Evaluation of cast-on-strap joints in lead-acid batteries

The effects of various processing parameters on the lug–strap joint quality of lead-acid auto-batteries are investigated using a laboratory scale cast-on-strap (C.O.S.) set-up. The results indicate that while good quality joints are easily obtained at low cooling rates, at high cooling rate all the C.O.S. parameters such as flux type, strap composition and melt temperature must be carefully controlled to achieve an acceptable joint. Surface treatment with commercially available fluxes, strap melt temperature of 460 °C and strap antimony content of 4.6wt.% Sb render good quality joints at a high strap cooling rate. Furthermore, a dimensionless parameter (relative contact length) for evaluation of lug–strap joint quality is introduced which combines the important lug–strap joint features into a single quantitative parameter and could be used for design of experiments (DOE) and process optimization in the industrial scale.     

On the behavior of bonded joints in composite material structures

The application of advanced reinforced composite materials in aerospace structures during the remainder of this century is widely predicted. The joining of structural components by adhesive bonding is extremely desirable, because both bolting and riveting result in the cutting of fibers as well as the introduction of stress concentrations, both of which reduce the structural efficiency. R.E. Watson states that, “The next two decades will surely see dramatic advances in structures as compared to those experienced over the last 30 years. Improved titanium alloys and the advanced high strength composites, with more strength per pound than aluminum, will be the principal materials used.” Further he writes, “New bonding techniques will gradually replace riveting in many applications, permitting greater design stresses and more efficient distribution of the materials.”Because in aerospace structures dynamic loads are always present, it is absolutely essential that the fatigue behavior of bonded joints between composite material components be better understood, in order to have available design principles and rationale to take advantage of the desirable characteristics of composite materials.To date the few isolated experimental studies of composite-composite or composite-metal adherend bonded joints have been conducted under static and/or constant amplitude cyclic loading, and no generally accepted cumulative damage theories have evolved.The present research is a systematic, analytical and experimental program of study concentrating on those parameters considered to be the most influential on the static and fatigue life of an adhesive bonded single lap joint. The objectives of the program are to better understand the reasons why certain parameters have such a large influence on the structural integrity of the joint. As a result it is hoped that considerable insight will be gained as to static and fatigue life of more complicated joints such as the doable lap, the scarf, and the stepped lap joints. The analytical as well as the experimental static and fatigue test portions of the program are reported on herein.The following parameters, deemed to be the most important, were selected for study: overlap length, adhesive thickness, orientation of the laminae of the laminated adherends (particularly the lamina immediately adjacent to the adhesive), and the effect on the fatigue life of whether or not the mean value of the fatigue load causes maximum stresses above or below the shear proportional limit of the adhesive material.The determination of stresses in the test specimens is made by an analysis method developed in this program.     

Bond–slip models for double strap joints strengthened by CFRP

This paper presents the results of a series of tension tests on CFRP bonded steel plate double strap joints. The main aim of this research is to provide detailed understanding of bond characteristics using experimental and numerical analysis of strengthened double strap joints under tension. A parametric study has been performed by numerical modelling with the variables of CFRP bond lengths, adhesive maximum strain and adhesive layer thicknesses. Finally, bond–slip models are proposed for three different types of adhesives within the range of the parametric study.     

End geometry and pin-hole effects on axially loaded adhesively bonded composite joints

An experimental investigation was performed to analyze the potential impacts of varying joint region geometries and adhesive filled pin holes on adhesively bonded composite structures. Tapers, especially half-length ones are observed to provide an anticipated progress in single lap joints. Besides, scarf joints with aligned adherends in the same plane exhibited enhanced stiffness and strength in consideration of single lap joints. In terms of the stiffness and strength, thickening of adherends was also found to be impressively efficient on composite single lap joints as well as scarf joints. Contrary to the expectation of that the hardened adhesive previously filled into the holes during adhesion would create a pin effect in load bearing, holey specimens exhibited poor performance and induced degradation in joint quality.     

