METAL CONTAMINATION DUE TO MINING AND MILLING ACTIVITIES AT THE ZAWAR ZINC MINE, RAJASTHAN, INDIA .1. CONTAMINATION OF STREAM SEDIMENTS

Ancient base-metal mining activity at Zawar has produced widespread and persistent dispersal of metals by the Tiri river, flowing past the region. With heavy input of mine and tailing water, the river sediments are enriched with heavy metals compared to the background sediments. Samples collected from the river bed have been analysed for Pb, Zn, Cu, Cd, Fe, Mn, Ca and Mg to recognise the extent of contamination and the geochemical process of dispersion. The river sediment is a mixture of natural erosional detritals, tailing discharges from the milling plant and hydrogenous precipitates. Besides the detrital carbonates derived from the dolomitic litho unit of the area, a significant amount of carbonate is likely to precipitate on the river bed due to influx of mine water. Correlation matrix and R-mode factor analyses revealed that coprecipitation of metals along with Fe-Mn-hydroxides is significant. Association of metals with the precipitated carbonates is by adsorption under alkaline to neutral pH conditions. Cu has poor association with the other heavy metals but has a strong affinity with the gross lithology of the sediments (i.e. Ca-Mg and Fe-Mn in the second factor). The heavy-metal concentrations are extremely variable in the sediments and have been recognised by several approaches such as: (a) extraction at pH 3; (b) total dissolution of sediment samples for bulk heavy-metal analysis; and (c) sequential chemical extraction. Geochemical partitioning of Pb, Zn, Cu and Cd into exchangeable, carbonate, organic, multiple hydroxide and lithogenic pools (operationally defined by A. Tessier) has been brought out utilising a sequential chemical extraction scheme. Nondetrital carbonates are found to be the most efficient scavengers of Pb, Zn and Cd, whereas Cu goes for organics. The results emphasize the importance of the precipitated carbonates and organics as sinks for the heavy metals, even in presence of a high concentration of multiple hydroxides. Of all the metals, Cd appears to be the most mobile element and Zn has preferentially accumulated more in the sediments. The apparent mobility and potential bioavailability of the metals have been found to be in the order of Cd > Pb > Zn > Cu

METAL CONTAMINATION DUE TO MINING AND MILLING ACTIVITIES AT THE ZAWAR ZINC MINE, RAJASTHAN, INDIA .2. DISPERSION IN FLOODPLAIN SOILS OF STREAM

The Tiri river carrying mine discharges and milling effluents frequently inundates its floodplains. Fresh deposition of metal-contaminated sediments is mixed with the top soils by ploughing and biological activity, and has caused a considerable increase in the heavy-metal concentration of top soil. Samples collected from the top soils on the floodplain have been analysed for Pb, Zn, Cu, Cd, Fe and Mn to recognize the extent of contamination and geochemical process of dispersion. With the help of simple statistics and curvilinear regression analysis a distance-decline pattern in levels of heavy metals on the floodplain soils is recognised. Correlation matrix and R-mode factor analyses of normalised soil metal data have been used to study the relationship among the different geochemical pools taking up metals in the soil. The R I factor indicates contribution from gross lithology of the terrain and association of Cu with this factor advocates it to be autochthonous. Pb-Zn-Cd with minor contribution from Fe-Mn-Cu in the R II factor are considered to be input from mine discharges. Atmospheric dust fallout and flash flooding of the river bank are the two factors contributing metals to the top soil. ''Easily exchangeable'', ''carbonate-bound'', ''reducible'' (bound to multiple hydroxides of Fe and Mn), ''oxidisable'' (organically bound and sulphidic) and ''lithogenic phase'' are the five operationally defined geochemical pools into which the heavy metals are positioned in the soil. Scavenging capacities (SC's) of these geochemical pools have been estimated for each heavy metal and competition ratios (CR's) are computed to examine the relative affinity of the metals for the above-mentioned pools. The reducible phase for Pb, and organics for Zn and Cu, and carbonates for Cd are found to be the dominant sinks in the floodplain soils

