Search

Materials of a gradient structure have been shown to possess both high strength and high ductility. To date, materials of a gradient structure can only be produced in small quantities. In this paper, we report a novel 'cyclic skin-pass rolling' (CSPR) technique capable of producing sheets of gradient structure in large quantities. Both experimental and analytical/numerical investigations are reported. In the experiments on aluminium sheets, the outer layer was subjected to 40 passes of CSPR with a reduction ratio of 1% per pass. After CSPR, the sample surface shows an ultrafine-grained microstructure with a mean grain size of 206 nm, while the annealed microstructure is retained in the core of the sample. Compared with cold-rolled aluminium sheets fabricated with the same total reduction ratio, CSPR-processed aluminium sheets have the same yield stress but improved uniform elongation (2.4 times). The scanning electron microscopy was used to study the fracture surface, and The transmission electron microscopy to examine the microstructure near the fracture end, in order to analyse the improvement in ductility. In addition, the finite element method was used to simulate the roll-sample contact pressure and strain distribution as well as residual stress on the sheet surface during CSPR, and to better understand the mechanism leading to improvement of ductility of the sheets by the CSPR technique.

The mechanical properties of the Ti-6Al-4V alloy are significantly determined by the process used for manufacture. In this study, the mechanical properties of the Ti-6Al-4V alloy manufactured using cold rolling, asymmetric rolling and asymmetric cryorolling were characterized by subjecting it to the tensile test and the microhardness test. The evolution in the microstructure was studied using scanning electron microscopy, transmission electron microscopy as well as energy dispersive X-ray spectrometry. Results show that the Ti-6Al-4V alloy sheets subjected to asymmetrical cryorolling with low rolling speed ratio between the upper and lower rolls have the highest tensile strength and microhardness. The tensile stress of the alloy samples after cold rolling was found to be 1008 MPa, 1046 MPa after asymmetric rolling, and 1113 MPa after asymmetric cryorolling. The highest Vickers hardness (HV395) is achieved by asymmetric cryorolling. We discuss the mechanical behavior using the criteria of grain size, size of second phase as well as dislocation density.

The blades of a large Horizontal Axis Wind Turbine (HAWT) are subjected to significant vibrations during operation. The vibrations affect the dynamic flow field around the blade and consequently alter the aerodynamic forces on the blade. In order to better understand the influence of blade vibrations on the aerodynamic loads, the dynamic stall characteristics of an S809 airfoil undergoing translational motion as well as pitching motion were investigated using Computational Fluid Dynamics (CFD) techniques. Simulation results indicated that both the out-of-plane and in-plane translational motions of the airfoil affect the unsteady aerodynamic forces significantly. In order to investigate the effects of blade vibration on the aerodynamic load on a large-scale HAWT blade during its operating lifetime, an aerodynamic model based on the Blade Element-Momentum (BEM) theory and the Beddoes-Leishman (B-L) dynamic stall model was proposed. The BEM model was revised to account for the vibration-induced velocity components in the calculation of the effective angle of attack. Aerodynamic load analysis of a 5 MW wind turbine was then performed and the impact of blade vibration on the lifetime aerodynamic fatigue loads was analysed.

Grain growth and grain refinement behavior during deformation determine the strength and ductility of ultrafine-grained materials. We used asymmetric cryorolling to fabricate ultrafine-grained copper sheets with an average grain width of 230 nm and having a laminate structure. The sheets show a high-true failure strain of 1.5. Observation of the microstructure at the fracture surface reveals that ultrafine laminate-structured grains were simultaneously transformed into both equiaxed nanograins and coarse grains under tensile deformation at room temperature.

The microstructure evolution and mechanical properties of ultrafine-grained (UFG) Al sheets subjected to accumulative roll bonding (ARB) and subsequent cryorolling was studied. Cryorolling can suppress the dynamic softening of UFG Al sheets subjected to ARB at room temperature. After the third ARB pass, the grains are slightly refined as the number of ARB passes increases. However, the grains are significantly refined further during cryorolling. The grain size of 460 nm achieved after the third ARB pass is reduced to 290 nm after two cryorolling passes with total reduction ratio 80%. Sheets subjected to ARB + cryorolling show improved mechanical properties compared to only ARB-processed sheets due to a change in the fraction of high-angle boundaries and elongated grains. The deformation mechanism for ultrafine grains at room temperature is determined by grain boundary sliding or dislocation-based recovery, while it is governed by dislocation glide at cryogenic temperature.

Grain growth and grain refinement behavior during deformation determine the strength and ductility of ultrafine-grained materials. We used asymmetric cryorolling to fabricate ultrafine-grained copper sheets with an average grain width of 230 nm and having a laminate structure. The sheets show a high-true failure strain of 1.5. Observation of the microstructure at the fracture surface reveals that ultrafine laminate-structured grains were simultaneously transformed into both equiaxed nanograins and coarse grains under tensile deformation at room temperature.

