Adhesively-bonded Joints Research Articles

A new method for estimating wood failure percentage in adhesive-bonded shear specimens

The traditional visual estimation of wood failure percent (WFP) in shear-failed adhesive-bonded joints is often marred by inconsistencies and produces results with large variations between examiners. This method of determining WFP has also been criticized as inaccurate and subjective. Therefore, an alternative method with improved accuracy and more consistent WFP estimations is desired. This study investigated the feasibility of Fiji-ImageJ software-assisted (F-IMJ-A) estimation of WFP in sheared block specimens of three wood species namely Eucalyptus grandis, Fagus sylvatica, and Pinus sylvestri bonded with three different adhesive systems viz. melamine-urea-formaldehyde, phenol-resorcinol-formaldehyde, and polyurethane. The consistency of the F-IMJ-A method was evaluated between three estimators and against the traditional ASTM D5266:2005 practice. The results obtained showed that the F-IMJ-A method improved, in most cases, the consistency of WFP estimations between the estimators. 5–33%, 1–36%, and 5–64% reduced WFP variations between estimators were recorded in E. grandis, F. sylvatica, and P. sylvestri-bonded joints respectively, across the different adhesive systems and wood failure modes. The F-IMJ-A procedures downscaled, by one-third, the 100% human-error-prone ASTM D5266 procedures as could be applicable with partially trained estimators. However, further improvement in the F-IMJ-A estimation is still desirable considering the range of variations between the estimators despite the recorded improvements. This study has demonstrated the suitability of the F-IMJ-A method in estimating WFP in shear-failed specimens of different wood species bonded with different adhesive systems.

Failure Studies on Adhesive Bonded and Bolted Joints of Natural Fiber Composites

Composites with natural fibers as reinforcements are playing a vital role in recent developments. The present work deals with the fabrication of okra and empty fruit bunch banana fiber polyester matrix composites with varying reinforcement content (5%, 10%, and 15%). Composites were fabricated by using the hand layup technique. After the fabrication process, composites were then adhesively bonded and also joined with bolts. The main objective of this work is to analyse the failure studies on adhesive bonded and bolted joints of okra and empty fruit bunch banana composite specimens. The specimens were tested under tensile load, flexural creep studies, and SEM analysis. It has been observed that empty fruit bunch banana fiber composites exhibited better joint strength properties under tensile loading when compared to the okra fiber composites. To estimate the flexural creep behaviour, all the samples were tested at a constant load of 2.5kg and 5kg. The deflections obtained during regular time intervals (four months) were noted. The presence of internal defects and void content was observed by using the scanning electron microscope. The results showed that adhesive-bonded composites were exhibited less deflection compared to the bolted joints. The empty fruit banana fiber composites exhibited higher creep than okra fiber composites. Decreased creep with the increased fiber has been observed in both cases. SEM Adhesively bonded joints possessing better sustainability as compared to the bolted joints in both the fiber-reinforced composites.

Modelling adhesively-bonded T-joints by a meshless method

Bonding of non-parallel substrates has many applications in the transport industry. Adhesively-bonded T-joints are employed for that purpose. However, geometrical dimensions, substrates’ shape and material choices are broad. The effect that varying upper substrate thickness has on the joint strength (P max ) was investigated in this work through numerical analyses. The numerical analysis was performed using a meshless method, the natural neighbour radial point interpolation method (NNRPIM), which has been proven accurate and robust in another adhesive joint configuration. Materials were considered elastic-plastic. A yield criterion developed for rubber-like materials, the Exponent Drucker-Prager, was used for the adhesive layer, while the metallic substrates were analysed with the von Mises yield criterion. P max was determined numerically using a strain-based continuum mechanics failure criterion. Normalised peel and shear stress distributions along the bond-line are presented. Effective strains, both elastic and plastic, were also obtained. The estimated P max was compared with experimental data; a good agreement was found. The stress distribution along the bond line becomes asymmetric in joints with unbalanced substrate thicknesses. At P max , from 10 to 25% of the bond-line has entered into plastic regime. The results indicate that the proposed methodology is suitable to analyse adhesively-bonded joints under different load solicitations.

