Faculty of Engineering - Papers (Archive)

The effect of welding speed and contact-tip-to-workpiece distance on the microstructural homogeneity and bead profile of Tandem GMA steel welds

Z. Sterjovski — Mon, 08 Apr 2013 16:45:16 PDT

Automated tandem gas metal arc welding (T-GMAW) has been identified as a welding system potentially capable of increasing productivity and minimising distortion in the fabrication of ship panels. The T-GMAW process was used in pulse-pulse mode on 6 mm plain carbon steel plate to determine the effect of welding travel speed (WTS) (1.0-2.0 m/min) and contact-tip-to-workpiece distance (CTWD) (20-35 mm) on weld metal microstructure and bead profile. In this mode, the leading and trailing welding wires alternately transfer metal into a single molten weld pool at welding travel speeds much greater than those used in conventional single-wire gas metal arc welding (GMAW). The results show that for the bead-onplate (BOP) welding of 6 mm plain carbon steel plate, adequate weld pool mixing and an acceptable level of microstructural homogeneity in the solidified weld metal were achieved for all welding conditions. BOP welding tests were also undertaken on 20 mm plain carbon steel plate which results in a greater weld cooling rate compared with the thin 6 mm plate. In the 20 mm plate, a relatively homogenous weld metal microstructure was also present, but there was evidence of limited weld pool mixing. Also, in-situ analysis of the arcs during welding and post test characterisation of the BOP samples showed that arc stability and bead profile are sensitive to both CTWD and WTS.

High-fidelity physics-based modelling of explosion seals for coal mines

Alex M. Remennikov — Wed, 03 Apr 2013 21:19:58 PDT

This paper presents a new approach to analytical design of coal mine seals to safely resist explosions during their intended life. Under the current Australian regulations, ventilation control devices (VCD) such as seals and stoppings are required to be tested to achieve pressure ratings of 14, 35, 70, 140 or 345 kPa. Since full-scale testing of seals under various loading regimes is economically prohibitive, a new trend is emerging where high-fidelity physics-based models calibrated using only one full-scale test are employed to predict ultimate strength of seals. In this paper, the explicit dynamics non-linear finite element code LS-DYNA is used to develop high-fidelity physics-based (HFPB) computer simulations to predict the results from physical testing of coal mine seals. Test data from live gas/coal dust deflagration explosions at Lake Lynn, PA, USDA are used to simulate a realistic loading environment caused by 140 kPa (20-psi) explosions. The benefits of the new approach are also outlined.

Structure-property relations of metallic materials with multiscale microstructures

C. Yang — Mon, 18 Mar 2013 21:31:27 PDT

Nanostructured metals have higher strength than those of the coarse grained metals but suffer from the extremely limited ductility. Development of the multiscale microstructures can improve the ductility of these high strength materials due to the introduction of a specific range of grain sizes in micro level. The present work relates the multiscale microstructures in metals to their overall structure properties using a fractal theory and the modified mean-field method, where three microstructural parameters are introduced and thus mechanical properties such as strength and ductility are presented as a function of these microstructural parameters. Meanwhile, with the applications of the finite element method, the multiscale unit cell approach is also critically developed and applied with a focus on predicting the related stress-strain relations of the metals with multiscale microstructures. For verification of these proposed theoretical and numerical algorithms, the mechanical properties of the pure copper with three-grain microstructures are investigated and the results from FEA and theoretical solutions have a reasonable agreement.

Microstructure evolution modeling during and after deformation in 304 austenitic stainless steel through cellular automaton approach

Nima Yazdipour — Mon, 18 Mar 2013 21:09:40 PDT

A 2D cellular automaton approach was used to simulate microstructure evolution during and after hot deformation. Initial properties of the microstructure and dislocation density were used as input data to the cellular automaton model. The flow curve and final grain size were the output data for the dynamic recrystallization simulation, and softening kinetics curves were the output data of static and metadynamic recrystallization simulations. The model proposed in this work considered the effect of thermomechanical parameters (e.g., temperature and strain rate) on the nucleation and growth kinetics during dynamic recrystallization. The dynamic recrystallized microstructures at different strains, temperatures, and strain rates were used as input data for static and metadynamic recrystallization simulations. It was shown that the cellular automaton approach can model the final microstructure and flow curve successfully in dynamic recrystallization conditions. The postdeformation simulation results showed that the time for 50% recrystallization decreases with increasing strain for a given initial grain size and that dynamic recrystallization slows the postdeformation recrystallization kinetics compared to a model without dynamic recrystallization.

