Experimental Study of Adhesively Bonded Single Lap Joint Behaviour in CFRP-to-CFRP, Al-to-Al, and CFRP-to-Al Configurations

Prestressed joints are widely used in construction using connectors in the form of screws, whose task is to strong clamping of joined parts, thereby the internal forces in joint are transferred by surface friction contact of the elements. In the automotive and aerospace industries hybrid joints are more widely applied. Mechanical connectors are added to the adhesive joint in form of rivets, screws or clinch increasing its strength properties. The aim of this study was to determine how the prestressed connectors influence the mechanical response of hybrid, single and double lap joints. The influence of different distribution of the connectors was also investigated. Numerical study was conducted in ABAQUS program. Mechanical connectors were modeled by using fasteners, that allowed for a considerable simplification of the numerical model. In their application, there is no need for an additional submodels for connectors in the form of the rivet or the bolt. Prestressing is activated by direct application of the force to the connector. In the numerical examples the authors assumed that the diameter of the mechanical connectors was equal to 6mm and shear strength was equal 1kN. Adhesive layers were modeled by using cohesive elements for which maximum shear stresses and fracture energy were specified. The layer thickness was assumed to be equal 0.1mm and it was initially removed from the areas where mechanical connectors were placed. Two types of joints were analysed in the study: the single lap joint with lap dimensions 40x40mm as well as the double lap joint with lap dimensions 40x20mm, from which it results that theoretical strength of both connections should be the same. The prestressing of connectors was introduced by the force 1.5kN. For all pure - mechanical joints and for single lap joints positive effects were obtained. For double lap joints additional prestressing did not significantly affect for their strength. The influence of distribution of mechanical connectors was additionally analyzed by consideration of three configurations, where the rows of rivets were located at distances of 5, 10 and 15mm from the lap edge. The maximum increase of the load capacity by 24% was achieved for single lap joint as well as 35.7% for double lap joint. The obtained numerical results indicate the positive effects of additional pressure and allows for practical suggestions how to correct and optimize spacing distance of mechanical connectors in hybrid joints to get better mechanical response.

The extensive utilization of composite materials has spurred the advancement of diverse joining techniques suitable for components constructed from such materials. This study focuses on the examination of two specific types of joints: single lap and joggle lap joints. The specimens utilized were composed of unidirectional carbon fiber composite combined with vinyl ester resin, manufactured via the vacuum-assisted resin infusion method. Vinyl ester adhesives were employed in the bonding process, with the joint surfaces undergoing sanding treatment prior to testing. Mechanical testing was conducted on the specimens according to ASTM D5868 standard, employing a constant crosshead speed until failure occurred. The test results reveal that the shear strength of single lap joints surpasses that of joggle lap joints. Within the single lap joint configuration, a mixed failure mode comprising both adhesive and cohesive failure is observed. Conversely, in joggle lap joints, substrate delamination is prevalent, suggesting the predominance of peel stress during loading.

This paper is focused on experimental evaluation and comparison of progressive damage behaviors in adhesively bonded single lap and double butt lap joints between aluminum and glass fiber reinforced plastic (GFRP). The effect of joint design and dissimilarity of adherents on damage evolution of adhesive bonding under tensile quasi static loading is analyzed. Bonding was created by toughened epoxy adhesive as one of the most important and widely used structural adhesives in aerospace, automobile and marine industries. Due to structural behaviour complexity of adherents and adhesive, the fracture takes place under mixed mode and the failure mechanism is characterized by the de-bonding area for the proposed joints. The results show that single lap joint could carry up to 30% more tensile load than the double butt lap joint with the same material properties while a combined failure mechanism could be observed and the most dominant ones were yielding of aluminum substrates, adhesive failure at bond-line on aluminum surface and cohesive failure of upper mat layers of composite material.

Carbon-carbon (C/C), carbon-carbon-silicon carbide (C/C-SiC) composites and titanium alloy substrates were bonded in single lap and overlap joints with phenolic resin to study the differences in joint strength of two similar and dissimilar materials under shear load. The results indicate that the bonding strength of single lap joint of C/C, C/C-SiC is more than the other ceramic and titanium alloy, whereas Ti-Ti bonded over lap joints show remarkable improvement in similar and dissimilar substrates. Scanning electron microscope (SEM) describes the surface morphology and indicates the bonded zone fractured in the form of thin film which shows strong interaction in between two surfaces. Key words: C/C composite, C/C-SiC composite, titanium alloy, adhesive joints, bonding strength.

