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1.
The aim of this research was to develop an experimental–numerical approach to characterize the effect of salt spray environment on adhesively bonded joints and predict the degradation in joint strength. Experiments were conducted on bulk adhesive specimens and single lap joints (SLJs) under salt spray condition and the corresponding experimental results were reported. The environment degradation factor, Deg, was incorporated into a bilinear cohesive zone model (CZM) to simulate the degradation process of the joints. The degraded CZM parameters, determined from static tests on bulk adhesive, were imported into the CZM using an approximate moisture concentration gradient approach. The reduction in residual strength of SLJ under salt spray environment was successfully predicted through comparing the experimental and numerical results.  相似文献   

2.
In order to enhance the strength of adhesively bonded single-lap joints (SLJs), the adhesively bonded SLJs with reinforcements were proposed. Adhesively bonded SLJs of different substrates and with different reinforcements were investigated experimentally and numerically. Scanning electron microscopy was performed on the fracture surfaces of the joints to analyze the failure mechanism. Shear stresses and peeling stresses of the adhesive layer were calculated with finite element analyses (FEA). Results showed that the deformation of the joints decreased with an increase in stiffness at the end of the overlap region. The strength increase in adhesively bonded SLJs with reinforcements was validated by the results from experimental tests and FEA.  相似文献   

3.
The use of a cohesive zone model (CZM) to predict the long-term durability of adhesively bonded structures exposed to humid environments has been investigated. The joints were exposed to high relative humidity (RH) environments and immersion in both tap and deionised water for up to a year before quasi-static testing to failure. Both stressed and unstressed conditions during aging were considered. The degradation was faster for the stressed joints and for those joints immersed in the more corrosive environments. Two mechanisms were suggested to explain this behaviour: cathodic delamination and stress-enhanced degradation. In the model, the cohesive zone parameters determine the residual strength of the joints. The degradation of these parameters was, in the first instance, related directly to the moisture concentration. The model was then extended to include degradation due to stress and more corrosive environments. Good correlation between the numerical modelling and the experimental results was obtained.  相似文献   

4.
The use of a cohesive zone model (CZM) to predict the long-term durability of adhesively bonded structures exposed to humid environments has been investigated. The joints were exposed to high relative humidity (RH) environments and immersion in both tap and deionised water for up to a year before quasi-static testing to failure. Both stressed and unstressed conditions during aging were considered. The degradation was faster for the stressed joints and for those joints immersed in the more corrosive environments. Two mechanisms were suggested to explain this behaviour: cathodic delamination and stress-enhanced degradation. In the model, the cohesive zone parameters determine the residual strength of the joints. The degradation of these parameters was, in the first instance, related directly to the moisture concentration. The model was then extended to include degradation due to stress and more corrosive environments. Good correlation between the numerical modelling and the experimental results was obtained.  相似文献   

5.
A progressive cohesive failure model has been proposed to predict the residual strength of adhesively bonded joints using a moisture-dependent critical equivalent plastic strain for the adhesive. Joints bonded with a ductile adhesive (EA9321) were studied for a range of environmental degradations. A single, moisture-dependent failure parameter, the critical strain, was calibrated using an aged, mixed-mode flexure (MMF) test. The mesh dependence of this parameter was also investigated. The parameter was then used without further modification to model failure in aluminum and composite single-lap joints (SLJ) bonded with the same adhesive. The FEA package ABAQUS was used to implement the coupled mechanical-diffusion analyses required. The elastic-plastic response of the adhesive and the substrates, both obtained from the bulk tensile tests, were incorporated. Both two-dimensional and three-dimensional modelling was undertaken and the results compared. The predicted joint residual strengths agreed well with the corresponding experimental data, and the damage propagation pattern in the adhesive was also predicted correctly. This cohesive failure model provides a simple but reliable method to model environmental degradation in ductile adhesive bonded joints, where failure is predominantly within the adhesive layer.  相似文献   