Application of molecular dynamics to evaluate the design performance of low aspect ratio carbon nanotubes in fibre reinforced polymer resin

In this paper, a methodology is developed to evaluate the design performance of polymer resin in a carbon fibre reinforced composite using atomistic simulation. Critical values are determined for strain invariants and related to the structural performance of the material system. The usefulness of the approach is demonstrated by evaluating the addition of low aspect ratio single walled carbon nanotubes (CNTs) to epoxy resin. Elastic modulus and strain invariants are evaluated to interpret the effect on the stiffness of the resin and resistance to distortional and dilatational failure

A fatigue life prediction model for Chopped Strand Mat GRP at elevated temperatures

Sul, J ORCiD: 0000-0003-0982-0921Experimental and analytical investigations for the low cycle-fatigue life prediction of Glass-Reinforced Polymer (GRP) in Chopped Strand Mat (CSM) form are studied. Based on the theories of modulus degradation and residual strength degradation, a novel model is proposed for the prediction of progressive stiffness loss in terms of tension–tension fatigue load and the number of cycles. The proposed model involves various loadings and environmental variables, which makes the reliable predictions suitable for structural analysts. Experiments were carried out at room and elevated temperatures to evaluate the validity of the proposed prediction model for the characterisation of temperature-dependent behaviour in fatigue. Predictions using the proposed model are in good agreement with the experiments that justify the use of the model to determine the extent of low-cycle fatigue damage accumulation in GRP–CSM at room and elevated temperatures

Improved crack resistance and fracture toughness using MWCNTmodified epoxy for delaminated composite structures

We studied the mechanical and fracture properties of multi walled carbon nanotube (MWCNT) reinforced epoxy composites motivated by an extensive literature review that confirmed nanocomposites with around 3% by weight MWCNTs. As they arevery efficient in arresting any potential cracks. Such nanocomposites have also been shown to prevent crack propagation by the possible mechanism of crack bridging, as well as exhibition of excellent mechanical properties. The initial phase of our experimental study – which comprised specimen preparation and tensile testing of MWCNT-epoxy composites – has concluded that there is excellent improvement in mechanical properties even with lower amounts of MWCNTs in the composite. We found with 0.3% by weight MWCNT in epoxy composite improves the mechanical properties by 75%, as exhibited in the modulus, ultimate tensile strength, and toughness from a tensile test on a dog-bone shaped specimen. Of interest, 0.1% MWCNT-epoxy specimen shows an overall increase by 20% in the mechanical properties. An intermediate experimental investigation of variation in sonication time intervals, curing temperatures, and curing time intervals indicated a minor deviation of around 4-5% in the mechanical properties, thus concluding that initial tensile improvements are robust against process conditions

AN INVESTIGATION INTO FATIGUE CRACK GROWTH THROUGH A WELD TOE RESIDUAL STRESS FIELD

Welds are a common method of joining metallic components in buildings, bridges and offshore structures, but they are susceptible to fatigue crack initiation and slow but accelerating growth arising due to fluctuating service loads, eventually resulting in fracture unless detected. Recently developed and unique Hellier-Brennan-Carr (HBC) parametric equations give the surface stress concentration factor (SCF) and stress distribution through the main plate thickness (i.e. the potential Mode I crack plane) at a T-butt weld toe as a function of a wide variety of weld geometries, for tension (membrane) loading. An existing Brennan-Dover-Karé-Hellier (BDKH) parametric equation is available for T-butt weld toe stress intensity factor (SIF) geometric Y-factor at the deepest point of a semi-elliptical surface crack, also subject to tension (membrane) loading. Three fatigue crack propagation programs have been written in FORTRAN. FATIGUE1 utilises the BDKH tension equation and the Paris Law to predict the (Stage 2) fatigue propagation life of a T-butt weld containing an initial semi-elliptical surface flaw. FATIGUE2 utilises the BDKH tension equation in conjunction with the Forman Equation to predict the semi-elliptical flaw fatigue life in the presence of a mean applied stress (i.e. with fixed stress ratio R > 0). FATIGUE3 utilises both the BDKH tension equation and the HBC tension equation in conjunction with the Forman Equation to predict the semi-elliptical flaw fatigue life in the presence of a known residual stress distribution from the literature (for 350 grade structural steel). The maximum and minimum stress values are calculated at each incremental crack length, from the applied stress at the crack tip given by the HBC tension equation added to the discretised value of residual stress at the same point. Thus the R-ratio is recalculated at the crack tip for every crack increment. Positive R-ratios increase the fatigue crack propagation rate; negative values result in some crack closure, reducing the propagation rate