This study focuses on the three-dimensional free vibration analysis and modal stress analysis of adhesively bonded composite single lap and tubular lap joints subjected to clamped-free conditions, and on the effects of fiber angle, fiber volume fraction, overlap length, plate/tube thickness, and tube radius on the natural frequencies and the mode shapes of adhesive joints using the back-propagation artificial neural network (ANN) method. Free vibration and stress analyses were carried out using the finite element method for random values of fiber angle, fiber volume fraction, overlap length, plate/tube thickness, and tube inner radius, so that the proposed ANN models can be trained successfully to predict the natural frequencies as well as the corresponding modal strain energies. The ANN models indicated that fiber angle was a more dominant parameter than fiber volume fraction on the natural frequencies and corresponding mode shapes, and plate/tube thickness, tube inner radius, and overlap length were important geometrical design parameters, whereas the adhesive thickness had a minor effect. In addition, genetic algorithm was combined with the trained ANN models to achieve the optimal joint design that satisfies maximum natural frequencyCONTENTS10.1 Introduction 252 10.2 Dynamic Equations of Motion 255 10.3 Micromechanics of Composite Materials 256 10.4 Free Vibration Analysis of Composite Single Lap Joint 258 10.5 Composite Tubular Single Lap Joint 271 10.6 Conclusions 286 References 288

Adhesive bonding has become a powerful joining technique during the last few decades. It has many applications in aerospace, automotive and other industries. One of the major advantages of adhesive bonding, compared to riveting or welding, lies in its superior fatigue resistance. In this paper, fatigue crack propagation in adhesively bonded joints is analysed and discussed. Three different bonded joints are considered in this study, namely Double Cantilever Beams, Single Lap Joints and Double Lap Joints. Experimental samples were made from carbon fibre composite substrates bonded with an epoxy adhesive. The joints were tested in constant amplitude fatigue at different loads and plots of load against number of cycles to failure were obtained. A crack propagation law was then derived from the experimental results of the Double Cantilever Beam and implemented in a finite element based predictive tool in order to predict the number of cycles to failure for Single Lap and Double Lap joints subjected to cyclic fatigue loading. The prediction technique is based on numerically integrating the crack growth law along the bonding line from an initial crack length to a final crack length. A comparison of mode I strain energy release (G(I)) and total strain energy release rate (G(T)) as failure criteria in the prediction procedures is presented.

Calculated torque transmission capability of adhesively bonded tubular lap joints using linear elastic material properties is usually much less than the experimentally-determined one because the majority of the load transfer of the adhesively bonded joints is accomplished by the nonlinear behavior of rubber-toughened epoxy adhesives. Although the adhesively bonded tubular double lap joint has better torque transmission capability and reliability than the single lap joint, the nonlinear analytic or numerical analysis for the adhesively bonded tubular double lap joint has not been performed because of numerical complications. An iterative solution that includes the nonlinear shear behavior of the adhesive was derived using the analytic solution. Since the iterative solution can be obtained very quickly due to the simplicity of the algorithm, it is an attractive method of designing adhesively bonded tubular single and double lap joints.

ABSTRACTFailure and fracture response of two shear resistive joints namely, single lap joint (SLJ) and double butt lap joint (DBLJ) of aluminium and GFRP adherents bonded with a ductile adhesive, has been investigated experimentally and numerically under static tensile loading. Numerical simulations were carried out by the CZM approach through 2D and 3D FE models. The joints progressive damages and effects of various cohesive parameters were analysed. In spite of some previous studies showing lower strengths in SLJs compared to DBLJs with aluminium adherents, here, the results indicated that in an AL-GFRP bonded SLJ, tensile strength may averagely be 33% higher than that for DBLJ. Failure load and stiffness were overestimated by the FEM with the CZM approach. A compound failure mechanism was observed in both type of joints with the most dominant failure mode of light fibre tear in mat layer of composite adherents and yielding of aluminium adherent.

