A Short Review on Lu-Hf Isotope System in Zircon: Implications for Crustal Evolution

Zircon has been recognized as the unaltered part of the Earth's history which preserves nearly 4 billion year record of earth's evolution. Zircon preserves igneous and metamorphic processes during its formation and remains unaffected by sedimentary processes and crustal recycling. U-Pb and Lu-Hf in zircon work as geochronometer and geochemical tracer respectively. Zircon provide valuable information about the source composition of the rocks and the intrinsic details of an unseen crust-mantle processes. The world wide data of U-Pb and Lu-Hf isotope systems in zircon reveal crustal evolution through geological history. Moreover, the U-Pb age pattern of zircons show distinct peaks attributed to preservation of crustal rocks or mountain building during supercontinent assembly. The histogram of continental crust preservation shows that nearly one-third of continental crust was formed during the Archean, almost 20% was formed during Paleoproterozoic and 14% in last 400 Ma.

Effect of Particle Concentration on Shape Deformation and Secondary Atomization Characteristics of a Burning Nanotitania Dispersion Droplet

Secondary atomization characteristics of burning bicomponent (ethanol-water) droplets containing titania nanoparticles (NPs) in dilute (0.5% and 1 wt.%) and dense concentrations (5% and 7.5 wt.%) are studied experimentally at atmospheric pressure under normal gravity. It is observed that both types of nanofuel droplets undergo distinct modes of secondary breakup, which are primarily responsible for transporting particles from the droplet domain to the flame zone. For dilute nanosuspensions, disruptive response is characterized by low intensity atomization modes that cause small-scale localized flame distortion. In contrast, the disruption behavior at dense concentrations is governed by high intensity bubble ejections, which result in severe disruption of the flame envelope.

Joint Strength and Wall Deformation Characteristics of a Single-Cell Geocell Subjected to Uniaxial Compression

Geocells are three-dimensional expandable panels with a wide range of applications in geotechnical engineering. A geocell is made up of many internally connected single cells. The current study discusses the joint strength and the wall deformation characteristics of a single cell when it is subjected to uniaxial compression. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely silty clay, sand, and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Experimental results were also validated using numerical simulations carried out using Lagrangian analysis software. The experiment and the numerical results were found to be in good agreement with each other. A simple analytical model based on the theory of thin cylinders is also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared with experimental and numerical values. (C) 2014 American Society of Civil Engineers.

Kinematic flow patterns in slow deformation of a dense granular material

The kinematic flow pattern in slow deformation of a model dense granular medium is studied at high resolution using in situ imaging, coupled with particle tracking. The deformation configuration is indentation by a flat punch under macroscopic plane-strain conditions. Using a general analysis method, velocity gradients and deformation fields are obtained from the disordered grain arrangement, enabling flow characteristics to be quantified. The key observations are the formation of a stagnation zone, as in dilute granular flow past obstacles; occurrence of vortices in the flow immediately underneath the punch; and formation of distinct shear bands adjoining the stagnation zone. The transient and steady state stagnation zone geometry, as well as the strength of the vortices and strain rates in the shear bands, are obtained from the experimental data. All of these results are well-reproduced in exact-scale non-smooth contact dynamics simulations. Full 3D numerical particle positions from the simulations allow extraction of flow features that are extremely difficult to obtain from experiments. Three examples of these, namely material free surface evolution, deformation of a grain column below the punch and resolution of velocities inside the primary shear band, are highlighted. The variety of flow features observed in this model problem also illustrates the difficulty involved in formulating a complete micromechanical analytical description of the deformation.

Influence of mode of deformation on microstructural heterogeneities in Ni subjected to large strain deformation

In the present work, the effect of deformation mode (uniaxial compression, rolling and torsion) on the microstructural heterogeneities in a commercial purity Ni is reported. For a given equivalent von Mises strain, samples subjected to torsion have shown higher fraction of high-angle boundaries, kernel average misorientation and recrystallization nuclei when compared to uniaxially compressed and rolled samples. This is attributed to the differences in the slip system activity under different modes of deformation.