6.
A progressive cohesive failure model has been proposed to predict the residual strength of adhesively bonded joints using a moisture-dependent critical equivalent plastic strain for the adhesive. Joints bonded with a ductile adhesive (EA9321) were studied for a range of environmental degradations. A single, moisture-dependent failure parameter, the critical strain, was calibrated using an aged, mixed-mode flexure (MMF) test. The mesh dependence of this parameter was also investigated. The parameter was then used without further modification to model failure in aluminum and composite single-lap joints (SLJ) bonded with the same adhesive. The FEA package ABAQUS was used to implement the coupled mechanical-diffusion analyses required. The elastic–plastic response of the adhesive and the substrates, both obtained from the bulk tensile tests, were incorporated. Both two-dimensional and three-dimensional modelling was undertaken and the results compared. The predicted joint residual strengths agreed well with the corresponding experimental data, and the damage propagation pattern in the adhesive was also predicted correctly. This cohesive failure model provides a simple but reliable method to model environmental degradation in ductile adhesive bonded joints, where failure is predominantly within the adhesive layer.  相似文献   

7.
The objective of this study is to analyze the effect of cyclic-temperature environment on adhesively bonded T-joints. Experiments on steel and aluminum T-peel joints were conducted to illustrate the influence of cyclic temperature on the ultimate load of T-joints. An environmental degradation factor Deg was utilized in conjunction with a cohesive zone model (CZM) to simulate the strength of T-joints caused by temperature variation. The experimental results showed that long-term cyclic-temperature exposure caused significant degradation on the ultimate load of the T-joints. And with the increase of the temperature cycles experienced, the ultimate load of the T-joints gradually decreased. In order to model the adhesive layer between joint components and simulate the damage propagation in the interface, a CZM implemented in the finite element code ABAQUS was used. Comparison between the experimental and numerical results proved the adopted modeling procedure be successful and effective.  相似文献   

8.
Abstract

The cohesive zone model approach is attractive for the analysis of failure of adhesively bonded structures. While the numerical implementation of cohesive elements has been well established, there remains a lack of cohesive material data. The present paper contributes to efforts to fill this void. An investigation of crack growth in the widely used structural adhesive Hysol EA-9394 is presented, and the adhesive is characterized by a cohesive zone law. Crack growth experiments were performed on specimens consisting of aluminum adherends bonded by use of the adhesive. Measurements of the surface topography leading reconstruction of fracture processes indicate that plastic deformation is absent during fracture. Thus, the cohesive zone law can directly be determined from the energy release rate and the material separation measured at the initial crack tip. The cohesive zone law is then applied in finite element model to predict crack growth. The predicted strain fields during crack growth are well matched to those obtained by digital image correlation measurements. An independent set of crack growth experiments was performed, and finite element models based on the cohesive law were used to predict the outcome of these experiments. Again good agreement between simulation and experiment was obtained. The results give confidence that the cohesive zone model parameters are transferable to the analysis of structures bonded with the adhesive Hysol EA-9394 in general. A comparison of the cohesive zone law for Hysol EA-9394 demonstrates that this adhesive possesses high strength and moderate toughness. Limits to the transferability regime are discussed.  相似文献   

9.
Cyclic debond data obtained from fatigue testing of four different specimen geometries having the same adhesive is considered. Fatigue properties of the adhesive are characterized in terms of linear elastic fracture mechanics concepts whereby debond growth rates are correlated to appropriate mixed mode fracture parameters. Stress analyses of the four specimens under maximum load indicate that in most cases inclusion of geometric nonlinearities is required for the determination of the fracture parameters. For three of the specimens considered, the debond growth laws based on total energy release rate as correlating mixed-mode fracture parameter were found to be similar. A number of potential reasons for the lack of similarity in debond growth laws in all four specimens are explored.  相似文献   