A study on fatigue crack propagation in thick composite adhesively bonded joints

The importance of Fibre Reinforced Polymers (FRPs) as a material used for civil engineering purposes has grown in the last decade. Especially the introduction of pultrusion at an industrial level as a way to produce big batches of FRP made it possible to offer the advantages – like the high strength-to-weight ratio or the good corrosion resistance – at a reasonable cost. One issue when designing with pultruded FRPs are the connections. Up to now, connections between pultruded FRPs have been designed in the same way as structural steel connections, mainly through bolts. Because of the fibrous and layered character and the anisotropy of pultruded FRPs, bolting is not a material-adapted way to connect. Adhesive bonding is by far better suited, but has not yet been investigated for the special case of pultruded FRPs. This research is intended to fill the gap by offering designing engineers a method allowing them to dimension safe and economic adhesively bonded joints of pultruded FRPs under static loads. The present Thesis is aimed to show the steps leading to this method. After a short introduction, where the objectives and methods used are listed, the actual state of the art is presented. The review of actual literature shows that not much has been done on the special field of adhesively bonded connections of pultruded FRPs, neither experimentally nor theoretically. Some publications treat the global aspect of bonded connections for special cases like the single and double lap joints, but all on idealized mechanical systems with isotropic adherents. Also, there are no detailed reports of a mechanical failure criterion for both describing and quantifying the failure of pultruded FRPs. To overcome this, experimental investigations were carried out at different levels: the basic FRP material has been investigated in both senses of revealing the fibre architecture – with the help of burn-off tests – and the material strength – using a device the Author especially developed for this purpose: the CCLab Shear-Tensile device. This device allows the determination of the material strength subjected to combinations of out-of-plane and shear stresses. The device was also used to determine an important basic material property necessary to numerically formulate the anisotropy: the out-of-plane E-Modulus. Besides the investigations on the basic material, experiments on bonded single and double lap joints were carried out where the influence of parameters like the length of the bonded overlap, the thickness of the adherents and stress reduction methods (like chamfers of fillets) on the ultimate load was investigated. All of these experimental investigations were carried out on relatively big specimens to avoid the influence of any size effects. The experimental results showed that the adhesive layer thickness and stress reduction measures like chamfers are by far less influential that former publications expected them. For selected geometric configurations, the axial strain development along the bonded splice was experimentally gathered using strain gauges. Comparisons with FEA showed that by using the right mechanical input parameters in regard to the anisotropy, it is possible to model, with sufficient accuracy the stresses inside adhesively bonded joints of pultruded FRPs. Some single and double lap joints were filmed using a high-speed camera (up to 2000 fps) to investigate the failure process. This failure process is closely linked to the fibre architecture in the sense that it has been shown that the failure is triggered inside the laminate. The entire group of experimentally investigated specimens were then modeled with the Finite Element Method using orthotropic elements. In combination with the experimentally gathered material failure criterion, it was possible to formulate a method based on the comparison of stresses in the joint and the material resistance to predict the ultimate load of single and double lap joints, which was validated for a wide range of geometrical configurations. A simplified version of this method, based on existing analytical formulae, was then developed to make the strength prediction of adhesively bonded joints of pultruded FRP shapes available for civil engineering purposes.

Adhesive-bonded joints are widely used in the industry. Recently, applications of adhesive bonding joints have been increased extensively in automobile and aircraft industry. The strength of adhesive joints is influenced by the surface roughness, adhesive shape, stress distribution, and etc. However, the magnitude of the influence has not yet been clarified because of the complexity of the phenomena. In this study, as the fundamental research of adhesive bonding joints, the effects of adhesive shape and loading speed on bonding strength properties and durability of aluminum to polycarbonate single-lap joints were studied. To evaluate the effect of adhesive shape, several modified shapes were used, and loading speeds were varied from 0.05 to 5 mm/min. As a result, the load-displacement distribution was shown a brittle fracture tendency. The trigonal edged single lap and bevelled lap joints showed the higher strength than the plain single lap, trigonal single lap, joggle lap and double lap joints in same adhesive area. The fractures of trigonal single lap and trigonal edged single lap joints that had the higher strength level were shown as the mixture type of the cohesive and interfacial-failure, mostly joggle lap joints that had the lower strength level were shown as the adhesive-failure.br/

Creep behaviour and tensile response of adhesively bonded polyethylene joints: Single-Lap and Double-Strap

In this paper by employing ANSYS Workbench software and three-dimensional finite element simulation, failure analysis of hybrid bonded and bolted single and double lap joints with laminated composite adherends subjected to axial, shear and bending loads were performed. In order to select an appropriate and optimized element number, the convergence behavior of single and double lap joints were investigated. Then the failure study of each single and double lap hybrid composite joints for the three time dependent loading cases were performed. To demonstrate the validity and precision of the presented simulations, the obtained results were compared with the results presented in the available literatures. The results of this research indicated that, in the single lap joint subjected to axial load, the replacement of hybrid bonded bolted joint instead of adhesive joint leads to significant increase of 56% in the load bearing capacity of the joint.

The effect of a crack in the overlap region of a single step lap joint is studied on the shear distribution in the adhesive layer. Each adherend is considered to be a lamina with unidirectional fibers aligned in the direction of the applied load. Crack location is selected to be in the top adherend, in the form of cut fibers and matrix bays. The shear-lag model is used to derive the equilibrium equations which are then solved using eigenvector expansion. Additionally, a finite element model of the lap joint was prepared and solved using ANSYS. The results of the two methods perfectly match each other. The effects of crack location along the length of the overlap, crack size, edge cracks, adhesive thickness, and type of fibers were investigated on the shear distribution in the adhesive layer and its corresponding peak values. The effect of dissimilar adherends was also investigated on the adhesive shear stress distribution. According to the results, in the presence of a crack, the peak adhesive shear stress is very susceptible to adhesive thickness and type of fibers used in each adherend. Other factors also influence the peak shear stress to some degree.

Numerical simulation and failure experiment of hygrothermal aged CFRP single and double lap joints