Loading Rate Effect on Nanohardness of Soda-Lime-Silica Glass

To understand how hardness, the key design parameter for applications of brittle solids such as glass concerning contact deformation, is affected by loading rate variation, nanoindentation with a Berkovich tip was used to measure the nanohardness of a 330-μm-thick soda-lime-silica glass as a function of loading rate (1 to 1000 mN·s⁻¹). The results showed for the very first time that, with variations in the loading rate, there was a 6 to 9 pct increase in the nanohardness of glass up to a threshold loading rate (TLR), whereafter it did not appreciably increase with further increase in loading rate. Further, the nanohardness data showed an indentation size effect (ISE) that obeyed the Meyer’s law. These observations were explained in terms of a strong shear stress component developed just beneath the nanoindenter and the related shear-induced deformation processes at local microstructural scale weak links. The significant or insignificant presence of shear-induced serrations in load depth plots and corresponding scanning electron microscopic evidence of a strong or mild presence of shear deformation bands in and around the nanoindentation cavity supported such a rationalization. Finally, a qualitative picture was developed for different deformation processes induced at various loading rates in glass.     

Understanding the mechanical properties of hot pressed Ba-doped S-phase SiAlON ceramics

In this contribution, we report the analysis and interpretation of the mechanical property measurements for a new class of SiAlON ceramic. The hardness and indentation fracture toughness were measured on the hot pressed Ba-doped S-SiAlON ceramic using Vickers indentation at varying loads (up to 300 N). An important observation was that all the investigated S-SiAlON exhibited the characteristic rising R-curve behavior with a maximum toughness of up to 10–12 MPa m^1/2 for ceramics, hot pressed both at 1700 and 1750 °C. Crack deflection by large elongated S-phase grains and crack bridging by β-Si₃N₄ needles has been found to be the major toughening mechanisms for the observed high toughness. Theoretical estimates, using a toughening model based on crack bridging and deflection by platelet shaped ‘S’-phase grains and β-Si₃N₄ needles, reveal the interfacial friction of around 200 MPa. Careful analysis of the indentation data reveals the average (apparent) hardness modestly increases with indent load in all S-SiAlON samples, with more significant effect for S-SiAlON, hot pressed at 1600 °C. This effect has been analyzed in the light of the established model of ‘indentation-induced cracking’ phenomenon. Our experimental results suggest that a modest combination of average hardness of 15 GPa and indentation toughness of around 12 MPa m^1/2 could be achieved in Ba-S-SiAlON ceramic and further improvement requires microstructural tailoring.     

Exploring the simultaneous effect of nano‐silica reinforcement and electron‐beam irradiation on a model LDPE/EVA‐based TPE system

BACKGROUND: The technical properties of polyolefinic thermoplastic elastomer (TPE) systems can be modified significantly using fillers like nano‐silica. Controlled irradiation can potentially be an effective way of tailoring the technical properties of such nano‐silica‐filled TPE systems. RESULTS: The effect of controlled electron‐beam irradiation on the properties of a pristine silica nanoparticle‐filled model low‐density polyethylene/ethylene–(vinyl acetate) (LDPE/EVA) TPE system is explored in this paper. The morphology of such a filled system was investigated using scanning electron microscopy (SEM) and field‐emission SEM. The dispersion of silica particles was analysed using transmission electron microscopy which clearly indicates that at low loading a fine dispersion of silica occurs in the polymer matrix. Swelling studies and Fourier transform infrared analyses indicate the occurrence of a favourable EVA–silica interaction. On the whole, it is observed that electron‐beam irradiation induces a high degree of reinforcement in all the silica‐filled samples through interfacial crosslinking as well as controlled crosslinking in the two polymer phases. In a few samples the processing characteristics are remarkably preserved following concurrent nano‐silica reinforcement and irradiation, while the technical properties of TPE systems, including set, solvent swelling and mechanical properties, are improved. However, the improvement in properties is a strong function of sequence of addition of filler in the LDPE/EVA blends. CONCLUSION: The green technique studied can be potentially extended for the improvement of the technical properties of conventional TPE systems. Copyright © 2009 Society of Chemical Industry     

