Adhesive Joints Research Articles

The effect of laser texturing of the surface of a titanium alloy on the adhesive strength of adhesive joints

The effect of laser texturing of the surface of a titanium alloy on the adhesive strength of adhesive joints

Analysis of the anisotropic mechanical properties of structural adhesive joints with curing-induced pre-deformations

In modern lightweight construction, multi-material design has become increasingly important. An increasing number of structures are being adhered because adhesive joining technology can be used regardless of the material of the bonded partners. Owing to the dissimilar coefficients of thermal expansion, thermally induced relative displacements of the adherend occur during heat curing. Following these pre-deformations, changes in the mechanical properties of adhesive joints were observed. In this study, thick adherend shear specimens were used to induce defined relative displacements in the shear plane during the curing process. Quasi-static tests showed a directional dependence in the pre-deformation. This anisotropic behaviour was investigated in detail. Results showed that shear band formation occurred in the adhesive owing to the load during the cooling of joined structures. The restructuring of the polymer structure leads to changes in the mechanical properties.

Effect of low velocity impact at different temperatures on hybrid adhesives in aluminium-composite single lap joints

This study aims to investigate the effect of a small stone impact on aluminum composite adhesive joints used in aircraft after exposure to various temperature conditions. In this context, single lap adhesive joints were prepared using 2024-T3 aluminium alloy sheets and 8-layer carbon fiber-reinforced epoxy hybrid composite sheets, with epoxy adhesive applied to the bonding surfaces. In addition, different types of hybrid adhesives were developed by reinforcing pure epoxy adhesive with various ratios (1%, 3% and 5% by weight) of graphene doped and undoped Nylon 6.6 (N6.6) nanofibers produced by electrospinning method to reduce brittleness. Low-velocity impact tests of 1.04 m/s under five different temperatures (−50, −20, 0, 23 and 50°C) were applied to all single lap adhesion joints produced and tensile tests were applied to the non-failed specimens to examine the loading conditions after low-speed impact. It was determined that approximately 1.5 J of the 3 J energy given by the low- velocity impact was absorbed in common in all samples, while the remaining part was returned and some separation occurred within the adhesion area due to the effect of this impact. While the low- velocity post-impact tensile strength of pure epoxy resin was measured as 2230.3 N at 23°C and 585.15 N at −50°C, the highest values were obtained in N6.6 reinforced epoxy adhesive with 1%GNP additive, which was measured as 3206.39 N at 23°C and 641.82 N at −50°C, and increased by 43.7% and 9.6% for 23°C and −50°C, respectively. In addition, the rupture surfaces of the specimens destroyed by the tensile test were examined by scanning electron microscopy (SEM) for damage analysis.

Experimental Analysis of the Behavior of Multiple Adhesive on the Single Lap Joint Strength

The usage of adhesively bonded lap joints in industrial applications has been growing in recent years because of the numerous advantages compared to other joining processes such as fastening, welding, and riveting. For effective design of the adhesively bonded engineering lap joints, it is essential to govern the failure potential of a particular adhesive joint under a certain load causing some stress and strain. In this work, study has been carried out by the application of multiple adhesives along the bondline region of lap joint. The objective of this paper is to experimentally examine the results of applications of single and multi-adhesives material with very different mechanical behavior along the bondline region in the single lap adhesive joint. Experimental investigations have been carried out for extracting load displacement data using tensile testing machine, Tensometer, having a capacity of 2 tonne. Multi Adhesive joint can minimize the stress concentration and improve joint strength by using different adhesive stiffness along the bondline region of lap joint and the outcome shows computable increase in the strength of the multiple adhesive bonded lap joints associated with those in which single adhesives were used over the full length of the bondline region.

