Adhesively-bonded Joints Research Articles

Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints

The main objective of this study is to compare the mechanical strength of friction stir spot welded (FSSW) joints and adhesive bonded single lap ones. The present study aims to compare the morphology and strength of welded and adhesive bonded joints. The welded joints were done by friction stir spot welding and the adhesive bonded ones by the use of the adhesive Araldite 420 A/B. The produced joints were subjected to morphology and microstructure analyzes, microhardness tests, tensile-shear tests and local strain analyzes. The welded joints have higher strength than adhesive-bonded joints. However, this difference is insignificant, around 5%, which is covered by the standard deviation. The connection by FSSW proves to be an alternative to adhesive bonded joints, offering the same strength, but with the connection at isolated points, inducing local stress concentration.

Mode II fracture energy characterization of brittle adhesives using compliance calibration method

AbstractThe end‐notched flexure (ENF) test is widely used for measuring the Mode II critical strain energy release rate of adhesively bonded joints (ABJs). Unstable crack growth in ENF joints with brittle adhesives is a common phenomenon. Classic data reduction methods like the direct beam theory (DBT) and the compliance‐based beam method (CBBM) usually result in unacceptable scatter when crack grows unstable. In this study, the application of a compliance calibration method (CCM) for ENF adhesive joints with a brittle adhesive is experimentally investigated. For this purpose, ENF specimens were manufactured and tested. Different data reduction methods were considered for treating the results. Afterwards, the obtained fracture energies were used as an input parameter in a finite element (FE) analysis with a cohesive zone model to evaluate the validity of the experimental data. It is shown that the fracture loads obtained by the CCM have the best agreement with the experimental ones comparing with the other data reduction approaches. To study the effect of geometry on the CCM results, ENF specimens with different adhesive thicknesses, substrate thicknesses and span lengths were also considered in this study, and some general conclusions are made about the geometrical parameters effect on the Mode II fracture energy.

Requirements and Variability Affecting the Durability of Bonded Joints.

This paper firstly reveals that when assessing if a bonded joint meets the certification requirements inherent in MIL-STD-1530D and the US Joint Services Standard JSSG2006 it is necessary to ensure that: (a) There is no yielding at all in the adhesive layer at 115% of design limit load (DLL), and (b) that the joint must be able to withstand design ultimate load (DUL). Secondly, it is revealed that fatigue crack growth in both nano-reinforced epoxies, and structural adhesives can be captured using the Hartman–Schijve crack growth equation, and that the scatter in crack growth in adhesives can be modelled by allowing for variability in the fatigue threshold. Thirdly, a methodology was established for estimating a valid upper-bound curve, for cohesive failure in the adhesive, which encompasses all the experimental data and provides a conservative fatigue crack growth curve. Finally, it is shown that this upper-bound curve can be used to (a) compare and characterise structural adhesives, (b) determine/assess a “no growth” design (if required), (c) assess if a disbond in an in-service aircraft will grow and (d) to design and life in-service adhesively-bonded joints in accordance with the slow-growth approach contained in the United States Air Force (USAF) certification standard MIL-STD-1530D.

Application of ultrasonic welding to repair adhesively bonded short carbon fiber reinforced Nylon 6 composites

A method of applying ultrasonic welding to repair adhesive-bonded 2.3 mm thick injection molded short carbon fiber reinforced Nylon 6 (Cf/PA6) composite with 30 wt% fiber was developed. The method included positioning the ultrasonic horn and anvil proximate the region on the workpieces having the partially adhesive-bonds and applying an ultrasonic oscillation at the workpieces where insufficient adhesive was dispensed at the faying surfaces. The effects of horn force, oscillation time, and inadequate adhesive on the quasi-static strengths of the nominal, partially adhesive-bonded and repaired joints were investigated. It was found out that the strengths of the partially adhesive-bonded joints with 0%, 25%,50% and 75% adhesive coverages were restored and achieved over 90% of the nominal joint strength (i.e., full adhesive coverage). Microstructure analyses of the repaired joints demonstrated that the second ultrasonic pulse produced viscoelastic heating and frictional heating, and consequently fused carbon fiber composites at the faying surfaces of the workpieces. The strengths of the repaired (i.e., weld-bonded) lap-shear joints were primarily from the combined contribution of adhesive-bond and ultrasonic weld at the faying surfaces, which were virtually unchanged regardless the amount of adhesive missing. Therefore, for the substrate and joint configuration and dimensions studied here, application of ultrasonic welding virtually restored the quasi-static strengths of partially adhesive-bonded lap-shear Cf/PA6 composites with 30 wt% fiber. Consequently, by the application of this repair method the scrap of the component assembly would be reduced.