10.
《The Journal of Adhesion》2007,83(6):553-571
It is important to be able to predict the mechanical response of adhesively bonded joints. To succeed in this, the accurate simulation of the behavior of adhesively bonded joints is an essential requirement because of the strain rate, temperature, and hydrostatic sensitivity of adhesive properties, which should be taken into consideration when developing a material model [1-111, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]. On the other hand, the load capabilities of adhesively bonded joints are affected by both applied pressure and temperature during cure. For this reason, in this study, the tensile load capabilities of single lap joints (SLJs) bonded with a flexible adhesive that possesses pressure-sensitive properties were experimentally investigated with respect to the applied pressure during the curing operation, and the experimental results were compared with finite element analysis (FEA) results. Finally, in addition to other parameters, such as the dependence on strain rate and the lack of yield criteria of adhesives, it was seen that the residual thermal stresses that occurred as a result of the applied pressure during the curing process at elevated temperature need to be taken into consideration to accurately simulate the mechanical behavior of adhesively bonded joints.  相似文献   

11.
Fibre reinforced polymer composites (FRP's) are often used to reduce the weight of a structure. Traditionally the composite parts are bolted together; however, increased weight savings can often be achieved by adhesive bonding or co-curing the parts. The reason that these methods are often not used for structural applications is due to the lack of trusted design methods and concerns about long-term performance. The authors have attempted to address these issues by studying the effects of fatigue loading, test environment and pre-conditioning on bonded composite joints. Previous work centered on the lap-strap joint which was representative of the long-overlap joints common in aerospace structures. However, it was recognised that in some applications short-overlap joints will be used and these joints might behave quite differently. In this work, double-lap joints were tested both quasi-statically and in fatigue across the temperature range experienced by a jet aircraft. Two variants on the double-lap joint sample were used for the testing, one with multidirectional (MD) CFRP adherends and the other with unidirectional (UD) CFRP adherends. Finite element analysis was used to analyse stresses in the joints. It was seen that as temperature increased both the quasi-static strength and fatigue resistance decreased. The MD joints were stronger at low temperatures and the UD joints stronger at high temperatures. It was proposed that this was because at low temperature the strength was determined by the peak stresses in the joints, whereas, at high temperatures, strength is controlled by creep of the joints which is determined by the minimum stresses in the joint. This argument was supported by the stress analysis.  相似文献   

12.
Fibre reinforced polymer composites (FRP's) are often used to reduce the weight of a structure. Traditionally the composite parts are bolted together; however, increased weight savings can often be achieved by adhesive bonding or co-curing the parts. The reason that these methods are often not used for structural applications is due to the lack of trusted design methods and concerns about long-term performance. The authors have attempted to address these issues by studying the effects of fatigue loading, test environment and pre-conditioning on bonded composite joints. Previous work centered on the lap-strap joint which was representative of the long-overlap joints common in aerospace structures. However, it was recognised that in some applications short-overlap joints will be used and these joints might behave quite differently. In this work, double-lap joints were tested both quasi-statically and in fatigue across the temperature range experienced by a jet aircraft. Two variants on the double-lap joint sample were used for the testing, one with multidirectional (MD) CFRP adherends and the other with unidirectional (UD) CFRP adherends. Finite element analysis was used to analyse stresses in the joints. It was seen that as temperature increased both the quasi-static strength and fatigue resistance decreased. The MD joints were stronger at low temperatures and the UD joints stronger at high temperatures. It was proposed that this was because at low temperature the strength was determined by the peak stresses in the joints, whereas, at high temperatures, strength is controlled by creep of the joints which is determined by the minimum stresses in the joint. This argument was supported by the stress analysis.  相似文献   

