اتصال چسبی

Orthotropic plates used in composite structures are subject to local buckling, including compressive buckling. In the process of designing and building most large structures or instruments with complex geometry, joints in the structure are unavoidable. Today, adhesive joints are widely used in connecting composite structures due to some advantages over mechanical joints. In this article, the buckling phenomenon of orthotropic rectangular multilayer plates connected with glue has been investigated, and the force effects of the glue layer under buckling loading conditions have been studied. In order to obtain the critical buckling loads under different boundary conditions, the generalized differential quadrature method (GDQM) has been used. Buckling analysis is presented based on first-order shear deformation theory (FSDT) for carbon/epoxy, glass/epoxy and Kevlar/epoxy composite materials with different porcelain layers. The effect of thickness and type of the adhesive as a bonding layer has been investigated. In plates made of a type of porcelain layer, two-way carbon epoxy plates show higher buckling strength, and in general, the higher the ratio of length to width of the plates is, the higher the buckling strength will be. In the connections, the obtained results have been compared with the results from the finite element analysis in ABAQUS commercial software.

The proper method for jointing Carbon fiber reinforced polymers (CFRP) to aluminum, which causes uniform stress distribution, more suitable fatigue performance and weight reduction, is adhesive bonded joint. In adhesive bonding, the interface of adhesives and adherent are sensitive areas for the initiation and propagation of failure. In order to eliminate surface contamination, adherents must be surface treated. In this research, the effect of the functional pattern of laser surface treatment on the strength of aluminum/composite adhesive bonded joint in the mode I fracture has been investigated. At first, laser surface treatments were performed throughout the specimen in order to find the parameters of the laser device that increase the strength of the adhesive bonding by creating a suitable surface quality. After that, the functional pattern of laser surface treatment with the appropriate parameters for ablation and cleaning of the adhesive surface is done. The results show a 15.5% increase in the critical strain energy release rate of the mode I for the all-over laser surface treatment specimen compared to the sanding method. Meanwhile, with the functional pattern of laser surface treatment, the critical strain energy release rate of the mode I has increased by 5.9% and 22.4% compared to all-over laser surface treatment and sanding, respectively. Examining the fracture surface of the specimen shows the delay in crack growth in the specimen of the functional pattern with changes from the adhesive failure to the fiber tearing, which has improved the strength of the adhesive bonding.

In this paper, the design, fabrication and testing of a single L-shaped adhesive bond between a composite sheet and an aluminum piece under tensile loading has been performed experimentally. In this experimental study, nanographene sheets with different weight percentages have been used to strengthen the composite and structural adhesive (compatible with the composite phase phase resin) to improve the mechanical properties of the joint. The effect of changing the base length of the aluminum L-shaped piece on the bond strength has also been investigated. 12 bonding modes with a combination of weight percentages of 1.0 and 0.3 for multilayer and weight percentages of 0.1, 0.3 and 0.5 for adhesive were made and examined by considering 5 repetitions of the test. has taken. By comparing and examining the tensile test results of the samples and photographs taken by scanning electron microscopy (SEM) of the separation of the multilayer and the L-shaped piece at the separation site, it was found that the bonding combined with zero weight percentage for multilayer and The weight percentage of 0.3 for the adhesive has the highest tensile strength. This means that the addition of nano-graphene without surface-modifying agent to the multilayer reduces the tensile strength and adding it to epoxy resin epr 1080 as a homogeneous adhesive with the composite improves the tensile strength of the joint. Finally, the effect of increasing the length of the overlap area of ​​the two adhesive pieces was investigated.

