Single Lap Composite Joints Research Papers (original) (raw)

The simplicity and efficiency of the adhesive joints have increased more and more their use in many fields. In ship construction the need to join different materials, such as the bonding of the hull/deck, the sea chest, the portholes, the windshields, the panels of cabins, etc. leads to choosing increasingly the adhesive joints. In this work we have evaluated the effects of both SMP (Silyl Modified Polymer) based adhesives and sealants on single lap joints (SLJs) with dissimilar substrates. Three pairs of single lap joints were taken into account among dissimilar adherends: stainless steel (AISI 316) with PMMA (or Altuglas s) and monolithic composite laminates bonded with glass or PMMA. Before tensile testing some SLJ samples were subjected to a three-dimensional computed tomographic analysis to evaluate how the presence of possible defects in the adhesive layer affects the failure mode. A design of experiments was defined in order to quantify the effect of the considered factors and their correlation. The obtained maximum tensile stress values confirm the data provided by the manufacturer, approximately between 2 and 2.5 MPa, showing generally cohesive fracture. Finally the considered SMP adhesives and sealants are well suited for the chosen different substrates, although special attention should be placed on the glass-GFRP joint as it is confirmed by statistical analysis.

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- Materials Engineering, Mechanical Engineering, Chemical Engineering, Materials Science

Adhesively bonded joints are increasingly being used in joining various structural components made of FRP laminated composites. Adequate understanding of the behavior of adhesively bonded joints is necessary to ensure efficiency, safety and reliability of such joints. While single lap joint has received considerable attention, very little work has been carried out on the double lap joint configuration. The present investigation deals with the static analysis of adhesively bonded double lap joint in laminated FRP composites using three-dimensional theory of elasticity based finite element method. The finite element model is validated with the theoretical concepts. The double lap joint made of generally orthotropic laminates subjected to longitudinal loading is analyzed. The out-of-plane normal and shear stresses are computed at the interfaces of the adherend and adhesive, and at mid surface of the adhesive for different ply orientations in the double lap joint are considered for the ...

- by Anand Kotta
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- by Anand Kotta
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- Materials Science, Structural Engineering, Finite element method, Adhesive

In this work, the effect of an Ytterbium fibre laser treatment on the adhesive properties of scarf bonded carbon fibre reinforced plastics (CFRP) joints has been investigated. The surfaces were scarfed and afterwards laser treated. The effect of laser treatment on the surface morphology was investigated with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The laser treatment resulted in a morphological and chemical change on the CFRP surface. The introduced thermal energy was able to partly strip and roughen up the carbon fibres. The laser treatment increased the carbon and decreased the oxygen, nitrogen and sulphur content on the surface. With the laser treatment the static and fatigue strength of the scarf bonded joints could be improved.

- by Nico Scharnagl
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Adhesively bonded joints are increasingly being used in joining various structural components made of FRP laminated composites. Adequate understanding of the behavior of adhesively bonded joints is necessary to ensure efficiency, safety and reliability of such joints. While single lap joint has received considerable attention, very little work has been carried out on the double lap joint configuration. The present investigation deals with the static analysis of adhesively bonded double lap joint in laminated FRP composites using three-dimensional theory of elasticity based finite element method. The finite element model is validated with the theoretical concepts. The double lap joint made of generally orthotropic laminates subjected to longitudinal loading is analyzed. The outof-plane normal and shear stresses are computed at the interfaces of the adherend and adhesive, and at mid surface of the adhesive for different ply orientations by varying the width of the double lap joint are considered for the analysis. It was predicted that when the fiber angle increases the stiffness of the plate in the longitudinal direction decreases and the interlaminar stresses at joint interfaces increases due to the effect of coupling and also the longitudinal displacement increases.

This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical nonlinearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) compositecomposite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: unidirectional ([0 8 ] T and [90 8 ] T) and quasi-isotropic laminates ([0/45/90/-45] S and [90/45/0/-45] S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.

The Fiber-Tear-Failure (FTF) is a common mode of failure in the adhesively bonded single lap joint having continuous fiber reinforced composite. Within single lap joints, presence of material and geometric discontinuities restrict the applicability of strength of material based approach for failure load prediction. Zone based approach appears promising in tackling discontinuity issues provided the right failure criterion and critical zone size are known. In this paper, a right failure prediction criterion is identified that can be used for the Fiber-Tear-Failure load prediction using zone based approach. Using a carbon fiber composite and an epoxy paste adhesive, failure modes were generated experimentally using different dimensions of lap joints. Several stress/strain based failure criteria for composite were tested. Critical zone size was calculated by performing the finite element analysis on a single lap joint with known failure load. For other joints, failure loads were calculated by adjusting the input loads in the analysis such that the failed zone size became the same as the critical zone size. The result reveals that Azzi-Tsai (Norris) criterion is capable of predicting failure loads of single lap joints with FTF.

- by Niat Rahman
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- Engineering, Materials Science, Structural Engineering, Composite Material

This paper presents the experimental results of a study investigating the effect of holes and notches made on the overlap ends on the strength of adhesive joints. Single-lap joints made of S235JR steel sheets bonded with Araldite 2024-2 epoxy adhesive were tested. For comparative reasons, static shear strength tests and high-cycle fatigue strength tests were performed. Adhesive-filled joints having three holes, each with a diameter of 3 mm, and notches, each 3 mm wide and 4 mm long, were tested and compared with reference joints, i.e. without modification. The assumption was to determine whether the structural modifications would reduce the peak peel and shear stresses that are typical of this type of joints. Results of the static strength tests showed no significant effect of the applied modifications on the strength of the joints. However, in terms of fatigue strength, the results demonstrated a significant improvement in fatigue life, the value of which increased in the low-cycle fatigue region by 328.6% for the joint with notches and by 640.8% for the joint with holes. A smaller yet still positive effect of the applied modifications was shown for high-cycle fatigue. For a variable load with the maximum value of 9 MPa, the fatigue life increased by 215.9% for the variant with notches and by 183.3% for the variant with holes. Surface topography of fatigue fractures was examined by determining roughness parameters on the overlap ends in the samples. Significant differences were shown, with the selected roughness parameters being significantly lower for the reference variant than for the variants with notches and holes. It was shown that the applied structural modifications led to increasing the fatigue strength to 8.5 MPa for the limit number of cycles equal to 2•106, when compared to the reference variant for which the fatigue strength was 8 MPa.

