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By D. A. Beattie

Talc is a commonly encountered gangue mineral in metal sulfide flotation. Talc is naturally hydrophobic, resulting in high recoveries if polymeric depressants are not used to specifically reject this MgO containing mineral. We have studied the adsorption of a selection of polymers onto talc using a variety of techniques. Adsorption isotherms have been determined using ex situ depletion techniques and in situ ATR-FTIR spectroscopy has been used to determine adsorption kinetics. Adsorbed layer thicknesses have been determined for the polymers on cleaved talc surfaces using the AFM. The effect of the adsorbed polymer layer on the properties of the talc surface has been quantified through contact angle measurements and single mineral flotation tests. Distinct correlations are observed between the adsorbed layer properties and the flotation performance of the polymers. These observations are discussed with reference to the bubble-particle attachment process and the molecular structure of the polymers.

Jan 1, 2006

By Youngjib Ham

Understanding energy performance of existing buildings is vital to increasing their efficiency and reducing the overall energy consumptions. This entails facility managers to systematically monitor building energy performance and reliably identify and analyze potential problems. Currently, infrared thermography is widely used as a primary diagnostic tool for the detection of building performance problems. Nonetheless, applications of thermal images for building inspection are mainly restricted to manual and labor-intensive identification and qualitative assessment of heating or cooling loss. Automated identification of potential problems and reliable cost analysis of the associated energy loss can help homeowners to minimize financial risk of retrofits and maximize energy savings. To that end, this paper presents a new automated method for calculating the cost of energy loss for building diagnostics. In the proposed method, first, using a hand-held thermal camera, the auditors collect digital and thermal imagery from the buildings under inspection. Then, using a recently proposed method for Energy Performance Augmented Reality (EPAR) modeling, an actual 3D spatio-thermal model is generated and superimposed with a computational fluid dynamics (CFD)-based expected energy performance model. The resulting EPAR model is placed into the method proposed in this paper for cost analysis of the energy loss. Through a new 3D thermal mesh modeling using k-d tree structure and nearest neighborhood searching, performance deviations between these models are automatically calculated. Using a temperature threshold, the areas associated with potential performance problems are detected in the EPAR model and are visualized using a metaphor based on traffic light colors. Then, the actual R-values of the detected areas are measured at the level of 3D points. Based on the measured R-values and the estimated air change rate for the detected air leaks, (1) the heat loss or gain caused either by poor insulation or air infiltration/exfiltration and (2) the associated energy costs are automatically calculated. The proposed method is validated on several locations of existing residential buildings. The preliminary results show the potential of the proposed method for minimizing the inspection time as well as the risk associated with the cost analysis of retrofitting potential building performance problems.

Aug 1, 2013

The paper will cover the basic reasons for alkaline leaching, a brief description of the circuit and the reasons for the flowsheet used. Changes made to the flowsheet, including the use of mechanical agitation of pachuca slurry, the use of oxygen and its effect on extraction, the use of lime and its effect on process economy, and the environment, will be described. A brief description of a unique semi-autogenous mill and future circuit changes will be included.

Jan 1, 1979

By Robert B. Parsons

"It is generally acknowledged that Canadian and foreign-based mining companies are spending relatively fewer dollars in Canada and more dollars abroad than was the case not many years ago. It is common to see the Canadian tax system being fingered as one of the causes in this shift in direction. However, if one takes the time to peel away the surface of our tax system, and to probe a little deeper into its substance, it will be found that the Canadian taxation of mining is generally quite competitive. IntroductionCross-border shopping in the mining industry? - Absolutely! Economics 100 teaches that dollars are votes in the capitalist system, and mining companies are going to cast their limited number of votes where they can achieve the highest return at the least risk. The Canadian consumer knows that taxes are a major factor in cross-border shopping, and mining company executives know that the same tenet holds true in their industry. Unfortunately, mining operations are subject to such a bewildering array of tax rules that making an intelligent decision is not always an easy matter.Statutory Tax RatesConsider, for example, the ""statutory"" tax rates shown in Table 1. (Statutory tax rate in this table refers to the simple sum of federal and provincial tax rates on profits as specified in the tax legislation.) Looking only at the total statutory tax rates (such as 66070 for Manitoba) , one might quickly observe that the Canadian mining industry is subject to a truly onerous tax regime, especially as compared to the United States where statutory tax rates can be in the 34% range."