Defects in adhesive joints are an important issue in the construction of space structures. In this paper, using lamp waves, suitable properties have been obtained to identify the size and position of the defects of the adhesive joints. Using finite element simulations, the effect of the defect on the propagation of the lamp waves has been investigated. Simulations have been performed for three different adhesive thicknesses, three different sizes of circular defects in 9 different positions, and the effect of each of them on the wave passing through the joint has been investigated. The signals obtained from the faulty connections were compared with the signal obtained from the healthy connection and the desired area was isolated from the total received signal for further analysis. The proper and correct separation of defects requires finding suitable characteristics for it. Therefore, 34 features were examined to differentiate and separate defects. Then, the neural network was used to provide the basis for creating appropriate patterns for the separation of defects. The percentage of correct detection of neural network for adhesive thickness separation was 93.8%, for defect area separation in terms of size 100% and for defect position separation in X and Y axes were 96.1 and 95.1%, respectively. The obtained results show the efficiency of the improved distance evolution method and the features selected to distinguish the defects of such connections.

In this article the effect of the displacement rate under tensile loading on the adhesive connection in glass-epoxy and carbon-epoxy composite and metal pipes has been investigated. For this purpose, bonded pipe specimens were fabricated with different thicknesses and adhesive areas (the length of 10, 20, and 30 mm and the thickness of 0.25, 0.10, and 0.40 mm). Then, samples were exposed to tensile loading at various displacement rates (0.5, 5, and 50 mm/min) and moreover, their strengths and failure types were determined. Based on the results, for the carbon-epoxy specimens, the maximum force increased by increasing the displacement rate. The fracture area was also changed from the adhesive area to the composite due to the increase in the displacement rate. It could be claimed about the glass-epoxy samples that under tensile loading, the maximum force enhanced gradually by increasing the displacement rate. Finally, the regression analysis for the maximum force and the elongation was not properly valid based on the sensitivity analysis.

In the present research work, the reduction of peel stress in the adhesively bonded single-lap joints has been studied. The distributions of normal and shear stresses generated in the adhesive joint were obtained using the two-dimensional elasticity theory, as well as the stress-strain and strain-displacement relationships. Minimization of the peel stress was performed using the bees algorithm, during which the process variables included the adhesive and adherends thicknesses.  The composite joint was loaded by a tensile force while the adherends and adhesive layers were considered to behave as isotropic materials with linear elastic properties. The results showed that based on an optimum thickness ratio of 2.54, the magnitude of the peel stress can be reduced by 36%. As Young's moduli ratio, and consequently, the asymmetric adhesion bonding increased, the maximum amount of peeling stress decreased. Also, the increase in Young's modulus of the bottom layer led to the disruption of stress distribution at the interface of the softer adherend (top layer) and the adhesive layer, while this effect was almost absent at the other interface.

Due to the need of some industries for the direct bonding of metal and composite layers to each other and its special applications in the industry, this paper examines the solution for adhesive bonding between steel and carbon-phenolic composite. Since this composite layer does not inherently have a good adhesion to the steel surface, steel substrate surface preparation is inevitable in order to create a resistant bonding. In this research, for the preparation of steel surfaces, the knurling process with four types of knurl wheels with different geometries and pitches was used and then, by applying the adhesion tensile test, the strength of adhesive bonding of the composite layer to their surface was investigated. The results showed that in about 50% of all samples, the knurling operation was able to increase the adhesive bond strength compared to the sample with smooth metal surface. In Comparison of adhesive bond strength for two cross and straight knurl patterns, the tensile bond strength created by straight knurl shape was reported about 5 times greater than the cross knurl shape in the case of equal tensile and at pitch equal 0.6 mm. Also, the highest value for adhesive bond strength was reported in 12.62 MPa for preparated surface by using of straight knurl shape at pitch equal 0.6 mm which increased by 76% compared to machined smooth surface.

In this research, effects of introducing 0.5wt% reduced graphene oxide (RGO) reinforcement on the creep behavior of the adhesivelybonded joints are investigated at 25oC,55oC. To this aim, uni-axial creep tests are conducted,creep deformations of the bulkspecimens produced via the neat adhesive,adhesive-RGO composite are recorded. Also, creep tests are performed to obtaincreep behavior of the single lap joints. Furthermore, results of the bulk specimen tests are used in a finite element based numericalanalysis to simulate the creep behavior of the joints. Results show that, a significant decrease in the creep deformations along with aremarkable increase of 30% in the creep life time occurs in the reinforced joints. Finally, comparing the numerical results andexperimental data shows that the numerical analysis accurately simulates the creep behavior of the joints.