- by Paulina Szawara
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- Science Technology

The three-dimensional (3-D) variation of stresses of the single lap joint (SLJ) made from hard steel and epoxy (AV119) under tensile loading is studied using 3-D FE (finite element) analysis. The peel (tension) stress, direct shear (inplane shear) stress and transverse shear (out-of-plane shear) stress are the responsible for opening (mode-I), sliding (mode-II) and tearing (mode-III) mode of failures, respectively, are computed in the overlap region of the joint. Thin adhesive layer used to join the upper (lap) adherend and the lower (strap) adherend is modelled by surface to surface contact elements. The nonlinear material properties of adhesive and adherend (stress and strain graph obtained from the experiments) are input to the finite element programme. The results show that the variations of peel stress and shear stresses in the overlap region are very complicated in nature and hence a 3-D FE analysis is recommended to have a clear visualisation of these stress variations. The peel stress among all the failure-inducing stresses at the overlap ends are dominant and important for adhesive bonded joint as adhesives are weaker than the stronger adherends. The results of the 3-D FE analysis of the SLJ are in good agreement with the experimental results. This research work is may be considered as detail study of the stress distributions in the vulnerable region of the joint under tensile loading.

- by Sambit Parida
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- Materials Science, Finite element method, Adhesive, Composite Material

In this paper by employing ANSYS Workbench software and three-dimensional finite element simulation, failure analysis of hybrid bonded and bolted single and double lap joints with laminated composite adherends subjected to axial, shear and bending loads were performed. In order to select an appropriate and optimized element number, the convergence behavior of single and double lap joints were investigated. Then the failure study of each single and double lap hybrid composite joints for the three time dependent loading cases were performed. To demonstrate the validity and precision of the presented simulations, the obtained results were compared with the results presented in the available literatures. The results of this research indicated that, in the single lap joint subjected to axial load, the replacement of hybrid bonded bolted joint instead of adhesive joint leads to significant increase of 56% in the load bearing capacity of the joint.

- by Ehsan Selahi
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- Materials Science, Structural Engineering, Finite element method, Adhesive

Adhesive joint Adherend Transient dynamic Laminated Composite Peel and shear stresses A novel semi analytical method is developed for transient analysis of single-lap adhesive joints with laminated composite adherends subjected to dynamical loads. The presented approach has the capability of choosing arbitrary loadings and boundary conditions. In this model, adherends are assumed to be orthotropic plates that pursuant to the classical lamination theory. Stacking sequences can be either symmetric or asymmetric. The adhesive layer is homogenous and isotropic material and modelled as continuously distributed normal and shear springs. By applying constitutive, kinematics, and equations of motions, sets of governing differential equations for each inside and outside of overlap zones are acquired. By solving these equations, the time dependent shear and peel stresses in adhesive layer as well as deflections, stress resultants, and moment resultants in the adherends are computed. The developed results are successfully compared with the experimental research presented in available literates. It is observed that the time variations of adhesive peel and shear stress diagrams are asymmetric for the case of symmetric applied load with high variation rate. Moreover, it is reported that although the magnitude of applied transverse shear force is reduced to 10% of applied axial force, however a significant increase of 40% in the maximum peel stress attained.

- by Ehsan Selahi
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- Materials Science, Adhesive, Isotropy

In this paper, considering an adhesively bonded composite single-lap joint, a novel approach is presented to predict the peel and shear stress distributions of the adhesive layer for an ASTM standard test sample. In the current method, the equilibrium equations are derived using the energy method and based on the Timoshenko's beam theory. Two solution procedures then are discussed; one of them represents a solution approach based on the direct variational method allied with use of the Ritz approximation; while the second one is based on a linear estimating function. Unlike previous methods, in which the variation of stress through the thickness of adhesive is neglected or is assumed to be linear and they cannot be used to analyze the joints with thick adhesive layers; considering the effects of adhesive thickness makes it possible to employ present method to analyze the joints with thick adhesive layers as well as thin ones.

- by Ehsan Selahi
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- Engineering, Materials Science, Stress field, Adhesive

Three-dimensional explicit dynamic simulations are carried out to study the failure of hybrid bolted-bonded vertical T-and L-joints under noncontact underwater explosion shock pressure. In this modelling, adherends are fibrous laminated composites having an orthotropic behavior, while bolts and adhesive layers exhibit an isotropic behavior. It is found that hybrid vertical T-and L-joints display appreciably higher joint resistance to underwater explosion shock pressure than adhesive Tand L-joints.