The microstructure evolution and mechanical properties of ultrafine-grained (UFG) Al sheets subjected to accumulative roll bonding (ARB) and subsequent cryorolling was studied. Cryorolling can suppress the dynamic softening of UFG Al sheets subjected to ARB at room temperature. After the third ARB pass, the grains are slightly refined as the number of ARB passes increases. However, the grains are significantly refined further during cryorolling. The grain size of 460 nm achieved after the third ARB pass is reduced to 290 nm after two cryorolling passes with total reduction ratio 80%. Sheets subjected to ARB + cryorolling show improved mechanical properties compared to only ARB-processed sheets due to a change in the fraction of high-angle boundaries and elongated grains. The deformation mechanism for ultrafine grains at room temperature is determined by grain boundary sliding or dislocation-based recovery, while it is governed by dislocation glide at cryogenic temperature.

Grain growth and grain refinement behavior during deformation determine the strength and ductility of ultrafine-grained materials. We used asymmetric cryorolling to fabricate ultrafine-grained copper sheets with an average grain width of 230 nm and having a laminate structure. The sheets show a high-true failure strain of 1.5. Observation of the microstructure at the fracture surface reveals that ultrafine laminate-structured grains were simultaneously transformed into both equiaxed nanograins and coarse grains under tensile deformation at room temperature.

The microstructure evolution and mechanical properties of ultrafine-grained (UFG) Al sheets subjected to accumulative roll bonding (ARB) and subsequent cryorolling was studied. Cryorolling can suppress the dynamic softening of UFG Al sheets subjected to ARB at room temperature. After the third ARB pass, the grains are slightly refined as the number of ARB passes increases. However, the grains are significantly refined further during cryorolling. The grain size of 460 nm achieved after the third ARB pass is reduced to 290 nm after two cryorolling passes with total reduction ratio 80%. Sheets subjected to ARB + cryorolling show improved mechanical properties compared to only ARB-processed sheets due to a change in the fraction of high-angle boundaries and elongated grains. The deformation mechanism for ultrafine grains at room temperature is determined by grain boundary sliding or dislocation-based recovery, while it is governed by dislocation glide at cryogenic temperature.

Grain growth and grain refinement behavior during deformation determine the strength and ductility of ultrafine-grained materials. We used asymmetric cryorolling to fabricate ultrafine-grained copper sheets with an average grain width of 230 nm and having a laminate structure. The sheets show a high-true failure strain of 1.5. Observation of the microstructure at the fracture surface reveals that ultrafine laminate-structured grains were simultaneously transformed into both equiaxed nanograins and coarse grains under tensile deformation at room temperature.

The microstructure evolution and mechanical properties of ultrafine-grained (UFG) Al sheets subjected to accumulative roll bonding (ARB) and subsequent cryorolling was studied. Cryorolling can suppress the dynamic softening of UFG Al sheets subjected to ARB at room temperature. After the third ARB pass, the grains are slightly refined as the number of ARB passes increases. However, the grains are significantly refined further during cryorolling. The grain size of 460 nm achieved after the third ARB pass is reduced to 290 nm after two cryorolling passes with total reduction ratio 80%. Sheets subjected to ARB + cryorolling show improved mechanical properties compared to only ARB-processed sheets due to a change in the fraction of high-angle boundaries and elongated grains. The deformation mechanism for ultrafine grains at room temperature is determined by grain boundary sliding or dislocation-based recovery, while it is governed by dislocation glide at cryogenic temperature.

In order to quantitatively evaluate the risk associated with the Carbon Capture and Storage (CCS) technology, a deeper understanding of CO2 dispersion resulting from accidental releases is essential. CO2 is a heavier-than-air gas. Its dispersion patterns may vary according to local conditions. This study focuses on CO2 dispersion over complex terrains. Computational Fluid Dynamics (CFD) models were developed to simulate the CO2 dispersion over two hypothetical topographies: (1) a flat terrain with an axisymmetric hill and (2) a simplified model of an urban area with buildings. The source strength, wind velocity and height of the buildings were varied to investigate their effects on the dispersion profile. The study may offer a viable method for assessment of risks associated with CCS.

The carbon capture and storage (CCS) and enhanced oil recovery (EOR) projects entail the possibility of accidental release of carbon dioxide (CO2) into the atmosphere. To quantify the spread of CO2 following such release, the 'Gaussian' dispersion model is often used to estimate the resulting CO2 concentration levels in the surroundings. The Gaussian model enables quick estimates of the concentration levels. However, the traditionally recommended values of the 'dispersion parameters' in the Gaussian model may not be directly applicable to CO2 dispersion. This paper presents an optimisation technique to obtain the dispersion parameters in order to achieve a quick estimation of CO2 concentration levels in the atmosphere following CO2 blowouts. The optimised dispersion parameters enable the Gaussian model to produce quick estimates of CO2 concentration levels, precluding the necessity to set up and run much more complicated models. Computational fluid dynamics (CFD) models were employed to produce reference CO2 dispersion profiles in various atmospheric stability classes (ASC), different 'source strengths' and degrees of ground roughness. The performance of the CFD models was validated against the 'Kit Fox' field measurements, involving dispersion over a flat horizontal terrain, both with low and high roughness regions. An optimisation model employing a genetic algorithm (GA) to determine the best dispersion parameters in the Gaussian plume model was set up. Optimum values of the dispersion parameters for different ASCs that can be used in the Gaussian plume model for predicting CO2 dispersion were obtained.

