Single-lap Adhesive Joints Research Articles

The Influence of MSR-B Mg Alloy Surface Preparation on Bonding Properties.

Nowadays, industrial adhesives are replacing conventional bonding methods in many industries, including the automotive, aviation, and power industries, among others. The continuous development of joining technology has promoted adhesive bonding as one of the basic methods of joining metal materials. This article presents the influence of surface preparation of magnesium alloys on the strength properties of a single-lap adhesive joint using a one-component epoxy adhesive. The samples were subjected to shear strength tests and metallographic observations. The lowest properties of the adhesive joint were obtained on samples degreased with isopropyl alcohol. The lack of surface treatment before joining led to destruction by adhesive and mixed mechanisms. Higher properties were obtained for samples ground with sandpaper. The depressions created as a result of grinding increased the contact area of the adhesive with the magnesium alloys. The highest properties were noticed for samples after sandblasting. This proved that the development of the surface layer and the formation of larger grooves increased both the shear strength and the resistance of the adhesive bonding to fracture toughness. It was found that the method of surface preparation had a significant influence on the resulting failure mechanism, and the adhesive bonding of the casting of magnesium alloy QE22 can be used successfully.

Joining technology of additively manufactured components: effects on the bonding strength for the adhesive application through inner channels

The maximum size of additively manufactured (AM) components is restricted due to the confined building space of the manufacturing machines. Component separation and subsequent joining can be an effective way of manufacturing larger components using AM processes. For joining of AM components, adhesive bonding provides great potential for not constraining the adherend’s geometry, as long as the adhesive can still be applied to the adhesive surfaces of the adherends. This work investigates the effectiveness and applicability of additively manufactured inner channels to improve the adhesive application. A circular adhesive single lap joint between a laser-based powder bed fusion (PBF-LB) component made of AlSi10Mg and a cold drawn aluminum round bar was considered. The PBF-LB components were designed with varying geometric complexity to implement different adhesive application concepts. Subsequently, the bonded joints were subjected to static tensile tests. The fracture strength of joints where the adhesive was applied by injection into AM inner channels exceeds the fracture strength of joints where the adhesive was injected into geometries manufacturable by subtractive machining, and also exceeds the fracture strength of joints where the adhesive was pre-applied.

Machine learning algorithms for deeper understanding and better design of composite adhesive joints

In this study, machine learning (ML), a subdivision of artificial intelligence (AI), is implemented to study the mechanical behavior of composite adhesive single-lap joints (SLJs) subjected to tensile loading. The experimental data for training and testing the ML models are compiled from peer-reviewed journal papers from various research groups to eliminate bias and increase the diversity within the dataset. The dataset consists of eight continuous SLJ input parameters, which are used to predict the SLJ damage mode and failure strength. Regression and classification models are built using deep neural networks (DNN) and random forests (RF). Finite element (FE) modeling is conducted, and the numerical performance is compared with the accuracy of the regression ML models. Results show that ML models can predict strength with high accuracy. Furthermore, both DNN and RF classify damage modes accurately without the need for complex failure criteria, which cannot be typically achieved using traditional FE methods. This study utilizes ML algorithms to gain a deeper understanding of the structure-property-performance relationships of SLJs, leading to better designs of composite adhesive joints with higher strength efficiency.

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.

Relationship between 3D surface roughness parameters and load capacity of adhesive joints after shot peening

The aim of the article was to investigate whether 3D roughness parameters can be used to assess the strengthening treatment and to predict the load capacity of lap adhesive joints subjected to shot peening. The analyzes were carried out for single-lap adhesive joints made of EN AW-2024-T3 aluminum alloy, whose overlaps were shot peened for 60 to 180 s using balls with a diameter of 0.5 to 1.5 mm with a compressed air pressure of 0.3 to 0.5 MPa. As a result of the regression and correlation analysis, it was found that within the adopted range of input parameters variability, the load capacity of adhesive joints subjected to shot peening is most closely related to the roughness parameter Sdr. It has been shown that increasing the value of the Sdr parameter contributes to increasing the load capacity of adhesive joints. A mathematical model describing the impact of treatment time, balls diameter and compressed air pressure on the value of the Sdr parameter was also built. The model was built in accordance with the the Hartley's PS/DS-P:Ha3 plan methodology. The obtained results allow to conclude that the Sdr parameter can be used to predict the load capacity of adhesive joints after shot peening and to assess the strengthening treatment (within the assumed range of input parameters variability). Additionaly, the simplicity and low cost of roughness measurements justify the use of this method in industrial purposes.

