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The stress driven growth of an expanding precipitate at a crack tip is studied. The material is assumed to be linearly elastic, and the expansion is considered to be isotropic or transversely isotropic. The extent of the precipitate is expected to be small as compared with the crack length and distance to boundaries. The problem has only a single length scale given by the squared ratio of the stress intensity factor and a critical hydrostatic stress that initiates the growth of the precipitate. Therefore, the growth occurs under self-similar conditions. The equations on non-dimensional form show that the free parameters are expansion strain, degree of anisotropy and Poisson’s ratio. It is found that the precipitate, once initiated, grows without remote load for expansion strains above a critical value. The anisotropy of the expansion strongly affects the shape of the precipitate but does not have a large effect on the crack tip shielding. open access

A range of data sources are now used to support the process of archaeological prospection, including remote sensed imagery, spy satellite photographs and aerial photographs. This paper advocates the value and importance of a hitherto under-utilised historical mapping resource—the Survey of India 1” to 1-mile map series, which was based on surveys started in the mid–late nineteenth century, and published progressively from the early twentieth century AD. These maps present a systematic documentation of the topography of the British dominions in the South Asian Subcontinent. Incidentally, they also documented the locations, the height and area of thousands of elevated mounds that were visible in the landscape at the time that the surveys were carried out, but have typically since been either damaged or destroyed by the expansion of irrigation agriculture and urbanism. Subsequent reanalysis has revealed that many of these mounds were actually the remains of ancient settlements. The digitisation and analysis of these historic maps thus creates a unique opportunity for gaining insight into the landscape archaeology of South Asia. This paper reviews the context within which these historical maps were created, presents a method for georeferencing them, and reviews the symbology that was used to represent elevated mound features that have the potential to be archaeological sites. This paper should be read in conjunction with the paper by Arnau Garcia et al. in the same issue of Geosciences, which implements a research programme combining historical maps and a range of remote sensing approaches to reconstruct historical landscape dynamics in the Indus River Basin.

A model is established that describes stress driven diffusion, resulting in formation and growth of an expanded precipitate at the tip of a crack. The new phase is transversely isotropic. A finite element method is used and the results are compared with a simplified analytical theory. A stress criterium for formation of the precipitate is derived by direct integration of the Einstein-Smoluchowski law for stress driven diffusion. Thus, the conventional critical concentration criterium for precipitate growth can be replaced with a critical hydrostatic stress. The problem has only one length scale and as a consequence the precipitate grows under self-similar conditions. The length scale is given by the stress intensity factor, the diffusion coefficient and critical stress versus remote ambient concentrations. The free parameters involved are the expansion strain, the degree of anisotropy and Poisson's ratio. Solutions are obtained for a variation of the first two. The key result is that there is a critical phase expansion strain below which the growth of the new phase is stable and controlled by the stress intensity factor. For supercritical expansion strains, the precipitate grows even without remote load. The anisotropy of the expansion strongly affects the shape of the precipitate, but does not have a large effect on the crack tip shielding. (C) 2018 The Authors. Published by Elsevier B.V.

It is a common belief that embedded expanding inclusions are subjected to an internal homogeneous compressive hydrostatic stress. Still, cracks that appear in precipitates that occupy a larger volume than the original material, are frequently observed. The appearance of cracks has since long been regarded as a paradox. In the present study it is shown that matrix materials that increases its volume even several percent during the precipitation process develop a tensile hydrostatic stress in the centre of the precipitate. This is the result of a complicated mechanical-chemical phase transformation process. The process is here studied using a Landau phase feld model. Before the material is transformed and incorporated in a precipitate it undergoes stretching beyond the elastic strain limit because of the presence of already expanded material. During the phase transformation, the accompanying volumetric expansion cannot be fully accommodated which instead creates an internal compressive stress and adds tension in the surrounding material. As the growth of the precipitate proceeds, a region with increasing tensile stress develops in the interior of the precipitate. This is suggested to be the most probable cause of the observed cracks. First the mechanics that lead to the tension is computed. The infuence of elastic-plastic properties is studied both for cases both with and without cracks. The growth history from microscopic to macroscopic precipitates is followed and the result is compared with observations of so called hydride blisters that are formed on surfaces of zirconium alloys in the presence of hydrogen. A common practical situation is when the zirconium is in contact with an object of lower temperature. Then the cooled spot attracts hydrogen that make the zirconium transform to a metal hydride with the shape of a blister. The simulations predicts a final size and position of the growing crack that compares well with the experimental observations. open access

