bluuebunny/crossref_metadata_2025 huggingface dataset:
EnvDB, a database for describing the environmental distribution of prokaryotic taxa
Authors: Pignatelli Miguel , Moya Andrés , Tamames Javier
Published: April 2009

EnvDB is a database that classifies the environmental samples and their associated 16S rDNA sequences currently stored in GenBank. The samples were categorized in a three‐level, hierarchical classification of media: the five upper levels (terrestrial, aquatic, thermal, host‐associated and other) are further decomposed in 20 intermediate (such as marine, marine sediments, freshwater, soil, gut, etc.) and 47 lower levels (for instance, soil is further decomposed in forest, agricultural, wetlands, grasslands, tropical, arid, etc.). Each sample was also characterized with nine environmental features: polluted, diseased (for clinical samples), acidic, alkaline, hot environment, cold environment, saline, anoxic and restricted (when the study is focused only in particular taxonomic groups). The classification of samples was aided by text‐mining techniques, complemented with careful curation and completion by human experts. EnvDB currently includes 359 928 sequences from 3502 samples. The sequences were clustered at several identity levels to obtain operative taxonomic units (OTUs). Sequences and OTUs have been taxonomically assigned to the maximum possible resolution by different procedures. The user can obtain information about sequences, OTUs, samples and environments, combining these tables using a flexible querying system that allows generating very diverse queries. Thus, the user can easily inspect the presence and abundance of particular taxa in particular samples and environments. The database also allows the users to run analyses with their own data: users can input their sequences and find the closest sequences or samples in the database. EnvDB can be accessed in the web address http://metagenomics.uv.es/envDB.
1,3-Dipolar cycloadditions of 5-(4-methoxyphenyl)- and 5-(1H-indol-3-yl)-substituted (1Z,4R*,5R*)-1-(arylmethylidene)-4-benzamido-3-oxopyrazolidin-1-ium-2-ides to olefinic dipolarophiles
Authors: Pezdirc Lidija , Stanovnik Branko , Svete Jurij
Published: April 2009

1,3-Dipolar cycloadditions of (1Z,4R*,5R*)-1-(arylmethylidene)-4-benzamido-5-(4-methoxyphenyl)-3-oxopyrazolidin-1-ium-2-ides 6a–6f and their 5-(1H-indol-3-yl) analogues 6g–6j to olefinic dipolarophiles 7–9 were studied. Stereochemistry was controlled by the structure of dipoles 6 and dipolarophiles 7–9. Reactions of ortho-unsubstituted dipoles 6a–6c, 6g gave the major isomers 10 and 14 with syn-oriented protons H-3 and H-5, whilst ortho-disubstituted dipoles 6d, 6e, 6j gave cycloadducts 11 and 12 with anti-oriented protons H-3 and H-5. In comparison with their 5-phenyl-substituted analogues, dipoles 6a–6e, 6g, 6j were less reactive in cycloadditions to olefinic dipolarophiles 7–9. This was reflected in longer reaction times, lower yields, and sometimes in lower selectivity as well. The relative configurations of cycloadducts were determined by NMR.
Strength of tree roots and landslides on Prince of Wales Island, Alaska
Authors: Wu Tien H. , McKinnell III William P. , Swanston Douglas N.
Published: April 2009

The stability of slopes before and after removal of forest cover was investigated. Porewater pressures and shear strengths were measured and the soil properties were determined by laboratory and in situ tests. A model of the soil–root system was developed to evaluate the contribution of tree roots to shear strength. The computed safety factors are in general agreement with observed behaviors of the slopes. Decay of tree roots subsequent to logging was found to cause a reduction in the shear strength of the soil–root system.
Hydrogeological testing associated with underground coal gasification
Authors: Vogwill R. I. J.
Published: April 2009

Four aquifer tests were completed at a site near Forestburg, Alberta, in order to determine aquifer parameters of a coal seam and thus aid in the evaluation of an underground gasification experiment and assess the effects of gasification on the groundwater regime.Analysis of the two pre-gasification aquifer tests indicated that the coal seam was a confined aquifer with small aquifer parameters and a strongly anisotropic hydraulic conductivity that appeared unrelated to known regional fracturing directions. The effect of this anisotropy on controlling directions of gasification was not established.The first post-gasification aquifer test indicated that the groundwater regime of the coal seam had been changed in various ways. Regionally, a general increase in hydraulic conductivity and a more pronounced anisotropy were observed. On a smaller scale, storage coefficients in the gasified block were greatly increased due to a change in the physical character of the coal. Subsequent excavation that exposed the gasified block confirmed these observations.The second post-gasification aquifer test indicated that fracturing in the coal seam was not consistent and that in undisturbed coal seams the direction of regional major fracturing and the major axis of anisotropy do, in fact, coincide.
Construction of Saline Creek Tunnel in Athabasca Oil Sand
Authors: Chatterji P. K. , Smith L. B. , Insley A. E. , Sharma L.
Published: April 2009