Effect of friction-stir weld parameters on hybrid bonded joints

ABSTRACT This research compares the mechanical behaviour of adhesive bonded (AB), friction stir spot welded (FSSW) and hybrid joints (H). The H joints were performed using both AB and FSSW. The influence of tool geometry, tool rotational speed and tool penetration depth on the joint strength were examined. The analysis of the mechanical performance of the joints was done using metallographic, hardness and tensile testing. In order to determine the local strains an optical extensometer with digital image correlation was used. Adhesive bonded joints displayed higher strength than welded or weld-bonded joints. Penetration of the tool pin into the lower plate increases the strength of the welded joint, although it has an unfavourable influence on defect formation. The weld-bonded (hybrid) joints have lower strength than adhesive-bonded joints or welded joints, as the uncured adhesive makes welding difficult, and the heat generated in the welding harms the adhesive.

Effect of Carbon Black Nanofiller on Adhesion Properties of SBS Rubber Surfaces Treated by Low-Pressure Plasma.

Studies on the surface modification of commercial styrene-butadiene-styrene (SBS) rubber with different carbon black (CB) nanofiller content (10–80 parts per hundred parts of rubber (phr)) performed by low-pressure oxygen plasma are presented in this paper. The adhesion properties of the rubber were determined by the peel test for adhesive-bonded joints prepared with a water-based polyurethane (PU) adhesive. The chemical structure and morphology of the SBS rubber surface before and after plasma treatment were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The peel tests showed that the plasma treatment significantly improved the strength of adhesive-bonded joints in the entire range of CB tested, revealing a clear maximum for approximately 50 phr of CB. It was also found that as a result of plasma treatment, functional groups that are responsible for the reactions with the PU adhesive, such as C−OH and C=O, were formed, and their concentration, similar to the peel strength, showed maximum values for approximately 50 phr CB. The occurrence of these maxima was explained using the bound rubber model.

Tehnika dubokog učenja bazirana na akustičnoj emisiji za predviđanje jačine adhezije kod laserski tretiranih CFRP kompozita

The high degree of inhomogeneity in material and intricacies created by machining of carbon fiber reinforced plastic (CFRP) composites hinder the accurate prediction of residual strength of the adhesive bond joint using analytical models. Recently, artificial intelligence techniques are effectively utilized as an alternative method for predicting the results of complex phenomena. In this paper, attempts were made to predict the bond strength of laser surface treated and adhesively bonded CFRP composite specimens using the artificial neural network (ANN) from the acoustic emission (AE) parameter recorded during the shear test. Twelve adhesively bonded specimens whose surfaces were pre-processed with 3W Nd:YAG laser at different processing parameters. ANN was trained using segregated AE data according to the failure mechanism and the percentage of failure load (5 to 100%). Predicted values were compared with experimental values and the results were analysed for the suitability of ANN with AE in the application.

Concurrent use of Z-pins for crack arrest and structural health monitoring in adhesive-bonded composite lap joints

Adhesive-bonded joints in carbon fibre-reinforced polymer laminates are cost effective, but their fatigue cracking potential currently limits aerospace certification. We investigated the concurrent use of Z-pins for crack arrest (including an analysis of underlying mechanisms) and structural health monitoring (SHM) in adhesive-bonded composite lap joints. The use of Z-pins resulted in a crack arrest capacity 33% higher than the joint's static limit load and produced a residual strength that far exceeded current ultimate loads (250 versus 150% of the limit load). The electrical resistance in the Z-pins was consistent with observed trends in crack growth, suggesting its viability for SHM.

Evaluation of an elastic meshless formulation to adhesive joints’ strength prediction against established methods

Adhesive joints are widely used in the production of goods, mainly in the transport industry. However, their industrial applications often have non-standard complex shapes. Computer simulation, like the finite element method (FEM), is widely used for their analysis but limitations still exist. Meshless methods have been in development and offer an option to overcome some limitations of the FEM; however, these are still in development. In this work, a recent meshless method, the NNRPIM, has been applied to the analysis of adhesive joints. First, experimental data corresponding to four overlap lengths and three different adhesives were measured, as a benchmark. Afterwards, joint strength was analytically obtained as a second benchmark. Then, all the joint geometries were simulated utilising the FEM and NNRPIM methodologies, joint strengths were calculated from those simulations. Finally, the results were compared against the first and second benchmarks. Meshless method proved to be a good alternative to the FEM, providing similar strength prediction with differences less than 3% between them. Moreover, the stress distribution curves were compared, differences of 5% in the peak shear stresses were found. In conclusion, the NNRPIM provides accurate results and could be utilised for further study of adhesively-bonded joints.