Electrical and thermal characteristics of multilayer thermionic power devices

Ben C. Lough — Sun, 03 Mar 2013 16:52:17 PST

Electron thermal transport in semiconductor thermionic devices is investigated numerically. The efficiency of thermionic devices is dramatically reduced by the conduction heat current, DeltaT/R^th. One approach to reduce the thermal conductivity is to use layered structures where interface scattering can increase the thermal resistivity. It is found that the temperature gradient across the devices can be increased by a factor of 2 in the presence of phonon scattering. The device is more efficient at elevated temperature.

The electron energy spectrum and thermionic device efficiency

Mark F. O'Dwyer — Sun, 03 Mar 2013 16:46:17 PST

The influence of the electron energy spectrum of solid-state thermionic devices on electronic efficiency is analyzed. Calculations are performed on both single and multibarrier GaAs/AlGaAs and InGaAs/InAlAs systems. Analysis reveals a wide barrier is desirable for single-barrier thermionic devices due to the associated sharpness in the electron energy spectrum. It is also shown that high electronic efficiency may be achieved in multibarrier thermionic devices consisting of thin barriers, which would separately give low efficiency, but together can be arranged to produce a desirable electron energy spectrum.

Magnetospectroscopy of Zn-Doped InP TO 30 T

R. Lewis — Sun, 03 Mar 2013 16:32:37 PST

Zn-doped p-type InP has been examined by far-infrared absorption magnetospectroscopy to fields much higher than previously. The impurity-related transitions observed confirm and greatly extend previous data and reveal new phenomena.

Fouling in nanofiltration

A. Schaefer — Sun, 03 Mar 2013 15:23:58 PST

According to Koros et al. [1] fouling is “the process resulting in loss of performance of a membrane due to deposition of suspended or dissolved substances on its external surfaces, at its pore openings, or within its pores”. Fouling is also decribed as flux decline which is irreversible and can only be removed by, for example, chemical cleaning [2]. This is different to flux decline due to solution chemistry effects or concentration polarisation which is described in more detail later in this chapter. Those flux declines can be reversed with clean water and are hence not considered as fouling.

Trace contaminant removal with nanofiltration

L. D. Nghiem — Sun, 03 Mar 2013 15:15:21 PST

The occurrence and fate of both organic and inorganic trace contaminants in the aquatic environment has long been recognized as an important issue of public health and environmental concern. A wide range of trace organics, both synthetic and natural, have been detected and identified as important contaminants in sewage and effluent impacted water bodies including surface and groundwater. Trace inorganic contaminants can also occur naturally in groundwater under certain geochemical conditions. Trace contaminants are defined as chemicals of concern to human health and the biotic environment due to a combination of their physicochemical toxicological properties. In the aquatic environment, they are present at trace levels, usually in the μg/L range or less. From a toxicological point of view, low concentrations of trace contaminants in ground and drinking water may not always be harmful to humans (in fact in most cases health effects are unknown at this stage), but they are undesirable in regard to the “precautionary principle” [1]. Although trace contaminant removal is an issue facing various industries, this chapter focuses mostly on the water purification process. The role of nanofiltration (NF) in water and wastewater treatment, occurrence of trace contaminants and their environmental implications, separation processes and a review of current studies are presented in this chapter.

An overview of streamed data authentication techniques

B. J. Wysocki — Sun, 03 Mar 2013 15:01:24 PST

In the chapter we present some of the techniques proposed for authenticating digital streams. We start with the so-called block signatures, where every packet contains full information needed for its authentication. Then, we describe two techniques based on a simple hash chain for an off-line authentication and its modification where one-time signatures are used for an on-line authentication. Later, we consider the TESLA scheme for authenticating streams in case of synchronous systems. This is followed by augmented hash chains with signature packets used once per a sequence of packets rather than for the whole stream. The chapter is concluded with a short comparison of the considered techniques.

Influence of temperature on coal sorption characteristics and the theory of coal surface free energy

Lei Zhang — Tue, 22 Jan 2013 16:12:42 PST

An experimental study was undertaken to examine the sorption and desorption characteristics of coal at temperatures of 35 °C, 45 °C and 55 °C. The study focused on the effect of changes in temperature and coal particle sizes on gas sorption and desorption characteristics. The coal size used ranged from fragmented coals, 16 mm, 8 mm, 2.4 mm, powdered coal of 150 μm and 54 mm core samples. The samples were tested in pressure vessels, known as “bombs”, charged with CO2 gas at different pressure levels up to a maximum of 4000 kPa. It was found that temperature has a significant influence on the sorption and desorption behaviour of gas in coal. The degree of hysteresis phenomenon was found to be influenced by the coal surface area as well as temperature. Based on the principle of surface chemistry, the method of calculating coal surface energy with sorption parameters was used and the main parameter of surface tension was analysed. The calculation result showed that reduced value of surface tension parameter decreased with increasing temperature. Also the reduced value of surface tension parameter of adsorption is smaller than the desorption. The theory of coal surface free energy can be used to explain the coal sorption characteristics with CO2 at higher temperatures. Results from this study have useful implication for enhanced CBM and gas drainage in coal mines.