Undisturbed oil sand is very dense and has a relatively high in situ shear strength. However, there is gas present within the oil sand, which causes it to swell once confining pressures are removed, and this results in a significant reduction in the strength of the material. Consequently, this swelling behaviour is a major concern in the design of tunnels in oil sand.Saline Creek Tunnel, located immediately south of the town of Fort McMurray, Alberta, is the first permanent tunnel constructed in the Athabasca Oil Sand. The finished diameter of the tunnel is 4.4 m and the tunnel is about 107 m long of which approximately 73 m is entirely within medium to rich oil sand. The maximum depth of overburden above the tunnel crown is 27.5 m.This paper documents the geotechnical investigation and design of the tunnel. The method of construction and the temporary and permanent tunnel support systems are described. Detailed observations on the behaviour of the oil sand around the tunnel opening during construction are also presented.
Normal and shear stress measurements on a strip footing
Authors: Bauer G. E. , Shields D. H. , Scott J. D. , Nwabuokei S. O.
Published: April 2009

This paper deals with the choice, calibration, and use of earth pressure cells in the measurement of the contact stress distribution across a strip footing. The footing was 30 cm wide, rough, and rigid; the measurements were made in a laboratory with the footing bearing on compact to dense, air dry, uniform, crushed quartz sand.Typical test results are compared with the theoretical distributions of both shear and normal stresses that have been proposed by various authors.
Structural behaviour of the Manicouagan 3 cutoff
Authors: Dascal Oscar
Published: April 2009

A positive double cutoff wall was used to control the foundation seepage and to minimize the danger of piping, for a 107 m (350 ft) high earthfill dam founded on 126 m (420 ft) of pervious and highly compressible alluvial deposits.At the end of the first year of operation (Dec., 1976), the cutoff walls had deflected 285 mm (11.2 in.) downstream and had been vertically compressed by 140 mm (5.5 in.). These deformations were caused by the combined action of the weight of the dam and the reservoir load and were monitored by a comprehensive instrumentation.The reading of the instruments indicates that 85% of the vertical deformation in the walls is mainly due to the load transmitted by the negative skin friction between the walls and the surrounding compressible alluvium, whereas the compression induced by the dam's weight, transferred directly through the inspection tunnel (acting as a pile cap), is only 15%. A large part of the wall's compression is attributed to the creep of the concrete.The presence of an arching effect in the foundation due to the particular shape of the canyon has been confirmed by the instrument readings. This phenomenon was previously brought to light by the finite element analysis.The structural analysis of the behaviour of the cutoff walls confirms the necessity of the twin walls, because the stresses induced in the single wall (negative friction on both sides) would have been dangerously close to the ultimate strength of the concrete.
A new method of sampling in sensitive clay
Authors: Lefebvre Guy , Poulin Claude
Published: April 2009

Many recent publications on the influence of sampling techniques indicate that, generally speaking, the quality of the samples increases with the diameter of the sampling equipment. However, all studies also conclude that even the large diameter samplers available on the market substantially damage the structure of the clays of eastern Canada, as compared to the sample quality obtained by block sampling. In addition to the difficulties associated with the excavation of the trenches necessary for block sampling, the depth of block sampling is limited, at least in soft clays.The sampling technique described in the present paper allows the retrieval of deep blocks, working from the ground surface and using a cutting method quite similar to that used for conventional block sampling. The large diameter borehole is filled with water or bentonite slurry to reduce the possibility of bottom heave. By comparing the results of unconfined compression tests it is shown that the samples obtained by this method are of a quality equal or superior to that of blocks sampled conventionally at the bottom of open cuts.
The bellow-hose settlement gauge
Authors: Bozozuk M. , Fellenius B. H.
Published: April 2009

Bellow-hose settlement gauges were used to measure vertical soil heave during the installation of concrete piles in sensitive marine clay. The equipment is described and the sources of error are discussed.
Hydroturf
Authors: Mitchell Robert , Komos Fadel El
Published: April 2009

As part of a general study of various applications of hydraulic stabilization in earthworks, a project on hydraulic stabilization of turfed surfaces was initiated. The principle use of a hydraulically stabilized turfed surface (Hydroturf) is to improve the performance characteristics of natural turf sports fields under adverse weather conditions. Hydroturf is composed of any natural topsoil underlain by a filter medium that can be maintained at pressures less than atmospheric pressure.Model tests reported in this paper show that the benefits of Hydroturf are increased surface strength under wet conditions and internal drainage of surface water during rainfall. The Hydroturf system is designed for temporary hydraulic stabilization and would generally be operated only when the surface is in use during rainfall. Hydroturf offers an economical alternative to artificial turfs for all-weather sports surfaces and is ideal for improving existing natural turf fields where only heavy-wear areas need to be improved.
Foundation problems in Champlain clays during droughts. II. Case histories
Authors: Silvestri V. , Soulié M. , Lafleur J. , Sarkis G. , Bekkouche N.
Published: April 2009

This paper presents the results of a 3 year monitoring program of the volumetric water content in two clay deposits on Montréal Island. The water content was monitored by means of a neutron depth moisture probe, which was lowered down in a series of 3–6 m deep, permanently installed, aluminium access tubes. These tubes are located at various distances from deep-rooted trees on two experimental sites. On the first site, a two-storey reinforced concrete building, surrounded by four rows of 15–20 m high silver maples, has suffered a differential settlement of over 150 mm. On the second site, a three-storey apartment block, surrounded on two sides by a row of 5–10 m high maples, has suffered a differential settlement of about 50 mm. The paper analyses the volumetric water content variations and compares them with both the rainfall deficits calculated for the period of observation and the elevation profiles of the building foundations. In addition, a comparison is made between the observed damages and a classification proposed by the Building Research Establishment of England. Key words : volumetric water content, trees, settlement, distortions, clay deposits, seasonal variations, damages.
Failure of a linear Voussoir arch: a laboratory and numerical study
Authors: Stimpson B. , Ahmed M.
Published: April 2009

