含镶嵌块单搭接接头应力分布的数值分析

利用有限元方法研究了金属镶嵌对单搭接接头应力分布的影响。结果表明,采用镶嵌块组成混合连接接头,改变了接头的应力流线分布,镶嵌块承载,降低了搭接区中部胶层中的应力;同时使被粘物中部的应力增大,提高了接头搭接区中部的承载能力;在重要部件或承载较大等情况下使用胶接接头,建议采用金属镶嵌方式对接头增强,具有更强的承载能力和可靠性,有重要的实用价值。     

单搭接接头峰值应力数值模拟的正交法分析

运用正交试验法研究了几个主要力学和几何参数如泊松比,弹性模量和被粘物厚对单搭接接头Von Mises等效应力的影响。有限元分析结果的极差分析、方差分析和最优方案的工程平均等结果表明:被粘物厚对单搭接接头Von Mises等效应力影响最大,弹性模量次之,泊松比影响程度最小。分析可知:高的泊松比、低弹性模量和被粘物厚的增大会使得Von Mises等效应力值显著降低。     

异质被粘物新型单搭接接头应力分析

利用有限元分析软件ANSYS建立了异质被粘物用2种胶分段粘接的单搭接接头的力学模型,分析了胶层中剪切应力的分布情况。结果表明,合理地布置高弹性模量胶粘剂及低弹性模量胶粘剂的位置,可以有效地降低刚度不对称接头胶层中应力的峰值,避免胶层因小刚度侧应力过高而导致接头过早地失效。     

同轴单搭接胶接接头应力分布的探讨

利用有限元方法研究了偏轴单搭接胶接接头和同轴单搭接胶接接头的力学性能.结果表明,同轴单搭接胶接接头可以使接头搭接末端的弯矩变为零,进而有效地降低剥离应力的峰值,减轻剪切应力的集中程度,是一种较为合理的胶接接头形式.     

基于有限元方法的单搭接接头可靠性设计

将概率统计的设计观念引入单搭接粘接接头,通过有限元分析方法分析了对粘接接头力学性能影响较大的因素,并在抽样100次的情况下,分析了单搭接粘接接头失效的概率。结果表明,该模型可以有效地反映接头的实际情况,为粘接结构的可靠度设计提供了依据。     

单搭接胶接接头的拓扑优化

在有限元方法的基础上，利用变密度法对单搭接胶接接头搭接区域的被粘物形状进行了拓扑优化，通过曲线拟舍得到了较为合理的轮廓。拓扑优化的结果表明：在体积减少20％的情况下。胶接结构的强度不会降低；经拓扑优化后，胶层中剪切应力的峰值比优化以前增加不大，约1％。     

胶粘剂弹性模量对折曲胶接接头应力分布的影响

通过ANSYS有限元软件建立了折曲胶接接头的弹塑性有限元模型,考察了胶粘剂的力学性能参数弹性模量对其应力分布的影响。研究结果表明:四种不同的胶粘剂,其弹性模量越大,胶层中各应力的峰值越大,搭接区被粘物剥离应力峰值逐渐呈现出上升的趋势;当胶粘剂弹性模量为50 MPa时,被粘物的各应力分量存在较大的应力尖角(应力集中现象)。     

斜削对折曲胶接接头的应力分布影响

采用弹塑性有限元法,研究了被粘物自由端外侧、内侧斜削角度对铝合金单搭接折曲接头中应力分布的影响。结果表明:被粘物自由端经外斜削处理后,胶层中间段的各应力分布无明显变化;外斜削角度越大,剥离应力峰值越高;被粘物自由端经内斜削处理后,内斜削角度越小,胶层端部的轴向应力峰值、剪切应力峰值越小,但剥离应力峰值越大。综合考虑胶层中部的应力分布情况,选择内斜削角度为5°时较适宜。     