Mechanical behavior of butt curved adhesive joints subjected to bending

Abstract Factors such as the surface geometry of a joint, the direction of the applied load, and the type of adhesive used have a great influence on the strength of a joint in adhesive bonding. In adhesively bonded joints (ABJ), it is possible to improve surface geometry by forming various geometric surfaces. ABJs are not very resistant to peeling stress, thus requiring that a bonding model be analyzed according to the direction of the applied load to prevent peeling stress. In this study, a butt curved joint was prepared from aluminum plates (A2024-T3) to improve the surface geometry of the joint. The mechanical behavior of the joints in three-dimensions and subjected to bending were investigated depending on an increase in the curvature radius. The adhesive DP810 was used for bonding. The finite element analysis was performed in ANSYS and cohesive zone modeling was used for a simulation of the damage growth in the adhesive layer. The results of bilinear and exponential models were found to be more appropriate to the experimental results. When the radius of curvature increases, the damage load carried decreases in the butt curved lap joints. It was seen that decreases in the curvature radius significantly decrease normal stress.

Stress-Function Variational Method for Accurate Free-Edge Interfacial Stress Analysis of Adhesively Bonded Single-Lap Joints and Single-Sided Joints

Large free-edge interfacial stresses induced in adhesively bonded joints (ABJs) are responsible for the commonly observed debonding failure in ABJs. Accurate and efficient stress analysis of ABJs is important to the design, structural optimization, and failure analysis of ABJs subjected to external mechanical and thermomechanical loads. This paper generalizes the high-efficiency semi-analytic stress-function variational methods developed by the authors for accurate free-edge interfacial stress analysis of ABJs of various geometrical configurations. Numerical results of the interfacial stresses of two types of common ABJs, i.e., adhesively bonded single-lap joints and adhesively single-sided joints, are demonstrated by using the present method, which are further validated by finite element analysis (FEA). The numerical procedure formulated in this study indicates that the present semi-analytic stress-function variational method can be conveniently implemented for accurate free-edge interfacial stress analysis of various type of ABJs by only slightly modifying the force boundary conditions. This method is applicable for strength analysis and structural design of broad ABJs made of multi-materials such as composite laminates, smart materials, etc.

A design-of-experiments approach to estimate the effect of plasma-treatment parameters on the mechanical resistance of adhesive-bonded joints

In this study, the design of experiments (DoE) approach was used to identify the effect of low-pressure plasma surface treatment parameters on the lap-shear strength of adhesive bonded joints realized using different substrates. In particular, four different polymeric substrates were considered: 5- and 7-layer carbon-fiber reinforced polymers and polyamide 6 and 6.6. Two-level, full-factorial designs were used to investigate the effects of two varying principal parameters, namely, plasma power and treatment time, for each type of substrate. The analysis was carried out by considering different types of processing gases. The objective function was the tensile shear strength of the adhesively bonded joints. For each set of joints, the shear strength values​​ ​​were compared using the DoE approach to detect any systematic behavior among different substrates. Finally, it was possible to identify the set-up parameters that gave the best performance in terms of shear strength, considering any equivalent conditions from a statistical point of view. This aspect is particularly important in consideration of the process optimization of the manufacturing cycle; indeed, it allows the maximization of the joint efficiency by limiting the energy cost for treatment.

A Methodological Study for the Stress Analysis to Evaluate Single Lap Adhesive Joint

The use of adhesive bonding is increased in load-bearing applications in place of conventional joining techniques such as bolted or rivets joints. The high-stress concentration occurs at the end of an adhesive-bonded lap joint so all failures begin at the end of the overlap region and get fractured in the end. The single-lap adhesive-bonded joint was used in the current study to examine the peel stress and shear stress results along the overlap region. The comparison of the analytical and experimental result was made to validate the results along with it the load vs displacement curve was obtained from results. Also, stress vs strain curve and peel stress vs overlap length of the one mm thickness of testing specimen was obtained.