The design of underground openings in horizontally layered strata on the basis of classical linear arching theory assumes the ultimate load capacity of the roof is limited by crushing or compressional failure at the centre of the arch or at the abutments. In this study, physical model tests on limestone, granite, and potash beams revealed a progressive failure mechanism dominated by discrete tensile fracturing, a quite different failure process to that assumed by classical theory. Subsequently, discrete crack propagation finite element analysis successfully simulated the failure mechanisms observed in the physical models. Key words : rock mechanics, underground design, roof stability, Voussoir arch, fracture.
Volume change indices during loading and unloading of an unsaturated soil
Authors: Ho D. Y. F. , Fredlund D. G. , Rahardjo H.
Published: April 2009

The paper presents the volume change theory and the designation of associated soil properties that must be measured for an unsaturated soil. The equipment required for the measurement of each of the relevant volume relationships is described. Several testing procedures for obtaining the volume change indices during loading and unloading of an unsaturated soil are presented. Typical results from loading and unloading tests on compacted silt and compacted glacial till specimens are presented and analyzed. The analysis is given in order to illustrate the application of the volume change theory to practical problems. Key words : unsaturated soil, volume change indices, constitutive relations, coefficients of volume change, oedometer tests.
Centrifugal testing of laterally loaded piles in sand
Authors: Georgiadis M. , Anagnostopoulos C. , Saflekou S.
Published: April 2009

Results of an investigation of the response of piles in sand, under lateral loads, are presented. Model piles of three different diameters and flexural stiffnesses were tested in a centrifuge apparatus to determine prototype pile behavior. The experimental results, consisting of pile head displacements and bending moment distributions along the pile length, were interpreted, analyzed, and compared with the results of several numerical analyses. The piles were treated as elastic beams on nonlinear springs, examining several different types of soil reaction relationship (p-y curves). A new p-y relationship was developed for piles in cohesionless soil which provided very satisfactory results. Key words : pile, sand, lateral loading, centrifuge, numerical analysis.
Random trials used in determining global minimum factors of safety of slopes
Authors: Chen Zu-Yu
Published: April 2009

The minimum factor of safety of a slope can be found by using various methods of optimization or by random search. This paper presents a combined approach that uses the random search to find an estimate of the global minimum which is employed by the methods of optimization as a starting point. Guidelines have been given to select an appropriate number of random trials. Two simplified methods for calculating the factors of safety are suggested to minimize the computing time of the random searches. The approach has proved to be more efficient than either a purely stochastic or a deterministic one. Key words : slope stability, landslide, factor of safety, critical slip surface, method of optimization, random search, Monte Carlo method.
Lateral load tests to examine large-strain (seismic) behaviour of piles
Authors: Naesgaard Ernest
Published: April 2009

Three different 406 mm diameter piles were tested with lateral, vertical, and moment loadings. The purpose of the full-scale field tests was to assess the ability of the piles to withstand large lateral deformations that may be caused by earthquake-induced soil liquefaction. Two concrete shaft piles were tested to failure with lateral displacements at the pile top of up to 300 and 650 mm and pile curvatures of up to 0.16 and 0.35 rad/m, respectively. The third pile, a concrete-filled steel pipe shaft pile, reached a maximum lateral displacement at the pile top of 550 mm and a curvature of 0.08 rad/m without failure or significant distress. It is concluded that stronger piles that push through the soil may tolerate larger lateral displacements than weaker piles and that reducing the spiral reinforcing pitch from 150to 100 mm on concrete piles greatly increases the pile ductility. Key words : lateral load test, piles, reinforced concrete, concrete-filled pipe, seismic, liquefaction, pile curvature.
Simplex reflection analysis of laboratory strength data
Authors: Shah Sandip , Hoek Evert
Published: April 2009

Linear regression and simplex reflection techniques for fitting laboratory strength data for rocks and soils to linear and nonlinear failure envelopes are presented. The simplex reflection technique is applied to the Hoek-Brown nonlinear failure criterion which is widely used for estimating the strength of jointed rock masses. A comparison between the simplex reflection technique and linear regression analysis, for assessing the parameters associated with the Hoek-Brown criterion, is discussed. The strengths and limitations of the two techniques are compared, and it is established that the simplex technique is superior for fitting the data to any nonlinear criterion. The implementation of the simplex reflection method is presented together with an algorithm in the form of a pseudocode for use on computers. Key words : linear regression, simplex reflection, failure criterion, stress, residuals.
Limiting equilibrium, closed-form elastic, and numerical plastic analyses of stability of earth wall reinforced with grouted rebar nails and cable anchors
Authors: Kirsten H. A. D.
Published: April 2009

