Rochechouart 2017-Drilling Campaign: First Results

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CIRIR programs: drilling and research opportunities at the Rochechouart Impact Structure

International audienc

Modelowanie uszkodzenia w granulowanych kompozytach lepkosprężystych przy pomocy podejścia wieloskalowego

The aim of this paper is to pursue, in the wake of the work by Nadot-Martin et al. (2003), a non-classical micromechanical study and scale transition for highly filled particulate composites with viscoelastic matrices. The present extension of a morphology-based approach due to Christoffersen (1983), carried forward to the viscoelastic small strain context by Nadot-Martin et al. (2003), consists here in introducing a supplementary mechanism, namely damage by grain/matrix debonding. Displacement discontinuities (microcracks) on grain/matrix interfaces are first incorporated in a compatible way within geometric and kinematic hypotheses regarding the grains-and-layers assembly of Christoffersen. Then, local field expressions as well as homogenized stresses are established and discussed for a given state of damage (i.e. for a given actual number of open and closed microcracks) and using the hypothesis of no sliding on closed crack lips. A comparison with the results obtained for the sound viscoelastic composite by Nadot-Martin et al. (2003) allows to quantify the damage influence on local and global levels. At last, the basic formulation of the model obtained by scale transition is completed by the second stage leading to a thermodynamically consistent formulation eliminating some superfluous damaged-induced strain-like variables related to open cracks. This second stage is presented here for a simplified system where delayed (viscoelastic) effects are (tentatively) neglected. It appears as a preliminary and crucial step for further generalization in viscoelasticity.Celem tej publikacji jest sformułowanie wieloskalowego modelu mikromechanicznego dla granulowanych kompozytów o wysokim stopniu upakowania inkluzji w osnowie lepkosprężystej. Przedstawiony model, będący rozwinięciem morfologicznego podejścia Christoffersena (1983) i Nadot-Martin i in. (2003) w zakresie małych odkształceń lepkosprężystych, polega na wprowadzeniu do analizy dodatkowego mechanizmu uszkodzenia - mikropękania na granicy inkluzji i osnowy. Mikroszczeliny na granicy inkluzji i osnowy uwzględniono w hipotezie geometrycznej i kinematycznej metody Christoffersena. Następnie, wyznaczono lokalne oraz uśrednione pola naprężenia dla zadanego stanu uszkodzenia (tzn. dla zadanej liczby otwartych i zamkniętych mikroszczelin przy pominięciu poślizgów na powierzchniach mikroszczelin zamkniętych). Porównanie z wynikami uzyskanymi przez Nadot-Martin i in. (2003) dla nieuszkodzonego kompozytu lepkosprężystego pozwoliło na określenie wpływu uszkodzenia na poziomie lokalnym i globalnym. Na koniec, podstawowy model wieloskalowy uzupełniono o drugą część sformułowania, która pozwoliła usunąć pewne nadmiarowe odkształcenia związane z mikroszczelinami otwartymi, czyniąc cały model termodynamicznie spójnym. Ta druga część modelu wieloskalowego jest przeprowadzona przy założeniu upraszczającym, polegającym na (tymczasowym) pominięciu efektów lepkosprężystych

Red blood cell distribution width (RDW) in the dog : A retrospective study of 1400 cases

The red blood cell distribution width (RDW) obtained with the hematological automate MS9, was analysed in 1400 adult dogs. Comparing values obtained in healthy dogs and in diseased dogs, higher RDW values were observed in iron deficient anemia and in regenerative anemia. Lower values were observed in case of inflammation. Some high values of RDW were observed in non anemic dogs and in dogs with non regenerative anemia. Some of them had porto systemic shunt or poodle macrocytosis

Urinary, hematologic and biological screening of 108 healthy adult Dogues de Bordeaux : a breed predisposed to a glomerulonephropathy

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A non-classical micro-macro transition towards the anisotropic damage behaviour of particulate composites

The complex problem of micromechanically based constitutive description of composite materials for which damage consists in grain-matrix debonding is treated employing the homogenization method initially proposed by Christoffersen [1] for elastic bonded granulates. The localization relations (microscopic level) as well as the homogenized stress are established and discussed for a fixed state of damage (i.e. for fixed numbers of open and closed cracks) and using the hypothesis of no sliding on closed crack lips. Finally, a complementary, thermodynamically motivated approach is performed in order to express the crack opening effect as a function of macroscopic strain and of two damage variables involving granular aspects and emerging from the scale transition

A probabilistic model for the ductile spalling of tantalum

The paper presents a probabilistic model of dynamic damage (ductile spalling) based on a Poisson-Weibull formulation for nucleation. This formulation accounts for inhibition of nucleation due to strong relaxation around growing voids. Based on the joint notion on inhibition and relaxation, a very simple damage model is proposed for the overall mechanical behaviour of the voided material. A closed-form solution is obtained for the case of ramp loading, thus allowing direct comparison between model predictions and experimental data in terms of spall strength and time to fracture vs. stress rate. Although very simple, the model gives good results in the loading range for which coalescence can be neglected