Mechanical behavior of a ductile polyamide 12 during impact

The mechanical behavior of a polyamide 12 is characterized using a viscoplastic law taking into account viscoelastic deformation. Experimental determinations are performed at constant and very low strain-rates in isothermal conditions during tensile tests. A finite elements code, based on this behavior, enables us to reproduce tensile tests even at different strain rates (up to 0.5 s⁻¹) provided that heat power dissipation due to deformation is taken into account. The same model partially reproduces multiaxial impact tests. Strain hardening is generally over-estimated by the calculation. It is pointed out that mechanical behavior should be characterized in ways closer to impact loading conditions than tensile tests to be more efficient because of the difference in microstructural evolutions during drawing.     

The effect of the skin thickness and spherulite size on the mechanical properties of injection mouldings

In this work are studied the relationships between the microstructure and the mechanical properties of an injection moulded propylene-ethylene copolymer. Distinct microstructures were obtained by processing, through a moulding programme that includes the variation of the injection and the mould temperatures and the injection flow rate. They were characterized by the skin ratio (measured by polarised light microscopy) and the spherulite size (evaluated by small angle light scattering system). Tensile tests were carried out at two different constant loading velocities: 2 mm/min (3.33 × 10^–5 m/s) and 3 m/s, in order to assess the initial modulus, the yield stress, the strain and the energy at break. The results are presented in terms of the relationships between the chosen microstructural parameters and the selected tensile properties. The skin thickness is evidenced as an important microstructural feature. The role of the core spherulite size is secondary or even negligible. The results also show that other microstructural parameters must be considered to establish more general microstructure-properties relationships.     

High resolution profiles of thallium, manganese and iron assessed by DET and DGT techniques in riverine sediment pore waters

High resolution profiles of Mn, Tl and Fe concentrations have been assessed in the pore waters of river Leie sediments at Warneton and Menen (at the border of Belgium and France) by DET (Diffusive Equilibrium in Thin Films) and DGT (Diffusive Gradients in Thin Films) techniques. The oxidized, solid Mn (IV), Tl (III) and Fe (III) compounds were reduced in the suboxic (+255 to -20 mV versus Standard Hydrogen Electrode (SHE)) riverine sediments and since these reduced species are much more soluble also they are released into the pore waters. The highest DET (total dissolved) concentrations of Fe (76 mg l(-1)), Mn (2 mg l(-1)) were observed at the station of Menen, while Tl maxima differed only slightly between the 3 surveys (21 to 27 microg l(-1)). The average ratios of Fe/Mn/Tl in the pore waters at the 3 sampling stations are fairly constant for both the DET and DGT samplings. However, the results indicate that compared to Fe and Tl a greater proportion of the Mn measured by DET is accumulated by DGT, reflecting the ready supply of Mn from solid phase to solution.     

Fibre optic sensor for physiological parameters

A fibre optic sensor structure is proposed for recovering the most relevant physiological parameters aiming at identifying the different sleep phases. The device comprises a multimode loss fibre optic sensor built into a watch casing. The sensor structure generates micro-deformations and allows a sensor to be made which is sensitive enough to detect the composite signal from the patient's wrist     

Carrier transport in HfO/sub 2//metal gate MOSFETs: physical insight into critical parameters

Electron and hole mobility in HfO/sub 2//metal gate MOSFETs is deeply studied through low-temperature measurements down to 4.2 K. Original technological splits allow the decorrelation of the different scattering mechanisms. It is found that even when charge trapping is negligible, strong remote coulomb scattering (RCS) due to fixed charges or dipoles causes most of the mobility degradation. The effective charges are found to be located in the HfO/sub 2/ near the SiO/sub 2/ interface within 2 nm. Experimental results are well reproduced by RCS calculation using 7/spl times/10/sup 13/ cm/sup -2/ fixed charges at the HfO/sub 2//SiO/sub 2/ interface. We also discuss the role of remote phonon scattering in such gate stacks. Interactions with surface soft-optical phonon of HfO/sub 2/ are clearly evidenced for a metal gate but remain of second order. All these remote interactions are significant for an interfacial oxide thickness up to 2 nm, over which, these are negligible. Finally, the metal gate (TiN) itself induces a modified surface-roughness term that impacts the low to high effective field mobility even for the SiO/sub 2/ gate dielectric references.     

French population exposure to radon, terrestrial gamma and cosmic rays

In France, natural sources account for most of the population exposure to ionising radiation. This exposure varies widely with area. Radon and gamma-ray exposure data come from national measurement campaigns; cosmic doses were calculated from city altitude. These data were corrected for season of measurement, housing characteristics and population density to study their relationship with health indicators. The crude average of indoor radon concentrations was 89 Bq m(-3), and the average corrected for season and housing characteristics was 83 Bq m(-3) (range over districts: 19-297). Weighting by district population density yielded a national average of 63 Bq m(-3). Gamma-ray dose rates averaged 55 nSv h(-1) (23-96) indoors and 46 nSv h(-1) (25-85) outdoors; corrections did not change the means. Corrected cosmic annual doses averaged 0.28 mSv (0.27-0.38). These corrections estimated the radiation exposure of the French population more accurately and represented its distribution well, thereby allowing its study as a cofactor in ecological studies.     

Effective viscoelastic behavior of short fibers composites using virtual DMA experiments

Mechanics of Time-Dependent Materials - May it be for environmental or economic reasons, mass reduction has become one of the main goals in mechanics. The short fiber thermoplastics composite is an...     

Elastomer monolayers adsorbed on mica surfaces by nitroxide-mediated polymerisation

We reported the first synthesis of Poly(n-butyl acrylate) by in situ nitroxide-mediated polymerisation from the surface of mica while preserving its lamellar structure. To obtain this polymer adsorbed to mica surface, a free radical initiator 2,2′-azobis(isobutyramidine hydrochloride) (AIBA) was attached by ion exchange to the surface of mica, and the resulting was used as a initiator to polymerise butyl acrylate. The kinetic studies show that the initiator adsorbed to mica surface successfully initiated the radical polymerisation of butyl acrylate. Adsorbed polymer was indeed obtained, in different amounts depending on reaction time, the XRD patterns of resulting products indicate that the polymer chains did not intercalate the aluminosilicate layers, as expected.     

Semianalytical models to predict the crystallization kinetics of thermoplastic fibrous composites

The growing interest for continuous fiber‐reinforced polymer composites leads to the development of new processes such as resin transfer molding for thermoplastics (RTM‐TP) or tape placement. In the aim of optimization, their simulations are required and have to include all involved physical phenomena and the associated couplings. During the consolidation step, the crystallization of the semicrystalline matrix occurs between the fibers of the multiscale reinforcement. A tricky task is to provide a realistic model able to describe the crystallization kinetics, which includes the effect of fibers on the polymer phase change and avoiding large computation time. In 2004, Haudin and Chenot proposed a generalization of the Avrami model, written in a differential form to compute the evolution of the crystallization of a neat thermoplastic in an infinite volume. In the present article, new extensions are proposed to predict the crystallization in long‐fiber thermoplastic composites, without or in the presence of transcrystallinity on fiber surfaces. In both cases, they are compared to three‐dimensional numerical simulations using a previously validated numerical method. All the numerical and analytical results are consistent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44508.     

亚硝盐对动物致癌作用的研究

<正>1978年9月“F．D．A．Consumer”公报详细报导了麻省理工学院(Massachu－setts Institute of Technology)的一项研究报告,该项研究已于1978年8月11日由美国食品药物管理局以及美国农业部公布。这项研究表明,广泛用作食品添加剂的亚硝盐会导致动物淋巴系统癌症,其作用机理明