Adhesively-bonded Single Lap Joints Research Articles

Investigation of low-cycle fatigue in adhesively-bonded single-lap joints

Adhesively bonded joints are used as an alternative to classical mechanical joining methods, e.g., bolts, rivets, welding, and soldering, due to their advantages such as high strength, uniform stress distribution, and good fatigue resistance. These adhesively bonded joints are becoming more and more important, especially in fields where weight is critical, such as aviation and aerospace. Adhesively bonded joints are preferred because they offer highly reliable connections. In the present study, the low-cycle fatigue of materials joined together as adhesively bonded single-lap joints were investigated experimentally and numerically. Joints of aluminum and steel samples were subjected to variable loads that were lower than the experimentally obtained average breaking loads, and the number of cycles was determined. As a result, the fatigue life of adhesively bonded single-lap stainless steel samples was observed to be higher than that of aluminum samples. In addition, it was also observed that smudging adhesive around the endpoints of the joint significantly increased the fatigue life of steel samples.

Experimental investigation on enhancing the adhesive bonding behaviour of titanium-di-oxide-based BK-9 adhesives under varying ambient temperature

ABSTRACT Adhesive bonding has become increasingly popular in the aeronautic and automobile sectors due to its ability to reduce weight, create strong bonds, and join dissimilar materials. The primary aim of the study is to conduct experimental analysis on Single-Lap Joints (SLJs), specifically focusing on varying ambient temperatures from (25°C to 65°C) while keeping the loading rate constant at 1.3 mm/min. This study used SAE 1020 steel, AA2024-T3, and BK-9 adhesive to manufacture SLJs. The adhesive-bonded SLJs were developed using dissimilar and similar adherends. The thermal behavior of the BK-9 adhesive was examined by conducting Digital Scanning Calorimetry (DSC) and Thermal Gravimetry Analysis (TGA) before and after subjecting it to elevated temperatures. The bonding quality has been examined using ultrasonic testing. The failure strength of the adhesive bond on SLJs was performed at the Universal Testing Machine (UTM) using tensile testing equipment, and a Field Emission Scanning Electron Microscope (FESEM) was utilized to determine the failure patterns. The result indicate that the SAE 1020-SAE 1020 steel joints exhibited superior mechanical behaviour, showing the highest failure load of 5.120 kN at 25°C room temperature, respectively.

Numerical analysis and optimization of adhesively-bonded single lap joints by adherend notching using a full factorial design of experiment

The objective of this study is to carry out experiments using the experimental design methodology to determine the optimal geometric configuration which improves the resistance of a single-lap joint with notched adherends subjected to uniaxial tensile load. On the sides of the adherends in contact with the adhesive layer, a longitudinal rectangular notch is introduced. A complete experimental design (15) of three factors at two levels: the adhesive thickness (tA), depth (dN) and extended length (LE) of the notch was used to determine their effects on strength of an adhesive joint. The response or dependent variable used was the resistance of a single lap joint (SLJ). Finite element (FE) analysis was conducted to investigate the effect of different notch parameters on the strength enhancement of the SLJs. A quadratic regression model with interaction is developed to relate the strength of an adhesive joint and the variables (tA, dN and LE). The regression model was validated using various statistical approaches. According to the ANOVA results, the model is highly significant and in good agreement with the experimental results. The quadratic regression model suggested was used for optimizing the resistance of the joint. The maximum joint strength occurs when the adhesive thickness is the smallest (left end) and when the adhesive thickness is the largest (right end) of the validated domain. The strength of SLJ increases when the notching parameters (dN and LE) increase in the validation zone. The numerical results show that to improve the resistance of an adhesive joint with notched adherend, it is necessary to minimize the thickness of the adhesive layer and to use notch with the highest depth and extension equal or greater than the overlap. The results show that using the adherend notching can significantly improve the load bearing capacity of SLJs.

