Numerical Study of Adhesive Single-Lap Joints with Composite Adherends Subjected to Combined Tension–Torsion Loads

The present investigation focuses on modifying the strength of single-lap adhesively bonded joints under tension–torsion loading with the use of three-dimensional finite element (FE) modeling. A single-lap adhesively bonded joint is reinforced by fibers and analyzed by means of ABAQUS-6.9.1 FE code. The adherends are considered to be made of orthotropic materials, while the adhesive is neat resin or reinforced by various types of fibers. The carbon and glass unidirectional fibers are used for adhesive reinforcement. In the FE modeling, the behavior of all the members is assumed to be linear elastic. The ultimate bond strength is increased as the fiber volume fraction in the adhesive is increased. By changing the properties and the behavior of the adhesive from neat resin (isotropic) to fiber composite adhesive (orthotropic) and with various fiber volume fractions and by changing the orientation of the fibers in the adhesive region with respect to the global axes, the bond strength in tension–torsion loadings are changed. Also, the excessive adhesive layer is modeled and its effect on the joint strength is investigated.     

Improved adhesive properties and bonding performance of HTPB‐based polyurethane elastomer by using aziridine‐type bond promoter

Theeffect of two aziridine‐type bond promoters on adhesive and mechanical properties of a hydroxyl terminated polybutadiene‐based elastomeric liner used in solid propellant rockets was investigated by varying the concentration to determine the optimum value. The performance of butyleneiminetrimesoylaziridine (BITA) was compared with that of tris[1‐2‐methylaziridinyl]phosphine oxide (MAPO) in the elastomeric liner of otherwise the same composition. The adhesive performance of the elastomer to the composite was determined by using metal‐elastomer‐composite tensile and peel tests. The adhesive performance of the elastomer to the metal was also determined, this time by using peel and shear tests. The mechanical characterization of the elastomer was done by tensile and hardness tests. A significant enhancement in the bonding performance of the elastomeric liner toward composite propellant and metal case was achieved by optimizing the concentration of bond promoter in the elastomeric composition. All the elastomer compositions with bond promoters BITA and MAPO loadings of 1.0, 1.5, and 2.0 wt % were found to be sufficient for the rocket motor operations because the interfacial adhesive strength of these compositions is higher than the cohesive strength of the composite. Compositions with bond promoter quantities of 1.0, 1.5, 2.0, and 2.5 wt % have better strength values than the others. Liner compositions with the bond promoter BITA give better bonding performance between the composite–metal system and better mechanical properties when compared with the elastomers with the bond promoter MAPO. The best results are obtained in terms of bonding performance and adhesive properties by using the bond promoter BITA in optimized quantities of 1.0 and 1.5 wt % loadings in the elastomer compositions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 806–814, 2001     

Mode-I adhesive fracture energy of carbon fibre composite joints with nanoreinforced epoxy adhesives

The effect of the addition of carbon nanoreinforcements to an epoxy adhesive on the strength and toughness of carbon fibre/epoxy composite joints was studied. The laminate surfaces, treated with peel ply, were characterised by profilometry, image analysis and wettability. The mechanical properties of the joints were determined by lap shear testing and double cantilever beam testing. The fracture mechanisms were studied by scanning electron microscopy.The addition of carbon nanofibres and carbon nanotubes caused an increase in the mode-I adhesive fracture energy, G_IC, of the joints while their lap shear strengths remained approximately constant. This improvement in the fracture behaviour was attributed to the occurrence of toughening mechanisms when carbon nanoreinforcements were added to the epoxy adhesive. Additionally, the use of carbon nanotubes improved the interfacial strength between the adhesive and the substrate, changing the crack growth behaviour and the macroscopic failure mode.     

Preparation and properties of in‐situ polymerized polyurethane/stearate intercalated layer double hydroxide nanocomposites

The present work deals with the effect of stearate intercalated layered double hydroxide (St‐LDH) loadings on the morphological, mechanical, thermal, adhesive and flame retardant properties of polyurethane (PU)/St‐LDH nanocomposites prepared by the in situ polymerization method. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation takes place at 3 wt% loading followed by intercalation at higher filler loadings in the PU matrix. The exfoliated structure has been further verified by atomic force microscopy. The measurements of stress‐strain, thermogravimetric analysis, dynamic mechanical analysis, lap shear strength and peel strength analysis showed that the nanocomposites containing 3 wt% St‐LDH exhibit excellent improvement in tensile strength (ca 175%) and log storage modulus (ca 14%), while PU/St‐LDH (5 wt%) possesses optimum improvement in glass transition temperature (ca 6 °C), lap shear strength (200%) and peel strength (130%) over neat PU. In addition, the gradual improvements in limiting oxygen index value with St‐LDH loading indicated the higher effectiveness in providing better barrier properties as well as better flame retardant behavior. Copyright © 2012 Society of Chemical Industry     