The development of the Carbon Capture and Storage (CCS) technique requires an understanding of the hazards posed by the operation of high-pressure CO2 pipelines. To allow the appropriate safety precautions to be taken, a comprehensive understanding of the consequences of unplanned CO2 releases is essential before the deployment of CO2 pipelines. In this paper, we present models for the predictions of discharge rate, atmospheric expansion and dispersion due to accidental CO2 releases from high-pressure pipelines. The GERG-2008 Equation of State (EOS) was used in the discharge and expansion models. This enabled more precise 'source strength' predictions. The performance of the discharge and dispersion models was validated against experimental data. Full-bore ruptures of pipelines carrying CO2 mixtures were simulated using the proposed discharge model. The propagation of the decompression wave in the pipeline and its influence on the release rate are discussed. The effects of major impurities in the CO2 mixture on the discharge rate were also investigated. Considering typical CO2 mixtures in the CCS applications, consequence distances for CO2 pipelines of various sizes at different stagnation pressures were obtained using the dispersion model. In addition, the impact of H2S in a CO2 mixture was studied and the threshold value of the fraction of H2S at the source for which the hazardous effects of H2S become significant was obtained.

Twin-roll strip casting is an effective technology to produce magnesium alloy strips economically. The aim of this work is to propose suitable (optimized) process parameters for manufacturing AZ61 strips using the twin-roll strip casting technology. Experiments on twin-roll strip casting of an AZ61 magnesium alloy were carried out. Temperature fields, fluid flow fields, and stress fields accompanying the process were simulated using thermal-fluid and thermal-mechanical finite element methods. The effects of casting speed and pouring temperature on temperature fields, fluid flow fields, and stress fields during the process were analyzed. It was found that the optimum pouring temperature should be in the range 690 similar to 715 degrees C and the optimum casting speed in the range 2.3 and 2.5 m/min.

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

The carbon capture and storage (CCS) and enhanced oil recovery (EOR) projects entail the possibility of accidental release of carbon dioxide (CO2) into the atmosphere. To quantify the spread of CO2 following such release, the 'Gaussian' dispersion model is often used to estimate the resulting CO2 concentration levels in the surroundings. The Gaussian model enables quick estimates of the concentration levels. However, the traditionally recommended values of the 'dispersion parameters' in the Gaussian model may not be directly applicable to CO2 dispersion. This paper presents an optimisation technique to obtain the dispersion parameters in order to achieve a quick estimation of CO2 concentration levels in the atmosphere following CO2 blowouts. The optimised dispersion parameters enable the Gaussian model to produce quick estimates of CO2 concentration levels, precluding the necessity to set up and run much more complicated models. Computational fluid dynamics (CFD) models were employed to produce reference CO2 dispersion profiles in various atmospheric stability classes (ASC), different 'source strengths' and degrees of ground roughness. The performance of the CFD models was validated against the 'Kit Fox' field measurements, involving dispersion over a flat horizontal terrain, both with low and high roughness regions. An optimisation model employing a genetic algorithm (GA) to determine the best dispersion parameters in the Gaussian plume model was set up. Optimum values of the dispersion parameters for different ASCs that can be used in the Gaussian plume model for predicting CO2 dispersion were obtained.

Twin-roll strip casting is an effective technology to produce magnesium alloy strips economically. The aim of this work is to propose suitable (optimized) process parameters for manufacturing AZ61 strips using the twin-roll strip casting technology. Experiments on twin-roll strip casting of an AZ61 magnesium alloy were carried out. Temperature fields, fluid flow fields, and stress fields accompanying the process were simulated using thermal-fluid and thermal-mechanical finite element methods. The effects of casting speed and pouring temperature on temperature fields, fluid flow fields, and stress fields during the process were analyzed. It was found that the optimum pouring temperature should be in the range 690 similar to 715 degrees C and the optimum casting speed in the range 2.3 and 2.5 m/min.

The development of the Carbon Capture and Storage (CCS) technique requires an understanding of the hazards posed by the operation of high-pressure CO2 pipelines. To allow the appropriate safety precautions to be taken, a comprehensive understanding of the consequences of unplanned CO2 releases is essential before the deployment of CO2 pipelines. In this paper, we present models for the predictions of discharge rate, atmospheric expansion and dispersion due to accidental CO2 releases from high-pressure pipelines. The GERG-2008 Equation of State (EOS) was used in the discharge and expansion models. This enabled more precise 'source strength' predictions. The performance of the discharge and dispersion models was validated against experimental data. Full-bore ruptures of pipelines carrying CO2 mixtures were simulated using the proposed discharge model. The propagation of the decompression wave in the pipeline and its influence on the release rate are discussed. The effects of major impurities in the CO2 mixture on the discharge rate were also investigated. Considering typical CO2 mixtures in the CCS applications, consequence distances for CO2 pipelines of various sizes at different stagnation pressures were obtained using the dispersion model. In addition, the impact of H2S in a CO2 mixture was studied and the threshold value of the fraction of H2S at the source for which the hazardous effects of H2S become significant was obtained.

