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

Master of Science / Glass has long been used in glazing applications because of its transparency, stiffness, hardness, resistance to corrosion, and recyclability. Despite these useful features, however, glass is a very brittle material, lacking the ability to usefully absorb energy. Multi-material laminates have been produced as an alternative for glazing applications to improve energy absorption and other functionality requirements. As the demand for these laminates has increased in the construction, automotive, and defense sectors, a need for a more durable system has become apparent. One such example is the laminated glass systems often used in automobiles where two sheets are bonded (laminated) together with a plastic interlayer. Several types of interlayers have been used for these laminated systems, with polyvinyl butyral (PVB) being the most prevalent. A more recently developed interlayer type is thermoplastic polyurethane (TPU), which has the ability to bond to substrates other than glass, making it useful for applications like ballistic-resistant glass laminates, which often involve sheets made of polycarbonate. This study aims to explore the durability of laminated polycarbonate systems by investigating the interaction of environment and TPU viscoelastic behavior on the time-dependent crack growth in these laminates. The main test utilized is the wedge test, where a wedge is inserted between two polycarbonate adherends bonded together with an interlayer. The wedge causes a debond (a crack) to form. This crack may then grow over time. The crack growth in wedge test specimens with different TPUs is evaluated at various temperature and humidity conditions. A separate test, referred to as dynamic mechanical analysis (DMA), is conducted to determine the thermomechanical properties of the TPUs. These properties are then used to analyze the results of the wedge tests. In addition to different TPU types, the effects of edge seals and surface treatment to improve bonding are compared. Models are used to analyze the resulting data to support the prediction of lifetimes of laminated polycarbonate systems employing the TPUs investigated.

It is known that the classical inverse square root singularity used in Linear Elastic Fracture Mechanics (LEFM) is lost as a crack intersects a stress free surface. As a result, the stress and displacement equations are given as eigenvalue series expansions, with the lowest order eigenvalue dominating the series. The thickness averaged stress and surface displacement singularity exponents were determined for a commercially available polyurethane. Multiple specimen geometries were used to “benchmark” the optical methods. Tests have been run to determine the surface effect on a straight front crack. Results of these tests were compared with analytical results and related to LEFM concepts. / Master of Science

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Este trabalho visa modelar e estabelecer procedimentos experimentais para permitir a construção de mapas de conformabilidade plástica dos metais fundamentados na mecânica da fratura não-linear elasto-plástica. Um critério de conformabilidade plástica foi desenvolvido pela utilização de uma integral invariante generalizada baseada no teorema de Noether das integrais invariantes. Discute-se também as limitações da teoria da plasticidade que impossibilitam a obtenção de critérios de conformabilidade por seu intermédio. É um importante objetivo proporcionar o surgimento de uma metodologia de ensaio contendo alto rigor técnico mas sendo de baixo custo e de fácil implementação em simples instalações industriais. O procedimento foi aplicado no estudo do caso do forjamento a frio em matriz aberta, simulado por ensaio de compressão em prensa hidráulica. / The present study is aimed to the development of a low cost, to be implemented with ease, and technicality satisfactory industrial type testing for metal forming workability analysis. It is concerned with the development of an experimental procedures to permit the building up the metal forming workability maps, based on the nonlinear elastic-plastic fracture mechanics. A generalized nonlinear fracture mechanics invariant integral was applied to the case problem of the cold forging in flat open die of a ductile metallic material. At end a fracture criterion was developed in order to be possible the construction of the fracture deformation maps of the case study.

This work describes the implementation of the eXtended Finite Element Method (XFEM) in the Abaqus software package. A user-defined element was developed containing the analytical functions relating to homogeneous and interface fracture mechanics. The long-term goal of such work is to increase the ability to analyze fractures and other imperfections in multimaterial systems containing large elastic mismatches, such as flexible electronics. A review of XFEM-related literature is presented, as well as an overview of fracture mechanics for both homogeneous and interface systems. The theoretical basis of the XFEM is then covered, including the concepts of Partition of Unity and stress intensity factor evaluation. Finally, numerical results of the implementation are compared to several benchmark cases, along with conclusions and suggestions for future work.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth and Planetary Science, 1977 / Vita. / Bibliography : leaves 135-137. / By Robert Wayne Siegfried, II. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Earth and Planetary Science