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Conceicao J.,University of Porto | Faria R.,University of Porto | Azenha M.,University of Minho | Mamede F.,Eletrobras | Souza F.,MultiMech Research and Development LLC
Engineering Structures | Year: 2014

Within massive structures hydration reactions of the cement present in the mixture promote an internal heat release. Due to the low thermal conductivity of concrete, the dissipation rate of this thermal energy is lower than the rate of production of hydration heat, so considerable temperature gradients occur. Therefore, thermal stresses arise as a consequence of differential thermal expansions or contractions. These self-induced stresses may be even higher in the scenario of additional external restraints (such as support conditions). If not adequately controlled, the self-induced tensile stresses may induce cracking of concrete at early ages. This paper describes the in-depth analysis of the concrete surrounding the spiral case of a hydroelectric turbine constructed in Brazil, with a comprehensive approach that includes: laboratory characterization of the concrete properties, numerical analyses to predict the temperature and stress fields, and the corresponding in-field monitoring. The consistency obtained between numerical results and in situ observations is discussed in detail. The thermally induced cracking risk is also evaluated. © 2014 Elsevier Ltd.

Kim Y.-R.,Kyung Hee University | Souza F.V.,Multimech Research and Development LLC | Teixeira J.E.S.L.,Federal University of Espirito Santo
Computational Mechanics | Year: 2013

This paper presents a quasi-static multiscale computational model with its verification and rational applications to mechanical behavior predictions of asphaltic roadways that are subject to viscoelastic deformation and fracture damage. The multiscale model is based on continuum thermo-mechanics and is implemented using a finite element formulation. Two length scales (global and local) are two-way coupled in the model framework by linking a homogenized global scale to a heterogeneous local scale representative volume element. With the unique multiscaling and the use of the finite element technique, it is possible to take into account the effect of material heterogeneity, viscoelasticity, and anisotropic damage accumulation in the small scale on the overall performance of larger scale structures. Along with the theoretical model formulation, two example problems are shown: one to verify the model and its computational benefits through comparisons with analytical solutions and single-scale simulation results, and the other to demonstrate the applicability of the approach to model general roadway structures where material viscoelasticity and cohesive zone fracture are involved. © 2012 Springer-Verlag.

Teixeira J.E.S.L.,Federal University of Espirito Santo | Kim Y.R.,University of Nebraska - Lincoln | Souza F.V.,Multimech Research and Development LLC | Allen D.H.,PSI Technologies Inc. | Little D.N.,Texas A&M University
Transportation Research Record | Year: 2014

The study reported in this paper presented a multiscale computational model, along with its validation and calibration, to predict the damage-dependent behavior of asphalt mixtures subjected to viscoelastic deformation and cracking. Asphalt mixture is a classic example of a multiphase composite that represents different lengths of scales. The understanding of the mechanical behavior of asphaltic materials has been a challenge to the pavement mechanics community because of the multiple complexities involved: heterogeneity, anisotropy, nonlinear inelasticity, and damage growth in multiple forms. To account for (his issue in an accurate and efficient way, the study reported here presented a two-way linked multiscale computational modeling approach. The two-way linked multiscale model had its basis in continuum thermomechanics and was implemented with a finite element formulation. With the unique multiscale linking between scales and the use of the finite element technique, this model could take into account the effects of material heterogeneity, viscoelasticity, and anisotropic damage growth in small-scale mixtures on the overall performance of larger-scale structures. Along with the brief theoretical model formulation, the multiscale model was validated and calibrated through the comparison of the numerical, analytical, and experimental results of three-point bending beam tests of asphalt mixture samples that involved viscoelasticity, mixture heterogeneity, and cohesive zone fracture.