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

The carbon capture and storage (CCS) and enhanced oil recovery (EOR) projects entail the possibility of accidental release of carbon dioxide (CO2) into the atmosphere. To quantify the spread of CO2 following such release, the 'Gaussian' dispersion model is often used to estimate the resulting CO2 concentration levels in the surroundings. The Gaussian model enables quick estimates of the concentration levels. However, the traditionally recommended values of the 'dispersion parameters' in the Gaussian model may not be directly applicable to CO2 dispersion. This paper presents an optimisation technique to obtain the dispersion parameters in order to achieve a quick estimation of CO2 concentration levels in the atmosphere following CO2 blowouts. The optimised dispersion parameters enable the Gaussian model to produce quick estimates of CO2 concentration levels, precluding the necessity to set up and run much more complicated models. Computational fluid dynamics (CFD) models were employed to produce reference CO2 dispersion profiles in various atmospheric stability classes (ASC), different 'source strengths' and degrees of ground roughness. The performance of the CFD models was validated against the 'Kit Fox' field measurements, involving dispersion over a flat horizontal terrain, both with low and high roughness regions. An optimisation model employing a genetic algorithm (GA) to determine the best dispersion parameters in the Gaussian plume model was set up. Optimum values of the dispersion parameters for different ASCs that can be used in the Gaussian plume model for predicting CO2 dispersion were obtained.

The development of the Carbon Capture and Storage (CCS) technique requires an understanding of the hazards posed by the operation of high-pressure CO2 pipelines. To allow the appropriate safety precautions to be taken, a comprehensive understanding of the consequences of unplanned CO2 releases is essential before the deployment of CO2 pipelines. In this paper, we present models for the predictions of discharge rate, atmospheric expansion and dispersion due to accidental CO2 releases from high-pressure pipelines. The GERG-2008 Equation of State (EOS) was used in the discharge and expansion models. This enabled more precise 'source strength' predictions. The performance of the discharge and dispersion models was validated against experimental data. Full-bore ruptures of pipelines carrying CO2 mixtures were simulated using the proposed discharge model. The propagation of the decompression wave in the pipeline and its influence on the release rate are discussed. The effects of major impurities in the CO2 mixture on the discharge rate were also investigated. Considering typical CO2 mixtures in the CCS applications, consequence distances for CO2 pipelines of various sizes at different stagnation pressures were obtained using the dispersion model. In addition, the impact of H2S in a CO2 mixture was studied and the threshold value of the fraction of H2S at the source for which the hazardous effects of H2S become significant was obtained.

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

Twin-roll strip casting is an effective technology to produce magnesium alloy strips economically. The aim of this work is to propose suitable (optimized) process parameters for manufacturing AZ61 strips using the twin-roll strip casting technology. Experiments on twin-roll strip casting of an AZ61 magnesium alloy were carried out. Temperature fields, fluid flow fields, and stress fields accompanying the process were simulated using thermal-fluid and thermal-mechanical finite element methods. The effects of casting speed and pouring temperature on temperature fields, fluid flow fields, and stress fields during the process were analyzed. It was found that the optimum pouring temperature should be in the range 690 similar to 715 degrees C and the optimum casting speed in the range 2.3 and 2.5 m/min.

The carbon capture and storage (CCS) and enhanced oil recovery (EOR) projects entail the possibility of accidental release of carbon dioxide (CO2) into the atmosphere. To quantify the spread of CO2 following such release, the 'Gaussian' dispersion model is often used to estimate the resulting CO2 concentration levels in the surroundings. The Gaussian model enables quick estimates of the concentration levels. However, the traditionally recommended values of the 'dispersion parameters' in the Gaussian model may not be directly applicable to CO2 dispersion. This paper presents an optimisation technique to obtain the dispersion parameters in order to achieve a quick estimation of CO2 concentration levels in the atmosphere following CO2 blowouts. The optimised dispersion parameters enable the Gaussian model to produce quick estimates of CO2 concentration levels, precluding the necessity to set up and run much more complicated models. Computational fluid dynamics (CFD) models were employed to produce reference CO2 dispersion profiles in various atmospheric stability classes (ASC), different 'source strengths' and degrees of ground roughness. The performance of the CFD models was validated against the 'Kit Fox' field measurements, involving dispersion over a flat horizontal terrain, both with low and high roughness regions. An optimisation model employing a genetic algorithm (GA) to determine the best dispersion parameters in the Gaussian plume model was set up. Optimum values of the dispersion parameters for different ASCs that can be used in the Gaussian plume model for predicting CO2 dispersion were obtained.

