Evolution du bilan énergétique dans les matériaux métalliques sous sollicitation cyclique.

In the case of cyclic plasticity, the validity of a constitutive model is usually assessed using stress-strain curves. However, this description can be enriched by adopting an energetic point of view. Thus, in the present work, a multiscale model is developed to estimate the amount of energy which is either dissipated into heat or stored in the material in a medium carbon steel under cyclic loading. The results emphasize the heterogeneous aspect of the stored and dissipated energy fields at a microscopic scale

Experimental and numerical study of the evolution of stored energy in metallic materials under cyclic loading

In-service loading conditions usually generate complex cyclic stress states. As such, the choice of an appropriate multiaxial fatigue criterion plays a crucial role in obtaining correct fatigue predictions. In the case of high cycle fatigue, the observation of the stabilized behavior is generally required to build either stress-based criteria or energy-based criteria. ...

Experimental and numerical study of the evolution of stored energy in metallic materials under cyclic loading

In-service loading conditions usually generate complex cyclic stress states. As such, the choice of an appropriate multiaxial fatigue criterion plays a crucial role in obtaining correct fatigue predictions. In the case of high cycle fatigue, the observation of the stabilized behavior is generally required to build either stress-based criteria or energy-based criteria. ...

Descente par \'eclatements en K-th\'eorie invariante par homotopie

These notes give a proof of the representability of homotopy invariant K-theory in the stable homotopy category of schemes (which was announced by Voevodsky). One deduces from the proper base change theorem in stable homotopy theory of schemes a descent by blow-ups theorem for homotopy invariant K-theory.Comment: in French; final versio

Biological impacts of Ce nanoparticles with different surface coatings as revealed by RNA-Seq in Chlamydomonas reinhardtii

In order to better understand the risks of engineered nanoparticles (ENPs), it is necessary to determine their fate and biological effects under realistic exposure scenarios (e.g. low ENP concentrations). RNA-Seq was deployed to characterize the relative biological impacts of three small Ce ENPs (i.e. nominal size < 20 nm, 70 μg L−1 Ce), with different coating properties (i.e. uncoated, citrate or poly-acrylic acid coated), towards a unicellular freshwater microalga, Chlamydomonas reinhardtii. After 2 h exposition at pH 7.0, distinct differences in tran- scriptomic effects were observed when comparing ionic Ce and Ce ENPs. Notably, Ce ENPs specifically modu- lated mRNA levels of genes related to the ubiquitin-proteasome system and to flagella structure. Compared to control conditions, transcriptomic effects induced by the citrate coated Ce ENPs were rather limited, as only 23 genes were differentially expressed by this treatment (Log2FC > |1.0|, padj < 0.001); compared to uncoated Ce ENPs (688); polyacrylic coated Ce ENPs (315) or a similar concentration of ionic Ce (138). Somewhat surpris- ingly, similar changes in the algal transcriptomes were observed for treatments with poly-acrylic acid coated Ce ENPs (mainly Ce(III), little dissolution) and uncoated Ce ENPs (mainly Ce(IV) atoms, largely agglomerated) (Log2FC > |1.0|, padj < 0.001). For the moderate exposure concentrations examined here, toxicity appeared to be minimal for both ionic Ce and Ce ENPs. Nonetheless, an important number of genes could not be assigned to a biological pathway. The study gives important insights with respect to the role of particle surface coatings on biological effects, the mechanisms of interaction of Ce ENP with a green alga, in addition to identifying several useful transcriptomic biomarkers of Ce ENP exposure

Development of a polycrystalline approach for the modelling of high cycle fatigue damage: Application to a HSLA steel

For many metallic alloys, fatigue crack initiation is governed by the development of a localized plastic activity at the grain scale. Because of the irreversible nature of plasticity, a significant proportion of the total work is dissipated into heat during a cyclic loading. As a consequence, one may expect some correlation between heat dissipation and high cycle fatigue damage as both phenomena are closely related. The purpose of the present work is to study such correlation for a ferritic high strength low alloyed steel subjected to various cyclic loading conditions. For several uniaxial fatigue tests carried out under different load ratios and stress levels, an experimental dataset consisting of stress, strain and temperature measurements is used to estimate the evolution of the amount of dissipated energy. A clear correlation between dissipated energy and the number of cycles to failure is observed.IRT Jules Vern