胶接接头受劈裂载荷作用应力分布研究

对金属胶接接头劈裂试样承载后的应力分布情况进行了实测分析，结果表明胶层沿胶接面试样长度方向上受到分布较宽的拉伸力的作用，印证了作者所提出的胶接接头受劈裂载荷作用力学模型是符合实际的。     

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S₁、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。     

金属胶接面上显微硬度分布的研究

本文通过测定正交拉和拉剪试样连续几次拉断后胶接面上的显微硬度分布,研究了胶接接头受载时应力的分布情况和断裂过程,结果表明被贴粘物表层存在着较大的显微硬度波动,确已发生了一定量的塑性变形,且某些区域存在着残余应力,同时也表明,试样受载时,正应力及剪应力的发布是不均匀的,如果所用过的试样不经处理,从新使用,当其受载时,粘接面上会继续发生性变形,且试样上正应力和剪应力的分布会变更加不均匀。     

剥离载荷作用下胶层内应力分布研究

讨论分析了现有的剥离力学模型,指出了其局限性与不足,建立了新的剥离力学模型以描述金属胶接接头的剥离载荷作用下胶层内的实际应分布情况,认为剥离试验中胶层中的压缩应力其实行不存在。     

胶接接头受劈裂载荷作用力学模型的建立

在讨论现有劈裂的力学模型基础上，建立了一个新的劈裂力学模型，以较好地描述在接头的胶层内的应力分布及力行为。认为载荷是以分布力的形式作用在胶层上的，该模型还可用于解释一些试验所得的结果。     

胶接接头耐久性的综合研究

以AG—80/DDS、环氧—聚砜和环氧—丁腈结构胶为胶粘剂,45~#钢和LY_(12)—CZ铝合金为被粘材料,综合研究了胶接接头的耐久性。研究结果表明,除胶粘剂外,内外应力、温度、介质和被粘物的表面状态均是影响接头耐久性的重要因素。激光双折射法测定胶接接头内应力是较可行的新方法。     

金属胶接接头的内应力及其消除

对引起金属胶接接头内应力的因素进行了分析，指出胶粘剂的受拘束收缩及受热时胶层内的塑性压缩应变发生是导致接头中出现拉伸内应力的主要原因。文中提出了消除或减轻金属胶接接头拉伸内应力的有效工艺措施。     

胶接接头力学研究回顾

回顾了胶接接头力学性能方面的研究进展 ,并讨论了进一步研究的方向。     

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．     

胶粘剂特性和厚度对劈裂载荷作用下胶接接头应力分布的影响

运用三维弹塑性有限元法对劈裂栽荷作用下的胶接接头(即劈裂接头)承载后的应力分布特征进行了分析，重点研究了胶粘剂层厚度对劈裂接头应力分布的影响。结果表明，胶粘剂的性能对应力分布有较大影响，提高胶粘剂强度和减小胶层厚度，均导致胶层应力集中加剧，各向正应力峰值呈上升趋势，各向剪切应力则正好相反；并且劈裂接头中应力分布以三向主应力为主，剪切应力的存在亦不可忽略。故在不引起过大应力集中和较大胶层缺陷条件下采用高强度的胶粘荆和较厚胶层对提高劈裂接头强度有利，实验结果与有限元分析相吻合。     

Load transfer in adhesive double-sided patch joints

In this work, the application of adhesively bonded joints to connect two structural elements with a double-sided patch is studied. On the basis of the shear lag model, a simple closed-form solution was obtained. The analytical solutions can be used to predict the shear stress in the adhesive and the load transfer between the structural elements and the external patches. The load and shear stress distributions in the adhesively bonded region are presented. For verification of the analytical model, finite element analyses were employed to calculate the load transfer and shear stress for the double-sided patch joint under static tensile loadings. Good agreement was found between the theoretical predictions and numerical results. To obtain a better understanding of the joints, the effects of adhesive thickness, adhesive shear modulus and patch Young's modulus on the load transfer and shear stress distributions were investigated. The results show that the maximum shear stress occurs at the edge of the adhesive. The maximum value of the shear stress increases as the adhesive shear modulus and patch Young's modulus increase and as the adhesive thickness decreases. A more gradual load transfer can be achieved by increasing the adhesive thickness and decreasing the adhesive shear modulus. The simple analytical solution presented in this paper has the advantages of avoiding the numerical difficulties and giving explicit relationship between the stress state and joint parameters. Moreover, from the designer's point of view a closed-form and easy-to-use solution is preferred.     

Study of the singular term in mixed adhesive joints

In the numerical modelling of mixed adhesive joints, where different materials are disposed along the bond-lines, trimaterial singularities may arise at the adhesive bands transition points, resulting in mesh-dependent models. This work is focused on the study, characterization and treatment of these type of singularities. Firstly, the selection of an intermediate adhesive material for generating a tailored transition between bands is addressed, using analytical solutions and then corroborating by means of a novel technique for determining the influence distance of the singularity with the finite element method as calculation tool. Furthermore, it is proved how a continuum material field transition between bands produces a convergent finite element solution applying the considerations of this framework (analytical asymptotic solutions). Finally, in order to achieve the best numerical convergence rate in the models, the optimum material transition function is obtained and checked through FEM.     