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

Twin-roll strip casting is an effective technology to produce magnesium alloy strips economically. The aim of this work is to propose suitable (optimized) process parameters for manufacturing AZ61 strips using the twin-roll strip casting technology. Experiments on twin-roll strip casting of an AZ61 magnesium alloy were carried out. Temperature fields, fluid flow fields, and stress fields accompanying the process were simulated using thermal-fluid and thermal-mechanical finite element methods. The effects of casting speed and pouring temperature on temperature fields, fluid flow fields, and stress fields during the process were analyzed. It was found that the optimum pouring temperature should be in the range 690 similar to 715 degrees C and the optimum casting speed in the range 2.3 and 2.5 m/min.

The development of the Carbon Capture and Storage (CCS) technique requires an understanding of the hazards posed by the operation of high-pressure CO2 pipelines. To allow the appropriate safety precautions to be taken, a comprehensive understanding of the consequences of unplanned CO2 releases is essential before the deployment of CO2 pipelines. In this paper, we present models for the predictions of discharge rate, atmospheric expansion and dispersion due to accidental CO2 releases from high-pressure pipelines. The GERG-2008 Equation of State (EOS) was used in the discharge and expansion models. This enabled more precise 'source strength' predictions. The performance of the discharge and dispersion models was validated against experimental data. Full-bore ruptures of pipelines carrying CO2 mixtures were simulated using the proposed discharge model. The propagation of the decompression wave in the pipeline and its influence on the release rate are discussed. The effects of major impurities in the CO2 mixture on the discharge rate were also investigated. Considering typical CO2 mixtures in the CCS applications, consequence distances for CO2 pipelines of various sizes at different stagnation pressures were obtained using the dispersion model. In addition, the impact of H2S in a CO2 mixture was studied and the threshold value of the fraction of H2S at the source for which the hazardous effects of H2S become significant was obtained.

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

The blades of a large wind turbine are subjected to significant vibrations during operation. The vibrations will impact the dynamic flow field around the blade and consequently alter the aerodynamic forces. In order to better understand the influence of blade vibrations on the aerodynamic loads, the dynamic stall characteristics of an S809 airfoil undergoing various types of motion were investigated using Computational Fluid Dynamics (CFD) techniques. Simulation results indicated that the in-plane and out-of-plane translational motions of the airfoil affect the aerodynamic forces significantly. Furthermore, the influence of vibrations on the aerodynamic loading on the blade of a 5 MW wind turbine was investigated using the Blade Element-Momentum (BEM) theory and the Beddoes-Leishman (B-L) dynamic stall model.

The behavior of internal crack healing in low-carbon steel samples undergoing hot plastic deformation was investigated using the MMS 200 thermo-mechanical simulator. The characterization of cracks after plastic deformation was analyzed using scanning electron microscopy under different heating temperatures, reduction ratios, numbers of deformation passes, strain rates, and holding time durations. It was found that the degree of crack healing increases with increasing heating temperature, reduction ratio, and holding time duration, and with decreasing number of deformation passes and strain rate.

The behavior of internal crack healing in low-carbon steel samples undergoing hot plastic deformation was investigated using the MMS 200 thermo-mechanical simulator. The characterization of cracks after plastic deformation was analyzed using scanning electron microscopy under different heating temperatures, reduction ratios, numbers of deformation passes, strain rates, and holding time durations. It was found that the degree of crack healing increases with increasing heating temperature, reduction ratio, and holding time duration, and with decreasing number of deformation passes and strain rate.

The behavior of internal crack healing in low-carbon steel samples undergoing hot plastic deformation was investigated using the MMS 200 thermo-mechanical simulator. The characterization of cracks after plastic deformation was analyzed using scanning electron microscopy under different heating temperatures, reduction ratios, numbers of deformation passes, strain rates, and holding time durations. It was found that the degree of crack healing increases with increasing heating temperature, reduction ratio, and holding time duration, and with decreasing number of deformation passes and strain rate.

The behavior of internal crack healing in low-carbon steel samples undergoing hot plastic deformation was investigated using the MMS 200 thermo-mechanical simulator. The characterization of cracks after plastic deformation was analyzed using scanning electron microscopy under different heating temperatures, reduction ratios, numbers of deformation passes, strain rates, and holding time durations. It was found that the degree of crack healing increases with increasing heating temperature, reduction ratio, and holding time duration, and with decreasing number of deformation passes and strain rate.

The development of CO2 pipelines for Carbon Capture and Storage (CCS) raises new questions regarding the control of ductile fracture propagation and fracture arrest toughness criteria. The decompression behaviour in the fluid must be determined accurately in order to estimate the proper pipe toughness. However, anthropogenic CO2 may contain impurities that can modify the fluid decompression characteristics quite significantly. To determine the decompression wave speed in CO2 mixtures, the thermodynamic properties of these mixtures must be determined by using an accurate equation of state. In this paper we present a new decompression model developed using the Computational Fluid Dynamics (CFD) package ANSYS Fluent. The GERG-2008 Equation of State (EOS) was implemented into this model through User Defined Functions (UDF) to predict the thermodynamic properties of CO2 mixtures. The model predictions were in good agreement with the experimental data of two 'shock tube' tests. A range of representative CO2 mixtures was examined in terms of the changes in fluid properties from the initial conditions, with time and distance, immediately after a sudden pipeline opening at one end. Phase changes that may occur within the fluid due to condensation of 'impurities' in the fluid were also investigated. Simulations were also conducted to examine how the initial temperature and impurities would affect the decompression wave speed.

