Publications

2015

• A new bond slip model for reinforced concrete structures: Validation by modelling a reinforced concrete tie
  
  • Mang Chetra
  • Jason Ludovic
  • Davenne Luc
  Engineering Computations, Emerald, 2015, 32 (7), pp.1934-1958. The paper presents a new bond-slip model for reinforced concrete structures. It consists in an interface element (3D) which represents the interface between concrete (modeled in 3D) and steel, modeled using 1D truss elements. The formulation of the interface element is presented and verified through a comparison with an analytical solution on an academic case. Finally, the model is compared with experimental results on a reinforced concrete tie. Contrary to the perfect or “no-slip” relation which supposes the same displacement between steel and concrete, the proposed model is able to reproduce both global (force-displacement curve) and local (crack openings) results. The proposed approach, applicable to large scale computations, represents a valuable alternative to the no-slip relation hypothesis to correctly capture the crack properties of reinforced concrete structures. (10.1108/EC-11-2014-0234)
  DOI : 10.1108/EC-11-2014-0234
• Some applications of optimal control to inverse problems in elastoplasticity
  
  • Stolz Claude
  Journal of Mechanics of Materials and Structures, Mathematical Sciences Publishers, 2015, 10 (3), pp.411-432. The aim of this paper is to present the applications of the optimal control theory to solve several inverse problems for elastoplastic materials and structures. The optimal control theory permits to determine the internal state of a body from the knowledge both of the initial and the final, residual, geometry resulting from an unknown loading history. (10.2140/jomms.2015.10.411)
  DOI : 10.2140/jomms.2015.10.411
• Internal stresses at the crystalline scale in textured ZrO2 films before lateral cracking
  
  • Berdin Clotilde
  • Pascal Serge
  • Tang Yan
  Journal of Nuclear Materials, Elsevier, 2015, 460, pp.44-51. Zirconium oxide layers are submitted to internal stresses that play a role in damage of the layer. Lateral cracking is often observed during Zr alloys oxidation. In this paper, we investigated the influence of the microstresses at the crystalline scale on the lateral cracking within a growing oxide on a plane substrate. A parametric study was carried out taking into account the crystallographic texture of the oxide and the presence of a tetragonal zirconia at the metal–oxide interface. Macroscopic computations and polycrystalline aggregate computations were performed. The result indicating the (1 0 View the MathML source) fiber texture as the most favorable was recovered. It was found that under macroscopic compressive stresses parallel to the plane metal–oxide interface, positive microstresses perpendicular to the interface develops. They can trigger the lateral cracking and the phenomenon is promoted by the presence of tetragonal zirconia at the metal–oxide interface
• Fatigue Crack Propagation in Gaseous Hydrogen Environment in Low Alloy Steel
  
  • Sarrazin-Baudoux Christine
  • Gardin Catherine
  • Pham Tuan Hiep
  • Chretien Gaëlle
  • Petit Jean
  • Tran Van-Xuan
  • Benoit Guillaume
  Procedia Engineering, Elsevier, 2015, 114, pp.354-360. Fatigue crack propagation in low alloyed steel (3.5Ni-1.5Cr-0.5Mo-V) used for turbine generator of nuclear plant is studied under 4 bar hydrogen atmosphere in comparison to ambient air and high vacuum. Tests are conducted on CT specimens and the variation of the fatigue crack growth rate da/dN with respect to the amplitude of the applied stress intensity factor ΔK is explored in a wide range and especially in the near threshold domain. The propagation behaviour under hydrogen atmosphere is shown similar to that obtained in air in the low rate range, i.e. when the maximum of the stress intensity factor Kmax is lower than a critical level of 16 MPam1/2 with higher crack growth rate than in high vacuum. This environment effect is related to the presence of residual water vapour in both gases. For Kmax higher than 16 MPam1/2, much faster growth rates under hydrogen atmosphere in comparison to air and vacuum are observed and related to hydrogen assisted intergranular propagation combining fatigue and sustained loading damage. The results are discussed on the basis of micrographic observations supporting the involved mechanisms. (10.1016/j.proeng.2015.08.079)
  DOI : 10.1016/j.proeng.2015.08.079
• A gradient approach for the macroscopic modeling of superelasticity in softening shape memory alloys
  
  • León Baldelli Andrés Alessandro
  • Pham Kim
  • Maurini Corrado
  International Journal of Solids and Structures, Elsevier, 2015, 52 (1), pp.45-55. (10.1016/j.ijsolstr.2014.09.009)
  DOI : 10.1016/j.ijsolstr.2014.09.009
• Pseudoelastic Shape Memory Alloys to Mitigate the Flutter Instability: A Numerical Study
  
  • Malher Arnaud
  • Doaré Olivier
  • Touzé Cyril
  , 2015, 168, pp.353-365. A passive control of aeroelastic instabilities on a two-degrees-of-freedom (dofs) system is considered here using shape memory alloys (SMA) springs in their pseudo-elastic regime. SMA present a solid-solid phase change that allow them to face strong deformations (∼10%) ; in the pseudo-elastic regime, an hysteresis loop appears in the stress-strain relationship which in turn gives rise to an important amount of dissipated energy. This property makes the SMA a natural candidate for mitigating undesired vibrations in a passive manner. A 2-dofs system is here used to model the classical flutter instability of a wing section in a uniform flow. The SMA spring is selected to act on the pitch in order to dissipate energy of the predominant motion. A simple phenomenological model for the SMA hysteresis loop is introduced, allowing for a quantitative study of the important parameters to optimize in view of an experimental design. Thanks to a simple phenomenological model for the SMA hysteresis loop, a quantitative numerical study is performed in order to exhibit the best tuning of the material parameters for controlling the flutter instability. (10.1007/978-3-319-19851-4_17)
  DOI : 10.1007/978-3-319-19851-4_17
• Adaptive zooming method for the analysis of large structures with localized nonlinearities
  
  • Llau Antoine
  • Jason Ludovic
  • Dufour Frédéric
  • Baroth Julien
  Finite Elements in Analysis and Design, Elsevier, 2015, 106, pp.73-84. Simulating concrete cracking requires nonlinear modelling applied on a refined mesh if a correct evaluation of crack properties needs to be achieved. Therefore, it is rather costly and even sometimes impossible when large reinforced concrete structures are considered. Alternative solutions have therefore to be proposed. This contribution presents a structural zooming method for the simulation of large reinforced concrete structures with localized nonlinearities. Our method is based on static condensation (Guyan 1965) and provides an adaptive framework for performance-oriented use of this method in nonlinear simulations. In particular, it only simulates the behavior of nonlinear interesting zones (detected by adapted criteria). The areas where refined modelling is not required are replaced by their equivalent stiffnesses. The linearity criteria, depending on the chosen mechanical models, are also used to activate new interesting zones during the simulation. This method substantially decreases the computational cost on both presented test cases (a two-dimensional concrete beam and a three-dimensional reinforced concrete building). (10.1016/j.finel.2015.07.011)
  DOI : 10.1016/j.finel.2015.07.011