Avaliação do comportamento cíclico do polietileno de ultra-alto peso molecular

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2016.Materiais poliméricos têm se destacado de maneira crescente na fabricação de componentes estruturais de alto desempenho. Particular ênfase tem sido dada à fabricação de próteses e implantes cirúrgicos pela indústria médica. Analisando a função mecânica desempenhada por esses materiais atualmente, faz-se necessária uma investigação mais detalhada sobre seu comportamento mecânico, tendo em vista que a falha destes componentes é extremamente indesejável, influenciando diretamente possíveis complicações na saúde de pacientes. O polietileno de ultra-alto peso molecular (UHMWPE) é, de maneira consolidada, um dos materiais mais utilizados na fabricação de implantes médicos. Apesar de sua larga utilização, o comportamento mecânico e os parâmetros associados deste polímero são de difícil acesso na literatura, por se tratar de um assunto relativamente recente. A influência de parâmetros como níveis de carregamento, temperatura, frequência e taxas de deformação no comportamento mecânico do UHMWPE tornam a avaliação deste material complexa, exigindo a obtenção de dados por meio de diferentes configurações de ensaios. O presente trabalho tem como objetivo investigar a influência dos níveis de carregamento, frequência de excitação, temperatura e taxa de deformação na resposta mecânica do UHMWPE, bem como o desenvolvimento de uma metodologia para caracterização do mesmo. Para tanto, foram realizados ensaios monotônicos de tração e ensaios cíclicos em diferentes taxas de deformação e diferentes temperaturas. Os resultados mostraram uma grande dependência do comportamento mecânico do UHMWPE em relação, principalmente, à taxa de deformação e à temperatura em que o ensaio é realizado para ambos os ensaios. O fenômeno de fluência cíclica, oriundo dos ensaios cíclicos, foi observado em todas as condições de ensaio realizadas. Este fenômeno apresentou uma forte dependência em relação aos níveis de carga em que os ensaios foram realizados.Abstract : Polymeric materials have been increasingly prominent in the manufacture of high performance structural components. Particular emphasis has been placed on the manufacture of prostheses and surgical implants by the medical industry. By analyzing the mechanical function performed by these materials today, a more detailed investigation of their mechanical behavior is necessary, since the failure of these components is extremely undesirable, directly influencing possible complications in the health of patients. Ultra-high molecular weight polyethylene (UHMWPE) is one of the most widely used materials in the manufacture of medical implants. Despite its wide use, the mechanical behavior and the associated parameters of this polymer are difficult to access in the literature, being a relatively recent subject. The influence of parameters such as loading levels, temperature, frequency and strain rates on the mechanical behavior of the UHMWPE makes the evaluation of this material complex, requiring data collection through different test configurations. The present work aims to investigate the influence of loading levels, excitation frequency, temperature and strain rate on the mechanical response of UHMWPE, as well as the development of a methodology to characterize it. For this purpose, monotonic traction tests and cyclic tests were carried out at different deformation rates and at different temperatures. The results showed a great dependence of the mechanical behavior of the UHMWPE mainly in relation to the deformation rate and to the temperature at which the test is performed for both tests. The cyclic creep phenomenon, from the cyclic tests, were observed in all test conditions. This phenomenon showed a strong dependence on the load levels at which the tests were performed

Experimental evaluation of the employment of a laminated composite material with sisal fibres as reinforcement in timber beams.

Abstract Timber is the oldest construction materials in the world, have been widely used in structures in addition to having a high longevity, if treated properly (maintenance). If this does not occur, the wood deteriorates due to the action of insects, fungi and other aggressive agents. There are several materials and techniques used to reinforce the damaged parts. This paper presents an experimental study ofEucalyptus grandis and Pinus elliiottiitimber bea ms rein forced with sisal fibres laminated composite materials. The co mposite material and the wood were prepared for testing. In order to simulate the defect, some parts were cracked. The study was to determine the maximu m load (rupture) applied on the timberin the conditions: without defect, with defect and without composite and with defect and with composite, aiming to verify the efficiency of the laminate as reinforcement in the wooden beams. The experimental results indicate the possible use of the laminated composite as reinforcement, presenting considerable increase in the maximu m strength supported by the timber when compared to unreinforced cracked condition, being more efficient for the Pinus elliiottii species

Characterization of Tropical Wood Species for Use in Civil Constructions

Abstract The wood is one of the most applicable materials in industrial activit ies due to its availability allied to its satisfactory mechanical p roperties, presenting a good strength/density relation. Its versatility is fundamental fo r the large expansion of its use on structure building. The explorat ion, init ially selective, turned to be selective and also predatory, what lead to a shortage, raising systematically the prices until the mo ment where it was not anymore probable to use it on the quantities registered until then. The solution was to define species, between more than 5.000 variet ies in AmazonicaTropical Forest, which could substitute the 100 co mmercially used ones. However, due to technical limitations, these species cannot be completely characterized, what leads to a misusing of timber, once its behaviour is not known completely when it is under mechanical stresses. This research presents some results of the characterizat ion of the following timber species: Canelão, Env ira Branca, Guarajá, Quaruba Rosinha and Breu Vermelho. These species are found close to Sinop (Mato Grosso -Brazil), and the results obtained reveal clearly the potential of each species under mechanical stresses, showing that some of them can be good substitutes to the commonly wood speciesused

Evaluation of Dimensional and Aerodynamic Parameters for an Aircraft Radio Controlled through Genetic Algorithms and Design of Experiments

Abstract This paper presents a study of aircraft configuration TKV2012 that is more optimized as possible in all aspects of stage length, questions and restrictions established by the SAE Co mpetit ion BRAZIL Aero Design 2012. The analytical method for estimation of the aircraft aerodynamic coefficients was performed using the linear appro ximation to the theory of Multhopp. Design of Experiments (DOE) was used integrated into the genetic algorith m through the interface ModeFRONTIER®, version 4.3, the company Esteco®. We used the algorithm and Planning SOBOL MOGA II, with about 28 input variables, given the requirements: project report (containing plants and forecast payload), oral presentation, maximu m loaded weight, high structural efficiency, "accuracy" Predict ion Weight Loaded (Accuracy Project) and bonuses. The primary outcome variab le was the total score, since the goal was to maximize their. The results allowed to identify and optimize the d imensional parameters of the aircraft, as well as signaling the main factors that influence the total score, helping to define the configuration of the aircraft 2012