This paper describes two separate field experiments involving the venting of natural gas pipelines. The pipelines were 32 km and 60 km in length respectively. The studies were carried out as part of an investigation of the phenomenon of Low Temperature Excursions (LTE) under the aegis of the Energy Pipelines Cooperative Research Centre (EPCRC), Australia. When a highly compressed gas is allowed to escape from a pipeline, the large drop in pressure is accompanied by a significant drop in the temperature of the gas. The general impression is that the pipeline material is also cooled to a comparable extent. This has often led to over-specification of the properties of the pipeline material. Theoretical and CFD studies have shown that although the gas undergoing severe decompression can indeed attain very low temperatures, the adjacent pipe wall does not experience cooling to a comparable extent. This appears to be in part due to the short time scales involved, and due to frictional effects at the gas-pipe wall interface [1]. In the field experiments described, in-situ measurements of gas pressure and pipe wall temperature were carried out. One of the field experiments also involved thermal imaging of the vent pipe surface. The measurements showed that even the most susceptible parts of the vent pipe were not excessively cooled during the event, i.e. much less than the cooling experienced by the gas at the corresponding location. CFD simulations of the highly transient flow in one of the field studies suggest that this may be due to a combination of the time scales involved, and frictional dissipation in severe pipeline decompression, i.e. rapid decompression from an initially high pressure level. Based on the above findings, work is in progress to improve the temperature calculations in computer applications.

Transportation of CO2 in high-pressure pipelines forms a crucial link in the ever-increasing application of Carbon Capture and Storage (CCS) technologies. An unplanned release of CO2 from a pipeline presents a risk to human and animal populations and the environment. Therefore it is very important to develop a deeper understanding of the atmospheric dispersion of CO2 before the deployment of CO2 pipelines, to allow the appropriate safety precautions to be taken. This paper presents a two-stage Computational Fluid Dynamics (CFD) study developed (1) to estimate the source strength, and (2) to simulate the subsequent dispersion of CO2 in the atmosphere, using the source strength estimated in stage (1). The Peng-Robinson (PR) EOS was incorporated into the CFD code. This enabled accurate modelling of the CO2 jet to achieve more precise source strength estimates. The two-stage simulation approach also resulted in a reduction in the overall computing time. The CFD models were validated against experimental results from the British Petroleum (BP) CO2 dispersion trials, and also against results produced by the risk management package Phast. Compared with the measurements, the CFD simulation results showed good agreement in both source strength and dispersion profile predictions. Furthermore, the effect of release direction on the dispersion was studied. The presented research provides a viable method for the assessment of risks associated with CCS.

The bond strength in bimetallic materials is an important material characteristic. In this study, 0.1-mm thick bimetallic foils (AA1050/AA6061) were produced using one pass of accumulative roll bonding followed by three passes of asymmetric rolling (AR). The AR passes were carried out at roll speed ratios of 1.0, 1.1, 1.2, 1.3, and 1.4 separately. Finite element simulation was used to model the deformation of the bimetallic foils for the various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA6061 layers in the simulation. The optimization of the roll speed ratio was obtained for improvement of the bond strength of the interface of AA1050/AA6061 bimetallic foils during AR process. In the simulation, the mean equivalent strain at the interface zone between the AA1050 and AA6061 layers was seen to reach a peak value at a roll speed ratio of about 1.2 to 1.3, which also corresponded to a high quality bond at the interface as observed experimentally.

It is interesting to imagine what would happen when a mixture of soft-boiled eggs and stones is deformed together. A foil made of pure Ti is stronger than that made of Cu. When a composite Cu/Ti foil deforms, the harder Ti will penetrate into the softer Cu in the convex shapes according to previously reported results. In this paper, we describe the fabrication of multilayer Cu/Ti foils by the roll bonding technique and report our observations. The experimental results lead us to propose a new deformation mechanism for a hard metal surrounded by a soft metal during rolling of a laminated foil, particularly when the thickness of hard metal foil (Ti, 25 mm) is much less than that of the soft metal foil (Cu, 300 mm). Transmission Electron Microscope (TEM) imaging results show that the hard metal penetrates into the soft metal in the form of concave protrusions. Finite element simulations of the rolling process of a Cu/Ti/Cu composite foil are described. Finally, we focus on an analysis of the deformation mechanism of Ti foils and its effects on grain refinement, and propose a grain refinement mechanism from the inside to the outside of the laminates during rolling.

