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- 3D printed devices to avoid hand contact with commonly shared surfacesPublication . Pais, A.; Ferreira, C.; Pires, V.; Silva, V.; Alves, J. Lino; Bastos, João; Belinha, JorgeIn the context of the COVID-19 pandemic, public spaces had to be quickly adapted to the new circumstances especially under the uncertainty of the pandemic development. Door handles are some of the most touched surfaces and so, this point of contagion was chosen to be tackled and two solutions were developed that would prevent direct touch with the handle: a portable and a fixed device. The portable device (HYHOOK + HYTIP) is a hook-like device holding a finger cover, which permits to open doors and push buttons safely. The fixed device (HANDGENIC) is meant to be assembled in door handles to equip buildings, such as universities or schools. With the fixed device, the user can open the door using their forearm which makes them less likely to transfer any particles to eyes, nose or mouth. The 3D printing Fused Filament Fabrication (FFF) process was selected as manufacturing technique, which allows the fast production of prototypes. This work portrays the development process and design iterations taking into consideration the concerns about the functioning of the devices and possible failures or alternative uses. To assure structural integrity of the parts, finite element (FE) analysis was used to verify its mechanical response. As conclusion, it was found that FE analysis indicate that the devices are structurally sound to be used in public spaces and that 3D printing is a useful way to rapidly develop devices while testing several design possibilities.
- Topology optimization using a natural neighbour meshless method combined with a bi-directional evolutionary algorithmPublication . Gonçalves, D.C.; Lopes, Joel; Campilho, R.D.S.G.; Belinha, JorgeDue to recent developments in the additive manufacturing industry, topology optimization is nowadays a powerful computational tool that allows to design feasible lightweight components. Although the Finite Element Method (FEM) is the most applied discretization technique, meshless methods are currently established as accurate numerical methods with relevant advantages in several engineering fields. Nonetheless, the state-of-the-art of meshless methods in topology optimization is still scarce. This work develops the combination of a bi-direction structural optimization (BESO) algorithm with the Natural Neighbour Radial Point Interpolation Method (NNRPIM), a meshless method combining the natural neighbours geometric concept with the RPI shape functions. First, several benchmark examples are solved to evaluate the algorithm capability under several algorithm parameters. The proposed methodology is then implemented to design new automotive lightweight components. The results from the numerical applications demonstrate that the NNRPIM is a solid technique to be incorporated in optimization algorithms. Additionally, innovative automotive industry designs for additive manufacturing can be obtained using the presented approach.
- 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.
- Elastoplastic Analysis of Plates with Radial Point Interpolation Meshless MethodsPublication . Belinha, Jorge; Aires, MiguelFor both linear and nonlinear analysis, finite element method (FEM) software packages, whether commercial or in-house, have contributed significantly to ease the analysis of simple and complex structures with various working conditions. However, the literature offers other discretization techniques equally accurate, which show a higher meshing flexibility, such as meshless methods. Thus, in this work, the radial point interpolation meshless method (RPIM) is used to obtain the required variable fields for a nonlinear elastostatic analysis. This work focuses its attention on the nonlinear analysis of two benchmark plate-bending problems. The plate is analysed as a 3D solid and, in order to obtain the nonlinear solution, modified versions of the Newton–Raphson method are revisited and applied. The material elastoplastic behaviour is predicted assuming the von Mises yield surface and isotropic hardening. The nonlinear algorithm is discussed in detail. The analysis of the two benchmark plate examples allows us to understand that the RPIM version explored is accurate and allows to achieve smooth variable fields, being a solid alternative to FEM.
- An evolutionary structural optimization algorithm for the analysis of light automobile parts using a meshless techniquePublication . Gonçalves, Diogo; Lopes, Joel; Campilho, Raul; Belinha, JorgePurpose The purpose of the present work is to develop the combination of the radial point interpolation method (RPIM) with a bi-directional evolutionary structural optimization (BESO) algorithm and extend it to the analysis of benchmark examples and automotive industry applications. Design/methodology/approach A BESO algorithm capable of detecting variations in the stress level of the structure, and thus respond to those changes by reinforcing the solid material, is developed. A meshless method, the RPIM, is used to iteratively obtain the stress field. The obtained optimal topologies are then recreated and numerically analyzed to validate its proficiency. Findings The proposed algorithm is capable to achieve accurate benchmark material distributions. Implementation of the BESO algorithm combined with the RPIM allows developing innovative lightweight automotive structures with increased performance. Research limitations/implications Computational cost of the topology optimization analysis is constrained by the nodal density discretizing the problem domain. Topology optimization solutions are usually complex, whereby they must be fabricated by additive manufacturing techniques and experimentally validated. Practical implications In automotive industry, fuel consumption, carbon emissions and vehicle performance is influenced by structure weight. Therefore, implementation of accurate topology optimization algorithms to design lightweight (cost-efficient) components will be an asset in industry. Originality/value Meshless methods applications in topology optimization are not as widespread as the finite element method (FEM). Therefore, this work enhances the state-of-the-art of meshless methods and demonstrates the suitability of the RPIM to solve topology optimization problems. Innovative lightweight automotive structures are developed using the proposed methodology.