Jan 1, 1992

By Liangtian Liu, Tie Ou, Guangqiang Li, Chenghuan Yu

For stabilizing the production of containing nitrogen steels, a study on nitrogen absorption behavior of killed molten steel has been carried out by means of the RH vacuum device in which nitrogen was used as a driving gas. The results showed that there was an increase of nitrogen content in molten steel under vacuum processing but the rate of nitrogen absorption was slowed down by the surface active elements. Therefore, a kinetic equation for nitrogen absorption of molten steel with apparent first order reaction was derived by constructing a modified model in which the adsorption of closed surface site was taken into account. The experimental results confiimed that the calculated values agreed with the observed ones. This model is suitable for the prediction of nitrogen adsorption operation for containing nitrogen steels.

Jan 1, 2004

By H. R. McCabe

"The study of a detailed series of structure and isopach maps of the Palaeozoic strata of southwestern Manitoba indicates that the principal Palaeozoic tectonic elements -the Williston Basin and Elk Point Basin -have been modified to a considerable extent by major tectonic features of the Precambrian basement. The principal basement feature is the break between the Churchill and Superior provinces, which coincides roughly with the Manitoba-Saskatchewan border. East-west-trending orogenic belts within the Superior crustal block may also be reflected to some extent in later Palaeozoic movements. In addition, the Superior crustal block, as a whole, appears to have had a slightly different response to the tectonic forces, giving rise to both basin subsidence and basin uplift. During periods of deposition, especially during Ordovician time, the Manitoba portion of the basin appears to have undergone a relatively higher rate of subsidence, whereas during periods of erosion relatively greater amounts of uplift and truncation have occurred. As a result, the depositional and erosional patterns for most of the Palaeozoic formations in southwestern Manitoba are somewhat anomalous relative to the regional basin framework.Some prominent Palaeozoic structures probably are the result of salt solution and differential compaction caused directly or indirectly by relatively minor tectonic movements related to Precambrian basement features. In particular, the prominent hinge line at the edge of the Devonian Prairie Evaporite salt basin may be due, in large part, to salt solution. Numerous other small structural lows, structural highs and isopach thicks, probably resulting from salt solution, occur along the salt edge and have been important in modifying and controlling Mississippian oil accumulation in the Daly-Virden producing area."

Jan 1, 1967

By The Staff

"SummaryDetermination of uranium in ores may be made by measurement of their radioactivity.The method most commonly used is that of measuring beta radiations with the tray-type beta counter. This will give an accurate uranium determination provided the sample does not contain thurium and that the beta and gamma activities have not been disturbed from their natural state of equilibrium. Such a loss of equilibrium will result from mining the ore or from the weathering of the surface rock.A method is described which eliminates errors due to loss of equilibrium. The beta and gamma activities are measured simultaneously in one simple operation. This method is recommended for assaying samples of products from milling operations and its use is limited only by the presence of thorium in a ratio greater than one part of thorium to twenty parts of uranium.A third method is recommended for the analysis of exploration samples and diamond drill cores, which may be assayed in the uncrushed state.Rapid determinations of a large number of samples is possible with the pressure ionization chamber, which is sensitive to gamma activity."

