Ends Of Overlap Research Articles

ÇEKME YÜKÜ UYGULANMIŞ BORU YAPIŞTIRMA BAĞLANTILARINDA BİNDİRME UÇ GEOMETRİSİNİN BAĞLANTI DAYANIMINA ETKİSİNİN ARAŞTIRILMASI

Yapıştırma bağlantıları, farklı bağlantı geometrilerinde oluşturulabilmektedir. Yapıştırma bağlantı tasarımlarında yoğun bir şekilde kullanılan ve üzerinde çok sayıda araştırma yapılmış yapıştırma bağlantı şekillerinden birisi de tek tesirli bindirme bağlantılarıdır. Yapılan çalışmalar sonucunda tek tesirli bindirme bağlantılarının bindirme uçlarında oluşan gerilme yığılmalarının hasarın oluşmasında etkin rol oynadığı belirtilmiştir. Tek tesirli bindirme bağlantılarında, bindirme uçlarında, malzeme azaltılması yapılmasının gerilme yığılmalarını düşürdüğü ve bunun sonucu olarak bağlantı dayanımının arttığı yapılan çalışmalardan anlaşılmaktadır. Dolayısıyla, yapıştırılan malzemelerin bindirme uçlarında malzeme azaltılmasının, farklı bağlantı geometrilerinde dayanıma etkisinin araştırılması önemli olmaktadır. Yapılan bu çalışmada, çekme yüküne maruz bırakılmış boru yapıştırma bağlantıları modellenerek, yapıştırılan boruların bindirme bölgesindeki farklı uç geometrilerinin bağlantı mukavemetine etkisi bir sonlu elemanlar analiz programı olan ANSYS kullanılarak araştırılmıştır. Yapılan çalışmada ilk olarak yapıştırılan boruların uç kısımlarındaki et kalınlığının bağlantı dayanımına etkisi araştırılmıştır. Daha sonra, borunun bindirme bölgesi boyunca et kalınlığı, bindirme ucundan itibaren farklı uzunluklarda modellenerek boru ucu uzunluk değişiminin bağlantı dayanımına etkisi çekme yükü altında araştırılmıştır. Sonuç olarak bu çalışma şartlarında ideal tasarımın Model-4 tasarımı olduğu bulunmuştur. Bu tasarımda yapıştırma bağlantılarında kritik bölge olan yapıştırıcı tabakasının dayanımı % 20,5 oranında artmıştır.

A comprehensive experimental study on bi-adhesive single lap joints using DIC technique

Stress concentrations at the overlap ends are one of the main reasons for strength reduction in adhesive joints. The bi-adhesive technique was introduced as an efficient solution to reduce the stress concentrations at the overlap ends. Although several works have dealt with the numerical analysis of edge effects in bi-adhesive joints, none of them have experimentally analyzed the strain distribution along the bi-adhesive bondline. Moreover, the interaction of some geometrical parameters on the performance of bi-adhesive joints has not been studied yet. The aim of the current research is to present a comprehensive experimental analysis of bi-adhesive single lap joints using the digital image correlation (DIC) technique. Therefore, two different adhesives (one stiff and one flexible) were selected. Different parameters such as adhesive thickness, substrate thickness and length ratio (length of flexible adhesive at one overlap end to the total overlap length) were considered. Furthermore, the interaction of these parameters were experimentally analyzed using the DIC method. A numerical analysis was also conducted to analyze the effect of length ratio on the strain distribution along the bondline. Based on the results, the failure initiates at the interface between the stiff and flexible adhesives and kinks through the brittle adhesive. DIC results illustrate that the effect of length ratio on the adhesive peel strain increases by increasing the adhesive thickness and decreases by increasing the adherend stiffness.

Numerical stress analysis for single-lap adhesive joint under thermo-mechanical load using non-linear material

A comprehensive stress analysis by means of Finite Element Method (FEM) for single-lap joint subjected to thermal and mechanical loads is presented in this paper. Simulation is used to predict the effect of residual thermal stresses (caused by difference of temperature of use and elevated temperature during the assembly of the joint) on stress distribution within adhesive layer. The residual thermal stresses are assigned to joint members as initial condition before the mechanical load is applied. The FEM model employs linear and nonlinear material model and accounts for geometrical nonlinearity. It is confirmed that the difference between the manufacturing and the ambient temperature results in high residual thermal stresses, especially in axial and lateral directions of the joint. The calculation of total stress as superposition of thermal and mechanical stresses works only for linear materials. Moreover, simultaneous application of temperature and mechanical load (applied strain in case of displacement controlled test) in FEM produces inaccurate results, since in real situation the strain is applied to already thermally loaded structure. It is also found that the residual thermal stresses may reduce the peel and shear stress concentration in the adhesive at the ends of overlap and the shear stress within the overlap.

