Search

For efficient use of adhesive joints, reliable prediction techniques should be made available to the designer. Simulation of these joints' behaviour is usually performed using the Finite Element Method (FEM). However, it is known that, in adhesive joints, the adhesive thickness (tA) is much smaller than the adherend thickness (tP), thus requiring a highly refined mesh to produce good results. Linked to this, the adhesive has to withstand high strains, causing mesh distortion and hindering the resolution. In these cases, meshless methods can be a good alternative. This work aims to implement the von Mises (vM) and Exponent Drucker-Prager (EDP) criteria combined with a meshless formulation based on the Radial Point Interpolation Method (RPIM), for the strength prediction of adhesively-bonded single-lap joints (SLJ). Validation with experiments is undertaken for joints with brittle to ductile adhesives, with varying overlap lengths (LO). Stress and strain distributions were plotted in the adhesive layer, and the failure load (Pm) was assessed by strength of materials failure criteria. Significant adhesive and LO effects were found on Pm. The RPIM proved to be a promising tool to predict the behaviour of bonded joints, although some limitations were found by using strength of materials criteria. [ABSTRACT FROM AUTHOR]

Adhesive joints are widely used in the production of goods, mainly in the transport industry. However, their industrial applications often have non-standard complex shapes. Computer simulation, like the finite element method (FEM), is widely used for their analysis but limitations still exist. Meshless methods have been in development and offer an option to overcome some limitations of the FEM; however, these are still in development. In this work, a recent meshless method, the NNRPIM, has been applied to the analysis of adhesive joints. First, experimental data corresponding to four overlap lengths and three different adhesives were measured, as a benchmark. Afterwards, joint strength was analytically obtained as a second benchmark. Then, all the joint geometries were simulated utilising the FEM and NNRPIM methodologies, joint strengths were calculated from those simulations. Finally, the results were compared against the first and second benchmarks. Meshless method proved to be a good alternative to the FEM, providing similar strength prediction with differences less than 3% between them. Moreover, the stress distribution curves were compared, differences of 5% in the peak shear stresses were found. In conclusion, the NNRPIM provides accurate results and could be utilised for further study of adhesively-bonded joints. [ABSTRACT FROM AUTHOR]

Adhesive bonding is a widely used joining technique with increasing applications in the automotive and aircraft industries. However, the numerical simulation of adhesively bonded joints is challenging due to the intricate mechanical behavior of the bonding layer, especially when structures are subjected to mixed-mode loading. This work proposes a meshless fracture propagation algorithm to simulate mixed-mode fracture propagation in single-leg bending (SLB) adhesive joints. The proposed algorithm combines the radial point interpolation method (RPIM) with a mixed-mode strain-based criterion to predict crack growth. The RPIM permits a flexible discretization of the fracture region and eases the geometric remeshing of the integration cells to account for the crack tip propagation. Additionally, the RPIM provides accurate and smooth strain/stress fields, allowing implementation of the mixed-mode fracture criterion. The numerical model was validated against experimental data for SLB adhesive joints with a brittle adhesive. The results showed that the proposed algorithm can accurately predict the resistance curves and critical energy release rates of the adhesive joints. [ABSTRACT FROM AUTHOR]

The use of adhesive joints has gathered increasing interest in recent years due to their advantages over conventional bonding techniques, namely lighter structures and decreased stress concentrations. Consequentially, the strength prediction of adhesive joints has been studied extensively. This review aims to describe and compare the most relevant methods for the strength prediction of adhesive joints. These methods can be divided into analytical and numerical methods. Analytical methods are generally limited to initial design evaluations or to simple joints. Numerical methods are more commonly used, especially when joint design is complex. Between the different numerical methods, Cohesive Zone Models (CZM) are the most popular method to predict the strength of adhesive joints. This approach is able to predict the strength of a wide range of joint designs with minimal errors. However, it requires the determination of cohesive laws that generally change depending on different geometrical parameters of the joints. Advanced numerical techniques, such as the eXtended Finite Element Method (XFEM) or Meshless Methods have been used to study adhesive joints, but their application needs improvements before they can be more extensively used. [ABSTRACT FROM AUTHOR]

A fracture propagation algorithm is extended to mixed-mode fracture propagation in adhesively bonded joints. Therein, single-leg bending (SLB) specimens bonding carbon-epoxy adherents with the brittle AV138® adhesive were experimentally tested to characterize the adhesive joint and validate the numerical application. Regarding the numerical analysis, the radial point interpolation method (RPIM), a meshless method, is considered to obtain the specimen's mechanical response at each crack tip increment. Using the RPIM allows a flexible discretization of the problem domain with a set of unstructured nodes, providing accurate and convergent structural analyses. Additionally, meshless methods expedite the development of the geometric crack tip propagation algorithm. The present numerical application demonstrates the proficiency of the present fracture propagation algorithm to analyse the mixed-mode fracture propagation in adhesively bonded joints. [ABSTRACT FROM AUTHOR]

• A meshless method is used to predict the fracture propagation of adhesive joints. • The crack tip is advanced using a remeshing technique combined with the RPIM. • The numerical methodology is validated against experimental data. In this work, a numerical methodology based on a meshless technique is proposed to predict the fracture propagation in Double Cantilever Beam (DCB) adhesive joints. The Radial Point Interpolation Method (RPIM) is used to approximate the field variable at each crack increment step. The meshless method permits a flexible discretization of the problem domain in a set of unstructured field nodes and eases the implementation of the geometric crack propagation algorithm. Regarding the fracture propagation algorithm, a recent adaptative remeshing technique is used combined with the RPIM. The crack tip is explicitly propagated by locally remeshing the field nodes and triangular integration cells in the crack tip vicinity. To predict the crack initiation, a fracture mechanics criterion based on the energy release rate in DCB is implemented. The proposed numerical methodology is validated with experimental data. [ABSTRACT FROM AUTHOR]

