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Orientador: José Ricardo Pelaquim Mendes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-22T11:39:24Z (GMT). No. of bitstreams: 1 Salmazo_Eduardo_M.pdf: 7818535 bytes, checksum: a2f7369fd589c6f6e85ce6c997e8c112 (MD5) Previous issue date: 2013 / Resumo: Neste trabalho discute-se os desafios associados à atividade de perfuração de poços de petróleo através de formações afetadas pela presença de domos salinos. Domos salinos podem induzir grandes tensões nas formações subjacentes e adjacentes, impondo a necessidade de um planejamento específico para a perfuração e manutenção de poços de petróleo. Durante a perfuração, em frente à zonda de sal, há relatos de problemas de aprisionamento de coluna, dissolução de sal no fluido de perfuração, ocasionando a formação de batentes mecânicos e cavernas. Há ainda, nas formações que rodeiam um domo salino, devido à alterações no campo de tensões, problemas de instabilidade nas paredes do poço aberto e formação de zonas anormalmente prossurizadas. Após o revestimento do poço, há casos de colapso do revestimento. Para prever e mitigar os riscos associados à essa atividade é de fundamental importância o entendimento dos fenômenos físicos que o ocasionam. Com essa finalidade, foi feito um estudo à respeito de tais mecanismo físicos como fluência e instabilidade hidrodinâmica, mais especificamente a instabilidade de Rayleigh-Taylor. Desenvolveu-se, a partir de tal estudo, um modelo analítico para prever o desenvolvimento de um domo salino e discutiu-se a forma como este pode interferir em parâmetros importantes para a atividade de perfuração como, por exemplo, o campo de tensões nas formações adjacentes às camadas de sal / Abstract: In this present work are discussed the challenges associated with the drilling activities in oil wells through formations affected by the presence of salt domes. This geological structures can induce large stresses in the underlaying and adjacent formations, imposing the necessity of specific planning for drilling and maintenance of such oil wells. During drilling, facing the salt, there are reports of problems of stuck pipe, salt dissolution, forming mechanical stops and caves. There are still, in formations around a salt dome, due changes in the stress field, problems of well instability and abnormally pressure zones. After casing, there are cases of case collapse. To prevent and mitigate risks associated to this activity, is crucial understand the physical phenomena behind it. With such finality, was made an study related with such physical mechanisms, such hydrodynamic instability, specifically the Rayleigh-Taylor instability. Was developed, from this study, an analytical model to predict the salt dome development and was discussed the way such it can interfer in important paramenters related to the drilling activity as, for exemple, the tension field in the formation around the salt dome / Mestrado / Explotação / Mestre em Ciências e Engenharia de Petróleo

Rapid development and stiff competition in material related industries such as the automotive, demand very high precision in end products in very quick time. The transformation of raw material into an intricate-shaped final product involves various intermediate steps like design, material selection, manufacturing processes, etc. In all these steps, an in-depth understanding of material behavior plays an important role. The available traditional methods such as trial-and-error, especially in the case of die design, become highly inefficient in terms of time and money. This, there is a growing interest in simulation of the final product in order to predict different parameters which are important in design and manufacturing. Currently available simulation techniques are based on existing theories of plasticity or large deformation. These theories have been developed over several decades and many theoretical and practical issues have been debated over the years. Though the theories have great utility in understanding and solving some practical problems, there are ranges of applications for which no acceptable models are available. Most of these theories are either materials or process-specific with oversimplified real physical situations using assumptions and empirical relations. Development of field equations from first principles to stimulate elasto-plastic deformation is one such, still a subject of on-going discussion. Materials and composites exhibit hysteresis even at very low stresses, i.e., inelasticity is always present under all types of loading. This observation shows that the representing constitutive relation cannot treat the elastic and plastic deformations separately. The deformation is due to changes in size and shape, and studies with varying strain rates show considerable material sensitivity to the rate of deformation. Therefore, a generalized field equation is developed from first principles in the Eulerian coordinate system using material resistance to changes in size and shape, and their rates. The formulation uses a unified approach representing continuous effect of elastic and plastic strains and strain rates. The field equation involves eight material parameters, viz. bulk modulus, shear modulus, material shear velocity, material bulk viscosity, and four more constants associated with activation points related to deviatoric and volumetric strains and plastic strain rates. The elastic moduli, bulk and shear, are constants, and so also the material viscosities, while plastic stain rates are functions of elastic strain rates. The field equation redces to Cauchy’s equation in the solid limit and Navier-Stokes equation in the fluid limit. Simple experimental measurements are suggested to obtain the numerical values of the material parameters. Uniaxial tension tests are carried out on commercially available mild steel and aluminium alloy at different strain rates to quantify any variations in the values of material parameters during large deformation. Experimental results and the classical understanding of material deformation reveal the constant nature of elastic moduli during large deformation and, from fluids, the viscosities seem to remain constant. Around the yield region, materials experience a sharp increase in absorbed energy which is modeled to represent the plastic strain rates. The variations and contributions from elastic and plastic strains, both volumetric and deviatoric, and the corresponding stresses are observed. The effects of strain rate on plastic stress and energy absorbed are investigated. The model is checked for different materials and loading conditions to ascertain the proposed changes to earlier theories. Available experimental data in the literature are used for this purpose. The analysis shows that, though the overall stress-strain relations of different materials look similar, their internal responses differ. The internal response of a material depends on various microstructural factors, like alloying elements, impurities, etc. The present model is able to capture those internal differences between various materials. Numerical solution of different plasticity problems have to be undertaken to ascertain the applicability, generality, realism, accuracy and feasibility of the model.

