Scarf Adhesive Joints Research Articles

Uncertainty Analysis of Tensile Strength of Scarf Adhesive Joints using Numerical Method and Validation through Experimentation

Adhesive joints represent a significant advancement in material bonding technology, offering benefits such as reduced weight and uniform stress distribution, which distinguish them from conventional joining methods. Among the various adhesive joints, the scarf adhesive joint stands out due to its mechanical advantages and potential for high-strength applications. This research investigates the impact of key parameters on the strength of scarf adhesive joints, including scarf angle, surface roughness, adhesive type, and adhesive layer thickness. By systematically varying these parameters and employing a design of experimentation (DOE) methodology, we aim to identify the optimal conditions that maximize joint strength. A series of scarf adhesive joint specimens with diverse parameter combinations will be fabricated and tested to evaluate the resultant joint strength. Statistical analysis of the experimental data will facilitate the understanding of how each parameter influences joint performance and contribute to the development of optimized adhesive joint designs. The findings of this study are expected to advance the application of scarf adhesive joints in various high-performance engineering fields, providing insights into the critical factors that govern their strength and reliability. Key Words: Scarf Adhesive Joint, Adherend Material, SS 304 Stainless Steel, Finite Element Analysis (FEA), Tensile Strength, Max von Mises Stress, Scarf Angle, Design of Experiments (DOE), Adhesive Properties, Surface Roughness.

Additively manufactured 3D micro scarf adhesive joints

AbstractHybrid manufacturing enables to overcome additive manufacturing (AM) constraints regarding the maximum feasible part dimension and/or complexity through part separation and subsequent adhesive joining of AM sub-parts. To ensure structural integrity of the joint at a minimum use of substrate volume, the AM inherent freedom of design can be exploited by realizing 3D micro scarf adhesive joints. The performance of this novel adhesive joint design was assessed by conducting optical measurements and static tensile tests using samples fabricated by laser-based powder bed fusion of metals (PBF-LB/M).

Study of different initiation and propagation criteria in the XFEM modelling of scarf adhesive joints

Scarf adhesive joints, characterized by an end-to-end connection between tapered adherents at a given scarf angle (α), are applicable in structural applications, e.g., fiber-reinforced structures, owing to their efficiency. This work presents an analysis on the tensile strength of scarf adhesive joints, considering a and the adhesive type as design parameters. A detailed numerical evaluation is presented, based on the eXtended Finite Element Method (XFEM), following the technique validation with experimental data, for adhesives with different characteristics. The XFEM technique was tested with varying damage initiation and propagation criteria. The XFEM technique was positively validated for specific damage initiation and propagation criteria.

Effect of adhesive type on the tensile behavior of tubular scarf adhesive joints

Effect of adhesive type on the tensile behavior of tubular scarf adhesive joints

Potential energy as a new approach for detection and monitoring of fatigue damage in scarf adhesive joints modified with nanoparticles

In this study, fatigue results of the scarf adhesive joints (SAJs) were extensively analyzed regarding the effect of the adhesive materials (neat epoxy (NE), and SiC and Al2O3-nanocomposite), bond thickness (0.17 mm and 0.25 mm) on their dynamic properties, which include loss factor (tan δ), loss modulus ( E''), dissipated energy ( U d), potential energy ( U p), and storage modulus ( E'). Safe fatigue lives of the NE, SiC, and Al2O3-SAJs were estimated at different reliability levels. The experimental measurements revelated that reducing the adhesive layer thickness from 0.25 mm to 0.17 mm result in enhancing the tensile strength and stiffness of the SiC-SAJs by 9.6% and 4.4%, respectively, in return of 9.5% and 5.4% for the Al2O3-SAJ relative to the NE-SAJ. The strength and stiffness of the SiC-SAJs with 0.17 mm bond thickness are higher than those of the Al2O3-SAJ by 15.4% and 3.3%, respectively. The highest improvement of 22.0% in the fatigue strength was occurred for the SiC-SAJ with bond thickness of 0.17 mm in return of 4.8% for the Al2O3-SAJ. The U p was used for the first time (except author works) for monitoring and predicting the damage in the adhesive joints practically the change in the enclosed area of the hysteresis loop is too small to cause a large variation in the tan δ, E'', and U d. Damping factor of the NE-SAJs is marginally increased with the stress levels compared to the aggravated increase of both SiC and Al2O3-SAJs. Zhang model predicts well the potential energy and storage modulus specially at higher stress levels.