Impact strength improvement of adhesively bonded structures using natural date palm tree fibers

Four different types of natural date palm tree fibers (DPTFs), including Rachis, Petiole, Bunch, and Mesh, were used as short fibers added to single lap adhesive joints subjected to quasi static and impact loading. The results show that the fibers have a remarkable effect on the static and impact strengths of the joints. Adding 2 wt% and 5 wt% of Bunch fibers to the adhesive layer impressively increased the impact strength by 196% and 62%, respectively. The analysis of fracture surfaces showed that DPTFs make the crack propagation more stable and increase the strength and the damping capacity of the joints.

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.

Effect of Temperature and Al2O3 NanoFiller on the Stress Field of CFRP/Al Adhesively Bonded Single-Lap Joints

In this paper, the effect of aluminum oxide, Al2O3, nanoparticles’ inclusion into Epocast 50-Al/946 epoxy adhesive at different temperatures, subjected to quasi-static tensile loading, is numerically investigated. The single-lap adhesive joint with two different types of material adherends (composite fiber-reinforced polymer (CFRP) and aluminum (Al) 5083 adherends) and adhesive Epocast 50-A1/hardener 946 were modeled in ABAQUS/CAE. A numerical methodology was proposed to analyze the effect on peel stress and shear stress by adding Al2O3 nanoparticles into the neat adhesive at 25 °C, 50 °C, and 75 °C temperatures at four different locations of the adhesive regions: the interface of the adhesive and aluminum adherend (location A), the middle plane of the adhesive region (location B), the middle longer edge (along the length of the adhesive, location C), and the middle shorter edge (along the width of the adhesive, location D). The results showed that adding nanoparticles into the neat adhesive improves joint strength at room and elevated temperatures. High peel and shear stresses were recorded near both edges of the locations (A, B, C, and D). For location A, adding nanofillers into the adhesive resulted in the reduction in peak peel stress by 1.3% for 25 °C; however, it increased by 2.7% and 10.7% for 50 °C and 75 °C temperatures, respectively. Furthermore, the peak shear stress observed a considerable reduction of 19.6% for 25 °C, but it increased by 7.7% and 8.7% for 50 °C and 75 °C temperatures, respectively, for location A. The same trend was also observed for other locations (i.e., B, C, and D). This signified that adding aluminum oxide nanoparticles in the adhesive resulted in increased stiffness at higher temperatures and increased ductility of the joint, as compared to the joint with neat adhesives at room temperature. Moreover, it was observed that locations A and B were more vulnerable to damage initiation, as the peak of stresses lay near the edges, indicating that the crack initiation would take place close to the edges and propagate towards the center, leading to ultimate failure.

Effect of Stacking Sequence on Fatigue Performance of CFRP–Al Single-Lap Adhesive Joints: Experimental Study

This study aimed to explore failure mechanisms of carbon fibre-reinforced plastic (CFRP)-aluminium (Al) single-lap adhesive joints which CFRP adherends had different stacking sequences. These results showed that fatigue performance of CFRP decreased as the number of 45° plies increased, which caused the initial failure location to gradually move from the adhesive layer towards the CFRP. Under high load levels, joint-failure models were influenced by the stacking sequence of CFRP; large-area cohesive failure occurred in joints when the CFRP stacking sequence was [0/90]4s and [0/45/-45/90]2s, and delamination failure occurred when the CFRP stacking sequence was [45/-45]4s, due to the weak interlaminar properties of CFRP. However, under low load levels, the stacking sequence of CFRP had little effect on the failure model of the joint, with interfacial failure being the main failure mode for all joints due to weakening of the mechanical interlock.