FRP-to-concrete joint assemblages anchored with multiple FRP anchors

Mechanical anchorage can enhance the strain capacity of externally bonded fibre-reinforced polymer (FRP) composite plates which are used for the strengthening of concrete members. Anchors made from FRP, which are known as FRP anchors or spike anchors, are an effective anchorage because they can be applied to a wide variety of FRP-strengthened structural elements such as beams and slabs. Limited research and understanding of FRP anchors in isolation or in groups is, however, hindering their rational design. As a result of such a knowledge gap, a series of tests is reported in this paper on forty-one FRP-to-concrete joints anchored with single as well as multiple FRP anchors in addition to two unanchored control joints. Apart from the number of anchors, the location of the anchors is investigated in addition to the method of anchor installation. The displacement controlled nature of the tests has enabled the complete load-slip responses of the joints to be captured, as well as FRP plate strains, and such results facilitate valuable insights to be gained in behaviour and understanding. The optimal arrangement of anchors tripled the strength of anchored joints relative to the unanchored control joint average. In addition, the slip capacity was generally increased at least five fold. Finally, a simple analytical model is also presented which is shown to compare reasonably well with the test results.     

Correlating bonded joint deformation with failure using a free surface strain field mining methodology

In this work we present a strain field mining methodology where the intensities and spatial distributions of strains in double lap strap epoxy (EA 9394) bonded joints are measured, analysed and correlated with bond strength. While the global behaviour of the bonded joints was linear elastic at room temperature, discrete regions of elevated (relative to the full field average) shear strains were observed. The size, spatial distribution and other features of these strain ‘hot spots’ were described with a metric called the homogeneity index. This index captures the uniformity of the strain field with respect to regions of positive and negative strain at a specific stress level. The linearity of the progression of the homogeneity index and its magnitude was correlated with a joint's fracture strength and failure mode. The index was a robust predictor of double‐lap strap bonded joint performance between 30% and 90% of a specimen's strength and can be used to improve joint design, manufacturing, quality assurance, maintenance and inspection.     

Stress-function variational method for stress analysis of bonded joints under mechanical and thermal loads

High interfacial stresses near the ends of adherends are responsible for debonding failure of bonded joints used extensively in structural engineering and microelectronics packaging. This paper proposes a stress-function variational method for determination of the interfacial stresses in a single-sided strap joint subjected to mechanical and thermal loads. During the process, two interfacial shear and normal (peeling) stress functions are introduced, and the planar stresses of adherends of the joints are expressed in terms of the stress functions according to the static equilibrium equations. Two coupled governing ordinary differential equations (ODEs) of the stress functions are obtained through minimizing the complementary strain energy of the joints and solved explicitly in terms of eigenfunctions. The stress field of the joints based on this method can satisfy all the traction boundary conditions (BCs), especially the shear-free condition near the adherend ends. Compared to results based on finite element method (FEM) and other analytic methods in the literature, the present variational method is capable of predicting highly accurate interfacial stresses. Dependencies of the interfacial stresses upon the adherend geometries, moduli and temperature are examined. Results gained in this study are applicable to scaling analysis of joint strength and examination of solutions given by other methods. The present formalism can be extended conveniently to mechanical and thermomechanical stress analysis of other bonded structures such as adhesively bonded joints, composite joints, and recently developed flexible electronics, among others.     

The effect of environment on the fatigue of bonded composite joints. Part 1: testing and fractography

In this work, the effect that test environment and pre-conditioning had on the fatigue behaviour of CFRP/epoxy lap–strap joints was investigated. It was shown that the fatigue resistance of the lap–strap joints did not vary significantly until the glass transition temperature, T_g, was approached, at which point a considerable reduction in the fatigue threshold load was observed. It was also noted that absorbed moisture resulted in a significant reduction in the T_g of the adhesive. This must be taken into account when selecting an adhesive to operate at elevated temperatures. The locus of failure of the joints was seen to be highly temperature dependent, transferring from primarily in the composite adherend at low temperatures to primarily in the adhesive at elevated temperatures. It was also seen that as the crack propagated along the lap–strap joint, the resolution of the forces at the crack tip tended to drive it into the strap adherend, which could result in complex mixed mode fracture surfaces.     