Finite element analysis of competitive damage mechanisms of composite scarf adhesive joints by considering thickness effect

Cohesive zone models are demonstrated to fail to predict damage mechanisms of adhesive layer with the increase of thickness, although the load response and ultimate failure strength of adhesive joints are evaluated well to some extent. This paper attempts to explore damage mechanisms of composite scarf adhesive joints with brittle adhesive material under quasi-static loading, where the competitive relationships between the damage behaviors of adhesive layer and the interface debonding between the adhesive layer and composite laminates are investigated. For the epoxy adhesive layer, the damage initiation criteria are developed by considering the hydrostatic pressure, the tension/compression asymmetry and frictional effects, and the damage evolution law is derived using continuum damage mechanics. The bilinear cohesive model and the modified Xu and Needleman’s exponential cohesive model are used to predict the interface debonding between the epoxy adhesive layer and glassy fiber/epoxy composite laminates, respectively. FEA is performed to study two competitive damage mechanisms of composite scarf adhesive joints by discussing the effects of the scarf angle, the thickness of adhesive layer and the shape of cohesive models. Results show that 1. two approaches with/without considering damage mechanisms of adhesive layer can be chosen alternatively within the thickness of adhesive layer 0.5–1.0 mm, by weighing calculation efficiency and precision appropriately; 2. damage features of adhesive layer deserve more attention as the thickness increases beyond 1.0 mm.

Failure analysis of scarf adhesive joints modified with SiC-nanoparticles under fatigue loading at room temperature

Adhesive joints were fabricated by joining two woven carbon fiber composite adherends with scarf angle of 5° using Epocast adhesive system of 50-A1/946 modified with optimum weight percent of 1.5 wt% SiC-nanoparticles. The scarf adhesive joints (SAJs) were characterized through static tensile as well as tension-tension fatigue loading. The stress-number of cycles to failure curves are useful in determining the fatigue life, but they do not give any indication about the fatigue damage development during the joint's lifetime. In consideration of early detecting damage development in the SAJs, many dynamic parameters were estimated from the analysis of the stress-local strain cycles, with the aim to obtain more accurate predictions. These parameters include loss and storage moduli, potential and dissipated energies, and damping factor. It has been found that the tensile strength and fatigue limit of the SiC-SAJ were increased by 9.6% and 55% respectively with decreasing the bondline thickness from 0.25 mm to 0.17 mm. Incorporation of SiC-nanoparticles into the adhesive layer improves the tensile strength and the fatigue limit of the SAJs with bondline thickness of 0.17 mm by 26.1% and 22% respectively compared to the unmodified joint. At higher stress levels, the storage modulus and potential energy can be modeled for early prediction of the joint life and thereby, help in preventing their catastrophic failure. Zhang model showed good agreement with the measured potential energy compared to the storage modulus.

Numerical evaluation of tensile-loaded tubular scarf adhesive joints

Tubular adhesive joints are widely employed when joining tubes and rods. The loads to which these joints are subjected may be axial or torsional. When loaded in the axial direction, cylindrical joints present stress concentrations in the adhesive layer, as is the case of lap joints. To improve the joint strength in the axial direction, the cross-section of the tubes can be chamfered to produce a scarf tubular joint. The geometrical variations produced by machining the chamfers increase the overall bonding area, leading to higher joint strength. This study aims to compare the tensile performance of tubular scarf joints (TSJ) with aluminium (AW6082-T651) adherends, considering the variation of the scarf angle (α) from 45° to 3.43°; the joints were bonded with a moderately ductile adhesive, the Araldite® 2015. Firstly, through the comparison of experimental tests and numerical analysis of tubular lap joints (TLJ), the cohesive zone model (CZM) technique and respective cohesive parameters were validated. A CZM analysis was then performed on the TSJ to analyse peel (σy) and shear stresses (τxy) in the adhesive layer. Damage and joint strength analyses were also carried out, as well as the study of the dissipated energy for the different joint configurations. The CZM technique was validated, and the numerical analysed showed a major α effect, with benefits for smaller α, and improved stress distributions over TLJ.