Detailed rigorous analyses for nail-reinforced excavation faces are not available. Limiting equilibrium, closed-form elastic, and numerical plastic analyses were accordingly developed as alternatives for the design of a 12 m deep excavation. It is shown that the nails subject the monolith to constant horizontal compressions equal to active pressures for the limiting equilibrium and elastic analyses. The corresponding boundary condition on the front surface is shown to be more accurate than considering the support as an anchored bulkhead in classical terms. In addition to the compressions induced by the reinforcement, the rear surface is considered to be subject to active pressures and to active pressures net of the cohesion of the retained mass as alternative loadings in the limiting equilibrium and elastic analyses. It is shown that a reliable design result could be obtained for this case by considering the rear surface to be subjected to active pressures net of 50% of the cohesion of the retained mass in addition to the horizontal compressions induced by the nails. The factors of safety against shearing failure at the toe and heel exceed unity, those for the limiting equilibrium analysis being more divergent than those for the elastic and plastic analyses. Otherwise, the various analyses gave similar factors of safety. The horizontal displacements determined from the elastic analysis for active pressures net of the cohesion of the retained mass corresponded closely to that actually observed under stable conditions. Those determined from the plastic analysis underestimated the observed displacements. The horizontal displacements determined from the plastic analysis for a simulated condition of failure compared closely with that observed. Key words : limiting, equilibrium, elastic, numerical, plastic, analysis, earth, wall, nails, anchors.
Application of empirical performance criteria and limiting equilibrium principles in design of an earth wall reinforced with grouted rebar nails and cable anchors
Authors: Kirsten H. A. D. , Dell A. G.
Published: April 2009

Soil nailing was employed to support the cut faces of a basement excavation for an apartment building. The layout detail and construction methods and procedures were similar to other successful applications of the technique with regard to depth of excavation, type of soil, width to height proportion of the reinforced monolith, spacing of nails, hole and reinforcement diameter, bench height, and drainage system. The design was based on limiting equilibrium principles with regard to two loading conditions, namely, active pressures and active pressures net of the cohesion of the retained mass. In the short term the monolith was free standing, and in the long term it was propped off the building in front of it. It was found for the short-term active loading case that the material in the lower sections of the front surface of the monolith and at the toe in the base was marginally overstressed. The factors of safety for the long-term active loading case exceeded unity by acceptable margins. The monolith was not overstressed for the active pressures net of the cohesion of the retained mass in the short or long term. The long-term stability of the monolith with regard to failure on deeply seated circular slip surfaces was also adequate. Key words : basement, excavation, reinforced, soil, nails, anchors, limiting, equilibrium.
A stochastic analysis of pollutant migration to evaluate the performance of clay liners
Authors: Layang J. , Rahman M. S.
Published: April 2009

A stochastic analysis is presented for the evaluation of the performance of a clay liner. The transport of a single solute through a clay liner under a landfill or lagoon is modelled by a one-dimensional advection-dispersion equation. The governing equation is solved by an available semianalytical method. The uncertainties associated with various model input parameters are studied using Monte Carlo simulation. The risk of aquifer contamination is evaluated in terms of probability of exceedance of the pollutant concentration over specified critical levels. Key words : stochastic, analysis, pollutant, migration, clay, liners, reliability, advection, dispersion, absorption.
Influence of cycling pore-water pressures and principal stress ratios on drained deformations in clay
Authors: Eigenbrod K. D. , Graham J. , Burak J.-P.
Published: April 2009

Seasonal changes in groundwater levels affect the rate of downhill creep movements in slopes. This process has been studied in triaxial tests on undisturbed specimens of a natural clay from Bluefish Lake, 50 km north of Yellowknife, N.W.T. Specimens were first anisotropically consolidated to low stresses that correspond to conditions at shallow depths in creeping slopes. Pore-water pressures (back pressures) in the specimens were then cycled systematically (over periods lasting 4–48 h) with the drainage leads open. Resulting axial and volumetric strains were measured, and shear and lateral strains deduced from them. Strain rates decreased with increasing total times of testing. They increased with increasing values of the ratio Δu/Δuf, with increasing values of deviator stress q, and with decreasing values of [Formula: see text]. Systematically increasing the pore-water pressures in the specimens produced clear estimates of failure at low stresses. Key words : slope, clay, creep, cyclic loading, ground water, triaxial.
Effect of loading history on the compression and uplift capacity of driven model piles in sand
Authors: Joshi R. C. , Achari Gopal , Kaniraj Shenbaga R.
Published: April 2009

Model piles were tested in dry uniform sand to study the effect of loading history on the behaviour of piles in compression and tension. A sand bed was prepared by the raining technique, and a smooth cylindrical instrumented pile was driven into the sand. Load tests on piles were conducted at a constant rate of penetration of 0.5 mm/min. The effects of length to diameter (L/D) ratio and sand density were also investigated. The load transfer along the pile surface was studied for an L/D ratio of 33. The pile tip resistance was measured for model piles with L/D ratios of 20–33 and was generally found to be constant. A significant decrease in the pile capacity both in tension and compression was noted for piles having a loading history. When a pile was loaded in compression after being loaded in tension, the tip load could be mobilized only after a certain movement of the pile. The mobilization of the shaft load, however, started immediately. Key words : load tests, model piles, dry sand, loading history, tip capacity, shaft capacity, compression, tension, load transfer.
MICROSTRUCTURE AND TENSILE PROPERTIES OF SQUEEZE CASTMg-Al-CaALLOYS
Authors: MASOUMI MOHSEN , ZHANG QIANG , HU HENRY
Published: April 2009