Adhesive bond quality classification using machine learning algorithms based on ultrasonic pulse-echo immersion data

In this study, we explored the detection of weak bonds (WBs) due to contamination and faulty curing (FC) using linear ultrasound and machine learning. For this purpose, aluminium single-lap adhesive joints containing three variants of bonding quality were investigated: perfect bond, WB due to release agent (RA) contamination, and WB due to FC. The data, according to the deviation of the bonding protocol, were arranged in two groups, creating two datasets: distinct and complete. Each dataset included all bonding conditions (perfect, RA, and FC), although the distinct dataset contained only marginal cases, which were expected to be well separable, whereas the complete dataset included data with minor deviations from the bonding protocol. Pulse-echo C-scan images were acquired for all prepared samples in the immersion tank, and 45 features were initially extracted from the time traces representing each bonding group. The initial data were analysed via a t-test and pairwise correlation analysis to reveal statistically significant features. Then, we performed dimensionality reduction using tree-based, recursive, sequential, and linear discriminant analysis (LDA) feature selectors to explore feature importance and classification accuracy with different feature subsets. Finally, the important features identified with the different feature selectors were fed to support vector machine (SVM) classifiers, and the classification accuracies were compared amongst the different feature subsets. The classification accuracy using a distinct dataset in some cases demonstrated nearly 99% accuracy, indicating that significant bonding protocol deviations could be easily detected. It was demonstrated that classification accuracy increased with the number of features. However, even in the case of the 2D feature space obtained using linear discriminant analysis, the bonding quality classification accuracy remained higher than 84%. The feature subspace reduction with LDA demonstrated sufficient classification accuracy and an improvement of nearly 40% in training time compared with that for the initial feature set. Thus, the classical ultrasonic pulse-echo C-scan with an LDA feature transformation and SVM classifier could be used to identify the deviations in the bonding protocol in aluminium single-lap adhesive joints.

Quasi-static cyclic loading assessment of GFRP single-lap adhesive joints reinforced with z-pins

Numerous studies have focused on the bond behavior of z-pinned composite joints under monotonic and fatigue loading. Despite this, research on quasi-static cyclic loading is still limited. In order to improve our understanding of the mechanical behavior of glass fiber reinforced polymer (GFRP) single-lap adhesive joints subjected to quasi-static cyclic loading, an experimental study was conducted, and the effects of z-pinning and the adhesive thickness of the bonding area on the strength and stiffness of joints were examined. In this regard, a series of the single-lap joints with 0.5 and 1 millimeter adhesive thickness without z-pin and reinforced with 9 and 16 z-pins were fabricated and monotonic, quasi-static cyclic, and monotonic after cyclic loadings were applied to each. It was found that in conditions where monotonic loading is only the case, and there is no quasi-static cyclic loading, the use of single-lap joints with 16 z-pins is recommended due to their effect on enhancing the ultimate load. For deciding on the adhesive thickness, the shear stiffness of the joint should be taken into consideration, as thinner adhesive thickness resulted in lower shear stiffness but higher ultimate load with the same number of z-pins. In the presence of quasi-static cyclic loading, inserting 16 z-pins along with 1 mm adhesive thickness is proposed. This number of z-pins significantly increased the ultimate load and the number of cycles the joint could tolerate. The impact of this thickness on reducing the level of stiffness degradation and displacement increment is noticeable as the cyclic loads progress.

Effect of graphene nano-particle reinforcement on the fatigue behavior of adhesively bonded single lap joints

Present study aims to investigate tensile fatigue behavior of adhesive single lap joints with a graphene nanoparticle modified adhesive (GNP). Carbon fiber reinforced plastic and 3 M DP460 was used as adherend and adhesive, respectively. In addition to the unreinforced adhesive, wt. 0.25%, wt. 0.5% and wt. 1% GNP reinforced adhesives were used. Tensile test results showed that increasing the GNP ratio increased the tensile strength of joints. The interior regions of the overlap region exhibited cohesive substrate failure and fiber tear failure, while the ends of the overlap region exhibited adhesive and cohesive failure. 0.5% GNP reinforced adhesive joints showed the highest fatigue life. Cohesive failure and adhesive failure were the main failure types for lower load levels. Increasing the fatigue load level caused different damage types to occur. The stiffness reduction didn't happen until the very end of the fatigue tests.