Fracture analysis under modes I and II of adhesive joints on CFRP in saline environment

This study analyzes the delamination behavior of adhesive joints after exposure to a saline environment for zero, one, and twelve weeks. Delamination was assessed under static and fatigue loading conditions in fracture Modes I and II, with a detailed analysis of fracture surfaces using Scanning Electron Microscopy (SEM) and Backscattered Electron (BSE) detection. The 3D images reveal significant morphological differences in fracture surfaces, showing variations in fatigue lines and the presence of impurities depending on the fracture mode. A probabilistic fatigue life analysis was performed using a Weibull regression model, showing notable changes, especially in Mode I at a high number of cycles. A chemical analysis using EDX and FTIR-ATR complemented the mechanical study, revealing an increase in sodium and chlorine concentrations with prolonged saline exposure. Oxidative degradation was also observed, with carbonyl groups increasing significantly over time, particularly in areas most exposed to the saline mist.

The Optimization of the Strength of Wood Adhesive Joints Supported by Steel Fasteners in Furniture Components

The Optimization of the Strength of Wood Adhesive Joints Supported by Steel Fasteners in Furniture Components

Utilizing a combination of experimental and machine learning methods to predict and correlate between accelerated and natural aging of CFRP/AL adhesive joints under hygrothermal conditions

AbstractThis study investigates how carbon fiber reinforced polymer (CFRP)‐to‐aluminum adhesive joints behave under accelerated aging conditions with hygrothermal exposure and compares these findings against naturally aged samples to evaluate material reliability in challenging environments. The CFRP‐to‐aluminum adhesive joints were manufactured and subjected to natural aging for durations ranging from 1 to 3 years with 6‐month intervals, as well as accelerated aging (hygrothermal) for periods ranging from 100 to 1200 h, with intervals of 50 h. Subsequently, the mechanical properties of the joints were evaluated using a three‐point bending test. To forecast natural aging times from accelerated aging data, five machine learning models were utilized: artificial neural network, support vector regression, linear regression, polynomial regression, and random forest regression. Hygrothermal aging significantly degraded the matrix, causing a shift in failure modes from cohesive to mixed types (cohesive, adhesive, and fiber tear failures), leading to a notable decline in bending strength. The study observed a 23.13% strength reduction in samples aged naturally for 3 years and a 24.33% decrease in those subjected to 1000 h of accelerated aging. The random forest regressor demonstrated superior accuracy in predicting natural aging times across different accelerated aging periods. Through the application of machine learning models, this study introduces a novel approach to forecast natural aging durations using data from accelerated aging experiments. This method shows potential for optimizing joints and composite structures, ultimately improving their durability and minimizing the likelihood of failures during operational use.Highlights Studied hygrothermal effects on accelerated aging of carbon fiber reinforced polymer/Aluminum (AL) adhesive joints. Noted strength reduction from hygrothermal aging. Used five machine learning models; random forest regression had the highest accuracy. Analyzed correlation between natural and accelerated aging of dissimilar adhesive joints.

Experimental Research on the Possibility of Changing the Adhesion of Epoxy Glue to Concrete

Among the many methods of joining different materials, gluing is characterized by its most specific nature. In comparison with, for example, welded, screwed, or overlapped connections, a glued connection depends on the largest number of factors. Many of them are related to the phenomenon of adhesion, which is complicated by definition. It has many shapes and forms, and its existence determines not only the durability of such a joint but also the possibility of its execution. Epoxy polymers are among the most commonly used adhesives. Their extremely good parameters can be easily modified by additives in the form of fillers. Compatibility between the filler and the adhesive allows for further improving the adhesive parameters in the glued joint. However, in order to effectively combine the adhesive and the filler, different, often specific mixing methods must be used. The following study presents the results obtained in an experimental research program, the aim of which was to increase the adhesion of epoxy resin to a properly prepared concrete substrate. As a method to increase the final adhesion, the addition of microsilica and carbon nanotubes in an experimentally determined amount was selected. The use of sonication as a mixing method together with cavitation allowed for improving the parameters which determine the final adhesion of the adhesive to concrete. The parameters which were selected to describe the course of changes in the adhesion of the adhesive to the concrete substrate were the viscosity, free surface energy, surface parameters, adhesion, and SEM images of the tested resin in various modification configurations. The obtained results make it possible to form stronger and more durable adhesive joints during the reinforcement of concrete structural elements using fiber-reinforced polymer (FRP) composites.

