Influência da geometria na análise de flambagem em cilindros de paredes finas
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Data
2018-02-23
Autores
Pessutto, Bernardo Luis
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Universidade Estadual Paulista (Unesp)
Resumo
Estruturas de parede fina são amplamente utilizadas na engenharia contemporânea devido à sua boa relação peso x resistência. Sua aplicação vai da construção civil, como cúpulas e pontes, até a aeronáutica e aeroespacial. Uma geometria de parede fina comum são os cilindros, observados em oleodutos, fuselagem e vasos de pressão. Para ser classificados como parede fina, a razão entre a espessura da parede e seu raio não deve ultrapassar 1:10. Eles ficam submetidos a esforços constantes e suscetíveis à instabilidade estrutural, em especial à flambagem, entrando em colapso repentinamente, muito abaixo da carga de projeto estipulada. Assim, compreender o comportamento desta instabilidade torna-se essencial para o avanço da engenharia. Para iniciar a compreensão da instabilidade, primeiro necessita-se conhecer as imperfeições geométricas da estrutura, ocasionadas, muitas vezes, pelo próprio processo de fabricação. A concepção destas imperfeições foi tratada por duas técnicas: CMM – Coordinates Mensuring Machine e CAI –Computer Aided Inspection. A primeira, tradicional, por contato, utilizando sensores LVDT – Linear Variable Differential Transformer, e, a segunda, vanguardista, sem contato, denominada "fotogrametria". Com isto, foi possível conceber uma estrutura tridimensional a ser analisada numericamente para obtenção das cargas críticas de flambagem, na qual estas duas técnicas apresentaram desvios condizentes com a literatura atual. Isto demonstrou, não somente, a acuracidade da técnica tradicional de contato para obtenção da geometria, mas, também, como a fotogrametria pode ser uma alternativa viável para inspeções rápidas de geometria.
Thin wall structures are widely used in contemporary engineering because of their good weight and strength ratio. Their application goes from civil construction such as domes and bridges, to aeronautics and aerospace. A common thin wall geometry are the cylinders, observed in oil pipelines, fuselage and pressure vessels. In order to be classified as thin wall, the ratio between the wall thickness and its radius must not exceed 1:10. They are subjected to constant efforts and susceptible to structural instability, especially buckling, suddenly collapsing, quite below the stipulated design load. Thus, understanding the behavior of this instability becomes essential for the advance of engineering. In order to begin the understanding of instability, it is firstly necessary to know the geometrical imperfections of the structure, often caused by the manufacturing process itself. The design of these imperfections was treated by two techniques, CMM – Coordinates Measuring Machine and CAI – Computer Aided Inspection. The first one, more conservative, by contact, using LVDT sensors, and, the second one, avant-garde, contactless, called “photogrammetry”. With this, it was possible to design a three-dimensional structure to be numerically analyzed to obtain the critical loads of buckling, in which these two techniques presented follow deviations from the current literature. This demonstrates not only the accuracy of the traditional contact technique to obtain geometry, but also how photogrammetry can be a viable alternative for rapid geometry inspections.
Thin wall structures are widely used in contemporary engineering because of their good weight and strength ratio. Their application goes from civil construction such as domes and bridges, to aeronautics and aerospace. A common thin wall geometry are the cylinders, observed in oil pipelines, fuselage and pressure vessels. In order to be classified as thin wall, the ratio between the wall thickness and its radius must not exceed 1:10. They are subjected to constant efforts and susceptible to structural instability, especially buckling, suddenly collapsing, quite below the stipulated design load. Thus, understanding the behavior of this instability becomes essential for the advance of engineering. In order to begin the understanding of instability, it is firstly necessary to know the geometrical imperfections of the structure, often caused by the manufacturing process itself. The design of these imperfections was treated by two techniques, CMM – Coordinates Measuring Machine and CAI – Computer Aided Inspection. The first one, more conservative, by contact, using LVDT sensors, and, the second one, avant-garde, contactless, called “photogrammetry”. With this, it was possible to design a three-dimensional structure to be numerically analyzed to obtain the critical loads of buckling, in which these two techniques presented follow deviations from the current literature. This demonstrates not only the accuracy of the traditional contact technique to obtain geometry, but also how photogrammetry can be a viable alternative for rapid geometry inspections.
Descrição
Palavras-chave
Instabilidade, Flambagem, Elementos finitos, Fotogrametria, Instability, Buckling, Finite element, Photogrammetry