- by Ehsan Selahi
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- Materials Science, Composite Material, Stress (Linguistics)

Growing awareness about sustainable development and the environmental problems involved in using nonbiodegradable materials has motivated the research community to develop environment-friendly materials. Developments have been achieved in the field of natural fibers and biopolymers, still there remain unanswered questions regarding the high-quality cost-effective manufacturing of natural fiber reinforced composites. The natural fiber-based polymeric composites are being used extensively in engineering applications, especially in the nonstructural parts and components. Near-net processing techniques such as compression molding, extrusion, and injection molding are well-developed for natural fiber reinforced composites. However, secondary processes such as joining, machining, and surface modification are still unexplored and need to be investigated in detail. The present research endeavor is an attempt to experimentally investigate the adhesive joining behavior of jute/sisal reinforced epoxy composites. The laminates based on three different material configurations in woven mat form, namely, pure jute, pure sisal, and hybrid jute/sisal reinforced epoxy have been fabricated by hand layup process. Different lap joint configurations with through holes in adherends overlapping area have been investigated. It has been established experimentally that the holes in the adherends provide a hinge-effect in the overlapping area and help in defining the failure load of the composite joint. The different arrangement of holes has been investigated and the best design of hole arrangement has been proposed for adhesive joining of jute/ sisal fiber reinforced epoxy laminates. It was found that the holes (filled with an epoxy adhesive) in the overlap area result in 6-18% improvement in the failure load for different materials as compared to the joints with only adhesive bonding. Moreover, the field-emission scanning electron microscopy micrographs have been used to understand the failure mechanism of the adhesively bonded natural fiber reinforced composite laminates.

- by Kassahun Gashu Melese ( Ph.D.)
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- Materials Engineering, Materials Science, Adhesive, Epoxy

Single Lap Joints are used extensively in the aerospace industry due to their lower weight and absence of stress concentration due to drilled holes. However, their lesser strength remains an important limitation. Different modes of failures have been reviewed in this article. The bond strength of a single lap joint can be varied by varying its overlap length, while, the strength does not strictly increase with increasing bonding length. Rather, it increases up to an optimum value and decreases further. This optimum value was obtained, which is found to be in agreement with previous studies in this regard. The surfaces of the bonded aluminum plates were modified by generating notch shaped pattern on bonding area. Due to notch pattern of bonding, the bond strength increases up to 75˚ notch angle and then decreases with further increase in the notch angle. The experimental results of bonded joints without notch also were obtained by software analysis. Maximum strength of joint length reached at optimum length and optimum notched surface pattern.

- by Nitinkumar Anekar
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- Mechanical Engineering, Materials Science, Adhesive, Composite Material

- by Andrzej Kubit
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- Science Technology

This paper deals with the structural design of single lap joints (SLJs) with delaminated adherends using fracture mechanics principles. The interlaminar stresses and Strain Energy Release Rate (SERR) are considered as damage characterizing parameters used for designing the SLJ when delamination damages are pre-embedded in both the adherends at similar positions. Three dimensional geometrically non-linear finite element analyses (FEAs) of SLJ with delaminated adherends have been performed to determine the interlaminar and SERR values along the delamination fronts by simulating the simultaneous interaction delamination damages when pre-embedded at similar positions in both the adherends. SERR values are evaluated using Modified Crack Closure Technique (MCCI) which is based on energy principle. The delaminations are assumed to be of linear front, and have been considered to be embedded in both the laminated FRP composite adherends beneath the surface ply of the adhesively bonded SLJ. The delamination damages are presumed either to pre-exist or get evolved at the interlaminar locations. Such delaminations have been modelled using the sublaminate technique. The critical issues of modelling pre-embedded delamination damages are discussed in detail. The numerical results presented in this paper are based on the validated FE model compared with the available literature. Based on the present analyses, the structural design recommendations have been made for the SLJ when pre-embedded delamination damages are present in both the adherends. It is observed from the stress based design that the delamination damage when present in the bottom adherend is more detrimental for failure of SLJ compared to that for the case when it is present in the top adherend. Also, SERR based design reveals that the opening mode predominantly governs the propagation of delamination damage for all positions of the pre-embedded delaminations in both the adherends of the SLJ.

The aim of this study is to investigate the effect of the adherend material on the mode I fracture behaviour of bimaterial composite bonded joints. Both single-material (steel-steel and composite-composite) and bi-material (steel-composite) joints bonded with a structural epoxy adhesive are studied. Additionally, two adhesive bondline thicknesses are considered: 0.4 mm (thin bondline) and 10.1 mm (thick bondline). The Penado-Kanninen reduction scheme is applied to evaluate the mode I strain energy release rate. The results show that the mode I fracture energy, G Ic , is independent of the adherend type and joint configuration (single or bi-material). G Ic shows average values between 0.60 and 0.72 N/mm for thin bondlines and 0.90-1.10 N/mm for thick bondlines. For thin bondlines, the failure is cohesive and the similar degree of constraint that is imposed to the adhesive by the high-modulus (i.e., steel) and/or relatively thick (i.e., composite) adherends results in similar values of G Ic for both single-and bi-material joint types. For thick bondlines, the crack grows closer to one of the adhesiveadherend interfaces, but still within the adhesive. The results show that the adhesive could deform similarly, although the crack has been constrained on one side by different types of adherends, either a steel or composite.

- by Rinze Benedictus
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- Engineering, Materials Science, Adhesive, Epoxy

The high fracture strength and exceptional impact resistance of polymer-based composites are of paramount importance to various industries like aerospace, automotive, and construction. The resin transfer molding (RTM) process is used to produce composite samples of superior quality, minimal porosity, and reduced lamination defects. In the present study, the RTM method was employed to fabricate glass fiber-reinforced composites, aiming to investigate their specific mechanical properties and structural performance. The study initially determined the ballistic limit of the produced samples. Subsequently, experimental investigations were carried out to examine the impact of hole drilling on the tensile strength, flexural strength, and impact resistance of the samples. The results revealed that the produced polymer plate demonstrated a ballistic limit with a pressure of 11 bar and a speed of 104 m/s, leading to ball restriction in the plate. The sample without holes showed the highest fracture force, while samples with three and five holes exhibited reduced fracture forces. Additionally, bending force and impact resistance were lower in samples with multiple holes compared to the sample without holes. The impact resistance of the sample with five holes was the lowest among all configurations. The study revealed that the presence of three holes arranged in a row has a lesser impact on reducing the ultimate tensile force compared to the effect of five holes. Moreover, the bending test results indicated that sample failure occurred on the side under tension, resulting in higher bending forces than tensile forces. Article highlights • Using resin transfer molding (RTM) method to produce high quality polymeric composite samples. • Determination of ballistic limit of glass fiber-reinforced composite samples. • Evaluation of the influence of the hole drilling on the tensile strength, flexural strength, and impact resistance of the samples. • Analysis of bonding and microstructural of the samples by SEM and EDX tests.

