Performance Of Adhesive Joints Research Articles

Advances in Adhesive Bonded Joints for Composite Materials: A Comprehensive Review

Adhesive bonded joints have become increasingly significant across various high-tech industries, including aerospace, automotive, marine, and construction. This growing importance is largely due to their efficiency in joining lightweight composite materials, which are integral to modern engineering applications. In this review paper, we offer a comprehensive update on the latest advancements in adhesive bonded joints specifically for composite materials. The paper delves into several critical aspects of adhesive bonding, beginning with surface preparation. Proper surface preparation is crucial for achieving optimal bond strength and durability, and this paper explores the latest techniques and best practices in this area. It also examines current testing methods used to evaluate the performance of adhesive joints, ensuring that they meet stringent industry standards. Durability is another key focus of the review. We discuss various considerations related to the long-term performance of adhesive bonded joints, including environmental factors, load-bearing capacity, and resistance to aging and degradation. The paper also highlights recent innovations in adhesive technologies. These advancements include new formulations and types of adhesives that enhance bonding capabilities and overall joint performance. Additionally, we cover the latest developments in surface treatments, which play a critical role in improving adhesion by modifying the surface properties of composite materials. In summary, this review offers a thorough and up-to-date examination of adhesive bonded joints for composite materials, highlighting both recent advancements and ongoing challenges, while providing valuable insights into future research directions

Effect of synergistic surface treatment on the bonding strength and durability performance of aluminum-lithium alloy adhesive joints

The effect of synergetic surface treatments on the adhesion performance and strength durability of aluminum-lithium alloy bonded joints was investigated. The synergistic modes combine the advantages of different surface treatments, rough morphologies were firstly generated and then porous oxide layer structures were produced on the rough surfaces, so more porous structures and suitable rough characteristics were generated on the substrate to enhance the bonding performance of adhesive joint. The surface characteristics, surface wettability, fracture morphology, shear strength and strength durability of samples subjected to different surface treatments were compared and analyzed. The experimental results indicated that the synergistic treatments had a positive effect on the strength performance and environmental durability of bonded joints, with the highest surface free energy of 80.6 mJ/m2 and shear strength of 40.2 MPa, and also had the best environmental durability with a strength reduction of 8.2 % during the hot-humid exposure.

Accelerated aging procedure of epoxy structural adhesive for marine offshore applications

Knowledge of the long-term performance of adhesive connections is undoubtedly of paramount importance to enable their deployment in civil, mechanical, and other engineering applications. Over time, adverse environmental conditions can strongly influence the performance of adhesive joints leading to a progressive deterioration of their initial mechanical properties. The use of adhesive connections for secondary structures in offshore applications is a technology that allows for the rapid creation of structural members that, however, cannot ignore the influence of hydrothermal effects on mechanical performance due to environmental conditions. In this context, the investigation of the hygrothermal durability of adhesive connections was undertaken through an extensive experimental programme. More specifically, 130 cylindrical steel joints bonded with a commercially epoxy resin for structural applications were tested in Mode I using an Arcan-modified device. Prior to test, the specimens were placed in climatic ovens capable of combining the effects of temperature and humidity for approximately 320 days. In addition, the glass transition temperature, Tg, was assessed by employing the differential scanning calorimeter (DSC) technique to correctly define the experimental ageing conditions. The experimental results show how ageing conditions influence the mechanical properties of the epoxy resin investigated. Finally, some predictive formulations are proposed to calculate the loss of strength of adhesive joints over time.

Effect of laser pre-treatment on adhesive joint performance and evaluation of interfacial strain distribution using mechanoluminescence

ABSTRACT In this study, factors that improve bonded joints structural response through laser surface pre-treatment on aluminum surfaces were investigated. Specifically, the focus was put on analyzing the laser treatment conditions, formation of the interface structure, and behavior of interface strength at the adhesive interface. The results revealed a specific range of laser treatment conditions in which tensile shear strength and fracture mode are stable. Although laser-treated adhesive joints showed cohesive failure similar to that observed in sandblasting or chemical treatment during the double cantilever beam test, the fracture toughness value was improved by a factor of 2 and 1.5, respectively. The laser-induced microstructure on the aluminum interface contributed to the improvement of fracture toughness. Furthermore, observation of the adhesive layer using a microscopic mechanoluminescence measurement system revealed that changes in the 3D structure of the interface significantly altered the stress luminescence pattern reflecting strain. As a result, direct visualization of interface strengthening via laser processing was achieved.

