Composition chimique, digestibilité et valeur fourragère des plantes fourragères pastorales pérennes de hautes montagnes de la région Nord du Maroc

Forest pastures represent the basis of livestock feed in the high mountains of the north region of Morocco. Unfortunately, the forage supply of pastoral species is subject to a continuous decrease, which exposes the livestock to under nutrition. In order to manage this situation and to improve the herd nutrition, knowledge of the energy and protein content and the digestibility of consumed plant species is essential. The analyses of 22 main pastoral forage species showed that the energy and protein values of these species are moderately low for UF (0.28 to 0.52 UFV/kg DM) and very low for PDI (16 to 52 g/kg/MS). The most abundant species consumed by goats, namely Quercus ilex, Quercus canariensis, Quercus suber and Pistacia lentiscus, present low energy (0.33 UF/kg DM) and low protein forage (28 g PDI/kg DM) foods. In general, these species are characterized by a satisfactory digestibility. This varies from 53% to 90% for the organic matter digestibility (DMO %). Some species have a lower DMO (52% to 66%). This is the case of Ceratonia siliqua, Cytisus scoparius, Olea europaea, Quercus Suber, Quercus ilex, Arbutus unedo, Rubus ulmifolius, Tetraclinis articulata. Similarly, a low protein digestibility is noted in Phillyrea media, Arbutus unedo and Pistacia lentiscus (64%, 65% and 66% respectively). On this basis, it appears that the pastures in these areas are also degraded in terms of nutrition.Les pâturages forestiers représentent la base de l’alimentation du cheptel animal en hautes montagnes dans le Nord du Maroc. Malheureusement, l’offre fourragère des espèces pastorales est sujette à une diminution continue, ce qui expose le cheptel à une sous nutrition. Pour pouvoir gérer cette situation et améliorer l’alimentation des troupeaux, la connaissance de l’apport énergétique et protéique et de la digestibilité des espèces de plantes consommées est indispensable. Les analyses menées sur 22 principales espèces fourragères pastorales, ont montré que la valeur énergétique et protéique de ces espèces est moyennement faible pour les UF (0,28 à 0,52 UFV/kg MS) et très faible pour les protéines (16 à 52 g de PDI/kg/MS). Les espèces les plus abondantes et les plus consommées par les caprins, à savoir Quercus ilex, Quercus canariensis, Quercus suber et Pistacia lentiscus, représentent les aliments les moins énergétiques (0,33 UF/kg MS) et les moins protéiques (28 g PDI/kg MS). De manière générale, ces espèces se caractérisent par une digestibilité satisfaisante qui varie de 53% à 90% pour la digestibilité de la matière organique (DMO%). Certaines espèces présentent une DMO moins élevée (52% à 66%). C’est le cas de Ceratonia siliqua, Cytisus scoparius, Olea europaea, Quercus Suber, Quercus ilex, Arbutus unedo, Rubus ulmifolius, Tetraclinis articulata. De même, on note une faible digestibilité des protéines chez Phillyrea media, Arbutus unedo et Pistacia lentiscus (64%, 65% et 66% respectivement). Sur cette base, Il apparait que les pâturages au niveau de ces zones sont aussi dégradés sur le plan nutritif

Modelling and experimental analyses based on microstructural characterisation by X ray imaging : application to thermoplastic composites reinforced with short glass fibres

Les thermoplastiques renforcés par des fibres de verre courtes sont devenus d’une large utilisation dans le secteur automobile. Toutefois les conditions opératoires de ces matériaux exigent un dimensionnement contrôlé pour éviter l’endommagement précoce. Dans ce contexte, les concepteurs se fient aux simulations numériques intégratives pour tenir compte des effets locaux de la microstructure telle que l’orientation des fibres. Cependant, les résultats numériques ne sont pas toujours en bon accord avec les mesures expérimentales surtout dans les endroits où la microstructure présente de fortes hétérogénéités à différentes échelles. Celles-ci correspondent d’une part à des distributions complexes d’orientation et de densité des fibres et d’autre part à la présence de défauts microstructuraux telles que des lignes de soudure ou des porosités micrométriques. Ces défauts sont difficiles à intégrer dans les simulations numériques basées sur les approches intégratives. Ce travail de thèse présente deux contributions principales. La première consiste à caractériser l’influence des hétérogénéités à une échelle micrométrique au voisinage de zones critiques sur les propriétés macroscopiques. Les cas d’applications considérés concernent des éprouvettes structures en polyamide 66 renforcé à 35% en masse par des fibres de verre courtes. La deuxième contribution consiste à évaluer l’effet de l’orientation des fibres et du conditionnement en humidité sur les mécanismes d’endommagement et leurs lois d’évolution. L’objectif est de formuler un modèle d’endommagement micromécanique à trois phases qui permet de prédire les sites d’apparition de fissures et de simuler leurs propagations.Short glass fibre reinforced thermoplastic composites have become widely used in the automotive sector. However, the operating conditions of these materials require accurate design modelling to prevent premature damage. In this context, designers rely on integrative computer simulations to consider the local microstructural effects induced by fibre orientations. However, the numerical results are not always in good agreement with the experimental measurements especially in places where the microstructure shows strong heterogeneity at different length scales. These heterogeneities correspond firstly to complex orientation and density distributions of fibres and secondly to the presence of microstructural defects such as weld lines or micrometric pores. These defects are difficult to integrate into the numerical simulations based on integrative approaches. This thesis presents two main contributions. The first is to characterize the influence of heterogeneities in a micrometric scale on the macroscopic properties in the vicinity of critical areas. The considered cases of application concern structural testing samples of polyamide 66 reinforced with 35% by weight of short glass fibres. The second contribution is to evaluate the effect of the fibre orientation and humidity conditioning level on damage mechanisms of damage and their evolution laws. The objective is to formulate a three-phase micromechanical damage model for predicting the cracking sites and simulate their propagation

