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- Analysis of stress singularity in adhesive joints using meshless methodsPublication . Ramalho, L.D.C.; Dionísio, J.M.M.; Sánchez-Arce, I.J.; Campilho, R.D.S.G.; Belinha, JorgeRecent years saw a rise in the application of bonding techniques in the engineering industry. This fact is due to the various advantages of this technique when compared to traditional joining methods, such as riveting or bolting. The growth of bonding methods demands faster and more powerful tools to analyze the behavior of products. For that reason, adhesive joints have been the subject of intensive investigation over the past few years. Recently, a fracture mechanics based approach emerged with great potential to evaluate joint behavior, called Intesity of Singular Stress Fields (ISSF), similar to the Stress Intensity Factor (SIF) concept. However, it allows the study of multi-material corners and does not require an initial crack. This approach was not yet tested with meshless methods. The present work intends to fill this gap, resorting to the Radial Point Interpolation Method (RPIM). With this purpose, adhesive joints with four different overlap lengths (LO) bonded with a brittle adhesive were studied. The interface corner's stresses were also evaluated. The predicted strengths were compared with the experimental data to assess the accuracy of the applied methods. In conclusion, the ISSF criterion proved to be applicable to meshless methods, namely the RPIM.
- Hyperelasticity and the radial point interpolation method via the Ogden modelPublication . Sánchez-Arce, I.J.; Ramalho, L.D.C.; Gonçalves, D.C.; Campilho, R.D.S.G.; Belinha, JorgeRubber-like and biological materials could show a hyperelastic behaviour, often studied using the Finite Element Method (FEM), limitations still exist due to the large deformations that this type of material experiment. Conversely, meshless methods are suitable for large deformations. The Ogden hyperelastic model can also represent the Neo-Hookean and Mooney–Rivlin models with ease, making it versatile but its implementation into meshless methods is yet to be done. In this work, the Ogden model was implemented into the Radial Point Interpolation Method (RPIM), a robust and accurate meshless method, within its iterative process allowing for future simulation of multi-material domains. Then, the implementation was tested with small deformations cases. The implementation was validated using three examples and a different hyperelastic model was used for each example, Mooney–Rivlin, Neo-Hookean, and Ogden, whilst their material properties were taken from the literature. The results were compared to FEM solutions and the literature, a good agreement was achieved with differences below 2%, indicating a successful implementation. This is the first implementation of the Ogden model into the RPIM. The ability to model hyperelastic structures together with the inherent advantages of meshless methods provides a good alternative for the analysis of industrial and biological structures.
- Meshless analysis of the stress singularity in composite adhesive jointsPublication . Ramalho, L.D.C.; Dionísio, J.M.M.; Sánchez-Arce, I.J.; Campilho, R.D.S.G.; Belinha, JorgeAdhesives 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 (LO) 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 (Hc) 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.
- Fracture propagation based on meshless method and energy release rate criterion extended to the Double Cantilever Beam adhesive joint testPublication . Gonçalves, D.C.; Sánchez-Arce, I.J.; Ramalho, L.D.C.; Campilho, R.D.S.G.; Belinha, JorgeIn 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.