Thermally activated composite with two-way and multi-shape memory effects

The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the composite structure is obtained during a bending test, by heating CBCM above thermal glass transition temperature of the used Epoxy polymer. The shape memory properties of these composites are investigated by a bending test. Three types of recoveries are conducted, two classical recovery tests: unconstrained recovery and constrained recovery, and a new test of partial recovery under load. During recovery, high recovery displacement and force are produced that enables the composite to perform strong two-way actuations along with multi-shape memory effect. The recovery force confirms full recovery with two-way actuation even under a high load. This unique property of CBCM is characterized by the recovered mechanical wor

Influence du mode de polymérisation de composites verre/polyester sur leur comportement mécanique

L’objet de cette communication est d’analyser les propriétés mécaniques de composites unidirectionnels verre/polyester obtenus par deux procédés différents de polymérisation : un procédé conventionnel thermique et un procédé photochimique. Les propriétés mécaniques de surface ont été étudiées par micro-indentation afin d’observer l’influence des conditions d’élaboration sur la réponse du composite à une pénétration. Il apparait que la dureté d’indentation HIT et le taux de conversion de la résine ne sont pas suffisants pour discriminer les échantillons. Les propriétés d’élasticité et de fluage sont également nécessaires pour comparer et comprendre le comportement des différents composites. Le procédé de photopolymérisation de la résine améliore les propriétés mécaniques du composite ainsi élaboré

Gestational weight gain charts for different body mass index groups for women in Europe, North America and Oceania

Background: Gestational weight gain differs according to pre-pregnancy body mass index and is related to the risks of adverse maternal and child health outcomes. Gestational weight gain charts for women in different pre-pregnancy body mass index groups enable identification of women and offspring at risk for adverse health outcomes. We aimed to construct gestational weight gain reference charts for underweight, normal weight, overweight, and grade 1, 2 and 3 obese women and compare these charts with those obtained in women with uncomplicated term pregnancies.Methods: We used individual participant data from 218,216 pregnant women participating in 33 cohorts from Europe, North America and Oceania. Of these women, 9,065 (4.2%), 148,697 (68.1%), 42,678 (19.6%), 13,084 (6.0%), 3,597 (1.6%), and 1,095 (0.5%) were underweight, normal weight, overweight, and grade 1, 2 and 3 obese women, respectively. A total of 138, 517 women from 26 cohorts had pregnancies with no hypertensive or diabetic disorders and with term deliveries of appropriate for gestational age at birth infants. Gestational weight gain charts for underweight, normal weight, overweight, and grade 1, 2 and 3 obese women were derived by the Box-Cox t method using the generalized additive model for location, scale and shape. Results: We observed that gestational weight gain strongly differed per maternal pre-pregnancy body mass index group. The median (interquartile range) gestational weight gain at 40 weeks was 14.2 kg (11.4-17.4) for underweight women, 14.5 kg (11.5-17.7) for normal weight women, 13.9 kg (10.1-17.9) for overweight women, and 11.2 kg (7.0-15.7), 8.7 kg (4.3-13.4) and 6.3 kg (1.9-11.1) for grade 1, 2 and 3 obese women, respectively. The rate of weight gain was lower in the first half than in the second half of pregnancy. No differences in the patterns of weight gain were observed between cohorts or countries. Similar weight gain patterns were observed in mothers without pregnancy complications.Conclusions: Gestational weight gain patterns are strongly related to pre-pregnancy body mass index. The derived charts can be used to assess gestational weight gain in etiological research and as a monitoring tool for weight gain during pregnancy in clinical practice

Les surfaces textiles aux échelles micro, meso et macroscopiques : propriétés thermiques et tribologiques

Les surfaces textiles se caractérisent par leurs paramètres géométriques et structuraux aux trois échelles : à l'échelle microscopique (morphologie des fibres), à l'échelle mésoscopique (assemblage des fibres entre elles) et à l'échelle macroscopique (assemblage des fils entre eux). L'objectif de ce travail est d'étudier l'influence de ces paramètres sur le comportement thermique en régime transitoire des structures fibreuses et simultanément sur le comportement tribologique des surfaces de ces structures. L'expérimentation est menée sur deux appareillages distincts : un tribomètre multi-directionnel et un prototype développé durant cette étude. Le tribomètre multi-directionnel fournit une information sur la rugosité de la surface et sur le frottement qu'elle induit.' L'appareillage thermique permet, par son procédé de régulation en température, d'évaluer la quantité de chaleur absorbée par la structure fibreuse lors des premiers instants qui suivent la mise en contact entre le textile et une plaque plane portée à une température supérieure. Les structures fibreuses étudiées sont des tricots dont la taille de la maille varie. lis sont fabriqués à partir de fils simples et retors (assemblage de deux fils simples entre eux). Les fibres employées à la réalisation des fils sont d'une part des fibres naturelles de coton et d'autre part des fibres synthétiques de polyester. Les résultats font apparaître l'existence d'un lien entre l'énergie absorbée par une structure fibreuse et son état de surface. Par exemple, lorsque la rugosité augmente, l'aire de la surface effective de contact diminue et le transfert de chaleur est moindre. Cette étude fait également apparaître des notions de couplages entre les paramètres structuraux aux différentes échelles ; les effets de ces couplages sont visibles sur les deux comportements étudiés. Il semble alors possible, grâce à la combinaison de paramètres aux différentes échelles, d'obtenir plusieurs surfaces textiles aux même propriétés.MULHOUSE-SCD Sciences (682242102) / SudocMULHOUSE-ENSISA (682242207) / SudocSudocFranceF