Recent Advances in Adhesive Bonding of 3D-Printed Parts and Methods to Increase their Mechanical Performance

The use of additive manufacturing (AM) has revolutionized the production of polymer-based materials, offering a wide range of design possibilities and geometric complexity. However, due to the limitations of 3D printers to produce large parts, the parts often must be printed in several separate components and further joined together to obtain the final 3D-printed part. 3D printing can be used to produce only the most complex parts, which can be further combined with simple, non-printed parts from other materials to make the final product. One way to join 3D-printed part is an adhesive-bonded method. This paper focuses on the recent advances in adhesive bonding techniques for 3D-printed parts and explores various methods to enhance their mechanical performance. The benefits and limitations of each technique were discussed, and highlighted promising paths for future research. Finally, this paper provides a comprehensive overview of the current strategies to improve the mechanical performance of adhesive joints with AM-based adherents, offering guidance for the design and fabrication of high-performance structures in a range of applications. It was concluded that the configuration of the bonding area represents an essential parameter that directly influences the bonding strength and overall structural integrity of AM adhesive joints, and that the implementation of customized joint geometries can lead to a substantial enhancement in the joint strength of 3D-printed parts. The incorporation of reinforcing materials, optimization of the printing parameters of adherents, pre and post-treatment methods show potential in enhancing the bonding strength of the 3D-printed joints. The synergistic integration of these cutting-edge technologies can yield mutual advantages that complement each other, ultimately resulting in an enhanced overall performance for AM parts.

Experimental study on structural adhesive properties of aluminum plate and carbon fiber-reinforced polymer heterogeneous materials

Structural adhesive bonding between aluminum and carbon fiber-reinforced polymer (CFRP) is an important part of the vehicle's lightweight design and must ensure high strength and durability during the life of the structural member. The paper presents a precise assessment scheme to accurately and reliably infer the performance of adhesive joints through a short-term experimental test method that focuses on intrinsic and extrinsic factors affecting bond strength. The experimental results show that the surface of CFRP is polished, which is beneficial to improve the bonding quality, and the damage type transitioned from adhesion damage to substrate or cohesion damage. Aluminum alloy electrophoresis and non-electrophoresis have no significant effect on the bonding performance. Secondly, the design of the bonding nodes should be considered to bring them into a state of shear stress and be able to withstand greater loads. Meanwhile, the moderate thickness of the adhesive layer and increased bonding area serve to enhance bond reliability. In addition, various environments can cause various physical and chemical changes within structural adhesives, which can reduce the cohesive strength and durability of adhesives. This experiment is designed to select process parameters and adhesive applications for structural adhesives, which are crucial in predicting and evaluating the performance of newly developed structural adhesives and bonded joints.

Assessing the Long-Term Performance of Adhesive Joints in Space Structures during Interplanetary Exploration.

Spacecraft experience minimal mechanical loads in space, but with the development of reusable spacecraft for interplanetary exploration and repeated landings, structures will be subjected to increased mechanical stress. The impact of the space environment on the aging of adhesive materials used in space structures over long-term applications is not well understood. This study investigates two commonly used adhesives in spacecraft assembly, namely Scotch-Weld™ EC-2216 and Scotch-Weld™ EC-9323-2, under two aging conditions: (1) high-energy electron irradiation using a Van de Graaf accelerator, and (2) thermal vacuum cycling. The research evaluates the evolution of intrinsic adhesive properties and adhesion to CFRP (carbon fiber-reinforced polymer) and aluminum adherents before and after exposure to these environmental conditions through tensile tests, peel tests, double-cantilever beam (DCB) tests, and dynamic mechanical analysis (DMA).

