3D printed hierarchical honeycombs with shape integrity under large compressive deformations

We describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shape integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment

Contribution à l'étude des propriétés optiques des particules non algales organiques

RÉSUMÉ: Les particules non-algales organiques (ONAP) représentent une grande partie des particules en suspension dans les milieux marins. Elles jouent un rôle important dans la chaîne alimentaire au sein de l’écosystème marin et font partie des constituants optiques. L'objectif de cette étude est de caractériser les propriétés optiques inhérentes (IOPs) des ONAP à partir de mesures en laboratoire et de simulations effectuées avec des données biogéo-optiques in situ, obtenues dans l'Estuaire du St-Laurent (ESL). Les expériences en laboratoire comprenaient des mesures optiques de phytodétritus dérivés de deux espèces de phytoplancton, Thalassiosira pseudonana (TP) et Dunaliella tertiolecta (DT). Les coefficients d'absorption et de diffusion des ONAP (aONAP et bONAP, respectivement) ont été mesurés dans la gamme spectrale visible-proche-infrarouge (longueur d'onde = 412-715 nm), en utilisant un instrument de mesure d'absorption-atténuation (ac-9, WetLabs). Les coefficients optiques spécifiques à la masse (aONAP* et bONAP*) ont été calculés en normalisant les valeurs de aONAP et de bONAP par la concentration des ONAP par unité de volume. Un modèle d'estimation de aONAP et de bONAP dans les eaux de surface (ie, 0-5 m de profondeur) de l’ESL a été développé avec des déterminations in situ effectuées durant deux campagnes (mai 2000 et avril 2001) et des paramètres biogé-optiques rapportés dans la littérature. Les résultats de laboratoire suggèrent des variations des IOPs des phytodétritus liées à des différences taxonomiques entre espèces de phytoplancton. En général, les détritus dérivés de DT avaient des valeurs de aONAP* plus élevées en comparaison aux ONAP provenant des cellules de TP. Cette variation a été attribuée à la faible densité des phytodétritus dérivés des flagellés. De même, les valeurs élevées des ratios spectraux bleu / rouge de bONAP* des phytodétritus des diatomées étaient liées à la présence d’opale. Les estimations de aONAP par région et calculées pour l'ESL n'ont pas montré de changements importants entre les années. De plus, des ratios spectraux bleu/rouge de bONAP plus élevés ont été observées en mai 2000 par rapport aux calcules pour avril 2001. Cette variation était liée aux changements de la composition des ONAP entre les missions en raison de variations des espèces dominant de phytoplancton (ex. diatomées et des microflagellés en mai 2000 et en avril 2001, respectivement). -- Mot(s) clé(s) en français : Propriétés optiques inhérentes, section transversale optique, particules non algales organiques, phytoplancton, détritus, bactérie, indice de réfraction. -- ABSTRACT: Organic non-algal particles (ONAP) account for a large proportion of suspended particles in aquatic environments. They play an important role in the food chain within the marine ecosystem and represent a major optical component in littoral waters. The objective of this study is to characterize the inherent optical properties (IOPs) of ONAP based on lab measurements and simulations performed with in situ biogeo-optical data obtained in the St Lawrence Estuary (SLE). Lab experiments encompassed bench optical measurements of phytodétritus derived from two phytoplankton species, Thalassiosira pseudonana (TP) and Dunaliella tertiolecta (DT). Absorption and scattering coefficients of ONAP (hereafter aONAP and bONAP, respectively) were measured within the visible-near-infrared spectral range (wavelength = 412-715 nm) using an absorption-attenuation meter (ac-9, WetLabs). Mass-specific optical coefficients (aONAP* and bONAP*) were computed by normalizing aONAP and bONAP values, respectively, by the concentration of ONAP per unit of volume. The model for estimating aONAP and bONAP in surface waters (i.e., 0-5 m depth) of the SLE was developed with in situ determinations made during two cruises (May 2000 and April 2001) and biogeo-optical parameters reported in the literature. Lab results suggest optical changes on phytodetritus due to phytoplankton taxonomic differences. In general, DT-derived detritus tended to have higher aONAP* values with respect to ONAP originated from TP cells. This variation was attributed to the lower apparent density of phytodetritus derived from microflagellates. Likewise, the larger blue/red spectral ratios of bONAP* in phytodetritus samples of diatoms were linked to the presence of opal. Regionally-weighted aONAP estimates did not show substantial changes between years. Also, blue/red spectral ratios of bONAP were larger in May 2000 with respect to April 2001. This variation was related to changes on ONAP composition between surveys due different phytoplankton assemblages (e.g., dominance of diatoms and microflagellates during May 2000 and April 2001, respectively). -- Mot(s) clé(s) en anglais : Inherent optical properties, optical cross-section, organic non-algal particles, phytoplankton, detritus bacteria, refractive index

FE analysis of the in-plane mechanical properties of a novel Voronoi-type lattice with positive and negative Poisson's ratio configurations

AbstractThis work presents a novel formulation for a Voronoi-type cellular material with in-plane anisotropic behaviour, showing global positive and negative Poisson’s ratio effects under uniaxial tensile loading. The effects of the cell geometry and relative density over the global stiffness, equivalent in-plane Poisson’s ratios and shear modulus of the Voronoi-type structure are evaluated with a parametric analysis. Empirical formulas are identified to reproduce the mechanical trends of the equivalent homogeneous orthotropic material representing the Voronoi-type structure and its geometry parameters

Experimental Study of Mechanical Behaviour of Renewable Fibre Reinforced Composite Materials Type (Cynara Cardunculus L/Polyester)

International audienceThis study is particularly focused on renewable materials of bio-composites. Our work draws on the extraction method and the mechanical characterisation of natural fibres of artichokes (Cyanara cardunculus L) which are produced naturally and in abundance in the northern regions of Algeria particularly so in the north-east. It also draws on the manufacturing of composite with bio-reinforcement models consisting of long fibres of laminated materials of the Cyanara cardunculus L type compiled with unsaturated polyester resin. Standardised sample test-pieces are then drawn from these models so as to carry out tensile and shear tests to evaluate their mechanical behaviour. Additionally, the diversity in characteristics necessitates the use of statistical approaches in order to estimate the proper Weibull parameters of natural fibres, based on a Weibull distribution

Experimental in-plane characterization of a cellular material composed by a cell with a normal re-entrant link and geometrical parameters effects on the structure mechanical properties

International audienceIn this work, we have characterized a cellular structure constituted by a new cell on which we carried out, initially, tensile and shear tests in order to get its in-plane mechanical properties; in the second time, we explored the effects that geometry will have on these mechanical properties by varying the geometric parameters of the cell. The specimens were designed by Computer Aided Design software and obtained by rapid prototyping (laser cutting). In the quest for results, we used the technique of marker tracking. This optical method of correlating images consists in measuring the plane components of the displacement of a plane surface leaving some marks on the specimen. This makes it possible to determine the in-plane components of the transformation gradient tensor and to reach the plane components of the deformation tensor under certain assumptions (axisymmetric or isochoric transformation, small deformations, etc). The material of the studied structure is a polymethylmethacrylate, often abbreviated to PMMA. The first results gave a negative Poisson's ratio, announcing an auxetic behavior. The following results have confirmed the auxetic character of the cell and show great influence of the geometric parameters on the mechanical properties of the new structure