Microstructure and tensile properties of squeeze cast Mg - Al - Ca alloys with different levels of calcium addition (AMC50X) were studied. The microstructural analysis by optical and scanning electron microscopy (SEM) shows that the squzeeze cast Mg - Al - Ca alloys contain primary α- Mg , ( Al , Mg )2Ca and Mn - Al intermetallic while the base alloy AM50 contains primary α- Mg , β- Mg12Al17and Mn - Al intermetallic. The addition of calcium varying from 1 to 4 wt.% increases the fraction area of Ca -containing secondary phases from 9.5% to 19.5%. The experimental observation confirms also that the calcium has a grain refining effect on the base alloy AM50A. The tensile testing results indicate that, as the calcium content of AMC50X alloys increases from 0 to 4%, the ultimate tensile strength (UTS) and elongation ( Ef) decrease dramatically at room temperature as their yield strengths (YS) improves slightly. At 150°C, however, both the UTS and YS of the alloys increase with increasing the Ca content.
HOT COMPRESSION BEHAVIOR OF ONE KIND OF META-STABLE β TITANIUM ALLOY
Authors: ZENG LIYING , GE PENG , MAO XIAONAN , ZHAO YONGQING , ZHOU LIAN
Published: April 2009

One kind of meta-stable β titanium alloy with grain sizes less than 1µm was developed using conventional plastic deformation process in Northwest Institute for Nonferrous Metal Research (NIN). The so called Ti - B 19 alloy ( Ti - Al - Mo - V - Cr - Zr ) possesses excellent strength and toughness. In order to excavate the potential workability of the alloy, isothermal compression tests were carried out on the Gleeble-1500 thermal simulator at the temperature from 750°C to 1000°C and strain rate from 0.001 s-1 to 10s-1. The results indicate that the flow stresses of the alloy will be heavily influenced by the strain rates and deformation temperature. The flow stress decrease with the increase of deformation temperature, and increase with the increment of strain rates. A constitutive equation for the flow stress has been defined and the test conditions for a homogeneous deformation evaluated, and the material constants including activation energy Q , stress exponent n and constant ln ( A ) were also obtained.
THE EFFECT OF FE ADDITIONS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A Ti-Al-Mn ALLOY
Authors: BETTLES C. J. , PUEHRINGER T. , MORTON A. J. , TOMUS D. , GIBSON M. A.
Published: April 2009

Alloys in the dilute Ti - Al - Mn system, which are considered to be near-α alloys, possess an attractive combination of strength and ductility, with the room temperature properties being intermediate between CP Ti and Ti -6 Al -4 V . Low levels of Fe are often tolerated in such alloys, but rarely introduced as deliberate alloying additions (with the exception of CP Ti grades), and from a processing perspective, it may indeed be desirable to have higher tolerances for Fe as it is often a common contaminant which must be controlled. In this presentation, the effect of 0.3 wt .% Fe on the microstructure and behavior of a Ti -0.75 wt .% Al -0.75 wt .% Mn is reported. It was found that annealing in the (α+β) phase field can lead to an increase in the ductility of the alloy without having a detrimental effect on the tensile strength.
REVIEW AND APPLICATIONS OF THERMAL CONDUCTIVITY MODELS TO ALUMINUM CELL SIDEWALL REFRACTORIES
Authors: PAN YUHUA , WRIGHT STEVEN , SUN SHOUYI
Published: April 2009

Silicon nitride bonded silicon carbide ( Si 3 N 4- SiC ) refractories are commonly used as the sidewall of aluminum electrolysis cells. They have to withstand an extremely corrosive molten electrolyte bath for long periods. The sidewall is normally protected with a layer of solidified electrolyte (called frozen ledge), which is sensitive to the thermal conductivity of the sidewall. In this work, through review of the literature on modeling methods for predicting the effective thermal conductivity of dense composites and porous materials, some selected methods were applied to calculate the effective thermal conductivity of Si 3 N 4- SiC refractories. The model predictions were compared with the thermal conductivity of a commercial Si 3 N 4- SiC refractory measured by using laser flash technique. The present study showed that, due to multi-phase nature and complex microstructure of Si 3 N 4- SiC refractories, most of the selected modeling methods individually do not give satisfactory predictions in one step. Recursive applications of one method or combinations of different methods are capable of giving satisfactory predictions.
MEASUREMENTS OF HEAT LOSSEST DURING SOLIDIFICATION OF LIGHT MEALS
Authors: DARGUSCH M. S. , HAMASAAID A. , DOUR G. , YAO X.
Published: April 2009

This paper describes the application of a new in-cavity thermal measurement method to determine the heat flux and calculate heat losses during high pressure die casting of aluminium A380 alloy and the magnesium alloy AZ91-D. Thermal management of the die is a critical concern in high pressure die casting and the development of microstructures after solidification. Detailed measurements were performed using infra-red probes linked to pyrometric chains and thermocouple arrays that accurately determine both casting and die surface temperatures enabling the determination of heat flux densities and interfacial heat transfer coefficients and the rapid evolution of these values with time during high pressure die casting of these alloys. The energy losses during the spray cycle can then be determined by integrating the heat flux curves for the duration of the spray application. The significance of the findings presented in this investigation arise from the uniqueness of the measurement methods applied to the determination of heat flux during the high pressure die casting of both magnesium and aluminium alloys. In particular the detailed knowledge of the thermal characteristics occurring at the cavity fill stages of the die casting process achieved through the selection of an array of fine rapid-response thermocouples integrated in one sensor along with the light pipe/pyrometric chain have enabled the accurate measurement of both the die and metal surface temperatures through the entire die casting cycle enabling the calculation of heat losses during solidification and processing.
INFLUENCE OF INITIAL MICROSTRUCTURE ON HOT WORKABILITY OF Ti-6Al-4V ALLOY
Authors: YEOM JONG-TAEK , KIM JEOUNG HAN , HONG JAE-KEUN , PARK NHO-KWANG , LEE CHONG SOO
Published: April 2009