13.
In cases where adhesively bonded joints may experience large displacements and rotations whilst the strains remain small, although all joint members behave elastically the small strain-small displacement (SSSD) theory cannot correctly predict the stresses and deformations in the adhesive joint members. Previous studies have shown that the small strain-large displacement theory considering the non-linear effects of the large displacements in the stresses and deformations has to be used in the analysis of adhesively bonded joints. In this study, the geometrical non-linear analysis of an adhesively bonded double containment corner joint was carried out using the incremental finite element method based on the small strain-large displacement (SSLD) theory. The objective of the study was to determine the effects of the large displacements on the adhesive and adherend stresses of the corner joint. Therefore, the corner joint was analysed for two different loading conditions; a compressive applied load, Px, at the free end of the horizontal plate and one normal to the plane of the horizontal plate, Py. The plates, support and adhesive layer were assumed to have elastic properties. In practice, the adhesive accumulations, called spew fillets, arising around the adhesive free ends were taken into account in the analysis since their presence results in a considerable decrease in the peak stresses around the free ends of the adhesive. The SSLD and SSSD analyses showed that the stress concentrations occurred around the free end of the adhesive, thus at the adherend (slot) corners inside the right vertical and the lower horizontal adhesive fillets, and inside the left vertical and the upper horizontal adhesive fillets for the loading conditions Px and Py, respectively. In addition, the plate regions around the adherend (slot) free ends along the outer fibres of the vertical and horizontal plates undergo very high stress concentrations. The SSLD analysis predicted a non-linear effect in the displacement and stress variations at the critical adhesive and plate locations, whereas the SSSD analysis showed their variations were lower and proportional to the applied incremental load. This non-linear effect became more evident for the loading condition Px, whereas both analyses predicted very close displacement and stress variations in the adhesive fillets and in the horizontal plate for the loading condition Py. As a result, the geometrical non-linear behaviour of the corner joint is strictly dependent on the loading condition and the large displacements affect the stress and deformation states in the joint members, and result in higher stresses than those predicted by the SSSD theory.  相似文献   

14.
One of the important processes in structural design is the joining technique. Failure of composite joints involves different failure mechanisms depending upon the joining technique. In this study, a progressive failure analysis was performed on adhesively, riveted, and hybrid bonded double-lap joints. In the joints, a woven-type fiberglass-reinforced composite material was used as the main material; AV 2015 was used as the adhesive, and steel as the rivet material. The analyses were performed using ANSYS 12.1 finite element package software via software written using parametric design language (APDL) codes. At the end of the progressive failure analysis, failure loads and failure modes were determined for 30-, 45-, and 60-mm overlap lengths in accordance with the Maximum Shear Stress Theory and Hashin Criteria. For 45-mm overlap lengths, the joint strength of hybrid joints proved to be 2.72 and 1.145 times higher, respectively, than adhesive and fastening joints. Results showed that the failure load of the joint increased when the overlap length increased. In riveted joints, the failure occurring in the composite plates began around the rivet hole and the catastrophic failure of these types of joints resulted from fiber tensile failure.  相似文献   

15.
In the present study, mechanical properties of different single lap joint configurations derived from adherends with different thicknesses subjected to tensile loading were investigated experimentally and numerically. For this purpose, experimental studies were conducted on two different types of SLJ samples, the first type with identical upper and lower adherend thicknesses and the second with different upper and lower adherend thicknesses. For the first type, five different thickness values were tested. For the second type, the lower adherend thickness was constant while five different upper adherend thickness values were tested. The adhesive was prepared from a two-part paste. After the experimental studies, stress analyses on the SLJs were performed with three-dimensional finite element analysis by considering the geometrical non-linearity and the material non-linearities of the adhesive (DP460) and adherend (AA2024-T3). It was observed that, in single lap joint geometry, variation in the thickness of the adherend and the use of lower and upper adherends with different thickness values changed the stress concentrations at the edges of the overlap regions, affecting the experimental failure load of the joints.  相似文献   

16.
The structural integrity of multi-component structures is usually determined by the strength and durability of their unions. Adhesive bonding is often chosen over welding, riveting and bolting, due to the reduction of stress concentrations, reduced weight penalty and easy manufacturing, amongst other issues. In the past decades, the Finite Element Method (FEM) has been used for the simulation and strength prediction of bonded structures, by strength of materials or fracture mechanics-based criteria. Cohesive-zone models (CZMs) have already proved to be an effective tool in modelling damage growth, surpassing a few limitations of the aforementioned techniques. Despite this fact, they still suffer from the restriction of damage growth only at predefined growth paths. The eXtended Finite Element Method (XFEM) is a recent improvement of the FEM, developed to allow the growth of discontinuities within bulk solids along an arbitrary path, by enriching degrees of freedom with special displacement functions, thus overcoming the main restriction of CZMs. These two techniques were tested to simulate adhesively bonded single- and double-lap joints. The comparative evaluation of the two methods showed their capabilities and/or limitations for this specific purpose.  相似文献   