Experimental study on CFRP-to-steel bonded interfaces

This paper presents an experimental study on the behaviour of CFRP-to-steel bonded interfaces through the testing of a series of single-lap bonded joints. The parameters examined include the material properties and the thickness of the adhesive layer and the axial rigidity of the CFRP plate. The test results demonstrate that the bond strength of such bonded joints depends strongly on the interfacial fracture energy among other factors. Nonlinear adhesives with a lower elastic modulus but a larger strain capacity are shown to possess a much higher interfacial fracture energy than linear adhesives with a similar or even a higher tensile strength. The variation of the interfacial shear stress distribution in a bonded joint as the applied load increases clearly illustrates the existence of an effective bond length. The bond–slip curve is shown to have an approximately triangular shape for a linear adhesive but to have an approximately trapezoidal shape for a nonlinear adhesive, indicating the necessity of developing different forms of bond–slip models for different adhesives.     

A bonded joint finite element for a symmetric double lap joint subjected to mechanical and thermal loads

A bonded joint finite element (FE) for a symmetric double lap joint is developed that is capable of predicting field quantities in the lap region. The element is a hybrid method and incorporates features of classical analytical and numerical methods. The element stiffness and load vector formulations have unique, load dependent, non‐linear shape functions based on an analytical solution. The adaptive shape functions are formulated in terms of the dimensionless mechanical load fraction $(\bar{\bar{\phi}}_P)$ and total load $(\bar{\bar{\phi}}_{\rm {tot}})$ and are capable of predicting the thermal and mechanical load response. The bonded joint element has been implemented as a user element in the Abaqus^® commercial FE code. A comparison of the stress predictions for the bonded joint element and a conventional 2D FE model is presented and are found to be in good agreement. Therefore, the element provides a computationally efficient and mesh‐independent stress prediction. The single element reproduces the analytical solution with minimal analyst input and can be easily incorporated into early design and sizing studies. Copyright © 2009 John Wiley & Sons, Ltd.     

The Parametric Analysis of a Bonded Overlap Joint Resulting in Design Guidelines and a Representation for Finite Element Analysis

Abstract: The sensitivity of the joint's stiffness to changes in certain parameters (geometric and material properties) has been investigated and an understanding of the joint's behaviour gained from this parametric study. This insight into simple overlap joint behaviour has been used to fashion some design guidelines aimed at increasing joint stiffness. A representation that can be successfully substituted for certain adhesively bonded overlap joints in finite element (FE) analyses is also suggested.     

Influence of FRP anchor fan configuration and dowel angle on anchoring FRP plates

To enhance the strain capacity of fibre-reinforced polymer (FRP) plates which have been bonded onto reinforced concrete (RC) members for strengthening purposes, FRP anchors can be utilised. Research on the characterisation of FRP anchors is still quite limited though despite the increasing use of FRP anchors in practice. In order to reduce such a knowledge gap, this paper reports the results of 30 single-shear FRP-to-concrete joint tests of which 26 joints were anchored with FRP anchors of differing geometric configurations and four joints were unanchored controls. More specifically for the anchored joints, the connection of the FRP anchor to the FRP plate via so called fan fibres was varied in addition to the angle of anchor insertion and these test parameters represent fundamentally important anchor components which have not been researched to date. Failure modes, joint strengths, load–slip responses as well as FRP plate strain distributions are reported and a relationship relating the influence of anchor insertion angle to joint strength is provided. A maximum increase in joint strength of 160% on average above the unanchored control joints was achieved. In addition, the maximum strain resisted by the FRP plate, relative to its elongation capacity, was increased on average from 25% for unanchored control joints to 67% for some anchored joints.     

Inelastic fracture of adhesively bonded overlap joints

Adhesive bonding offers a simple and efficient way of joining structural components without weakening them by holes or welding.This article develops a new model to predict the fracture load of bonded overlap joints using a fracture mechanics approach. The bondline fracture resistance and effects of the nonlinear inelastic behaviour of structural adhesives are accounted for separately. For bonded single overlap joint configurations the model is expressed as simple explicit formulas.An experimental programme is presented where the design parameters that a designer can adjust to obtain the desired joint capacity are systematically varied. Comparison of test results with the predictions by current strength-of-materials capacity models highlights disparities between the theoretical predictions and experimental evidence. In contrast, the new model shows good agreement with the experimental results.It should be noted that the simple new formulas apply to a well-defined range of bonded overlap joint configurations and do not purport to apply in general to every other joint configuration.     

