Tensile flow and work hardening behavior of hot cross-rolled AA7010 aluminum alloy sheets

The present work describes the tensile flow and work hardening behavior of a high strength 7010 aluminum alloy by constitutive relations. The alloy has been hot rolled by three different cross-rolling schedules. Room temperature tensile properties have been evaluated as a function of tensile axis orientation in the as-hot rolled as well as peak aged conditions. It is found that both the Ludwigson and a generalized Voce-Bergstrom relation adequately describe the tensile flow behavior of the present alloy in all conditions compared to the Hollomon relation. The variation in the Ludwigson fitting parameter could be correlated well with the microstructural features and anisotropic contribution of strengthening precipitates in the as-rolled and peak aged conditions, respectively. The hardening rate and the saturation stress of the first Voce-Bergstrom parameter, on the other hand, depend mainly on the crystallographic texture of the specimens. It is further shown that for the peak aged specimens the uniform elongation (epsilon(u)) derived from the Ludwigson relation matches well with the measured epsilon(u) irrespective of processing and loading directions. However, the Ludwigson fit overestimates the epsilon(u) in case of the as-rolled specimens. The Hollomon fit, on the other hand, predicts well the measured epsilon(u), of the as-rolled specimens but severely underestimates the epsilon(u), for the peak aged specimens. Contrarily, both the relations significantly overestimate the UTS of the as-rolled and the peak aged specimens. The Voce-Bergstrom parameters define the slope of e Theta-sigma plots in the stage-III regime when the specimens show a classical linear decrease in hardening rate in stage-III. Further analysis of work hardening behavior throws some light on the effect of texture on the dislocation storage and dynamic recovery.

Postliquefaction Undrained Shear Behavior of Sand-Silt Mixtures at Constant Void Ratio

A detailed study on the postliquefaction undrained shear behavior of sand-silt mixtures at constant void ratios is presented in this article. The influence of different parameters such as density, amplitude of cyclic shear stress, and drainage conditions on the postliquefaction undrained response of sand-silt mixtures has been investigated, in addition to the effect of fines content. The results showed that the limiting silt content plays a vital role in the strength of the soil under both cyclic and monotonic shear loading. Both the liquefaction resistance and postliquefaction shear strength of the soils are found to decrease with an increase in the fines content until the limiting silt content is reached. However, further increase in the silt content beyond the limiting silt content increases the liquefaction resistance as well as the postliquefaction shear strength of the soils. It is also observed that these variations on the liquefaction and postliquefaction resistance of soils are closely related to the variations in relative density. (C) 2013 American Society of Civil Engineers.

Melting and solidification behavior of Pb-Sn embedded alloy nano-particles

Nano-sized bimetallic dispersoids consisting of (Pb) and beta-(Sn) phases of eutectic composition (Pb26.1Sn73.9) embedded in aluminum and Al-Cu-Fe quasicrystalline matrices have been prepared by rapid solidification processing. The two phases, face centered cubic (Pb) and body center tetragonal, beta-(Sn) solid solution co-exist in all the embedded nanoparticles at room temperature. The phases bear crystallographic orientation relationship with the matrix. In situ TEM study has been carried out for the alloy particles to study the melting and the solidification behavior. The detailed microscopic observations indicate formation of a single-phase metastable fcc (Pb) in the nano-particles prior to the melting during heating. Solidification of these particles begins with nucleation of fcc (Pb), which phase separates into fcc (Pb) and beta-(Sn) lamellae in the solid state. In situ X-ray diffraction study is carried out to obtain lattice parameter of metastable fcc (Pb) and thereby an estimate of amount of Sn dissolved in the metastable (Pb) prior to the melting. The results are discussed in terms of a metastable phase diagram between fcc Pb and fcc Sn and invoking the size effect on the metastable phase diagram. The size factor is found to play a critical role in deciding the pathway of phase transformation as well as the extension of solid solubility of Sn in fcc (Pb) in the nano-particles.