Jan 1, 1950

By John Drobe, Robert M. Cann

"Abstract - The Minas de Oro Cu-Au skarn and replacement deposits are located in the highlands of central Honduras, 90 km north-northwest of the capital of Tegucigalpa.The deposits formed in Cretaceous volcano-sedimentary rocks following the emplacement of an early Paleocene granodiorite to dacite intrusive complex. Three types of skarn (Type IA, IB, and IC) and a low-temperature replacement mineralization (Type II) are recognized. Type IA skarn consists of massive brown-green andradite and lesser magnetite and pyroxene. Type IB skarn has magnetite + hematite as the main constituent and garnet <50%. Type IC skarn comprises >50% pyrrhotite + chalcopyrite with interstitial garnet or pyroxene. Au and Cu occur in potentially economic concentrations in all skarn types while other metals such as Ag, Pb, Zn, and Mo are locally present in significant quantities. The highly variable distribution and nature of the skarn deposits is controlled by: (1) intrusive activity, (2) composition of host rocks, (3) faulting and fracturing, and (4) attitude of host carbonates.Type II Au-Cu-As mineralization occurs in calcareous sandstone and conglomerate 2 km distal from skarns and comprises clots of Cu sulfides hosted within a zone of brecciation and quartz flooding. Garnet and/or magnetite skarn is not present and the mineralizing event appears to have been a low-temperature replacement type.The similarity of coeval Au-Cu-Fe skarns in central Guerrero, southern Mexico to Minas de Oro skarns, and the similar local stratigraphy is consistent with the generally accepted theory that the Chortis block originated from southern Mexico and during the Tertiary moved southeast to its present position."

Jan 1, 2000

By Jan Rosenkranz, Anders Sand, Lisa Malm, Nils-Johan Bolin

Within flotation technology the general trend is towards very large cells. Scale-up is usually done by postulating geometrical similarity, which implies keeping the aspect ratio constant when increasing cell volume. Consequently, the design of flotation circuits typically involves several cells of identical geometry within a bank. Using a few standard sizes in a flotation plant simplifies design, manufacturing and maintenance of the cells, but does not necessarily guarantee optimal performance and selectivity of the flotation process. Geometry parameters for a given cell volume that influence flotation cell performance include cell height, which causes changes in the hydrostatic pressure and suspension hydrodynamics, and also influences the travel distance of particle-bubble agglomerates as well as the homogeneity of the mixing. Also the thickness of the froth layer depends on the aspect ratio of the cell. The objective of this work is to gain a better understanding of material distribution and properties within a flotation cell and, based on this information, elucidate how alterations of the cell geometry can influence separation efficiency. For this purpose systematic measurements and analyses of the spatial distribution of the different phases within a 160 m3 flotation cell have been carried out with a particular focus on an industrial, low-grade copper ore beneficiation process. The concepts for sampling at different vertical and lateral positions of the flotation cell are introduced. The results from the experimental work give an understanding of internal material distribution within flotation cells. Based on the measured phase distribution and concentrations as well as particle properties at various positions within the cell, the implications for an optimized scaling and design of individual flotation cells within a flotation circuit are discussed.

Jan 1, 2016

By C. J. R. Braithwaite, Giancarlo Rizzi

"The Navan zinc-lead ore deposit (70 million tonnes) is hosted principally (97%) by the Meath Formation (Lower Carboniferous, Courceyan, Navan Group), comprising a lower, mainly carbonate mudstone unit, the Stackallan Member, and an upper grainstone-dominated unit. TheStackallan Member, about 60 m thick, comprises about 35 peritidal cycles including an oolitic grain-stone interval. Grainstones forming the upper part of the formation, about 150 m thick, comprise at least six shallowing-upward ramp cycles. Emergence horizons are indicated by subaerial dissolution surfaces, in situ breccias, and a single palaeosol.Most dolomitization at Navan is con?ned to the Meath Formation. The linear dolomite body,trending NE-SW, has a ?attened, laterally limited, tabular geometry in cross-section, suggesting that dolomitizing ?uids initially rose vertically, cross-cutting stratigraphic and sedimentological bound-aries, although ?uid ?ow was subsequently controlled by these features.Three stages of dolomitization are indicated by textural relationships, cathodoluminescence (CL),oxygen isotopes, and ?uid inclusion data. Stage 1 crystals, with generally dully luminescing cores and up to six overlying subsidiary zones, are the main replacive phase. Crystal surfaces are commonly corroded and overlain by bright stage 2 rhombs (which also form new nuclei lining molds and fractures). Three subsets of zones are present in stage 2 crystals: bright, non-luminescent, and dull; these are locally separated by additional corrosion surfaces. Stage 3 comprises relatively large baroque crystals, generally dully luminescent but with up to seven sub-zones. Isotopic and ?uid inclusion data suggest growth of successive stages from waters which became progressively hotter(60°–160°C).The distribution of the ores follows the dolomite trend. Ores were precipitated between Stages1 and 2 of dolomite growth, following Stage 2, and also during the nucleation and growth of Stage3 crystals. Dolomitization and mineralization appear to have been temporally and genetically related. The cyclic sedimentation of the host rocks, which accentuates lithological and petrographical contrasts between depositional units, controlled dolomitization. The relationship between dolomitization and mineralization, which is closely associated with faults, provides powerful exploration criteria. The recognition of these features in limestones elsewhere in the Irish ore ?eld may point toward unrecognized zinc-lead prospects."