An analytical solution for the analysis of symmetric composite adhesively bonded joints

Analytical solutions for adhesively bonded balanced composite and metallic joints are presented in this paper. The classical laminate plate theory and adhesive interface constitutive model are employed for this deduction. Both theoretical and numerical (finite element analysis) studies of the balanced joints are conducted to reveal the adhesive peel and shear stresses. The methodology can be extended to the application of various joint configurations, such as single-lap and single-strap joints to name a few. The methodology was used to evaluate stresses in several balanced adhesively bonded metallic and composite joints subjected to the tensile, moment and transverse shear loadings. The results showed good agreements with those obtained through FEM.     

复合材料夹芯管胶接连接结构力学特性分析

针对在航空结构中广泛应用的复合材料蜂窝夹芯圆管中的接头这一最脆弱的部分,发展了一种分析复合材料蜂窝夹芯圆管胶粘接头力学特性的解析模型.该模型根据Gibson修正公式得到了蜂窝芯子的等效弹性参数,再运用经典的复合材料壳理论和线弹性理论得到管接头的控制方程,并通过状态空间法进行求解.运用本文模型,计算了管接头在扭矩和弯矩作用下胶层内的剪应力和剥离应力;同时采用有限元法对模型进行了数值模拟,并将模拟结果与模型计算结果进行了对比,最后分析了搭接长度对胶层内应力的影响.     

Elastic analysis of hybrid bonded joints and bonded composite repairs

The authors extend the closed-form bonded joint linear elastic analysis method of Delale et al. [Delale F, Erdogan F, Aydinoglu MN. Stresses in adhesively bonded joints: a closed-form solution. J Compos Mater 1981;15:249–71] and Bigwood and Crocrombie [Bigwood DA, Crocombe AD. Elastic analysis and engineering design formulae for bonded joints. Int J Adhes Adhes 1989;9(4):229–42] to include the composite deformation mechanisms and the thermal residual strains that arise in hybrid metal-composite joints such as those presented by bonded composite repairs applied to metallic aircraft structures. The analytical predictions for the adhesive stresses and the compliance are compared to the results of a linear elastic finite element model that has itself been validated by comparison with experimental results. The results are applied to the problem of coupled linear extension and bending of a bonded composite repair applied to a cracked aluminum substrate. The resulting stress intensity factor and crack-opening displacement in the repaired plate are compared to the results of a three-dimensional finite element analysis, and also exhibit excellent results. Throughout the text, observations are made regarding the practical application of the results to failure prediction in hybrid joints, whereby the authors demonstrate the need for consistency in the analytical methods used to determine the fatigue and failure of composites from the coupon level to the analysis of the final structural details.     

Adhesively-bonded joints in metallic alloys, polymers and composite materials: Mechanical and environmental durability performance

