Estudo do efeito da orientação de uma ligação roscada em tecido ósseo cortical através de um ensaio de arrancamento
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2017
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Neste trabalho realizou-se a caracterização numérico-experimental do comportamento de uma ligação aparafusada em tecido ósseo, submetida a um esforço de arrancamento, empregando parafusos corticais. Estudou-se o efeito do ângulo formado pelo eixo do parafuso e o plano da placa do material usado como substituto do tecido ósseo. Esta substituição prendeu-se com limitações geométricas do tecido ósseo referentes à realização de ensaios mecânicos, tendo-se optado pela madeira de Pinus pinaster Ait.
À semelhança da madeira, o tecido ósseo cortical exibe um comportamento ortotrópico, caracterizado por três direções de simetria material: a direção longitudinal (L), a direção radial (R) e a direção tangencial (T). Desta disposição estrutural resulta a necessidade de se efetuar uma caracterização mecânica da ligação aparafusada, em função do ângulo de aplicação da carga, uma vez que esta influencia de forma significativa o desempenho da ligação. Os ensaios experimentais foram realizados considerando os seguintes ângulos entre o parafuso e a direção longitudinal da madeira: 0, 22,5º e 45º. Para tal, a madeira foi previamente cortada com as direções desejadas, sendo que o ensaio de arrancamento teve por base a norma ASTM F 1691 – 96.
Criou-se um modelo de elementos finitos tridimensionais realista que reproduziu fielmente a configuração do filete de rosca, assim como o provete (peça de madeira) e uma placa de retenção destinada à imobilização do provete, que foi validado experimentalmente. Este procedimento permitiu identificar a influência dos parâmetros geométricos da ligação mais relevantes de cada uma das montagens testadas. A simulação por elementos finitos revelou que a propagação do dano nesta ligação ocorre em modo misto.
In this work a numerical and experimental characterization of the mechanical behavior of a cortical bone bolted-joint submitted to a pullout action was performed. The effect of the angle between the screw axis and the plane of the plate used as substitute of the cortical bone was studied. Due to limitations associated to geometrical restrictions of the bolted-joint, Pinus pinaster Ait. was used as the testing material in this study. Similarly to wood, cortical bone tissue exhibits an orthotropic behavior, which is characterized by three orthogonal directions of material symmetry: longitudinal (L), radial (R) and tangential (T). According to this structural arrangement it turns evident that the mechanical characterization of the analyzed bolted-joint had to be performed for different loading angles (0, 22.5 and 45°). The experiments were executed following the procedures issued by the standard ASTM F 1691 – 96. A realistic three dimensional finite element model was created to replicate the configuration of the screw thread accurately, as well as the specimen (wood sample) and the retaining plate, used to immobilize the joint. Cohesive zone modelling was implemented to allow simulating damage onset and propagation in the dummy material under mixed-mode loading. Then, experimental results were used to validate the numerical model. Geometrical parameters were dully simulated in the analyzed screw-joint, allowing to identify the influence of the most relevant ones in regards to the stability of the joint. The numerical model revealed that damage propagation occurs under mixed-mode (I+II+III) loading.
In this work a numerical and experimental characterization of the mechanical behavior of a cortical bone bolted-joint submitted to a pullout action was performed. The effect of the angle between the screw axis and the plane of the plate used as substitute of the cortical bone was studied. Due to limitations associated to geometrical restrictions of the bolted-joint, Pinus pinaster Ait. was used as the testing material in this study. Similarly to wood, cortical bone tissue exhibits an orthotropic behavior, which is characterized by three orthogonal directions of material symmetry: longitudinal (L), radial (R) and tangential (T). According to this structural arrangement it turns evident that the mechanical characterization of the analyzed bolted-joint had to be performed for different loading angles (0, 22.5 and 45°). The experiments were executed following the procedures issued by the standard ASTM F 1691 – 96. A realistic three dimensional finite element model was created to replicate the configuration of the screw thread accurately, as well as the specimen (wood sample) and the retaining plate, used to immobilize the joint. Cohesive zone modelling was implemented to allow simulating damage onset and propagation in the dummy material under mixed-mode loading. Then, experimental results were used to validate the numerical model. Geometrical parameters were dully simulated in the analyzed screw-joint, allowing to identify the influence of the most relevant ones in regards to the stability of the joint. The numerical model revealed that damage propagation occurs under mixed-mode (I+II+III) loading.
Descrição
Dissertação de Mestrado em Engenharia Mecânica
Palavras-chave
Tecido ósseo cortical , Ligação roscada