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Grondin F.,CNRS Research Institute in Civil Engineering and Mechanics | Matallah M.,CNRS Research Institute in Civil Engineering and Mechanics | Matallah M.,Abou Bekr Belkaid University Tlemcen
Cement and Concrete Research | Year: 2014

Because the ITZs' thickness in concrete surrounding aggregates is tiny, it is difficult to take them into account explicitly in the modelling of concrete. A methodology is suggested to consider the effect of the ITZs on the mechanical behaviour of concrete at the mesoscopic scale. For that, the mechanical ITZ properties have been calculated according to the hydration of cement at various distances of the aggregate boundary. Then, we have defined an effective mixed interphase (EMI) around each aggregate which is formed by the ITZ and a volume fraction of the bulk cement paste. Simulations have been performed to show the influence of this EMI on the tensile failure of concrete. Results have shown that the maximum strength of the specimens depends on the local tensile strength of the ITZs. Stresses were more diffused for the cases without the ITZs and with the ITZs having a lower tensile strength. © 2014 Elsevier Ltd.


Bastidas-Arteaga E.,CNRS Research Institute in Civil Engineering and Mechanics | Stewart M.G.,University of New South Wales
Structural Safety | Year: 2015

Reinforced concrete (RC) structures are subject to environmental actions affecting their performance, serviceability and safety. Among these actions, chloride ingress leads to corrosion initiation and its interaction with service loading could reduce its operational life. Experimental evidence indicates that chloride ingress is highly influenced by weather conditions in the surrounding environment and therefore by climate change. Consequently, both structural design and maintenance should be adapted to these new environmental conditions. This work focuses on the assessment of the costs and benefits of two climate adaptation strategies for new RC structures placed in chloride-contaminated environments under various climate change scenarios. Their cost-effectiveness is measured in terms of the benefit-to-cost ratio (BCR) and the probability that BCR exceeds unity - i.e., Pr(BCR. > 1). It was found that increasing concrete strength grade is more cost-effective than increasing design cover. The results also indicate that the cost-effectiveness of a given adaptation strategy depends mainly on the type of structural component, exposure conditions and climate change scenarios. © 2014 Elsevier Ltd.


El-Qoubaa Z.,CNRS Research Institute in Civil Engineering and Mechanics | Othman R.,King Abdulaziz University
Materials and Design | Year: 2015

Semi-crystalline polymers are increasingly used in structural applications where they can withstand dynamic loads. It is then, of highly importance, to measure and model their mechanical behavior over a wide range of strain rates. In this paper, the polyetheretherketone's yield stress is investigated under quasi-static (0.0001-0.1/s), intermediate (5-500/s) and high (500-10,000/s) strain rates. Four experimental set-ups were used to achieve this task. It was shown that the mechanical behavior is highly sensitive to strain rate. The yield stress at 10,000/s is 115% higher than at 0.0001/s. Moreover, the strain rate sensitivity increases with increasing strain rate. A new three-material-constant constitutive equation is proposed to take into account the increase of strain rate sensitivity at very high strain rates. An identification approach is also developed to consider the influence of the strain rate range. The material constants, of the new constitutive equation and of three constitutive equations available in the literature, are identified. For each equation, we have reported the strain rate range where each model best fits the experimental data. The new model gives the best trade-off of fitting the experimental data with a good accuracy while minimizing the number of material constants. © 2014 Elsevier Ltd.


Verron E.,CNRS Research Institute in Civil Engineering and Mechanics
Rubber Chemistry and Technology | Year: 2010

Our objective is twofold: (1) to offer a short state of the art on the framework of configurational mechanics to rubber researchers and engineers, and (2) to show that it is well adapted to rubber mechanics. The state of the art presents the general theory but also highlights the physical meaning of the Eshelby stress tensor and of its path integrals; then, we propose a list of recent applications involving configurational mechanics. Attention is then focused on rubber applications: recent work on the simulation of fracture in inelastic materials and on the development of predictors for fatigue crack initiation is presented.


Chevreuil M.,CNRS Research Institute in Civil Engineering and Mechanics | Nouy A.,CNRS Research Institute in Civil Engineering and Mechanics
International Journal for Numerical Methods in Engineering | Year: 2012

A priori model reduction methods based on separated representations are introduced for the prediction of the low frequency response of uncertain structures within a parametric stochastic framework. The proper generalized decomposition method is used to construct a quasi-optimal separated representation of the random solution at some frequency samples. At each frequency, an accurate representation of the solution is obtained on reduced bases of spatial functions and stochastic functions. An extraction of the deterministic bases allows for the generation of a global reduced basis yielding a reduced order model of the uncertain structure, which appears to be accurate on the whole frequency band under study and for all values of input random parameters. This strategy can be seen as an alternative to traditional constructions of reduced order models in structural dynamics in the presence of parametric uncertainties. This reduced order model can then be used for further analyses such as the computation of the response at unresolved frequencies or the computation of more accurate stochastic approximations at some frequencies of interest. Because the dynamic response is highly nonlinear with respect to the input random parameters, a second level of separation of variables is introduced for the representation of functions of multiple random parameters, thus allowing the introduction of very fine approximations in each parametric dimension even when dealing with high parametric dimension. © 2011 John Wiley & Sons, Ltd.