Hot workability of Ti -6 Al -4 V alloy with different initial microstructures was investigated by considering processing maps and the dynamic material deformation behavior. The emphasis has been focused on the effect of initial microstructure (equiaxed versus bimodal structure). Process maps were generated using the dynamic material model (DMM), unifying the relationships between constitutive deformation behavior, hot workability and microstructures evolution. Also, the flow instability was investigated using the various flow instability criteria and microstructural analysis. To establish the processing maps with different initial microstructures, high temperature compression tests were carried out at various temperatures and strain rates up to a true strain of 0.7. Microstructural changes occurring during the deformation were analyzed in terms of high temperature deformation mechanisms. Finally the useful instability criterion for predicting the forming defects was suggested through the compression test results with different temperatures and strain rates.
EFFECT OF CARBON AND OXYGEN ADDITIONS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Ti-4.3Fe-7.1Cr-3Al ALLOY
Authors: SONG XIPING , CHEN LONG , LI KUN , CHEN GUOLIANG
Published: April 2009

The effects of carbon and oxygen additions on the microstructure and mechanical properties of a new type low-cost beta titanium alloy Ti -4.3 Fe -7.1 Cr -3 Al have been studied. The results showed that with the carbon addition the grain size was refined significantly, followed by the tensile strength increase and ductility improvement. At 0.2 wt.% carbon addition the 0.2%YS increased by 22% and elongation increased to a peak value of 23%. Also with the carbon addition the oxygen content in the alloy could be allowed to reach 0.2wt.% without tensile property decrease. After ageing treatment, it was found that ageing temperature other than carbon content played a key role on the α-phase precipitation and ageing hardness. The hot-rolling deformation accelerated the ageing response. The optimal ageing process was decided to be 500°C for 1h under the pretreatment of 850°C hot-rolling followed by immediately water quenching. The reasons for these improvements were discussed in terms of the carbide pinning and α-phase precipitation.
RESEARCH ON ALLOYING TECNIQUES OF MISCHMETAL IN DIE CASTING MAGNESIUM ALLOY
Authors: XU YULEI , ZHANG KUI , LI XINGGANG , ZHANG KANG , LEI JIAN , YUAN HAIBO
Published: April 2009

An aim of the experiments is to study alloying techniques of dollop-like MM , as-cast and extruded Mg - MM master alloy in die casting AZ91D magnesium alloy at conventional cold chamber die casting temperature. The as-cast AZ 91 D -1.2 wt % MM alloys were prepared and MM was added by different way at 720°C. The results showed that the efficiency of alloying achieved less than 50% within 30 min when dollop-like MM was added. When MM was added by as-cast and extruded Mg -21 wt % MM master alloy, the efficiency of alloying was improved significantly. The microstructure and analytical studies were carried out using optical microscopy and differential scanning calrimetry (DSC). Testing results showed the Mg - MM master alloy could melt easily down at die casting temperature because Mg - RE phases with lower melting point were formed. The grain refining efficiency of the master alloy was improved by extrusion. The improvement could be attributed to the decrease in Mg - RE particle size and increase in the number of nucleating sizes for Mg . Then die-casting AZ 91 D -0.44 wt % MM test bars were produced with addition of extruded Mg -21 wt % MM master alloy and the efficiency of alloying was around 80%.
MECHANICAL PROPERTIES OF HIGH STRENGTH Al-Mg ALLOY SHEET
Authors: CHOI BONG-JAE , HONG KYUNG-EUI , KIM YOUNG-JIG
Published: April 2009

The aim of this research is to develop the high strength Al alloy sheet for the automotive body. For the fabrication Al - Mg alloy sheet, the composition of alloying elements was designed by the properties database and CALPHAD (Calculation Phase Diagram) approach which can predict the phases during solidification using thermodynamic database. Al - Mg alloys were designed using CALPHAD approach according to the high content of Mg with minor alloying elements. After phase predictions by CALPHAD, designed Al - Mg alloys were manufactured. Addition of Mg in Al melts were protected by dry air/Sulphur hexafluoride (SF6) mixture gas which can control the severe Mg ignition and oxidation. After rolling procedure of manufactured Al - Mg alloys, mechanical properties were examined with the variation of the heat treatment conditions.
MICROSTRUCTURAL EVOLUTION OF Al-Cu-Mg-Ag ALLOY WITH TRACE Zr ADDITION DURING TWO-STEP HOMOGENIZATION
Authors: MA FEIYUE , LIU ZHIYI
Published: April 2009

