A new yield function for compressible materials

A new yield function for compressible materials has been derived based upon a yield criterion postulated by the authors. This function was experimentally verified for the uniaxial state of compressive stress using the aluminum alloy X7091 as a model material, and excellent agreement was found between theoretical and experimental results for the density dependence of the yield and geometrical hardening. Yield surfaces for various density levels have been generated in a three-dimensional principal-stress space using computer graphics.     

Thermo mechanical properties of organically modified halloysite nanotubes/cyclic olefin copolymer composite

This report deals with the development of unmodified and modified halloysite nanotube (HNT) based cyclic olefin copolymer (COC) composites. Maleic anhydride grafted polyethylene (MA‐g‐PE) has been used as a compatibilizer. Exfoliation of organically modified HNTs (mHNTs) and dispersion of it in polymer matrix was observed by X‐ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy analysis, respectively. Augmented dynamic mechanical and thermal properties of the composites were provided by incorporating mHNTs into the pure matrix. In this work, we have proposed that the modification of HNTs enhanced the dispersion and strong interfacial interaction which led to better performance of the composites where MA‐g‐PE acts as a bridging tool between polar clays and nonpolar COC. POLYM. COMPOS., 36:955–960, 2015. © 2014 Society of Plastics Engineers     

An innovative strategy for open loop control of hot deformation processes

A new strategy for systematically calculating near optimal control parameters for hot deformation processes is presented in this article. This approach is based on modern control theory and involves deriving state-space models directly from available material behavior and hot deformation process models. Two basic stages of analysis and optimization are established in this strategy for nonlinear, open loop control system design for producing required microstructural characteristics, uniformity of deformation and temperature distribution, and other important physical requirements of hot worked products.     

Synergistic Effect of Halloysite Nanotubes and MA-g-PE on Thermo-Mechanical Properties of Polycarbonate-Cyclic Olefin Copolymer Based Nanocomposite

This article explores the synergistic effect of halloysite nanotubes along with maleic anhydride grafted polyethylene on the physical, mechanical, and thermo-mechanical properties of polycarbonate/cyclic olefin copolymer polymer blend system. Halloysite nanotubes filled polycarbonate/cyclic olefin copolymer blend nanocomposites were prepared in the presence and absence of polymeric compatibilizer by melt blending. Besides the constructive outcome of nanotubular fillers, the maleic anhydride grafted polyethylene played a complementary role in improving the properties of the nanocomposites. Structural changes of blend matrix, nanofiller distributions, nanofiller-polymer matrix interaction, nucleating effect, storage modulus, and thermal stability were widely investigated with various sophisticated instruments.     

A Facile Synthesis of a Palladium-Doped Polyaniline-Modified Carbon Nanotube Composites for Supercapacitors

Supercapacitors have evolved as the premier choice of the era for storing huge amounts of charge in the field of energy storage devices, but it is still necessary to enhance their performance to meet the increasing requirements of future systems. This could be achieved either through advancing the interfaces of the material at the nanoscale or by using novel material compositions. We report a high-performance material composition prepared by combining a transition metal (palladium)-doped conductive polymer with multiwalled carbon nanotubes (MWCNTs). MWCNTs/palladium-doped polyaniline (MWCNTs/Pd/PANI) composites and multiwalled carbon nanotube/polyaniline (MWCNTs/PANI) composites (for comparison) were prepared via in situ oxidative polymerization of aniline monomer. The reported composites were characterized by Fourier-transform infrared (FTIR), x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) studies. FESEM and TEM studies indicated the narrow size distribution of the π-conjugated polymer-protected palladium nanoparticles on the surface of the carbon nanotubes. All the electrochemical characterizations were executed using a three-electrode system in 1 M H₂SO₄ electrolyte. Cyclic voltammetry (CV) analysis was performed to observe the capacitive performance and redox behavior of the composites. The ion transfer behavior and cyclic stability of the composites were investigated by electrochemical impedance spectroscopy (EIS) analysis and cyclic charge–discharge (CCD) testing, respectively. The MWCNTs/Pd/PANI composite was found to exhibit an especially high specific capacitance value of 920 F/g at scan rate of 2 mV/s.     

Modeling of dynamic material behavior in hot deformation: Forging of Ti-6242

A new method of modeling material behavior which accounts for the dynamic metallurgical processes occurring during hot deformation is presented. The approach in this method is to consider the workpiece as a dissipator of power in the total processing system and to evaluate the dissipated power co-contentJ = ∫_o ^σ ε ⋅dσ from the constitutive equation relating the strain rate (ε) to the flow stress (σ). The optimum processing conditions of temperature and strain rate are those corresponding to the maximum or peak inJ. It is shown thatJ is related to the strain-rate sensitivity (m) of the material and reaches a maximum value(J _max) whenm = 1. The efficiency of the power dissipation(J/J _max) through metallurgical processes is shown to be an index of the dynamic behavior of the material and is useful in obtaining a unique combination of temperature and strain rate for processing and also in delineating the regions of internal fracture. In this method of modeling, noa priori knowledge or evaluation of the atomistic mechanisms is required, and the method is effective even when more than one dissipation process occurs, which is particularly advantageous in the hot processing of commercial alloys having complex microstructures. This method has been applied to modeling of the behavior of Ti-6242 during hot forging. The behavior of α+ β andβ preform microstructures has been exam-ined, and the results show that the optimum condition for hot forging of these preforms is obtained at 927 °C (1200 K) and a strain rate of 1CT^•3 s^•1. Variations in the efficiency of dissipation with temperature and strain rate are correlated with the dynamic microstructural changes occurring in the material.     

Superficial contamination of bovine carcasses by Escherichia coli O157:H7 in a slaughterhouse in Normandy (France)

In 1997, analyses were carried out on 255 bovine carcasses to determine the extent of superficial contamination by E. coli O157. A 50-cm(2) meat sample taken from all carcasses was collected and tested using immunomagnetic separation method to detect E. coli O157. One strain of E. coli O157 bacterium was isolated and sent to the reference national center (Institut Pasteur, Paris). The strain was confirmed as E. coli O157:H7 and found to contain two out of the three pathogenicity genes (eae and EHEC-hlyA) necessary for enteropathogenicity. Shiga toxin genes were not detected. Superficial contamination of E. coli O157:H7 was established, but at low level (0.4%).