A Massive Open Online Course (MOOC) on engineering mechanics: data analytics informing learning design and improvement

Our MOOC on Engineering Mechanics aims to develop in our learners ‘Engineers’ eyes’. Over 50 small videos support three interdependent strands: experiments that learners can do themselves; classical Engineering Analysis; and design applications. Learning activities span the technology spectrum from on-line Adaptive Tutorials to paper and pencil ‘Retro Tutorials’. It all produces a flood of data on student backgrounds, their progression, and their response to the course. To avoid being overwhelmed by this invaluable resource, we have automated the analysis. Attrition rates are typical of MOOCs (despite continuous improvement), but learners who stay the course give glowing reports

An Investigation into Fatigue Crack Growth through a Weld Toe Residual Stress Field

Welds are a common method of joining metallic components in buildings, bridges and offshore structures, but they are susceptible to fatigue crack initiation and slow but accelerating growth arising due to fluctuating service loads, eventually resulting in fracture unless detected. Recently developed and unique Hellier-Brennan-Carr (HBC) parametric equations give the surface stress concentration factor (SCF) and stress distribution through the main plate thickness (i.e. the potential Mode I crack plane) at a T-butt weld toe as a function of a wide variety of weld geometries, for tension (membrane) loading. An existing Brennan-Dover-Karé-Hellier (BDKH) parametric equation is available for T-butt weld toe stress intensity factor (SIF) geometric Y-factor at the deepest point of a semi-elliptical surface crack, also subject to tension (membrane) loading. Three fatigue crack propagation programs have been written in FORTRAN. FATIGUE1 utilises the BDKH tension equation and the Paris Law to predict the (Stage 2) fatigue propagation life of a T-butt weld containing an initial semi-elliptical surface flaw. FATIGUE2 utilises the BDKH tension equation in conjunction with the Forman Equation to predict the semi-elliptical flaw fatigue life in the presence of a mean applied stress (i.e. with fixed stress ratio R > 0). FATIGUE3 utilises both the BDKH tension equation and the HBC tension equation in conjunction with the Forman Equation to predict the semi-elliptical flaw fatigue life in the presence of a known residual stress distribution from the literature (for 350 grade structural steel). The maximum and minimum stress values are calculated at each incremental crack length, from the applied stress at the crack tip given by the HBC tension equation added to the discretised value of residual stress at the same point. Thus the R-ratio is recalculated at the crack tip for every crack increment. Positive R-ratios increase the fatigue crack propagation rate; negative values result in some crack closure, reducing the propagation rate

Application of molecular dynamics to evaluate the design performance of low aspect ratio carbon nanotubes in fibre reinforced polymer resin

In this paper, a methodology is developed to evaluate the design performance of polymer resin in a carbon fibre reinforced composite using atomistic simulation. Critical values are determined for strain invariants and related to the structural performance of the material system. The usefulness of the approach is demonstrated by evaluating the addition of low aspect ratio single walled carbon nanotubes (CNTs) to epoxy resin. Elastic modulus and strain invariants are evaluated to interpret the effect on the stiffness of the resin and resistance to distortional and dilatational failure