- by Alireza Nouri
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- Polymer Composites, Ballistic Impact, Resin Transfer Molding, Impact Resistance

In this study, surface patterning with CNC vertical machining center was applied to the aluminum surface for the enhancement of the shear strength of the epoxy-bonded lap joints. It was found that the pattern shape affected shear strength and among vertical, square, horizontal, 45 degree and diamond patterns, 45-degree provided the highest shear strength of 24.6 MPa. Moreover, the pattern features also affected the shear strength. A decrease in the depth led to slightly lower shear strength, whereas an increase in the depth gave a slight enhancement. The optimum depth was found as 300 μm and the obtained shear strength was calculated as 25.5 MPa. Additionally, an increase in the width length led to lower shear strength. On the other hand, a decrease in the width length provided higher shear strength. The increment became smaller as the width length increased. Also, after a point, the trend reversed and the shear strength decrease slightly. The optimum width length and the corresponding shear strength were found as 1.0 mm and 28.0 MPa, respectively.

- by Harun YAKA
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- Materials Science, Composite Material, Soil Shear Strength

According to the fracture mechanics concept, the distribution of three-dimensional (3-D) three major stresses, i.e. peel stress for mode I, direct shear stress for mode II and transverse shear stress for mode III, are computed at different interfacial layers on curved laminated FRP composite single lap joint (SLJ), subjected to different ply orientation in adherend with application of tensile load. The three interfacial adhesive layers have been considered as; bottom layer (in between lower adherend and adhesive layer), middle layer (mid plane of adhesive layer) and top layer (in between upper adherend and adhesive) for determining the critical location of damage initiation by using failure index criteria. The results show that the variations of peel stress and shear stresses in the overlap region are very complicated in nature and hence a 3-D finite element analysis (FEA) is recommended to have a clear visualization of these stress variations. A comparative analysis due to ply orientation of adherends of SLJ has been carried out. It has been observed that the adhesion failures (in between adherend and adhesive) are more dominated than cohesion failure (within the adhesive layer).

- by Dr. Ranjan Kumar Behera
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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.

- by Dr. Ranjan Kumar Behera
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Single shear or single lap joints are the most prevalent type of adhesive joints used in advanced engineering applications, where they are exposed to fatigue loadings in their services. Although their mechanical performances under static loading have been investigated extensively, the studies related to the fatigue performances were limited. For that purpose, single lap joints’ (SLJs) reaction to fatigue tensile loading was studied by varying the adherend thickness (3 mm to 6 mm) and fatigue load (3250 N to 1500 N). ABAQUS/Standard was used to create its advanced FE model. To represent the progressive damage in the adhesive layer, the fatigue damage model via the Paris Law, which links the rate of the crack expansion to the strain energy release rate (SERR), was integrated into the cohesive zone model with bi-linear traction–separation characteristics. The model was written in a UMAT subroutine. The developed model was validated using experimental data from the literature. The crack...

- by Murat Demiral
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- Aerospace

Adhesion can be greatly improved by the correct surface preparation techniques. One of the most common and useful technique is specific surface structuring which leads to mechanical interlocking and greater adhesion. This work describes the effect of laser-induced line pattern surface structuring on the mechanical interlocking mechanism and so on the adhesive bonding of carbon fiber reinforced polymer (CFRP) composites. Surface patterns with different laser scribes were obtained by CO 2 laser treatment. The effect of the number of a laser shot, the scribe depth, the number of the scribe and the angle between the direction of the laser scribes and mechanical test direction on the adhesive bonding strength of CFRP/CFRP joints was investigated by performing the single lap shear tests according to the ASTM D5868-01. After destructive tests, damaged surfaces were analyzed for determining the failure mechanisms. Mechanical tests showed that laser scribe characteristics especially the number of laser shot and the number of scribes have significant effects on the mechanical interlocking mechanism and so on the adhesion bonding strength. It is suggested that in order to improve the adhesion strength of CFRP/CFRP joints, mechanical interlocking mechanism shall be obtained by optimized laser scribe patterns. POLYM. COMPOS.

- by Arif Demir
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- Materials Engineering, Materials Science, Adhesive, Polymer Composites

Adhesively bonded composite-composite single-lap joints, with cross-ply GFRP adherends, have been cyclically loaded to initiate disbonding at either end of the overlap length. Disbond initiation and growth have been monitored using a combination of in situ photography (the joint is transparent) and a single chirped fibre Bragg grating (CFBG) sensor embedded within one composite adherend (with the low-wavelength end of the sensor adjacent to the cut end) and not in the adhesive bondline. Sensors having the same spectral bandwidth (20 nm), and lengths in the range 15 mm to 60 mm have been tested. The experimental results have been modelled using a combination of finite-element analysis and commercial software for predicting FBG spectra, and the predictions are in very good agreement with the experimental results. In all cases, it has been shown that the position of the disbond front can be located using the CFBG sensors with a precision of about 2 mm.

