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In this work a generic rugged fracture surface was modeled starting from the fractal theory. This fracture surface (or crack profile) was considered as being a self-affine fractal, with averaged dimension, H (Hurst’s exponent). A relationship between the real fractured area (rugged) and the projected area (it planes) was obtained. Surfaces of fractures and experimental cracks were analyzed and compared with the model. Was concluded that the Hurst dimension of ruggedness is capable to express the irregularities of fracture surfaces to different materials, characterizing its fractal morphology. Soon after, the geometry fractal was introduced in Elasto-Plastic Fracture Mechanics (EPFM) with the purpose of modeling the fracture and the stable crack propagation in brittle and ductile materials. The equation that defines the elasto-plastic energy release rate, J, [ANDERSON 1995] was modified to take in account the ruggedness of fracture surface, using the mathematical expression that relates the rugged surface with the projected surface. By means of this relationship it was obtained, an mathematical expression to J-R curves that depends of noch size, the minimum fracture size, the Griffith critical size and the fractal dimension of fracture, showing with this the advantageous consequences of this modification. Experimental testings of J-R curve, to different materials, were accomplished by the compliance method, whose results were shown in great agreement with the proposed model. As a consequence of theoretical fitting curves to the experimental measures of integral-J, it was obtained the energy, geometric and fractais parameters of the fracture such as, the effective energy of fracture surface, 2geff = 2ge + gp, and the minimum crack size, lo, and the ruggedness dimension, H, (exponent Hurst). In particular the parameter H, obtained by the fitting, was compared with that obtained by the ruggedness fractal characterization, H, to each fractured sample. It was shown with that, of an inambiguous way, the rising of the J-R curve has a strong correlation with the fractal dimension and with the ruggedness dimension (Hurst’s exponent) of the fractured surface. The proposition of this work was compared with others authors showing that it differs from those currently used in the literature, differing the results for therein presented. As consequence it was shown too a correction for the mathematical expressions proposed by MU [1988] and LUNG [1988], that they relate the fractal dimension with the elastic energy released rate, Go, and also for the mathematical expressions proposed by MECHOLSKY and PASSOJA [1989] that relate the fractal dimension with the fracture toughness, KIC. By last, as a consequent fracture of the fractal fracture scaling, was shown the existence of a new property equivalent to fracture toughness. Therefore the fractal theory, become possible a mathemathical revision of the Classical equations of Fracture Mechanics (FM) which was historically established using the Euclidian geometry. But now, was made a mathematical reformulation of CFM using the fractal geometry, in order to obtain relationships that include in a explicit way the ruggedness of fractured surface becoming the mathemathical description most realistic and authentic. Therefore this work tried to study a way for which the fractal theory can enrich and elucidate several aspects of the Fracture Mechanics. The results obtained in this work can solve some of the existent doubts in the literature when the fractal scaling is used in the formulation of physical greatness that depend on the ruggedness and the projected area of fracture.
A superfície de fratura é um registro das informações do processo de fratura. É possível então relacionar o relevo desta superfície com grandezas da mecânica da fratura utilizando a técnica de caracterização fractal. Este trabalho teve como objetivo verificar a relação do perfil fractal de fratura de cerâmicas vermelhas com a resistência a fratura, em diversas temperaturas de sinterização. Para tanto, amostras de argila vermelha em forma de barrinhas foram sinterizadas em temperaturas de 800, 900 e 1000°C por duas horas. Estas amostras foram caracterizadas através de módulo de ruptura em flexão em 3 pontos, absorção de água, porosidade aparente e retração linear. Um modelo fractal auto-afim para o comprimento rugoso da trinca foi proposto e os resultados experimentais concordaram com o modelo. Verificou-se uma relação entre a dimensão fractal e aumento da temperatura de sinterização e conseqüentemente com a redução da porosidade e com o aumento da densidade
Neste capítulo será visto a fundamentação matemática básica da teoria do campo escalar, vetorial e tensorial em um meio irregular, onde desenvolveremos o cálculo analítico das equações dos fluxos nos volumes, nas superfícies e nos contornos, em termos da fração volumétrica irregular efetiva( ) e da rugosidade (fractalidades), com a presença da rugosidade no contorno e da fração volumétrica irregular efetiva no domínio geométrico do problema. Será proposto um modelo escalar para a fração volumétrica irregular efetiva e um modelo escalar, vetorial e tensorial para a rugosidade de contornos irregulares e fractais. Os problemas do calor, da elasticidade e da fratura serão colocados em pauta com uma proposta de modificação das equações constitutivas desses fenômenos para campos escalares e vetoriais, respectivamente.
2000 •
Paisagens Críticas - Robert Smithson: arte, ciência e indústria
Paisagens Críticas - Robert Smithson: arte, ciência e indústria2010 •
Rev Bras Ensino Fis
Sistemas complexos, criticalidade e leis de pot�ncia2004 •
Synergismus Scyentifica Utfpr
Fractais como Pontos Fixos de Funções Iteradas2009 •
2005 •
IEEE Latin America Transactions
A new Bandwidth Estimation Approach for Fractal Processes2005 •
2000 •