A rational approach to model the behavior of bonded soils

The paper presents a rational approach to model the behavior of bonded soils within the frame work of hardening plasticity. The approach is based on the premise that the resistance of bonded materials is a superposition of the two components of cement bond strength and soil frictional strength and that the deformation of the soil is associated with the frictional component of stresses just as in the case of a remoulded soil, the bonds offering additional resistance at any given strain level. This concept is similar to two stiffnesses acting in parallel for the same strain response. The proposed model considers the constitutive laws separately for the two components (bond and frictional) and adds the two to get the overall response. The unbonded soil component is described by the well known 'modified Cam clay' model. The response of the bond component is also described by a strain softening elasto-plastic model, considering the behavior to be elastic up to the yield surface and elasto-plastic beyond yield surface. To illustrate the capability of the proposed, model some laboratory test results of both compression and-extension shear tests are predicted. Despite the model being simple, several typical features of the behavior of bonded materials are well reproduced. The model parameters are well defined and easily determinable.

High emission currents and low threshold fields in multi-wall carbon nanotube-polymer composites in the vertical configuration

In this work, we present field emission characteristics of multi-wall carbon nanotube (MWCNT)-polystyrene composites at various weight fractions along the cross-section of sample. Scanning electron microscope images in cross-sectional view reveal that MWCNTs are homogeneously distributed across the thickness and the density of protruding tubes can be scaled with weight fraction of the composite film. Field emission from composites has been observed to vary considerably with density of MWCNTs in the polymer matrix. High current density of 100 mA/cm(2) was achieved at a field of 2.2 V/lm for 0.15 weight fraction. The field emission is observed to follow the Fowler-Nordheim tunneling mechanism, however, electrostatic screening is observed to play a role in limiting the current density at higher weight fractions. (C) 2012 American Institute of Physics. [doi:10.1063/1.3685754]

Andaman Postseismic Deformation Observations: Still Slipping after All These Years?

More than six years after the great (M-w 9.2) Sumatra-Andaman earthquake, postevent processes responsible for relaxation of the coseismic stress change remain controversial. Modeling of Andaman Islands Global Positioning System (GPS) displacements indicated early near-field motions were dominated by slip down-dip of the rupture, but various researchers ascribe elements of relaxation to dominantly poroelastic, dominantly viscoelastic, and dominantly fault slip processes, depending primarily on their measurement sampling and modeling tools used. After subtracting a pre-2004 interseismic velocity, significant transient motion during the 2008.5-2010.5 epoch confirms that postseismic relaxation processes continue in Andaman. Modeling three-component velocities as viscoelastic flow yields a weighted root-mean-square (wrms) misfit that always exceeds the wrms of the measured signal (26.3 mm/yr). The best-fitting models are those that yield negligible deformation, indicating the model parameters have no real physical meaning. GPS velocities are well fit (wrms 4.0 mm/yr) by combining a viscoelastic flow model that best fits the horizontal velocities with similar to 50 cm/yr thrust slip down-dip of the coseismic rupture. Both deep slip and flow respond to stress changes, and each can significantly change stress in the realm of the other; it therefore is reasonable to expect that both transient deep slip and viscoelastic flow will influence surface deformation long after a great earthquake.

Cytocompatibility property evaluation of gas pressure sintered SiAlON-SiC composites with L929 fibroblast cells and Saos-2 osteoblast-like cells

Although the oxide ceramics have widely been investigated for their biocompatibility, non-oxide ceramics, such as SiAlON and SiC are yet to be explored in detail. Lack of understanding of the biocompatibility restricts the use of these ceramics in clinical trials. It is hence, essential to carry out proper and thorough study to assess cell adhesion, cytocompatibility and cell viability on the non-oxide ceramics for the potential applications. In this perspective, the present research work reports the cytocompatibility of gas pressure sintered SiAlON monolith and SiAlON-SiC composites with varying amount of SIC, using connective tissue cells (L929) and bone cells (Saos-2). The quantification of cell viability using MTT assay reveals the non-cytotoxic response. The cell viability has been found to be cell type dependent. An attempt has been made to discuss the cytocompatibility of the developed composites in the light of SiC content and type of sinter additives. (C) 2011 Elsevier B.V. All rights reserved.