复合材料单搭接胶接头破坏声发射监测

采用声发射技术对单向拉伸载荷作用下复合材料单搭接胶接头的剪切破坏试验进行实时监测的方法,研究搭接长度对单搭接胶接头损伤破坏的影响规律及其相应的声发射响应特征。结果表明,随搭接长度的增加,引起单搭接胶接头的受力不均匀性增加,损伤易发生在胶层边缘应力集中区域,胶接头承载能力不断上升的同时,平均剪切应力逐渐降低;胶层边缘应力集中更明显,从而出现较多的声发射信号,且幅度在60~80 dB的声发射信号明显增多,声发射撞击累积数有上升趋势。声发射相对能量、幅度分布等声发射信号与胶层的损伤破坏过程相对应。     

折曲胶接接头应力分布的数值分析

运用有限元法研究了偏轴、同轴和折曲型等三种单搭接胶接接头的工作应力分布规律。结果表明：与其他两种接头相比,折曲型单搭接胶接接头可有效降低搭接区端部的剥离应力和剪切应力峰值;在数值分析所用参数及条件下,Ⅰ型折曲接头的剥离应力降幅超过了75％,其他峰值应力的降幅也超过了45％～50％,并且应力分布趋于均匀;Ⅰ型折曲接头使出现应力峰值的位置从搭接区的端部转移至中部,从而显著提高了接头的承载能力,是一种优于普通同轴接头的胶接接头形式;对于受剪切载荷作用的接头而言,采用Ⅱ型折曲接头更为合理,可进一步提高接头承受剪切载荷的能力。     

Experimental study of the effect of microspheres and milled glass in the adhesive on the mechanical adhesion of single lap joints

This article describes several experiments conducted on single lap joints (SLJ) subjected to tensile mechanical loads. Two epoxy adhesives, with slow and fast curing, were used, with a weight of 0%, 3%, and 10% of glass microspheres and milled glass particles, respectively. The adherends used in the construction of the specimens were fiber-reinforced polymers. The types of failures produced in the SLJ specimens were classified according to ASTM standards. The results of the experimental tests on the SLJ with fast-curing epoxy adhesive showed that the use of milled glass and glass microspheres improved the strength of the joint compared with the neat fast-curing epoxy adhesive. As for the experimental test on the joint with slow-curing epoxy adhesive, the results showed that the use of milled glass and glass microspheres decreased its strength when using different additive concentrations compared with the neat slow-curing epoxy adhesive.     

同轴单搭接胶接接头力学性能的研究

利用有限元方法研究了偏轴单搭接胶接接头和同轴单搭接胶接接头的力学性能,结果表明：同轴单搭接胶接接头可以使接头趾部的弯矩为零,进而有效地降低剥离应力的峰值和减轻剪切应力的集中程度,是一种极为合理的胶接接头形式。     

Effect of temperature on the shear strength of aluminium single lap bonded joints for high temperature applications

An experimental and numerical investigation into the shear strength behaviour of adhesive single lap joints (SLJs) was carried out in order to understand the effect of temperature on the joint strength. The adherend material used for the experimental tests was an aluminium alloy in the form of thin sheets, and the adhesive used was a high-strength high temperature epoxy. Tensile tests as a function of temperature were performed and numerical predictions based on the use of a bilinear cohesive damage model were obtained. It is shown that at temperatures below T_g, the lap shear strength of SLJs increased, while at temperatures above T_g, a drastic drop in the lap shear strength was observed. Comparison between the experimental and numerical maximum loads representing the strength of the joints shows a reasonably good agreement.     

Experimental and numerical analysis of single lap bonded joints: Epoxy and castor oil PU-glass fibre composites

ABSTRACT

Currently, there is a growing concern for the environment. Several studies of new materials to reduce environmental impact have been carried out by different research groups, and many companies have replaced parts made of fossil sources by renewable materials. The use of polyurethane (PU) derived from castor oil as a matrix for composite materials and adhesives is one example. Hence, the present work aims to compare the numerical and experimental analyses of castor oil PU and epoxy resin not only as a matrix of composite materials, but also as an adhesive of bonded joints. The joint coupons were manufactured by using castor oil PU-glass fibre and epoxy-glass fibre as adherents, which were bonded by epoxy or castor oil PU. Thus, four combinations of adherents and adhesives were investigated. Specimens with identical geometry were used in all tests, which were based on guidelines for single lap bonded joints. Computational simulations via Finite Element Method were performed for predictions of the adhesive layer stresses and strength. In addition, a material model is proposed to predict the failure of the adhesive layer. The experimental and numerical results showed that PU derived from castor oil has good mechanical performance, making this material a feasible alternative for bonded joints, mostly nowadays when environment is a major concern.     