Influence of properties at micro- and meso-scopic levels on macroscopic level for weft knitted fabrics

International audienceKnitted fabrics and particularly weft knitted fabrics are used as composite material reinforcements due to their ability to be draped and to give three-dimensional shape by molding or by knitting. This paper presents the strong connection of all the scales of the knitted fabric (fiber, yarn and fabric) on the final knitted fabrics and its mechanical and physical properties. For this purpose, only one polymer material is used, made of two different fibers in terms of length and fineness. These fibers are used to make different yarns with two structures then three plain-weft-knitted-fabrics are considered in terms of the loop length. The fibers have not the same bending rigidity because fiber cross-section areas are different. This has an influence on the three-dimensional loop shape and on the roughness, thickness and real area of contact of fabrics. This phenomenon is the same with the two yarn structures. The results presented here bring into light that the loop length does not influence the fabric thickness

Influence du mode de polymérisation de composites verre/polyester sur leur comportement mécanique

This paper aims to analyze the mechanical properties of unidirectional glass / polyester composites manufactured by two different processes: a conventional thermal polymerization and a photochemical process. The mechanical surface properties were studied by micro-indentation in order to observe the influence of the elaboration conditions on the response of the composite to penetration. It was demonstrated that the indentation hardness HIT and the degree of conversion are not sufficient to discriminate the samples. The elasticity and creep properties are also necessary to understand the behavior of the various composites. The photochemical resin improves the mechanical properties of the composite.L’objet de cette communication est d’analyser les propriétés mécaniques de composites unidirectionnels verre/polyester obtenus par deux procédés différents de polymérisation : un procédé conventionnel thermique et un procédé photochimique. Les propriétés mécaniques de surface ont été étudiées par micro-indentation afin d’observer l’influence des conditions d’élaboration sur la réponse du composite à une pénétration. Il apparait que la dureté d’indentation HIT et le taux de conversion de la résine ne sont pas suffisants pour discriminer les échantillons. Les propriétés d’élasticité et de fluage sont également nécessaires pour comparer et comprendre le comportement des différents composites. Le procédé de photopolymérisation de la résine améliore les propriétés mécaniques du composite ainsi élaboré

Characterisation by indentation of glass / polyester composites: effect of the resin polymerisation process

http://euromat2017.fems.eu/programme/final-scientific-program/For several years, the use of photochemical resins to produce composites has encountered problems related to the manufacturing process. It is clear that the UV rays could be dangerous, but the difficulty of controlling the flux, and its penetration within the composite, make impossible to keep the percentage of polymerised resin under control. Recently, some advanced technologies using robot-based deposition systems and the introduction of LED lamps have put again this technology forward. It is well known that the progress of the resin polymerization have a strong influence on the mechanical behavior. The purpose of this work is to present and compare the mechanical properties of unidirectional glass / polyester composites. Two different processes: conventional thermal polymerization and photochemical polymerization were used to polymerize the polyester resin. The surface mechanical properties were studied by micro-indentation carried out with a Berkovich indenter under a maximum load of 500 mN. The speed of charge and discharge and the time during that the maximum load remains constant was chosen to analyze the creep behavior of the material. The indentation hardness HIT is not sufficient to discriminate the samples. Elasticity and viscoelasticity properties are necessary to compare the differen composites. For the composites elaborated by thermal polymerization, a post curing step improves the hardness and decreases the creep. For photo cured composites, a long step of vacuum allows a better fiber impregnation by the resin. As a consequence, the hardness and stiffness of the structure are enhanced. Finally, this work shows that photopolymerised composites exhibit better mechanical properties compared to conventional one obtained by thermal process. The differences in hardness and indentation modulus are quantified and related to the elaboration proces

On the possibility of synthesizing multilayered coatings in the (Ti,Al)N system by RGPP: A microstructural study

International audienceRadiofrequency magnetron sputtering combined with reactive gas pulsing process was used to synthesize two titanium aluminum nitride multilayer films using a periodically controlled nitrogen flow rate changing from 0.4 to 1 sccm (sample S04-1) and from 0 to 1 sccm (sample S0-1). A metallic TiAl buffer layer was deposited on the etched substrates before the deposition to enhance their adhesion. The films were characterized using mainly transmission electron microscopy and electron diffraction. The role of the crystallinity of the buffer TiAl metallic layer deposited before gas introduction on the growth orientations is emphasized. It is shown that the formation of a multilayer structure is conditioned by stopping periodically and completely the nitrogen flow rate. Particular attention is paid to the role that residual oxygen can play on the microstructure and to transient regime that occurs when the flow rate drops from 1 sccm to 0 sccm