Browsing by Author "Ramalho, L.D.C."
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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.
- Elasto-plastic adhesive joint design approach by a radial point interpolation meshless methodPublication . Resende, R.F.P.; Resende, B.F.P.; Sanchez Arce, I.J.; Ramalho, L.D.C.; Campilho, R.D.S.G.; Belinha, JorgeFor 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.
- 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.
- 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.
- A new structural two-component epoxy adhesive: Strength and fracture characterizationPublication . Cardoso, M.G.; Pinto, J.E.C.; Campilho, R.D.S.G.; Nóvoa, P.J.R.O.; Silva, Francisco J. G.; Ramalho, L.D.C.In the past decades, adhesive technology has been useful in order to solve numerous issues related with conventional joining techniques (bolting, riveting and welding). Several advantages of adhesive bonding can be pointed out, such as low weight (relevant in the automotive and aeronautical industries), capability to resist to adverse environmental conditions, lower manufacturing costs and possibility to join different materials. To predict crack propagation of an adhesive joint by advanced fracture mechanics-based techniques such as cohesive zone models (CZM) it is not enough to know the traditional mechanical properties, such as Young’s modulus (E), shear modulus (G), tensile strength (σf) and shear strength (τf). Actually, it is also mandatory to estimate the tensile (GIC) and shear fracture energies (GIIC). The purpose of this work is to carry out the mechanical and fracture property characterization of a new structural two-component epoxy adhesive. With this purpose, four tests which were conducted: tensile testing to bulk specimens, shear testing with thick adherend shear tests (TAST), double-cantilever beam (DCB) and end-notched flexure (ENF). With these tests, it was possible to determine the mechanical and fracture properties of the adhesive in tension and shear. Different data reduction methods were evaluated for the fracture properties. The test results agreed with the data provided by the manufacturer and will enable the design of bonded structures with this adhesive.
- Numerical analysis of the dynamic behaviour of adhesive joints: A reviewPublication . Ramalho, L.D.C.; Sánchez-Arce, Isidro J.; Gonçalves, Diogo C.; Belinha, Jorge; Campilho, R.D.S.G.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.