This treatise collects and reflects the major developments of direct (discrete) variational calculussince the end of the 17th century until about 1990, with restriction to classical linear elastome-chanics, such as 1D-beam theory, 2D-plane stress analysis and 3D-problems, governed by the 2nd order elliptic Lamé-Navier partial differential equations.The extension of the historical review to non-linear elasticity, or even more, to inelastic deformations would need an equal number of pages and, therefore, should be published separately.A comprehensive treatment of modern computational methods in mechanics can be found inthe Encyclopedia of Computational Mechanics.The purpose of the treatise is to derive the essential variants of numerical methods and algorithmsfor discretized weak forms or functionals in a systematic and comparable way, predominantly usingmatrix calculus, because partial integrations and transforming volume into boundary integrals with Gauss’s theorem yields simple and vivid representations. The matrix D of 1st partial derivativesis replaced by the matrix N of direction cosines at the boundary with the same order of non-zero entries in the matrix.
This paper presents a formulation for material and geometrical nonlinear analysis of composite materials by immersion of truss finite elements into triangular 2D solid ones using a novel formulation of the finite element method based on positions. This positional formulation uses the shape functions to approximate some quantities defined in the Nonlinear Theory of Elasticity and proposes to describe the specific strain energy and the potential of the external loads as function of nodal positions which are set from a deformation function. Because the nodal positions have current values in each node, this method naturally considers the geometric nonlinearities while the nonlinear relationships between stress and strain may be considered by a pure nonlinear elastic theory called hyperelasticity which allows to obtain linearised constitutive laws in its variational form. This formulation should be able to include both viscoelastic and active behavior, as well as to allow the consideration of nonlinear relations between stresses and deformations. It is common to adopt hyperelastic constitutive laws. Few are the works that use the strategy of approaching the problem such as fibers immersed in a matrix. The immersion of fibers in the matrix makes it possible to include both a viscoelastic behavior in a simple and direct way. The examples are simple cases, some of them even with analytical solutions, mainly for validation purposes of the presented formulations. By modeling a structure, the examples show the potentialities of the concepts and proposed formulations.
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In this paper we obtain a limit model for a turbine blade fixed to a 3D solid. This model is a three-dimensional linear elasticity problem in the 3D part of the piece (the rotor) and a two-dimensional problem (the nonlinear shallow shell equations) in the 2D part (the turbine blade), with junction conditions in the part of the turbine blade fixed to the rotor. To obtain this model, we perform an asymptotic analysis, starting with the nonlinear three-dimensional elasticity equations on all the pieces and taking as a small parameter the thickness of the blade.
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