Tube hydroforming is a forming method which has several advantages. By using pressure in combination with material feeding it is possible to manufacture products with high structural integration and tight dimensional tolerances. The forming method is especially suited for aluminium alloys which have a relatively low ductility. Finite Element simulations are used extensively in the sheet metal stamping industry, where the methodology has contributed to a better understanding of the process and the new prediction capability has significantly reduced costly die tryouts. Similarly, the tube hydroforming industry can benefit from Finite Element simulations, and this simulation methodology is the topic of this dissertation. Deep drawing and tube hydroforming have a basic difference, namely that the latter process essentially is a force controlled process. This fact, in combination with the anisotropic behaviour of aluminium tubes, enforces a need for accurate constitutive descriptions. Furthermore, the material testing needs to account for the specifics of tube hydroforming. The importance of proper material modelling is in this work shown for hydrobulging and hydroforming in a die with extensive feeding. The process parameters in hydroforming are the inner pressure and the material feeding, where a correct combination of these parameters is crucial for the success of the process. It is here shown, that Finite Element simulations together with an optimisation routine are powerful tools for estimating the process parameters in an automated procedure. Finally, the reliability and quality of the simulation results depend on how failure is evaluated, which in the case of hydroforming mainly oncerns wrinkling and strain localisation. Since tube hydroforming often is preceded by bending operations this fact also demands the criteria to be strain path independent. In this work, it is shown that the prediction of strain localisation depends on the ability to predict diffuse necking, which in turn is strongly related to the chosen constitutive model.

This thesis addresses normal axisymmetric contact of dissimilar elastic solids at finite interfacial friction. It is shown that in the case of smooth and convex but otherwise arbitrary contact profiles and monotonically increasing loading a single stick-slip contour evolves being independent of loading and profile geometry. This allows developing an incremental procedure based on a reduced problem corresponding to frictional rigid flat punch indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, was solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, a tailored cumulative superposition procedure was developed to resolve the original problem to determine global and local field values for two practically important geometries: flat and conical profiles with rounded edges and apices. Results are given for relations between force, depth and contact contours together with surface stress distributions and maximum von Mises effective stress, in particular to predict initiation of fracture and plastic flow. It is also observed that the presence of friction radically reduces the magnitude of the maximum surface tensile stress, thus retarding brittle fracture initiation. Hertzian fracture through indentation of flat float glass specimens by steel balls has been examined experimentally for a full load cycle. It has been observed that if the specimen survived during loading to a maximum level it frequently failed at decreasing load. It has been proposed by Johnson et al. (1973) that the underlying physical cause of Hertzian fracture initiation during load removal is that at unloading frictional tractions reverse their sign over part of the contact region. Guided by these considerations a robust computational procedure has been developed to determine global and local field values in particular at unloading at finite friction. In contrast to the situation at monotonically increasing loading, at unloading invariance properties are lost and stick-slip regions proved to be severely history dependent and in particular with an opposed frictional shear stress at the contact boundary region. This causes an increase of the maximum tensile stress at the contour under progressive unloading. It is shown that the experimental observations concerning Hertzian fracture initiation at unloading are at least in qualitative correlation with the effect friction has on the maximum surface tensile stress. A contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been further investigated analytically and numerically for a wider range of material parameters and contact geometries. With the issue of Hertzian fracture initiation in mind, results concerning the influence of the friction coefficient and compliance parameters on the absolute maximum surface tensile stress during a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation. Fracture loads are measured with steel and tungsten carbide spherical indenters in contact with float glass specimens at monotonically increasing loading and during a load cycle. Computational predictions concerning the fracture loads are given based on Hertz and frictional contact theories combined with a critical stress fracture criterion. The computational results obtained for frictional contact are shown to be in better agreement with experimental findings as compared to the predictions based on the Hertz theory. The remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects on the fracture loads at monotonic loading, Weibull statistics was introduced. The predicted critical loads corresponding to 50% failure probability were found to be in close agreement with experimentally observed ones. / QC 20100729

Until the twentieth century, theories of elastic rods and shells arose from collections of geometric and mechanical assumptions and approximations. These theories often lacked internal consistency and were appropriate for highly proscribed and sometimes unknown geometries and deformation sizes. The pioneering work of Truesdell, Antman, and others converted mechanical intuition into rigorous mathematical statements about the physics and mechanics of rods and shells. The result is the modern, geometrically exact theory of finite deformations of rods and shells.In the latter half of the twentieth century, biomechanics became a major focus of both experimental and theoretical mechanics. The genesis of residual stress by non-elastic growth has significant impact on the shape and mechanical properties of soft tissues. Inspired by the geometry of blood vessels and adopting a formalism found in elasto-plasticity, mechanicians have produced rigorous and applied results on the effect of growth on finite elastic deformations of columns and hollow tubes. Less attention has been paid to shells.A theory of growing elastic plates has been constructed in the context of linear elasticity. It harnessed many results in the theory of Riemann surfaces and has produced solutions that are surprisingly similar to experimental observations. Our intention is to provide a finite-deformation alternative by combining growth with the geometrically exact theory of shells. Such a theory has a clearer and more rigorous foundation, and it is applicable to thicker structures than is the case in the current theory of growing plates.This work presents the basic mathematical tools required to construct this alternative theory of finite elasticity of a shell in the presence of growth. We make clear that classical elasticity can be viewed in terms of three-dimensional Riemannian geometry, and that finite elasticity in the presence of growth must be considered in this way. We present several examples that demonstrate the viability and tractability of this approach.

This thesis is intended to be a ground for the implementing of solid mechanics calculations of an expander axle in an existing CAD programme. The main parameters to be calculated are: effective stress, stress components in axial and radial direction, shear stress as well as maximum force and fatigue analysis. In order to achieve the above mentioned goal, calculations were made by hand. At the end of any of the chapters, a diagram on the input/output data and the equations needed for performing the calculations was drawn.