ANN Prediction of Mode I Fracture Energy in Epoxy Adhesive Joints: Adherend, Adhesive, and Strain Rate Effects

In this investigation, the mode I fracture behavior of an epoxy adhesive joint has been investigated to probe the combined effects of adherend Young's modulus and thickness, strain rate, and adhesive length. Experimental fracture testing was conducted on double-cantilever beam (DCB) specimens under three various strain rate thresholds, namely, quasi-static (0.0005 s-1), low (0.015 s-1), and intermediate (0.5 s-1). The specimens were constructed with varying adherend materials (i.e., copper, aluminum), thickness (12-20 mm), and adhesive lengths (25-75 mm). The fracture load was measured in each experiment, and the critical strain energy release rate, JCi, was calculated via a finite element analysis (FEA) in each case. Results with a 95% confidence interval showed adherend thickness had a negligible effect within the investigated range (p-value = 0.462). JCi was significantly impacted by adhesive length (p-value = 0.009) and two other investigated parameters (p-values = 0.000). The development of artificial neural networks (ANNs) with Levenberg-Marquardt (LM) led to the prediction of JCi based on the examined parameters. With a mean absolute percentage error (MAPE) of 8.9% and a mean squared error (MSE) of 683 J2/m4 on unseen test data, the ANN model built in this study was able to predict the JCi in epoxy adhesive joints, indicating its potential to produce an accurate prediction for JCi in epoxy adhesive joints. This work offers insights for precise fracture behavior prediction under mode I stress conditions as well as some helpful information that can be utilized to optimize adhesive joint design.

Effect of elevated temperature on the bond behaviour of adhesive shear joints between glass substrate and iron-based shape memory alloy strip

Glass has been increasingly used as structural elements, such as glass beams or fins. Previous feasibility studies have shown increased initial and post-fracture load-bearing capacity of laminated glass beams post-tensioned with adhesively bonded iron-based shape memory alloy (Fe-SMA) strips. However, the potential elevated service temperatures were not considered, which significantly degraded the material properties of the adhesive. This study experimentally investigated the mechanical behaviour of Fe-SMA-to-glass lap-shear joints with an epoxy adhesive at different temperatures of 23 °C, 50 °C, and 80 °C, representing room temperature and typical elevated service temperatures. The results showed that, compared with the one at room temperature, the load-carrying capacity remained nearly unchanged at 50 °C and decreased by approximately 20% at 80 °C. On the contrary, the effective bond length increased from approximately 116mm to 250-300mm. The failure modes, the tensile strain of the iron-based shape memory alloy, the bond-slip behaviour, and the fracture energy of the joints were also evaluated. The current study fills a significant research gap in the engineering application of strengthening glass structures by bonded pre-stressed Fe-SMA strips. Moreover, the results may also significantly contribute to the future application of the selected adhesive at elevated temperatures.

Distributed Backface Strain Sensing of Composite Adhesively Bonded Joints under Mode II Fatigue Loading

When investigating the fracture behaviour of adhesive joints, accurate crack tip localization is under mode II loading is particularly challenging due to the absence of crack opening. The crack front often has a curved shape, so methods that inspect the side of the specimen cannot capture the crack length throughout its width. In this study, distributed backface strain sensing using Optical Backscatter Reflectometry fibre sensors is used to monitor fatigue crack growth in adhesively bonded composite End Notched Flexure Specimens. The obtained backface strain profiles were compared with analytical and Finite Element solutions to understand their relationship with the crack length. Results show that the crack tip position can be found by a local extremum in the first derivative of the strain profile. The proposed monitoring technique was compared with more established techniques for crack length measurement, such as Visual Testing, Compliance Monitoring, and Phased Array Ultrasonic Testing, and was shown to provide good accuracy. The evaluation of these techniques not only plays a crucial role in ensuring accurate testing, but can also contribute to the development of effective strategies for inspection and monitoring of adhesive joints.