Experimental study of the influence of adhesive reinforcement in lap joints for composite structures subjected to mechanical loads

The paper deals with experimental investigations on reinforcing the adhesive in single lap joints subjected to mechanical loads such as tensile, bending, impact and fatigue. The adhesive used for bonding was an epoxy reinforced with unidirectional and chopped glass fibres as well as micro-glass powder. The adherends were glass reinforced composite laminates. The bonding surfaces were prepared before joining. In the case of unidirectional fibres in the adhesive region, the fibre orientations considered were 0°, 45° and 90°. The volume fraction of fibres in the adhesive layer in all the cases was 30%. The volume fractions of micro-glass powder were 20%, 30% and 40%. The tensile, bending, impact and fatigue tests on the prepared specimens were conducted according to ASTM standards. The results show that except the 90° unidirectional orientation, reinforcing the adhesive with glass fibres or powder increases the joint strength. The use of volume fraction of 30% of micro-glass powder gave the best performance in the above loading conditions. The fatigue life increased by 125%, the ultimate joint strength in tension increased by 72%, the bending ultimate joint strength increased by 112% and the impact joint strength increased by 63%. The microstructure of the debonded area was examined and three modes of failure could be observed namely cohesive failure, light fibre-tear failure and thin layer cohesive failure.     

The Effect of PEEK Fibres and Powder on Joints Made with a High Temperature Adhesive

High temperature adhesives typically exhibit low levels of peel strength since they tend to be more brittle than typical toughened adhesives used for lower temperature applications. It was found that incorporating thermoplastic fibres or powder into the bondline of a joint made with a high temperature epoxy-based adhesive resulted in significant improvements in peel strength. Poly(ether ether ketone) (PEEK) fibres and powder were incorporated into the adhesive resin and used in aluminium joints. These were tested in peel and single lap shear using a range of fibre lengths, orientations and volume fractions. It was seen that large increases in peel strength could be achieved but that lap shear strength was degraded with most types of modification. However, some modifications resulted in significant increases in peel strength with limited decrease in lap shear strength. These improved properties have been achieved using physical modifications rather than chemical alteration of the resin.     

Single and dual adhesive bond strength analysis of single lap joint between dissimilar adherends

The emerging trends for joining of aircraft structural parts made up of different materials are essential for structural optimization. Adhesively bonded joints are widely used in the aircraft structural constructions for joining of the similar and dissimilar materials. The bond strength mainly depends on the type of adhesive and its properties. Dual adhesive bonded single lap joint concept is preferred where there is large difference in properties of the two dissimilar adherends and demanding environmental conditions. In this work, Araldite-2015 ductile and AV138 brittle adhesives have been used separately between the dissimilar adherends such as, CFRP and aluminium adherends. In the dual adhesive case, the ductile adhesive Araldite-2015 has been used at the ends of the overlap because of high shear and peel strength, whereas in the middle of the bonded region the brittle adhesive AV138 has been used at different dimensions. The bond strength and corresponding failure patterns have been evaluated. The Digital Image Correlation (DIC) method has been used to monitor the relative displacements between the dissimilar adherends. Finite element analysis (FEA) has been carried-out using ABAQUS software. The variation of peel and shear stresses along the single and dual adhesive bond length have been captured. Comparison of experimental and numerical studies have been carried-out and the results of numerical values are closely matching with the experimental values. From the studies it is found that, the use of dual adhesive helps in increasing the bond strength.     