An asymmetric cryorolling technique was used to reduce the thickness of an Al-Mg-Si alloy sheet from 1.5 mm to 0.19 mm. The samples were subsequently aged for 48 h at 100 degrees celcius. The hardness and tensile strength of both rolled and aged sheets increased with the number of passes up to the sixth pass, but the tensile stress decreased after the seventh pass. Investigation of the microstructure of the sheets showed that the grain size after seven passes was about 235 nm and revealed the presence of Fe-Cr-Mn-Si particles in the samples. The deformation of Fe-Cr-Mn-Si particles and sheet thickness affects the ductility when the sheet thickness is less than 0.4 mm, and the strength when the thickness is less than 0.2 mm.

This paper reports a new technique that combines the features of Accumulative Roll Bonding (ARB) and Asymmetric Rolling (AR). This technique has been developed to enable production of ultra-thin bimetallic foils. Initially, 1.5 mm thick AA1050 and AA6061 foils were roll-bonded using ARB at 2006C, with 50% reduction. The resulting 1.5 mm bimetallic foil was subsequently thinned to 0.04 mm through four AR passes at room temperature. The speed ratio between the upper and lower AR rolls was 151.3. The tensile strength of the bimetallic foil was seen to increase with reduction in thickness. The ductility of the foil was seen to reduce upon decreasing the foil thickness from 1.5 mm to 0.14 mm, but increase upon further reduction in thickness from 0.14 mm to 0.04 mm. The grain size was about 140 nm for the AA6061 layer and 235 nm for the AA1050 layer, after the third AR pass.

ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of material fracture. Since the gas is generally transported under high operating pressures, it must be ensured that the gas pipeline is sufficiently tough to arrest the propagation of any potential fracture. For several decades, control of gas pipeline fracture propagation has been under scrutiny due to economic considerations and ecological and safety hazards related to pressurised pipe failure. The Battelle Two Curve approach has been widely used to determine the minimum material arrest toughness by comparing the gas decompression wave velocity with the fracture velocity, both as functions of the local gas pressure. Sufficient knowledge of the gas decompression behavior following the rupture is therefore crucial in determining running fracture arrest toughness levels. The decompression behaviour is influenced by the operating conditions, fluid composition and the material properties of the pipeline itself. This paper describes a two-dimensional decompression model developed using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. The GERG-2008 Equation of State has been implemented into this model to simulate the rapid decompression of common natural gas mixtures. The evolution of the decompression wave speed and phase changes under arbitrary initial conditions is reported. Comparison with experimental results obtained from shock tube tests showed good agreement between simulation and experiment.

ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of material fracture. Since the gas is generally transported under high operating pressures, it must be ensured that the gas pipeline is sufficiently tough to arrest the propagation of any potential fracture. For several decades, control of gas pipeline fracture propagation has been under scrutiny due to economic considerations and ecological and safety hazards related to pressurised pipe failure. The Battelle Two Curve approach has been widely used to determine the minimum material arrest toughness by comparing the gas decompression wave velocity with the fracture velocity, both as functions of the local gas pressure. Sufficient knowledge of the gas decompression behavior following the rupture is therefore crucial in determining running fracture arrest toughness levels. The decompression behaviour is influenced by the operating conditions, fluid composition and the material properties of the pipeline itself. This paper describes a two-dimensional decompression model developed using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. The GERG-2008 Equation of State has been implemented into this model to simulate the rapid decompression of common natural gas mixtures. The evolution of the decompression wave speed and phase changes under arbitrary initial conditions is reported. Comparison with experimental results obtained from shock tube tests showed good agreement between simulation and experiment.

ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of material fracture. Since the gas is generally transported under high operating pressures, it must be ensured that the gas pipeline is sufficiently tough to arrest the propagation of any potential fracture. For several decades, control of gas pipeline fracture propagation has been under scrutiny due to economic considerations and ecological and safety hazards related to pressurised pipe failure. The Battelle Two Curve approach has been widely used to determine the minimum material arrest toughness by comparing the gas decompression wave velocity with the fracture velocity, both as functions of the local gas pressure. Sufficient knowledge of the gas decompression behavior following the rupture is therefore crucial in determining running fracture arrest toughness levels. The decompression behaviour is influenced by the operating conditions, fluid composition and the material properties of the pipeline itself. This paper describes a two-dimensional decompression model developed using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. The GERG-2008 Equation of State has been implemented into this model to simulate the rapid decompression of common natural gas mixtures. The evolution of the decompression wave speed and phase changes under arbitrary initial conditions is reported. Comparison with experimental results obtained from shock tube tests showed good agreement between simulation and experiment.

ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of material fracture. Since the gas is generally transported under high operating pressures, it must be ensured that the gas pipeline is sufficiently tough to arrest the propagation of any potential fracture. For several decades, control of gas pipeline fracture propagation has been under scrutiny due to economic considerations and ecological and safety hazards related to pressurised pipe failure. The Battelle Two Curve approach has been widely used to determine the minimum material arrest toughness by comparing the gas decompression wave velocity with the fracture velocity, both as functions of the local gas pressure. Sufficient knowledge of the gas decompression behavior following the rupture is therefore crucial in determining running fracture arrest toughness levels. The decompression behaviour is influenced by the operating conditions, fluid composition and the material properties of the pipeline itself. This paper describes a two-dimensional decompression model developed using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. The GERG-2008 Equation of State has been implemented into this model to simulate the rapid decompression of common natural gas mixtures. The evolution of the decompression wave speed and phase changes under arbitrary initial conditions is reported. Comparison with experimental results obtained from shock tube tests showed good agreement between simulation and experiment.