Investigation of the accuracy of multi-input models using deep learning to estimate the tensile shear strength of adhesive joints

The correlation between the fracture surface images and residual tensile shear strength of adhesive joints immersed in water was investigated using deep learning. Multi-input models were used to investigate the effects of input parameters on the estimated strength. Specifically, the immersion time and temperature were added as inputs to the fracture surface image to identify the effects of multiple inputs and the conditions that contribute to the improved estimation accuracy. The estimation results showed that the highest accuracy was obtained when both immersion time and immersion temperature were added as input parameters. The variance in the estimated strength tends to be smaller for each additional parameter. To improve the accuracy of estimation using a multi-input model, approximate trends should be estimated for each input parameter alone. Conversely, the use of input parameters for which the trend cannot be estimated may reduce the estimation accuracy.

Polycarbosilane-modified phosphate adhesives for porous Si3N4 ceramic pressure-free bonding at high temperatures

Si3N4 ceramics are widely employed in the aerospace and automotive sectors owing to exceptional mechanical performances, anti-oxidant nature, and corrosion resistance properties. However, their brittleness makes manufacturing complex components challenging, while the intricate nature of welding restricts its use. A Si3N4 ceramic adhesive joint capable of withstanding high-temperature conditions was formed under ambient conditions. Polycarbosilane was introduced into the phosphate adhesive to improve high-temperature thermal matching between the adhesive and substrate, At 600 and 800 ℃, the compressive shear strength increased by 25% and 83%, respectively. After 48h at 1000 ℃, the compressive shear strength was 8.6MPa, indicating excellent oxidation resistance. The adhesive penetrated the matrix pores under capillary action, forming network bonding, and an interfacial reaction generated Si5AlON7, buffering thermal stress. This represents the first phosphate adhesive for bonding Si3N4 ceramics, demonstrating excellent forming capabilities, with bond strengths comparable to that of conventional welds, showing high potential for engineering applications.

Evaluating the moisture absorption percentage in the adhesive layers of carbon fiber reinforced plastic joints via electromagnetic induction testing and diffusion analysis

In this study, we propose a method that combines moisture absorption analysis and electromagnetic induction testing (EIT) to detect weak bonds formed in the adhesive layers of carbon fiber reinforced plastic (CFRP) joints due to moisture absorption. Although EIT is effective for assessing CFRP joint adhesive moisture absorption, early detection of weak bonds is challenging. Our method addresses this by combining calculations of moisture absorption percentage via the diffusion equation and EIT-based measurements. First, we conducted diffusion analysis using the finite difference method (FDM). The moisture absorption percentage calculated via the FDM was validated by comparing it with the results of the moisture absorption tests of the CFRP adhesive joints, and good agreement was observed. Second, EIT was applied to the CFRP adhesive joints, and the experimental results indicated that the moisture absorption percentage of the CFRP joint adhesive layer can be qualitatively evaluated using EIT. Finally, the moisture absorption of the CFRP joint adhesive layer was quantitatively evaluated by combining the results of EIT on the CFRP joints with those of the numerical analysis. Therefore, the proposed method enables the previously difficult quantitative evaluation of the initial moisture absorption percentage of CFRP joint adhesive layers and is effective for the early detection of weak bonds created by moisture absorption in CFRP joints.

Separation of adhesive joints of pouch cells in the context of battery module disassembly

The increase in demand for electric vehicles due to the transformation to electromobility will lead to a large number of batteries reaching the end of life and needing to be disposed of. Direct recycling of batteries requires disassembly down to cell level. However, adhesive bonds present a major obstacle to mechanical disassembly. In this work, adhesive bonds between pouch cells are characterised and possible separation processes are identified. Based on this, an industrial system concept for cutting the adhesive bonds, particularly with a rope cut, is developed and tested. A stable and safe process parameter space was identified. The separation process can enable further circular economy strategies such as remanufacturing or reusing the battery cells.

