Strength Of Adhesive Joints Research Articles

Determining the Vapour Resistance of Breather Membrane Adhesive Joints.

Due to increasingly stringent requirements, tapes and adhesive joints are a commonly used method to ensure tightness and energy efficiency in modern building envelopes. Previous studies have researched and tested properties such as the strength and tightness of adhesive joints. So far, water vapour resistance has been neglected. This article aims to determine the vapour resistance and shed light on possible consequences of vapour-tight adhesive joints in breather membranes used in roof assemblies. Laboratory measurements of vapour resistance were conducted according to NS-EN ISO 12572:2016, known as the cup method. Eleven products of breather membranes were tested. Results from the laboratory measurements were used to evaluate the impact of vapour-resistant adhesive joints related to the drying of built-in moisture. The simulation programs WUFI 2D and WUFI Mould Index VTT were used to model scenarios for moisture transport and risk for mould growth. Laboratory results show that the vapour resistance of breather membrane adhesive joints varies from 1.1 to 32 m in sd-value. Three of the tested products have a vapour resistance larger than 10 m, while four products have an sd-value less than 2.0 m. The sd-values of the membranes themselves range between 0.027 and 0.20 m. All tested adhesive joints are considerably more vapour tight than the Norwegian recommended value for breather membranes (<0.5 m). However, the mould growth analysis shows that the risk of mould growth is low in most practical cases, except when using adhesive joints with the highest vapour resistance in roofs assembled during autumn.

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.

Robotised atmospheric plasma treatment to improve the adhesion of vulcanised and thermoplastic rubber materials for a more sustainable footwear

Surface treatment is essential to ensure the resistance and durability of adhesive upper-to-sole joints for footwear. This study investigates robotised atmospheric pressure plasma technology to increase adhesion on styrene-butadiene vulcanised (SBR) and styrene-butadiene-styrene thermoplastic (SBS) rubbers, which constitutes a more sustainable surface treatment as an alternative to solvent-based chemical treatments (i.e., halogenation). In this work, the different parameters such as application speed and distance of the nozzle of the atmospheric plasma system have been optimised and the effects of the plasma treatment on the physicochemical properties in the materials’ surface, roughness, wettability, as well as the adhesion properties have been evaluated by means of different experimental techniques: Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron (FESEM), Contact Angles (CA) and Surface Free Energy (SFE) measurements and T-peel strength tests. The results show that the values obtained for the T-peel strength of the reactive hot melt polyurethane adhesive (HMPUR) joints studied exceed the minimum quality requirements for footwear according to standardised tests. In consequence, the optimisation and validation of operating plasma conditions and adhesion properties of rubbers could consolidate atmospheric plasma as a solvent-free alternative for the preparation of footwear soling materials. The great advantage of this technology is its introduction into the production line by fully automating the bonding process with the use of robots.

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.

Experimental methods for the analysis of the tensile behavior of concrete joints

AbstractAdhesion plays an important role in the evaluation of hydraulic structures with unreinforced concrete joints. The experimental determination of joint tensile strength as a quantifiable parameter is not standardized, resulting in a variety of test setups found in literature. The present paper highlights advantages and disadvantages of three of the most common tension tests for plain concrete and concrete joints through both theoretical and laboratory experimental analysis on specimens with artificial joints. Splitting tension tests were found to be inexpensive but tend to overestimate the adhesive strength of weak joints. Direct tension tests require an elaborate test setup but may yield information on the tension softening behavior. Pull‐off tests stand out for their ability to yield in‐situ results but deliver inconclusive results.

The effect of inclusions embedded in the adhesive on the stress distribution and strength of single-lap adhesive joints: analytical and numerical analysis

In this study, an analytical analysis and a finite element method (FEM) study of the overall strength and interfacial stress distribution of single lap joints with an embedded inclusion in the adhesive layer were performed. The stress analysis model for the single lap adhesive joints including inclusion layers was firstly established, and the effects of the thickness and stiffness of the inclusions on their mechanical strength were discussed in detail. The results show that the bond strength of the adhesive joints is highly dependent on the geometric parameters and properties of the inclusions, and increases with the inclusion thickness and stiffness. When the stiffness of inclusions is lower than that of the adhesive layers, their introduction degrades the bond strength of the single lap adhesive joints. The interface stress distribution and failure mechanism caused by the inclusion layers are intuitively analyzed by FEM, which is in good agreement with the analytical analysis.

