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Estudo numérico da propagação da fratura num suporte de um Dispositivo de Proteção Lateral com recurso a Métodos sem Malha
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Esta dissertação de mestrado apresenta o estudo numérico de propagação de fratura num
suporte de fixação vertical de um Lateral Protection Device (LPD) aplicado a veículos pesados
de mercadorias. Um LPD constitui um componente mecânico crítico no âmbito da segurança
rodoviária passiva, projetado de acordo com o Regulamento n.º 73 da United Nations Economic
Commission for Europe (UNECE) para mitigar as consequências de colisões laterais e evitar o
esmagamento de peões, ciclistas e motociclistas sob a estrutura do veículo pesado. Face à
severidade operacional do setor automóvel, o componente pode estar sujeito a severos
fenómenos de concentração de tensões. A simulação numérica através do tradicional método
dos elementos finitos apresenta limitações, nomeadamente a dependência de uma malha com
conectividade fixa e a necessidade de algoritmos de reconstrução de malha
computacionalmente onerosos para simular a propagação de fissuras. Como alternativa para
superar estes obstáculos, neste trabalho investigam-se os Métodos sem Malha, com foco no
método Radial Point Interpolation Method (RPIM) e o Natural Neighbour Radial Interpolation
Method (NNRPIM).
Assim, o objetivo principal consiste em prever e analisar de forma rigorosa as trajetórias de
fratura e a distribuição dos campos de tensão no suporte estrutural elaborado sob diferentes
cenários de solicitação. Procura-se, deste modo, validar a eficiência e a fiabilidade dos métodos
sem malha na análise de componentes da indústria automóvel.
A metodologia adotada compreendeu a implementação numérica e paramétrica de diferentes
casos de estudo no software computacional Finite Element and Meshless Analysis Software
(FEMAS), integrando pré-fendas nas faces inferior e superior da peça. Além do método dos
elementos finitos, foram aplicados o Radial Point Interpolation Method (RPIM) e o Natural
Neighbour Radial Interpolation Method (NNRPIM), formulados sob o princípio dos trabalhos
virtuais. A direção e o avanço autónomo da fratura foram definidos pelo critério da Tensão
Tangencial Máxima.
Os resultados geométricos demonstram uma forte correspondência na propagação das
trajetórias da fratura geradas pelas abordagens sem malha e o modelo de referência em
elementos finitos. Na análise dos campos de tensão, constatou-se que o desempenho dos
métodos sem malha face ao método dos elementos finitos, proporciona uma maior nitidez
cromática, mapeando o nível de tensões e a transição de tensões de forma contínua, fluida e
suave.
Conclui-se que os métodos sem malha assumem-se como alternativas computacionais
robustas, viáveis e precisas. A supressão de restrições de conectividade fixa baseada em
elementos permitiu capturar a descontinuidade física da fratura de forma contínua e
automatizada, mitigando o custo computacional associado a processos de construção de malha
sucessivos. Por fim, o estudo paramétrico evidenciou que a localização da pré-fenda imposta
condiciona não só a magnitude dos picos de tensão, mas também a estabilidade do
componente.
This Master's degree presents a numerical study on crack propagation in the vertical mounting bracket of a Lateral Protection Device (LPD) applied to heavy goods vehicles. An LPD is a critical passive road safety component, designed in accordance with UNECE Regulation No. 73 to mitigate the consequences of side-impact collisions and prevent pedestrians, cyclists, and motorcyclists from being crushed under the heavy vehicle's structure. Given the operational severity of the automotive sector, this component can be subjected to severe stress concentration phenomena. Numerical simulation using the traditional finite element method presents limitations, namely the dependence on a fixed connectivity mesh and the need for computational costly remeshing algorithms to simulate crack propagation. As an alternative to overcome these obstacles, Meshless Methods are investigated, focusing on the Radial Point Interpolation Method (RPIM) and the Natural Neighbour Radial Interpolation Method (NNRPIM). Thus, the main objective is to accurately predict and analyze the fracture trajectories and stress field distributions in the structural bracket under different loading scenarios. Consequently, this study aims to validate the efficiency and reliability of meshless methods in the analysis of automotive industry components. The adopted methodology comprised the numerical and parametric implementation of different case studies in the computational software Finite Element and Meshless Analysis Software (FEMAS), integrating pre-cracks on both the lower and upper faces of the part. In addition to the finite element method, RPIM and NNRPIM were applied, formulated under the principle of virtual work. The direction and autonomous advance of the fracture were governed by the Maximum Tensile Stress criterion. The geometric results demonstrated a strong correspondence in the propagation of fracture trajectories generated by the meshless approaches and the finite element reference model. In the analysis of the stress fields, it was found that the performance of meshless methods, compared to the finite element method, provides higher chromatic sharpness, mapping the stress level and transition in a continuous, fluid, and smooth manner. In conclusion, meshless methods prove to be robust, viable, and precise computational alternatives. The suppression of fixed connectivity restrictions based on elements allowed capturing the physical discontinuity of the fracture in an automated and continuous way, mitigating the computational cost associated with successive meshing processes. Finally, the parametric study evidenced that the location of the imposed pre-crack deterministically conditions not only the magnitude of the stress peaks but also the stability of the component.
This Master's degree presents a numerical study on crack propagation in the vertical mounting bracket of a Lateral Protection Device (LPD) applied to heavy goods vehicles. An LPD is a critical passive road safety component, designed in accordance with UNECE Regulation No. 73 to mitigate the consequences of side-impact collisions and prevent pedestrians, cyclists, and motorcyclists from being crushed under the heavy vehicle's structure. Given the operational severity of the automotive sector, this component can be subjected to severe stress concentration phenomena. Numerical simulation using the traditional finite element method presents limitations, namely the dependence on a fixed connectivity mesh and the need for computational costly remeshing algorithms to simulate crack propagation. As an alternative to overcome these obstacles, Meshless Methods are investigated, focusing on the Radial Point Interpolation Method (RPIM) and the Natural Neighbour Radial Interpolation Method (NNRPIM). Thus, the main objective is to accurately predict and analyze the fracture trajectories and stress field distributions in the structural bracket under different loading scenarios. Consequently, this study aims to validate the efficiency and reliability of meshless methods in the analysis of automotive industry components. The adopted methodology comprised the numerical and parametric implementation of different case studies in the computational software Finite Element and Meshless Analysis Software (FEMAS), integrating pre-cracks on both the lower and upper faces of the part. In addition to the finite element method, RPIM and NNRPIM were applied, formulated under the principle of virtual work. The direction and autonomous advance of the fracture were governed by the Maximum Tensile Stress criterion. The geometric results demonstrated a strong correspondence in the propagation of fracture trajectories generated by the meshless approaches and the finite element reference model. In the analysis of the stress fields, it was found that the performance of meshless methods, compared to the finite element method, provides higher chromatic sharpness, mapping the stress level and transition in a continuous, fluid, and smooth manner. In conclusion, meshless methods prove to be robust, viable, and precise computational alternatives. The suppression of fixed connectivity restrictions based on elements allowed capturing the physical discontinuity of the fracture in an automated and continuous way, mitigating the computational cost associated with successive meshing processes. Finally, the parametric study evidenced that the location of the imposed pre-crack deterministically conditions not only the magnitude of the stress peaks but also the stability of the component.
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Palavras-chave
Fracture Mechanics Meshless Methods Crack Propagation Finite Element Method LPD Mecânica da fratura Métodos sem Malha Propagação da fratura Métodos dos Elementos Finitos