Strength Of Single Lap Joints Research Articles

The effects of using intermittent metal part reinforcement and countersink on the strength of adhesively bonded joints

This study investigates the impact of two innovative methods, namely, intermittent metal part reinforcement and countersinking, on the strength of single lap joints (SLJs). In the former method, metal inserts are strategically integrated within the adhesive layer, while the latter involves the application of countersinks on the adherends to create conical depressions for adhesive application. The metal inserts and countersink samples were fabricated using a 5-axis CNC milling machine. Subsequently, the joints were produced by subjecting the samples to 0.15 MPa pressure and 70 °C temperature for 120 min with the aid of a hot press. Tensile tests were conducted on single lap joints (SLJs) featuring five different configurations of intermittent metal part reinforcement joints (IMRJs) with varying sizes and positions of reinforcements, as well as six countersunk reinforced joints (CRJs) with different orientations of countersinks, all while keeping the width and overlap length constant. A two-dimensional finite element (FE) model of the IMRJ was constructed using ABAQUS software, incorporating cohesive zone elements to simulate the behavior of the adhesive layer (DP 460). The model's accuracy was confirmed through experimental verification. Additionally, fractographic analysis of the failure surfaces of both types of joints was carried out. The inclusion of IMRJs and CRJs in the SLJs increased their load-carrying capacity by more than 10 % and 30 %, respectively.

The effect of co-creation of notches and recesses in the adhered material on the strength of single-lap adhesive joints: Experimental and numerical analysis

For decaces, many different adhesive joint geometries have been used in aerospace and automotive applications, with the idea that adhesively-bonded joints can be an alternative to traditional joining methods in aerospace applications. The single-lap joint geometry is today one of the most frequently used joint geometries in research. In this joint geometry, due to eccentric loading, peel stresses occur, which cause damage in the overlap region. Reducing these stresses increases joint strength. In this study, the strengths of single-lap joints (SLJ) obtained by creating notches and recesses of different lengths and depths in the adhered material were investigated experimentally and numerically. First, the strengths of the SLJ obtained by using different lengths and thicknesses of recesses and notches of different widths and depths in the adherend were investigated. After this examination, the strength of the joints with the best recess and notch joints together in terms of joint strength were examined. As a result, making a recess of the adherend on the outer part of the overlap region in single-lap joints increases the joint strength by approximately 29%, and making a notch increases the strength of the connection by approximately 27%. These increases in the joint strength vary according to the geometry of the recess and notch formed in the adherend. In addition, the use of both the notch and the recess in the joint improves the joint strength further. Additionally, in the presented study, experimental data were compared with numerical analysis and it was observed that the data were quite consistent with each other.

Effects of adherends’ misalignment on the strength of single-lap joints under 3-point and 4-point bending tests

Effects of adherends’ misalignment on the strength of single-lap joints under 3-point and 4-point bending tests

Tensile Behaviour of Double- and Triple-Adhesive Single Lap Joints Made with Spot Epoxy and Double-Sided Adhesive Tape.

Dual adhesives are mainly used to increase the strength of single lap joints (SLJs) by reducing the stress concentration at its ends. However, they can also be used to design the characteristics of the joint so that its operation and failure occur in several stages. This paper presents the results of uniaxial tensile tests for dual-adhesive and triple-adhesive SLJs. The adherends were made of aluminum and glass fiber-reinforced polymer (GFRP) composite. For dual-adhesive SLJs, 10 epoxies and 1.6 mm thick double-sided adhesive tape were used. The stiffest (Epidian 53 (100 g) + "PAC" hardener (80 g)) and most elastic (Scotch-Weld 2216 B/A Translucent) joints were determined, which were then used in a triple-adhesive joint with the same double-sided adhesive tape. Circular holes of different diameters from 8 mm to 20 mm were made in the double-sided adhesive tape, which were filled with liquid epoxy adhesive by injection after the adherends were joined. By using the double-sided adhesive tape, the geometry of the epoxy joints was perfect, free of spews, and had a constant thickness. The effect of the spot epoxy joint diameters and the arrangement of stiff and elastic joints in the SLJs were analyzed using digital image correlation (DIC).