On the von Mises elastic stress evaluations in the bi-adhesive single-lap joint: a numerical and analytical study

Bi-adhesive joints are an alternative stress-reduction technique for adhesively bonded joints. The joints have two types of adhesives in the overlap region. The stiff adhesive should be located in the middle and the flexible adhesive at the ends. This study is the extension of our previous paper to the von Mises stress evaluation and discusses the values and importance of the von Mises stresses in the bi-adhesive single-lap joint. Both analytical and numerical analyses were performed using three different bi-adhesive bondline configurations. The Zhao’s closed form (analytic) solution used includes the bending moment effect. In the finite element models, overlap surfaces of the adherends and the adhesives were modeled using surface-to-surface contact elements. The contribution levels of the peel and shear stresses for producing a peak von Mises stress are also studied. It is concluded that the contribution level of the shear stress at where von Mises stress becomes peak is more than that of the peel stress. Joint strength analyses were performed based on the peak elastic von Mises stresses. It is seen that joint strength can be increased using bi-adhesive bondline. The analytical and numerical results show that the appropriate bond-length ratio must be used to obtain high joint strength.     

Assessment of test methods for a cryogenic liquid containment system

This paper presents a study demonstrating the selection and use of adhesive joint test methods for the design and validation of an adhesively bonded, foam-composite membrane, cryogenic insulation system for the marine transportation of liquefied natural gas (LNG). The study considered the performance of epoxy and polyurethane adhesives under ambient and sub-zero operating temperatures. Double-lap, sandwich panel and double cantilever beam (DCB) joint tests, essential in “calibrating” the interpretation of finite element analysis (FEA), were performed along with FEA in order to assess the stress states (in-plane, peel and shear stress) in the adhesive layer that, under defined loads and extensions, are comparable with the stress levels in the LNG container under service conditions.The study reinforces the view that the presence of barrier film substrates has a major effect on performance, and that the critical state of stress for the integrity of the flexible composite barrier film (FSB) to rigid composite barrier film (RSB) bond in the cryogenic containment system is the tensile peel stress at the ends of the joint. Sandwich panel tests conducted using the two adhesives indicate that failure tends to occur when the peel stress exceeds the tensile strength of the bulk adhesive with the polyurethane adhesive exhibiting more robust adhesion properties than the epoxy with consequences for future design of LNG containers.     

Hygrothermal Properties of Adhesively Bonded Joints and Their Correlation with Bulk Adhesive Properties

The combined effects of heat (50[ddot]C) and humidity (95% R.H.) on the lap shear and T-peel strengths of 120[ddot]C, 150[ddot]C and 215[ddot]C service epoxy film adhesives have been characterized. Experimental results have indicated that effects of hygrothermal conditioning on lap shear and peel properties vary with exposure time and final testing temperatures and type of adhesive tested. In the cases where cohesive failure was observed in the shear and peel specimens, a correlation could be established between the bulk properties of the adhesives (tensile strength and elongation) and their adhesively bonded joint properties (shear and peel). When testing was carried out at room temperature, a general correlation between the tensile elongation and T-peel or shear could be obtained. At below freezing temperatures, lap shear strength seemed to be correlated with bulk tensile strength while peel correlated with bulk tensile elongation. At elevated temperatures, the relative contributions of bulk strength and elongation were the decisive factors as far as shear and peel strengths are concerned.     

Parametric study of factors affecting the pull-out strength of steel rods bonded into precast concrete panels

This paper deals with the effect of bond thickness, embedment length and type of epoxy adhesive formulation on the adhesion of steel anchors to concrete. The test results indicate that the shear strength of the epoxy adhesive formulation prepared from a diglycidylether of bisphenol A (DGEBA) and an ethyleneamine curing agent is independent of bond thickness from approximately 1–4 mm. However, the same is not found to be true for the DGEBA epoxy resin cured using an alkylenediamine curing agent where considerably more complex behaviour is observed. The adhesive shear strength of this system is shown to pass through a maximum value at 2 mm bond thickness. At thickness beyond 2 mm, the strength undergoes a reduction until a value is reached which remains essentially constant with increased thickness. The variation in concrete strength is regarded as a main factor responsible for this complexity. The addition of filler to epoxy adhesive formulations results in a reduction in the adhesive shear strength, the magnitude of the decline being largely dependent upon the quantity of filler used in the mixture. The quadratic equations reviewed in this study provide a basis for assessing trends in the mechanical behaviour of filled epoxy systems. The shear strength of an epoxy adhesive anchor can be determined by an elastic behavioural model. The curves for epoxy adhesives indicate that the elastic solution does fit the experimental data very well. Increasing embedment of an anchor beyond a certain point does not increase the ultimate tension capacity of the anchor.     