Effect of Extensometer Usage on Obtaining the Force-Displacement Curve of the Adhesively Single Lap Joint

Structural adhesively bonded joints are frequently used in many areas spearheaded by the industries such as automotive, marine space, and aviation due to the great advantages they provide. Besides, load capacities of adhesively bonded joints which have different geometries, are generally determined experimentally. Being compatible of experimental and numerical analysis of adhesively bonded joints in the means of both load carrying capacity and displacement has a great importance. But, one of the most common problems in comparison of experimental and numerical analyses is in spite of the coherence of experimental and numerical analyses in load carrying capacity, it is observed that in the means of the displacement analysis, there is incompatibility between those analyses. In the present study, force-displacement curves of the single-lap cohesively bonded joints are obtained experimentally by using both strokes of two different tensile test machines which have identical calibrated load cells and video extensometer. Experimentally obtained result was compared with numerical analysis. In the experiments, AA2024-T3 aluminium and two-component Araldite 2015 were used as adherend and adhesive, respectively. As a result, there is considerable difference between the force-displacement curves of the single-lap overlap joints which obtained experimentally from stroke and video extensometer. Also, being new or old of the tensile test machines which have identical calibrated load cells varies the displacement curve of the joint. When the experimental data were compared with the results of the numerical analysis, it is concluded that, obtaining the force-displacement curves of joints by using video extensometer is more accurate.

Durability of wet lay-up BFRP single-lap joints subjected to freeze–thaw cycling

Freeze–thaw (FT) cycling is one of the primary concerns for the application of fiber reinforced polymer (FRP) in cold regions. Existing studies have shown different levels of degradation on the mechanical behavior of carbon FRP (CFRP) or glass FRP (GFRP) and FRP adhesively-bonded joints after FT cycling. This paper presents experimental and numerical studies on the FT durability of basalt FRP (BFRP) single-lap joints (SLJ). BFRP, epoxy resin tensile coupons and BFRP SLJ were prepared and tested before and after FT cycling. Test results indicate that the tensile properties of BFRP and BFRP SLJ are not significantly influenced by FT cycling, while considerable degradation was observed for the epoxy resin and the bond behavior of fiber-to-matrix interface. Numerical simulations were conducted to expand test parameters of the BFRP SLJ before and after FT cycling. Finally, FT durability mechanisms of both BFRP and BFRP SLJ are discussed.

Simulating and Ensuring the Reliability of the Elements and Joints of Three-Dimensional Microelectronics Modules

In order to ensure the operability, durability, and reliability of three-dimensional microelectronic modules, the engineering calculation of the structures, including the simulation of adhesive-bonded joints, as well as a valid choice of materials and constructive decisions, is necessary. The main operational and physical specifications for three-dimensional microelectronic modules and the advantages of the application of adhesive materials in the structures of modules are presented. It is established that the structural strength of three-dimensional microelectronic modules and the operating characteristics of adhesive-bonded joints depend on many factors. The most important factors among them are the properties of the adhesive material, the structure of the joints and the operating conditions. The types of loads, which affect the modules during their operation and their influence on the structural strength are considered. It is revealed that irregular loads, such as peeling and bending, are the most dangerous loading types for the adhesive-bonded joints of modules. It is established that in peeling a high concentration of edge stresses arises, which leads to the destruction of the joints, and in bending there is a concentration of normal and tangential stresses along the length of the glue lines. The types of adhesive materials which are used for assembling the modules are analyzed. The adhesive materials are selected taking the main design and technological constraints and the requirements on adhesive-bonded joints into account. The module’s structures are simulated and the influence of the physical, mechanical, and thermal properties of the adhesive materials on the stresses in the adhesive-bonded joints and the strength of the products under the impact of inertial loads with an acceleration of 1000g and heated by 40°С is determined. Recommendations on the simulation of adhesive-bonded joints of three-dimensional microelectronic modules are made. The obtained results revealed that the stresses depend on the elastic properties of the adhesive-bonded joints, as well as on the nature and value of the load on them, and they are determined by the mechanical strength and rigidity of the adhesive material. In order to reduce the stresses, it is necessary to use more rigid structural materials, and the adhesive materials need to be chosen based on the operating conditions of the microelectronic module.

