[pt] Foi desenvolvido um método computacional para a determinação dos fatores de intensidade de tensão, para os modos de abertura I e II, a partir de configurações de franjas isocromáticas. O método se caracteriza pela generalização na formulação do campo de tensões na vizinhança da ponta de trinca, que busca determinar, além dos fatores de intensidade de tensão, alguns parâmetros significativos do campo de tensões não singular, associados a diferentes geometrias, que interferem no campo singular, próximo à trinca. Um programa de computador foi desenvolvido para a obtenção KI, KII e dos demais fatores considerados. O erro das respostas pode ser calculado a partir das diferentes opções de saída do programa. O método foi testado em modelos de barras com trincas a 90 e 45 graus e os resultados comparados com dados experimentais e analíticos disponíveis na literatura. Como fatores de influência na determinação de KI e KII forma estudados: a quantidade e a posição dos pontos de coleta de dados, e o número de parâmetros considerados no campo não singular. Foram analisados ainda, como exemplo de aplicação ainda, como exemplo de aplicação, três modelos de solda de topo com trincas a 45 e 90 graus com diferentes posicionamentos em relação ao reforço de solda. / [en] A computational method has been developed to determine mixed-mode stress intensity factors from isochromatic fringe patterns. The method proposes a general formulation of the stress field around a crack tip. It searches to obtain not only the stress intensity factors but also all the other non-singular stress field parameters, associated to different geometries, which interfere with the singular field near the crack. The method has been tested in bars with 90 and 45 degree cracks and the results, compared to experimental and analytical data found in literature. Three factors influencing in KI and KII determination have been studied: the quantity of data collecting points, its position and number of parameters considered in the non-singular field. Three models of transverse butt welded joints with 45 and 90 degrees cracks placed in different positions relative to weld reinforcement, have been analyzed as application examples.

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A technique for obtaining values of the stress intensity factor from photoelastic data for three dimensional cracked body problems is described. The stress intensity determination is accomplished without resorting to stress separation methods through employing an expression for the maximum in-plane shearing stress consisting of a singular term which is related to the stress intensity factor and a constant term which is related to the regular stress field. The technique itself identifies the zone dominated by the singular stresses. The effects of using artificial cracks and a model material which exhibits a Poisson's ratio v = 0.5 are assessed. The application of the technique to a variety of technologically important three dimensional problems is illustrated for Mode I loading and combined Mode I - Mode II loading. The major advantages and limitations of the technique are discussed. Replications of identical test geometries indicate a scatter of the stress intensity factor determination of less than ± 5%. It is concluded that the method is a valid means for the independent determination of values of the stress intensity factor. / Ph. D.

Master of Science

The stress concentration factors for rectangular slots with semicircular ends with their major axes inclined to the direction of a uniaxial tension field were investigated by photoelastic methods. A major portion of this thesis deals with the problem of loading a circular disk such as to create an approximately uniform tension field. This circular disk was used to investigate the stress concentration factors of the slots which were compared to the known results of a slot perpendicular to a tension field in a rectangular plate. The maximum value for the stress concentration factor occured when the slot was perpendicular to the direction of the tension field. A method of determining the stress concentration was developed which required only the recording of the load at which each fringe appeared on the edge of the slot. This method gave results with 6% of accepted values. / Master of Science

In the experimental work conducted, two cases have been considered for the six- finned internal star cylinder: the semi-elliptic natural crack and a machined V-cut crack extending the length of the cylinder, both originating from the axis of symmetry of the fin tip. The V-cut crack constitutes a plane strain approximation and is used in current design rationale. Results show that the normalized stress intensity factor (SIF) for the V-cut case are at least equal to, but in most cases are greater than, the natural crack cases. These results were compared to experimental results from Smith and his associates for motor grains having similar shaped off-axis cracks, and similar trends were achieved. Comparisons were also made between the natural crack models and the modified boundary element method of Guozhong, Kangda, and Dongdi (GKD) for a semi-elliptic crack in a circular cylinder and the V-cut crack models to the modified mapping collocation technique of Bowie and Freese (BF), which constitutes the plane strain solution to a circular cylinder with a crack extending the length of the bore. For both cases general trends were similar. Using the numerical results, a relation for estimating the plane strain SIF for the finned cylinder models was developed. The situation of a finned cylinder containing a crack the length of the bore constitutes the worst case scenario. Testing has shown, however, that under normal loading conditions this case is conservative. Penetration tests have shown that a crack penetrating the outer boundary retains its semi-elliptic shape, thus the use of a semi-elliptic crack in design more accurately represents reality. / Master of Science

An investigation into the influence of cracks in bonded specimens is conducted. Photoelastic specimens containing a bondline are subjected to a constant displacement boundary condition created by bonded end grips. Specimens containing various crack orientations are analyzed to determine stress intensity factors at the induced crack tips. Specimens containing interface and sub-interface cracks were investigated. Two global geometries were used in this investigation, square and rectangular. The constant displacement boundary condition was induced on the specimen through dead weights hung from bonded aluminum end grips. Stress intensity factors were determined using photoelastic techniques. The stress intensity factors were examined to determine trends in the results as a function of changes in geometry. The effects of the induced boundary condition, the specimen geometry, and the bondline were investigated. The results from this investigation were compared to known solutions with a similar specimen geometry. These tests exhibited influences from the bondline, the boundary conditions, and the specimen geometry. The bondline tended to decrease the stress intensity factor for specimens with small crack lengths and tended to increase the stress intensity factor for specimens containing long crack lengths. As the crack length increased so too did the stress intensity factor. A reduction in the bondline to crack distance with sub-interface crack specimens caused a reduction in the stress intensity factor. A reduction in the global height of the specimen caused a reduction in the stress intensity factor also. The results from this investigation will aid in the understanding of the influence of interface and sub-interface cracks in bonded specimens. / Master of Science

The future of most underground coal mining in the USA will entail the extraction of coal under multi-seam mining conditions. Mine design in such an environment will require the accurate prediction of stress transfer between adjacent seams. The available knowledge on criteria controlling stress transfer has been exhaustively reviewed and critical factors affecting multi-seam mining investigated. Young's Moduli of rock layers, thickness of rock layers, number of these layers and the coefficient of friction between these layers were identified as important parameters which affect stress transfer from mining of one seam to another. These parameters were studied using photoelastic methods and results analyzed both qualitatively and quantitatively. Finite element studies were also performed using UTAH2PC. Data obtained from field studies was used to correlate laboratory findings with prototype observations. Excellent correlation was obtained between laboratory and field data. Validity of the research is demonstrated using case studies. / Master of Science