A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite adhesive joints

Traditional adhesive joints with straight edged adherends suffer from a significant stress concentration in the composite coincident with the edge of the metal adherend, which can lead to accelerated translaminar failure of the substrate. In this work, we developed a novel profiling concept which improves the mechanical performance of adhesive joints between metallic adherends and composite substrates. We conducted quasi-static four-point bending (4PB) tests which showed that profiling the edge of the metallic adherend could improve the peak load by at least 27%, and that the stability of failure was simultaneously improved. We investigated varying the profile parameters and were able to conclude that further significant mechanical performance gains could be achieved by increasing any of the profile: amplitude, frequency, or number of fractal length-scales. By analysing in-situ acoustic emission (AE) monitoring data we were able to observe that profiling of the metallic adherend results in failure initiation occurring at higher loads, which suggests that the concept is successful in providing better stress distributions and lowering peak stresses. By analysing the fracture surfaces, it is apparent that the profiling concept is successful in deflecting the translaminar fracture path; and additionally that a debonding mechanism occurs at the profile tips which is thought to be an important additional mechanism for creating damage tolerant joints.

Performance enhancement of adhesive joints of additive manufactured parts by using different types of fibre reinforcements

The main objective of this study was to investigate experimentally the mechanical performance of adhesive joints made of additive manufactured (AM) polymeric parts reinforced with different types of fibres. PLA (PolyLactic Acid) and ABS (acrylonitrile butadiene styrene) AM adherends were fabricated by fused deposition modelling (FDM). Further, natural (jute and curauá) and synthetic (glass) fibre reinforcement fabrics were laminated on the outer sides of the AM parts using an epoxy resin via compression moulding. The type of reinforcement (natural or synthetic) and the effect of the number of the layers (1 and 2 layers) on the performance of the bonded joints was studied by testing single lap joints (SLJs) bonded with an epoxy structural adhesive. It was found that the mechanical performance of adhesively bonded SLJs is improved by using different types of fibre reinforcements to the 3D printed core adherends. The failure load varied as a function of fibre type and number of layers used as reinforcement, as well as the material used for the core of the adherends. The ABS SLJs presented lower strength compared to PLA SLJs, mainly due to the ABS adherend inferior mechanical properties. In addition, the PLA core specimens presented a better interface adhesion with the epoxy resin used in this study to laminate the reinforcements, when compared to the ABS core reinforced specimens. The best results in terms of improvement in failure load were obtained for the curauá fibre reinforced PLA 3D printed SLJ specimens (the average joint strength was more than 1.5 times higher than the neat-PLA SLJ specimens).

Adhesive behavior of sisal and jute composite exposed to three months cyclic temperature variation

Fiber Reinforced Plastics (FRPs) are being used extensively in various engineering applications ranging from aerospace to sports goods. In recent years, environmental concerns and awareness have challenged engineers and scientists to develop materials that are sustainable and have the potential to replace the traditional FRPs. Natural fiber-based polymeric composites (NFRPC) are now being investigated and proposed worldwide for various applications, especially automotive components and domestic products. To ensure the fabrication of highly intricate composite products, joining becomes inevitable. Adhesive joining is the most commonly employed fabrication process for composite joints. However, the performance of adhesive joints is susceptible to their exposure to different environmental conditions. In the present experimental investigation, the joint strength of woven fiber mat (sisal, jute, and hybrid) reinforced epoxy composites has been investigated in Three Months Cyclic Temperature Variation, and the natural fiber reinforced epoxy adherends have been successfully joined using adhesive along with two/four holes in the overlap area. The performance of the adhesive joints has been investigated under a daily thermal cycle from 5 °C (12 hrs.) to 40 °C (12 hrs.), for three consecutive months. It was observed that the hybrid composites recorded better-joining performance. Moreover, the Field Emission Scanning Electron Microscopy (FE-SEM) has been used to understand the failure mechanisms during tensile testing of adhesively bonded natural fiber-reinforced composite laminates. It has been found that the exposure of the composite joints to a variable temperature during the day has a significant effect on their tensile behavior. The major factors affecting the performance of joints exposed to the thermal cycle are; the type of natural fiber, the number of holes in the adherend area, and the duration of exposure. The results are important for the designers of composite structures with adhesively bonded joints.

