Creep behavior of nuclear grade 316LN austenitic stainless steel at 873 K and 923 K

Mechanics of Time-Dependent Materials - Creep deformation and rupture behavior of nitrogen-alloyed (0.14 wt.%) nuclear grade 316LN austenitic stainless steel were investigated for the varying...     

Thermoresponsive Conductivity of Graphene-Based Fibers

Smart materials are versatile material systems which exhibit a measurable response to external stimuli. Recently, smart material systems have been developed which incorporate graphene in order to share on its various advantageous properties, such as mechanical strength, electrical conductivity, and thermal conductivity as well as to achieve unique stimuli-dependent responses. Here, a graphene fiber-based smart material that exhibits reversible electrical conductivity switching at a relatively low temperature (60 °C), is reported. Using molecular dynamics (MD) simulation and density functional theory-based non-equilibrium Green's function (DFT-NEGF) approach, it is revealed that this thermo-response behavior is due to the change in configuration of amphiphilic triblock dispersant molecules occurring in the graphene fiber during heating or cooling. These conformational changes alter the total number of graphene-graphene contacts within the composite material system, and thus the electrical conductivity as well. Additionally, this graphene fiber fabrication approach uses a scalable, facile, water-based method, that makes it easy to modify material composition ratios. In all, this work represents an important step forward to enable complete functional tuning of graphene-based smart materials at the nanoscale while increasing commercialization viability.     

Experimental investigation with optimal prediction of emission in diesel engine using combined NSR–SCR catalyzer

Clean Technologies and Environmental Policy - The utilization of catalytic converters is one of the well-known strategies to clean the exhaust. The catalytic converters oxidize the destructive...     

Thiophene adsorption studies on clean and hydrogen-preadsorbed MoS2(100) surface

It is known from temperature-programmed desorption studies that the binding energy of thiophene over Mo/-Al₂O₃ and Co-Mo/-Al₂O₃, hydrodesulfurization catalysts, is lower in the presence of hydrogen. The adsorption of thiophene on clean and hydrogen-adsorbed MoS₂ was modelled using extended Hückel tight binding band structure calculations. In the ¹ adsorption configuration the calculations show a lower binding energy for adsorption on the hydrogen-preadsorbed surface similar to that observed experimentally. The lowering is due to an increased occupancy of the Mo density of states in the presence of hydrogen.     

Seepage Velocity and Piping Resistance of Coir Fiber Mixed Soils

In the context of sustainable watershed management, natural fibers mixed with soil have applications in irrigation and drainage projects such as river levees, contour bunds, temporary canal diversion works, temporary check dams, soil structures, stream restoration, etc., for controlling seepage. In this study, a number of experiments were carried out for determining the seepage velocity and piping resistance of different types of soils mixed randomly with coir fibers. Three types of soils are used in this study. The experiments were carried out for various hydraulic heads, fiber contents, and fiber lengths. Discharge velocity and seepage velocity of flow of water through soil is calculated in each case and compared with plain soil. It is observed that fibers reduce the seepage velocity of plain soil considerably and thus increase the piping resistance of soil. Regression equations based on experiments are developed for quantifying the seepage velocity and piping resistance considering hydraulic gradient, fiber contents, and fiber lengths. Suitability of coir fibers for field applications with typical examples is also highlighted. The results show that coir fiber mixed soil can be used to increase the piping resistance and reduce seepage velocity in the above mentioned applications.     

Numerical modelling of isothermal release and distribution of helium and hydrogen gases inside the AIHMS cylindrical enclosure

Hydrogen is a highly flammable gas and accidental release in confined space can pose serious combustion hazards. Numerical studies are required to assess the formation of flammable hydrogen cloud within confined spaces. In the present study, numerical investigations on the release of helium and hydrogen gases as high-velocity jets and their subsequent distribution inside an unventilated cylindrical enclosure (AIHMS facility) has been carried out as a first step towards numerical studies on hydrogen distribution in confined spaces for safety assessments. Experimental data for jet release of helium at volume Richardson number 0.1 and subsequent distribution has been used as benchmark data. Sensitivity studies on the influence of grid sizes, time-steps and turbulence models are performed. The performance of the validated numerical model is evaluated using statistical performance parameters. Similarity relations are used to determine input parameters for hydrogen jet for corresponding experimental data with helium jets. Finally, the mixing and flammability aspects of hydrogen distribution inside the enclosure are studied using four numerical indices that quantify mixing and deflagration potential of a distribution. It is concluded that the helium experiments can be used for validation of numerical models for hydrogen safety studies and any one of the similarity relationships, viz., equal buoyancy, equal volumetric flow, or equal concentration can be used for assessing the behaviour of hydrogen release and distribution within confined spaces.     

Polymerization of methacrylamide in the presence of ultrasound and peroxomonosulphate

Polymerization of methacrylamide has been carried out in the presence of ultrasound and peroxomonosulphate for the first time. The rate of polymerization and the rate of disappearance of peroxomonosulphate were followed simultaneously. A first order dependence on monomer and half order dependence with respect to peroxomonosulphate were found towards rate of polymerization. However, a first‐order dependence on peroxomonosulphate was noted with rate of peroxomonosulphate disappearance. A suitable reaction scheme is suggested to fit with the experimental results. The composite rate constants for the polymerization were evaluated and compared for acrylamide and methacrylamide polymerization in the presence of ultrasound. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 524–529, 2000     

Optimising process parameters for gas tungsten arc welding of an austenitic stainless steel using genetic algorithm

Automated Gas Tungsten Arc Welding (GTAW) with filler wire addition using a wire feeder is a candidate process for welding of 316LN austenitic stainless steel, which is the major structural material for the Indian 500 MWe Fast Breeder Reactors. In GTAW, the quality of the weld is characterized by the weld-bead geometry as it influences the mechanical properties and its performance during service. This paper discusses the development of computational model using genetic algorithm for determining the optimum/near-optimum GTAW process parameters for obtaining the target weld-bead profile during automatic welding of 316LN stainless steel. Using the experimental data generated on the influence of process variables on weld-bead geometry, regression models correlating the weld-bead shape parameters with the process parameters were developed for determining the objective function in genetic algorithm. Close agreement was achieved between the target weld-bead profile and the model-computed weld-bead profile. This study has shown that use of genetic algorithm is an appropriate methodology for optimising process parameters to obtain target weld-bead profile in GTAW with wire feeder of 316LN stainless steel.