Temperature dependent magnetic ordering and electrical transport behavior of nano zinc ferrite from 20 to 800 K

The nano ZnFe2O4 compound was prepared by eco-friendly hydrothermal method. The characterization of the sample for its structure, morphology and composition were done by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), dynamic light scattering, Fourier transform infrared spectroscopy, zeta surface profiler and UV-Visible spectroscopy studies. The PXRD measurement reveals that the compound shows spinel cubic phase belong Fd (3) over barm (227) space group. Morphology of the compound from SEM and surface profile shows nearly spherical agglomerated particles with well defined grains and grain boundaries. The material shows the semiconducting behavior with E-g of 2.3 eV at room temperature (RT). The variation in the magnetic ordering was observed for wide range of temperature. The compound behaves like a soft magnetic material with ferrimagnetic at various temperatures except at RT. Both magnetic and EPR studies supports the superparamagnetic behavior of the the sample. The DC conductivity, dielectric and AC conductivity behavior of the 1000 degrees C pellets sintered for 2 h shows good frequency dependent transport properties. The present study facilitate in selecting the suitable materials for the nanoelectronics and spintronic applications. (C) 2013 Elsevier B.V. All rights reserved.

Monotonic and low cycle fatigue behavior of an O+B2 alloy at high temperatures

Low cycle fatigue behavior of an O+B2 alloy was evaluated at 650 degrees C in ambient atmosphere under fully reversed total axial strain controlled mode. Three different microstructures, namely equiaxed O plus aged B2 (fine O plates in B2 matrix), lenticular O laths plus aged B2 and a pancake composite microstructure comprising equiaxed alpha 2, lenticular O and aged B2, were selected to study the effect of microstructure on low cycle fatigue behavior in this class of alloys. Distinct well-defined trends were observed in the cyclic stress-strain response curves depending on the microstructure. The cyclic stress response was examined in terms of softening or hardening and correlated with microstructural features and dislocation behavior. Fatigue life was analyzed in terms of standard Coffin-Manson and Basquin plots and for all microstructures a prevailing elastic strain regime was identified, with a single slope for microstructures equiaxed and composite and a double slope for lenticular O laths. (c) 2014 Elsevier B.V. All rights reserved.

Magnetic field induced tailoring of mechanical behavior of fluid filled micro porous carbon nanotube foam

Compressive loading of the carbon nanotube (CNT) has attracted much attention due to its entangled cellular like structure (CNT foam). This report investigates the mechanical behavior of magnetorheological fluid impregnated micro porous CNT foam that has not been realized before at this scale. Compressive behavior of CNT foam is found to greatly depend on the variation in both fluid viscosity as well as magnetic field intensity. Moreover, maximum achieved stress and energy absorption in CNT foam followed a power law behavior with the magnetic field intensity. Magnetic field induced movement of both CNT and iron oxide particles along the field direction is shown to dominate compressive behavior of CNT foam over highly attractive van der Waals forces between individual CNT. Therefore, this study demonstrates a method for tailoring the mechanical behavior of the fluid impregnated CNT foam. (C) 2014 AIP Publishing LLC.

Role of Cu2+ ions substitution in magnetic and conductivity behavior of nano-CoFe2O4

Cobalt copper ferrite nanopowders with composition Co1-xCu5Fe2O4 (0.0 <= x <= 0.5) was synthesized by solution combustion method. The powder X-ray diffraction studies reveal the formation of single ferrite phase with particle size of similar to 11-35 nm. Due to increase in electron density with in a material, X-ray density increase with increase of Cu2+ ions concentration. As Cu2+ ions concentration increases, saturation magnetization decreases from 38.5 to 26.7 emu g(-1). Further, the squareness ratio was found to be similar to 0.31-0.46 which was well below the typical value 1, which indicates the existence of single domain isolated ferrimagnetic samples. The dielectric and electrical modulus was studied over a frequency range of 1 Hz to 1 MHz at room temperature using the complex impedance spectroscopy technique. Impedance plots showed only one semi-circle which corresponds to the contributions of grain boundaries. The lower values of dielectric loss at higher frequency region may be quite useful for high frequency applications such as microwave devices. (C) 2014 Elsevier B.V. All rights reserved.

Antioxidant activity and electrochemical elucidation of the enigmatic redox behavior of curcumin and its structurally modified analogues

Here, we report studies on the antioxidant activity and redox behavior of curcumin and its structurally modified synthetic analogues. We have synthesized a number of analogues of curcumin which abrogate its keto-enol tautomerism or substitute the methylene group at the centre of its heptadione moiety implicated in the hydride transfer and studied their redox property. From cyclic voltammetric studies, it is demonstrated that H-atom transfer from CH2 group at the center of the heptadione link also plays an important role in the antioxidant properties of curcumin along with that of its phenolic -OH group. In addition, we also show that the conversion of 1, 3-dicarbonyl moiety of curcumin to an isosteric heterocycle as in pyrazole curcumin, which decreases its rotational freedom, leads to an improvement of its redox properties as well as its antioxidant activity. (C) 2014 Elsevier Ltd. All rights reserved.

Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1ms(-1), against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting-abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45 degrees slope angle. Unlike other alloys, 60 degrees slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60 degrees cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45 degrees slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60 degrees slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60 degrees cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.

Asymptotic behavior and interpretation of virtual states: The effects of confinement and of basis sets

A real-space high order finite difference method is used to analyze the effect of spherical domain size on the Hartree-Fock (and density functional theory) virtual eigenstates. We show the domain size dependence of both positive and negative virtual eigenvalues of the Hartree-Fock equations for small molecules. We demonstrate that positive states behave like a particle in spherical well and show how they approach zero. For the negative eigenstates, we show that large domains are needed to get the correct eigenvalues. We compare our results to those of Gaussian basis sets and draw some conclusions for real-space, basis-sets, and plane-waves calculations. (C) 2016 AIP Publishing LLC.

Indentation Creep Behavior in Ce-Based Bulk Metallic Glasses at Room Temperature

The room temperature creep behaviors of Ce-based bulk metallic glasses were examined by the use of nanoindentation. The creep rate and creep rate sensitivity of Ce-based BMGs were derived from indentation creep curves. The low creep rate sensitivity of Ce-based BMGs indicates that the room temperature creep is dominated by localized shear flow. The experimental creep curves can be described by a generalized Kelvin model. Furthermore, the creep retardation spectrum is calculated for the Ce-based metallic glasses. The results showed that creep retardation spectrum consists of two relatively separated peaks with the well defined characteristic relaxation times.

3D Anisotropic Elastoplastic-Damage Model and its Application in Simulating the Behavior of Rock Materials

A 3D anisotropic elastoplastic-damage model was presented based on continuum damage mechanics theory. In this model, the tensor decomposition technique is employed. Combined with the plastic yield rule and damage evolution, the stress tensor in incremental format is obtained. The derivate eigenmodes in the proposed model are assumed to be related with the uniaxial behavior of the rock material. Each eigenmode has a corresponding damage variable due to the fact that damage is a function of the magnitude of the eigenstrain. Within an eigenmodes, different damage evolution can be used for tensile and compressive loadings. This model was also developed into finite element code in explicit format, and the code was integrated into the well-known computational environment ABAQUS using the ABAQUS/Explicit Solver. Numerical simulation of an uniaxial compressive test for a rock sample is used to examine the performance of the proposed model, and the progressive failure process of the rock sample is unveiled.

Behavior of Multiple Shear Bands in Zr-Based Bulk Metallic Glass

The deformation behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass was studied by in situ scanning electron microscopy (SEM) quasi-static uniaxial compression tests at room temperature. Multiple shear bands were observed with a large plasticity. Microscopic examination demonstrates that slipping, branching and intersecting of multiple shear bands are the main mechanisms for enhancing the plasticity of this metallic glass. Additionally, nano/micro-scale voids and cracks at the intersecting sites of shear bands and preferential etching of shear bands were observed as well. These observations demonstrated that the formation of shear bands in bulk metallic glasses is resulted mainly from local free volume coalescence.

The interlaminar fracture-behavior and toughening mechanisms of new carbon-fiber-reinforced bismaleimide composites

The interlaminar fracture behaviour of carbon fibre-reinforced bismaleimide (BMI) composites prepared by using a new modified BMI matrix has been investigated by various methods. Laminates of three typical stacking sequences were evaluated. Double cantilever beam, end-notch flexure and edge-delamination tension tests were conducted under conventional conditions and in a scanning electron microscope. The strain energy release rates in Mode I and Mode III G(lc) and G(llc), as well as the total strain energy release rate, G(mc), have been determined and found to be higher than those for laminates with an epoxy matrix. Dynamic delamination propagation was also studied. The toughening mechanisms are discussed.

Experimental investigation of Very-High-Cycle Fatigue behavior for a structural steel

Very-High-Cycle Fatigue (VHCF) test for a medium carbon structural steel (40Cr) has been performed and a stepwise S-N curve was obtained by employing cantilever-type rotary bending fatigue machine with hourglass shape specimen. The S-N curve was well explained as a combination of curves for surface-induced fracture and interior inclusion-induced fracture with fish-eye patterns. The morphology of the fish-eye pattern was illustrated in order to clarify subsurface crack initiation and propagation behavior.