Surface Modification Using MAPLE Technique for Improving the Mechanical Performance of Adhesive Joints

The adhesive bonds that ensure the appropriate mechanical properties for metal joining imply the surface chemical and wetting modification characteristics of the substrates. In this work, matrix-assisted pulsed laser evaporation (MAPLE) was used for the surface modification of Al via the deposition of two chemical compounds, polyvinyl alcohol (PVA) and triethanolamine (TEA), from frozen aqueous solutions. The deposition of the TEA and PVA layers was evidenced by FT-IR, SEM, and AFM analysis. The contact angle measurements evidenced the change in the hydrophilicity of the surface and surface free energies. The performance of the commercial silyl-based polymer adhesive Bison Max Repair Extreme Adhesive® was evaluated by tensile strength measurements. This method led to a change in tensile strength of 54.22% in the case of Al-TEA and 36.34% for Al-PVA compared with the control. This study gives preliminary insights into using MAPLE, for the first time in adhesive applications, as a pretreatment method for Al plates for adhesive bonding reinforcement.

Machine learning approach for analysing and predicting the modulus response of the structural epoxy adhesive at elevated temperatures

ABSTRACT For bonded Fibre Reinforced Polymer (FRP) strengthening systems in civil engineering projects, the adhesive joint performance is a key factor in the effectiveness of the strengthening; however, it is known that the material properties of structural epoxy adhesives change with temperature. This present paper examines the implied relationship between the curing regimes and the storage modulus response of the adhesive using a Machine Learning (ML) approach. A dataset containing 157 experimental data collected from the scientific papers and academic theses was used for training and testing an Artificial Neural Network (ANN) model. The sensitivity analysis reveals that the curing conditions have a significant effect on the glass transition temperatures (Tg ) of the adhesive, and consequently on the storage modulus response at elevated temperatures. Curing at an extremely high temperature for a long time does not, however, guarantee a better thermal performance. For the studied adhesive, curing in a warm (≥ 45°C) and dry (near 0 % RH) environment for 21 days is recommended for practical applications. A software with a Graphical User Interface (GUI) was established, which can predict the storage modulus response of the adhesive, plot the corresponding response curve, and estimate the optimum curing condition.

The effect of hygrothermal aging on the adhesion performance of nanomaterial reinforced aluminium adhesive joints

Adhesive joints are subjected to various environmental factors such as humidity and temperature, depending on their use in industrial applications. It is important to examine and improve the performance of adhesive joints formed with polymeric adhesives, which are known to be sensitive to humidity and temperature parameters, under these conditions. For this reason, in this study, FPL-etched AA7075-T6 aluminium adherends bonded with nonreinforced and BNNP (boron nitride nanopowder), ANP (alumina nanopowder) and MWCNT (multiwalled carbon nanotubes) reinforced epoxy adhesive as a single lap adhesive joint. Thereafter, performance of the adhesive joints that exposed hygrothermal aging conditions of 1, 2, 4 and 6 weeks at 100% relative humidity (RH) and 60 °C were investigated. Glass transition temperature (Tg) values of nonreinforced and reinforced epoxy adhesives before and after hygrothermal aging were determined by DSC (Differential Scanning Calorimeter) analyses. Depending on the nanomaterial types, the tendency of the adhesive joints to water uptake was determined and compared with nonreinforced adhesive joints. When the shear strength findings were investigated, it was defined that the adhesive joints reached almost saturation after 2 weeks of hygrothermal aging. In addition, the most effective nanomaterial type against hygrothermal aging was determined as MWCNT. After 2 weeks hygrothermal aged, the shear strength decreases of MWCNT reinforced adhesive joints were 21.77% and 16.97% less than BNNP and ANP reinforced adhesive joints, respectively. Although the adhesive deteriorates chemically after hygrothermal aging, its adhesion performance improved with the physical benefits of nanomaterials. However, ANP, which is cheaper in terms of price/shear strength performance in long-term aging times, showed similar results with MWCNT. In addition, fracture mechanisms were examined in more detail with SEM (Scanning Electron Microscope) analyses before and after aging, and the effects of hygrothermal aging on the adhesive joints were determined.