Elasto-plastic adhesive joint design approach by a radial point interpolation meshless method

ABSTRACT For efficient use of adhesive joints, reliable prediction techniques should be made available to the designer. Simulation of these joints’ behaviour is usually performed using the Finite Element Method (FEM). However, it is known that, in adhesive joints, the adhesive thickness (t A) is much smaller than the adherend thickness (t P), thus requiring a highly refined mesh to produce good results. Linked to this, the adhesive has to withstand high strains, causing mesh distortion and hindering the resolution. In these cases, meshless methods can be a good alternative. This work aims to implement the von Mises (vM) and Exponent Drucker-Prager (EDP) criteria combined with a meshless formulation based on the Radial Point Interpolation Method (RPIM), for the strength prediction of adhesively-bonded single-lap joints (SLJ). Validation with experiments is undertaken for joints with brittle to ductile adhesives, with varying overlap lengths (L O). Stress and strain distributions were plotted in the adhesive layer, and the failure load (P m) was assessed by strength of materials failure criteria. Significant adhesive and L O effects were found on P m. The RPIM proved to be a promising tool to predict the behaviour of bonded joints, although some limitations were found by using strength of materials criteria.

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.

Meshless approach to material plasticity in adhesive joints

For an efficient use of adhesive joints, reliable prediction techniques should be made available to the designer. Simulation is usually accomplished by the Finite Element Method (FEM). However, in adhesive joints, the adhesive thickness is much smaller than that of the adherends, thus requiring a refined mesh to produce good results. Linked to this, the adhesive has to withstand high strains, causing mesh distortion and making difficult to attain solution. In these cases, meshless methods can be a good alternative, although these are not sufficiently validated yet. This work aims to implement the von Mises (vM) and Exponent Drucker-Prager (EDP) criteria into a user-built meshless method software based on the Radial Point Interpolation Method (RPIM), for the strength prediction of adhesively-bonded single-lap joints (SLJ). Validation with experiments is undertaken for a medium-ductile adhesive (Araldite® 2015) with varying overlap lengths (LO). Stress and strain distributions were plotted in the adhesive layer, and the failure load (Pm) was assessed by continuum mechanics failure criteria. The meshless method showed to be promising in predicting the behavior of bonded joints, although limitations were found by using continuum mechanics criteria.

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 fracture load analysis of different support patches in adhesively bonded single-lap joints

Adhesively bonded joints are frequently used in the aviation and automotive industries. Bending appears in the bonded materials as a result of eccentric loading when tensile loading is applied to an adhesively bonded single-lap joint (SLJ) geometry. As a result of this bending, moment effect occurs in the overlap region in the joints joined with the adhesive. This moment effect causes peel stresses at the edges of the overlap region of the joint such that these stresses are the main reasons of the damage in the joint. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. In this study, support patches were added at a varying distances from the overlap region to decrease the bending effect occurring in adhesively bonded single-lap joints. In the study, adhesive bonded single-lap joints were produced by using DP460 liquid structural epoxy as the adhesive, AA2024-T3 aluminum alloy as the adherend and flat or curved AA2024-T3 aluminum alloy and AISI 304 steel with different thickness as the support patches. As a result, when the failure load obtained from the experiments was examined, the use of support patches in single-lap joints increased the damage load of the joint between approximately 16% and 94%. However, such increases in the damage load are highly dependent on the type, thickness, geometry (flat or curved) and positioning of the support patches.

Investigation of internal step and metal part reinforcement on joint strength in the adhesively bonded joint: Experimental and numerical analysis

Many studies have been performed to increase the failure load of adhesively bonded joints, which enable different types of materials to be joined together for use in the aerospace and automotive sectors. In studies from published literature, various methods have been used to increase the failure load of joints, such as altering the joint geometry, investigating additives to the adhesive or changing the overlap area parameters. This study experimentally and numerically investigated the mechanical properties of single lap joints obtained by applying internal steps of different lengths to the overlap region of the joints and adding metal pieces of different lengths. In the study, adhesive bonded single-lap joints were produced by using DP460 liquid structural epoxy as the adhesive, AA2024-T3 aluminum alloy as the adherend and AISI 1040 steel as the metal piece. As a result, the internal step lap joint (ISLJ) and metal piece reinforced lap joint (MRLJ) type was found to carry more load than single lap joint (SLJ) type. Also, the change in the step length in the ISLJ and the metal piece length in the MRLJ type had a significant effect on the failure load of the joint. The ISLJ and MRLJ geometry carried about 26–60% and 17–41% more load than the SLJ geometry, respectively. When the failure loads obtained in the experiments and the numerical analysis were examined, it was concluded that their results were quite compatible with each other when the cohesive zone model was used in the numerical analysis.