- by Swee Chuan Tjin
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- Engineering, Materials Science, Adhesive, Fiber Bragg grating

Structures made of carbon fiber-reinforced polymer (CFRP) can be assembled using adhesive bonding. However, such bonding is prone to brittle delamination, and a method to improve delamination resistance is desirable. Here, we propose a technique to introduce crack-arrest features that increase the R-curve response by engineering the adhesive bondline/interface. We specifically designed a wavy net-like thermoplastic insert that was embedded into the thermoset adhesive bondline where the new mechanisms of energy dissipation were generated. We demonstrate that the technique is effective at improving mode I fracture toughness of secondary bonded carbon/ epoxy by more than 400%. The hybrid thermoset/thermoplastic bondline architecture was carefully tailored to achieve its best performance. We demonstrate that introducing porosities in the adhesive bondline (by adding a limited amount of thermoset adhesive) further improves the fracture toughness. This toughness improvement originates from the extrinsic toughening of the crack-arrest feature, which is enabled by the insert ductility and microstructures (via strand formation, anchoring and stretching).

- by A. Yudhanto
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- Engineering, Materials Science, Composite Material, Fracture Toughness

Fiber Reinforced Plastics (FRPs) are being used extensively in various engineering applications ranging from aerospace to sports goods. In recent years, environmental concerns and awareness have challenged engineers and scientists to develop materials that are sustainable and have the potential to replace the traditional FRPs. Natural fiber-based polymeric composites (NFRPC) are now being investigated and proposed worldwide for various applications, especially automotive components and domestic products. To ensure the fabrication of highly intricate composite products, joining becomes inevitable. Adhesive joining is the most commonly employed fabrication process for composite joints. However, the performance of adhesive joints is susceptible to their exposure to different environmental conditions. In the present experimental investigation, the joint strength of woven fiber mat (sisal, jute, and hybrid) reinforced epoxy composites has been investigated in Three Months Cyclic Temperature Variation, and the natural fiber reinforced epoxy adherends have been successfully joined using adhesive along with two/four holes in the overlap area. The performance of the adhesive joints has been investigated under a daily thermal cycle from 5 • C (12 hrs.) to 40 • C (12 hrs.), for three consecutive months. It was observed that the hybrid composites recorded better-joining performance. Moreover, the Field Emission Scanning Electron Microscopy (FE-SEM) has been used to understand the failure mechanisms during tensile testing of adhesively bonded natural fiber-reinforced composite laminates. It has been found that the exposure of the composite joints to a variable temperature during the day has a significant effect on their tensile behavior. The major factors affecting the performance of joints exposed to the thermal cycle are; the type of natural fiber, the number of holes in the adherend area, and the duration of exposure. The results are important for the designers of composite structures with adhesively bonded joints.

In this study, a novel reinforcing method for glass-fiber reinforced composites, which consists of interadherend glass fibers (IAF) that get through the composite adherend like a pin, was investigated experimentally and numerically. Two types of joints were investigated. One is the traditional single lap joint without inter-adherend (Type A) and the other is Type B in which the fiber pin was used. Static tensile tests were performed at ambient environment in accordance with ASTM standards. In the numerical analysis, ANSYS 12.0 software package was used. The results show that the fibers improve the ultimate strength and damage tolerance of composite joints. In addition, the numerical results show a good agreement with the experimental ones.

- by alaattin aktas
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- Engineering, Materials Engineering, Mechanical Engineering, Materials Science

An essential question to predict the structural integrity of bi-material bonded joints is how to obtain their fracture properties under pure mode I. From open literature, it is found that the most commonly used design criterion to test mode I fracture is matching the flexural stiffnesses of the two adherents in a DCB coupon. However, the material asymmetry in such designed joints results in mode II fracture as well. In this paper, a new design criterion is proposed to obtain pure mode I fracture in adhesively bonded bi-material DCB joints by matching the longitudinal strain distributions of the two adherends at the bondline-longitudinal strain based criterion. A test program and Finite Element modelling have been carried out to verify the proposed design criterion using composite-metal bonded DCB joints. Both the experimental and numerical results show that pure mode I can be achieved in bi-material joints designed with the proposed criterion. G II /G I ratio is reduced by a factor of 5 when using the proposed longitudinal strain based criterion in comparison with the flexural stiffness based criterion.

- by Wandong Wang
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- Engineering, Materials Science, Composite Material

Over the past few decades, the automotive and aerospace industries have shown increased interest in carbon fiber reinforced plastic composite (CFRP) materials due to their light weight and low production cost. However, these composite materials exhibit poor performance in structural applications due to the weak interface when bonded to other dissimilar materials, such as adhesives, metals and polymers. As carbon-based materials, CFRPs have low surface energy that presents bonding challenges. Surface residual contaminants originating in mold release materials or handling also contribute to poor adhesive joint strength. Treatment under atmospheric pressure plasmas (APPs) has emerged as an alternative solution to engineer composite surfaces without affecting the bulk properties of the materials. The technology utilizes a dry gaseous medium and does not involve any harsh liquid solvent chemistries. APPs contain gaseous species that can react and remove organic surface contaminants very ...

- by Daphne Pappas
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In this work, peel tests were used to assess the adhesion quality between carbon fiber reinforced polymers (CFRP) and carbon steel plates. The tests were performed according to the ASTM standard of floating roller peel tests (D3167–97) with a new specimen layup. The layup and geometry of specimens was defined in order to have the CFRP as the rigid substrate and the steel plate as a flexible substrate. The aim is to assess the adhesion quality of the interface in dry-conditions (short-term) and after ageing (long term). Specimens were inside the salt spray cabinet for 30 days to absorb the moisture. Results show that peel load are not significantly affected by the ageing condition. The specimens tested at dry-conditions and ageing condition showed a cohesive failure within the adhesive layer, which indicates a good adhesion between the CFRP-Steel interfaces. Long term durability is suggested by keeping the specimen for longer duration in order to observe the degraded trend and adhesi...