One of the causes of failure of adhesive joints is the stress singularity that often occurs at the free edge of the bond end. Geometric model change at the joint end can be used to reduce the stress concentration at this location. In this study, a new design called "arc adhesive model" is suggested for adhesively bonded joint of the cap of a rotational composite tank; and is compared with two conventional geometrical models including baseline model, and concave end model. Regarding to importance of transverse shear stress and normal peeling stress in examination of bonding strength, the stresses at the free end of bond are investigated using numerical analysis for all three models. Also, effect of tank rotation frequency on the stress components is investigated. Results show that the arc adhesive model can cause a significant decrease in transverse shear stress and peeling stress in adhesive joint of the cap.

In this article, failure and damage in second mode of adhesive composite joint was investigated according to the bending in endnotch flexure specimen. To create an adhesive joint between two composite plates made of unidirectional glass fiber, Araldite 2011 resin was used which is widely capable in manufacturing turbine blades and aerospace industries. At the first, failure of second mode fracture of adhesive joint mechanisms has experimentally investigated. Then with considering this result with strain energy release rate on mode II of fracture in specimen for Araldite 2011, 776.22 J/m2 was calculated. In the following calculating critical strain energy release rate on mode II by using experimental results, XFEM method used for modeling crack growing in adhesive joint by using Abaqus software. At the end the amount of mode II fracture toughness for Araldite 2011 is calculated from numerical method which is 40.53MPa√m.

The main objective of this study is the feasibility of using Modified Park-Paulino-Roesler (M-PPR) cohesive zone model to simulate The damage in adhesive layer of the double cantilever beam specimen with metal adherents. Considering VIS method for capturing the crack initiation, fracture energy of Araldite® AV138 adhesive with bond-line thickness equal 0.2 mm has been identified based on the linear elastic fracture mechanics (i.e. classic beam theory (CBT), corrected beam method (CBM) and compliance based beam method (CBBM)) and J-integral method (Pradeep method). Following, the bi-linear traction-separation law is first utilized to numerically simulate damage in adhesive layer. The force-displacement curve results obtained through experiments would further be compared with the simulated model and thus bi-linear parameters for this specific adhesive thickness would be inversely obtained. The M-PPR cohesive parameters can be determined by satisfying the boundary conditions along with bi-linear extracted cohesive parameters. First, it is concluded that CBBM is the best method to obtain adhesive fracture toughness in mode I. Using the obtained cohesive parameters and calibration of both models, M-PPR cohesive model in addition to use in metal adhesive joints, presented comparative advantage relative to bi-linear model to simulate adhesive joints under peeling. Meanwhile, effects of the geometrical parameters such as the initial length of the crack and the thickness of substrates on the ultimate strength and stiffness of the adhesively bonded joint have been evaluated.

In this article, the interfacial stresses in single and double lap joints are studied. A quadratic displacement field is assumed in the adhesive layer. For Analyzing stress in joint the free body diagram element of fiber in adhesive and unadhesive part of join has been drawn. By writing the static equation for this elements, the differential equation for joint has been derived. Then by solving this differential equation and using the boundary condition equation, displacement in fibers and so the shear stress in adhesive and axial force in fibers has been derived. The effect of thermal and hygrothermal stresses are also included. It is observed that the peak shear stress developed within the adhesive layer is function of mechanical and physical parameters as Young’s module, Poisson’s ratio, thickness, thermal and hygrothermal coefficients of expansion. The results show that the double lap joint appears to reduce the peak shear stress within the joint significantly. For example maximum shear stress in double lap joints are nearly the half of single lap joints. The results are validated by FEM solution. An excellent agreement is observed between analytical and FE methods.