The microstructural evolution in an Al - Cu - Mg - Ag alloy with trace Zr addition during homogenization treatment was characterized by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDS). It was shown that the low-melting-point phase segregating toward grain boundaries is Al 2 Cu , with a melting point of 523.52°C. A two-step homogenization process was employed to optimize the microstructure of the as-cast alloy, during which the alloy was first homogenized at a lower temperature, then at a higher temperature. After homogenized at 420°C for 6 h, Al 3 Zr particles were finely formed in the matrix. After that, when the alloy was homogenized at an elevated temperature for a longer time, i.e., 515°C for 24 h, most of the precipates at the grain boundaries were removed. Furthermore, the dispersive Al 3 Zr precipitates were retained, without coarsening greatly in the final homogenization step. A kinetics model is employed to predict the optimal homogenization time at a given temperature theoretically, and it confirms the result in present study, which is 420°C/6h+515°C/24h.
HOT WORKABILITY DURING SUBTRANSUS DEFORMATION AT HIGHER STRAIN RATES OF TC11 ALLOY WITH WIDMANSTĂTTEN MICROSTRUCTURE
Authors: SONG HONGWU , ZHANG SHIHONG , CHENG MING , MEN FEI , BAO CHUNLING
Published: April 2009

The effect of processing parameters on hot workability and microstructure evolution during subtransus deformation of TC11 alloy with widmanstăten microstructure was studied using isothermal compression tests. Testing was conducted at strain rates of 0.1-10s-1, temperature ranges 920-980°C and height reductions of 30-70%. The influence of hot working parameters on flow behavior, hot workability and microstructure evolution was systemically investigated. The results showed that all the flow curves exhibited a peak stress at very low strains (<0.1) followed by extensive flow softening. Surface fracture, cavitations and localized shear flow were found to be main factors that limited the hot workability of TC11 alloy. At low strains, lamellar kinking started to occur due to the orientation between the colony α lamellar and stress axis. With deformation continues, reorientation of the lamellar colony occurred and the deformed lamellar became elongated and thinner. At high stains, segmentation and globularization of α lamellar took place to produce a refined microstructure with α grain size around 1 µm that is technologically desirable for secondary processes such as superplastic forming. A microstructure mechanism map based on the previous results was then established and applied to process design considering defect and microstructure control.
MORPHOLOGY EVOLUTION OF PRIMARY PARTICLES IN LSPSF RHEOCASTING PROCESS
Authors: Guo Hong-Min , Yang Xiang-Jie
Published: April 2009

Experimental and microstructure simulation approaches were taken to investigate the morphological evolutions of primary particles in an Al -20 wt % pct Cu alloy under LSPSF (low superheat pouring with a shear field) rheocasting conditions. The results indicate that crystals are globular and present in non-entrapped eutectic, after 3s of solidification. The morphology of these crystals during the subsequent free growth is determined by both the number of free crystals and the cooling intensity of melt. Analyzed results from microstructure simulation and two stability models suggest that the primary globular particles formed in the earlier stage of solidification can attain growth stability up to a larger size scale.
EFFECT OF Al-Ti-B ON MAGNESIUM ALLOY MICRO-ALLOYED WITH Ca
Authors: FANG CANFENG , QI GUOHONG , ZHANG XINGGUO , HAO HAI , JIN JUNZE
Published: April 2009

Effect of Al - Ti - B master alloy on the microstructure and mechanical properties was investigated in AZ31 magnesium alloys micro-alloyed with Ca . During the casting process, electromagnetic field was also introduced. The results suggest that the micro addition of Ca to magnesium alloy retards the oxidation rate during melting process, improves casting qualities of magnesium alloy ingots. The grain size of AZ31 magnesium alloy has been effectively reduced by optimum addition of 1 wt.% (designed composition) Al - Ti - B master alloy. In this process, the addition level of Ti is the key factor to affect grain size of magnesium alloy, in which two grain refinement mechanisms are built by both TiB 2 and residual Ti . Moreover, the electromagnetic field leads to uniform distribution of temperature field and solute field in the molten pool, increases casting qualities and refines grain size further.
MECHANICAL PROPERTIES AND MICROSTRUCTURE OF Mg-5Li-5Al-3Zn-xCd ALLOYS
Authors: LIU XUHE , WU RUIZHI , ZHANG MILIN
Published: April 2009

Mg -5 Li -5 Al -3 Zn - xCd ( x =0,2,3,4,5) alloys were prepared. The densities of these alloys were measured with Archimedes' method. The influence of Cd element on the microstructure and the properties of these alloys were also studied. The results indicate that these alloys possess low density ranging from 1.5 to 1.7 g·cm-3. The addition of Cd has the refining effect on the α- Mg phase and causes the formation of Mg 3 Cd intermetallic compound. The refinement and the formation of Mg 3 Cd improve the mechanical properties of alloys. When the Cd content is 3 wt.%, the tensile strength of alloy reaches its peak value(288 MPa).
THE NEW HEAT TREATMENT TECHNOLOGY OF A356 ALUMINIUM ALLOY PREPARED BY PTC
Authors: ZHANG LIANYONG , JIANG YANHUA , MA ZHUANG , WANG WENKUI
Published: April 2009

Phase Transition Cooling (PTC), using the absorbed latent heat during the melting of phase transition cooling medium to cool and solidify alloys in the process of casting, is a new casting technology. Specimens of A356 casting aluminum alloy were prepared by this method in the paper. The new heat treatment process (cast and then aging directly without solid solution) of A356 alloy was performed. For comparison, the conventional T6 heat treatment (solution and then aging treatment) was performed too. The mechanical properties of A356 alloy with different heat treatments were measured by tensile strength testing methods and microstructures of the alloy with different heat treatment process were investigated by optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-rays diffraction (XRD) and transmission electron microscopy (TEM) too. The results show that ultimate tensile strength (UTS) of A356 alloy with the new heat treatment process is much higher than that with conventional heat treatment while the elongations with the two heat treatment processes are very close. This is due to the grain refinement obtained after PTC processing.
TEXTURE EVOLUTION OF BT20 ALLOY IN BACKWARD TUBE SPINNING
Authors: YANG GUOPING , XU WENCHEN , SHAN DEBIN
Published: April 2009