Composites of Graphene and Other Nanocarbons with Organogelators Assembled through Supramolecular Interactions

Carbon nanomaterials (CNMs), such as exfoliated graphene (EG), long-chain functionalized EG, single-walled carbon nanotubes (SWNTs), and fullerene (C-60), have been investigated for their interaction with two structurally different gelators based on all-trans tri-p-phenylenevinylene bis-aldoxime (1) and n-lauroyl-L-alanine (2) both in solution and in supramolecular organogels. Gelation occurs in toluene through hydrogen bonding and van der Waals interactions for 1 and 2 in addition to pp stacking specifically in the case of 1. These nanocomposites provide a thorough understanding in terms of molecular-level interactions of dimensionally different CNMs with structurally different gelators. The presence of densely wrapped CNMs encapsulated fibrous network in the resulting composites is evident from various spectroscopic and microscopic studies, indicating the presence of supramolecular interactions. Concentration- and temperature-dependent UV/Vis and fluorescence spectra show that CNMs promote aggregation of the gelator molecules, leading to hypochromism and quenching of the fluorescence intensity. Thermotropic mesophases of 1 are altered by the inclusion of a small amount of CNMs. The gelCNM composites show increased electrical conductivity compared with that of the native organogel. Rheological studies of the composites demonstrate the formation of rigid and viscoelastic solidlike assembly due to reinforced aggregation of the gelators on CNMs. Synergistic behavior is observed in case of the composite gel of 1, containing a mixture of EG and SWNT, when compared with other mixtures of CNMs in all combinations with EG. This affords new nanocomposites with interesting optical, thermal, electrical, and mechanical properties.

Spark plasma sintering of novel ZrB2-SiC-TiSi2 composites with better mechanical properties

We report here the development of ultrafine grained ZrB2-SiC composites using TiSi2 as the sintering aid and spark plasma sintering (SPS) as the processing technique. It was observed that the presence of TiSi2 improved the sinterability of the composites, such that near theoretical densification (99.9%) could be achieved for ZrB2-18 wt.% SiC-5 wt.% TiSi2 composites after SPS at 1600 degrees C for 10 min at 50 MPa. Use of innovative multi stage sintering (MSS) route, which involved holding the samples at lower (intermediate) temperatures for some time before holding at the final temperature, while keeping the net holding time to 10 min, allowed attainment of full densification of ZrB2-18 wt.% SiC-2.5 wt.% TiSi2 at a still lower final temperature of 1500 degrees C at 30 MPa. TEM observations, which revealed the presence of anisotropic ZrB2 grains with faceted grain boundaries and TiSi2 at the intergranular regions, suggested the occurrence of liquid phase sintering in the presence of TiSi2. No additional phase was detected in XRD as well as TEM, which confirmed the absence of any sintering reaction. The as developed composites possessed an excellent combination of Vickers hardness and indentation toughness, both of which increased with increase in TiSi2 content, such that the ZrBi2-18 wt.% SiC-5 wt.% TiSi2 (SPS processed at 1600 degrees C) possessed hardness of similar to 20 GPa and indentation toughness of similar to 5 MPa m(1/2). The use of MSS SPS at 1500 degrees C for ZrBi2-18 wt.% SiC-2.5 wt.% TiSi2 composite resulted in improvement in hardness of up to similar to 27 GPa and attainment of high flexural strength of similar to 455 MPa. (C) 2011 Elsevier B.V. All rights reserved.

Dielectric Barrier Discharge Cascaded with Red Mud Waste to Enhance NOX Removal from Diesel Engine Exhaust

Red mud is a waste by-product generated during the processing of bauxite, the most common ore of aluminium. With the presence of ferric oxide, high surface area, resistance to poisoning and low cost, red mud made itself a good alternative to the existing commercial automobile catalyst. The cascading of dielectric barrier discharge plasma with red mud improved the NOX removal from diesel engine exhaust significantly. The DeNO(X) efficiency with discharge plasma was 74% and that with red mud was 31%. The efficiency increased to 92% when plasma was cascaded with red mud catalyst operating at a temperature of 400 degrees C. The NOX removal was dominated by NO2 removal. The studies were conducted at different temperatures and the results were discussed.

Modified Adomian decomposition method for fracture of laminated uni-directional composites

In this paper, the well-known Adomian Decomposition Method (ADM) is modified to solve the fracture laminated multi-directional problems. The results are compared with the existing analytical/exact or experimental method. The already known existing ADM is modified to improve the accuracy and convergence. Thus, the modified method is named as Modified Adomian Decomposition Method (MADM). The results fromMADM are found to converge very quickly, simple to apply for fracture(singularity) problems and are more accurate compared to experimental and analytical methods. MADM is quite efficient and is practically well-suited for use in these problems. Several examples are given to check the reliability of the present method. In the present paper, the principle of the decomposition method is described, and its advantages form the analyses of fracture of laminated uni-directional composites.