- by Silvio de Barros
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- Materials Science, Adhesion, Adhesive, Steel

Carbon fiber-reinforced polymer (carbon-polymer) is an advanced lightweight composite material with high strength and excellent resistance to corrosion and fatigue. Over the past decades, application of fiber-reinforced polymers has been spread from the aerospace to other branches of industry such as automobile and civil engineering. Unidirectional carbon-polymers have a high potential for replacing steel in tensile members. Recently, the first carbonpolymer stress-ribbon bridge has been constructed in Germany. The non-laminated strip-loop carbon-polymer thin strips were used as the load bearing components in this bridge. In comparison with the laminated components, the applied cables are characterized by a more uniform strain distribution though reduced structural integrity. Alternative jointing technologies of carbon-polymer laminates are considered in this paper with an intention to increase the structural integrity and reliability of the production. Tensile behavior of the singl...

- by Algirdas Juozapaitis
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- Civil Engineering, Materials Science, Structural Engineering, Adhesive

Failure mode and failure load of composite joint design has become a very vital research area for being a weak part of composite structures in aircraft segments. So the objective of this study is to investigate the effect of different parameters on the shear strength and failure mode of adhesively bonded single-lap and scarf joints. The parameters included the overlap length, adherend thickness, and adhesive thickness of single-lap joints, and also the effect of single and double scarf angles of scarf joints. The results showed that in single-lap joints, the increasing overlap length led to increase shear strength until the length-to-width ratio becomes same value. The final failure mode of most tested thin adherends bonded joints with similar specimens was the delamination, while the interfacial failure mode occurred in thick adherends bonded joints. The shear strength increased when the adhesive thickness was reduced. On the other hand, in scarf joints, the ultimate shear strength was obtained when the scarf angle was around h = 18°, while when scarf angle reached h = 75°, the shear strength was decreased. The failure mode of scarf joints occurred at the interfaces between the scarf angles.

- by Ghada Essa
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- Materials Science, Adhesive, Composite Material, Failure Mode and Effects Analysis

Experimental studies have been undertaken to investigate the static and fatigue response of metal laminate doublers (MLD) joints under tension loading after ageing in deionised water at a temperature of 50 o C up to 2 years. It was found that absorbed water did not have a significant effect on the static and fatigue degradation of the MLD; however corrosion pits located on the aluminium surfaces caused a reduction in fatigue life. Inevitably the laminate contained butts where co-planar aluminium sheets were joined, and it was found that the position of the butt affected the static response of the MLD but, due to a restricted dataset, it has not been possible to assess the effect under fatigue loading. The backface strain technique in conjunction with video microscopy has been utilised to monitor the damage of the adhesive bondlines, the butts and the aluminium layers and successfully identified both the localised and the global damage in the MLD. Most of fatigue failures initiated at the stringer bondline edge and at the aluminium layers where the butt was located. A careful design should be made to reduce the stress concentration at the stringer edge and to avoid positioning the butts at the upper layer of aluminium close to the stringer edge.

Perturbation(s) in the adhesive’s properties originating from the manufacturing, glue-line application method and in-service conditions, may lead to poor performance of bonded systems. Herein, the effect of such uncertainties on the adhesive stresses is analyzed via a probabilistic mechanics framework built on a continuum-based theoretical model. Firstly, a generic 2D plane stress/strain linear-elastic model for a composite double-lap joint with a functionally graded adhesive is proposed. The developed model is validated against the results obtained from an analogous finite element model for the cases of bonded joints with metal/composite adherends subjected to mechanical and thermal loadings. Subsequently, the proposed analytical model is reformulated in probabilistic mechanics framework where the elastic modulus of the adhesive is treated as a spatially varying stochastic field for the cases of homogeneous and graded adhesives. The former case represents stochastic nature of conventional joints with a homogeneous bondline while the later case showcases the perturbation in the properties of functionally graded joints. To propagate the uncertainty in the elastic modulus to shear and peel stresses, we use a non-intrusive polynomial chaos approach. For a standard deviation in the elastic modulus, the proposed model is utilized to evaluate the spatial distribution of shear and peel stresses in the adhesive, together with probability and cumulative distribution functions of their peaks. A systematic parametric study is further carried out to evaluate the effect of varying mean value of the adhesive’s Young’s moduli, overlap lengths and adhesive thicknesses on the coefficient of variation/standard deviation in peak stresses due to the presence of a random moduli field. It was observed that the joints with stiffer adhesives and longer bondlengths show smaller coefficient of variation in peak stresses. The findings from this study underscore that the predictive capability of the proposed model would be useful for the stochastic design of adhesively bonded joints.

The joining techniques of lightweight and strong materials in the transport industry (e.g. automotive, aerospace, shipbuilding industries) are very important for the safety of the entire structure. In these industries, when compared with other joining methods, the use of adhesively bonded joints presents unique properties such as greater strength, design flexibility, and reduction in fuel consumption, all thanks to low weight. The aim of this study was the analysis of the tensile fatigue behavior of adhesively bonded glass fiber/epoxy laminated composite single-lap joints with three different specimen types including 30, 40 and 50 mm overlap lengths. In this study, composite adherents were manufactured via vacuum-assisted resin transfer molding and were bonded using Loctite 9461 A&B toughened epoxy adhesive. The effect of a surface treatment method on the bonding strength was considered and it led to an increment of about 40%. A numerical analysis based on a finite element model was...