Evaluation of grit-blasting as a pre-treatment for carbon-fibre thermoplastic composite to aluminium bonded joints tested at static and dynamic loading rates

Light-weighting of transportation structures necessitates multi-material design employing composites and aluminium, with thermoplastic composites being of increasing interest to the industry. Adhesive bonding is a viable solution for joining dissimilar materials, but joint performance can be considerably affected by surface preparation. In this paper, alumina grit-blasting is investigated as a surface preparation technique for thermoplastic-matrix composites to be bonded to aluminium alloys. Grit-blasting is performed on composite adherends for varying durations, and the resulting chemical and morphological modifications are analysed using goniometry, profilometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Adhesively-bonded single-lap joints are tested at quasi-static and dynamic (0.5 m/s) loading rates, and fractography analysis is performed at macro and micro scales. It is found that high lap shear strength and work-to-failure can be achieved through optimisation of the grit-blasting parameters. The optimised process produces a composite surface with plasticised matrix, minimal fibre exposure, and favourable surface chemistry for adhesive bonding. Grit-blasting can thus be a simple, yet effective surface preparation technique for composites to be bonded to aluminium.

Failure behaviour of the single lap joints of angle-plied composites under three point bending tests

In this paper, the response of adhesively-bonded single lap joints (SLJs) with angle-plied composite adherends subjected to flexural loading was investigated. The experiments were carried out for the adherends, glass reinforced polymer matrix, with three kinds of stacking sequence. A three-dimensional finite element (FE) model was developed using ABAQUS/Explicit. The three dimensional Hashin failure criterion with an appropriate damage evolution law was used to characterize the damage inside a ply. Cohesive zone elements were used to model the damage in the adhesive layer (AF163-2K) and the interply failure, that is, the delamination. The developed numerical model was verified with the performed experiments. The SLJs of [±20]5s and [±45]5s failed due to failure in the adhesive layer and the delamination between the plies, whereas that of [±10]5s failed mainly due to the former failure. The intralaminar damage was not noticed for any case. The influence of the fiber angle of plies in the adherends, adherend thickness, overlap length, and the thickness of adhesive layer on the damage in the adhesive layer and the delamination were investigated in terms of the competition between these two failures and activation of different failure modes in each thoroughly.

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.

An Experimental Investigation of Adhesive Bonded Single-Lap Joints

An Experimental Investigation of Adhesive Bonded Single-Lap Joints

Observations on fem modelling of adhesive joint debonding

Polymeric adhesives are widely used to join components in many structural and non-structural applications. Many experimental tests are required to determine critical parameters essential for strength estimation for this type of joints. Observations from numerical analyses, useful for numerical estimation of the break force in an adhesive-bonded single-lap joint, are presented. A formulation of surface energy with the use of data from numerical simulation and the obtained results are shown. The break force of a single lap joint from numerical simulations was compared with the results of the experimental test.

ALÜMİNYUM OKSİT VE TİTANYUM DİOKSİT PARTİKÜL TAKVİYELİ YAPIŞTIRICILARLA BİRLEŞTİRİLMİŞ BAĞLANTILARIN MEKANİK ÖZELLİKLERİNİN DENEYSEL OLARAK BELİRLENMESİ

Havacılık alanında kullanılan yapısal yapıştırıcılar içerisine partikül katılarak elde edilen kompozit yapıştırıcılar, nano teknolojide meydana gelen son gelişmelerle birlikte yapıştırma bağlantılarının tasarımına yeni bir bakış açısı kazandırmıştır. Bu çalışmada; farklı özelliklerdeki yapısal yapıştırıcılar içerisine alüminyum oksit ve titanyum dioksit katılarak elde edilen tek tesirli bindirme bağlantılarının mekanik özellikleri çeki yükü altında deneysel olarak incelenmiştir. DP460, DP270, Araldite2015 ve AV138 yapıştırıcı olarak, ağırlıkça % 1 ve % 2 oranında alüminyum oksit (Al 2 O 3 ) ve titanyum dioksit (TiO 2 ) katkı maddesi olarak, AA2024-T3 alüminyum alaşımı ise yapıştırılan malzeme olarak kullanılmış ve tek tesirli bindirme bağlantı numuneleri üretilmiştir. Deneylerden elde edilen sonuçlar incelendiğinde; partikül katkılı yapıştırıcıların kullanılmasıyla elde edilen bağlantılarda çeki hasar yükünün arttığı görülmüştür. Ayrıca bağlantıların kuvvet-yer değiştirme eğrileri incelendiğinde, partikül katkılı yapıştırıcıyla birleştirilmiş bağlantıların yer değiştirme kapasitelerinin de arttığı belirlenmiştir.

