No description available.

No description available.

No description available.

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.

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

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

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

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

A resina acrílica encontra-se entre os materiais mais utilizados na odontologia. Apesar de suas qualidades, o polimetilmetacrilato ainda mostra-se um material com resistência comprometida. Para tanto, diversos reforços têm sido propostos na literatura e entre eles encontram-se as fibras de vidro e aramida. Apesar de acrescerem na resistência da matriz acrílica pouco se sabe sobre como os esforços aplicados sobre a resina reforçada por fibras são transmitidos e distribuídos às áreas de sustentação, o que motivou a realização deste estudo. Foram confeccionados dez corpos-de-prova em resina acrílica termopolimerizável divididos em cinco grupos segundo o reforço utilizado: fibras de vidro filamentares tratadas por imersão no monômero acrílico (Grupo F), fibras de vidro em malha submetidas ao mesmo tratamento (Grupo M), fibras de vidro trançadas com aramida e tratadas por imersão na mistura monômero/polímero (Grupo H) e fibras de vidro trançadas com aramida e tratadas por silanização (Grupo HS). Como grupo controle (C) foram utilizadas amostras de resina acrílica termicamente ativada sem a associação de fibras de reforço. Após a adaptação dos corpos-de-prova à matriz fotoelástica os mesmos foram submetidos a ensaio de flexão através da Máquina Universal de Ensaios (EMIC-modelo DL 2000, S. J. dos Pinhais, PR, Brasil) acoplada ao Polariscópio Circular (Desenvolvido na Faculdade de Engenharia Mecânica - UFU, Uberlândia, MG, Brasil). Os resultados mostraram valores para a Energia de Distorção, em Kgf/mm2, de 223,124 para o grupo F; de 218,710 para o grupo H; 217,692 para o grupo M; 215,810 para o grupo HS e de 210,122 para o grupo C. Também foi observado que a energia de distorção apresentou distribuição homogeneamente crescente em todos os grupos estudados. Concluímos que a associação de fibras à resina acrílica gerou aumento da energia acumulada na área de sustentação protética sendo que os maiores valores foram observados para o grupo de fibras de vidro filamentares. Observamos também que a silanização da fibra híbrida contribuiu para uma menor transmissão de tensão à matriz fotoelástica. / Acrylic resin is found among the most used materials in dentistry. Despite its qualities, the polymetilmetacrylate yet shows itself as a material with questionable resistance. Therefore, lots of reinforcements have been proposed in literature and among them we find glass fibers and aramid. Although they add to the resistance of the acrylic matrix, little is known about how the efforts applied upon the resin strengthened by the fibers are transmitted and distributed over the sustaining areas, which motivated the course of this study. Ten specimens made of termcured acrylic resin were created and divided into five groups according to the reinforcement used: roving glass fibers treated by immersion in the acrylic monomer (Group F), mesh glass fibers given the same treatment above (Group M), glass fibers braided with aramid and treated by immersion in the blending momer/polimer (Group H) and glass fibers braided with aramid and treated by signalization (Group HS). As control group (C) were used samples of acrylic resin termically activated without the addition of fibers. After adapting the specimens to the photoelastic matrix, the former were submitted to flexural tests through the Universal Machine of Rehearsal (EMIC-model DL 2000, S. J. Dos Pinhais, PR, Brazil) joint to the Circular Polariscope ( developed in the Mechanical Engineering College ? UFU, Uberlândia, MG, Brazil. The results show values to the Distortion Energy, in Kgf /mm2, of 223,124 for group F; 218,710 for group H; 217,692 for group M; 215,810 for group HS and 210,122 for group C. It was also observed that the distortion energy presented homogeneous growing distribution in al the groups studied. We conclude that the association of fibers to the acrylic resin generated an increase of the energy accumulated in the area of prosthetic support, thus the highest values were observed in the group with roving glass fibers. We noticed that the silanization of the hibrid fiber contributed to a smaller tension transmission to the photoelastic matrix.