Adhesive joints are being increasingly used in various industries, including the automotive or the wind turbines industries. Such increasing interest is a direct result of its high structural efficiency and also the product of its related scientific research. Therefore, the state-of-the-art on adhesive joints is significantly expanding. The current work aims to discuss the most recent works dedicated to the numerical analysis of the dynamic behaviour of adhesive joints. Dynamic behaviour was divided into three separate fields: fatigue, variable strain rate and impact, and modal analysis. It was found that Cohesive Zone Models are a popular approach to study fatigue, variable strain rates and impact. Additionally, the available literature focused on fatigue and impact is more extensive than the one focused on modal analysis. Overall, it was found that the available research on the numerical analysis of the dynamic behaviour of adhesive joints is increasing at a solid rate, and many geometrical and material variations have been tested numerically. With this review designers and researchers of adhesive joints should be able to choose the most suitable numerical technique for their specific dynamic analysis. [ABSTRACT FROM AUTHOR]

Adhesives are an exceptionally well-suited method for joining composites. Unlike other methods, such as bolting or riveting, adhesives do not introduce holes in their joining material. This is a significant advantage in the case of composites because the holes required by bolting or riveting induce stress concentrations and can also lead to tears, burrs or delamination. A point of concern in adhesive joints is the adhesive/adherend interface corner where a stress singularity occurs, and failure usually initiates. Thus, it is crucial to study this stress singularity to better understand adhesive joints' mechanical behaviour. The goal of this work is to validate the application of the Intensity of Singular Stress Fields (ISSF) criterion to meshless methods, in this case, the Radial Point Interpolation Method (RPIM). With this purpose, eight overlap lengths (L O) in single-lap joints (SLJ) composed of Carbon Fibre Reinforced Polymer (CFRP) and bonded with a brittle adhesive were experimentally and numerically tested. Furthermore, an extrapolation based method is implemented to determine the critical stress singularity components (H c) necessary for the strength predictions. In the end, the experimental and numerical results are compared to assess the suitability of the method. It was found that the ISSF criterion can be accurately applied to meshless methods and composite materials successfully, given the simplicity of the method applied. [ABSTRACT FROM AUTHOR]

Structural design has significantly changed over the years driven by a weight reduction goal. In that sense, composite materials established themselves as the material of excellence in most engineering areas, replacing wood, steel and aluminium. Connection processes also experienced a transformation, with adhesive bonding standing out. Those new materials and techniques require deep research until they could be applied to structures. These studies led to the appearance of different methods for evaluating material and bond performance. Fracture mechanics is an approach based on material discontinuities or defects. Recently, a new fracture mechanics based technique arose called Intensity of Singular Stress Fields (ISSF). It hinges on the Stress Intensity Factors (SIF) approach but does not require an initial crack. This investigation aims to evaluate the applicability of this technique to composite materials. For that, Single-Lap Joints (SLJ) made from Carbon Fibre Reinforced Polymer (CFRP) bonded with a brittle adhesive and eight different overlap lengths (L O) are analysed. The numerical simulations and strength predictions are performed through the Finite Element Method (FEM) and MATLAB software. Finally, the numerical predictions are compared to the experimental data. It can be concluded that the ISSF is applicable to orthotropic materials. [ABSTRACT FROM AUTHOR]

Modern transportation, medical, and leisure equipment are often manufactured with non-metallic and composite materials bonded with adhesives. Numerical analyses of these joints are commonly performed using the Finite Element Method (FEM). In adhesive joints, the bond line is small compared to the substrates requiring highly refined meshes to perform the analyses. Also, adhesives can reach higher strains compared to the substrates, and so causing mesh distortion and compromising the solution. Alternatively, meshless methods (MM) can be employed. Single-lap joints (SLJ), during loading, present tensile and compressive stresses along the adhesive layer. Commonly, in elastic-plastic analyses, equal adhesive's strength in tension and compression is considered (using von Mises (vM) yield criterion), but it has been reported that adhesives are stronger in compression. Thus, a yielding criterion such as the Exponent Drucker-Prager (EDP) can be used; however, no MM implementations are available in the literature. This work seeks to implement the EDP into a MM, the Natural Neighbour Radial Point Interpolation Method (NNRPIM). Then, using the NNRPIM elastic-plastic parametric analyses of SLJ with aluminium substrates were performed considering four overlap lengths (L O) and two different ductile adhesives. All the cases were also evaluated using MM and the vM yield criterion, as a benchmark. Stress and strain distributions along the bond-line were obtained; afterwards, joint strength (P m a x ) was determined by using continuum mechanics failure criteria, and then, evaluated and compared. Then, the results were compared against experimental data. The cases solved using the EDP predicted P m a x closer to the experimental data; the joints with intermediate overlap lengths L O = 25.0 mm presented the closest values. In conclusion, the results' correlation with experimental data indicates the EDP is closer than vM to the actual adhesive behaviour in the joints. Also, the EDP was successfully implemented. Overall, the NNRPIM is a strong and accurate alternative for elastic-plastic analyses of adhesive joints. [ABSTRACT FROM AUTHOR]