Use of adhesively bonded joints in structures has been increased in recent years because of their advantages. In structural applications, fatigue is generally considered to be the most important form of loading in respect to long-term service life. In this paper, experimental tests have been performed in order to examine the fatigue damage process of double lap adhesive joints, composed of E-glass laminates and epoxy adhesive with TiO2 particles, under fatigue loading and then a method was proposed for fatigue life prediction based on initial stiffness. The scatter in results shows that the fatigue life is mostly dependent on initial stiffness. According to this, an exponential equation based on the initial stiffness has been proposed to have an initial estimation of fatigue life of the adhesive joints. In addition to the initial stiffness, stiffness degradation of the joints under fatigue loading influences on their final performance and therefore the initial estimation of fatigue life based on the initial stiffness could be modified. Also to have an online control of the fatigue damage process during the fatigue loading, a damage index using stiffness degradation was introduced.

In this paper, the strain energy release rate of first mode of failure in the adhesive bonding of two composite plates composed of unidirectional glass fiber is calculated using double cantilever beam specimen. Araldite 2011 adhesive connection which is widely used in the aerospace industry has been employed. Strain energy release rate is calculated by the modified beam method, compliance calibration method and modified compliance calibration method from experimental results. For modeling crack growth in adhesive bonding of two composite plates, the Extended Finite Element Method has been employed. Average value of critical strain energy release rate calculated by the modified compliance calibration method is considered as software input. After comparing force - displacement curve obtained from experimental data and numerical solution that represents good precision of the Extended Finite Element Method in calculating the maximum force and corresponding displacement and also linear part of force-displacement curve, strain energy release rate - force curve, stress intensity factor – force curve, strain energy release rate – displacement of the load effective point and failure stress - stress intensity factor curve are evaluated.

The strength of adhesively bonded joint plays very important role on the behavior of loaded composite structures. In the present paper debonding behavior of the adhesive joint between sandwich panel and pultruded profile is investigated by the finite element method. Cohesive zone model and contact elements are used in order to simulate the adhesive joint between stiffener and the panel. Representing the adhesive material, an embedded layer is modeled between the sandwich panel and profile. The effects of geometrical parameters including the thickness of the adhesive layer and profile on the behavior of joint are investigated. Moreover, the effect of initial defect in the adhesive joint on the debonding results is studied. The results present that in the prefect bonding, increasing in the thicknesses of the profile and adhesive layer improves the joint behavior against debonding. However in defected joint, increasing the profile thickness decreases the debonding load and presence of initial defect decreases the debonding load by 51%. The results also show that presence of embedded adhesive layer has positive effect on the debonding behavior of the joint. Initial debonding load without adhesive layer decreases by 40% in comparison with the joint containing 10 mm adhesive layer.

One of the most important issues in the manufacturing of composite structures is the ability to connect and assemble them. Design and manufacturing of connections with the appropriate strength is essential. One of the strengthening methods of composite connection is the employment of reinforcing elements in the adhesive layer. The use of additional elements in the adhesive layer leads to uniform stress distribution and consequently improves the joint strength and toughness. In this paper, the idea of using metal wire for enhancing the adhesive joints was developed for the first time. Parameters such as the number of wires, wire diameter and mechanical property of wire were considered as the influencing parameters on the joint strength. Experimental tests were designed in order to evaluate the effect of these parameters and the obtained results were described with the finite element outcomes. It was observed that the joint strength improved more than 90% using 20 wires as reinforcing elements in Araldite 2015 adhesive. It was also found that increasing the number of wires, wire diameter and wire stiffness led to the more uniform stress distribution and increased the joint strength.

Increasing in the adhesive joint strength is followed by expanding on its application. Employment of wavy edge configuration in comparison to the traditional single lap joint is a one way to increase the adhesive joint strength with thin adherent. In this paper the effects of wavy configuration on the strength of the wavy joints were studied. Araldite 2015 was employed in this study. Araldite 2015 is a two component¡ room temperature curing paste adhesive giving a resilient bond. It was observed that the wavy joints have more strength than the single lap joint about 35%. For more investigation¡ a 3D finite element model was developed. In this study the cohesive zone model (CZM) was used for simulating the adhesive behavior. The effects of wave shape and number on the strengthening of wavy joints were studied. The finite element results were in good accordance with the experimental outcomes for the strengthening of wavy edges.