Jan 1, 1997

By C. J. R. Braithwaite, Giancarlo Rizzi

"Abstract-The Navan zinc-lead ore deposit (70 million tonnes) is hosted principally (97%) by the Meath Formation (Lower Carboniferous, Courceyan, Navan Group), comprising a lower, mainly carbonate mudstone unit, the Stackallan Member, and an upper grainstone-dominated unit. The Stackallan Member, about 60 m thick, comprises about 35 peritidal cycles including an oolitic grainstone interval. Grainstones forming the upper part of the formation, about 150 m thick, comprise at least six shallowing-upward ramp cycles. Emergence horizons are indicated by subaerial dissolution surfaces, in situ breccias, and a single palaeosol.Most dolomitization at Navan is confined to the Meath Formation. The linear dolomite body, trending NE-SW, has a flattened, laterally limited, tabular geometry in cross-section, suggesting that dolomitizing fluids initially rose vertically, cross-cutting stratigraphic and sedimentological boundaries, although fluid flow was subsequently controlled by these features. Three stages of dolomitization are indicated by textural relationships, cathodoluminescence (CL), oxygen isotopes, and fluid inclusion data. Stage 1 crystals, with generally dully luminescing cores and up to six overlying subsidiary zones, are the main replacive phase. Crystal surfaces are commonly corroded and overlain by bright stage 2 rhombs (which also form new nuclei lining molds and fractures). Three subsets of zones are present in stage 2 crystals: bright, non-luminescent, and dull; these are locally separated by additional corrosion surfaces. Stage 3 comprises relatively large baroque crystals, generally dully luminescent but with up to seven sub-zones. Isotopic and fluid inclusion data suggest growth of successive stages from waters which became progressively hotter (60°-160°C).The distribution of the ores follows the dolomite trend. Ores were precipitated between Stages 1 and 2 of dolomite growth, following Stage 2, and also during the nucleation and growth of Stage 3 crystals. Dolomitization and mineralization appear to have been temporally and genetically related. The cyclic sedimentation of the host rocks, which accentuates lithological and petrographical contrasts between depositional units, controlled dolomitization. The relationship between dolomitization and mineralization, which is closely associated with faults, provides powerful exploration criteria. The recognition of these features in limestones elsewhere in the Irish ore field may point toward unrecognized zinc-lead prospects."

Jan 1, 1997

By I. Southern, S. Kelebek

"Smelting furnace bricks contain significant quantity of base metals trapped in refractory material. A series of flotation tests were carried out on samples of old bricks from Sudbury area to examine upgrading behaviour for recycling purposes. Depending on the grind size used nickel recoveries varied from 60 to 90.6% with corresponding grades of 20% and 14.7%Ni. There is a trade-off between nickel and copper. The nickel has responded well to fine grinding, however, the copper recovery suffered from it. Mineralogical characteristics and flotation behaviour of the brick material are discussed in reference to those from the primary ore. INTRODUCTIONMineral processing is well recognized as a mature technology not only for the mining industry, but also for the environmental industry for the purpose of remediation and recycling. Materials available for recycling are usually the products of many years ago. There are multiple stake holders in this area. In general, when the processing results in a product that can be reused or sold, the company carrying out the remediation makes a profit, while the regulators and the public are pleased due to a cleaner environment. From these points of view, there have been many papers published over the years on various mineral processing techniques applied to separation of many different materials including from mining and metallurgical industries (Wilson et al., 1994; Tsunekawa et al., 2005; Saikia et al., 2012).Flotation may be viewed as the backbone of the mining and metallurgical industry since its invention for separation of solids from one another almost a century ago. It is capable of recovering a variety of finely divided different solids following their liberation from each other. Its versatility and highly competitive nature in terms of cost per tonne of material processed, accounts for its occasional uses in the environment engineering area. In the mining industry, flotation is the standard method used for the sulphide ores. It can be applied as a bulk flotation and/or differential flotation. Bulk flotation, which refers to co-flotation of several components from their source, is most suitable for environmental cleanup objectives. Desulphurisation of various plant tailings is a typical example of this (Benzazzoua et al., 2000)."