The influence of external and internal factors on ensuring adhesive interaction of a polymeric sealant with a substrate surface (a review)

This paper analyzes literature data on the influence of various factors affecting the strength and durability of adhesive bonds, as well as presents a characterization of the methods described in the literature for conducting relevant studies. It is shown that one of the main characteristics of adhesive joints is the interaction at the interface between the substrate and the adhesive. The adhesive capability of a sealant largely depends on the structure of the polymer component, as well as the presence of components in the sealant that enhance this property. The structure and condition of the substrate surface significantly affect the nature of the interaction between the adhesive and the substrate. Various methods are used to determine the strength of the adhesive bond, differing in the type of applied loads and the nature of the surface fracture. An important indicator is the determination of the wetting angle of the substrate by the sealant, which characterizes the surface energy. The durability of adhesive bonds is significantly influenced by environmental factors as well as operational conditions. Moisture, atmospheric oxygen, ultraviolet radiation, and microorganisms have a particularly strong effect on the properties of polymeric sealants.

Shear strength comparison of single lap and joggle lap adhesive joints in carbon fiber composites manufactured via vacuum-assisted resin infusion

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

Experimental Investigation on the Important Factors on Structural Adhesive Joint Strength of Fiber-Reinforced Epoxy Composites

The static strength of fiber-reinforced epoxy composite structural adhesive lap joints was examined experimentally. Surface roughness and geometrical control parameters (adherent and adhesive kinds) were assessed for their effects. To examine load, elongation, and strength at failure, tensile tests were conducted. Cyanoacrylate glue outperformed SHCP 268 resin, and glass fiber-reinforced epoxy composites outperformed sisal fiber-reinforced epoxy composites. The study offers information on how to maximize adhesive bonding for lightweight multi-material design construction.

Effect of carbon fibers modification on joint adhesion steel-epoxy resin-aluminum

The combination of high-performance steel with aluminum or aluminum alloys shows a wide range of application in high technologies field like aerospace, smart materials, etc. The problem in using of adhesive bonding technology for these substrates is the weak mechanical occlusion between steel/aluminum and common coatings. In this study, different methods of treatment of carbon fiber were employed to enhance the adhesion strength in steel-epoxy resin filled with carbon fiber-aluminum triplex. The treatment of carbon fibers with 3-glicidyloxypropyl-trimetoxysilane after their oxidation in 65 wt.% nitric acid leads to the additives which improve the adhesion strength of epoxy resins at 15 wt.% contain on 67.5% in comparison with neat epoxy up to 20 MPa. This result can be explained by the change of failure mechanism from “cohesive’ to “adhesive” that leads to an increase of adhesion strength to steel and aluminum. The SEM study shown that 60–80 nm thick two-layer interphase formed between carbon fiber and epoxy matrix. The mechanical strength of this interphase governs the mechanical and adhesion performance of steel-epoxy resin-aluminum triplex. Taking into account the mechanical properties and adhesive strength of these composites, it emerges as a potential candidate for advanced materials.

Fatigue life prediction of CFRP flat-fold-flat adhesive joints

Taking the flat-fold-flat (FJF) adhesive joints of carbon fiber reinforced bismaleimide resin-based composite materials as the object, the regularized fatigue life model and residual stiffness model of the one-way plate and the cohesive model parameters of the adhesive layer were fitted experimentally, and based on this, the fatigue life of the adhesive joint was predicted by ABAQUS software. The results show that under specific maximum load conditions, the predicted cracking life of the adhesive layer at the end of the lap joint and the final fatigue life are not greater than the error values of the test results 3% , which has a relatively good calculation accuracy. The cracking life of the adhesive layer at the end of the lap joint is approximately equal to the final fatigue life of the adhesive joint, indicating that the cracking of the adhesive layer at the end of the lap joint accounts for the main part of the total life of the adhesive joint, and the crack propagation life of the adhesive layer can be ignored.