General framework for acoustic emission during plastic deformation

Despite the long history, so far there is no general theoretical framework for calculating the acoustic emission spectrum accompanying any plastic deformation. We set up a discrete wave equation with plastic strain rate as a source term and include the Rayleigh-dissipation function to represent dissipation accompanying acoustic emission. We devise a method of bridging the widely separated time scales of plastic deformation and elastic degrees of freedom. While this equation is applicable to any type of plastic deformation, it should be supplemented by evolution equations for the dislocation microstructure for calculating the plastic strain rate. The efficacy of the framework is illustrated by considering three distinct cases of plastic deformation. The first one is the acoustic emission during a typical continuous yield exhibiting a smooth stress-strain curve. We first construct an appropriate set of evolution equations for two types of dislocation densities and then show that the shape of the model stress-strain curve and accompanying acoustic emission spectrum match very well with experimental results. The second and the third are the more complex cases of the Portevin-Le Chatelier bands and the Luders band. These two cases are dealt with in the context of the Ananthakrishna model since the model predicts the three types of the Portevin-Le Chatelier bands and also Luders-like bands. Our results show that for the type-C bands where the serration amplitude is large, the acoustic emission spectrum consists of well-separated bursts of acoustic emission. At higher strain rates of hopping type-B bands, the burst-type acoustic emission spectrum tends to overlap, forming a nearly continuous background with some sharp acoustic emission bursts. The latter can be identified with the nucleation of new bands. The acoustic emission spectrum associated with the continuously propagating type-A band is continuous. These predictions are consistent with experimental results. More importantly, our study shows that the low-amplitude continuous acoustic emission spectrum seen in both the type-B and type-A band regimes is directly correlated to small-amplitude serrations induced by propagating bands. The acoustic emission spectrum of the Luders-like band matches with recent experiments as well. In all of these cases, acoustic emission signals are burstlike, reflecting the intermittent character of dislocation-mediated plastic flow.

Stability analysis of thick piezoelectric metal based FGM plate using first order and higher order shear deformation theory

This paper presents the stability analysis of functionally graded plate integrated with piezoelectric actuator and sensor at the top and bottom face, subjected to electrical and mechanical loading. The finite element formulation is based on first order and higher order shear deformation theory, degenerated shell element, von-Karman hypothesis and piezoelectric effect. The equation for static analysis is derived by using the minimum energy principle and solutions for critical buckling load is obtained by solving eigenvalue problem. The material properties of the functionally graded plate are assumed to be graded along the thickness direction according to simple power law function. Two types of boundary conditions are used, such as SSSS (simply supported) and CSCS (simply supported along two opposite side perpendicular to the direction of compression and clamped along the other two sides). Sensor voltage is calculated using present analysis for various power law indices and FG (functionally graded) material gradations. The stability analysis of piezoelectric FG plate is carried out to present the effects of power law index, material variations, applied mechanical pressure and piezo effect on buckling and stability characteristics of FG plate.

Effect of Nb orientation and deformation on the growth of Nb3Sn intermetallic superconductor by bronze technique

The growth of Nb3Sn by bronze technique on single crystals and deformed Nb is studied. The grain boundary diffusion-controlled growth rate is found to be higher for Nb-(0 1 3) than Nb-(0 1 1) because of smaller grain size of Nb3Sn. The difference in grain size is explained with the help of surface energies leading to different nucleation barrier. Significantly finer grains and higher growth rate of the product phase is found for rolled Nb because of available defects acting as potential nucleation sites.

Quantitative In Situ Analysis of Deformation in Sliding Metals: Effect of Initial Strain State

Using in situ, high-speed imaging of a hard wedge sliding against pure aluminum, and image analysis by particle image velocimetry, the deformation field in sliding is mapped at high resolution. This model system is representative of asperity contacts on engineered surfaces and die-workpiece contacts in deformation and machining processes. It is shown that large, uniform plastic strains of 1-5 can be imposed at the Al surface, up to depths of 500 mu m, under suitable sliding conditions. The spatial strain and strain rate distributions are significantly influenced by the initial deformation state of the Al, e.g., extent of work hardening, and sliding incidence angle. Uniform straining occurs only under conditions of steady laminar flow in the metal. Large pre-strains and higher sliding angles promote breakdown in laminar flow due to surface fold formation or flow localization in the form of shear bands, thus imposing limits on uniform straining by sliding. Avoidance of unsteady sliding conditions, and selection of parameters like sliding angle, thus provides a way to control the deformation field. Key characteristics of the sliding deformation such as strain and strain rate, laminar flow, folding and prow formation are well predicted by finite element simulation. The deformation field provides a quantitative basis for interpreting wear particle formation. Implications for engineering functionally graded surfaces, sliding wear and ductile failure in metals are discussed.