Jan 1, 2012

By H. H. Wang

Construction safety documents regulate significant safety actions and requirements by which construction workers or employees should abide in order to secure them from occupational hazard events. Therefore, facilitating faster identification of applicable safety requirements from the documents has become an important topic in the construction safety domain. To address the need in this regard, tools and techniques have been developed and research efforts have been made. One of the research efforts is to utilize ontology, a knowledge representation and reasoning approach, as the methodology to achieve the goal of identifying applicable safety requirements. In such ontology-based researches, the development and construction of the safety concept ontology is an essential task as the concepts and the relationships between the concepts both representing key safety knowledge need to be carefully identified. In this paper, the author focuses on the safety documents without predefined concept structure and aims to address the concept and relationship identification difficulties. Specifically, the author leverages the Formal Concept Analysis (FCA) methodology, a theory of data analysis that identifies conceptual structures among data sets, to mine and analyze the documents in order to discover safety concept structure and to further assist the development of the concept ontology for the construction safety documents. The author expects the application of FCA to construction safety domain can eventually benefit the ontology-based approaches for identification of applicable safety requirements.

Aug 1, 2013

By Walter Curlook

"With Inco recording record profits over the past year, most people have forgotten the painful years of the last recession/depression when Inco was losing up to a million dollars a day for a short period . While high nickel prices have contributed to the exceptional recent profits, the real achievements stem from the tremendous advances in productivity and cost improvements that make Inco one of the lowest cost nickel producers.Some of the major advances in productivity have occurred in the mines. The establishment of Mining Research Departments in both Thompson and Copper Cliff in 1979/80 provided the stimulus and the opportunity to dedicate personnel to specific research projects, on a full-time basis; and more particularly to concentrate on the efficiency of the total mine system. The Copper Cliff North Mine was brought back into production as a research mine dedicated to the development and testing of new mining methods and equipment. A shop facility known as the ""Murray Shop"" was set up as the centre of innovation for the development and construction of prototype equipment required for new bulk mining methods. While other expenditures were being curtailed , investment in mining research was being increased. An early success was an ""in the hole"" drill that could be broken down into small components to access even the remotest sectors of a mine to convert labour intensive undercut-and-fill mining to "" vertical crater retreat "" , VCR, bulk mining. A new mine manufacturing company-Continuous Mining Systems-was incorporated with the objective of building innovative mining equipment, with strong focus on automated continuous sytems. Continuous Mining Systems has now grown to a $25 million per year business. With these synergistic thrusts, the VCR bulk mining method was implemented in all of the Ontario Division mines, raising the percentage of ore mined by bulk mining techniques from 320/0 in 1981 to over 90% today. Coupled with re-designed job responsibilities, sup- ported by appropriate training, mine productivity more than doubled. It was discovered that VCR mining could be adapted to the narrower Thompson mine ores with identical improvements in productivity. Development of the Thompson Open Pit North had an additional favourable impact on production cost s in Thompson. The timing of the open pit development could not have been better. It permitted Inco to rapidly increase production at high productivity and low cost, in years of record demand and prices."