17.
Adhesively bonded joints have been used extensively for many structural applications. However, one disadvantage usually limiting the service life of adhesive joints is the relatively low strength for peel loading, especially under dynamic cyclic loading such as impulsive or vibrational forces. Moreover, accurately predicting the fatigue life of bonded joints is still quite challenging. In this study, a combined experimental–numerical approach was developed to characterize the effect of the cyclic-vibration-peel (CVP) loading on adhesively bonded joints. A damage factor is introduced into the traction-separation response of the cohesive zone model (CZM) and a finite element damage model is developed to evaluate the degradation process in the adhesive layer. With this model, the adhesive layer stress states before and after being exposed to various CVP loading cycles are investigated, which reveals that the fatigue effect of the CVP loading starts first in the regions close to the edges of the adhesive layer. A good correlation is achieved when comparing the simulation results to the experimental data, which verifies the feasibility of using the proposed model to predict the fatigue life of adhesively bonded joints under the CVP type of loading.  相似文献   

18.
    
A novel concept for joining materials is presented which employs adhesive joints with interlocking bond-surface morphology formed on the surfaces of male and female adherends that mechanically interlock in shear when brought together. In the present work, miniature, single-lap joint specimens with a single truncated square pyramid interlocking profile, centred in the bond area, are investigated. The performance of the concept is assessed through finite element analysis (FEA) by incorporating yield criteria representing plasticity in the adherends and a cohesive zone model to represent damage in the adhesive layer. This allows for effective simulation of the joint response until ultimate failure and thus, full assessment of the concept's performance. Various interlocking geometries are explored and refined through an adaptive surrogate modelling design optimisation procedure coupled with FEA. The results indicated that significant improvements in work to failure, of up to 86.5%, can be achieved through the more progressive failure behaviour observed compared to that of a traditional adhesively bonded joint. Improvements in the joint's ultimate failure load can also be achieved with a relatively ductile adhesive system.  相似文献   

19.
The capabilities of structural bonding are more and more used. Estimating the abilities of an adhesive to endure repetitive loadings and to keep stable its mechanical properties along service life is an essential point to analyze in order to conduct fatigue assessments. The aim of this study is to develop a predictive tool for describing the fatigue behavior of an adhesive in an assembly under cyclic loadings. The approach developed analyzes the influence of viscosity on the mechanical behavior of an adhesive in an assembly based on monotonic and creep test results. Thanks to the evaluation of viscous phenomena, it is possible to predict the cyclic response of the adhesive. The experimental approach uses a unique bonded joint designed to limit the stress concentrations and with a maximum stress state in the center of the adhesive. In this paper, following the strategy developed under monotonic loading, experimental results under cyclic loading are presented for different types of loading using several load ratios and amplitudes. These results underline that the evolution of viscous deformations depends on the loading type. Under shear loading and for a ductile structural adhesive, the experimental results are well described using a viscoelastic–viscoplastic constitutive model with nonlinear viscous parameters. This model makes it possible to analyze the influence of different parameters on the mechanical response of bonded joints under cyclic shear loadings.  相似文献   

20.
Stress distributions and deformation of adhesive butt joints are analyzed by an elastoplastic finite element method when the joints of similar and dissimilar shafts are subjected to external bending moments. The effects of the ratio of Young's modulus for the adherends to that for an adhesive and the effects of the adhesive thickness on the interface stress distribution are investigated. Joint strength is predicted by using the elastoplastic interface stress distributions. It is found that the singular stress at the edge of the interfaces increases with an increase of the ratio of Young's modulus. Measurement of strains in joints and experiments on joint strength were conducted. The numerical results are in fairly good agreement with the experimental results. It is observed that the joint strength for dissimilar shafts are smaller than those for similar shafts. A fracture of dissimilar adhesive up-bonded shafts occurred from the interface of the adherend with smaller Young's modulus. It is seen that joint strength increases as the adhesive thickness increases.  相似文献   

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