Modelling of Harmonic Response of Scarf Adhesive Joints

Adhesives are used for attaching structures to various spacers such as tubular and scarf joints to replace the traditional joining methods of welding, brazing, soldering, etc. Many of the unique features associated with adhesives are low manufacturing cost, long component life, and lightweight. Accordingly, a considerable amount of study has been carried out and is still underway to develop. The main objective of this study is to investigate the response of the scarf joints when exposed to a harmonic load. The finite element method (FEM) using ANSYS is availed to study and analysis the natural frequencies, mode shape, and frequency response. Additionally, the influence of the adhesion angle is examined.

Modelling of Harmonic Response of Scarf Adhesive Joints

Adhesives are used for attaching structures to various spacers such as tubular and scarf joints to replace the traditional joining methods of welding, brazing, soldering, etc. Many of the unique features associated with adhesives are low manufacturing cost, long component life, and lightweight. Accordingly, a considerable amount of study has been carried out and is still underway to develop. The main objective of this study is to investigate the response of the scarf joints when exposed to a harmonic load. The finite element method (FEM) using ANSYS is availed to study and analysis the natural frequencies, mode shape, and frequency response. Additionally, the influence of the adhesion angle is examined.

Dynamic analysis of scarf adhesive joints in CFRP composites modified with Al2O3-nanoparticles under fatigue loading at different temperatures

Fatigue tests were conducted on scarf adhesive joints (SAJs) with composite substrates at room temperature (RT) and 50 °C. The adhesive layer was modified with Al2O3-nanoparticles. Dynamic parameters such as damping factor, storage modulus, dissipated energy and potential energy (Up) were measured from the stress–strain hysteresis loops of the SAJs with the aim of knowing which ones are best for early prediction of joint collapse. Incorporation of Al2O3-nanoparticles into the adhesive layer improves the fatigue strength by about 4.8 and 24.5% at RT and 50 °C respectively. The glass transition temperature was improved by 8.3% and thus, at 50 °C the fatigue strength of the Al2O3-SAJs was decreased by 5.4% in return of 20.3% for the NE-SAJs. The variation of the Up with fatigue life is more pronounced compared to the other dynamic parameters and thus, can be modeled to monitor the integrity of the joint and preventing their catastrophic failure.

Dynamic Analysis of Scarf Adhesive Joints in Carbon-Fiber Composites at Different Temperatures

The dynamic performance of scarf adhesive joints (SAJs) in fiber-reinforced polymer composites is a new topic that is not available in the literature yet; introducing it is one of the objectives of this study. Changes in stiffness, ratcheting strain, loss factor (), loss modulus (), storage modulus (), dissipated energy (), and potential energy () with the number of fatigue cycles were measured at room temperature (RT), , and 50°C. It was found that fatigue lives were longer at than at RT and 50°C. Fatigue life at plastic strain threshold was decreased by about 98% of the joint lifetime at 50°C. The behavior of agrees qualitatively with and . The improved ductility of the SAJs at 50°C induces significant changes in and , and hence they can be used to monitor the integrity of the SAJs and early prediction of fatigue failure. At , the and behave approximately in a linear constant manner up to sudden failure without warning. Accordingly, safe design fatigue life based on time to first failure was applied to evaluate the stress versus number of cycles to failure curves of the SAJs at different reliabilities.

Impact and bending analysis of composite scarf adhesive joints modified with MWCNTs at room and hot temperatures

Scarf adhesive joints (SAJs) have attracted an increasing attention in joining/repairing of carbon-fiber reinforced epoxy (CFRE) composite structures due to their zero eccentricity, which provides better aerodynamic surfaces. This study evaluated for the first time, the performance of SAJs in CFRE composites under thermo-mechanical impact loads. The adhesive was modified with optimum percentage of multi-walled carbon nanotubes (CNTs). The impact tests were performed at room temperature of +25°C, +50°C and +75°C. The residual flexural properties of the unfailed impacted joints were measured using three-point bending test. Results from impact tests at temperature of 25°C, 50°C and 75°C showed improvement in the impact bending stiffness of the modified SAJs with CNTs by 8.3%, 7.4% and 11.8% and maximum contact force by 15.6%, 21.3% and 18.9%, respectively. The energy at failure of the CNT-SAJs was increased by 15.2% and 16.4% respectively at temperatures of 25°C and 50°C. At test temperature of 75°C the SAJs have hysteresis load-displacement behavior and energy-time curve with rebound energy of 35% and absorbed (damage) energy of 65%. The residual flexural strength of the modified and unmodified SAJs is 98.2% and 86.1% respectively, while their residual moduli have remarkable decrease to 71.7% and 81.3%.

