A large strain thermoviscoplastic formulation for the solidification of S.G. cast iron in a green sand mould

This paper presents a large strain thermoviscoplastic formulation for the analysis of the solidification process of spheroidal graphite (S.G.) cast iron in a green sand mould. This formulation includes two different non-associate constitutive models in order to describe the thermomechanical behaviour of each of such materials during the whole process. The performance of these models is evaluated in the analysis of a solidification test.     

A unified plasticity model for cyclic behaviour of clay and sand

This paper presents the development and an experimental evaluation of a simple unified bounding surface plasticity theory for modelling the stress–strain behaviour of sand and clay under both drained and undrained cyclic loading conditions. The model concerned is called CASM-c, which is based on the unified critical state model CASM developed by Yu [Yu, H.S., 1995. A unified critical state model for clay and sand. Civil Engineering Research Report No. 112.08.1995. University of Newcastle, NSW 2308, Australia; Yu, H.S., 1998. CASM: a unified state parameter model for clay and sand. International Journal of Numerical and Analytical Methods in Geomechanics 22, 621–653]. CASM is a relatively simple model as it only requires seven model constants, five of which are the same as those used in the modified Cam-clay model. All these constants have clear physical meanings and may be easily determined from the results of triaxial tests. A key advantage of CASM over many other existing critical state models lies on its simplicity and unified nature as it can model the behaviour of both clay and sand.The extension of the model CASM presented in this paper consists of adopting the bounding surface plasticity theory and treating the reloading and unloading processes differently when calculating the hardening modulus. As a result, a smooth transition of stiffness and gradual accumulation of permanent strain and/or pore pressure in unload–reload cycles as well as the hysteretic behaviour can be reproduced. The results of model simulations show an encouraging agreement with experimental data from triaxial tests subjected to both one-way and two-way cyclic loading conditions.     

Application of a Sequential Extraction Procedure to Calcareous Soil Samples: Preliminary Studies

Abstract

The localization of trace metals in soils is usually performed by sequential extraction procedures. Our purpose was to study the fractioning of copper in calcareous soils, in order to predict its mobility, using the extraction procedure proposed by Tessier et al. This preliminary study is devoted to the improvements of this method applied to calcareous soil samples.

First, it was necessary to assess the experimental conditions allowing the complete solubilisation of the different compartments involved in the extraction procedure with their appropriate reagent (acetic acid-sodium acetate and carbonates, iron hydroxide and hydroxylamine, organic matter and hydrogen peroxide, fluorhydric-perchloric acid and residual fraction). The complete solubilisation of each compartment was tested by measuring the residual phase.

Secondly, it was necessary to study the analytical protocol for the determination of copper with electrothermal atomic absorption; an improvement of this determination was particularly necessary for the reagent used for the exchangeable fraction (sodium acetate at pH = 8.5).

According to the experimental results, the quality (repeatability, concordance of the sum of fractions with the total content of copper determined with independent measurement) of the proposed protocol seems to be quite good.

Some results of the fractioning of copper in calcareous soil samples are given; these samples are characterised by a high value of copper in the residual fraction corresponding to a poor availability of this element.     

Chemical Imaging for PAH Analysis in Particulate Materials

Abstract

Chemical imaging is a new analytical science, related to a combination of spatial and chemical resolutions. Several new chemical imaging tools have been developed and applied to environmental analysis. The advantages of such methods, which provide simultaneous morphological/geometrical and chemical speciation, are pointed out and exemplified in several environmental analytical applications. These include fast analysis of PAH contaminated aerosols at low concentrations, analysis of contaminated quartz sand particles, as well as improvement of laser induced fluorescence detection of PAH compounds in natural water, in the presence of various microparticles. It is shown that chemical imaging has a considerable potential in environmental applications and can provide detailed and unique information when particulate materials are concerned.     

