Un modelo de hormigón basado en plasticidad no asociada y fractura

Se presenta un modelo para el análisis de estructuras de hormigón mediante el método de elementos finitos. El modelo se basa en la teoría de plasticidad no asociada y en la teoría de la fisura difusa. La implantación numérica en un programa general no lineal de elementos finitos motivó desarrollos específicos en el esquema de integración de las relaciones constitutivas y en el uso de matrices de rigidez simétricas.A model for the analysis of concrete structures by the finite element method is presented. The model is based on the non-associated platicity theory and the smeared crack approach. The numerical implantation in a general purpose nonlinear finite element program led to developments in the scheme for the integration of the constitutive relation and to the use of symmetric stiffness matrices.Peer Reviewe

Un modelo de hormigón basado en plasticidad no asociada y fractura

Se presenta un modelo para el análisis de estructuras de hormigón mediante el método de elementos finitos. El modelo se basa en la teoría de plasticidad no asociada y en la teoría de la fisura difusa. La implantación numérica en un programa general no lineal de elementos finitos motivó desarrollos específicos en el esquema de integración de las relaciones constitutivas y en el uso de matrices de rigidez simétricas.A model for the analysis of concrete structures by the finite element method is presented. The model is based on the non-associated platicity theory and the smeared crack approach. The numerical implantation in a general purpose nonlinear finite element program led to developments in the scheme for the integration of the constitutive relation and to the use of symmetric stiffness matrices.Peer Reviewe

A multiscale approach for modeling crystalline solids

In this paper we present a modeling approach to bridge the atomistic with macroscopic scales in crystalline materials. The methodology combines identification and modeling of the controlling unit processes at microscopic level with the direct atomistic determination of fundamental material properties. These properties are computed using a many body Force Field derived from ab initio quantum-mechanical calculations. This approach is exercised to describe the mechanical response of high-purity Tantalum single crystals, including the effect of temperature and strain-rate on the hardening rate. The resulting atomistically informed model is found to capture salient features of the behavior of these crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate

A multiscale approach for modeling crystalline solids

In this paper we present a modeling approach to bridge the atomistic with macroscopic scales in crystalline materials. The methodology combines identification and modeling of the controlling unit processes at microscopic level with the direct atomistic determination of fundamental material properties. These properties are computed using a many body Force Field derived from ab initio quantum-mechanical calculations. This approach is exercised to describe the mechanical response of high-purity Tantalum single crystals, including the effect of temperature and strain-rate on the hardening rate. The resulting atomistically informed model is found to capture salient features of the behavior of these crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate

Multiscale modelling of hardening in BCC crystal plasticity

International audienceThe mechanical behavior of polycrystalline metals can be successfully modeled by macroscopic theories, such as Von Mises plasticity. On the other hand, numerous studies can be performed on the atomic scale, either by atomistic or dislocation dynamics models. The proposed model attempts to bridge those two scales by deriving constitutive relations between slip strains, dislocation densities and resolved shear stresses on crystallographic planes, from mechanisms of deformation playing at the level of the dislocation line. The resulting "mesoscopic" hardening relations are controlled by dislocation self energies and junctions strengths. Temperature and strain rate dependence result from the presence of thermally activated mechanisms such as Peierls barriers or pair annihilation by cross slip. A set of material parameters is identified for Tantalum by fitting the numerical stress strain curves from these tests with experimental results gathered in the literature. These parameters prove to be in very good agreement with the values which can be derived from molecular dynamics computations

A micromechanical model of hardening, rate sensitivity and thermal softening in BCC single crystals

International audienceThe present paper is concerned with the development of a micromechanical model of the hardening, rate-sensitivity and thermal softening of bcc crystals. In formulating the model, we specifically consider the following unit processes: double-kink formation and thermally activated motion of kinks; the close-range interactions between primary and forest dislocations, leading to the formation of jogs; the percolation motion of dislocations through a random array of forest dislocations introducing short-range obstacles of different strengths; dislocation multiplication due to breeding by double cross-slip; and dislocation pair annihilation. The model is found to capture salient features of the behavior of Ta crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate

Effective Thermal Expansion Property of Consolidated Granular Materials

Thermally-assisted compaction of granular materials is of keen interest in many engineering applications. A proper estimation of the material behavior of compacted granular materials is contingent upon the knowledge of microstructure formation, which is highly dependent on the bulk material properties and processing conditions, during the deformation stage. Originating from the pair interactions between particles, the macroscopic properties are obtained using various homogenization techniques and postulating continuum constitutive laws. While pioneers in this field have laid fundamental groundwork regarding effective medium descriptions, there exists a discrepancy between discrete and continuum level solutions. In our previous work, we elaborated a Particle Mechanics Approach (PMA) that integrates thermal contact and Hertzian deformation models to understand the thermo-mechanically-coupled consolidation problem. We also considered the analogous problem from the perspective of the conventional Continuum Mechanics Approach (CMA). In this study, following the multi-scale modeling framework, we propose an effective thermal expansion coefficient for the thermally-assisted compaction of granular materials

Modeling and simulation of the coupled mechanical–electrical response of soft solids

ABSTRACT Dielectric elastomer (DE) is one type of electro-active polymers (EAP) that responds to electrical stimulation with a significant shape and size change. As EAPs, dielectric elastomers are lightweight, inexpensive, pliable and can be fabricated into various shapes, all of which are attractive properties to justify the intense research in the field. This paper presents a nonlinear, electrical and mechanical coupled, large deformation finite element formulation for DEAs. Maxwell's equations for the electroquasistatic fields were solved simultaneously with equation of linear momentum. The hyperelastic Ogden model and total Maxwell stress methods were combined to describe the material. The formulation was based on the weak forms of Maxwell's equation and linear momentum expressed in the reference configuration. The closed form consistent tangent moduli for dielectric elastomers were derived. To our knowledge, the large deformation electric-mechanical coupled finite element application and the closed-form expressions of the tangent moduli have not been reported previously. The results of the simulation have demonstrated the validity of the method from the computational aspect