Micromechanisms of damage nucleation during contact deformation of columnar multilayer nitride coatings

In order to resolve some missing micromechanistic details regarding contact deformation in nitride multilayer coatings we report here observations from cross-sectional transmission electron microscopy and focused ion beam studies of the Vickers indentations on TiN/TiAlN multilayer films of various total thicknesses as well as bilayer periods. The study of damage induced by contact deformation in a nitride multilayer coating is complemented by stress calculated using an analytical model. Kinked boundaries of sliding columns give rise to cracks which propagate at an angle to the indentation axis under a combination of compressive and shear stresses. It is seen that multilayers provide more distributed columnar sliding, thereby reducing the stress intensity factor for shear cracking, while interfacial dislocations provide a stress relief mechanism by enabling lateral movement of material. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Structure and deformation correlation of closed-cell aluminium foam subject to uniaxial compression

We report the results of an experimental and numerical study conducted on a closed-cell aluminium foam that was subjected to uniaxial compression with lateral constraint. X-ray computed tomography was utilized to gain access into the three-dimensional (3-D) structure of the foam and some aspects of the deformation mechanisms. A series of advanced 3-D image analyses are conducted on the 3-D images aimed at characterizing the strain localization regions. We identify the morphological/geometrical features that are responsible for the collapse of the cells and the strain localization. A novel mathematical approach based on a Minkowski tensor analysis along with the mean intercept length technique were utilized to search for signatures of anisotropy across the foam sample and its evolution as a function of loading. Our results show that regions with higher degrees of anisotropy in the undeformed foam have a tendency to initiate the onset of cell collapse. Furthermore, we show that strain hardening occurs predominantly in regions with large cells and high anisotropy. We combine the finite element method with the tomographic images to simulate the mechanical response of the foam. We predict further deformation in regions where the foam is already deformed. Crown Copyright (C) 2012 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.

Fabrication of Transparent BaNaB9O15 Glass-Microcrystal Composites

Transparent glasses in the BaO-Na2O-B2O3 (BNBO) system were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by x-ray powder diffraction (XRD) and differential thermal analysis (DTA), respectively. Cyclic heat treatment of the as-quenched glasses yielded transparent glass-microcrystal composites. The volume fraction of the crystallites and their sizes could be easily controlled by this process. Heat-treated samples were highly transparent owing to the minimum mismatch between the refractive indices of the crystallites and the glass residual matrix. BNBO samples that were heat treated at 540A degrees C for 4 h for 10 cycles were found to be 60% to 70% transparent in the 500 nm to 900 nm wavelength range.

Reactive Interdiffusion: A Method for Making Composition Graded Metal-ceramic Composites

Presented is a new method for making composition graded metal-ceramic composites using reactive inter-diffusion between a metal and a complex ceramic. Composition variation in both metal and ceramic phases with distance along the direction of diffusion is achieved. The design criteria for developing such composites are discussed. The system should exhibit extensive solid solubility in both metallic and ceramic phases, a defined gradation in the stabilities of the oxides, and mobility of electrons or holes in the oxide solid solution. The complex ceramic used for making the composite should be polycrystalline with sufficient porosity to accommodate the volume expansion caused by alloy precipitation. An inert atmosphere to prevent oxidation and high processing temperature to facilitate diffusive transport are required. The process is illustrated using the reaction couples Fe-NiTiO3, Fe-(Mg,Co)TiO3 and Fe-(Ni,Co)TiO3.

Deformation field in indentation of a granular ensemble

An experimental study has been made of the flow field in indentation of a model granular material. A granular ensemble composed of spherical sand particles with average size of 0.4 mm is indented with a flat ended punch under plane-strain conditions. The region around the indenter is imaged in situ using a high-speed charge-coupled device (CCD) imaging system. By applying a hybrid image analysis technique to image sequences of the indentation, flow parameters such as velocity, velocity gradient, and strain rate are measured at high resolution. The measurements have enabled characterization of the main features of the flow such as dead material zones, velocity jumps, localization of deformation, and regions of highly rotational flow resembling vortices. Implications for validation of theoretical analyses and applications are discussed.