废弃型壳砂混凝土的基本力学性能研究

通过一系列试验证明了废弃型壳砂具有良好的级配，其有害物质含量基本符合使用要求．此外，废弃型壳砂混凝土的配置试验和基本力学性能试验结果进一步表明，废弃型壳砂混凝土的流动性较差，水灰比、砂率和龄期对废弃型壳砂混凝土的抗压强度影响巨大．最后并通过拟合得到了废弃型壳砂混凝土的受压应力-应变全曲线方程．     

原子吸收光谱法研究自然沙粒对pb2+的吸附性能

通过扫描电镜(SEM)、静态氮吸附(NSA)和红外光谱(FTIR)法对塔卡拉玛干沙漠自然沙粒(简称沙粒)的粒状及其表面结构、比表面积和功能基团进行了分析,以FAAS作为检测手段,动态法研究了沙粒对pb2+的吸附性及其影响因素并优化了吸附条件;将沙粒作为填料制备了5.0 cm×5 mm i.d.预富集分离微柱,将其与FA...     

爆炸冲击下珊瑚砂动态本构模型

以珊瑚砂为主要覆盖域的岛礁在面临动力灾变时,确定岛礁工程抵抗极端冲击荷载的阈值至关重要,珊瑚砂的动态本构关系是防护工程设计的关键要素。本文中,根据SHPB实验和静态压缩实验的结果,提出了一种基于应变率强化规律确定珊瑚砂物态方程的方法,并确定了珊瑚砂动态本构模型的参数。分别基于流体弹塑性模型和Perzyna黏塑性帽盖模型,结合LS-DYNA有限元程序,通过对侵彻和爆炸的数值计算,验证了模型的适用性。基于建立的模型,对不同相对密实度的珊瑚砂开展了侵彻和爆炸数值计算,结果表明,密实度对爆炸波的衰减影响较大、对侵彻深度的影响较小。     

基于模拟退火地震反演技术——以X油田某区为例

为了提高地震反演预测的分辨率和可信度,提出了线性反演与非线性反演二者相结合的反演方法——以稀疏脉冲反演结果为约束背景的基于模拟退火的反演方法,阐述了基于模拟退火法的反演机理,并以X油田某区为例,开展了基于模拟退火地球物理反演预测,从反演分辨率、可信度和误差三个方面进行分析和定量研究.结果表明,非线性的随机反演与线性反演相结合有效地提高了反演分辨率,纵向上能够精细到单砂体级,反演结果多个概率的实现最大程度上降低反演的多解性,并且,反演结果的精度较高,2m以上砂岩反演符合率均在90%以上.     

Sorption of Europium (III), Cobalt (II) and Cesium (I) by Fresh Water Sediment Fractions Part 2: Effect of Some Environmental Ligands

The sorption behaviour of the radiotracers Eu⁹⁺, Co²⁺ and Cs⁺ by the sediment fractions: sand, coars silt, fine silt and clay was investigated from aqueous solutions containing the complexing agents; humic acid, sodium phosphate or disodium EDTA. The effect of ligand concentration on the sorption of these elements by the sediment fractions was elucidated at varying pH values. The results obtained are interpreted in the light of the complex formation between the ligand and the metal cations beside the interaction between the ligand and the respective sediment fraction investigated.     

Radioactivity in Montenegro beach sands and assessment of the corresponding environmental risk

Activity concentrations of the naturally occurring radionuclides ²²⁶Ra, ²³²Th, ⁴⁰K and anthropogenic ¹³⁷Cs in sand samples collected from 20 renowned beaches on the Coast of Montenegro have been determined using an HPGe (high purity Ge spectrometer). The average activity concentrations were found to be 7.4, 5.2, 97.3 and 0.5 Bq kg^?1, respectively. For all sand samples, the radium equivalent activity has been evaluated and found to be lower than the limit of 370 Bq kg^?1. External and internal hazard indices were less than unity. The gonadal dose equivalent was estimated to be on average 75 μSv y^?1, which is about four times lower than the global average for soil (0.3 mSv y^?1). Calculated values of absorbed dose rates showed the range from 3.1 to 28 nGy h^?1, which is below the world median of average values (57 nGy h^?1). The effective dose rate in the range from 3.8 to 34.4 μSv y^?1 was significantly below the recommended limit value for the public (1 mSv y^?1). The highest dose rate was found for the Velika Plaza locality, which also showed heavy metal contents (As, B, Cd, Hg, Cr, Cu, Mn, Ni, Pb, Zn and Ba) significantly higher than in the sand from Jaz, a locality with one of the lowest dose rates.