Multiphysical failure processes in concrete: a consistent multiscale homogenization procedure

Durability and strength capabilities of concrete materials are vastly affected by the combined action of temperature and mechanical loading, which give rise to multiphysical failure processes. Such a phenomenon involves complex cracking, degradation and transport mechanisms on different scale lengths of concrete mixtures which, in turn, depend on the particular properties of the different constituents. Thus, the macroscopic observation of relevant concrete mechanical features such as strength, ductility and durability are the result of several different properties, processes and mechanisms which are not only coupled but moreover, depend on multiple scales. Particularly, regarding the pore pressure and thermal actions, most of the degradation processes in concrete are controlled by the heterogeneities of the microscopic scale. In the case of the mechanical actions both the micro and mesoscales play a relevant role. In this context, multiphysical failure processes in cementitious material-based mixtures like concrete can only and fully be understood and accurately described when considering its multiscale and multiconstituent features. In the realm of the theoretical and computational solid mechanics many relevant proposals were made to model the complex and coupled thermo-hydromechanical response behavior of concrete. Most of them are related to macroscopic formulations which account for the different mechanisms and transport phenomena through empirical, dissipative, poromechanical theories. Moreover, although relevant progress was made regarding the formulation of multiscale theories and approaches, none of the existing proposals deal with multiphysical failure processes in concrete. It should be said in this sense that, among the different multiscale approaches for material modeling proposed so far, those based on computational homogenization methods have demonstrated to be the most effective ones due to the involved versatility and accuracy. In this work a thermodynamically consistent semi-concurrent multiscale approach is formulated for modeling the thermo-poro-plastic failure behavior of concrete materials. A discrete approach is considered to represent the RVE material response. After formulating the fundamental equations describing the proposed homogenizations of the thermodynamical variables, the constitutive models for both the skeleton and porous phases are described. Then, numerical analyses are presented to demonstrate the predictive capabilities of the proposed thermodynamically consistent multiscale homogenization procedure for thermo-mechanical failure processes in concrete mixtures

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Mathematical models of supersonic and intersonic crack propagation in linear elastodynamics

This paper presents mathematical models of supersonic and intersonic crack propagation exhibiting Mach type of shock wave patterns that closely resemble the growing body of experimental and computational evidence reported in recent years. The models are developed in the form of weak discontinuous solutions of the equations of motion for isotropic linear elasticity in two dimensions. Instead of the classical second order elastodynamics equations in terms of the displacement field, equivalent first order equations in terms of the evolution of velocity and displacement gradient fields are used together with their associated jump conditions across solution discontinuities. The paper postulates supersonic and intersonic steady-state crack propagation solutions consisting of regions of constant deformation and velocity separated by pressure and shear shock waves converging at the crack tip and obtains the necessary requirements for their existence. It shows that such mathematical solutions exist for significant ranges of material properties both in plane stress and plane strain. Both mode I and mode II fracture configurations are considered. In line with the linear elasticity theory used, the solutions obtained satisfy exact energy conservation, which implies that strain energy in the unfractured material is converted in its entirety into kinetic energy as the crack propagates. This neglects dissipation phenomena both in the material and in the creation of the new crack surface. This leads to the conclusion that fast crack propagation beyond the classical limit of the Rayleigh wave speed is a phenomenon dominated by the transfer of strain energy into kinetic energy rather than by the transfer into surface energy, which is the basis of Griffiths theory

Coupled thermo-mechanical interface model for concrete failure analysis under high temperature