Experimental investigation of the effects of adhesive defects on the strength and creep behavior of single-lap adhesive joints at various temperatures

ABSTRACT In this article, the creep behavior and strength of single-lap adhesive joints ( s) including defects have been studied, and the effect of the position of defects on the creep behavior and strength of s have been investigated. The defects were created on various sides of the Araldite 2011 adhesive layer and joints were subjected to the tensile and creep tests. The creep tests were done at three different temperatures; 23 ℃ (Room Temperature), 45 ℃, and 55 ℃. The results showed that the presence of a defect in the adhesive layer caused the greatest decrease in the strength of the joints in the defective joint with the defect in the middle and both sides. Also, the presence of a defect in the adhesive layer increases the creep displacement, which is much higher than the amount of this displacement in the joint without a defect. Increasing temperature to 45 ℃, and 55 ℃ has increased the creep displacement by almost 90%, compared to the creep displacement at room temperature (RT). Based on the results, the presence of defects on both sides has the greatest effect on reducing the strength of the joint (defect in the middle) and increasing the creep displacement (defect in the edge).

The effect of laser surface treatment of titanium samples on the adhesive strength of adhesive joints

The article considers the strength of adhesive joints of specimens made of OT-4 titanium alloys, the surface of which has been treated with laser radiation. The paper presents the results of the dependence of the macro- and microgeometry of the obtained surface, chemical composition, wetting angle and adhesion strength of adhesive joints under shear on laser processing modes. The purpose of this work is to determine the optimal parameters of laser processing for obtaining high strength adhesive joints. The results obtained can be used for gluing spacecraft structural elements. The studies were carried out on the adhesive pair «Titan – Titan». Depending on the processing mode, characteristic surface textures were identified, which were combined into groups «B», «K» and «C». High-energy modes of laser surface treatment of samples before gluing lead to a significant increase in the strength characteristics of the adhesive joint (up to 70 %) due to an increase in the area of the gluing surface and mechanical locking of the adhesive in the microrelief of the texture of the samples. In addition, the use of this method, in comparison with mechanical and chemical methods, significantly increases the productivity of surface treatment.

Effect of functionalised and non-functionalised GNPs addition on strength properties of high viscous epoxy adhesive and lap shear joints

This research explores the combinative effects of graphene nanoplatelets (GNPs) addition, functionalisation, and filler concentration on the mechanical behaviour of high viscous structural adhesive (Araldite 2011) and lap shear joints strength. Non-functionalised, carboxylate (COOH) and amine (NH2) functionalised GNPs were mixed in the amounts of 0.25, 0.5, 0.75 and 1 wt% in the host resin by a modified solution mixing technique. Two configurations of lap joints i.e. single lap joint (SLJ) and double lap strap joint (DLSJ) were manufactured using aluminium alloy 5083 adherends. The strength properties of GNPs/epoxy adhesive and lap shear joints were determined by tensile testing. In the case of adhesive, an increase in the value of elastic modulus and tensile strength were observed, accompanied by a decrease in fracture strain. A maximum increase of 13% in the tensile strength and 39% in elastic modulus was observed with the addition of 1 wt% non-functionalised GNP. The lap joints also showed improvement in terms of joint strength with the addition of GNPs. A maximum improvement in failure load of 36% for SLJ and 25% for DLSJ was observed by the inclusion of 0.75 wt% non-functionalised GNP. Optical and Scanning Electron Microscopy (SEM) was utilized for the analysis of fracture surfaces, and the correlation between nano-reinforcement and strengthening mechanisms was critically discussed.

Adhesive Joints of Additively Manufactured Adherends: Ultrasonic Evaluation of Adhesion Strength.

Adhesive joints are widely used in the construction of machines and motor vehicles. Manufacturers replace them with the welding and spot-welding methods due to the lack of damage to the material structure in the joint area. Moreover, it is aimed at reducing the weight of vehicles and producing elements with complex shapes. Therefore, additive manufacturing technology has been increasingly used in the production stage. This fact has not only changed the view on the possibilities of further development of the production technology itself, but it has also caused an intense interest among a greater number of companies in the advantages of structural optimization. There is a natural relationship between these two areas in the design and production, allowing for almost unlimited possibilities of designing new products. The main goal of the research described in this article was to determine the correlation between the strength of the adhesive joint of elements produced using additive technology and the parameters of the ultrasonic wave propagating in the area of the adhesive bond. The tests were carried out on samples made of AlSiMg0.6 material and a structural adhesive. Strength tests were performed to determine the shear force which damaged the joint. Furthermore, an ultrasonic echo technique enabling the determination of a nondestructive measure of the quality and strength of the joint was developed. The samples of the adhesive joints had a strength of about 18.75–28.95 MPa, which corresponded to an ultrasonic measure range of 4.6–7.8 dB. The determined regression relationship had a coefficient of determination at the level of 0.94. Additional ultrasonic tests of materials made with the additive technology confirmed its different acoustic properties in relation to aluminum produced with the standard casting or extrusion process. Designated dependence combining the mechanical strength and the decibel difference between the first and second impulses from the bottom of the joint may constitute the basis for the development of a nondestructive technique for testing the strength of adhesive joints.

