Publications

2015

• Multi-axial Fatigue Criteria with Length Scale and Gradient Effects
  
  • Zepeng Ma
  • Maitournam Habibou
  • Le Tallec Patrick
  Procedia Engineering, Elsevier, 2015, 133, pp.60 - 71. The objective of the work is first to extend some classic high cycle fatigue (HCF) criteria (as Crossland, Dang Van, Papadopoulos, ...) to take into account a sensitivity of the criteria to stress spatial variations occurring at length scale lg, and second to compare the performances of the extensions through numerical simulations of experimental fatigue tests. After an introduction of the basic criteria and their gradient based extensions proposed by Luu et al., we focus on the Crossland criterion to propose a more practical and simple expression taking into account the gradient of the stress amplitude and the maximum hydrostatic stress. The proposition is then tested and applied to different simple situations: 4-point bending and cantilever rotative bending. The relative errors between the exact solutions and the numerical simulations are estimated. Biaxial bending-torsion tests are also simulated to demonstrate the capabilities of the approach. The generalization of the approach to other multiaxial fatigue criteria is briefly shown through the case of Papadopoulos 2001 proposal. Finally, the present study develops a simple formulation of gradient multi-axial fatigue criteria extending the classical HCF criteria. In this work only stress gradient with a beneficial effect on fatigue have been considered. (10.1016/j.proeng.2015.12.624)
  DOI : 10.1016/j.proeng.2015.12.624
• Simulating the fluid forces and fluid-elastic instabilities of a clamped–clamped cylinder in turbulent axial flow
  
  • de Ridder Jeroen
  • Doaré Olivier
  • Degroote Joris
  • van Tichelen Katrien
  • Schuurmans Paul
  • Vierendeels Jan
  Journal of Fluids and Structures, Elsevier, 2015, 55, pp.139-154. In this article, the fluid forces and the dynamics of a flexible clamped-clamped cylinder in turbulent axial flow are computed numerically. In the presented numerical model, there is no need to tune parameters for each specific case or to obtain coefficients from experiments. The results are compared with the dynamics measured in experiments available in literature. The specific case studied here consists of a silicone cylinder mounted in axial water flow. Computationally it is found that the cylinder loses stability first by buckling. The threshold for buckling is in quantitative agreement with experimental results and weakly-nonlinear theory. At higher flow speed a fluttering motion is predicted, in agreement with experimental results. It is also shown that even a small misalignment between the flow and the structure can have a significant impact on the dynamical behavior. To provide insight in the results of these fluid-structure interaction simulations, forces are computed on rigid inclined and curved cylinders, showing the existence of two different flow regimes. Furthermore it is shown that the inlet turbulence state has a non-negligible effect on these forces and thus on the dynamics of the cylinder. (10.1016/j.jfluidstructs.2015.03.001)
  DOI : 10.1016/j.jfluidstructs.2015.03.001
• 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
• 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
• 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