Weld Metal Microstructure Prediction in Submerged Arc Weld Metal of C‐Mn Steel

The prediction model has been developed for steel weld metal microstructural constituents as a function of flux ingredients such as CaO, MgO, CaF₂ and Al₂O₃ in submerged arc welding carried out at fixed welding parameters. The results of quantitative measurements of micro‐structural constituents on eighteen weld metal samples were utilised for developing the prediction equations of microstructural constituents applying statistical design of experiment for mixtures. Among the flux ingredients, CaO appears to be most important as an individual as well as interaction with other ingredients viz. CaF₂ and Al₂O₃ in influencing the amount of microstructural constituents in weld metal. The prediction equations have been checked for adequacy by performing tests on welding using randomly designed flux and found satisfactory. The iso‐response curves were developed for selected microstructural constituents to show their output levels at different percentage of flux ingredients.     

Chemically deposited zinc oxide thin film gas sensor

Zinc oxide (ZnO) thin films were prepared by a low cost chemical deposition technique using sodium zincate bath. Structural characterizations by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) indicate the formation of ZnO films, containing 0.05–0.50 m size crystallites, with preferred c-axis orientation. The electrical conductance of the ZnO films became stable and reproducible in the 300–450 K temperature range after repeated thermal cyclings in air. Palladium sensitised ZnO films were exposed to toxic and combustible gases e.g., hydrogen (H₂), liquid petroleum gas (LPG), methane (CH₄) and hydrogen sulphide (H₂S) at a minimum operating temperature of 150 °C; which was well below the normal operating temperature range of 200–400 °C, typically reported in literature for ceramic gas sensors. The response of the ZnO thin film sensors at 150 °C, was found to be significant, even for parts per million level concentrations of CH₄ (50 ppm) and H₂S (15 ppm).     

Tape Cast Multilayer Composite of Nano Zirconia with High Toughness

During the last decade, worldwide attention of researchers has focused on nano-ceramic composites with superior mechanical behavior and improved reliability for structural applications. Here we report the development of a multi-layer composite (MLC) of tape cast nano zirconia with high failure energy. The MLC samples were fabricated by thermocompression of green tapes prepared from 3 mole % yttria stabilized zirconia (3-YSZ) powder with a primary crystallite size of 27 nm. Depending on the number of layers, the MLC samples exhibited failure energy (238.97 KJm^-3) more than two times higher than that of the single tape (≈107 KJm^-3) with a reasonably high bi-axial flexural strength (≈630 MPa), high hardness (≈ 13 GPa at 49 N), and indentation fracture toughness nearly four times as high as that of the single tape. In addition, these MLC materials showed the presence of a R-curve behavior.     

Generalised disturbance adaptive optimal regulator

In the present work, choosing a varying output weighting matrix, an optimal regulator having state feedback terms with variable gain and feed-forward terms dependent on input as well as output disturbances has been proposed.     

Homogeneous reduction of aromatic nitrocompounds by a triphenylphosphine complex of palladium

The complex Pd₂(PPh₃)₂Cl₄ has been used as a homogeneous catalyst for the reduction of C₆H₅NO₂ and p-ClC₆H₄NO₂ in basic ethanol. A reaction intermediate [Pd(PPh₃) (C₆H₅NO₂)Cl₂] has been isolated and characterised. Reduction of C₆H₅NO₂ produced aniline (75%), azobenzene (5%) and azoxybenzene (15%) under conditions of atmospheric pressure, while under conditions of high pressure the reduction product contained aniline (95%) only. The yield of p-ClC₆H₄NH₂ was highest (75%) at normal pressure and decreased with increasing pressure.