Surface topography following pulsed laser texturing: Implications for adhesion and wettability

A model for predicting surface topography following nanosecond pulsed laser texturing of metals is applied to calculating the areal surface roughness, Sa, average ablation depth, Da, and Wenzel roughness factor or adhesion area ratio, r, for a range of representative cases relating to adhesion and wettability. Optimisation of the laser scanning strategy, number of laser passes and focused spot size is performed by considering the ratio of increases in Sa and r with respect to the average ablation depth: and where Highest values of and are achieved where the pulse separation distance is equal to the focused spot size in both the scanning and lateral directions. Increases in Sa, r and can be achieved by performing multiple laser passes, while r and can be increased independently of Sa and by reducing the focused laser spot size. These results suggest that r and Sa can be optimised effectively and independently in line with a given application. Finally, laser texturing experiments are performed on AA 6082 aluminium alloy and 316L austenitic stainless steel specimens with the aim of confirming model outcomes, after which tensile tests are performed on adhesive-bonded joints prepared with the same laser treatments. Further to demonstrating the benefits of laser texturing, it is shown that optimum results are not necessarily associated with a single value of Sa or r, but are instead a compromise between maximising these parameters and limiting the ablated volume.

Resistance Spot Weld assisted with Adhesive Bonding

This paper presents an experimental investigation of the weld bonding of low carbon steel (JIS G3141) together with adhesive layers to increase the mechanical properties of weld bonding. Epoxy adhesive was used in this research applied on the sheet thickness of 1.2 mm. The weld-bonding was carried out by applying layer of adhesive followed by resistance spot welding on surface samples. The relative properties and characteristics of the resulting weld-bonded-adhesive joints are evaluated and compared with the conventional spot-welding through tensile-shear, peel, hardness tests and macro-etching observations. The strength of weld bond joints was calculated and compared with those in as-weld and adhesive-bond joints. Results showed that the strength of weld-bond adhesive is higher than as-weld specimen. The hardness distribution of weld bond adhesive joints was investigated, at three regions i.e. base metal (BM), the heat-affected zone (HAZ), and the fusion zone (FZ) using micro-hardness Vickers machine. It can conclude that the presence of adhesive does not affect the hardness of weld-bonded. From macro- etching observation, the layer adhesive influenced the weld bond via the size nugget of weld-bonded which is smaller than as-weld. The introduction of adhesive layer in spot welding improves the joint strength and quality of spot weld.

Effect of adherend deflection on lap-shear tensile strength of laser-treated adhesive-bonded joints

Laser surface treatment was used as a surface preparation method for adherend prior to adhesive bonding, which significantly improved the fracture mode from mixed to cohesive and consequently increased the lap-shear tensile strength by 27.5% and 28.2% for aluminum alloys AA7075 and AA6022 adhesive-bonded joints, respectively. Nevertheless, the laser-treated AA7075 joint exhibited a 13.9% higher strength compared to laser-treated AA6022 joint although both joints showed cohesive fracture modes, which was attributed to smaller adherend deflection of laser-treated AA7075 joint than that of laser-treated AA6022 joint. Digital image correlation technique was applied to monitoring the deflections of laser-treated AA7075 and AA6022 joints during lap-shear tensile testing, and the stress analysis of adhesive-bonded lap-shear joints was conducted by finite element simulation. It was found that the deflection angle of the laser-treated AA6022 joint reached to 6.1° at the peak tensile load and was ∼69% larger than that of laser-treated AA7075 joint (i.e. 3.6°), which resulted in a mixed stress state with higher peel stress (i.e. ∼8 MPa) on edges of adhesive bonding region and consequently led to a premature fracture due to the low peel resistance of adhesive-bonded joints. Furthermore, the effect of decreased adherend deflection on lap-shear tensile strength was investigated, and a linear increase of lap-shear tensile strength was found with the decrease of deflection angle for adhesive-bonded joints showing cohesive fracture modes.

Stress analysis of double-lap bi-material joints bonded with thick adhesive

Mechanics of double-lap Steel-to-CFRP adhesively-bonded joints loaded in tension are investigated experimentally using Digital Image Correlation (DIC) and Acoustic Emission (AE), analytically using a one-dimensional closed-form solution and numerically with Finite Element analysis. The double-lap bi-material joints are fabricated of a steel core adhesively bonded to two CFRP skins with adhesive thickness of ~ 8 mm, using an Epoxy-based and MMA-based adhesives. In order to capture the in-plane deformation of the joint, full field strain/displacement maps are obtained using DIC. This data is used to validate the shear-lag model predictions of the adhesive shear stress/strain distribution as well as the linear-elastic Finite Element Model (FEM) results. In addition, they are used to capture the susceptible damage locations and their effect on the displacement contour maps, strain distribution and load transfer between the joint's different constituents. A correlation between the DIC displacement and the AE signals is obtained for damage detection in both joints. Moreover, a good agreement amongst the analytical, FE and DIC strain/stress distributions along the bond-line is observed. This study introduces the analytical shear-lag model as an alternative to predict the stress state in thick-adhesive double-lap joints, with an acceptable level of accuracy and robustness.