Orientador: Eugênio José Zoqui / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-25T10:40:39Z (GMT). No. of bitstreams: 1 Ruiz_CamilaSola_M.pdf: 6048222 bytes, checksum: 79aed3e14ecfcc03b879d0fca306314b (MD5) Previous issue date: 2014 / Resumo: O objetivo para este trabalho foi avaliar a tixoconformabilidade de ligas Al¿Si¿Cu produzidas via refino de grão, abrangendo desde a obtenção das ligas tixofundidas até sua completa caracterização em termos de metalografia colorida e convencional no comportamento viscoso. Ligas Al¿2,0wt%Si¿2,5wt%Cu, Al¿3,0wt%Si¿2,5wt%Cu, Al¿4,0wt%Si¿2,5wt%Cu e Al¿7,0wt%Si¿2,5wt%Cu foram produzidas via ultra-refino de grãos utilizando o refinador Al¿5,0wt%Ti¿1,0wt%B. Os materiais foram submetidos a tratamentos térmicos de reaquecimento pelos tempos de 0s e 210s, para duas condições de frações sólidas, 45% e 60%. As ligas contendo 2,0wt%Si, 3,0wt%Si, 4,0wt%Si e 7,0wt%Si mostraram-se bastante próximas em termos de viscosidade aparente, no entanto, a liga com 4,0wt%Si apresentou melhor desempenho em termos de globularização. Já a liga contendo 7,0wt%Si mostrou-se dendrítica para todas as condições estudadas, o que dificulta sua aplicação nos processos de tixoconformação / Abstract: The target for this work was the analyses to evaluate the thixoformability of Al¿Si¿Cu alloys produted by grain refining, including the thixocasting of all alloys and their complete characterization in terms of color metallography and conventional on rheological behavior Al¿2.0wt%Si¿2.5wt%Cu , Al¿3.0wt%Si¿2.5wt%Cu , Al¿4.0wt%Si¿2.5wt%Cu and Al¿7.0wt%Si¿2.5wt%Cu alloys were produced by ultra-refining by addiction of Al¿5.0wt%Ti¿1.0wt%B master alloy. The materials were submitted to pre-heating treatment for 0s and 210s in two conditions, 45% and 60% of solid fraction. 2.0wt%Si, 3.0wt%Si, 4.0wt%Si and 7.0wt%Si alloys showed very similar results for apparent viscosity; however the 4.0wt%Si alloy showed better performance in terms of globularization / Mestrado / Materiais e Processos de Fabricação / Mestra em Engenharia Mecânica

This thesis is concerned with the deformation and adhesion of thin elastic sheets that come into contact with an underlying substrate. The focus of this work is on the interplay between material and geometric properties of a system and how this interplay determines the equilibrium states of sheet and substrate, particularly in the regime of geometrically nonlinear deformations. We first consider the form of an elastic sheet that is partially adhered to a rigid substrate, accounting for deflections with large slope: the Sticky Elastica. Starting from the classical Euler Elastica we provide numerical results for the profiles of such blisters and present asymptotic expressions that go beyond the previously known, linear, approximations. Our theoretical predictions are confirmed by desktop experiments and suggest a new method for the measurement of material properties for systems undergoing large deformations. With the aim to gain better understanding of the initial appearance of blisters we next investigate the deformation of a thin elastic sheet floating on a liquid surface. We show that, after the appearance of initial wrinkles, the sheet delaminates from the liquid over a finite region at a critical compression, forming a delamination blister. We determine the initial blister size and the evolution of blister size with continuing compression before verifying our theoretical results with experiments at a macroscopic scale. We next study theoretically the deposition of thin sheets onto a grooved substrate, in the context of graphene adhesion. We develop a model to understand the equilibrium of the sheet allowing for partial conformation of sheet to substrate. This model gives phys- ical insight into recent observations of ‘snap-through’ from flat to conforming states and emphasises the crucial role of substrate shape in determining the nature of this transition. We finally present a theoretical investigation of stiction in nanoscale electromechanical contact switches. Our model captures the elastic bending of the switch in response to both electrostatic and van der Waals forces and accounts for geometrically nonlinear deflections. We solve the resulting equations numerically to study how a cantilever beam adheres to a fixed bottom electrode: transitions between free, pinned and clamped states are shown to be discontinuous and to exhibit significant hysteresis. The implications for nanoscale switch design are discussed.

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<p dir="ltr">Magnetorheological elastomers (MREs) are a type of smart material composed of ferrous particles suspended in a solid elastic matrix [5, 6]. When an external magnetic field is applied to an MRE, the ferrous particles tend to align with the field, causing either deformation and/or a change in the mechanical properties of the system. MREs are utilized in applications such as soft robotics, actuators, sensors, vibration control systems, and mechanical metamaterials[20, 19, 27, 5, 6, 13]. Recent demand for theses technologies has motivated an increasing focus on the material properties of MRE’s over the last 20 years [6]. Multiple authors have proposed a variety of hyperelastic mechanical and magnetomechanical models to describe these materials [16, 12, 15, 25, 14, 38, 2, 6, 8, 24]. The research presented in this dissertation focuses on the modeling and characterization of MRE’s using a systematic development of the conservation and balance laws, Maxwell’s equations, and constitutive equations needed to describe the MRE as a multi-constituent system. The material parameters resulting from the derived constitutive equations are estimated using data collected from a series of compression experiments coupled with an externally applied magnetic field. The multi-constituent constitutive equations predicted the stress of the MRE in these compression experiments for a variety of ferrous particle concentrations.</p>

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