Effects of Mode Mixity on the Failure Mechanism of Aged Adhesive Joints

The strength and the performance of adhesive joints can be significantly influenced by the ageing procedure. However, the role of aging in the failure mechanism of adhesive joints as a function of loading conditions has not been studied yet. The current research aims to investigate the effect of mode mixity on the failure mechanism of aged adhesive joints using Arcan samples. Based on the results loading the tested joints in shear led to a higher percentage of interfacial failure than in tensile. However, it was also found that the shear loading mode is less sensitive (compared to tensile loading) to the ageing conditions.

Combined effect of surface pretreatment and nanomaterial reinforcement on the adhesion strength of aluminium joints

Nowadays, it is known that adhesive and cohesive forces should be developed in order to improve the mechanical performance of adhesive joints. In this context, while the adhesive forces are improved with surface pretreatments applied to the adherends, the adhesive and cohesive forces are improved with the nanomaterial reinforcement to the adhesive. For this purpose, in this study, AA7075-T6 aluminium alloy adherends were combined with epoxy adhesive as a single lap joint. As a preliminary study, abrading and FPL-etching (Forest Products Laboratory) surface pretreatments were applied to aluminium alloy adherends and after two different surface pretreatments, the changing surface morphology (with optical microscope, contact angle, profilometer measurements) and shear strength were compared. With abrading and FPL-etching surface pretreatments, an increase of 40.83% and 69.63%, respectively, was determined in the shear strength compared to untreated adhesive joints. After the preliminary study, in order to increase the mechanical performance of the adhesive joints, nano sized ANP (alumina nanopowder), MWCNT (multiwalled carbon nanotubes) and SNP (silica nanopowder) were added to the adhesive. Thus, it was investigated how the combined effect of different surface pretreatments and nanomaterial types at various reinforcement ratios changed the shear strength of the adhesive joints. After shear tests, significant increase in shear strength was observed in FPL-etched adhesive joints compared to abraded adhesive joints in all reinforcement nanomaterial types and reinforcement ratios. And also, significant improvements in the shear strength of adhesive joints were determined in all types of nanomaterial reinforcements. The highest shear strength was obtained at 10.0 wt % SNP reinforcement with 104.32% improvement in FPL-etched adhesive joints compared to nonreinforced FPL-etched adhesive joints. The evaluation of shear strength was supported by the failure images taken from the fracture surfaces after shear tests, and it was determined that the failure type was changed from adhesive to cohesive with nanomaterial reinforcement compared to nonreinforced adhesive joints.

The effect of protective and decorative coatings on the strength of adhesive joints of hot-dip galvanized steel sheets

The influence of chromate, phosphate, glossy and brightening coatings on the performance of adhesive joints of hot-dip zinc-coated steel sheets was compared. The contribution of this study has been to compare the adhesive joint strength in adherends with two types of coatings: steel sheet with zinc coating and additional coating. Two types of bisphenol A (BPA) epoxy adhesives were used to assemble the joints, that were subject to shear stresses. The surface of the adherends was described in terms of surface roughness parameters. The highest value of the shear strength was recorded for the adhesive joints of the hot-dip zinc-coated steel sheets with chromate passivation and brightening. The poorest performing joints were of the glossy galvanized steel sheets.