- by Emre Kara
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- Mechanical Engineering, Materials Science, Finite Element Methods, Composite Materials

In aerospace and many types of civil infrastructure applications, the use of adhesive-bonded composite joints have been constantly increasing. In this study, fracture behaviour of adhesively bonded single lap joint (SLJ) with pre-existing damage at the interface of free edge of the top adherend and adhesive along the width of the joint is studied by strain energy release rate (SERR) approach using virtual crack closure technique (VCCT). Adherends are four layered laminated fiber reinforced plastic (FRP) composite plates and each lamina of adherend having either +45° or-45° fiber angle. The distributions of strain energy release rates along the delamination front are predicted by evaluating 3D local displacement fields and reaction forces required to close them, along the delamination length and width. The present investigation reveals that strain energy release rates are not constant along the delamination front, insisting on three dimensional modeling of problem. It is observed that location of damage propagation and mode of failure responsible for damage propagation varies with lay-up sequence of +45° or-45° ply oriented laminas within the top and bottom adherends. Total strain energy release rate (G) values are very high in the SLJs having (+45/-45) s FRP laminated adherends and in the SLJ with (-45/+45) s FRP laminated adherends, when compared with SLJs having (+45/-45) as and/or (-45/+45) as FRP laminated adherends.

Current research focuses on the fabrication of the dye-sensitized solar cells (DSCs) based on titanium dioxide (TiO2) compact layer deposited by the spray pyrolysis deposition (SPD) technique. TiO2 compact layers have been grown on fluorine-doped tin oxide (FTO) glass substrates by the experimental aerosol-assisted SPD setup. This setup is designed and constructed for the research under the following conditions: substrate temperature of 300 °C, 400 °C, and 500 °C; initial solution concentration of Ti (IV) isopropoxide and ethanol of 0.5 ml and 100 ml, respectively; carrier gas pressure of 0.1 bar; nozzle-to-substrate distance of 20–30 cm; and spraying time of 5–10 s. The characterization instruments such as HITACHI (S-2700) scanning electron microscopy (SEM), BRUKER (D500) X-ray diffractometer (XRD), and JENWAY 7310 UV-Vis spectrophotometer have been used to investigate the film properties. Dye-sensitized solar cells (DSCs) were assembled based on a bare FTO glass, FTO coated with T...

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 singlelap 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 singlelap 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.

- by Kübra Demir
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- Mechanical Engineering, Civil Engineering, Applied Mathematics, Materials Science

A simple predictive stress analysis model for adhesive joints with nonlinear adhesives is presented. The model allows for the treatment of various joint designs with shear-flexible laminate or isotropic adherends. Both elastic-plastic and hyperelastic adhesives are covered. Using a general sandwich-type model of the adhesive bondline, the governing differential equations are derived analytically and solved numerically.

- by Nicolas Stein
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- Mathematics, Materials Science, Structural Engineering, Adhesive

In this work, an efficient analytical model for the stress analysis of single lap joints with a functionally graded adhesive bondline is proposed which considers peel as well as shear stresses in the adhesive. The model takes into account the nonlinear geometric characteristics of a single lap joint under tensile loading and allows for the analysis of various adhesive Young's modulus variations. The obtained stress distributions are compared to results of detailed Finite Element analyses and show a good agreement for several single lap joint configurations. In addition, different adhesive Young's modulus distributions and their effect on the peel and shear stresses are studied and discussed in detail.

- by Nicolas Stein
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- Materials Science, Structural Engineering, Adhesive

Given high strength-to-weight and stiffness-to-weight ratios, sandwich composite materials are continually being considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased ease of manufacture and are recyclable making them even more attractive than thermoset composites. This investigation evaluates the adhesion of 13 adhesives with 8 surface treatments on both nylon and polypropylene thermoplastic adherends made from Towflex® preimpregnated fabric. A method of manufacture of these plates without contaminating the bonding surface while establishing an acceptable surface finish was developed. Adhesives and surface treatments were investigated and the candidates with the greatest likelihood of success without overlap were chosen. Initial testing was performed using the qualitative spot adhesion test (ASTM D3808) to identify the most likely adhesive and surface treatment parameter groups with each thermoplastic. From these results, 10 parameter groups were identified and tested quantitatively using the lap shear test (ASTM D 3163). Comparative bond strengths are calculated from the peak load and bonded area of each specimen. The results for the nylon were similar between the two tests, but the polypropylene was generally inconsistent. The results indicate that further testing to completely develop joining methods with nylon thermoplastic treated at least with an acid wash and bonded with Lord 320/322 could result in a method of adhesively joining thermoplastic sandwich composites.

- by Jared Nelson
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- Materials Science, Adhesive, Polypropylene, Composite Material