Analysis of the low temperature-dependent behaviour of a ductile adhesive under monotonic tensile/compression–shear loads

Various models exist to describe the non-linear behaviour of an adhesive in an assembly, taking into account the two stress invariants, hydrostatic stress and von Mises equivalent stress, which can be explained by the nature of the adhesive, i.e., a polymer. The identification of the material parameters of such pressure-dependent constitutive models requires a large experimental database taking into account various tensile–shear loadings. Under quasi-static loadings at low temperature, for a given strain rate range, viscous effects can be neglected, but only a few experimental results are available to model the behaviour of an adhesive in a bonded assembly accurately under realistic loadings. Moreover, edge effects often have a large influence on the mechanical response. This paper presents the possibility of combining the use of a modified Arcan device, which strongly limits the influence of the stress concentrations, with a usual thermal chamber. Experimental results, underlining the temperature-dependent non-linear responses of an adhesive, are presented in the case of various tensile/compression–shear monotonic loadings for a temperature range between 20 °C and −60 °C. The analysis of experimental results, obtained in the load-displacement diagram, focuses herein on the modelling of the initial temperature-dependent yield surface; but such results are also useful for the development of the flow rules in the case of pressure-dependent models.     

Influence of elevated temperatures on epoxy adhesive used in CFRP strengthening systems for civil engineering applications

This paper presents experimental investigations about the influence of elevated temperatures on the mechanical behaviour of an epoxy adhesive typically used in carbon fibre reinforced polymer (CFRP) strengthening systems and numerical investigations about the influence of changes underwent by the adhesive on the response of bonded joints between CFRP strips and concrete. The experiments included shear and tensile tests at elevated temperatures (up to 120 °C) on a commercial epoxy adhesive. In both types of tests, the mechanical response of the adhesive at different temperatures was assessed, namely in terms of stress vs. strain curves, stiffness, strength and failure modes. The results obtained highlighted the considerable reduction of both shear and tensile properties with increasing temperatures: at 70 °C the shear and tensile strengths are both reduced to around 15% of the corresponding ambient temperature strengths, while the tensile and shear moduli can be considered negligible. Analytical formulae were fit to the test data, describing the reduction with temperature of the adhesive's tensile and shear properties. In the numerical investigations, three-dimensional finite element models were developed to simulate previous double-lap shear tests performed on concrete blocks strengthened with CFRP strips according to either the externally bonded reinforcement (EBR) or the near surface mounted (NSM) techniques, using the epoxy adhesive characterized in the present study. Two distinct modelling strategies were adopted for the concrete-CFRP bond in order to assess the relative importance of the adhesive distortion and interfacial slippage at the concrete-adhesive-CFRP interfaces in the overall slip between concrete and CFRP: (i) to explicitly simulate the adhesive, considering the mechanical properties determined in the tests and assuming a perfect bond at all interfaces; and, alternatively, (ii) to simulate the CFRP-concrete interaction by means of global bilinear bond-slip laws for different temperatures. Comparison between numerical results and test data allowed quantifying the relative importance of the adhesive distortion and of the interfacial slippage at the bonded interfaces as a function of temperature, providing a better understanding of the contribution of these two mechanisms to the CFRP-concrete bond at elevated temperature. While the former effect is the most relevant at ambient temperature, with elevated temperature the interfacial slippage at the bonded interfaces becomes the most relevant mechanism.     

Stress Transfer Function for Interface Assessment in Composites with Plasma Copolymer Functionalized Carbon Fibres

Radio-frequency-induced plasma copolymerization of acrylic acid/1,7-octadiene was used to produce a range of functionalized plasma copolymer coatings with controlled degree of adhesion. The single-fibre fragmentation test was used to characterize the adhesion of plasma copolymer coated fibres to epoxy resin. The cumulative stress transfer function (CSTF) and Kelly-Tyson approaches were used to evaluate the degree of adhesion. By continuous monitoring of the fragmentation process, it was found that the mechanical performance of a composite material could be evaluated using the CSTF methodology at strain well below saturation. The degree of debonding was a good measure of relative interface/interphase adhesive strength. The trend in the CSTF is consistent with the propagation of interfacial debonds during the test. For a completely debonded fibre a normalized CSTF value, referred as stress transfer efficiency (STE), was found to provide a more consistent analysis that was able to differentiate between fibres with similar degrees of debonding. The calculated values of interfacial shear strength (IFSS) were only valid for a fully debonded fibre (1,7-octadiene plasma homopolymer coating) where the assumption of a constant shear stress, as in the Kelly-Tyson model, applied. However, IFSS did not provide the same ranking. Where debonding does not occur, the stress transfer efficiency also provides a sensitive measure of the interface/interphase performance. Improved adhesion over the untreated-unsized carbon fibre was observed for both of the plasma copolymer-coated and commercially treated carbon fibres. Since there is a concentration dependence of carboxyl groups on adhesion, the mechanism appears to relate to covalent bond formation with the epoxy group. Plasma copolymer coatings on carbon fibres also causes an increased tensile strength and Weibull modulus.     

