Numerical modeling of strain rate hardening effects on viscoplastic behavior of metallic materials

The main goal of the present work is to provide a finite strain elasticviscoplastic framework to numerically account for strain, strain rate hardening, and viscous effects in cold deformation of metallic materials. The aim is to provide a simple and robust numerical framework capable of modeling the main macroscopic behavior associated with high strain rate plastic deformation of metals. In order to account for strain rate hardening effects at finite strains, the hardening rule involves a rate dependent saturation hardening, and it accounts for linear hardening prevailing at latter deformation stages. The numerical formulation, finite element implementation, and constitutive modeling capabilities are assessed by means of decremental strain rate testing and constant strain rate loading followed by stress relaxation. The numerical results have demonstrated the overall framework can be an efficient numerical tool for simulation of plastic deformation processes where strain rate history effects have to be accounted for

Formulation of reference solutions for compaction process in sedimentary basins

This paper is devoted to the development of semianalytical solutions for the deformation induced by gravitational compaction in sedimentary basins. Formulated within the framework of coupled plasticity–viscoplasticity at large strains, the modeling dedicates special emphasis to the effects of material densification associated with large irreversible porosity changes on the stiffness and hardening of the sediment material. At material level, the purely mechanical compaction taking place in the upper layers of the basin is handled in the context of finite elastoplasticity, whereas the viscoplastic component of behavior is intended to address creep-like deformation resulting from chemomechanical that prevails at deeper layers. Semianalytical solutions describing the evolution of mechanical state of the sedimentary basin along both the accretion and postaccretion periods are presented in the simplified oedometric setting. These solutions can be viewed as reference solutions for verification and benchmarks of basin simulators. The proposed approach may reveal suitable for parametric analyses because it requires only standard mathematics-based software for PDE system resolution. The numerical illustrations provide a quantitative comparison between the derived solutions and finite element predictions from an appropriate basin simulator, thus showing the ability of the approach to accurately capture essential features of basin deformation

Um modelo multifásico para estruturas em concreto armado considerando a fissuração do concreto

Assessing the global behavior of reinforced materials from the individual properties of their components has been the subject of a considerable amount of experimental and theoretical works in the last years. The so-called multiphase model is an alternative generalization of the homogenization method and it relies upon the idea that, at the macroscopic scale, the reinforced concrete is a geometrical superposition of the matrix phase (concrete) and the reinforcing phase (steel bars). This technique was already successfully employed in several geotechnical structures. Considering the particular case of concrete structures, Figueiredo et al [1] analyzed the mechanical behavior of reinforced concrete flat slabs under prescribed loading using the multiphase model in elastoplasticity. The present contribution extents a previously numerical code to account for concrete cracking based on a smeared crack approach. Comparison with direct simulation results emphasizes the advantage of such multiphase model in terms of reduced computational cost.Determinar o comportamento global de materiais reforçados a partir das propriedades individuais de seus componentes vem sendo tema de um considerável número de trabalhos experimentais e teóricos nos últimos anos. A modelagem multifásica é uma generalização alternativa do método de homogeneização cujo princípio básico consiste em descrever o concreto armado como a superposição geométrica da fase matriz (concreto) e da fase reforço (barras de aço). Esta técnica foi empregada com sucesso em uma série de trabalhos envolvendo estruturas geotécnicas. No caso da estruturas de concreto, Figueiredo et al (2009) estuda o comportamento mecânico de placas de concreto armado sob a ação de carregamento prescrito com o uso da modelagem multifásica em elastoplasticidade. No presente trabalho é acrescentado ao modelo previamente desenvolvido o algoritmo que leva em conta a fissuração do concreto baseado no modelo de fissuras distribuídas apresentado por Hinton (1988). São realizadas comparações com simulações diretas clássicas visando salientar as vantagens do modelo como a redução significativa do custo computacional

A limit analysis approach to the stability assessment of reinforced concrete panels in fire conditions

The present study investigates the stability conditions of reinforced concrete panels subjected to fire loading within the framework of limit analysis theory. The method relies in a first step upon the preliminary determination of the temperature dependent interaction diagrams of the structural element. Interaction diagrams derived from the static approach are shown to depend on the geometry of panel cross-section as well as on the strength properties of the constituents, which degrade continuously as fire proceeds. The second step of the method consists in determining the deformed configuration of panel from the analysis of thermo-elastic equilibrium of the structure. The stability analysis and design of the panel in its deformed geometry are then carried out by comparing the distribution of internal efforts to its reduced strength capacities expressed by means of the associated interaction diagrams evaluated in the first step. Several numerical examples are presented to assess the effect of relevant parameters on the overall fire safety of the structure, emphasizing the effectiveness of the approach for design purposes