Experimental analysis of composite scarf adhesive joints modified with multiwalled carbon nanotubes under bending and thermomechanical impact loads

Scarf adhesive joints have attracted an increasing attention in joining/repairing of carbon fiber reinforced epoxy composite structures due to their zero eccentricity, which provides lower stress distribution across the adhesive layer and better aerodynamic surfaces compared to other bonded joints. The main objective of this study is to evaluate the performance of the scarf adhesive joints in carbon fiber reinforced epoxy composites under thermomechanical impact loads, which is very important for the aerospace and automotive industries. The adhesive was modified with optimum percentage of multiwalled carbon nanotubes. The impact tests were performed at 25 ℃, 50 ℃, and 75 ℃. The residual flexural properties of the unfailed impacted joints were measured using three-point bending test. Results from impact tests at 25 ℃, 50 ℃, and 75 ℃ showed improvement in the impact bending stiffness of the modified scarf adhesive joints by 8.3%, 7.4%, and 11.8% and maximum contact force by 15.6%, 21.3%, and 18.9%, respectively. The energy at failure of the modified scarf adhesive joints with multiwalled carbon nanotubes was improved by 15.2% and 16.4% respectively at 25 ℃ and 50 ℃. At test temperature of 75 ℃, the scarf adhesive joints have hysteresis load–displacement behavior and energy–time curve with rebound energy of 35% and absorbed (damage) energy of 65%. The residual flexural strength of the modified and unmodified scarf adhesive joints is 98.2% and 86.1% respectively, while their residual moduli have remarkable decrease to 71.7% and 81.3%.

Effect of material hybridization on the strength of scarf adhesive joints

Adhesively-bonded joints have become more efficient due to the improvement of adhesives’ characteristics. On the other hand, with the use of composites in structures it is possible to reduce weight. Due to this, new techniques are being explored, including adhesively-bonding different materials. Nowadays, in many high performance structures, it is necessary to combine composite materials with other light-weighted metals such as aluminium or titanium. This work reports on an experimental and numerical study for hybrid scarf joints between composite and aluminium adherends, and considering different values of the scarf angle (α). The numerical analysis by Finite Elements (FE), using the software Abaqus®, enabled the obtainment of peel (σy) and shear stresses (τxy), which are then used to discuss the strength between different joint configurations. Cohesive zone modelling (CZM) was used to predict the joint strength and the results were compared to the experiments for validation. The joints’ behaviour was highly dependent on α, and CZM were validated for the design process of hybrid scarf joints.

The influence of surface treatment on the tensile properties of carbon fiber-reinforced epoxy composites-bonded joints

The surface characteristics of carbon fiber-reinforced composites significantly influence the tensile properties of adhesive-bonded joints. The main objective of this study was to research the effect of surface treatment by sandpaper rubbing on the strength of adhesive joints. In the present research, surfaces were prepared using four grades of sandpaper with grit sizes of up to 60, 220, 400, 800, and polish grit. Further, the two types of joints (single lap joint and scarf adhesive joint) were tested to investigate the effects of the grit sizes and sanding direction of the sandpaper (parallel to the fiber direction, perpendicular to the fiber direction, and random direction) on the tensile properties. The experimental results showed that the highest bonding strength could be achieved when the surface was sanded in the random direction. Moreover, the grit sizes of the sandpaper significantly influenced the surface characteristics, including the surface profile, surface roughness, surface contact angle, and surface free energy of the specimens, and then affected the bonding strength of the joints by mechanical interlocking and adsorption effect. Furthermore, for both single lap and scarf adhesive joints, the failure mode and the force of the adhesive layer under tensile load were different; therefore, the dominant factors affecting the bonding enhancement mechanism were consequently different.