Assessment of the elongational properties of HIPS membranes based on full-field strain measurements during positive thermoforming

International audienceIn the field of experimental mechanics, interest is more and more attributed to designing original single multiaxial tests which can exhibit heterogeneous mechanical responses for parameters identification. In fact, classical identification procedures of biaxial thermoplastic properties which rely on simple isotropic behavior obtained from uniaxial mechanical tests generally lack precision. Such aspect is mostly confirmed by the inaccuracy of the mechanical behavior when the same parameters identified from uniaxial loads are used in multiaxial cases. Membrane inflation constitutes one particular example of biaxial loading tests. It is characterized by imposing combined but different stretching levels along the principle directions [1,2]. The pole region is submitted to equibiaxial stretching whereas the regions near the base of the spherical shape are submitted to planar tension. As reported in literature, with the use of optical measurement techniques such as stereo digital image correlation (S-DIC) analysis of strain full-fields, the identification of material parameters of elastomers [3] or biological tissues [4] has become more reliable. Moreover, biaxial load configurations have various forms and can even be performed during the shaping of plate sheets via the thermoforming process. As recently reported by Van Mieghem et al., S-DIC has the potential to monitor large out-of-plane deformations taking place during thermoforming. The authors provided an original experimental procedure for validation of plastic-processing simulation packages based on thickness distribution under the assumption of material incompressibility [5,6]. In the present study, by investigating a different case from the previously stated authors, we shed more light on the potential of stereo digital image correlation (S-DIC) and positive thermoforming for identification of elongational properties of a high impact polystyrene (HIPS) at different temperatures (higher than its glass transition). In this context, an industrial thermoforming machine (Illig Ed100) is used. A thin thermoplastic sheet is pre-heated and pre-stretched at the rubbery state by applying an air-flow to form a spherical bubble of almost 55 mm radius within 1.5 seconds duration. Then, the pre-stretched sheet is further deformed by using a large wooden positive mould (Figure 1). This mould has a particular form which imposes a large out-of-plane displacement level of 250 mm at less than 2 seconds. During the mechanical deformation the sheet surface temperature is monitored using multiple thermocouples. Complementarily, a pressure sensor (of the type JUMO AP-30) is used to measure the air pressure during the inflation phase. Material deformations during the whole thermoforming cycle are monitored by using a S-DIC system from LaVision equipped with two 4M pixels cameras that allow detection of a set of pair images at 150 fps at a full resolution of (2048×2048 pixels). Only the full-field strain data evaluated during the plate membrane inflation step will be presented (up to 55 mm /250 mm), in the current study. First, the displacement profiles during the mechanical load along the principle directions will be used to confirm the axisymmetry of the problem. Second, the full-field experimental data at the polar region will be used for identification of the material elongational parameters of a hyperelastic model such as the Mooney-Rivlin model (classically used for HIPS) by using a Finite Element Model Updated (FEMU) procedure [7,8]. Boundary conditions and preliminary results of the identification procedure will be presented. Finally, with respect of the assumption of material incompressibility, the validation procedure will be based on the comparison between numerically calculated and experimental measured thickness distributions along the major axes of the HIPS sheet

Fisher-KPP with time dependent diffusion is able to model cell-sheet activated and inhibited wound closure

International audienceThe popular 2D Fisher-KPP equation with constant parameters fails to predict activated or inhibited cell-sheet wound closure. Here, we consider the case where the collective diffusion coefficient is time dependent, with a 3-parameter sigmoid profile. The sigmoid is taken S-shaped for the activated assays, and Z-shaped for the inhibited ones. For two activated and two inhibited assays, our model is able to predict with a very good accuracy features of the wound closure like as the time evolution of the wound area and migration rate. The calibrated parameters are consistent with respect to different subsets of the experimental datasets used for the calibration. However, the assumption of sigmoid time profile for the proliferation rate yields calibrated parameters critically dependent on the dataset used for calibration

Techniques d’imagerie rapide appliquées au thermoformage des thermoplastiques

National audienc

Techniques d’imagerie rapide appliquées au thermoformage des thermoplastiques

National audienc

Techniques d’imagerie rapide appliquées au thermoformage des thermoplastiques

National audienc

Assessment of the elongational properties of HIPS membranes based on full-field strain measurements during positive thermoforming