Carbothermal reduction of ilmenite concentrates and synthetic rutile in different gas atmospheres

Mohammad Dewan — Tue, 22 Jan 2013 16:12:41 PST

Carbothermal reduction of ilmenite concentrates and synthetic rutile was studied in isothermal experiments in hydrogen, argon and helium in a tube reactor. Concentrations of CO, CO₂ and CH₄ in the off gas were measured online using an infrared gas analyser. The reaction products were analysed by X-ray diffraction. Pseudorutile and ilmenite were the main phases in ilmenite concentrates. Reduction of ilmenite concentrates and synthetic rutile in hydrogen was significantly faster than that in inert atmosphere. The effect of gas atmosphere became stronger for lower grade ilmenite containing more iron oxides. The conversion rate of titania to titanium oxycarbide in hydrogen decreased with increasing grade of ilmenite concentrate. In inert gas, the reduction rates of secondary ilmenite and HYTI70 were close to that of primary ilmenite. Reduction of synthetic rutile was faster in comparison with ilmenite concentrates.

Response of foam- and concrete-filled square steel tubes under low-velocity impact loading

Alexander Remennikov — Tue, 22 Jan 2013 16:12:41 PST

This paper presents the results of experimental and numerical studies of the comparative behavior of square hollow section (SHS) tubes filled with rigid polyurethane foam (RPF) and concrete undergoing transverse impact loading. A series of instrumented drop hammer tests were performed on mild steel and stainless steel SHSs for both filled and unfilled constructions. The concrete-filled tubes had the highest impact resistance and energy absorption capacity, followed by the steel tubes filled with RPF, and then the hollow tubes. The results also show that RPFs can be used as an effective infill material in structural steel hollow columns when expedient enhancement of the energy absorption capacity is required, e.g., to increase blast and impact resistance of hollow structural elements. Nonlinear dynamic finite-element analyses were carried out to simulate drop hammer test conditions. The predicted impact forces, deformation histories, and failure modes were found to be in good agreement with the experimental results.

Low-temperature synthesis of aluminium carbide

Jiuqiang Li — Tue, 22 Jan 2013 16:12:40 PST

The Hall-Héroult process, the only commercial technology for aluminum production requires high energy and is a major origin of perfluorocarbons and green house gases. A promising alternative process, carbothermal reduction of alumina to metallic aluminum has advantages of lower capital cost, less energy consumption, and lower emission of green house gases. Carbothermal reduction processes under development are based on formation of aluminum carbide-alumina melts at high temperatures. Solid state carbothermal reduction of alumina is possible at reduced CO partial pressure. This paper presents results of experimental study of carbothermal reduction of alumina into aluminum carbide in argon, helium and hydrogen atmospheres at 1500–1700°C. The reduction rate of alumina increased with increasing temperature, and was significantly faster in helium and hydrogen than in argon. Increasing gas flow rate and pellet porosity, and decreasing pressure favour the reduction.

Carbothermal reduction and nitridation of titanium dioxide in the H2-N2 gas mixture

Sheikh Rezan — Tue, 22 Jan 2013 16:12:39 PST

This article examines carbothermal reduction/nitridation of rutile in a H₂–N₂ gas mixture in the temperature-programmed and isothermal experiments in a fixed-bed reactor. The aim of this investigation was to establish the reduction/nitridation sequence, the reaction degree, and the rate of synthesis of titanium oxycarbonitride under different experimental conditions. The off-gas composition was monitored using an infrared sensor (CO, CO₂, and CH₄) and a dew point analyzer (H₂O). Extents of reduction and nitridation were determined from the off-gas composition and LECO analysis. Phase composition of reduced samples was analyzed using powder X-ray diffraction (XRD). Rate and extent of conversion of titanium oxides to titanium oxycarbonitride increased with increasing temperature. The conversion of titania into titanium oxycarbonitride at 1150°C was completed in 180 min; the conversion time decreased to 30 min at 1300°C. Increasing temperature resulted in formation of titanium oxycarbonitride with higher TiC content. Porosity had a minor effect on the reduction/nitridation of titania with the tendency to increase the reduction rate with increasing porosity. Reduction/nitridation of titania at 1150°C followed the sequence: TiO₂→Ti₅O₉→Ti₄O₇→Ti₃O₅→TiO_xC_yN_z.

