A coupled damage model for creep

Alloy steels of type 9Cr1Mo are being developed worldwide for the boiler and turbine components of supercritical and ultra supercritical thermal power plants and for the pressure vessel of fast breeder reactors. These steels exhibit very complex high temperature creep cavitation processes with coupled influences of creep strain, material softening and ageing etc. A new viscoplastic model considering both deformation and damage evolution has been developed in this work to predict high temperature creep deformation and damage of a 9Cr1Mo steel. Smooth tensile specimens have been analysed using this new model and the evolution of creep damage has been predicted. The results have been compared with those of experiment from literature. From the initial results, it is observed that this approach is very promising to carry out design and fitness-for-purpose of service of actual plant components.     

Preparation and Characterization of Novel Polyimide/SiO2 Nano-hybrid Films by In Situ Polymerization

A silicon-based aromatic polyimide (PI) containing pendent aryl rings was synthesized by solution polycondensation of a silicon-containing diamine with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride. Its nano-hybrids with different colloidal SiO₂ concentrations were synthesized by in situ polymerization. The reactions were carried out in presence of 3-aminopropyltriethoxysilane as a coupling agent. The inclusion of the coupling agent in the polymer chain and its co-condensation with SiO₂ nanoparticles afforded a silica network that was interconnected chemically with the PI matrix. The chemical structure of the hybrid materials was analyzed by Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. The morphology of the hybrid films and the surface roughness were characterized by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results indicated that nanometer-scale inorganic particles were homogeneously dispersed throughout the PI matrix with 50–70 nm size range. The best results and favorable miscibility between polymer and silica phases in the nano-hybrids were obtained when up to 40 wt% nanoparticles were introduced into the backbone of PI matrix.     

Effect of Clay Types on the Mechanical,Dynamic Mechanical and Morphological Properties of Polypropylene Nanocomposites

In the present investigation Polypropylene–Maleic anhydride grafted polypropylene–organically modified MMT (PP-MAPP-OMMT) nanocomposites were prepared by melt mixing in a twin screw extruder followed by injection molding. The effect of clay chemistry and compatibilizer on the properties of the nanocomposites has been studied. Sodium montmorillonite has been organically modified using quaternary and alkyl amine intercalants. A comparative account with commercial quaternary ammonium modified clays i.e Cloisite 20A, Cloisite 15A and Cloisite 30B has been presented. Storage modulus of PP matrix also increased in the nanocomposites, indicating an increase in the stiffness of the matrix polymer with the addition of organically modified nanoclays. The morphology of the nanocomposites has been examined using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Morphological findings revealed efficient dispersion of organically modified nanoclays within the PP matrix. MAPP compatibilized PP/Cloisite 15A nanocomposites displayed finely dispersed exfoliated nanomorphology as compared with other systems.     

Controlling Properties of HSLA Line Pipe Steels for Oil and Gas Applications

DANIELI has recently implemented its Coil Quality Estimator (DANIELI-CQETM) system to the Hot Strip Mill of United Metallurgical Company (OMK) at Vyksa,Russia.This system is developed for the purpose of real time assessment and control of mechanical properties for hot rolled coils.Mechanical properties such as strength,toughness,ductility and hardness are predicted over the entire length of a strip while it is processed.The property estimation is based on the final microstructure as predicted from a group of interconnected physically based metallurgical models,supplemented by Artificial Neural Network.The CQE system is used for prediction and control of properties of HSLA line pipe grades steel and other grades.The system performance,is judged by accuracy and reliability of prediction,has been compared with the physical material testing data from the plant.The results are found to be excellent.CQE is found useful for generation of test certificate of coil,quality assurance,process control,product development,and customer claim assessment.It is used for resource optimization for production,and other operational improvements such as reduction of downgrades.The present paper shares the results of CQE performance for prediction of HSLA line pipe grade steels.     

Enhancement of aquareovirus infectivity by treatment with proteases: mechanism of action

The effects of protease digestion on the polypeptide composition and on the infectivity of striped bass virus, an aquareovirus, were examined. Both trypsin and chymotrypsin enhanced the infectivity of the virus. Enhancement of infectivity was correlated with the digestion of the outer capsid protein, VP7. These studies support the assertion that VP7 is the outermost capsid protein and suggest that VP4 and VP5 are exposed on the outer surface of infectious particles. The possible role of VP7 in the variation in virulence observed among aquareovirus isolates is discussed.     

Differential evolution to synthesize low sidelobe thinned isophoric time‐modulated planar array with increased directivity

In this article, a novel method for synthesizing rectangular planar array through thinning and time‐modulation is proposed. A new differential evolution based approach that generates a rank based population is adopted to find out the optimum element off position for thinning and ontime duration to modulate the antenna elements in time domain. The proposed synthesis method defines a preservative boundary at the array center where the antenna elements are not thinned and time‐modulated rather uniformly excited. It is shown that this proposed thinning and time‐modulation strategy with an optimum preservative boundary helps to realize low side lobe radiation pattern with increased directivity by controlling less number of optimization variables as compared to traditional approach. It also reduces the feed network complexity specifically for large antenna arrays.     

Cobalt(III)‐mediated microemulsion polymerization of acrylonitrile: Kinetics and particle morphology

The catalytic effect of trans‐dichloro‐bis(ethylenediamine)cobalt(III) chloride (trans‐[Co(en)₂Cl₂]Cl) complex on the microemulsion polymerization of acrylonitrile, in the absence of added emulsifier, was investigated. Polymerization was studied at varying concentrations of initiator, monomer, complex, and solvent over the temperature range of 30–70°C. The overall activation energy (E_a, 39.26 kJ/mol), energy of dissociation of initiator (E_d, 61.62 kJ/mol), number of micelles (0.122 × 10¹⁸), and viscosity average molecular weight of the polymer were computed. The distribution of particle sizes was determined by transmission electron microscopy (TEM). It was found that the oil‐in‐water microemulsion polymerization was stabilized by the presence of the Co(III) complex, reducing the particle size into the nano range. The average diameters of PAN nanoparticles, obtained by TEM, were in the range of 50–150 nm at maximum conversion. The experimental particle size was mainly dependent on the concentration of complex and temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3120–3126, 2004