Root Causes and Mechanisms of Failure of Wind Turbine Blades: Overview

A review of the root causes and mechanisms of damage and failure to wind turbine blades is presented in this paper. In particular, the mechanisms of leading edge erosion, adhesive joint degradation, trailing edge failure, buckling and blade collapse phenomena are considered. Methods of investigation of different damage mechanisms are reviewed, including full scale testing, post-mortem analysis, incident reports, computational simulations and sub-component testing. The most endangered regions of blades include the protruding parts (tip, leading edges), tapered and transitional areas and bond lines/adhesives. Computational models of different blade damage mechanisms are discussed. The role of manufacturing defects (voids, debonding, waviness, other deviations) for the failure mechanisms of wind turbine blades is highlighted. It is concluded that the strength and durability of wind turbine blades is controlled to a large degree by the strength of adhesive joints, interfaces and thin layers (interlaminar layers, adhesives) in the blade. Possible solutions to mitigate various blade damage mechanisms are discussed.

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.

Effects of ageing frequency on the interfacial failure and tensile properties of adhesively bonded Arcan joints exposed to cyclic ageing environments

The strength and durability of adhesive joints are significantly influenced by environmental conditions. When working in a humid environment, the adhesive tends to absorb moisture and this phenomenon can drastically reduce the mechanical performance of the adhesive joints. In practise, joints are usually subjected to cyclic ageing due to moisture absorption and desorption. Accordingly, it is necessary to study the ageing behaviour of the adhesives when they are exposed to environments with cyclic humidity conditions. Accordingly, the current study investigates the mechanical properties of adhesive joints with an epoxy-based adhesive subjected to cyclic ageing conditions using Arcan joint specimens. To this aim, static tensile tests were performed for both cyclic aged, dried, and unaged Arcan joints. The effect of cyclic ageing and drying conditions, such as absorption and desorption mechanisms, on the mechanical properties of the joints were studied. In the numerical part, an experimentally obtained diffusion coefficient (D) was used to simulate the water diffusion in Arcan joint. The results showed that key mechanical properties, such as tensile strength and displacement of the joints are reduced by the number of ageing cycles. The maximum strength degradation of the aged joints compared to the unaged condition was 94% for the third ageing cycle. For the dried condition, the strength of the joints was recovered although it was not fully returned to the initial stage. It was also found that the recovery ratio increases with the ageing cycles. It is shown that a short drying process can significantly recover the mechanical response of the cyclically aged adhesive joints, especially at higher ageing cycles.

Cohesive zone parametric analysis in the tensile impact strength of tubular adhesive joints

The use of tubular adhesive joints has considerably grown, including applications in truss/vehicles frames and fluid transportation pipelines, but the impact performance of these joints is under addressed in the literature. It thus becomes pertinent to propose modelling techniques to predict and characterize tubular joints to withstand these loads, which involve a higher modelling complexity than the static loading case. This work evaluates, by cohesive zone modelling (CZM), the tensile impact strength of tubular joints between AW6082-T651 aluminium alloy adherends and bonded with different adhesives. Initially, CZM validation was accomplished with single-lap joint (SLJ) data. For the tubular joints, the influence of geometric parameters was evaluated by changing the overlap length ( LO) and outer tube thickness ( tSE). The analysis begins with an elastic stress analysis to the adhesive layer, followed by maximum load ( Pm) and dissipated energy at failure ( U) predictions using CZM, impact velocity effect and comparison with static analytical solutions. With this study, it was possible to evaluate the different geometrical parameters, select the optimal geometry and adhesive type, and to validate the CZM technique for the impact strength prediction of tubular adhesive joints.

Effects of loading rate, temperature, and thickness on the tensile strength of precision adhesive joints

The influences of the micron bondline thickness, temperature, and loading rate on the tensile strength of adhesive joints were studied for the precision adhesive structures, and the fractured surfaces were analyzed by the infrared imaging and SEM methods. The testing results show that the tensile strength increases and then linearly decreases with the increase of bondline thickness; the peak tensile strength is always acquired at the bondline thickness of around 30 μm; the maximum tensile strength increases up to 28.6% as the thickness increases from 10 to 30 μm at the loading rate of 1 mm/min; the strength decreases by more than 33% and finally reaches a closed value at different bondline thicknesses as the temperature rises from −30 to 110 °C. The results indicate that reducing the bondline thickness, less than about 10 μm, could result in a weak bonding interface; the tensile strength increases with the increase of the loading rate, exhibiting the strain-rate hardening effect below the Tg; the plastic-damage characteristic appears and becomes clearer on the fractured surface as the temperature increases. Under the tested conditions, the temperature shows the most significant effect on the tensile strength, then the bondline thickness followed by the loading rate.

