution and reduced the maximum and average stress values in the adhesive layer. For the appropriate reinforcing wire parameters, the joint strength increased more than 90% in this study. It also observed that the using metal wires as a reinforcing element was more effective in the ductile adhesion than the brittle ones.     

Single and dual adhesive bond strength analysis of single lap joint between dissimilar adherends

The emerging trends for joining of aircraft structural parts made up of different materials are essential for structural optimization. Adhesively bonded joints are widely used in the aircraft structural constructions for joining of the similar and dissimilar materials. The bond strength mainly depends on the type of adhesive and its properties. Dual adhesive bonded single lap joint concept is preferred where there is large difference in properties of the two dissimilar adherends and demanding environmental conditions. In this work, Araldite-2015 ductile and AV138 brittle adhesives have been used separately between the dissimilar adherends such as, CFRP and aluminium adherends. In the dual adhesive case, the ductile adhesive Araldite-2015 has been used at the ends of the overlap because of high shear and peel strength, whereas in the middle of the bonded region the brittle adhesive AV138 has been used at different dimensions. The bond strength and corresponding failure patterns have been evaluated. The Digital Image Correlation (DIC) method has been used to monitor the relative displacements between the dissimilar adherends. Finite element analysis (FEA) has been carried-out using ABAQUS software. The variation of peel and shear stresses along the single and dual adhesive bond length have been captured. Comparison of experimental and numerical studies have been carried-out and the results of numerical values are closely matching with the experimental values. From the studies it is found that, the use of dual adhesive helps in increasing the bond strength.     

Specific Interactions, Initial and Equilibrium Bond Strength in Polymer/Polymer Assemblies

This paper reports on bonding characteristics of assemblies using as substrates poly(vinyl chloride) (PVC), acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP), and as melt adhesives an ethylene-vinyl acetate (EVA) copolymer, a polyurethane (PUr), and low density polyethylene (LDPE). Peel strength measurements on freshly assembled joints were compared with results for samples aged under inert and humid conditions. Significant time-dependent variations of bond strength were observed in all cases, but the direction of change varied among the assemblies. Those involving only dispersion-force materials displayed losses of bond strength, attributable to the gradual accumulation of cohesively weak layers at the substrate/adhesive interface. In assemblies involving materials able to interact by non-dispersion (acid/base) forces, as indicated by inverse gas chromatographic data, a variety of responses was obtained. These have been rationalized by the ability of the EVA and PUr adhesives to reorient when in contact with an appropriate polymer substrate. Reorientation, leading to bond strength increments, was associated with substrate/adhesive pairs (e.g., PVC/EVA and ABS/PUr), in which significant acid/base interaction could take place.     

Behavior of adhesively bonded coated steel for automotive applications under impact loads

Novel manufacturing techniques and the application of new materials in the automotive industry increase the challenges in adhesive bonding. One of these is the bonding of coated materials such as high-strength steels with anti-cindering multi layers or painted components. In both cases, the entire build-up of the joint has to be taken into account to determine its strength.Based on common testing methods, i.e. lap-shear or butt-joint tests, this paper presents modifications and possible interpretations of these testing methods for the characterization of adhesive joints of coated materials under impact loading. Another aspect presented here is a laser-based approach for the removal of paint, to achieve higher bond strength. It has been found that the mechanical strength of the bond is influenced significantly by coatings and paints. Furthermore large dependence on the nature of the paint can be found. In general it can be noticed that the weakest layer within the entire joint is the coating or paint. Therefore, these additional layers have to be carefully considered during a product׳s development phase.