BASİT BİNDİRMELİ YAPIŞTIRMA BAĞLANTILARINDA BİNDİRME BÖLGESİ UÇ AÇI DEĞİŞİMİNİN BAĞLANTI MUKAVEMETİNE ETKİSİNİN SAYISAL OLARAK İNCELENMESİ

In adhesive bonded joints, it is recommended to design the bonding region, which is the critical zone, so that the shear stress acts. In general, the peel stresses in the adhesive joints are primarily effective in causing failure. In simple overlap joints with tensile load applied, peel stresses occur in the overlap ends by the effect of rotation. When designing simple overlap joints, it is important to design so as to minimize the effect of peel stress. In this study, in order to investigate the effect of designing the overlapping ends of the bonded materials at different angles on the joint strength, simple overlap connection models with six different tip angles (90° , 75° , 60° , 45° , 30° and 15°) were created in Ansys finite element analysis program and nonlinear stress and failure analysis was performed under the applied tensile load of the joints. As a result of the analysis, it was seen that the bond strength increased in angled models compared to the reference model (90° end angle model). According to the reference model, a strength increase of 29.1% was detected in the 15° end angle model.

Numerical modelling of multi-material graded joints under shear loading

Due to environmental concerns, modern transportation solutions demand drastic reductions of fuel consumption and emissions, which can only be achieved with advanced structures using high-performance lightweight materials. For joining these dissimilar materials, adhesive bonding appears as an optimal solution, since mechanical fastening adds weight to the structure, and welding technology is not easily applicable to reinforced plastics and composites. However, one of the major drawbacks associated with bonded joints is the presence of stress concentrations at the overlap ends, especially in single lap joints. In order to reduce these stress concentrations, several techniques have been developed. One of these is the functionally graded adhesive, in which the adhesive properties gradually vary along the overlap length, leading to a more uniform stresses distribution and improving the joint strength. However, the manufacture of an adhesive layer with properties which gradually vary is complex in practice and so is the creation of numerical models that represent these configurations. In the present work, a numerical model for different-graded distribution of adhesive properties along the overlap was developed, using programmed step functions on finite element analysis background in order to discretize and simplify the continuous properties distribution gradient. Cohesive zone modelling was introduced in the numerical model, enabling it to effectively predict graded joint strength. The model was validated with experimental results of functionally graded joints available in the literature. The numerical model developed presents itself as a powerful tool to predict joint strength for functionally graded joints, without imposing large computational demands.

Thermoelastic effect on inter-laminar embedded delamination characteristics in Spar Wingskin Joints made with laminated FRP composites

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.

Three-dimensional adhesion failure analysis of the single lap joint having pre-embedded circular defects

The present research aims to study the growth of the circular adhesion failure pre-existing at the interfaces of the strap adherend and the adhesive in a single lap joint. Three-dimensional nonlinear finite element analysis of adhesively bonded single lap joints made with high strength steel adherends under uniformly applied extension have been carried out. The interfacial stresses and strain energy release rate values, being indicative parameters, in the growth of the adhesion failures are computed in the vicinity of the pre-existing circular adhesion failure fronts when the load on single lap joint increases till failure. The magnitudes of the strain energy release rate are computed using the virtual crack closure technique. The results show that the sizes of the adhesion failure significantly influence the magnitudes of the interfacial stresses, the three modes of strain energy release rates and the load-bearing capacity of the single lap joint. The finite element analysis predicts that pre-embedded circular adhesion failures will not have grown from the pre-embedded circular adhesion failure front, instead the failure will be initiated from the overlap ends upon loading for the adhesive bonded single lap joint made with strong adherends and AV119 adhesive. The finite element analysis also proposes a method to calculate the strength of this type of joint configurations using the global shear strength of the adhesive and the intact bonded area. The finite element analysis predicted failure strength of the single lap joint is in good agreement with the experimentally obtained strength for the single lap joint containing pre-existing circular adhesion failure.