Effect of cure temperature on the mechanical properties of epoxy-aluminium single lap joints

ABSTRACT Mixed adhesive joints combining different stiffnesses and strengths in the same overlap is a good strategy to increase the mechanical properties. For this purpose, different adhesives with distinct curing temperatures are used, whose optimization is crucial to maximize the mechanical performance. In this context, this study considers Araldite® AV 4076–1/HY 4076 and Araldite® AW 106/HV 953 U adhesives to evaluate the effect of curing temperature on tensile strength, creep and stress relaxation response and fatigue strength of single lap joints. It was possible to conclude that both adhesives exhibited higher static strength, lower stress relaxation and lower creep displacements with increasing curing temperature, but while for the brittle adhesive this trend occurred up to 150°C for the ductile one it was only up to 70°C. After this value, all properties regressed due to the degradation of the ductile adhesive with temperature. Considering values corresponding to 25% of the tensile strength, for example, it was noted that the ductile adhesive relaxes 54.7% more than the fragile one and presents a creep displacement around 95.1% higher. On the other hand, while the fatigue life was shown to be insensitive to the curing temperature for the brittle adhesive, in the case of the ductile one it decreases after 70°C. Therefore, when these adhesives are combined into a mixed adhesive joint, the curing temperature must never exceed 70°C.

Evaluation of aluminum to composite bonded lap joints

Adhesive bond is one of the best suitable joining technique for fiber reinforced polymer (FRP) composite structures used in aerospace applications. The weight of the composite structure greatly reduces by using structural adhesives for the joining processes. The surface preparation plays a major role for achieving the better bond strength. The present work deals with the validation of the bond strength of single lap joint(SLJ) with dissimilar adherends. The Al adherend has been considered for the surface treatments such as sand paper, NaOH and Resin pre-coating (RPC) for SLJs. The angle of contacts for the different surface treated specimens has been measured using the Young–Laplace method. X-Ray radiography and ultrasonic testing has been carried to verify the internal defects of bonded joint. The bonding strength was evaluated using a tensile and flexural test rig in polymer UTM. The bond strength of the RPC surface treated bonded joints showed better performance in terms of peak load and shear strength. The maximum shear strength has been increased up to 154.63 percentage when compared to untreated surface specimens, similar trend was observed in flexural strength. A numerical simulation model has been developed for validating the results. The comprehensive analysis for the de-bonded joints at maximum loading conditions has been done with morphological studies.

The effect of stepped notches and recesses on joint strength in adhesive bonded joints: Experimental and numerical analysis

In this study, the strengths of single-lap joints (SLJ) obtained by creating stepped notches and recesses of different number of steps, lengths and depths in the adhered material were investigated experimentally and numerically. In the study, the DP460 structural adhesive was used as the adhesive, and the AA2024-T3 aluminum alloy was used as the adherend. Firstly, the strengths of the SLJ obtained by creating two-stepped and three-stepped recesses of different lengths and thicknesses in the adhered were examined. Then, the strengths of the SLJ obtained by creating two-stepped and three-stepped notches of different lengths and thicknesses were examined. As a result of these examinations, the mechanical properties of the new SLJ geometry, in which the best two-stepped and three-stepped recessed and protruding joints were formed together, were obtained. As a result, while making two or three-stepped of the recess to the adherend in the adhesive joints increases the strength of the joint by approximately 33% to 40%, making two or three-stepped notches increases the strength of the joint by approximately 37% to 38%. However, in the case of gradual recess and notch in the joint being together, the joint strength increases by approximately 50% to 54%.

SIMULATION OF JOINT STRENGTH OF SINGLE LAP JOINT OF COMPOSITE PLATES BASED ON VARIATIONS OF PLATE THICKNESS AND OVERLAP LENGTH

In this study, finite element simulation of joint strength of single lap joint of composite plates based on variations of joint thickness and overlap length is presented by using ANSYS software. In the simulation, plate thickness and overlap length of the joint structure are varied. Based on the variations of plate thickness and overlap length, it is found that the largest joint strength is obtained at the values of plate thickness and overlap length of 2 mm and 55 mm, respectively. Also, it appears that the applied loading type will affect to the simulation results.