Amorphous alloys possess attractive combinations of mechanical properties (high elastic limit, ~2%, high fracture toughness, 20-50 MPa.m1/2, etc.) and exhibit mechanical behavior that is different, in many ways, from that of the crystalline metals and alloys. However, fundamental understanding of the deformation and fracture mechanisms in amorphous alloys, which would allow for design of better metallic glasses, has not been established on a firm footing yet. The objective of this work is to understand the deformation and fracture mechanisms of amorphous materials at various length scales and make connections with the macroscopic properties of glasses. Various experimental techniques were employed to study the macroscopic behavior and atomistic simulations were conducted to understand the mechanisms at the nano level. Towards achieving these objectives, we first study the toughness of a Zr-based bulk metallic glass (BMG), Vitreloy-1, as a function of the free volume, which was varied by recourse to structural relaxation of the BMG through sub-Tg annealing treatment. Both isothermal annealing at 500 K (0.8Tg) for up to 24 h and isochronal annealing for 24 h in the temperature range of 130 K (0.65Tg) to 530 K (0.85Tg) were conducted and the impact toughness, Γ, values were measured. Results show severe embrittlement, with losses of up to 90% in Γ, with annealing. The variation in Γ with annealing time, ta, was found to be similar to that observed in the enthalpy change at the glass transition, ΔH, with ta, indicating that the reduction of free volume due to annealing is the primary mechanism responsible for the loss in Γ with annealing. Having established the connection between sub-atomic length scales (free volume) and macroscopic response (toughness), we investigated further the affects of relaxation on intermediate length scale behavior, namely deformation induced by shear bands, by employing instrumented indentation techniques. While the Vickers nano-indentation response of the as-cast and annealed glasses do not show any significant difference, spherical indentation response shows reduced shear band activity in the annealed BMG. Further, relatively high indentation strain was observed to be necessary for shear band initiation in the annealed glass, implying an increased resistance for the nucleation of shear bands when the BMG is annealed. In the absence of microstructural features that allow for establishment of correlation between properties and the structure, we resort to atomistic modeling to gain further understanding of the deformation mechanisms in amorphous alloys. In particular, we focus on the micromechanisms of strain accommodation including crystallization and void formation during inelastic deformation of glasses. Molecular dynamics simulations on a single component system with Lennard-Jones-like atoms suggest that a softer short range interaction between atoms favors crystallization. Compressive hydrostatic strain in the presence of a shear strain promotes crystallization whereas a tensile hydrostatic strain was found to induce voids. The deformation subsequent to the onset of crystallization includes partial re-amorphization and recrystallization, suggesting important mechanisms of plastic deformation in glasses. Next, a study of deformation induced crystallization is conducted on two component amorphous alloys through atomistic simulations. The resistance of a binary glass to deformation-induced-crystallization (deformation stability) is found to increase with increasing atomic size ratio. A new parameter called “atomic stiffness” (defined by the curvature of the inter-atomic potential at the equilibrium separation distance) is introduced and examined for its role on deformation stability. The deformation stability of binary glasses is found to increase with increasing atomic stiffness. For a given composition, the internal energies of binary crystals and glasses are compared and it is found that the energy of glass remains approximately constant for a wide range of atomic size ratios unlike crystals in which the energy increases with increasing atomic size ratio. This study uncovers the similarities between deformation and thermal stabilities of glasses and suggests new parameters for predicting highly stable glass compositions.