Experimental and numerical investigations of adhesively bonded CFRP single-lap joints subjected to tensile loads

In this study, both experimental tests and numerical simulation are implemented to investigate the tensile performance of adhesively bonded CFRP single-lap joints (SLJs). The study considers 7 different overlap lengths, 5 adherend widths and 3 stacking sequences of the joints. Three-dimensional (3D) finite element (FE) models are established to simulate the tensile behavior of SLJs. The failure loads and failure modes of SLJs are investigated systematically by means of FE models and they are in good agreement with those of experiments, proving the accuracy of finite element method (FEM). It is found that increasing the adherend width can improve the load-carrying capacity of the joint better than increasing the overlap length does. Moreover, choosing 0° ply as the first ply is also beneficial for upgrading joint's strength. With respect to failure modes, cohesive failure in adhesive and delamination in adherend take dominant, while matrix cracking and fiber fracture only play a small part. With overlap length increasing or adherend width decreasing, cohesive failure takes up a smaller and smaller proportion of whole failure area, but the opposite is true for delamination. SLJs bonded with [0/45/-45/90]3S adherends are prone to cohesive failure, and [90/-45/45/0]3S adherends are easy to appear delamination. Both shear and peel stress along the bondline indicate symmetrical and non-uniform distributions with great stress gradient near the overlap ends. As the load increases, the high stress zone shifts from the end to the middle of the bondline, corresponding to the damage initiation and propagation in the adhesive layer.

Numerical stress analysis in adhesive joints under thermo-mechanical load using model with special boundary conditions

A numerical study of the adhesivejoint made of similar and dissimilar adherends subjected to thermo-mechanical loading is presented. A comprehensive numerical model was used for this purpose with the novel displacement coupling conditions which are able to correctly represent monoclinic materials (off-axis layers of composite laminates). The geometrical nonlinearity as well as nonlinear material model are also taken into account. Three different types of single-lap and double-lap adhesive joints are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). This paper focuses on the parameters which have the majoreffect on the peel and shear stress distribution within adhesive layer at the overlap ends. The comparison of behaviour of single-and double-lap joints in relation to these parameters is made. The master curves for maximum stress (peel and shear) at the ends of the overlap with respect to the bending stiffness and axial modulus of the adherends are constructed by analysing stress distributions in the middle of the adhesive.The main conclusions of this paper are: the maximum peel stress value for SLJ is reduced with increase of the adherend bending stiffness and for DLJ,similar behaviour was observed at the end next to the inner plate corner, while, at the end next to the outer plate corner peel stress is reduced with increase of adherend axial modulus.

Surface toughening – a concept to decrease stress peaks in bonded joints

ABSTRACTBy using fiber-reinforced plastics as the material for lightweight structures, adhesive bonding becomes an increasingly focused solution for joining these components. In comparison to bolted joints, adhesive bonding has a lot of known benefits, e.g. sealing, no weakening of adherends and a homogeneous load transfer. However, the stress distributions in single-lap joints are not homogeneous all over. Both the shear and peel stress distribution have a peak at the overlap ends of the joint and a lower loaded part in the middle, as shown by Volkersen and Goland and Reissner. In order to reduce these stress concentrations, there are known concepts for the modification of the joint. In this paper, adherend chamfering, different adhesive spew fillet geometries, and the mixed adhesive joint are investigated and compared to a novel local adherend surface toughening concept by using a thermoplastic PVDF layer. A high-resolution digital image correlation is used to visualize the deformation in the bondline. While the state-of-the-art used concepts do not show a high increase of joint strength for single lap joints, the joint strength for the surface toughening specimens can be increased by up to 84%.

3D explicit finite element analysis of tensile failure behavior in adhesive-bonded composite single-lap joints

The tensile failure behavior in adhesive-bonded composite single-lap joints with different overlap lengths is investigated through experiments and various three-dimensional (3D) explicit finite element methods (FEMs). Different failure modes are observed in different overlap lengths. Three parameterized finite element models are developed to discuss the accuracy and applicability of the 3D explicit FEMs based on different modeling strategies and improved failure criteria. All criteria are programmed with the explicit user subroutines employing element deletion to avoid convergence problems caused by element distortion. The load-displacement curves predicted by these models are consistent with the experimental results, while the prediction of failure morphology depends on model types. The models neglecting interface elements cannot simulate the delamination when cohesive zone models (CZMs) are adopted to predict adhesive failure. The influence of CZMs on delamination is analyzed comprehensively to address this problem. Analysis of stress distribution in an overlap of a length of 10 mm indicates that the peak stress of the adhesive layer occurs on the overlap ends along the axial direction, coinciding with implicit results.