Application a direct/cohesive zone method for the evaluation of scarf adhesive joints

With the increasing use of structures with adhesive bonds at the industrial level, several authors in the last decades have been conducting studies concerning the behaviour and strength of adhesive joints. Between the available strength prediction methods, cohesive zone models, which have shown good results, are particularly relevant. This work consists of a validation of cohesive laws in traction and shear, estimated by the application of the direct method, in the strength prediction of joints under a mixed-mode loading. In this context, scarf joints with different scarf angles (α) and adhesives of different ductility were tested. Pure-mode cohesive laws served as the basis for the creation of simplified triangular, trapezoidal and exponential laws for all adhesives. Their validation was accomplished by comparing the numerical maximum load (Pm) predictions with the experimental results. An analysis of peel (σ) and shear (τ) stresses in the adhesive layer was also performed to understand the influence of stresses on Pm. The use of the direct method allowed obtaining very precise Pm predictions. For the geometric and material conditions considered, this study has led to the conclusion that no significant Pm errors are incurred by the choice of a less appropriate law or by uncoupling the loading modes.

Comparison between 2D and 3D applications of the coupled criterion to crack initiation prediction in scarf adhesive joints

Crack initiation of scarf adhesive joints with similar adherends is predicted through 2D and 3D applications of the coupled criterion. The joint adhesive crack initiation topology and loading are determined as a function of the joint angle and of the specimen width, using both an energy and a stress criterion consisting of the maximum interface normal or shear stress to strength ratio. Adherend/ adhesive interface strength and toughness are determined by indirect confrontation to experimental results under tensile loading. The blind application of the proposed method to crack initiation of scarf adhesive joints under bending leads to a good agreement with experimental data. Compared to the 2D case, the 3D application of the coupled criterion allows determining the crack topology and leads to a slight better agreement with experimental results.

Static and fatigue analysis of bolted/bonded joints modified with CNTs in CFRP composites under hot, cold and room temperatures

The present study evaluated for the first time, the tensile and fatigue properties of bolted/bonded scarf adhesive joints (SAJs) in carbon fiber reinforced polymer (CFRP) composites at room temperature of +25 °C, +50 °C and −70 °C. The adhesive layer of the SAJs was modified with multi-walled carbon nanotubes (CNTs) and the results are compared with respect to neat adhesive and adhesive thickness. A new simple approach was developed to measure bolt-hole elongation, which successfully differentiates between bearing failure and interfacial shear failure modes and loads. Results from tensile tests showed that the bolted/bonded SAJs can perform well at −70 °C with maximum loss in strength of 9.6% and stiffness improvement of 30%. Incorporation of CNTs into the adhesive layer improved fatigue lives, at +25 °C, by about 72.1%–97.8% compared with that of neat-adhesives. Interfacial shear failure, cohesive failure and CNTs pull-out are the dominated failure modes in the SAJs, whereas bearing, shear-out, longitudinal splitting and bolt fracture are observed for the bolted joints. Considerable attention was given to analyze the scatter in the tensile strength and fatigue life results.

Adhesive layer analysis for scarf bonded joint in CFRE composites modified with MWCNTs under tensile and fatigue loads

The effects of bondline thicknesses (0.17 & 0.25-mm) and scarf angles (5° & 10°) on the tensile and fatigue properties are investigated, for the first time, for carbon-fiber/epoxy composites scarf adhesive joints (SAJs) modified with optimum weight percentages of multi-walled carbon nanotubes (CNTs). New experimental/analytical model was developed to measure the adhesive displacement parallel to the adherend surface (Δux) using instrumented specimens with extensometer and strain-gauge. The measured values of Δux were used to determine the deformations, normal stresses, in-plane shear stresses and Young’s moduli of the adhesive layers in the SAJs under tensile loads. Results from tensile tests showed remarkable increase in apparent and local stiffnesses for the SAJs with CNT-adhesive, 0.17-mm bondline thickness and 10°-scarf angle. The Young’s moduli of the adhesive layers of the 5°-SAJs is about 2–3.2 times higher than that of bulk adhesives. The tensile strength of CNT-SAJs is 15.9–33% higher than that of the neat-SAJs with different bondline thicknesses and scarf angles. On the other hand, CNTs have marginal effect on the fatigue strength at lower lives and insignificant effect at fatigue limits (107-cycles). The fatigue strength/life of the SAJs was improved with decreasing scarf angle from 10° to 5° and bondline thickness from 0.25-mm to 0.17-mm.