The factors affecting the mechanical and environmental durability (or stability), and performance of the adhesively bonded joints in various adherends including metallic alloys, polymers and composite materials are studied in detail. The primary function of a joint is to transfer load from one structural member to another. In most bonded joints the load transfer takes place through interfacial shear. At present, the use of adhesive bonded joints are largely applied to secondary non-critical structures. Whereas the use of adhesive bonding in primary structural applications has been somewhat limited because of the difficulty in defining and predicting joint strength, and designing the joint geometry to optimize strength and reliability. The determination of adhesive joint strength is complicated primarily by the nature of the polymeric material itself. Since these problems are mainly mechanical in nature, stress analysis is required to understand how the force loads are distributed along the adherends and adhesive layer. Most structural engineers consider the durability or stability of a joint to be fatigue related. This is only partly true for adhesive bonds as most durability issues are driven by environmental resistance rather than fatigue loads. The environmental resistance of an adhesive bond is determined by the chemical bonds formed during cure of the adhesive and the resistance of the chemical bonds to environmental degradation. Environmental resistance is fundamental to the durability of a bonded joint or repair. Most in-service failures are caused by environmental degradation of the interface between the bonding surface and the adhesive. Although the use of adhesive bonding is increasing rapidly, there are still important issues which need to be addressed in joint analysis, design, durability, and performance considerations. Therefore, the study of joints usually involves consideration of (a) joint geometries, (b) materials (i.e., adhesives and adherends), (c) loading conditions (i.e., static and dynamic loadings), (d) failure modes (i.e., cohesive, adhesive or mixed failure modes), and (e) temperature and moisture or environmental effects (humidity, solvents, corrosion, temperature extremes, thermal cyling etc.). Therefore, in the present paper the adhesive joints are critically assessed in terms of these factors which affect the durability and performance of them.There are two basic mathematical approaches for the analysis of adhesively bonded joints: (a) closed-form or analytical model and (b) numerical solutions (i.e., finite element analysis, FEA). In the closed-form approach, a set of differential equations and boundary conditions is formulated. The solutions of these equations are analytical expressions which give values of stresses at any point of joint. The analytical approach for the solution of complex stress distributions in the joints has been progressively refined until recent times. In the second approach, solutions of differential equations are obtained by numerical methods or the continuum is represented by a discrete model at the outset. The solution of these equations gives displacements at the determined points from which strains and stresses can be obtained for any point within the model. Among the numerical methods, finite element analysis (FEA) has been extensively used with success. The two- and three-dimensional finite element analyses approaches have been extensively applied by many workers to analyse the adhesive joints considering the linear and geometric nonlinearities.     

A review on the environmental degradation effects on fatigue behaviour of adhesively bonded joints

The structural applications of adhesively bonded joints on transportation industries have been increasing, and it is expected that this rising trend persists in the future. The appropriate design of these joints should address two main issues: fatigue behaviour and environmental effects. Environmental effects consist of the degradation of the bonded joints by means of harmful influence of temperature, moisture or both simultaneously. These effects can have an impact on the fatigue behaviour of bonded joints because they influence the quality of the bonding. The combination of environmental effects and fatigue lead to synergetic consequences resulting in premature and unpredictable rupture, which transforms these issues into relevant and actual research topics. The present paper describes the most recent works addressing the referred subjects. Experimental works and analytical/numerical approaches are also described aiming to give a picture of the real state‐of‐the‐art. Actual limitations and perspectives of future evolution are also discussed.     

Analysis of composite-to-metal joints with bondline flaws

Stress analysis techniques have been developed for load transfer in metal-to-composite adhesively bonded joints with bondline flaws such as variable bondline thickness and debond in the adhesive layer. Two joint configurations, namely, single-step-lap bonded joint and smoothly tapered scarf joint, have been investigated. The problem is formulated on the basis of the assumptions that both the metal and the composite are under generalized plane stress conditions and that the adhesive acts as a shear spring. Differential equations are obtained for the load transfered from the metallic layer to the composite layer. Numerical results are obtained for the force and stress in the composite layer, the stress in the metal and the stress in the adhesive. The influence of bondline flaw location on the stresses in the adhesive and the adherends has been investigated.     

Invariability of singular stress fields in adhesive bonded joints

A numerical study of the influence of adherend stiffness on adhesive bonded joints provided an insight into some of their fundamental properties. The stress yield in the vicinity of singular locations, in stiff and flexible adherend joints, was investigated. Linear elastic finite element analysis was used to compare the different systems. A special gradual refinement technique in the vicinity of stress singularities was used and proved to be very efficient. Parametric finite element analysis allowed for development of closed form expressions for the stress distribution in the vicinity of the singular points The singular stress distribution zone is limited by the adhesive strip thickness. Thus the stress intensity factors are attenuated in comparison with homogeneous bodies. The stress field in the singular region normalized to the developed stress concentration factor, appears to be invariant, and independent of joint configuration. The subsequent invariability leads to a general relationship between the Stress Concentration Factor SCF, unique for adhesively bonded joints.