Adhesion failure propagation analyses of Spar Wingskin Joints made with curved laminated FRP composite and FGM panels

Spar Wingskin Joint (SWJ) comprises of a thin spar which overlaps and is co-cured to a thick wingskin by suitable adhesive materials. These joints are mostly used in integral modular fabrication of aircraft and fuselage wing structures usually made with curved laminated Fibre Reinforced Polymeric (FRP) composite panels. This paper deals with the analyses of initiation of adhesion failure and its propagation in SWJs subjected to transverse loadings using Finite Element Analyses (FEA) and fracture mechanics approach. Normal and shear stress distributions at different interfacial locations between the adherends and the adhesive have been evaluated. Tsai-Wu coupled stress failure criteria have been used to identify the location of onset of adhesion failure. The critical location for onset of adhesion failure has been found to be at the toe-end of the spar wingskin overlap region. Pre-embedded adhesion failure has been simulated at this location and Strain Energy Release Rate (SERR) components corresponding to Mode I, Mode II and Mode III of adhesion failure have been determined using the principle of Virtual Crack Closure Technique (VCCT). Rate of propagation of adhesion failure has been evaluated by sequential release of Multi-Point Constraint (MPC) and contact finite elements provided at the pre-embedded failure front. It has been observed that Mode I component of SERR primarily governs the process of adhesion failure propagation. The appropriate spar overlap length on the wingskin has been determined in order to prevent adhesion failure. Further, an attempt has been made to improve the structural integrity of the SWJ by reducing the stress concentration at the ends of spar and wingskin overlap. This has been achieved by obtaining a favourable stress distribution over the entire joint structure by using Functionally Graded Materials (FGM) in the spar and wingskin adherend instead of FRP composite panels. Exponential gradation indices have been used for material grading of the spar and wingskin adherends. It has been seen that peel and shear stresses and values of SERR components as well as total SERR reduce significantly by use of FGMs with suitable exponential material grading index.

Evaluation of optimum configuration of adhesively bonded reverse bent joints

Adhesive bonding techniques have increased its application in automobile industries. The most common bonded joint configuration is the lap-shear joint, which when subjected to loading shows a differential substrate straining at the overlap ends. One of the methods to improve its performance is by introducing a reverse bent angle to the adherends at the overlap area. In this paper, the parameters which affect the strength of the reverse bend joints are found out by conducting experiments on different specimens. A detailed study was carried out showing the trends in the joint performance by varying the input parameters. Preformed angle at the overlap area, overlap length, ultimate tensile strength and modulus of the substrates have shown significant effect on the improvement of strength. For most of the adherends used in the automotive industries it has been found that a 10 degree preformed reverse bend joint consistently showed a 15 percent improvement in the strength compared to the traditional lap-shear joint. A model was developed based on Artificial Neural Networking system identification methods to predict the optimum joint configuration based on the given input parameters. This can be used to design high-performance adhesive bonded joints for parts and assemblies in automotive and aerospace industries.

Tensile Strength Assessments of CFRP Adhesive Bonded Joint

In this paper, stress distribution analysis and tensile strength assessment of CFRP bonded joint were studied. First a mixture of Epoxy adhesives and MWCNT was fabricated. Since failure is initiated at the ends of overlap, the stress distribution at the ends of the overlap and bonded joint was numerically analyzed. After the stress distributions were analyzed based on the result obtained the experimental steps were followed to assess the tensile strength of bonded joint. The stress distribution analysis and the tensile strength assessment results showed an agreement that the geometrical factors directly affect the reliability of the bond.

Motor Protein Accumulation on Antiparallel Microtubule Overlaps

Biopolymers serve as one-dimensional tracks on which motor proteins move to perform their biological roles. Motor protein phenomena have inspired theoretical models of one-dimensional transport, crowding, and jamming. Experiments studying the motion of Xklp1 motors on reconstituted antiparallel microtubule overlaps demonstrated that motors recruited to the overlap walk toward the plus end of individual microtubules and frequently switch between filaments. We study a model of this system that couples the totally asymmetric simple exclusion process for motor motion with switches between antiparallel filaments and binding kinetics. We determine steady-state motor density profiles for fixed-length overlaps using exact and approximate solutions of the continuum differential equations and compare to kinetic Monte Carlo simulations. Overlap motor density profiles and motor trajectories resemble experimental measurements. The phase diagram of the model is similar to the single-filament case for low switching rate, while for high switching rate we find a new (to our knowledge) low density-high density-low density-high density phase. The overlap center region, far from the overlap ends, has a constant motor density as one would naïvely expect. However, rather than following a simple binding equilibrium, the center motor density depends on total overlap length, motor speed, and motor switching rate. The size of the crowded boundary layer near the overlap ends is also dependent on the overlap length and switching rate in addition to the motor speed and bulk concentration. The antiparallel microtubule overlap geometry may offer a previously unrecognized mechanism for biological regulation of protein concentration and consequent activity.