Some references to relevant papers reported in the Publication section are quoted in parenthesis) Experimental analysis of turbulent flows. Turbulent flows in complex geometries (port and in-cylinder flows (B1)) by Laser Doppler Anemometry and visualisation techniques. Development of a procedure to account for step noise amplitude in LDV-measured turbulent spectra (J6). Transport phenomena in spray and jets Extensive LDV-PDA study of air entrainment characteristics in jets and sprays under different temperature and pressure conditions (J2, J9, B3-B5, P9). Development of a theoretical model for predicting air entrainment in steady sprays (J8). Modelling of transport phenomena in Diesel sprays (J26,P28,P34) Optical techniques in jet and sprays analysis Development of a technique based on an unconventional use of conventional PDA to reconstruct coherent structures in spray flows (B2). Development of a laser based technique to measure the instability growing rate in liquid laminar jets (J4). Spray/wall and jet/wall interaction Experimental (LDV-PDA-Visualisation) analysis of the impact of gaseous jets and sprays (Diesel) (P4,P6,P7)onto solid walls. Interface dynamics: drop impact on walls and films Experimental analysis (PDA, High speed visualisation) of single and multiple drop impact onto solid dry (hot and cold) walls and liquid film (J5,J12,J13,J23,J28,J29),. Evidence of the wall effusivity effect on the secondary atomisation (J22). Cratering after drop impact on liquid surfaces (P31,J27,J30,P33,P35) Periodic heat transfer Theoretical analysis of periodic heat transfer problems (periodic heat conduction under Fourier and non-Fourier hypothesis (J11,J20,J24), periodic Graetz problem (J25), dynamic heat storage (J18.J19), inverse problem (J10)). Boundary layer flows Theoretical studies of boundary layer flows under unconventional boundary conditions (J14,J16,J17). Droplet evaporation in high temperature environment. Development of theoretical models to predict drop evaporation in high temperature environment (P29, J32). Atomisation models in sprays Development of atomisation models for fire-supression sprays (P30,P32). Consultancy activities Consultancy and applied research for industry in the following fields: Multimode heat and mass transfer in complex geometries. Development of ink-jet heads for industrial printing. Heat pumps for residential and industrial heating and cooling. Energy assessment of thermo-hydraulic systems. Modelling of heat and mass transfer in dryers for asphalt production Most relevant publications International Journals J1) "Measurements of Tip Penetration of Confined High Density Gaseous Jets by Laser Beam Deflection "

- by Marco Marengo
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- Mechanical Engineering, Chemical Engineering, Physics, Classical Physics

In the present study, mechanical properties of different Single Lap Joint (SLJ) configurations with different adherent width values subjected to tensile loading were investigated experimentally and numerically. Using AA2024-T3 aluminum alloy as adherend and DP460 as paste adhesive, eight different types of single-lap joint samples (width of the adherent was 5, 10, 15, 20 or 25 m; overlap length was 5 ,10, 15, 20 or 25 mm) were produced for experimental studies. Stress analyses in the SLJ were performed non-linear finite element method by considering the geometrical non-linearity and the material non-linearities of the adhesive (DP460) and adherend (AA2024-T3). As a result, in SLJ geometries, increasing the adherent width raises the load-carrying capacity of the joints higher when compared to increasing overlap length. The failure load value of the joint increases as the area of bonding varies from rectangle to square. In addition, it was found that the data obtained from finite element analysis were coherent with experimental results.

- by adnan özel
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- Engineering, Materials Science, Structural Engineering, Finite element method

- by Vladimir Kulakov
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- Civil Engineering, Materials Science, Structural Engineering, Stiffness

This Paper complies the study of effects of various filler materials on Mechanical Properties of Carbon-Epoxy Composite. The paper gives the diversified description of the behavior of the Carbon-Epoxy Composite, under different loadings and conditions. The Carbon-Epoxy Composite was fabricated using various fillers such as, Coremat, Aerosil and Granite. The Composition of the Carbon-Epoxy Composite consists of 50% Carbon Fiber, 40% Resin and 10% fillers by weight. Three different types of Carbon-Epoxy Composite specimen were fabricated using three different Fillers, as mentioned above. The Method Adopted to fabricate the Carbon-Epoxy Composite is conventional Hand Lay-up technique. Furthermore, the Carbon-Epoxy Composite specimen was subjected to various Test Conditions, namely Tensile Test, Impact Test and Water Absorption Test and the behavior of the same is recorded and described in this paper.

- by NIKHIL ANIGOL
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The effect of through-thickness reinforcement by thin 1 mm steel needles (z-pins) on the static tensile strength of double-lap joints of a carbon/epoxy composite was investigated. Two types of joints-z-pinned and hybrid (including glued ones)-were considered. The joints were reinforced in the overlap region with 9, 25, or 36 z-pins. Comparing mechanical properties of the double-lap joints with the corresponding characteristics of their unpinned counterparts, the z-pins were found to be highly effective: the strength and stiffness of the pinned joints increased up to 300% and 280%, respectively. These improvements were due to a transition in the failure mechanism from debonding of the joint in the absence of z-pins to pullout or shear rupture of z-pins or to the tensile failure of laminate adherends, depending on the volume content of the pins.

- by aleksandr arnautov and +1
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- Engineering, Materials Science, Materials, Medicine

The fatigue performance of welded steel connections has been generally enhanced by adhesively FRP materials patching. In this study, load-carrying cruciform welded joints with adhesively bonded FRP materials were investigated regarding the fatigue performance. Full penetration weld was proposed as the type of welding. The (2-D) finite element method (FEM) was utilized and modeled for two cases. The first Case during the preliminary analysis to evaluate the effect of using only FRP materials on SIF (KI), while the second case was to study the effect of FRP materials fixed with head plate and bolts on SIF (KI). Stress intensity factors of mode I (KI) were calculated for unrepaired and repaired specimens with various FRP materials by J-integral approach. In addition, FEA results of the unrepaired cruciform joint were verified with an analytical results approach. The reduction of stress intensity factors with FRP patch...

- by Kamal Sharobim
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A pilot project has been carried out to investigate the effect of impact on single-lap bonded composite joints based on AS4-8552 laminates and Cybond BR4535A adhesive. Low velocity impacts at an energy level sufficient to cause barely visible impact damage, were conducted on single lap joint specimens at different joint positions. Impact caused delaminations in the upper and lower laminates and localised through-thickness cracking in the adhesive. Residual tensile joint strengths of the impacted joint specimens with near-edge damage were reduced to approximately 50% of the un-impacted value. Failure surface inspections revealed localised through-thickness adhesive shear cracking as a governor of the original impact delamination pattern in the laminates and laminate delamination as the cause of ultimate tensile failure.

- by I. Farrow
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- Materials Science, Damage, Impact, Composite Material