Estudio de estructuras sometidas a esfuerzos de impacto en régimen elastoplástico y con grandes deformaciones por el método de los elementos finitos. Parte I: Formulación teórica

Se desarrolla en este primer artículo, la formulación teórica para el estudio tridimensional de cuerpos sometidos a acciones de contacto-impacto. Despues de desarrollar las ecuaciones básicas de equilibrio, se estudian las ecuaciones constitutivas utilizadas. El elemento usado es el hexaedrico de ocho nodos, del cual se establecen algunas propiedades, que serán de utilidad para la integración numérica. En un artículo posterior, se desarrollará el algoritmo de contacto-impacto estudiado, así como varios ejemplos.Peer Reviewe

Estudio de estructuras sometidas a esfuerzos de impacto en régimen elastoplástico y con grandes deformaciones por el método de los elementos finitos. Parte II: Algoritmo de contacto-impacto y ejemplos

En este segundo articulo, se expone el algoritmo de contacto-impacto utilizado para problemas tridimensionales. Se desarrolla fundamentalmente el metodo de las penalizaciones hallando el valor de la máxima rigidez estable. Se incluyen asimismo tres ejemplos de aplicación.Peer Reviewe

A computational framework for polyconvex large strain elasticity

This paper presents a novel computational formulation for large strain polyconvex elasticity. The formulation, based on the original ideas introduced by Schröder etal. (2011), introduces the deformation gradient (the fibre map), its adjoint (the area map) and its determinant (the volume map) as independent kinematic variables of a convex strain energy function. Compatibility relationships between these variables and the deformed geometry are enforced by means of a multi-field variational principle with additional constraints. This process allows the use of different approximation spaces for each variable. The paper extends the ideas presented in Schröder etal. (2011) by introducing conjugate stresses to these kinematic variables which can be used to define a generalised convex complementary energy function and a corresponding complementary energy principle of the Hellinger-Reissner type, where the new conjugate stresses are primary variables together with the deformed geometry. Both compressible and incompressible or nearly incompressible elastic models are considered. A key element to the developments presented in the paper is the new use of a tensor cross product, presented for the first time by de Boer (1982), page 76, which facilitates the algebra associated with the adjoint of the deformation gradient. For the numerical examples, quadratic interpolation of the displacements, piecewise linear interpolation of strain and stress fields and piecewise constant interpolation of the Jacobian and its stress conjugate are considered for compressible cases. In the case of incompressible materials two formulations are presented. First, continuous quadratic interpolation for the displacement together with piecewise constant interpolation for the pressure and second, linear continuous interpolation for both displacement and pressure stabilised via a Petrov-Galerkin technique

Estudio de estructuras sometidas a esfuerzos de impacto en régimen elastoplástico y con grandes deformaciones por el método de los elementos finitos. Parte II: Algoritmo de contacto-impacto y ejemplos

En este segundo articulo, se expone el algoritmo de contacto-impacto utilizado para problemas tridimensionales. Se desarrolla fundamentalmente el metodo de las penalizaciones hallando el valor de la máxima rigidez estable. Se incluyen asimismo tres ejemplos de aplicación.Peer Reviewe

Estudio de estructuras sometidas a esfuerzos de impacto en régimen elastoplástico y con grandes deformaciones por el método de los elementos finitos. Parte I: Formulación teórica

Se desarrolla en este primer artículo, la formulación teórica para el estudio tridimensional de cuerpos sometidos a acciones de contacto-impacto. Despues de desarrollar las ecuaciones básicas de equilibrio, se estudian las ecuaciones constitutivas utilizadas. El elemento usado es el hexaedrico de ocho nodos, del cual se establecen algunas propiedades, que serán de utilidad para la integración numérica. En un artículo posterior, se desarrollará el algoritmo de contacto-impacto estudiado, así como varios ejemplos.Peer Reviewe

Stabilized updated Lagrangian corrected SPH for explicit dynamic problems

Smooth Particle Hydrodynamics with a total Lagrangian formulation are, in general, more robust than nite elements for large distortion problems. Nevertheless, updating the reference con¯guration may still be necessary in some problems involving extremely large distortions. However, as discussed here a standard updated formulation suffers the presence of zero energy modes that are activated and may spoil completely the solution. It is important to note that, unlike an Eulerian formulation,the updated Lagrangian does not present tension instability but only zero energy modes. Here an stabilization technique is incorporated to the updated formulation to obtain an improved method without mechanisms and capable to solve problems with extremely large distortions

Updated Lagrangian formulation for corrected smooth particle hydrodynamics

Smooth Particle Hydrodynamics (SPH) are, in general, more robust than finite elements for large distortion problems. Nevertheless, updating the reference configuration may be necessary in some problems involving extremely large distortions. If a standard updated formulation is implemented in SPH zero energy modes are activated and spoil the solution. It is important to note that the updated Lagrangian does not present tension instability but only zero energy modes. Here an stabilization technique is incorporated to the updated formulation to obtain an improved method without mechanisms

Mixed model for the analytical determination of critical buckling load of passive reinforcement in compressed RC and FRC elements under monotonic loading

[EN] Compressed reinforcements on reinforced concrete (RC) and steel fibre reinforced concrete (SFRC) columns are generally submitted to cyclic and monotonic loading, which can buckle. This phenomenon can cause the reduction of both ductility and peak loads, which is why design standards propose constructive details to avoid this. Although the bibliography mentions that steel fibres in concrete can delay buckling of reinforcements, design codes do not distinguish between concrete types (with and without fibres) in these constructive details. Analytical models that determine the length and critical buckling stress of reinforcements may consider this effect. Nowadays, analytical models can be classified as discrete and distributed depending on whether they consider transverse reinforcement stiffness and the stiffness of the concrete cover that concentrates on transverse reinforcements, or if they are distributed along the element, respectively. Both discrete and distributed models are valid for small transverse reinforcement separations, while distributed models that only consider the concrete cover effect are valid for large transverse reinforcement separations. This paper proposes a mixed model to determine critical buckling loads of compressed reinforcements subjected to monotonic loading to use the stress-strain relationships of reinforcing bars, including buckling, that are found in the scientific-technical literature. This model considers transverse reinforcements discretely and concrete cover distributedly. The model can be applied to any transverse reinforcement configuration, and to any concrete type (with or without fibres). An analytical equation is also proposed to determine critical compressed reinforcement loads, whose result is presented as abaci. Finally, to calibrate the model in normal-strength concrete columns under eccentric loading, with or without fibres, a programme is presented in which the critical load of longitudinal reinforcements is experimentally determined. The proposed analytical model is calibrated and a procedure to determine critical buckling loads of compressed reinforcements under monotonic loading is proposed.The model presented herein forms part of a research line that is being undertaken at the Concrete Science and Technology Institute (ICITECH) of the Universitat Politècnica de València (UPV). The authors are sincerely grateful to the Spanish Ministry of Economy and Competitiveness for the help it has provided through Project BIA2012-32645 and to the European Union for financial support obtained from FEDER fundsPereiro Barceló, J.; Bonet Senach, JL. (2017). Mixed model for the analytical determination of critical buckling load of passive reinforcement in compressed RC and FRC elements under monotonic loading. Engineering Structures. 150(1):76-90. doi:10.1016/j.engstruct.2017.07.026S7690150

Continuous blending of SPH with finite elements

This paper proposes a methodology for the continuous blending of the finite element method and smooth particle hydrodynamics. The coupled approximation with finite elements and particles, and the discretization of the boundary value problem with a coupled integration, are described. An integration correction is also proposed to stabilize the solution. Some numerical examples demonstrate the applicability of the method