Analysis of mixed adhesive joints considering the compaction process

Incorporating a material properties variation along the bondlines has proved to be a useful method for improving adhesive joints performance. In this work, the potential of the technique is analysed for a single lap joint using the mixing adhesives approach. In order to include the compaction process effect in the structural analysis during the joint assembly, a computational fluid-dynamic model capable of integrating different resins along the bondline has been developed. Then, the results obtained from this model are mapped into a finite element model through an application developed for this purpose. Several parametric studies have been carried out comparing different configurations in terms of maximum load capacity of the joints. Finally, one of these joints configurations has been manufactured using a special device developed for assembling these mixed adhesive joints and tested. This banded configuration have shown both numerically and experimentally an ultimate load improvement of over 70%.     

Reliability analysis of bonded joints with variations in adhesive thickness

Bonded joints are used in several industrial applications as a surrogate of more expensive repairs, but their reliability must be ascertained. Failure in a bonded joint mainly occurs in the adhesive due to stress concentrations that directly depend on the adhesive thickness. In practice, it is difficult to ensure a good accuracy of the final adhesive thickness, leading to uncertainty to its spatial variability. This uncertainty greatly influences the strength of the bonded joint. This work deals with one of the main key issues in bonded joints: the influence of the spatial variations in the adhesive thickness on the reliability of the joint and an excessive shear stress level caused by the adhesive thickness variations may lead to failure. This paper provides reliability analysis by considering the adhesive thickness as a stochastic field. The experimental thickness field is obtained so as to identify the stochastic parameters. These parameters are then introduced in a structural reliability model to evaluate the failure probability. Results show the influence of adhesive thickness uncertainty on bonded joint failure.     

Determination of the strain distribution in adhesive joints using Fiber Bragg Grating (FBG)

This work focuses on the development and testing of a technique used to measure strain levels inside an adhesive joint. As more industries adopt high performance structural adhesives, the need for structural monitoring and quality control of adhesive joints rises. The method presented in this work, based on optic fibers, is proposed as a possible means for real-time health monitoring of adhesive connections. In the first part of this work a procedure for embedding optical fibers etched with Bragg sensors is explained. Instrumented, single lap joints were fabricated and subjected to tensile test. The results were compared with finite element models to ensure the accuracy and provide a better understanding of the measurement process.     

The effect of a multicomponent silane primer on the interphase structure of aluminum/epoxy adhesive joints

The structure of films formed by a multicomponent silane primer applied to an aluminum adherend and the interactions of this primer with an amine-cured epoxy adhesive were studied using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and attenuated total reflectance infrared spectroscopy. The failure in joints prepared from primed adherends occurred extremely close to the adherend surface in a region that contained much interpenetrated primer and epoxy. IR spectra showed evidence of oxidation in the primer. Fracture occurred in a region of interpenetrated primer and adhesive with higher than normal crosslink density. The primer films have a stratified structure that is retained even after curing of the adhesive.     

3-D FEM stress analysis and strength evaluation of single-lap adhesive joints subjected to impact tensile loads

The stress wave propagations and interface stress distributions in the single-lap adhesive joint under impact tensile loads are analyzed using the three-dimensional finite element method (3D-FEM) taking into account the strain rate sensitive of the adhesive using Cowper–Symonds constitutive model. It is found that the rupture of the joint initiates near the middle area of the edges of the interfaces along the width direction. In addition, the effects of Young's modulus of the adherend, the overlap length and the thickness of the adhesive layer, and the initial impact velocity of the impacted mass on the stress wave propagations and the interface stress distributions are examined. The characteristics are compared with those of the joint under static loads, which show the different properties. Furthermore, experiments are also carried out for measuring the strain responses and the joint strength. A fairly good agreement is observed between the numerical and the measured results. The strength of the single-lap adhesive joint, which is described using impact energy, is obtained between 5.439 and 5.620 J for the present joint.     

Stress wave propagation in a through-thickness functionally graded adhesive layer

In this study, an improved mathematical model is presented to investigate the stress wave propagation in two circular cylinders bonded with a functionally graded adhesive layer. In the proposed model, the spatial derivatives of mechanical properties are included in the governing equations of the wave propagation. Also, the finite-difference method was used for the solution of the governing equations and boundary conditions. The Mori-Tanaka homogenization scheme was employed to evaluate the through-thickness mechanical properties of the adhesive layer. The effects of the spatial derivatives of the local mechanical properties and the through-thickness material composition variation in the adhesive layer were examined in detail. The presence of the material spatial derivatives in the governing equations mitigated the stress and displacement levels as well as axial and radial wave speeds.