Modeling of single-lap composite adhesive joints under mechanical and thermal loads

Two-dimensional (plane-stress and plane-strain) theoretical models are presented for stress analysis of adhesively bonded single-lap composite joints subjected to either thermal or mechanical loading or a combination thereof. The joints consist of similar/dissimilar orthotropic or isotropic adherends and an isotropic adhesive interlayer. The governing differential equation of the problem is obtained using a variational method which minimizes the complementary strain energy in the bonded assembly. In this formulation, through-thickness variation of shear and peel stresses in the interlayer is considered. Both shear and normal traction-free boundary conditions are exactly satisfied. Peel and shear stresses obtained from plane-strain analytical models considering a homogeneous adhesive interlayer are in close agreement with those of the finite element predictions. A systematic parametric study is also conducted to identify an ideal set of geometric and material parameters for the optimal design of single-lap composite joints.     

Stress Transfer Function for Interface Assessment in Composites with Plasma Copolymer Functionalized Carbon Fibres

Radio-frequency-induced plasma copolymerization of acrylic acid/1,7-octadiene was used to produce a range of functionalized plasma copolymer coatings with controlled degree of adhesion. The single-fibre fragmentation test was used to characterize the adhesion of plasma copolymer coated fibres to epoxy resin. The cumulative stress transfer function (CSTF) and Kelly-Tyson approaches were used to evaluate the degree of adhesion. By continuous monitoring of the fragmentation process, it was found that the mechanical performance of a composite material could be evaluated using the CSTF methodology at strain well below saturation. The degree of debonding was a good measure of relative interface/interphase adhesive strength. The trend in the CSTF is consistent with the propagation of interfacial debonds during the test. For a completely debonded fibre a normalized CSTF value, referred as stress transfer efficiency (STE), was found to provide a more consistent analysis that was able to differentiate between fibres with similar degrees of debonding. The calculated values of interfacial shear strength (IFSS) were only valid for a fully debonded fibre (1,7-octadiene plasma homopolymer coating) where the assumption of a constant shear stress, as in the Kelly-Tyson model, applied. However, IFSS did not provide the same ranking. Where debonding does not occur, the stress transfer efficiency also provides a sensitive measure of the interface/interphase performance. Improved adhesion over the untreated-unsized carbon fibre was observed for both of the plasma copolymer-coated and commercially treated carbon fibres. Since there is a concentration dependence of carboxyl groups on adhesion, the mechanism appears to relate to covalent bond formation with the epoxy group. Plasma copolymer coatings on carbon fibres also causes an increased tensile strength and Weibull modulus.     

Bond behavior of epoxy resin–polydicyclopentadiene phase separated interpenetrating networks for adhering carbon fiber reinforced polymer to steel

The performance of bonded joints of carbon fiber reinforced polymer (CFRP) and steel relies on the mechanical properties of the adhesive used. Despite the high strength and modulus of epoxy adhesives, their brittleness limits their application to defect-sensitive structures. The development of interpenetrating polymer networks (IPNs), either homogeneous or phase separated, provides a route to toughen the epoxy while maintaining its high strength and modulus. Microphase separated IPNs consisting of a diglycidyl ether of bisphenol A-based epoxy resin and a thermoset with high toughness, polydicyclopentadiene (PDCPD), has been previously shown to demonstrate superior combinations of strength and toughness. This work investigates the most critical adhesive properties that affect bond strength by characterizing CFRP-steel double-lap shear joints containing the epoxy resin–PDCPD blend as the adhesive, using a wet lay-up manufacturing technique. The epoxy resin–PDCPD blend adhesives realized much higher bond strengths compared to either neat epoxy or neat PDCPD. Correlations between the bond strength and the bulk material properties are presented. Theoretical calculation of the bond strength indicates that the higher bond strength that can be achieved by using the epoxy resin–PDCPD blend adhesive is due to the increased shear toughness of the new formulations. POLYM. ENG. SCI., 60:104–112, 2020. © 2019 Society of Plastics Engineers     

