Estudo do efeito de escala na taxa crítica de libertação de energia do betão
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2010
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Nesta Tese efectuou-se um estudo de averiguação do efeito de escala sobre um parâmetro relevante da Mecânica da Fractura, designado por taxa crítica de libertação de energia GIc. Para esse efeito, escolheu-se a geometria Single-Edge-Notched beam loaded in Three-Point-Bending (i.e., o ensaio de flexão em três pontos, de uma viga pré-entalhada a meio vão), por forma a induzir a fractura em puro modo I. Escolheu-se o betão como material de teste, tendo-se ensaiado duas dimensões de provetes em regime de controlo de deslocamento. Como as dimensões dos provetes escolhidos são consideráveis, desenvolveram-se dois métodos alternativos destinados à determinação da propriedade de fractura, que tem em conta o efeito do peso próprio. De seguida, procedeu-se à validação dos métodos de avaliação da taxa crítica de libertação de energia, recorrendo a modelos coesivos. Tendo por base a informação experimental relativa às dimensões testadas, bem como um método fiável de determinação da propriedade de fractura, constatou-se o que parece ser um ténue efeito de escala sobre GIc.
A study was carried out to investigate the size effect on a relevant parameter of Fracture Mechanics, known as the critical energy release rate GIc. To this end, the Single-Edge-Notched beam loaded in Three-Point-Bending (SEN-TPB) was chosen in order to induce fracture under pure mode I. Concrete was chosen as the testing material, involving specimens geometrically similar of two sizes. As mass is not negligible, two alternative methods have been proposed evaluate the Resistance curve (R-curve), taking into account the specimen self weight. Then, based on the cohesive modeling (CZ) of the material damage, the numerical validation of the proposed methods has been performed, realizing that the proposed methods are able to retrieve an R-cure with a horizontal asymptote equal to the fracture energy used in the FEM computations. Based on experimental data (i.e., P-d curves) of both specimen sizes, a method has been chosen to determine fracture properties, thus permitting to observe what appears to be a slight size effect on GIc.
A study was carried out to investigate the size effect on a relevant parameter of Fracture Mechanics, known as the critical energy release rate GIc. To this end, the Single-Edge-Notched beam loaded in Three-Point-Bending (SEN-TPB) was chosen in order to induce fracture under pure mode I. Concrete was chosen as the testing material, involving specimens geometrically similar of two sizes. As mass is not negligible, two alternative methods have been proposed evaluate the Resistance curve (R-curve), taking into account the specimen self weight. Then, based on the cohesive modeling (CZ) of the material damage, the numerical validation of the proposed methods has been performed, realizing that the proposed methods are able to retrieve an R-cure with a horizontal asymptote equal to the fracture energy used in the FEM computations. Based on experimental data (i.e., P-d curves) of both specimen sizes, a method has been chosen to determine fracture properties, thus permitting to observe what appears to be a slight size effect on GIc.
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Dissertação de Mestrado em Engenharia Civil