Inter-laminar delamination analyses of Spar Wingskin Joints made with flat FRP composite laminates

3D Finite Element Analyses have been carried out for Spar Wingskin Joints made with laminated Graphite Fibre Reinforced Plastic composites subjected to uniformly distributed transverse load. The delamination has been pre-embedded at the most likely location, i.e. in resin layer between the top and next ply of the fibre reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar peel and shear stresses responsible for causing delamination damage have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Mode I Strain energy release rate (GI) primarily governs the process of delamination propagation.

Progressive failure and experimental study of adhesively bonded composite single-lap joints subjected to axial tensile loads

Experimental tests and finite element method (FEM) simulation were implemented to investigate T700/TDE86 composite laminate single-lap joints with different adhesive overlap areas and adherend laminate thickness. Three-dimensional finite element models of the joints having various overlap experimental parameters have been established. The damage initiation and progressive evolution of the laminates were predicted based on Hashin criterion and continuum damage mechanics. The delamination of the laminates and the failure of the adhesive were simulated by cohesive zone model. The simulation results agree well with the experimental results, proving the applicability of FEM. Damage contours and stress distribution analysis of the joints show that the failure modes of single-lap joints are related to various adhesive areas and adherend thickness. The minimum strength of the lap with defective adhesive layer was obtained, but the influence of the adhesive with defect zone on lap strength was not decisive. Moreover, the adhesive with spew-fillets can enhance the lap strength of joint. The shear and normal stress concentrations are severe at the ends of single-lap joints, and are the initiation of the failure. Analysis of the stress distribution of SL-2-0.2-P/D/S joints indicates that the maximum normal and shear stresses of the adhesive layer emerge on the overlap ends along the adhesive length. However, for the SL-2-0.2-D joint, the maximum normal stress emerges at the adjacent middle position of the defect zone along the adhesive width; for the SL-2-0.2-S joint, the maximum normal stress and shear stress emerge on both edges along the adhesive width.

Bending moment calculation for single lap joints with composite laminate adherends including bending-extensional coupling

This work deals with the analytical determination of section forces and moments in adhesively bonded single lap joints with composite laminate adherends including bending-extensional coupling. The analysis is also valid for unbalanced joints and the adhesive thickness is taken into account in the model. Several types of boundary conditions can be applied, e.g. simply supported ends, fixed ends, bonded doubler and single strap joints. Various configurations are studied and the results are compared to finite element analyses and other analytical approaches. Good agreement is achieved over a wide range of configurations. A closed form analytical solution is given for the section forces and moments at the overlap ends.

Behaviour of Bi-Adhesive in Double-Strap Joint with Embedded Patch Subjected to Bending

Abstract In this study, behaviour of bi-adhesive used in the repair of damaged parts was analyzed, using the finite element method. In a double-strap joint with an embedded patch, patch is embedded into the adherents for structural requirements. In addition, to increase the strength of the joint, two adhesives are used to bond the adherents. This approach reduces stress concentration at the overlap ends, increases the load capacity and delays the failure. These effects give rise to higher joint strength. For this purpose, a stiff adhesive, FM73 produced by Cytec Fiberite, was applied in the middle portion of the overlap, while a softer adhesive, SBT9244 from 3M, was applied towards the edges, prone to stress concentrations. Non-linear finite element analyses were carried out to predict the failure loads, to assist with the geometric design and to identify effective ratios of sizes to maximize joint strength.

Strength of single-lap-joint assemblies of continuous unidirectional carbon fibre-reinforced thermoplastic matrix tapes under tensile loading

Unidirectional tape-placement technologies appeared as a promising alternative due to their potential in large-scale component production. While the optimization strategies used to define the tape lay-out can be of different nature, the utilization of tape-to-tape joints is inevitable. Whereas several studies have focussed their efforts on the process and design stages, no study has yet addressed the influence of the manufacturing process on the mechanics of unidirectional tape joints. In this study, the strength of single-lap-joint assemblies of carbon fibre-reinforced thermoplastic tapes under tensile loading was analysed. The dependence of the strength on the overlap geometry and the manufacturing pressure was of main focus. Single-lap-joint assemblies with rectangular and rounded overlaps of the same overlap area were prepared employing a pre-heating stage at 250℃ and forming pressures from 3 to 100 bar. Failure of the assemblies was not observed on the overlap itself but instead on the zone near the overlap end on the adherend. Traditional determination of strength of single-lap-joint assemblies is not applicable in this case. Consequently, a typical Hashin failure criterion was used to model the failure of the assemblies. The study showed that although cohesive failure is not likely within the analysed pressure range, overlap geometry and forming-pressure affect the strength of single-lap-joint assemblies under tensile loading.