Experimental study on CF/PEEK thermoplastic fastener: Effects of fastener matrix crystallinity and fibre content on the strength of single-lap joint

Composite materials are widely used in the aerospace structures due to their characteristics of light weight and high strength, while composite material components are currently joined by heavy titanium fasteners. We propose here a novel joining method using unidirectional CF/PEEK thermoplastic composites fastener (TPCF). CF/PEEK TPCFs are prepared via mechanically machining unidirectional CF/PEEK composites laminates. The joining of TPCF is through a hot-press and cooling process. Single-lap joints reinforced by CF/PEEK TPCFs are subjected to tensile tests and compared with titanium riveted joint. Experiments results show that the failure of the TPCF joint is shear off in fastener, while the composite laminate of titanium riveted joint undergoes a bearing failure and the rivet is pulled out from the laminate. The TPCF joint strength is lower than that of titanium riveted joint, but the TPCF joint has a higher specific joint strength. The TPCF joint strength increases with increasing carbon fibre mass fraction of TPCF. Also, we find that the TPCF joint strength increases with decreasing cooling rate. The DSC tests of TPCF show that the low cooling rate leads to an increase in crystallinity, which enhances the mechanical property of TPCF and then improves the joint strength. This provides a new process to control the TPCF joint strength by changing its cooling rate. The fracture face of TPCF is observed. It is found that the TPCF has a ‘U-shaped’ stepped fracture face after structure failure, which is caused by shear force and impact load.

Effects of impact fatigue on residual static strength of adhesively bonded joints

In most industrial applications, adhesive joints experience impact fatigue loads in service. The energy of each impact is too low to cause joint failure. Although the repetitive impacts usually do not apparently affect the joints, they can significantly reduce the strength of adhesively bonded structures. Accordingly, understanding the effect of impact fatigue on the residual strength of the bonded components is crucial in real applications. This study deals with this issue where the effect of impact fatigue on the residual static strength of single lap joints is analyzed. To achieve this, the manufactured single lap joints were categorized into four different groups. Group 1 joints were tested under static loading conditions. Joints in group 2 were tested under impact to obtain the impact strength of the single lap joints. To analyze the impact fatigue life of the joints, the single lap joints in group 3 were tested under cyclic impact at different energy levels until failure. To investigate the effect of impact fatigue on the residual static strength of the joints, single lap joints in group 4 were tested under a specific number of impact cycles followed by a static tensile test. Using microscopic analysis, the fracture surfaces of the tested specimens were analyzed. The results showed that cracks initiate from the middle of the bonded area as a result of cyclic impact stress waves. Then, by increasing the number of impacts, a large number of cracks nucleate from the edges of the joints and grow along the width to the middle of the overlap. A 3D finite element method was employed to analyze the stress distribution along the bondline under impact loads.

Experimental investigations on fatigue life enhancement of composite (e-glass/epoxy) single lap joint with graphene oxide modified adhesive

With the increased use of composites in various sectors as a lightweight material exhibits high strength to weight ratio with tailor made properties. It becomes necessary to focus on various joining methods and different types of composite joints and their strength. The present study aims to improve the mechanical strength of single lap joint of composite material comprises of E-glass fibers and nano modified adhesive. Epoxy adhesive has been modified by dispersing Graphene Oxide (GO) to investigate the possibility of enhancement in the fatigue strength and fracture resistance of the single lap joint. Modified Hummer’s method has been used for synthesis of Graphene Oxide. Experimental investigations have been carried out for comparison of tensile and fatigue strength which shows significant improvement in the number of failure cycles for 0.25 wt.% and 0.75 wt.% GO concentrations respectively as compared to neat adhesive. Tension test results showed a significant increase in the fracture toughness of the joint due to addition of GO nanoparticles. There has been 33% and 19% increase in fracture toughness in 0.25 wt.% and 0.75 wt.% GO samples respectively as compared to neat adhesive. Improvement in fracture toughness, among all other nano-reinforcements has been obtained using GO, mainly because of its better capability of deviating the crack growth path to the longer path causing the final failure to retard and consequently improving mechanical properties of the adhesive for the tensile and fatigue strength parameters.

A new geometry for improving the strength of single lap joints using adherend notching technique

ABSTRACT In this study, the adherend notching technique is reconsidered by introducing a rectangular or a semi-circular notch on the outer surface of the adherends in the single lap joint (SLJ). Firstly, an extensive finite element (FE) analysis was conducted to numerically investigate the effect of different notch parameters on the strength enhancement of the SLJs. Improvement of the peak of peel stress along the overlap length was selected as the determinative factor for obtaining the optimum parameters of the introduced notch. Then, a set of experiments were performed on the notched SLJs based on the optimum notch parameters derived in the FE analyses and the experimental failure loads were compared with the un-notched SLJs. The experimental results showed that introducing a notch can improve the strength of SLJs up to 110% which demonstrates the effectiveness of the proposed technique in this paper. Furthermore, it was seen that there is not a meaningful difference between the improvements of rectangular and semi-circular notch which shows that the improvement of the adherend notching technique are not dependent on the geometry of the introduced notch.