Jan 1, 1990

By P. J. Urso

"The coal reserves of the Crow's Nest Basin in British Columbia have been known since the late 1860's. The 51.0-million-long-ton (over 15 years) sale of low-volatile coking coal to Japanese steel mills, as finalized in 1968, establishes the importance of these coal reserves in the world markets.In the early stages of the exploration program, which began in January, 1967, emphasis was placed on deter-mining the reserve of underground low-pitch coal within the No. 10 or Balmer seam of the Kootenay coal forma-tion. The finding of low-cover reserves in excess of 100,000,000 tons altered the initially planned underground program. Extensive tests were performed, establishing the excellent coking characteristics of the open-cast Balmer coal. Due recognition was given to the ultimate reclamation costs of mined lands and associated spoil areas.t was determined that, to achieve the costs desired, a high productivity was necessary, requiring large mining equipment. Operating criteria were set out, based on producing 4.2 million tons of clean coal per year. To optimize recovery, the preparation plant feed size was fixed at Yi in. x 0. The initial basic design capacity of the plant was 1,000 tph. The washing plant is composed essentially of four separate cleaning sections: a dedusting section; a multi-stage heavy media cyclone section; water cyclones; and flotation cells. Subsequent to the basic program, additional sales were made of 6.0 million long tons over the initial three-year period and the plant capacity was raised to 1,400 tph through the addition of a 400-tph coarse-coal treatment section. All wet coal products from the fine coal plant will be dried in a 70-tph (water) heat dryer. A unit-train concept of coal transportation between the mine site and the Westward Terminals at Roberts Bank has been negotiated with the Canadian Pacific Railroad. Facilities at the port will include a 4,000-tph rotary car bumper, 400,000-ton clean-coal stockpiles, and a bucket reclaiming system having a total ship-loading capacity of 6,000 tph."

Jan 1, 1969

By A. Scheltema Beduin, H. Oterdoom, A. Haaks, C. Kempe, A. Liedtke

The bath level measurement is applied in many furnaces to keep control of the level of slag and metal or matte inside. The BLM is used mainly in bath processes, and has not seen much evolution in its basic functionality. For a closed DC FeCr furnace, special demands based on the furnace design and extreme process conditions were considered for the design of a bath level measurement in order to collect valuable information about the furnace operation. This paper will describe these demands and the solutions for them, followed by some of the uses for the BLM in a closed FeCr furnace. Some of the future developments on the BLM conclude this presentation.

Jan 1, 2015

By J. Budac, R. Kofluk, S. Mankasingh

Stainless steels such as 316L or 304 are normally relatively resistant to attack by nitric acid. However research at Sherritt International’s Fort Saskatchewan Operation reveals that when the stainless steel is immersed in an aqueous system in which nitric acid is used to dissolve metals such as cobalt or nickel, the steel can be seriously corroded. Sherritt is patenting a simple process for arresting the corrosion via the use of copper. This process is expected to substantially eliminate corrosion in processes where nitric acid is used to dissolve metals attached to a stainless steel substrate.

Jan 1, 2014

By H. J. Rowley

THERE are many varieties of limestone, but for the general purposes of the pulp and paper industry, two classifications are sufficient: (1) High-calcium stone, which should be quite free from impurities and contain not less then 90 per cent calcium carbonate. (2) High-magnesium stone, containing not less than 25 per cent of magnesium carbonate. Before proceeding with detail on the use of limestone and lime in the industry, a few words regarding the pulp products made in Canada are desirable. By far the largest tonnage is made by grinding spruce and balsam logs on rotating sandstones or on artificial abrasive stones of the Norton or Carborundum types. This mechanical or groundwood pulp finds its largest use in the production of newsprint paper, of which it comprises about 80 per cent of the total fibrous substance employed-the remaining 20 per cent being unbleached sulphite pulp. No limestone or lime is directly employed in making groundwood pulp, as contrasted with the chemically prepared pulps, all of which require one or the other form of the base for their processing. Sulphite pulps comprise the next largest tonnage group. They are produced by boiling, under pressure and at elevated temperatures, spruce and balsam wood in chip form in solutions of bisulphites and sulphurous acid. The usual bisulphites employed are those of calcium and magnesium. Sodium, potassium, and ammonium bisulphites give progressively better pulps, but to date, in the absence of efficient recovery methods, cost has precluded their use.