Chlorination of reduced ilmenite concentrates and synthetic rutile

Andrew Adipuri — Tue, 22 Jan 2013 16:12:39 PST

Chlorination of reduced ilmenites of different grades (primary, secondary and HYTI 70) and synthetic rutile was investigated at 235 °C. The main phases of primary and secondary ilmenites were Fe₂Ti₃O₉ and FeTiO₃; HYTI 70 contained TiO₂; synthetic rutile consisted of titania with titanium suboxides and trace amount of iron. Iron oxides were reduced to metallic iron. Titanium oxides were reduced to titanium oxycarbide or oxycarbonitride; reduced samples contained a small amount of titanium suboxides. In chlorination of reduced ilmenite concentrates and synthetic rutile, titanium oxycarbide or oxycarbonitride, metallic iron, and Ti₂O₃ were chlorinated. The degree of chlorination of both iron and titanium oxycarbide/oxycarbonitride was 95–98%; chlorination of iron was faster than that of titanium oxycarbonitride. The removal of iron by leaching increased the chlorination rate of titanium oxycarbide/oxycarbonitride; it was close to completion in 35 min.

Response of a PIN diode and SOI microdosimeter to the TSL quasi-monoenergetic neutron field

Dale Prokopovich — Tue, 22 Jan 2013 16:12:38 PST

The response of a Silicon On Insulator (SOI) Microdosimeter and a silicon PIN diode were tested at the TSL quasimonoenergetic neutron beamline at Uppsala university. The objective was to determine the response of both the SOI Microdosimeter and silicon PIN diode to a high energy quasi-monoenergetic neutron field for potential future application of the devices in aviation dosimetry. PIN diode angular response dependence was also measured to determine the suitability of PIN diodes in a multidirectional high energy neutron field as encountered in aviation environments. Simulations of the response from the SOI Microdosimeter and PIN diode to the field using GEANT4 were obtained to assist in interpreting the experimental measurements.

An efficient dynamic authenticated key exchange protocol with selectable identities

Hua Guo — Tue, 22 Jan 2013 16:12:37 PST

In the traditional identity-based cryptography, when a user holds multiple identities as its public keys, it has to manage an equal number of private keys. The recent advances of identity-based cryptography allow a single private key to map multiple public keys (identities) that are selectable by the user. This approach simplifies the private key management. Unfortunately, the existing schemes have a heavy computation overhead, since the private key generator has to authenticate all identities in order to generate a resultant private key. In particular, it has been considered as a drawback that the data size for a user is proportional to the number of associated identities. Moreover, these schemes do not allow dynamic changes of user identities. When a user upgrades its identities, the private key generator (PKG) has to authenticate the identities and generate a new private key. To overcome these problems, in this paper we present an efficient dynamic identity-based key exchange protocol with selectable identities, and prove its security under the bilinear Diffie–Hellman assumption in the random oracle model.

Numerical simulation of reinforced granular soils using DEM

Jayan Vinod — Tue, 22 Jan 2013 16:12:37 PST

This paper explores the potential of Discrete Element Simulation (DEM) to model the behavior of reinforced granular soils. Biaxial element test were carried out on these assembles with and with out horizontal reinforcement layers to understand the behavior of reinforced granular soils from grain scale level. Numerical simulations were carried out using PFC^2D with assemblies of 1800 uni sized circular particles of size 0.1 mm. In the current investigation, reinforcing element was modeled by a chain of circular particles by assigning contact bond between particles horizontally at all predetermined contact locations. Influence of parameters such as number of reinforcement layer, thickness and packing geometry on the behavior of reinforced granular materials were studied and reported.

Factors affecting kinked steel grid reinforcement in MSE structures

N. Tin — Tue, 22 Jan 2013 16:12:36 PST

In order to investigate the factors affecting kinked steel grid reinforcement in Mechanically Stabilized Earth (MSE) structures, pullout tests were conducted to find out the new structure of steel grid reinforcement by making one or two triangular kinks on it to effect yielding in the steel grid. The pullout resistance is higher at larger pullout displacement when more kinks are made in the steel grid. Adding more kinks in the steel grid allowed sufficient lateral yielding with sufficient displacements to achieve the active condition as opposed to at-rest condition and thereby reduce the loading in the reinforcements.