International audienceIn the field of experimental mechanics, interest is more and more attributed to designing original single multiaxial tests which can exhibit heterogeneous mechanical responses for parameters identification. In fact, classical identification procedures of biaxial thermoplastic properties which rely on simple isotropic behavior obtained from uniaxial mechanical tests generally lack precision. Such aspect is mostly confirmed by the inaccuracy of the mechanical behavior when the same parameters identified from uniaxial loads are used in multiaxial cases. Membrane inflation constitutes one particular example of biaxial loading tests. It is characterized by imposing combined but different stretching levels along the principle directions [1,2]. The pole region is submitted to equibiaxial stretching whereas the regions near the base of the spherical shape are submitted to planar tension. As reported in literature, with the use of optical measurement techniques such as stereo digital image correlation (S-DIC) analysis of strain full-fields, the identification of material parameters of elastomers [3] or biological tissues [4] has become more reliable. Moreover, biaxial load configurations have various forms and can even be performed during the shaping of plate sheets via the thermoforming process. As recently reported by Van Mieghem et al., S-DIC has the potential to monitor large out-of-plane deformations taking place during thermoforming. The authors provided an original experimental procedure for validation of plastic-processing simulation packages based on thickness distribution under the assumption of material incompressibility [5,6]. In the present study, by investigating a different case from the previously stated authors, we shed more light on the potential of stereo digital image correlation (S-DIC) and positive thermoforming for identification of elongational properties of a high impact polystyrene (HIPS) at different temperatures (higher than its glass transition). In this context, an industrial thermoforming machine (Illig Ed100) is used. A thin thermoplastic sheet is pre-heated and pre-stretched at the rubbery state by applying an air-flow to form a spherical bubble of almost 55 mm radius within 1.5 seconds duration. Then, the pre-stretched sheet is further deformed by using a large wooden positive mould (Figure 1). This mould has a particular form which imposes a large out-of-plane displacement level of 250 mm at less than 2 seconds. During the mechanical deformation the sheet surface temperature is monitored using multiple thermocouples. Complementarily, a pressure sensor (of the type JUMO AP-30) is used to measure the air pressure during the inflation phase. Material deformations during the whole thermoforming cycle are monitored by using a S-DIC system from LaVision equipped with two 4M pixels cameras that allow detection of a set of pair images at 150 fps at a full resolution of (2048×2048 pixels). Only the full-field strain data evaluated during the plate membrane inflation step will be presented (up to 55 mm /250 mm), in the current study. First, the displacement profiles during the mechanical load along the principle directions will be used to confirm the axisymmetry of the problem. Second, the full-field experimental data at the polar region will be used for identification of the material elongational parameters of a hyperelastic model such as the Mooney-Rivlin model (classically used for HIPS) by using a Finite Element Model Updated (FEMU) procedure [7,8]. Boundary conditions and preliminary results of the identification procedure will be presented. Finally, with respect of the assumption of material incompressibility, the validation procedure will be based on the comparison between numerically calculated and experimental measured thickness distributions along the major axes of the HIPS sheet

Numerical Analysis for the Two-Dimensional Fisher-Kolmogorov-Petrovski-Piskunov Equation with Mixed Boundary Condition

International audienceIn this paper, a finite difference scheme is presented for the initial-boundary value problem for the two-dimensional nonlinear Fisher–Kolmogorov–Petrovski–Piskunov (Fisher–KPP) equation with mixed boundary conditions. Using Energy functional, stability of the suggested scheme is achieved. Unique solvability of the difference solutions is proved. Furthermore, the second-order convergence in the discrete H1-norm is established. Finally, two numerical experiments are reported to validate the theoretical analysis

Experimental quantification of heat haze errors in stereo-DIC displacements: Application to thermoplastics thermoforming temperature range

Stereo digital image correlation (Stereo-DIC) is recurrent in photo-mechanics to measure kinematic fields which can be of high interest for instrumenting open-mould forming processes. Nevertheless, in the presence of pre-heating operations, as observed in the context of thermoforming processes, natural convective heat flows risk emerging and causing optical distortions in the recorded images. Consequently, this alters the precision of the measured full-fields of displacements. To address these challenges, this study proposes an experimental approach with two distinctive features. Firstly, it focuses on regenerating the heat haze effect at a laboratory scale within a partially opened vertical enclosure and without utilizing any filtering air flows. Secondly, the study quantifies the spatial and temporal variations of errors through statistical analyses of the differences between measurements obtained from quasi-static speckle translations and known imposed displacements. Experimental results indicate that the main cause of displacement errors is related to the 3D nature of the hot air turbulence caused by the natural convection phenomenon. This observation is supported by the detection of feather-shaped heat flows causing optical out-of-plane surface deviations. Furthermore, the study validates the possibility of obtaining time-dependent corrective functions for bias errors, which characterize the performance of the calibrated Stereo-DIC system in the presence of heat haze. Despite the limitation of extensive measurements required by the proposed approach, this study contributes to addressing the heat haze effect and constitutes a step towards extending the use of stereo-DIC for in-situ instrumentation of short-duration thermomechanical tests in the presence of heat haze