Adhesion failure propagation in adhesively-bonded single-lap laminated FRP composite joints

This paper deals with three-dimensional non-linear finite element analyses to study the behaviour of embedded adhesion failure propagation in adhesively-bonded single-lap laminated FRP composite joints clamped at one end and subjected to uniform extension at the other end. Because of loading eccentricity and joint material heterogeneity, the embedded adhesion failure is likely to initiate from the stress singularity points and will propagate from either end of the adhesive layer along the adherend–adhesive interfaces. The effects of interaction of such failures and their propagations along the interfaces of the adherends and adhesive are the main concerns of this paper. The peel and shear stresses have been computed along the mid-surface of the adhesive layer for varying adhesion failure lengths to find out the influence of adhesion failure length on the strength of the joint being analyzed. The concept of fracture mechanics has been used to calculate the strain energy release rate (SERR) as the adhesion failure propagates using the virtual crack closure technique (VCCT). It is seen that mode-II SERR is predominant in the propagation of such adhesion failures. The SERR values computed with respect to the adhesion failure lengths being propagated from the two ends of the adhesive layer are seen to be different.     

The effect of nanoalumina silanisation in tetraglycidylether epoxy adhesive

The efficiency of different surface modifications on alumina nanoparticles on both filler dispersion and the final properties of the resulting adhesive nanocomposites have been investigated. A tetraglycidyldiaminodiphenylmethane (TGDDM) epoxy resin and three sample series of nanocomposites were prepared via in-situ incorporation of alumina nanoparticles into the reactor. The alumina/TGDDM nanocomposites were prepared individually using neat or non-treated alumina nanoparticles and two kinds of silane-grafted alumina nanoparticles, i.e., APS-treated alumina and GPS-treated alumina. The presence of different alumina nanoparticles in the epoxy matrices resulted in different states of nanofiller dispersion as revealed in SEM and AFM micrographs. It was elucidated that the silane treatment on alumina nanoparticles is crucial for the desired dispersion in the epoxy matrix. Besides, the appropriate filler dispersion resulted in improved thermal resistance and high degree of cure, especially for the adhesive nanocomposite containing APS-treated alumina nanoparticles. In adhesion tests, the shear strength was improved in both nanocomposites containing silane-grafted alumina with more pronounced values for the nanocomposite containing APS-treated alumina nanoparticles. The shear strength reached from 6.6 MPa for the neat epoxy adhesive to 10.2 MPa for the adhesive nanocomposite containing 5 wt % APS-treated alumina nanoparticles mainly due to high levels of dispersion of the high modulus alumina nanoparticles and effective interfacial interactions with the epoxy matrix. The adhesive peel strength of alumina/TGDDM nanocomposites showed a similar trend as in shear strength with more pronounced variations. A noticeable increase in the peel strength of the nanocomposites containing silane-grafted alumina nanoparticles appeared to correlate with greater levels of crack deflection and hence dissipation of fracture energy as observed in SEM pictures.     

Design and analysis of functionally graded adhesively bonded double supported tee joint of laminated FRP composite plates under varied loading

The present research deals with three-dimensional nonlinear finite element analyses for a functionally graded adhesively bonded tee joint made of laminated fiber reinforced polymeric composites when the tee joint is subjected to different types of loadings. The out-of-plane stress components have been evaluated along the interfacial surfaces of bond line of the tee joint. Using the stress values, the failure indices are computed by using Tsai–Wu coupled stress failure criterion in order to predict the location of onset of failures within the interfacial surfaces. Accordingly, critical location is identified based on the magnitude of failure indices for varied load conditions. It has been observed that tee joint under bending load is vulnerable for early failure compared with that when the joint is subjected to tensile and compressive loading. The location of failure is found to be different in tee joint under bending load compared with tensile and compressive loadings. Further, efforts have been made to reduce out-of-plane stress concentration by implementing functionally graded adhesive (FGA) with appropriate smooth and continuous gradation function profile. Further, effects of material gradation function profile with varied modulus ratios on out-of-plane stresses and failure indices are observed along the different interfacial surfaces. Series of numerical simulation result significant reduction in peak values failure index. Based on the present research findings, the FGA is recommended for higher and efficient joint strength. Results also exhibit delayed failure onset and improved structural integrity in the tee joint structure with the use of FGA material.