- Topology optimization of light structures using the natural neighbour radial point interpolation methodPublication . Gonçalves, D. C.; Lopes, Joel; Campilho, R.D.S.G.; Belinha, JorgeIn this work, a bi-directional evolutionary topology optimization algorithm capable of reinforcing the structure at critical high stress regions is combined with the Natural Neighbour Radial Point Interpolation Method (NNRPIM). The NNRPIM uses the Voronoï diagram and natural neighbour concept to establish the background integration points, enforce the nodal connectivity, and construct the RPI shape functions. State-of-the-art of meshless methods in topology optimization is limited when compared with the classic Finite Element Method. Hence, this work originally introduces an accurate truly meshless method, the NNRPIM, to the topology optimization field. The proposed algorithm is validated by solving several benchmark topology optimization problems. A parametric study on algorithm parameters and mesh influence is performed, and the computational processing time is also evaluated Finally, the proposed calibrated method is extended to design lightweight aircraft industry components.
- Introductory application of a natural neighbour meshless elastic formulation to double-lap adhesive jointsPublication . Gonçalves, Diogo C.; Sánchez-Arce, Isidro J.; Ramalho, Luís D. C.; Campilho, Raul; Belinha, JorgeNowadays, adhesive bonding is an essential joining technique in top-end sectors, such as aircraft, automotive, and construction industries. Due to their advantages over traditional joining methods, adhesive joints research has been under huge developments in recent years, being the development of accurate and efficient numerical techniques a leading challenge in adhesive joint design. Although the finite element method (FEM) is an established discretisation technique, meshless methods emerged as alternative discretisation methods to evaluate adhesive joints. Nonetheless, meshless techniques still require deeper research in adhesive joint simulations, where strength prediction is hindered by intricate stress states and material behaviour. This paper aims to evaluate the natural neighbours radial point interpolation method (NNRPIM) in the linear analysis of adhesive joints. The capability of the method was addressed by comparing it with analytical models, the FEM and experimental data. As the applications of meshless methods to analyse adhesive joints are scarce, this work evaluates the behaviour of double-lap joints (DLJ) considering distinct overlap lengths and adhesive materials. DLJ has a different behaviour than single-lap joints, which are more commonly analysed. Thus, this work provides a preliminary linear analysis, which could be the basis for further analyses of adhesive joints combining the NNRPIM with elastic–plastic, hyper-elastic, and large deformations formulations. Although it is remarked that elastic formulations underpredict joint strength, the NNRPIM shows similar results to the FEM, which supports the extension of the NNRPIM to more representative mathematical formulations and complex joint designs.
- 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.
- Computational simulation of cellular proliferation using a meshless methodPublication . Barbosa, M.I.A.; Belinha, Jorge; Jorge, R.M. Natal; Carvalho, A.X.Background and objective: During cell proliferation, cells grow and divide in order to obtain two new genetically identical cells. Understanding this process is crucial to comprehend other biological processes. Computational models and algorithms have emerged to study this process and several examples can be found in the literature. The objective of this work was to develop a new computational model capable of simulating cell proliferation. This model was developed using the Radial Point Interpolation Method, a meshless method that, to the knowledge of the authors, was never used to solve this type of problem. Since the efficiency of the model strongly depends on the efficiency of the meshless method itself, the optimal numbers of integration points per integration cell and of nodes for each influence-domain were investigated. Irregular nodal meshes were also used to study their influence on the algorithm. Methods: For the first time, an iterative discrete model solved by the Radial Point Interpolation Method based on the Galerkin weak form was used to establish the system of equations from the reactiondiffusion integro-differential equations, following a new phenomenological law proposed by the authors that describes the growth of a cell over time while dependant on oxygen and glucose availability. The discretization flexibility of the meshless method allows to explicitly follow the geometric changes of the cell until the division phase. Results: It was found that an integration scheme of 6 × 6 per integration cell and influence-domains with only seven nodes allows to predict the cellular growth and division with the best balance between the relative error and the computing cost. Also, it was observed that using irregular meshes do not influence the solution. Conclusions: Even in a preliminary phase, the obtained results are promising, indicating that the algorithm might be a potential tool to study cell proliferation since it can predict cellular growth and division. Moreover, the Radial Point Interpolation Method seems to be a suitable method to study this type of process, even when irregular meshes are used. However, to optimize the algorithm