Topological optimization of a symmetric single-lap adhesive joint

The profile optimization problem for layers overlapped with an interjacent adhesive layer is considered. The joint is considered according to the Volkersen model, according to which the base layers are considered as rods that act only in stress-strain, and the adhesive layer acts only in shear. The aim of the optimization is to design a joint structure of minimum mass under the strength restrictions for the adhesive layer and the minimally allowable base layer thickness. The base layers profile is described by a Fourier series expansion. The direct stress state problem for the joint of variable thickness rods is solved by the finite difference method. The optimization problem is reduced to the problem of determining Fourier series coefficients and the joint length. A genetic optimization algorithm was used. The model problem is solved.

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.

Assessment of Surface Treatment Degree of Steel Sheets in the Bonding Process.

The aim of the paper is to determine the influence of the surface treatment on the adhesive properties of steel sheet surfaces and the strength of the adhesive joints of steel sheets. The paper also aims to assess the degree of steel sheets’ surface treatment in the bonding process. Due to the many methods of surface treatment and types of materials, the assessment of the surface treatment method is extremely important in adhesive processes. Two variants of the surface treatment were used: without a paint coating and with a paint coating, divided into two groups (without degreasing and with degreasing). Additionally, in the case of the analysis of the steel samples without the paint coating, mechanical treatment was applied. Two-component epoxy adhesive, prepared on the basis of bisphenol A and a polyamide curing agent, was used to prepare the single-lap adhesive joints of the steel sheets. The tests determined: (i) the adhesive properties of the steel sheets’ surface based on the measurement of the contact angle of polar and apolar liquids (including wettability, work of adhesion, and surface free energy), (ii) surface roughness parameters (PN EN ISO 4287), and (iii) mechanical properties (load capacity and shear strength) of the steel sheets’ adhesive joints (EN DIN 1465). Contact angle measurements of the steel sheet surfaces showed that the polar liquid better reflects the obtained strength results of the analyzed adhesive joints than the apolar liquid. Furthermore, better wettability of the surface of steel sheets with both polar and apolar liquids was obtained for samples whose surface was subjected to degreasing. It can also be concluded that the wettability of the surface can be used as one of the indicators of the degree of the surface treatment for the bonding process.

Novel Modeling of Heat and Moisture Diffusion in Adhesive Joints

Abstract A novel two-dimensional shear stress-heat and moisture diffusion model is proposed for adhesive single-lap joints. Spatial and time-dependent material properties are derived from coupled partial differential equations governing moisture diffusion and heat transfer through the exposed adhesive edges. Constituting differential equations are numerically solved for the shear stress distribution in the bonded area. Several diffusion scenarios and boundary conditions are analyzed. Significant improvements are achieved in the prediction of the shear stress distribution in the adhesive layer when compared to the one-dimensional models in the literature. Scenarios of moisture diffusion generate stress gradients through the bondline, while the relatively fast internal thermal conductivity reduces temperature differentials within the joint. Moisture diffusion in the adhesive layer is significantly accelerated at high temperatures. The results of the proposed model show reasonable agreement with a three-dimensional finite element 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).

