Approximate yield criteria for anisotropic metals with prolate or oblate voidsCritères macroscopiques pour des métaux plastiques anisotropes contenant des cavités non sphériques

Following the study of Gologanu et al. (1997) which has extended the well-known approach of Gurson (1975), we propose approximate yield criteria for anisotropic plastic voided metals containing non spherical cavities. The plastic anisotropy of the matrix is described by means of Hill's quadratic criterion. The procedure to establish the closed form expression of approximate macroscopic criteria, in which void shape and plastic anisotropic effects are included, is detailed. The new criteria allow us to recover existing results in the cases of spherical and cylindrical voids in an Hill type plastic matrix. Moreover, they agree with previous criteria for non spherical voids in an isotropic plastic matrix. Finally, for validation purposes, we provide, in the general case of non spherical cavities in the anisotropic matrix, a comparison with the numerical exact two field criteria. To cite this article: V. Monchiet et al., C. R. Mecanique 334 (2006).     

Anisotropic behaviour law for sheets used in stamping:: A comparative study of steel and aluminium

For a car manufacturer, reducing the weight of vehicles is an obvious aim. Replacing steel by aluminium moves towards that goal. Unfortunately, aluminium's stamping numerical simulation results are not yet as reliable as those of steel. Punch-strength and spring-back phenomena are not correctly described. This study on aluminium validates the behaviour law Hill 48 quadratic yield criterion with both isotropic and kinematic hardening. It is based on the yield surface and on associated experimental tests (uniaxial test, plane tensile test, plane compression and tensile shearing). To cite this article: J.-J. Sinou, B. Macquaire, C. R. Mecanique 331 (2003).     

Modèles discrets de structures tissées : Analyse de stabilité et de drapéDiscrete models of woven structures: stability and draping analysis

A discrete model of a woven fabric structure is established, whereby nodes endowed with a mass and a rotational rigidity are connected by rigid bars to form a two-dimensional truss. The set of four bars that delineate a quadrilateral area is further endowed with a torsion deformation mode. The kinematics of the truss reproduces the large rotations and displacements encountered for real tissues. The equilibrium shape of such a structure is obtained as the minimum of its total potential energy versus the whole set of kinematic translational and rotational variables, accounting for eventual kinematic constraints due to contact with a rigid surface by the Lagrange multipliers method. A stability analysis is conducted, and the potentiality of the model is illustrated by fabric draping simulations. To cite this article: B. Ben Boubaker et al., C. R. Mecanique 330 (2002) 871–877.     

Ethyl Acetate Extract from Artemisia argyi Prevents Liver Damage in ConA-Induced Immunological Liver Injury Mice via Bax/Bcl-2 and TLR4/MyD88/NF-κB Signaling Pathways