Adhesive bonding of a mixed short and continuous carbon-fiber-reinforced Nylon-6 composite made via fused filament fabrication

Abstract This experimental work aims at evaluating the mechanical and failure behavior of adhesive-bonded single-lap joints made of a thermoplastic composite 3D-printed via Fused Filament Fabrication technology. Carbon fiber was selected as the reinforcement and used in the form of both short and continuous fibers embedded in the Nylon-6 matrix, forming the composite's hybrid structure. An approach based on progressive improvement of surface treatment effectiveness (solvent degreasing, abrasion, and low-pressure plasma) has been adopted to verify how the additively-manufactured composite responds to bonding when increased interfacial adhesion is attained by preparing the outer printed layer. Roughness measurements, wettability evaluations, and XPS analyses have been carried out to assess any modifications of morphology and functionalization exhibited by the different surfaces after treatment. The experimental findings demonstrate that the intrinsic non-homogeneity of 3D-printed composites is emphasized when low-pressure plasma is used, as it generates interfacial bonds between adhesive and adherend that are more effective than the interlaminar ones within the substrate. In this condition, the ultimate resistance of the joint corresponds to that of the base material. In particular, fracture-mechanism analysis allowed precise identification of the crack path, highlighting defects and current limitations of the additively-manufactured system and suggesting pivotal aspects to develop in future work to improve joint performance.

Viscoelastic model to capture residual stresses in heat cured dissimilar adhesive bonded joints

The thermal loading during the curing process of an adhesive-bonded joint induces residual stresses in the joint, thereby affecting its performance. The problem becomes worse in the case of a multi-material joint involving varying coefficients of thermal expansion (CTE) for different parts. A novel approach was developed to model the properties of automotive grade structural adhesives during the heat curing process. The material model was divided into two components: curing kinetics model and viscoelastic mechanical model. The models were calibrated using experimental data from Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) tests performed on an epoxy-based single-component adhesive. The calibrated material model parameters were fed into a finite element simulation and the prediction results were compared to a unique set of experiments utilizing two substrate combinations of adhesive-bonded single lap shear joints. An excellent agreement between the simulated and experimental results (displacement across the bond, force applied by the adhesive) was achieved. The modeling results give a better understanding of the residual stresses and agree with the experimental trend on the effect of bondline thickness on the joint.

Thermal Stresses in Adhesively Bonded Joints: Numerical and Analytical Analysis

The adhesive technique is observing a considerable increase in applications in various fields. Unlike traditional joining methods, this technology allows the stress peaks and the weight of the resulting structure to be reduced. Adhesive joints during their service life not only undergo mechanical but also thermal stresses. The thermal compatibility between the adhesive and the adherents used is a fundamental aspect to consider in the design phase. This paper reports on and analyses the results obtained from a linear Finite Element Method (FEM) simulation for a hybrid adhesive joint, as the thickness and characteristics of the adhesive layer vary. An analytical solution for adhesive free joints is presented according to both beam and plate theories. The analytical and numerical results, in case of no adhesive, are in good agreement with good approximation. The introduction of the adhesive layer allows to obtain higher displacement values than in the adhesive-free configuration. The increase in displacement and therefore in ductility confirms the effectiveness of the adhesive joint for real applications.