Single lap joint strength prediction using the radial point interpolation method and the critical longitudinal strain criterion

Adhesive joining is currently a very popular joining method. This increases the necessity for better strength prediction tools to aid in the design of these joints. Currently, Cohesive Zone Modeling (CZM) is the most popular method to study joint strength. However, CZM requires traction-separation laws, which define the adhesive behavior, and these are dependent on the adhesive thickness (tA). This means that, when using CZM, the traction separation law parameters have to be measured multiple times to predict the strength of joints with different tA. The recently proposed Critical Longitudinal Strain (CLS) criterion is a criterion based on continuum mechanics, which was previously used with the Finite Element Method (FEM) to predict the strength of Single Lap Joints (SLJ). The use of meshless methods to predict the strength of adhesive joints is scarce and the CLS criterion has never been used with the Radial Point Interpolation Method (RPIM). In this work, the CLS criterion was used with the RPIM to determine the strength of SLJ bonded with three different adhesives. The strength predictions with this approach were accurate for the three adhesives, which ranged from brittle to highly ductile.

Strength enhancement of bonded composite laminate joints reinforced by composite Pins

This paper presents an experimental and numerical investigation in the static strength enhancement of composite laminate Single Lap bonded Joints (SLJ), reinforced by pins made of Uni-Directional (UD) fibre reinforced plastic composite materials. Bonded lap joint specimens were experimentally tested in tension to obtain the failure loads and failure modes. The specimens were subsequently benchmarked against the hybrid version of the joint resulted from the introduction of composite Pins. The Pin reinforcement enhanced the hybrid single lap joint strength by an average of 19.1% increase. Numerical models generated were used for correlation with the experimental results. Numerical and experimental results observation indicated that increased strength of the hybrid bonded/Pinned joint was partly attributed to the load sharing between the adhesive and the Pin past the adhesive failure initiation as well as to the enhanced out-of-plane bending stiffness after the Pin introduction on the lap joint. Numerical investigations were performed as well with hybrid SLJ reinforced by composite pins versus designs employing metallic Pins. The simulations showed that for the investigated lap joint design parameters, the hybrid metallic pin joint failed at a higher failure load. Nevertheless, the hybrid joint utilizing the composite Pin could benefit from the enhanced corrosion resistance properties. In the case of applying a larger composite Pin diameter and/or rearranging the fibre orientation in the Pin, the hybrid SLJs could potentially achieve higher strength characteristics before the adhesive bond ultimate failure in relation to the steel Pin, as well as resulting to additional weight saving up to 46.9%.

A cohesive model with a multi-stage softening behavior to predict fracture in nano composite joints

The scope of this research is presenting a new traction-separation law for composite adhesive joints in the presence of nanoparticles in mode I and II fracture. The experimental work involved evaluation of nanoparticles effects on bridging laws, cohesive mechanism, and traction-separation laws in mode I and II fracture. Nanocomposite samples have been undergone double cantilever beam, and end notched flexure tests. The experimental bridging laws were converted into traction-separation models applicable to user-defined interface/cohesive finite elements, and a new modified model was presented to simulate and predict fracture in mode I and mode II. The obtained traction-separation laws for various nanoparticles contents can be utilized in the finite element methods for numerical simulation. A damage evolution formulation was presented, and contributing parameters were modified. Numerical modeling in Abaqus software was implemented to compare experimental results of single lap joint strength and predicted mechanism within the new proposed model.

Strength improvement in single lap adhesive joints by notching the adherends

In this study, an easy procedure is proposed to improve the strength of Single Lap Joints (SLJs) by introducing a notch in the adherends right after the overlap length. At first, the effect of different notch parameters on the peel, shear and von Mises stress distributions of the adhesive mid-plane layer is investigated by using the Finite Element (FE) method. The considered parameters are the notch angle, the notch width, the notch depth, and the notch distance from the overlap length. Afterwards, a simple 90-degree notch angle which can be easily manufactured is selected for adherend notching based on the numerical results. In addition, in order to experimentally investigate the effects of different notch parameters on the failure load of adhesive joints, five various notch depths with two different adhesive curing methods are considered. Finally, the experimentally obtained fracture loads are compared with the theoretical ones which are based on the predictions of von Mises stress and peel. The results show that using the adherend notching can significantly improve the load bearing capacity of SLJs. For instance, a simple notch with 20% notch depth ratio can improve the load bearing capacity of the SLJ about 60%.