Effect of surface treatment on the performance of composite‐composite and composite‐metal adhesive joints

AbstractThe use of Fiber‐Reinforced Polymer Composites (FRPCs) in automotive, aerospace, and naval applications has increased significantly due to the requirement for a high performance‐to‐weight ratio. One the issue in using composite parts is their joining to the metal parts in the global structure. Several joining techniques such as mechanical joining, adhesive, vibration joining, and hybrid joining are used for this purpose. Being lighter in weight and lower in cost in comparison to other techniques, adhesive bonding is mostly used for composite‐composite and composite‐metal joining. To achieve reliable adhesive joining, surface preparation of the joining substrates is of utmost importance. Though the effect of physical surface treatments on the performance of joints has been reported in the literature, however, the effect of chemical surface treatment of composites on the mechanical performance of adhesive joints was rarely studied. In this article, the effect of chemical treatment (alkaline permanganate), of the composite surfaces on the single lap shear strength and Izod impact strength of composite‐composite and composite‐metal adhesive joints is reported. The results showed that the chemically treated joints demonstrate a significant improvement in these properties.

Effect of thermally expandable particle additives on the mechanical and reversibility performance of adhesive joints

This paper provides an experimental investigation of the effect of Thermally Expandable Particle (TEP) adhesive additive on the mechanical and reversibility performance of epoxy-bonded load single lap joints (SLJs). Joint substrates are made of aluminum 6061 and woven carbon fiber reinforced plastic 0/90/0 substrates. TEP additive is used for modifying the structural epoxy adhesive used in this study. An electrically charged RF coil is placed around the joint bond area; generated electromagnetic field would heat the aluminum substrate which would in turn heat the modified adhesive. Very large volumetric expansion of the hollow spherical Thermally Expandable Particles (TEPs) would significantly reduce adhesive strength and lead to joint debonding under a minimal load of 100 N. Various weight concentrations of the TEP in the range of 5% to 25% with particulate size from 6 to 16 µm are used for investigating the effect on joint static and fatigue strength as well as the reversibility performance. Measured time to achieve full debonding of the joint (under charged RF coil), is used for assessing the reversibility performance.

Effect of nylon fabric reinforcement on the mechanical performance of adhesive joints made between glass and GFRP

The use of reinforcements in adhesive joints makes the stress distribution more uniform, improving their mechanical performance and adhesion. The present paper aims to verify the effectiveness and efficiency of the insertion of nylon 6 fabric in the adhesive layer, to study their applicability and functionality in building components. The increase in stiffness achieved by applying nylon 6 fabric in the adhesive layer between glass and GFRP pultruded profiles and steel laminates applied to GFRP beams is investigated. Three different epoxy adhesives and one epoxy resin are used and compared. Three different types of tests are carried out in order to study the different properties of the reinforcement system: tensile tests on GFRP/GFRP single-lap adhesive joints, with and without nylon fabric reinforcement; tensile tests on double-lap adhesive joints between float glass and pultruded GFRP profiles reinforced with nylon fabric according to four configurations (in the middle plane of the adhesive layer, on the glass surfaces, on the GFRP surfaces, on both GFRP and glass configurations) to verify the influence of its position; three-point bending tests on long GFRP tubular profiles reinforced with steel plates and nylon fabric in different configurations, to study resistance to bending loads. The results from the experimental campaign show the effectiveness of the reinforcement system using nylon fabric 6. In general, both a reduction in ultimate strength and an increase in joint stiffness compared to unreinforced configurations are observed.

The influence of interfacial failure on the tensile S–N response of aged Arcan joints

AbstractThe strength and durability of adhesive joints are significantly influenced by environmental conditions. Humidity absorption can cause deleterious effects on the adhesive joint's performance. The current study investigates the tensile properties of an epoxy‐based adhesive using Arcan joints (which is a kind of butt joint) subjected to different aging levels and loading conditions. To this end, joints with different aging times, as well as reference‐dried samples, were subjected to both the static and cyclic loading conditions. To construct the S–N curves, different cyclic load levels were applied to the joints. The static results showed that the mechanical properties, such as tensile strength of the joints decreased with an increase of the aging time. The fatigue strength and the fatigue lifetime were significantly decreased by the increase of aging levels, mainly due to an interfacial aging phenomenon. The water diffusion in interfacial aging is faster than that of the adhesive aging, which resulted in a premature failure of the joints for both the static and fatigue conditions. Based on the experimental results, the interfacial diffusion coefficient was calculated using an inverse method. According to the results, the rate of water uptake along the interface is more than 30 times higher than that which occurs in the adhesive.