К ТЕОРИИ ЛАЗЕРНОЙ ГЕНЕРАЦИИ УПРУГИХ ВОЛН В ФЕРРОМАГНИТНЫХ МЕТАЛЛАХ ПРИ ТЕМПЕРАТУРЕ МАГНИТНОГО ФАЗОВОГО ПЕРЕХОДА

Laser generation of ultrasound has found wide application in modern technologies: to control the quality of composite materials, to detect layer separation in adhesive-bonded joints, subsurface and surface defects, as well as the quality of a product's surface in the process of manufacture. For excitation of waves in metals, pulse laser is normally used. In metallurgy, as well as in promising 3D technologies, it is necessary to control products at high temperatures (800°С and higher). To design ultrasound equipment with a pulsed laser radiation generator as the ultrasound source, it is required to conduct theoretical research of the process of laser generation of ultrasound in ferromagnetic metals at the temperature of magnetic phase transition, since the hot metal conversion for ferrum and ferrum-based alloys is, as a rule, performed namely at this temperature of 768 °С. The results of the experimental works allow to conclude that the temperature dependence of normalized amplitude of acoustic pulse in ferrum is of extreme character in the range of magnetic phase transition, i.e., in the range of Curie point. In this work a goal has been set to study the process of laser generation of ultrasound in ferromagnetic metal in the condition of non-linear dependence of the volume-expansion coefficient on the temperature. The task of thermoelastic excitation of longitudinal and transverse waves in ferromagnetic metal by a laser pulse at the temperature of magnetic phase transition has been solved. Diagrams of longitudinal and transverse wave patterns when ferromagnetic metal is exposed to laser pulses of various diameters have been obtained. Recommendations for effective use of laser generation of ultrasound in non-destructive testing and thickness measurement have been given.

Effect of adhesive thickness and adherend material with a surface roughness on lap shear strength of joints in tensile and compressive loading

ABSTRACT The lap shear strength of epoxy adhesive is determined experimentally using adhesive-bonded single lap joints with two similar adherends, aluminium alloy and steel, following ASTM standards D1002 and D905 in tensile and compressive loading. Thicknesses of the adhesive layer are 25 μm, 50 μm, 75 μm, 100 μm and 125 μm. Both tensile and compressive shear strength increase with increase in thickness of adhesive layer up to 100 μm, and it decreases at 125 μm of thickness of adhesive layer. Analysis of fractured surfaces of joints reveals that cohesive mode of failure dominated for the joint with 100 μm of thickness of adhesive layer. Compressive shear strength of the joints is higher than the tensile shear strength of joints at all the thicknesses. Further, the shear strength of joints with aluminium alloy adherends is higher than that of joints with steel adherends for both types of loading. The higher strength of aluminium alloy joints could be attributed to the surface roughness and materials of the adherends. The effect of surface roughness on shear strength is more pronounced compared to the material of adherends, i.e. aluminium alloy and steel.

The effect of joint configuration on the strength and stress distributions of dissimilar adhesively bonded joints

The recent increase in the use of adhesively bonded joints (ABJs) made from dissimilar adherends demands the acquisition of a better understanding of the strength and behaviour of these joints, including their failure mechanisms. Several studies have reported on such joints individually, however few have compared the performances of dissimilar ABJs with varying configurations and design parameters, in order to determine the optimal design configuration for hybrid structures. In this work, a comparative study using experimental methods and finite element analysis was conducted, focusing on four joint configurations (scarf joints, stepped-lap joints, half-lap splice joints and single-lap joints), with the aim of evaluating the ways in which their performances differ. In addition, the effects of overlap length (L0) and the mechanical properties of the adherends on the overall success of each joint were particularly closely analysed and compared. The results showed that the scarf joint provided the best performance of all the designs discussed, and it was found that increasing the overlap length was only significantly beneficial for certain joint configurations and adherend combinations. When the overlap length was increased from 12.5 mm to 25 mm, the failure load increased by 47.50% and 21.25% for the scarf and the stepped-lap joints, respectively. In comparison, the percentage increases for the half-lap splice and single-lap joints under the same conditions were less than 10%. Moreover, the mechanical properties of the adherends considerably affected the failure mechanisms of the dissimilar joints, and for all four joint configurations, the failure was initiated by a crack at the adherend-adhesive interface adjacent to the adherend with a lower modulus.

Fatigue behavior of carbon fibre reinforced plastic and aluminum single-lap adhesive joints after the transverse pre-impact

This study aims to investigate the fatigue degradation of carbon fibre reinforced plastic (CFRP) composite and aluminum (CFRP/Al) adhesively-bonded joints after certain levels of transverse pre-impact. The CFRP/Al adhesive joints were tested post impact under quasi-static loading and different levels of cyclic loading to study fatigue behaviors. Based upon the fatigue testing results and a two-parameter Weibull distribution method, the S-N curves were established at different reliabilities to provide fundamental data for engineering applications. The experimental results showed that the fatigue life of the CFRP/Al adhesively-bonded joints decreased with increase of pre-impact energy in general. The post impact fatigue load-bearing mechanisms of the joints could come from the harmful effect caused by the pre-impact damage and beneficial effect due to mechanical interlock induced by certain plastic deformation of aluminum adherend. The adhesive failure was identified to be the major failure mode regardless of the pre-impact energy and cyclic loading levels. Meanwhile, the fatigue life of the joints decreased with increase in the cyclic loading, and was more sensitive to a higher load as indicated from the S-N curves obtained.