Damage analysis of composite–aluminium adhesively-bonded single-lap joints

Adhesive bonding is used to fabricate structures of complex shape that could not be manufactured in one piece. In many high performance structures, joints between composite materials with other light metals such as aluminium are required for structural optimization. This work numerically and experimentally addresses adhesive joints between aluminium and carbon–epoxy composites, considering different adhesives and value of overlap length (LO). Numerically, the Finite Element Method (FEM) coupled with cohesive zone models (CZM) is used to perform a detailed stress analysis that enables the comparison between different planes in the joint and LO values. A damage analysis during damage and crack growth is also considered to fully describe the failure process. The use of the proposed numerical technique enables predicting the joint strength and creating a simple and rapid methodology that can be used in the design of hybrid structures, e.g. in the selection of the joint geometry and adhesive. The joints’ strength and failure modes were highly dependent on the adhesive, and this behaviour was successfully modelled numerically. Using a brittle adhesive resulted in a negligible maximum load (Pm) improvement with LO. The joints bonded with the ductile adhesive showed a nearly linear improvement of Pm with LO.

Simple approach for 2D-DIC with dual field of view

A simple and cost-effective optical layout based on the dual field of view for the 2D digital image correlation (DIC) method is used to simultaneously measure in-plane displacement fields of large and small portions of a specimen. This optical configuration was composed of two high-resolution cameras with two different lenses and a beam splitter. The surface of a specimen was acquired simultaneously using both cameras with narrow and wide fields of view. One of the two cameras was placed directly in front of a specimen, whereas the other camera acquired the image of the same specimen reflected from the beam splitter. All stored images were appropriately processed using a digital image correlation algorithm to extract displacement and strain fields. To show the applicability and usefulness of this configuration, two tests were performed: (i) lower and upper adherends deflections of an adhesive-bonded single lap joint specimen were obtained, and shear strain in the adhesive layer at the edge of the overlap was also attained; and (ii) relatively large displacements of a cracked cantilever beam were evaluated, and maps of small deformation near crack tip were assessed. The results were obtained considering different speckle patterns and distinct subset sizes.

Dynamic strain distribution measurement and crack detection of an adhesive-bonded single-lap joint under cyclic loading using embedded FBG

In this study, the dynamic strain distribution measurement of an adhesive-bonded single-lap joint was carried out in a cyclic load test using a fiber Bragg grating (FBG) sensor embedded into the adhesive/adherend interface along the overlap length direction. Unidirectional carbon fiber reinforced plastic (CFRP) substrates were bonded by epoxy resin to form the joint, and the FBG sensor was embedded into the surface of one substrate during its curing. The measurement was carried out with a sampling rate of 5 Hz by the sensing system, based on the optical frequency domain reflectometry (OFDR) throughout the test. A finite element analysis (FEA) was performed for the measurement evaluation using a three-dimensional model, which included the embedded FBG sensor. The crack detection method, based on the longitudinal strain distribution measurement, was introduced and performed to estimate the cracks that occurred at the adhesive/adherend interface in the test.

Acoustic Emission on Adhesively Bonded Single-Lap Joints of Composite Laminate during Tensile Test

Acoustic emission (AE) was used to monitor the tensile test of composites with adhesive specimens. The mechanical response behavior, damage and failure characteristics, and the corresponding AE characteristics of the composites have been investigated. The results show that the load of the join with defect in the adhesive layer is lower than the join with no defect. The higher AE relative energy and the AE amplitude were obtained in the adhesive specimen with defect in the adhesive layer whereas the variation of the AE relative energy is different from the adhesive specimen with on defect. The characteristics such as AE amplitude distribution, relative energy and cumulative hits are connected with the tensile damage and failure of the adhesively bonded single-lap joints of composite laminate. In the actual AE monitoring, these feature parameters should be considered entirely assess the damage and failure of the composites structures.

J0450304 分布型光ファイバセンサを用いた接着継手試験片のはく離検知に関する研究([J045-03]知的材料・構造システム(3),機械材料・材料加工部門)

J0450304 分布型光ファイバセンサを用いた接着継手試験片のはく離検知に関する研究([J045-03]知的材料・構造システム(3),機械材料・材料加工部門)