A thermo–mechanical interface model for failure analysis of concrete subjected to high temperature is presented in this work. The model is an extension of a fracture energy-based interface formulation which now includes thermal damage induced by high temperature and/or fire. The coupled thermal–mechanical effect in the interface model is taken into account through the formulation of a temperature dependent maximum strength criterion and fracture energy-based softening or post-cracking rule. In this sense, the strong variation of concrete ductility during failure processes in mode I, II or mixed types of fracture is described through the consideration of temperature dependent ductility measures and of the specific work spent in softening. Moreover, a temperature-based scaling function is introduced to more accurately predict the thermal effect affecting the interface strength and post-cracking response. After outlining the mathematical formulation of the interface model, numerical analyses are presented to validate its soundness and capability. A wide range of experimental results, available in the scientific literature, are analyzed at both material and structural scale of analysis using the proposed interface model and in the framework of the discrete crack approach. The results demonstrate the predictive capabilities of the proposed interface constitutive theory for temperature dependent failure behavior of concrete.Fil: Caggiano, Antonio. Universidad de Buenos Aires. Facultad de Ingenieria. Laboratorio de Metodos Numericos En Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Etse, Jose Guillermo. Universidad de Buenos Aires. Facultad de Ingenieria. Laboratorio de Metodos Numericos En Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Degradation of Concrete Mechanical Behavior due to Temperature Effects

In this work, the capabilities of a material model to describe and predict the degradation of concrete capacity and mechanical behavior due to temperature effects are presented. The predictions of the numerical model are compared with experimental results of concrete subjected to different temperatures. The results in this work show the severe consequences of the long term exposure to temperature of concrete main features such as strength and stiffness and, in this sense, it is also shown the effect of this mechanical features degradation on the safety condition of the related structures. Moreover, the numerical results demonstrate the accuracy and capacity of the mathematical model proposed by the Authors regarding concrete structure behavior subjected to combined action of temperature and mechanical loading

Sobre inestabilidad e integracion de tensiones de formulaciones viscoplásticas para hormigón

In this work, the consequenses of the stability conditions in elasto-plastic and elastoviscoplastic constitutive formulations for concrete materials are analyzed. In particular, the criterion for local instability by Hill is considered and its performance is analyzed by means of the directional stiffness modulus. The numerical results for the stress path of the instability test by Smith illustrate the influence of the grade of nonassociativity and of the viscosity in the performance of the instability condition

Zero-thickness interface model for coupled thermo-mechanical failure analysis of concrete

A discontinuous-based thermo-mechanical model for concrete subjected to high temperatures is presented. The model is an extension of a fracture energy-based elastoplastic interface formulation which now includes damage induced by high temperatures and fire. The coupled thermo-mechanical effects due to high temperature fields in concrete are taken into account through a temperature dependent maximum strength criterion and post-cracking law. Thereby, the different characteristics of concrete failure behaviour in mode I and mode II type of fracture are considered by means of specific work softening rules in terms of temperature-dependent fracture energy-based formulations. The temperature effects in the interface strength and its post-cracking behaviour are considered in the proposed constitutive model through a dehydration scaling function. After outlining the mathematical formulation of the constitutive model for interface elements, numerical analysis of available experimental results in the literature are presented to validate its soundness and capability. \ua9 2014 Taylor & Francis Group

Continuous Microplane Theory and Interface Approach for Failure Form Analysis of Steel Fiber Reinforced Concrete

A fracture energy-based microplane constitutive theory for steel fiber reinforced concrete (SFRC) is presented to evaluate the properties of the discontinuous bifurcation condition under different scenarios of stress states, fiber contents and directions. The constitutive model considers a CAP-cone yield surface of C1 continuity at the microplane level. Its evolution in the post-peak regime is described by means of a fracture energy-based work softening which is defined differently for mode I and II type of failure. The effect on the post-peak ductility introduced by the fiber content is also taken into account, while the directional properties of the steel fibers are considered through the relative directions between microplanes and fibers. The main objective of the discontinuous bifurcation analysis proposed in this work, is to evaluate the capabilities of the microplane theory to capture the directional enrichment provided by steel fibers to the ductility and also, to reproduce the particular microcrack directions which (in the framework of the smeared crack approach) are mathematically represented by the spectral properties of the critical localization tensor. Firstly, the localized failure features in the form of discontinuous bifurcation of SFRC are identified by means of numerical analysis. Mono- and multidirectional fiber distributions and different steel fiber contents are considered in the localized failure analysis to be performed on stress states corresponding to critical strengths of SFRC under both uniaxial and biaxial tension and compression. Then, microplane model are compared with the FE predictions obtained with the interface model for FRC previously proposed by the authors. In the last case, the crack evolutions and their directions are explicitly described throughout the so-called discrete crack approach