Experimental study on failure mechanism of CFRP-to-aluminium single-lap adhesive joints under tension after out-of-plane pre-impact

ABSTRACT This paper presents the influence of impact energy and impact surface on the impact damage characteristics and residual tensile performances of carbon fibre reinforced plastics (CFRP)-to-aluminium single-lap adhesive joints. Experimentally, the internal damage morphologies of joints after pre-impact were inspected with X-ray micro-computed tomography (X-CT). The failure processes and detailed fracture surfaces were obtained by the digital image correlation (DIC) system and scanning electron microscopy (SEM). The results show that the joints impacted on aluminium surfaces exhibit superior impact resistance to the CFRP pre-impact surface under the out-of-plane impact load. The joints pre-impacted on different surfaces have similar failure processes during the tensile process. Firstly, the delamination damage propagates from the impact location to the edge of overlap region. Subsequently, the delamination damage reaches the CFRP end, where the local stiffness of CFRP adherend is significantly reduced, and cracks appear in the adhesive layer. Finally, the cracks propagate from the CFRP end to the overlap area centre with further increased tensile load, and the joint rapid fracture occurs after the tensile load reaching its peak. The delamination damage of CFRP adherends caused by out-of-plane impact load is the dominant factor to affect the bearing capacity of CFRP-to-aluminium single-lap adhesive joints.

Effect of Halloysite Nanotube Additive on Shear Strength in Al-GFRP Single Lap Adhesive Joint

Bu çalışmada, havacılık, otomotiv ve uzay gibi mühendislik alanlarında düşük yoğunluklu malzeme olarak sıklıkla tercih edilen alüminyum (Al) ve cam elyaf takviyeli kompozit (GFRP) malzemelerinin tek bindirmeli bağlantılarının (SLJ) kayma ve kırılma performanslarına halloysit nanotüp (HNT) parçacık katkısının etkileri incelenmiştir. Bu amaçla, HNT parçacıkları beş farklı oranda (ağırlıkça %1.0, %1.5, %2.0, %2.5 ve %3.0) Araldite 2014-2 epoksi tabanlı yapıştırıcıya eklenmiş, hazırlanan numuneler bindirme kesme testine tabi tutulmuştur. Elde edilen sonuçlar, %3.0 HNT katkılı numuneler dışında bütün katkı oranlarında numunelerin saf numunelere göre daha yüksek kayma dayanımı sonuçları verdiğini göstermiştir. Maksimum kayma dayanımı sergileyen %2.0 HNT katkılı numunelerin (11.76 MPa) saf numunelere (9.02 MPa) kıyasla dayanımının %30.4 arttığı bulunmuştur. Ayrıca, %2.0’den daha fazla miktarda HNT katkısı, nano parçacıkların topaklanmasından (agglomeration) kaynaklanan yerel gerilme konsantrasyonları oluşumu nedeniyle düşüş eğilimi göstermiştir. Öte yandan HNT katkılarının yapıştırma bağlantılarının performanslarının arttırmasını sağlayan çatlak köprüleme ve çatlak pinlenmesi gibi tokluk mekanizmaları gösterdiği SEM görüntüleri ile belirlenmiştir. Sonuç olarak HNT katkısının belli miktarlarda yapıştırma bağlantılarında kullanılması, bu yapıların kayma dayanımlarını arttırarak daha dayanımlı malzemeler türetildiğini kanıtlamaktadır.

Load capacity of single-lap adhesive joints made of 2024-T3 aluminium alloy sheets after shot peening

The goal of the work reported was to determine the influence of selected shot peening parameters on the deflection of the Almen strip and the load capacity of single-lap adhesive joints made of 2-mm-thick aluminium alloy EN AW-2024-T3. Moreover, the research was aimed at checking the possibility of using the Almen strip deflection indicator to predict the load capacity of adhesive joints after shot peening. The analysis was carried out according to Hartley’s PS/DS-P:Ha3 plan. The input factors were the shot peening parameters: treatment time t (60–180 s), ball diameter dk (0.5–1.5 mm) and compressed air pressure p (0.3–0.5 MPa). It has been proved in this work that shot peening treatment of the outer surface of single-lap adhesive joints can be used to strengthen the joint. The maximum increase in the load capacity of the shot peened joints was 33.4%. It was observed that the load capacity of the joints decreases with an increase in the deflection of the Almen strip (in the assumed area of variability of technological parameters). Moreover, the results obtained indicate that the adoption of too intensive treatment, manifested in high values of deflection of the Almen strip, may weaken single-lap adhesive joints.