Jan 1, 1939

By A. Giacomini, M. Nazem, E. Fathi Salmi

"Numerical simulation of collapse of tunnels in weak rocks is one of the challenging problems in rock mechanics. Collapse can impose technical and financial difficulties during the construction of underground excavations. This phenomenon, particularly in shallow excavations, may lead to propagation of a caved zone toward the surface and formation of chimney subsidence. Chimney subsidence has numerous catastrophic consequences such as the adverse environmental impacts and damage to surface structures in vicinity of excavations. Due to the importance of subsidence in civil engineering, the main goal of this study is to propose an appropriate method for preventing the formation of subsidence in shallow tunnels in weak rocks. The Dolaei road tunnel is investigated as a case study, where a large chimney subsidence has occurred. The geology of the area and the geostructural characteristics of the rock mass surrounding the tunnel are briefly reviewed in this paper. Two-dimensional as well as threedimensional numerical simulations are conducted to study the tunnel stability. Moreover, the effects of staged excavation and pre-supporting method on controlling the ground movements are studied. Outcomes of this study indicate that employing forepoling and staged excavation can be a practical remedy to control the ground movements and prevent the formation of chimney subsidence.INTRODUCTIONPredicting the formation of subsidence, mainly sinkhole subsidence over civil or mining excavations, is a very challenging task. An accurate prediction of subsidence is required for selecting an appropriate control and mitigation system to reduce the level of ground movements and its impact on the surface life (Bétournay et al. 1994; Leca and New 2007). Excavations, particularly in weak grounds, could result in surface subsidence; they modify the in-situ stress conditions as well as the hydrogeology of the area. Construction of unsupported excavations in soft soils and relatively weak rocks usually leads to the formation of a failure zone behind the face. In a very soft ground, the failure zone can extend towards the ground ahead of the tunnel face. Propagation of this zone toward the ground surface results in generation of sinkholes."

Jan 1, 2015

By G. Guiglionda, A. Deschamps, F. De Geuser, M. Langille, B. J. Diak

"Increased demand for light-weighting in passenger vehicles has created a need for strong, light, ductile materials to be used in body-in-white applications. The AA6xxx-series of aluminum alloys are suitable candidates meeting most requirements but can fall short of the formability demands of designers, necessitating an understanding of what controls the formability in this alloy series. This work examines the effect of copper alloying in AA6xxx on the pre-ageing and natural ageing responses of the microstructure and mechanical properties. The changes in microstructure observed by differential scanning calorimetry and hardness testing are related to the work-hardening and strain-rate sensitivity parameters for these alloys measured by tensile testing. An observed asymmetry in the measured strain-rate sensitivity associated with increasing versus decreasing strain rate changes suggests that a different mechanism operates for the two conditions. It is postulated how this asymmetry in strain-rate sensitivity will impact the necking and ductility behaviour of these alloys.INTRODUCTION The widespread use of AA6xxx series alloys in the form of sheets has provided the need for a more thorough understanding of the complex interactions between composition, processing, resulting microstructure and ultimately, the mechanical properties of the alloys. Conventional industrial practices involve the production of rolled AA6xxx sheet (typically 1 mm thick) to be used for body-in-white (BIW) applications for auto body panels (Hirsch, 2004, 2014). The final metallurgical step prior to the shipment of these panels to manufacturers involves a solution heat treatment (SHT) reverting the ageing products of the alloys into solid solution and the product is then shipped to the customer. During this shipping time and while sheets are waiting to be used, the natural ageing (NA) process occurs whereby the strength of the alloys increases resulting in reduced formability. This can result in a product that is unable to meet the formability demands of the automotive manufacturer. As a result, industry has moved towards performing pre-ageing (PA) treatments to prolong the “shelf-life” of the material prior to it having insufficient formability. Once formed into BIW panels, the parts are then painted and subsequently undergo the paint curing heat treatment which consists of a short period of time at medium temperature, typically 20 minutes at 170–190°C. This short artificial ageing (AA) treatment, known as the paint bake (PB), provides additional strength and improved dent resistance for the material, but reduced formability. The PB result is strongly dependent on the PA treatment performed prior to the forming operation. Furthermore, the addition of copper (Cu) to a base Al-Mg-Si composition is known to increase the alloy’s strength. The goal of this work is to study the effect of Cu on strength, strain hardening, and strain-rate sensitivity (SRS) of these alloys, to understand the strength-formability compromise, for two separate heat treatment schedules; one including and one excluding the PA treatment, both followed by NA."

Jan 1, 2018