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

No description available.

The finite element method has been demonstrated previously to provide an effective means for the analysis of two dimensional elastic and plastic continua. The method is applied herein to the axially symmetric, solid, and is extended to fracture analysis. The numerical analysis may be broken into three parts. The first involves the role of linear elasticity, the second deals with the elastic-plastic deformations, and the third is concerned with the interaction between such deformation and the fracture process. For the finite solid element method, the crack is thought to initiate below the surface of a notch, approximately in the region of highest triaxiality of the stress σ_ii under the ultimate load, rather than at the root of the notch. Thus the maximum value of σ_ii at ultimate load becomes the assumed criterion for the first phase of the fracture; i.e., the brittle fracture. The crack propagates inward and outward until the octahedral shear stress 𝜏_C, in the remainder of the cross section are above the triaxial stresses. At this stage, the specimen fails in shear and a shear lip forms at the root of the notch, provided it is not exceptionally sharp, and at the inner circumference of the hole of the hollow notched specimens. Thus 𝜏_C becomes the criterion of fracture during this second stage. For the lattice analogy method, the fracture is assumed to progress as each critically stresses member reaches its ultimate and is deleted from the remaining assembly. Both the finite solid element method and the lattice analogy method are used to analyze numerically the solid and hollow notched tensile specimens with the ultimate load held constant during fracture. The finite solid element analysis was also made with this load decreased so as to keep σ_ii and/or 𝜏_C constant at their original maximum values. Comparisons with analytical and exp7rimental results are made and found to be satisfactory. / Ph. D.

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.

No description available.

No description available.

No description available.

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