Background: Immunological liver injury (ILI) is a common liver disease and lacks potent drugs for treatment. Artemisia argyi Lévl. et Vant. (A. argyi), a medicinal and edible homologous plant usually used in diet therapy to cure various liver diseases, provides a great option for the prevention of ILI. Purpose: To investigate the effect that ethyl acetate extract of A. argyi (AaEA) on Concanavalin A (ConA)-induced ILI and the mechanism of regulating Bax/Bcl-2 and TLR4/MyD88/NF-κB signaling pathways. Methods: The chemical components of AaEA were studied by LC-MS. In animal experiments, the positive control group was administrated diammonium glycyrrhizinate (DIG, 100 mg/kg), while different doses of AaEA groups (AaEA-H, AaEA-M, AaEA-L) were pretreated with AaEA 2.00, 1.00, and 0.50 g/kg, respectively, by intragastric for seven days, once every day. Then, ConA (12.00 mg/kg) was used through tail intravenous injection to establish the ILI model. The blood samples and livers were collected to test the degree of liver dysfunction, inflammation, oxidative stress, histopathological changes, and cell apoptosis. Real-time PCR and Western blotting analysis were used to explain the mechanism of regulating Bax/Bcl-2 and TLR4/MyD88/NF-κB signaling pathways. Results: The way in which AaEA prevents liver damage in immunological liver injury (ILI) mice caused by ConA was investigated for the first time. Pretreatment with AaEA reduced the expression of ALT, AST, and inflammatory factors (TNF-α and IFN-γ). Meanwhile, AaEA also reduced MDA levels but upregulated the contents of IL-4, SOD, and GSH-px, alleviating oxidative stress induced by ILI. Western blotting and real-time PCR analysis demonstrated that AaEA could regulate the expression level and relative mRNA expression of key proteins on Bax/Bcl-2 and TLR4/MyD88/NF-κB signaling pathways. Finally, 504 components from AaEA were identified by LC-MS analysis, mainly including flavones, phenolic acids, and terpenoids with anti-inflammatory and liver protective activities, which highlights the potential of AaEA for diet treatment of ILI. Conclusion: AaEA can work against ConA-induced ILI in mice by regulating Bax/Bcl-2 and TLR4/MyD88/NF-κB signaling pathways, which has the potential to be a great strategy for the prevention of ILI.     

The elastic torus: anomalous stiffness of shells with mixed typeLe tore élastique : raideur anormale des coques de type mixte

We investigate the deformation of a thin elastic torus under axisymmetric surface loads. The strain concentrates near the top and bottom parallels and the inner and outer halves essentially undergo rigid-body translations in opposite directions. An analysis of the inner boundary layers is presented, which allows one to compute the effective stiffness of the torus for this loading. This stiffness is found anomalous compared to classical shells. These mechanical properties are interpreted using purely geometrical arguments. To cite this article: B. Audoly, Y. Pomeau, C. R. Mecanique 330 (2002) 425–432.     

Solutions exactes de fissure d'interface sous contact frottant avec un milieu indéformableExact solutions of the interface crack between elastic and rigid bodies under contact with friction

One considers an interface crack between an elastic half-plane and a rigid half-plane, in the presence of Coulomb's friction. There exists two singular solutions at the semi-infinite crack tip, which correspond physically to the push-in and the pull-out of a rigid fiber in an elastic matrix. The exact solutions show that only the mode II is present and there is no oscillatory behavior of the stress and the displacement near the crack tip, but an oscillatory behavior is observed at the transition point with the stress free zone. There exists four types of singular solutions for finite crack in bounded medium, but only one in an infinite medium. To cite this article: H.D. Bui, A. Oueslati, C. R. Mecanique 332 (2004).     

Représentation à l'échelle microscopique d'un mécanisme de rupture dans un milieu a joints

. A representation of a class of failure mechanisms defined on a homogenized jointed medium by a velocity jump along a planar surface, is analyzed at the scale of the joints. The approach consists in representing a velocity jump at the macroscopic level by the kinematics of a finite band in the heterogeneous medium characterized by a piecewise rigid body motion of elementary blocs. The equivalence (in the sense of the yield design theory) between the macroscopic and macroscopic representations of such failure mechanisms is ensured by the equality of the corresponding maximum resisting rates of work. To cite this article: S. Maghous et al., C. R. Mecanique 333 (2005).     

Le satellite Encelade source d'ions N dans la magnétosphère de Saturne

The first pass of the Cassini probe in the vicinity of Saturn, above the E-ring, demonstrated a plasma consisting of water group ions (H⁺, O⁺, OH⁺, H₂O⁺) with a small N⁺ ion component (3%). Using a simple model for the transport of magnetospheric ions, we show that the N⁺ ions can be traced back to the Enceladus satellite. Such a result can be explained by the existence in this icy satellite, supposed to be still geologically active, of volatile components such as ammonia NH₃, or by the previous implantation of N⁺ ions of external origin on its surface. To cite this article: M. Bouhram et al., C. R. Physique 6 (2005).