Souza F.V.,Federal University of Ceará | Castro L.S.,MultiMech Research and Development LLC
Construction and Building Materials | Year: 2012

Roadways are key structures for the living and development of society since they are responsible for a large portion of the transportation of goods and people. Moreover, according to the Asphalt Pavement Alliance, 94% of the highway system in America is paved with asphalt materials, especially due to its low lifetime cost. In many countries, the roadway system happens to be in bad conditions caused not only by the traffic loads but also by environmental conditions. In the case of asphalt pavements, temperature changes not only cause the material to expand/contract but also changes the material viscoelastic properties of asphalt mixtures. Unfortunately, most practitioners currently do not take into account either of these phenomena in the design of pavement structures. In the present manuscript thermo-mechanical numerical simulations are performed in an attempt to understand the combined effect of temperature variations and mechanical loading on the mechanical response of viscoelastic asphalt pavements. The results emphasize the importance of considering temperature variations and thermo-viscoelasticity in the design of asphalt pavements. © 2011 Elsevier Ltd. All rights reserved.

Souza F.V.,MultiMech Research and Development LLC | Allen D.H.,University of Texas–Pan American
Mechanics of Advanced Materials and Structures | Year: 2013

Engineering applications are increasingly facing structural challenges. Restrictive economic constraints and more complex geometric design have led to the use of advanced materials, such as fiber-reinforced composites. The behavior of such materials is governed by their microstructure, thus demanding the use of multiscale approaches. The present article aims at the verification of a two-way coupled multiscale finite element code previously developed by the authors. A two-scale analytical solution for a functionally graded elastic material subject to dynamic loads is herein derived in order to verify the multiscale code. Comparisons to overkilled single scale finite element solutions are also presented. Copyright © Taylor &Francis Group, LLC.

Souza F.V.,MultiMech Research and Development LLC | Allen D.H.,University of Texas–Pan American
Plastics, Rubber and Composites | Year: 2013

The classical approach to modelling the thermomechanical response of composites employs a framework embodied within the concept of continuum mechanics. This approach may not always lead to success in that some failure mechanisms such as molecular scale phenomena may not be accurately captured by the continuum approximation. On the other hand, the continuum approach may be quite powerful and accurate for predicting failure in a variety of circumstances. For any continuum mechanics based approach to have hope of accuracy it is, however, necessary for that model to in some sense capture the physics of all of the cogent energy dissipative processes that are engendered in the actual application. The current paper takes the approach that failure due to fracture in viscoelastic composites can indeed be modelled entirely within the framework of continuum mechanics, but that in order to accurately predict failure due to fracture it is often necessary to deploy a model that is simultaneously cast within multiple length scales, each using the framework of continuum mechanics. This approach is taken for the simple reason that experimental observation suggests that in viscoelastic composites cracks form on the microscale, and these cracks eventually coalesce into macroscale cracks that cause the part to fail due to catastrophic facture. While predictions of these events may seem extraordinarily costly and complex, there are multiple structural applications where effective models would save considerable expense. The formulation for such an approach will be presented herein. This approach has been implemented into a finite element code and some example problems will be given in order to demonstrate the capabilities of the method. © 2013 Institute of Materials, Minerals and Mining 2013 Published by Maney on behalf of the Institute.

Kim Y.-R.,Kyung Hee University | Souza F.V.,Multimech Research and Development LLC | Park T.,Hanyang University
Journal of Engineering Materials and Technology, Transactions of the ASME | Year: 2013

This study presents a multiscale computational model and its application to predict damage dependent mechanical behavior of bituminous mixtures subjected to cyclic loading. Two length scales (global and local) are two-way coupled in the model framework by linking a homogenized global scale to a heterogeneous local scale representative volume element. Based on the unique two-way coupled multiscaling and the use of the finite element technique incorporated with the material viscoelasticity and cohesive zone fracture, the model approach can successfully account for the effect of mixture heterogeneity, material viscoelasticity, and damage accumulation due to cracks in the small scale on the overall performance of larger scale mixtures or structures. This step requires only the properties of individual constituents. To demonstrate the model and its features, bending beam fatigue testing of a bituminous mixture, which is composed of elastic aggregates and viscoelastic bitumen, is simulated by altering the mixture's constituent properties. The model clearly presents progressive damage characteristics with repetitive loading cycles and the analysis clearly demonstrates the sensitivity of the approach to constituent material properties. The multiscale model presented herein is expected to drastically reduce time-consuming and expensive fatigue tests, which, when performed in the traditional manner, require many replicates and do not define the cause of microstructural fatigue, damage, and failure. Copyright © 2013 by ASME.

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