Nouy A.,CNRS Research Institute in Civil Engineering and Mechanics
Archives of Computational Methods in Engineering | Year: 2010

Uncertainty quantification and propagation in physical systems appear as a critical path for the improvement of the prediction of their response. Galerkin-type spectral stochastic methods provide a general framework for the numerical simulation of physical models driven by stochastic partial differential equations. The response is searched in a tensor product space, which is the product of deterministic and stochastic approximation spaces. The computation of the approximate solution requires the solution of a very high dimensional problem, whose calculation costs are generally prohibitive. Recently, a model reduction technique, named Generalized Spectral Decomposition method, has been proposed in order to reduce these costs. This method belongs to the family of Proper Generalized Decomposition methods. It takes part of the tensor product structure of the solution function space and allows the a priori construction of a quasi optimal separated representation of the solution, which has quite the same convergence properties as a posteriori Hilbert Karhunen-Loève decompositions. The associated algorithms only require the solution of a few deterministic problems and a few stochastic problems on deterministic reduced basis (algebraic stochastic equations), these problems being uncoupled. However, this method does not circumvent the "curse of dimensionality" which is associated with the dramatic increase in the dimension of stochastic approximation spaces, when dealing with high stochastic dimension. In this paper, we propose a marriage between the Generalized Spectral Decomposition algorithms and a separated representation methodology, which exploits the tensor product structure of stochastic functions spaces. An efficient algorithm is proposed for the a priori construction of separated representations of square integrable vector-valued functions defined on a high-dimensional probability space, which are the solutions of systems of stochastic algebraic equations. © CIMNE, Barcelona, Spain 2010.


Legrain G.,CNRS Research Institute in Civil Engineering and Mechanics | Chevaugeon N.,CNRS Research Institute in Civil Engineering and Mechanics | Dreau K.,CNRS Research Institute in Civil Engineering and Mechanics
Computer Methods in Applied Mechanics and Engineering | Year: 2012

In this contribution, a strategy is proposed for uncoupling geometrical description and approximation with the X-FEM. The strategy is based on an uniform coarse mesh that defines a high order approximation of the mechanical fields and an adapted mesh that defines the geometrical features by means of levelsets. The connection between the geometry and the approximation is obtained by sharing the quadtree trees of the two meshes. Numerical examples involving level-set based parts, convergence studies, mechanical computations and numerical homogenization show good promise for this approach. © 2012 Elsevier B.V.


Stainier L.,CNRS Research Institute in Civil Engineering and Mechanics
Mechanics Research Communications | Year: 2011

In this paper, we detail a consistent approximate expression for incremental dissipation pseudo-potentials which appear in the variational formulation of coupled thermo-mechanical boundary-value problems. We explain why the most intuitive expression does not work in the case of an explicit temperature dependence in the dissipation, and propose an alternative expression ensuring consistent results when reducing the time increment towards zero. © 2011 Elsevier Ltd.


Huneau B.,CNRS Research Institute in Civil Engineering and Mechanics
Rubber Chemistry and Technology | Year: 2011

Strain-induced crystallization of natural rubber was discovered in 1925 by the means of x-ray diffraction and has been widely investigated by this technique until today. The studies devoted to the structure of the crystalline phase of natural rubber are first reviewed. This structure is strongly anisotropic and can be related to the exceptionally good strength and fatigue properties of this material. The relationships between strain-induced crystallization of natural rubber and its mechanical response, during static or tension-retraction tests, are also reviewed and discussed; in particular, the hysteresis of the stress-strain curve is mainly explained by strain-induced crystallization. The kinetics of crystallization under both static and cyclic deformation is also discussed, as well as the influence of different factors, depending either on material composition (crosslink density, carbon black fillers) or on external parameters (temperature, strain rate. . . ).


Hicher P.-Y.,CNRS Research Institute in Civil Engineering and Mechanics
Geotechnique | Year: 2013

Presented here is a numerical method able to predict the mechanical behaviour of granular materials subjected to particle removal. The purpose of this study is to improve understanding of the mechanical behaviour of soils subjected to internal erosion in hydraulic works. The approach is based on a homogenisation technique for deriving the stress-strain relationship of a granular assembly from forces and displacements at the particle level. The soil's local behaviour is assumed to follow a Hertz-Mindlin elastic law and a Mohr-Coulomb plastic law. Sliding resistance on each plane is made to depend on the actual void ratio of the granular assembly. The solid fraction removal is modelled by progressively increasing the granular assembly void ratio, which provokes a decrease of the sliding resistance of each interparticle contact, leading to macroscopic deformations of the soil specimen. At elevated stress levels, large deformations can develop and lead to soil failure. Numerical simulations also demonstrate that a type of failure called diffuse failure can occur in eroded soil masses whenever an increase in pore pressure is generated within the soil. These numerical results appear to be coherent with observations made on embankment dams that have suffered internal erosion and in particular, with the description of their modes of failure. © 2013 Thomas Telford Ltd.

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