Backward tube spinning experiment of BT20 ( Ti -6 Al -2 Zr -1 Mo -1 V ) alloy was carried out with an aim to examine texture evolution of titanium alloy in spinning process. The initial texture and the spinning texture were investigated by X-ray diffraction, and deformation history of a single-pass spinning was analyzed using finite element method. Tilt basal texture occurs when thickness reduction reaches a medium level (~ 49% for the outer surface and ~ 58% for the inner surface in the present study) and that further deformation promotes the formation of central basal texture. During early several passes basal texture in the outer surface develops more rapidly and intensely than that in the inner surface due to much larger deformation. However, the maximum intensity of texture in the inner surface reaches a higher level in subsequent passes for the following two reasons: (1) the discrepancy between equivalent deformation in the internal layer and that in the external layer reduces with increasing deformation; (2) material in the inner surface undergoes much smaller transverse shear deformation. Spinning texture is characterized by its asymmetry, which results from asymmetric spinning deformation investigated by analyzing deformation histories of material particles located in the inner and outer surface.
ANALYSIS ON THE MICROSTRUCTURE OF THE AS-CAST AND EXTRUDED Mg-(6-10)Li-3Al-Ce-Ca ALLOYS
Authors: CHENG LIREN , CAO ZHANYI , WU RUIZHI , ZHANG MILIN
Published: April 2009

Microstructural characterization of as-cast and extruded experimental alloys as (A) Mg -6.86 Li -3.02 Al -1.12 Ce -0.7 Ca (B) Mg -8.15 Li -3.07 Al -1.12 Ce -0.72 Ca (C) Mg -10.54 Li -3.54 Al -1.23 Ce -0.94 Ca are researched in this paper. The results show that the as-cast specimens of (A) and (B) are composed of α ( Mg ) phase, β ( Li ) phase, rod-like and bulk Al 2 Ce compound. On the other hand, β phase ( Li ), bulk and rod-like Al 2 Ce compound, Al2 Ca compound at boundaries are observed in the as-cast (C) alloy. The addition of Ce and Ca also shows in the microstructure the presence of Al - Ce - Ca phase, a solid solution of Ca in Al 2 Ce compound. In the extruding alloys, the microstructure is refined and the β phase has the effect of coordination during deformation. The long rod-like and the bulk compounds become short rods and fine clumps distributing evenly in the extruding direction after extruding process. The microstructure of extruded Mg -10.54 Li -3.54 Al -1.23 Ce -0.94 Ca alloy testified the existence of eutectic structure.
A STUDY OF DYNAMIC RECRYSTALLIZATION IN TA15 TITANIUM ALLOY DURING HOT DEFORMATION BY CELLULAR AUTOMATA MODEL
Authors: HE DONG , ZHU JING CHUAN , WANG YANG , LIU YONG
Published: April 2009

The dynamic recrystallization (DRX) of TA 15 ( Ti -6 Al -2 Zr -1 Mo -1 V ) titanium alloy during the hot deformation process was studied by the Cellular Automata (CA) model which is base on the dislocation density theory. To build the CA model, the dislocation density model, dynamic recovery model, nucleation model and grain growth model were introduced and developed. The influences of strain rate on the microstructure evolution and flow stress character were investigated which shows that high strain rate leads to later DRX appearance, high flow stress peak value, small mean size of recrystallizing grains( R -grains) and low DRX percentage, but they have the similar Avrami curve. The characteristic of DRX process in a modeling non-uniform temperature filed (NTF) has been studied. All the simulation results show good agreement with the pioneer's work and experimental results.
THE EFFECT OF POROSITY ON HEAT TRANSFER AND MASS TRANSFER OF Mg-3Ni-2MnO2 HYDROGEN STORAGE MATERIALS REACTION BED
Authors: ZHANG WENCONG , WANG GANG , MA JUNFEI , WANG ZHAOYOU , WANG ERDE
Published: April 2009

Hydrided Mg -3 Ni -2 MnO 2 composite powders were prepared by mechanical milling under hydrogen atmosphere. Heat and mass transfer, the effective thermal conductivity (ETC) of the hydrided Mg -3 Ni -2 MnO 2 powder reaction bed with various porosities were measured using a self-made apparatus. The effect of porosity on the bed is also analysized. The results show that the ETC of reaction bed is poor and it increases with decreasing porosity. Three porosities, 0.37, 0.53, 0.63 were selected in the present work. The bed with 0.53 porosity exhibits relatively fast reaction rates in both hydrogenation and dehydrogenation process. The hydrogenation process is a fast exothermic reaction resulting in a quick increase if the temperature of the bed during this process, and there is a temperature gradient: the temperature close to the bed wall is lower but higher at the center of bed. In dehydrogenation of the bed, the temperature of hydrided bed decreases due to the endothermic reaction, and the temperature at the center falls the lowest and keep at that temperature for a long time. The analyses reveal that increase of ETC don't always helps to improve the bed's hydriding and dehydriding rates. There should be an optimal porosity which helps to transfer both the heat and the mass.