Today, farmers in many regions of eastern Asia sow their barley grains in the spring and harvest them in the autumn of the same year (spring barley). However, when it was first domesticated in southwest Asia, barley was grown between the autumn and subsequent spring (winter barley), to complete their life cycles before the summer drought. The question of when the eastern barley shifted from the original winter habit to flexible growing schedules is of significance in terms of understanding its spread. This article investigates when barley cultivation dispersed from southwest Asia to regions of eastern Asia and how the eastern spring barley evolved in this context. We report 70 new radiocarbon measurements obtained directly from barley grains recovered from archaeological sites in eastern Eurasia. Our results indicate that the eastern dispersals of wheat and barley were distinct in both space and time. We infer that barley had been cultivated in a range of markedly contrasting environments by the second millennium BC. In this context, we consider the distribution of known haplotypes of a flowering-time gene in barley, Ppd-H1, and infer that the distributions of those haplotypes may reflect the early dispersal of barley. These patterns of dispersal resonate with the second and first millennia BC textual records documenting sowing and harvesting times for barley in central/eastern China.

Cold worked and stress relieved Zr-2.5 wt%Nb alloy was annealed at 900 degrees C for 5-90 min and quenched in water, which resulted in formation of alpha' martensite and primary alpha phase. Reheating of the same samples to 700 degrees C leads to alpha' -> alpha(Zr) + beta(Zr) transformation following JMAK kinetics (n = 0.55 and k = 0.34). Tensile samples in annealed condition were deformed at 625-700 degrees C over strain rates of 2 x 10(-5)-1x10(-2) s(-1). With the increase in annealing time, strain rate sensitivity and activation energy for deformation were found to change from 0.42 to 0.20 and 181.4-685 kJ/mol respectively. The maximum peak stress (136.5 MPa) obtained at 700 degrees C from present results suggests higher load bearing ability of the Zr-2.5Nb alloy in annealed and quenched condition compared to that of cold-rolled and stress-relieved condition. (C) 2014 Elsevier B.V. All rights reserved.

Niobium-based alloys are well-established refractory materials; as a result of their high melting temperature and good creep properties, these alloys find their applications in nuclear reactors. The present study deals with a microstructural response of these materials during hot working. The evolution of microstructure and texture during high-temperature deformation has been investigated in the temperature range 1500-1700A degrees C and strain rate range of 0.001-0.1 s(-1). For each deformed sample, the microstructure has been examined in detail. The microstructural features clearly revealed the formation of a substructure and the occurrence of dynamic recrystallization in a proper temperature-strain rate window. At low strain rates, the necklace structure formation was more prominent.

Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5

Precipitates that form as a result of phase transformation are studied with regard to mechanical behaviour and initiation of internal cracks. The focus is on precipitates occupying a larger volume than the surrounding matrix. Further the study is restricted to precipitates growing by incorporating material transformed from being matrix material to the phase of the precipitate. The phase transformation is here treated as a simple homogeneous swelling. The classical solutions for expanding inclusions predict that the inclusion becomes subjected to a constant homogeneous hydrostatic compression. During the process analysed here, added transformed material progressively relieve the compressive stress in the interior of the precipitate. As the process continues the stresses change from compression to tension in both radial and tangential directions in the centre of the precipitate. Further, growth of cracks in precipitates with poor fracture mechanical properties are studied. To simplify the analysis it is assumed that the fracture toughness is insignificant. The prediction is that around a third of the precipitate will fracture. The presence of a crack only has an insignificant effect on the load exerted by the swelling precipitate on the matrix.