Application of an Artificial Neural Network in the Modelling of Heat Curing Effects on the Strength of Adhesive Joints at Elevated Temperature with Imprecise Adhesive Mix Ratios.

This paper is a discussion of the results of tests intended to (i) estimate the effects of component mix ratios and heat curing of an adhesive joint on the tensile strength, and (ii) to determine the adhesive component mix ratio for which heat curing is insignificant to the strength of adhesive butt joints. Experimental tests were carried out at ambient temperature and elevated temperature during which adhesive butt joints were loaded with a tensile force until failure. The variables were the mix ratio of epoxy adhesive components and the application of heat holding at the adhesive curing stage. An LSTM (long short-time memory) forecast was used to determine the point corresponding to the mix ratio of adhesive components at which heat holding of the adhesive joint no longer has a positive and significant importance to the final tensile strength of the joint.

Effect of overlap length on the strength of adhesive joints of steel sheets

The study evaluates the shear strength of the single-lap adhesive joints made of C45 carbon steel. The influence of the overlap length on the shear strength of the adhesive joint was tested. The elongation of the samples was also tested. Before the bonding process, the samples were treated with P180 abrasive paper and degreased. The adhesive joints were made using the Epidian 53/Z1/100:10 adhesive composition. The strength tests were carried out on a Zwick/Roell Z150 testing machine. The maximum value of the shear strength was obtained for the lap Lz1 = 13 mm and the minimum for Lz4 = 19 mm.

THE INFLUENCE OF SHOT PEENING ON THE STRESS STATE IN THE ADHESIVE LAYER AND THE LOAD CAPACITY OF ADHESIVE JOINTS

The aim of the article was to determine the influence of shot peening of the outer surface of the overlap on the stress state in the adhesive layer and the load capacity of single lap adhesive joints made of EN AW-2024-T3 aluminum alloy. Experimental investigations and numerical simulations were carried out. According to the results of experimental analyses, shot peening with balls with a diameter of 1 mm for 120 s with a compressed air pressure of 0.5 MPa increased the load capacity of the adhesive joints by 33%. Numerical simulations have shown that shot peening, by deforming the joined elements, reduces the stress perpendicular to the surface of the adhesive layer which results in a reduction of equivalent (von Misses) stress and an increase in strength of adhesive joints.

Study on the impact of Nano-reinforcements on the fatigue strength of adhesive joints

Single overlap joints had been created by combining two AISI 302 stainless steel sheets with the help of 3 M DP270 grade epoxy and their fatigue characteristics were examined under shear stress condition. Further, the effect of adding three distinct proportions of nano-titania with epoxy, on the mechanical characteristics of the joint was analyzed. The overlap lengths was selected as 20 mm and nano-titania proportions were elected as 1.0%, 2.0% and 4.0%, respectively during shear load condition. When the experimental findings were analyzed, it was shown that the mean damaging load associated with the usage of nano-dispersed adhesives rose significantly in general. As a consequence of the trials, it was discovered that the most effective nanoparticles proportion for boosting the fracture strength of adhesive joints is 4.0 percent, and the enhancement in rate of failure strength increase was noted as 85.52 percent. Additionally, it was shown that strain of nanoparticle had a noteworthy role in the shear characteristics of the adhesive junctions. Additionally, it has been shown that incorporating nanoparticles into the glue enhances junction extension. When the adhesive interfaces of the specimens were inspected, impairment was detected as adhesion dissociation, but nanoparticle replenishment had been detected as a combination of cohesive as well as adhesive characteristics.

Examination of plastic region size and two singular stress field on the ISSF adhesive strength evaluation method

In an adhesive joint under certain conditions, the adhesive joint strength is larger than the bulk adhesive strength. In this study, the fracture of adhesive joints by using the elastic-plastic behavior is considered. Then, the validity of evaluating the adhesive strength by two ISSFs based on the elastic analysis is discussed. Even when the butt joint strength is larger than the bulk adhesive strength, the small-scale yielding is occurred. Therefore, it is shown that the ISSF strength evaluation method is appropriate.