Effect of operating temperature on aged single lap bonded joints

Abstract In recent decades, designers have increasingly focused on the stability of assemblies in composite materials over time, particularly when used in structural applications. The use of structural adhesives allows for realising assemblies without mechanical fasteners. In fact, bonding is an assembly technique that prevent corrosion, ensures uniform stresses in the joint, and grows the specific resistance of the assembly. The knowledge of the behaviour of bonded joint is necessary to ensure the reliability of this technique over time, especially in aggressive environments. The aim of this work consists in investigating the combined effect of hydrothermal ageing and temperature test on the lap shear strength of single lap joints realised in CFRP. The results showed a higher influence of the ageing on paste adhesive compared to film adhesive. However, the ageing, combined with the operating temperature, played a fundamental role on the shear strength of the bonded joints.

Experimental Investigation on Mechanical Joint of Lontar (Borassus Flabellifer) Fiber Reinforced Polyester Composites under Static Flexural Test

This study has been conducted to investigate the flexural strength of Borassus Flabellifer Fiber/BFF reinforced polyester composite joint under static condition. Tests were carried out to study the flexural strength of double strap butt joint and single lap joint of BFF polyester composite. In addition, post observation of macroscope was used to map failure behavior. The results shown that the flexural strength of single lap joint is higher compared to double strap butt joint of BFF polyester composite. The larger cross-sectional area and the existence of gap area could be the main reason for lower flexural strength generated by double strap butt joint of BFF polyester composite. The failure of BFF polyester composite joints under flexural test indicated the brittle failure behaviour that fiber breakage was found to be the final failure mechanism which start with matrix cracking and fiber-matrix debonding failure mechanisms.

Investigation of the effect of use of Nano-Al2O3, Nano-TiO2 and Nano-SiO2 powders on strength of single lap joints bonded with epoxy adhesive

In this study, single lap joints were formed by adding nano-Al2O3, nano-TiO2 and nano-Al2O3 powders in various proportions to the epoxy adhesive and using the additive-free epoxy adhesive; and also the mechanical properties of the connections were experimentally investigated at 20, 25, 30, 50 and 70 mm overlap lengths under shear load. In the experimental work, DP460 epoxy adhesive was used as adhesive and AISI 304 stainless steel plate as adherent material. When the results obtained from the experiments were examined, it was revealed that the average damage load in connection with the use of nanoparticle-added adhesives increased considerably in general. As a result of the experiments, the most effective nanoparticle in increasing the failure strength of the adhesive joints with nano-Al2O3 particles and the maximum failure strength increase rate was 20 mm in overlap length and 97% in 4 wt% nano-Al2O3 reinforced specimens. It was also found that the nanoparticle strain was an important parameter in the tensile strength of the adhesive joints. In addition, it has been found that the addition of nanoparticles into the adhesive increases the elongation of the joints. When the adhesion surfaces of the samples were examined as in the case of plain adhesives, damage was observed as adhesion separation while nanoparticle reinforcement was observed as a mixture of adhesion and cohesion.

Multivariate analysis of high through-put adhesively bonded single lap joints

The goal of this research was to experimentally demonstrate the correlations between processing variables (adhesive type, bondline thickness, adherend thickness, surface pretreatment, overflow fillet) and effective strength in adhesively bonded single lap joints. While generalizations between effective strength and individual joint design parameters have been assumed for decades, the multifaceted interplay between parameters is complex and remains difficult to understand. Traditionally reported studies of the adhesive bond strength of single lap joints are often limited in the sample size populations needed to statistically probe concurrent design variables. To overcome sample size limitations a test matrix of 1200 single lap joints, partitioned by 96 unique fabrication conditions, was processed and tested using a workflow protocol orchestrated through a relational database. The enhanced pedigree and integrity enabled by using a relational database centered workflow allowed for multivariate principal component analysis of the joint design parameters, with all experimental data input available for peer audit. The results of this study revealed that the adhesive type biases the remaining joint configuration variables towards more influence with respect to either mechanical load or displacement to failure.