A methodology for estimating the stress field in the matrix surrounding a semi-constrained inclusion is proposed. The stress free misfit volume associated with the inclusion was partitioned into semi-constrained and constrained components. The objective was achieved by carrying out a series of sectioning, cutting and imposition of constrained misfit displacement on an imaginary notch of geometry identical to that of the inclusion–matrix contour. The stress field was computed using elastic finite element analysis for plane stress condition. The misfit displacement model thus developed was applied to compute the stress field around a hydride blister grown under controlled thermal boundary condition in Zr–2.5Nb pressure tube (PT) alloy and was validated by interpreting the hydride platelet orientation in the matrix surrounding the blister. Finally, an assessment of the structural integrity of the Zr–2.5Nb PT material containing hydride blister was made in view of this analysis., © Elsevier

International audience; Electrochemical properties of plasma-fluorinated graphite samples have been investigated in 1 mol dm−3 LiClO4 ethylene carbonate (EC)/diethyl carbonate (DEC) solution at 25 °C. Fluorine contents in plasma-fluorinated graphite samples were in the range of 0-0.3 at.% by elemental analysis and surface fluorine concentrations obtained by X-ray photoelectron spectroscopy (XPS) were in the range of 3-12 at.%. Raman spectroscopy revealed that surface disordering of graphite was induced by plasma fluorination. Plasma treatment increased the surface areas of graphite samples by 26-55% and the pore volumes for the mesopores with diameters of 1.5-2 and 2-3 nm. Plasma-fluorinated graphites showed capacities higher than those of original graphites and even higher than the theoretical capacity of graphite, 372 mAh g−1, without any change of the profile of charge-discharge potential curves. The increments in the capacities were approximately 5, 10 and 15% for graphites with average particle diameters, 7, 25 and 40 μm, respectively. Furthermore, the coulombic efficiencies in first cycle were nearly the same as those for original graphites or higher by several percents.

Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221 005 Thin films of Co304, NiCo204, LaNiO3, Lat-xSrxCoO3 and of Ni-Fe alloys were prepared on conductive supports and their physicochemical and electrocatalytic properties towards oxygen evolution reaction in alkaline medium have been investigated. The electrode kinetic parameters such as, the Tafel slope and the reaction order with respect to OH-concentration have been determined. Based on the results suitable mechanisms for the oxygen evolution reaction are suggested.

During high temperature tensile testing of a modified 9Cr-1Mo steel in tempered martensitic condition, serrated plastic flow, implying the occurrence of dynamic strain aging, was observed. The serrated stress-strain curves were unique in the sense that the serrations appeared almost at the beginning of deformation and disappeared before the ultimate strengths were attained. Moreover, the strains to the disappearance of serrations varied systematically with the test temperature and strain-rate. A brief literature survey revealed that in studies on Nickel alloys and ferritic-martensitic steels, the disappearance of serrated flow was found to be a thermally activated process and that the phenomenon manifested in the higher temperature regime by either a progressively larger strains to the onset of serrations or a progressively smaller strain to the disappearance of serrations of the flow curve. However, it appears that the type of serrated flow curves observed in this study, has not yet been reported in any other ferritic-martensitic steels. It was thus felt necessary to carry out a detailed investigation of dynamic strain aging in this steel. In this paper, the possible mechanism controlling the appearance of serrations and their disappearance of the stress-strain curves are discussed.

Several major cereal groups have been identified as staples used by the pre-urban, urban and post-urban phase populations of the Indus Civilisation (3200–1500 BCE): wheat, barley, a range of small hulled millets and also rice, though their proportional exploitation is variable across space and over time. Traditional quantification methods examine the frequency, intensity and proportionality of the use of these crops and help ascertain the ‘relative importance’ of these cereals for Indus populations. However, this notion of ‘importance’ is abstracted from the daily lives of the people using these crops and may be biased by the differential production (as well as archaeological survival) of individual cereals. This paper outlines an alternative approach to quantifying Indus cereals by investigating proportions of calories. Cereals are predominantly composed of carbohydrates and therefore provided much of the daily caloric intake among many late Holocene farming populations. The four major cereal groups cultivated by Indus farmers, however, vary greatly in terms of calories per grain, and this has an impact on their proportional input to past diets. This paper demonstrates that, when converted to proportions of calories, the perceived ‘importance’ of cereals from five Indus sites changes dramatically, reducing the role of the previously dominant small hulled millet species and elevating the role of Triticoid grains. Although other factors will also have affected how a farmer perceived the role and importance of a crop, including its ecological tolerances, investments required to grow it, and the crop’s role in the economy, this papers suggests that some consideration of what cereals meant in terms of daily lives is needed alongside the more abstracted quantification methods that have traditionally been applied.

53 ref.; International audience