Fatigue behaviors and mechanism-based life evaluation on SPR-bonded aluminum joint

Fatigue behaviors of hybrid joint, the combination of cold-formed mechanical fastening with adhesive bonding, are yet to be understood comprehensively even though they have been widely used in industries. The lack of understanding is mainly attributed to the complicated load transfer path and possible interactions between the two types of joining techniques, namely mechanical interlocking and adhesive bonding. In the present work, fatigue tests are performed on self-piercing riveted (SPR) joint, adhesive-bonded joint, and the SPR-bonded joint under lap shear and 45° loading conditions. Failure mechanisms are evaluated based on terminated fatigue test and numerical analysis. Periodical and asymmetric failure mode can be identified in SPR-bonded joint. Although both crack pinning and asymmetric failure mode induced by SPR suppress the crack growth in adhesive bonding, the effect of crack pinning is significant only when crack approaches SPR. The asymmetric failure also leads to load transfer path evolution, intensifying damage on SPR joining. A mechanism-based fatigue life evaluation method is proposed by characterizing the interactions with crack growth method and structural stress method. The calculated results are compared with the experimental ones, and good correlations are observed for both lap shear and 45° loading conditions.

Recent trend in developing advanced fiber metal laminates reinforced with nanoparticles: A review study

Recently, fiber metal laminates (FMLs) have attracted considerable application in many industries due to their outstanding properties. FMLs are hybrid materials that are fabricated by adhesion of thin layers of metals and fiber-reinforced composites. It should be noted that the reinforcing mechanisms of nanoparticles on the polymeric composites have been well-established, but there is limited literature regarding the influence of nanoparticles on the mechanical behavior of FMLs and adhesively bonded joints (ABJs) between metal sheets and polymeric composites. To date, various nanofillers including carbon nanotubes, graphene nanoplatelets, clay nanoparticles and oxide nanoparticles have been used for improving the mechanical properties of FMLs, and ABJs. The performed studies revealed that the efficiency of nanoparticles in improving the properties of FMLs and ABJs mainly dependent on various factors such as surface treatment of metal sheets, type of nanoparticles, the morphology of nanoparticles, the size of samples, fabrication parameters, etc. However, the effects of parameters on the properties of FMLs and ABJs reinforced with nanoparticles have not considerably discussed in the literature. This review paper aims to review the existing related papers regarding the effects of nanoparticles on the mechanical properties of FMLs and ABJs in the term of adhesion between metal sheets and polymers.

Pulsed laser texturing for improved adhesive-bonded polyethylene (PE) joints

Nanosecond pulsed laser texturing was performed on pigmented polyethylene (PE) specimens with a 1064 nm fiber laser with the aim of improving adhesive-bonded joint strength. A Design-of-Experiments (DoE) was employed to optimize process parameters and determine the effects of average laser power, scanning velocity and hatch spacing on the resulting failure load of PE joints bonded with Teroson 9399. Failure load increased with laser energy dose up to the onset of macroscopic melting. Laser scanning strategies minimizing heat accumulation yielded best results as the energy dose could be increased as much as possible prior to onset of melting. The process exhibited highest sensitivity to heat accumulation in the laser scanning direction, favoring large pulse separation distances in the scanning direction and moderate pulse overlap in the lateral direction. With a focused spot diameter of 60 μm and a repetition rate of 20 kHz, a maximum failure load of 0.93 kN (1.49 MPa, standard deviation 0.01 kN) was achieved with a crossing-line laser scanning strategy, 25 μm hatch spacing, 3 W average power and 2500 mm/s scanning velocity. Under these conditions, purely cohesive failure took place yielding a 79% improvement in failure load over standard primed joints.