The effect of adherend alignment on the behaviour of adhesively bonded double lap joints

For an adhesively bonded double lap joint, end mismatch between the two outer adherends can not be removed completely although it can be controlled within a manufacturing tolerance. This paper shows that the end mismatch introduces local bending and, consequently, results in a significant effect on the surface normal displacement. Furthermore, the end mismatch also affects the shear and peel stresses in the adhesive. To include the end mismatch effect, a modified equation is developed to characterise the peel stress in the adhesive layer in terms of the surface normal displacement measured using the holographic interferometry technique. The surface normal displacement predicted by the FEM is validated experimentally. A good correlation is also noted between the adhesive peel stress computed using the FEM and that calculated using the modified equation and the measured surface normal displacement.     

Numerical analysis of the strength and interfacial properties of adhesive joints with graded adherends

The strength and interfacial behavior of single lap joints with graded adherends subjected to uniaxial tensile loading are investigated in the present paper. A bilinear cohesive zone model coupled with the finite element method is adopted to describe the damage and failure process of the adhesive layer. The peak loading, the rotation angle between the overlap of the joint and the horizontal direction, as well as the failure energy are investigated comprehensively. It is interesting to find that adopting different variation law in the graded adherends may result in varying strength of adhesive joints. By means of choosing proper material and geometry parameters of adhesive joints, the peak loading, the rotation angle and the failure energy of joints can be greatly improved. What is more, the strength of the SLJ is found to depend much more on the property of the soft part near the adhesive layer. The results should be helpful to guide the design of novel structures of adhesive joints in present and potential applications.     

Non-linear analysis and optimization of adhesively bonded single lap joints between fibre-reinforced plastics and metals

Non-linear finite element methods are applied in the analysis of single lap joints between fibre-reinforced plastics (FRP) and metals. The importance of allowing for both geometric and material non-linearities is shown. The optimization of single lap joints is done by modifying the geometry of the joint ends. Different shapes of adhesive fillet, reverse tapering of the adherend, rounded edges and denting are applied in order to increase the joint strength. The influence of the joint-end geometry is shown for different metal adherend/FRP adherend/adhesive combinations. The results of the numerical predictions suggest that with a careful joint-end design the strength of the joints can be increased by 90–150%.     

The effect of orientations of metal macrofiber reinforcements on mechanical properties of adhesively bonded single lap joints

A method for improving the mechanical behavior of adhesive joints is embedding metal macrofibers to the adhesive layer. The effect of the orientation of metal macrofibers laid across the length and width of the joint (longitudinal and transversal directions) on the strength and elongation at failure of single lap joints (SLJs) was investigated experimentally by testing SLJs reinforced with metal macrofibers laid in different orientations. The experimental results indicated that increasing the number of metal macrofibers in the longitudinal direction improved the shear strength and elongation at failure of SLJs. However, the improvements were found to be dependent on the normalized horizontal distance between the metal macrofibers for which a proper value of 1 was determined. While embedding metal macrofibers in the transversal direction degraded the mechanical properties of SLJs. Finite element analyses were undertaken to investigate the effects of fibers orientation and horizontal distance on the adhesive peel and shear stress distributions. The results revealed that decreasing the horizontal distance between the metal macrofibers laid in the longitudinal direction decreased the adhesive shear stress values indicating improvement of the joint strength, while in SLJs reinforced with metal macrofibers laid in the transversal direction decreasing the fibers distance increased the adhesive peel stress values resulting in joint strength reduction.     

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.