High temperature deformation behavior of Nb-1 wt.%Zr alloy

The hot deformation behavior of Nb-1 wt.%Zr alloy was studied using uniaxial compression tests carried out in vacuum to a true strain of 0.6 in the temperature range of 900 to 1700 degrees C and the strain rate range of 3 x 10(-3) to 10 s(-1). The optimum regime of hot workability of Nb-1Zr alloy was determined from the strain rate sensitivity (m) contour plots. A high m of about 02 was obtained in the temperature and strain rate range of 1200-1500 degrees C and 10(-3) to 10(-1) s(-1) and 1600-1700 degrees C and 10(-1) to 1 s(-1). Microstructure of the deformed samples showed features of dynamic recrystallization within the high strain rate sensitivity domain. Compared to the study on Nb-1Zr-0.1C alloy, Nb-1Zr showed a lower flow stress and an optimum hot working domain at lower temperatures. In the 1500 to 1700 degrees C range the apparent activation energy of deformation for Nb-1Zr was 259 kJ mol(-1), the stress exponent 5, and the activation volume about 200 to 700 b(3). (C) 2015 Elsevier Ltd. All rights reserved.

Archean tectonics and crustal evolution of the Biligiri Rangan Block, southern India

The Southern Granulite Terrain in India is a collage of crustal blocks ranging in age from Archean to Neoproterozoic. This study investigate the tectonic evolution of one of the northernmost block- the Biligiri Block (BRB) through a multidisciplinary approach involving field investigation, petrographic studies, LA-ICPMS zircon U-Pb geochronology, Hf isotopic analyses, metamorphic P-T phase diagram computations, and crustal thickness modeling. The garnet bearing quartzofeldspathic gneiss from the central BRB preserve Mesoarchean magmatic zircons with ages between 3207 and 2806 Ma and positive epsilon Hf value (+2.7) which possibly indicates vestiges of a Mesoarchean primitive continental crust. The occurrence of quartzite-iron formation intercalation as well as ultramafic lenses along the western boundary of the BRB is interpreted to indicate that the Kollegal structural lineament is a possible paleo-suture. Phase diagram computation of a metagabbro from the southwestern periphery of the Kollegal suture zone reveals high-pressure (similar to 18.5 kbar) and medium-temperature (similar to 840 degrees C) metamorphism, likely during eastward subduction of the Western Dharwar oceanic crust beneath the Mesoarchean BRB. In the model presented here, slab subduction, melting and underplating processes generated arc magmatism and subsequent charnockitization within the BRB between ca. 2650 Ma and ca. 2498 Ma. These results thus reveal Meso- to Neoarchean tectonic evolution of the BRB. The spatial variation of crustal thickness, derived from flexure inversion technique, provides additional constraints on the tectonic linkage of the BRB with its surrounding terrains. In conjunction with published data, the Moyar and the Kollegal suture zones are considered to mark the trace of ocean closure along which the Nilgiri and Biligiri Rangan Blocks accreted on to the Western Dharwar Craton. (C) 2016 Elsevier B.V. All rights reserved.

Deformation pathways and breakup modes in acoustically levitated bicomponent droplets under external heating

Controlled breakup of droplets using heat or acoustics is pivotal in applications such as pharmaceutics, nanoparticle production, and combustion. In the current work we have identified distinct thermal acoustics-induced deformation regimes (ligaments and bubbles) and breakup dynamics in externally heated acoustically levitated bicomponent (benzene-dodecane) droplets with a wide variation in volatility of the two components (benzene is significantly more volatile than dodecane). We showcase the physical mechanism and universal behavior of droplet surface caving in leading to the inception and growth of ligaments. The caving of the top surface is governed by a balance between the acoustic pressure field and the restrictive surface tension of the droplet. The universal collapse of caving profiles for different benzene concentration (<70% by volume) is shown by using an appropriate time scale obtained from force balance. Continuous caving leads to the formation of a liquid membrane-type structure which undergoes radial extension due to inertia gained during the precursor phase. The membrane subsequently closes at the rim and the kinetic energy leads to ligament formation and growth. Subsequent ligament breakup is primarily Rayleigh-Plateau type. The breakup mode shifts to diffusional entrapment-induced boiling with an increase in concentration of the volatile component (benzene >70% by volume). The findings are portable to any similar bicomponent systems with differential volatility.