Experimental study on the influences of different surface treatment processes and adhesive type on the aluminum adhesive-bonded joint strength

Surface roughness obtained from different preparation processes such as sanding, shot blasting, and sand blasting were considered in this study. The effects of surface roughness on shear strength of single-lap adhesive joint were examined. 2024-T3 aluminum sheets were cut into standard pieces and then sanded with seven sandpapers with different mesh, shot blasted for four different duration times and sandblasted under four different pressures. Pairs of prepared surfaces were attached using Araldite 2015 adhesive with high viscosity and HPL1012/HPH112 epoxy adhesive with low viscosity. Results show that the ultimate lap shear strength of the sanded samples initially increase and then decrease as surface roughness is increased. The lap joint strength continuously increases as the surface roughness of shot blasted and sand blasted samples are increased. In sanding, the optimum surface roughness is different for both high and low viscosity adhesives. However, for shot blasting and sand blasting, the optimum surface roughness is the same for both adhesive types. The maximum ultimate lap shear strength of joints for both types of adhesives obtained for sand blasting under 0.6 MPa pressure with 0.6 μm surface roughness.

Investigation of the dynamic characteristics of a carbon-fiber-reinforced epoxy with adhesive-jointed structure

Structural adhesives are used extensively in the automotive industry, especially in lightweight composite structures where conventional welding is not possible. Nevertheless, in finite element modeling, adhesive modeling introduces errors in the analysis results. In this paper, the authors propose the concept of modeling composite structures assembled with a structural adhesive for structural dynamic analysis. Several models of a double-flanged hat–plate adhesive-bonded joint structure were virtually constructed from carbon-fiber reinforced epoxy, and their performances were compared in a parametric study. All performance criteria were linked to the computational cost, permitting an efficient structural dynamic analysis. To smooth any pre-assembly uncertainties, the individual components were updated by a sensitivity and optimization app (MSC Nastran SOL 200). The dynamic characteristics of the structures were obtained in impact tests under free–free boundary conditions. To assess the accuracies of the FE models of the adhesive-jointed structures, the natural frequencies and mode shapes of each structure were compared with their experimental counterparts. Different types of feasible element connectors for the structural adhesive were also investigated. The proposed ADHSV-based element model was found to represent the structural adhesives both accurately and efficiently.

Experimental analysis and prediction of strength of adhesive-bonded single-lap composite joints: Taguchi and artificial neural network approaches

Adhesive-bonded joints made up of composite materials offer complex structures with the ease of joining similar or dissimilar materials. The failure behavior of adhesive-bonded joints is influenced largely by geometrical parameters (overlap length and adhesive thickness) and adherend surface preparations. The glass fiber-reinforced epoxy composites are prepared for single-lap adhesive joints to know their strength with different sets of geometrical factors. The adherend surfaces of composites are roughened to 2 ± 0.1 µm, prior to joint preparation. Taguchi L9 experimental matrix representing different combinations of overlap length and adhesive thickness is employed to know the behavior of failure load (FL) and shear strengths (SS) of the adhesive-bonded single-lap composite joints. The results showed that the impact of overlap length of adhesive-bonded joints is more compared to that of adhesive thickness. The interaction effects of geometrical parameters are found negligible toward both the outputs. The optimal factor levels received the highest load to fracture; the joints are found equal to 6096.1 N for FL and 80 MPa for SS, respectively. The empirical relationship based on multiple linear regression (MLR) equations is derived for both the failure load and shear strength. Levenberg–Marquardt algorithm-trained neural networks (NNs) are used for the prediction of both responses. Ten experimental cases are used to check the prediction capabilities of both MLR and NNs. The mean absolute percent error in prediction of both the responses is found equal to 2.27% for NNs and 3.12% for MLR. The NNs and MLR results in accurate prediction might be due to the model development process based on experimental input–output data, rather than assumption-based theoretical and numerical methods.