Effect of adhesive type on mechanical properties of galvanized steel/SMC adhesive-bonded joints

Adhesive bonding provides a solution for joining sheet molding compound (SMC) and metals. In this study, three typical automotive structural adhesives (i.e. polyurethane adhesive A236, epoxy adhesive 120HP and acrylic adhesive M10) were applied to joining galvanized steel and SMC to investigate the compatibility of adhesive type and adherend materials in terms of the lap-shear tensile strength of as-fabricated joints. In addition, adhesive-bonded joints after immersion in 63 °C deionized water for 0, 7, 14 and 21 days were mechanically tested. Results show that the joint strength gradually decreased with increasing exposure time. Among the adhesive-bonded joints fabricated from three adhesives, the lap-shear strength of A236 joints is the highest before and after water soak. It is also observed that the fracture mode of A236 joints switched from SMC substrate failure to the interfacial failure between galvanized steel and adhesive after exposure, while 120HP joints and M10 joints always fractured at the galvanized steel/adhesive interface during lap-shear tensile testing. The fracture surface observations indicate that the corrosion of galvanized steel extends inward the bonding area with an increase of exposure time, which is verified with an energy dispersive spectrometry (EDS) and can be explained by the moisture diffusion along the galvanized steel/adhesive bonding interface.

Modification of surface treatment on the strength of 30CrMnSiA steel adhesively bonded joints

30CrMnSiA steel substrate was treated with sandblasting and laser texturing to improve its adhesive-bonded strength. The characterization of treated substrate was performed by surface morphology, surface roughness (Ra and Rz) and wettability. The water contact angle (WCA) was measured and solid surface energy was calculated. The adhesive-bonded single lap joints were then prepared and tested. For comparison, the similar discussion was established for the metal substrate with degreasing. Fracture surface was observed and analyzed by SEM and EDS. The results indicated that the surface roughness was increased both with sandblasting and laser texturing. The wettability was improved due to the decrease of WCA and the increase of surface energy. The tensile shear strength of adhesive-bonded joints after sandblasting and laser texturing increased by 151% and 465.9% respectively. The proportion of adhesive on the same side (left side) of joints was 1.5%, 29.3% and 67.7% under three types of joints. The fracture mode of specimens with degreased and sandblasted substrate was found to be an interfacial fracture, while it was mixed fracture with laser textured substrate.

Damage characterization of adhesively-bonded Bi-material joints using acoustic emission

The aim of the present study is to characterize the damage in bi-material steel-to-composite double-lap adhesively-bonded joints using Acoustic Emission (AE). Two different structural adhesives, a ductile (Methacrylate-based) and brittle (Epoxy-based), were used to bond CFRP skins to a steel core. The fabricated joints were loaded in tension while damage evolution was monitored by AE. Due to the difference in the fracture nature of the adhesives “ductile vs. brittle”, different damage mechanisms were observed; including cohesive failure within the adhesive layer, steel deformation, failure at the adhesive/adherends interface (adhesive failure) and delamination in the CFRP skin. To classify these damages by AE, the AE features of each damage mechanism were first obtained by conducting standard tests on the individual constituents. Then, these AE reference patterns were used to train an ensemble decision tree classifier. The best parameters of the ensemble model were obtained by Bayesian optimization, and the confusion matrix showed that the model was sufficiently trained with the accuracy of 99.5% and 99.8% for Methacrylate-based and Epoxy-based specimens respectively. Afterwards, the trained model was used to classify the AE signals of the double-lap specimens. The AE demonstrated that the dominant damage mechanisms in the case of the Methacrylate-based were cohesive and adhesive failures while in the case of the Epoxy-based they were CFRP skin failure and adhesive failure. These results were consistent with the Digital Image Correlation, Fiber Optic Sensor and camera results. This study demonstrates the potential of AE technique for damage characterization of adhesively-bonded bi-material joints.

Adhesive Joints of Heterogeneous Materials in Protective Wares

Different materials are often combined in protective sewing goods. Multifunctional adhesive film material for adhesive joints of protective materials is created. The results of experimental estimate of adhesive joint physic-mechanical properties of materials with heterogeneous properties are represented. Adhesive-bonded joints of goods for personal protection are investigated.