Globally, steel pipelines are widely used to transport energy in the form of liquid petroleum and natural gas. The steel used in the manufacture of these pipelines must have high strength and toughness, and high resistance to fracture. The Drop Weight Tear Test (DWTT) is the most widely used test to assess brittle fracture characteristics in steel. The zones of ductile and brittle fracture during DWTT characterize the quality of pipeline steels. In this paper, the Gurson-Tvergaard-Needleman (GTN) fracture models are coupled in a Finite Element model. The ductile and brittle fracture zones in the samples are analyzed under different conditions. The results show that the change in fracture mode during the DWTT is from the brittle to the ductile, then again to the brittle. The calculated absorbed energies during DWTT compare well with experimental findings. Finally, we present an analysis of the transition from ductile to brittle fracture under different conditions.

An asymmetric cryorolling technique was used to reduce the thickness of an Al-Mg-Si alloy sheet from 1.5 mm to 0.19 mm. The samples were subsequently aged for 48 h at 100 degrees celcius. The hardness and tensile strength of both rolled and aged sheets increased with the number of passes up to the sixth pass, but the tensile stress decreased after the seventh pass. Investigation of the microstructure of the sheets showed that the grain size after seven passes was about 235 nm and revealed the presence of Fe-Cr-Mn-Si particles in the samples. The deformation of Fe-Cr-Mn-Si particles and sheet thickness affects the ductility when the sheet thickness is less than 0.4 mm, and the strength when the thickness is less than 0.2 mm.

This paper reports a new technique that combines the features of Accumulative Roll Bonding (ARB) and Asymmetric Rolling (AR). This technique has been developed to enable production of ultra-thin bimetallic foils. Initially, 1.5 mm thick AA1050 and AA6061 foils were roll-bonded using ARB at 2006C, with 50% reduction. The resulting 1.5 mm bimetallic foil was subsequently thinned to 0.04 mm through four AR passes at room temperature. The speed ratio between the upper and lower AR rolls was 151.3. The tensile strength of the bimetallic foil was seen to increase with reduction in thickness. The ductility of the foil was seen to reduce upon decreasing the foil thickness from 1.5 mm to 0.14 mm, but increase upon further reduction in thickness from 0.14 mm to 0.04 mm. The grain size was about 140 nm for the AA6061 layer and 235 nm for the AA1050 layer, after the third AR pass.

The Eckert number emerges as an important non-dimensional parameter, in addition to the Reynolds number and the Prandtl number, in problems involving heat transfer in compressible flows. The Eckert number is considered to represent a ratio of the flow kinetic energy at the wall and the specific enthalpy difference between the wall and the fluid, and is important when viscous dissipation is significant. This paper investigates the role played by the Eckert number during rapid decompression of high pressure gas pipelines. During such processes, the gas temperature attains very low values corresponding to sonic flow at the vent location, and it is often assumed that the pipeline material is also cooled to a comparable degree ("Low Temperature Excursions"). This has often led to over-specification of the properties required of the pipeline material. In this paper, it is shown using Computational Fluid Dynamics (CFD) simulations that the highly complex flow during rapid decompression of high-pressure gas pipelines leads to significant frictional dissipation (heating) adjacent to the pipe wall. This prevents the pipeline from attaining excessively low temperatures. It is shown that frictional heating may sometimes lead to a heat transfer reversal. This finding may help pipeline designers in making appropriate recommendations regarding the properties required of the pipeline materials. The paper also describes a preliminary experiment designed carried out to validate the CFD simulations. More detailed experiments are under way.

The Eckert number emerges as an important non-dimensional parameter, in addition to the Reynolds number and the Prandtl number, in problems involving heat transfer in compressible flows. The Eckert number is considered to represent a ratio of the flow kinetic energy at the wall and the specific enthalpy difference between the wall and the fluid, and is important when viscous dissipation is significant. This paper investigates the role played by the Eckert number during rapid decompression of high pressure gas pipelines. During such processes, the gas temperature attains very low values corresponding to sonic flow at the vent location, and it is often assumed that the pipeline material is also cooled to a comparable degree ("Low Temperature Excursions"). This has often led to over-specification of the properties required of the pipeline material. In this paper, it is shown using Computational Fluid Dynamics (CFD) simulations that the highly complex flow during rapid decompression of high-pressure gas pipelines leads to significant frictional dissipation (heating) adjacent to the pipe wall. This prevents the pipeline from attaining excessively low temperatures. It is shown that frictional heating may sometimes lead to a heat transfer reversal. This finding may help pipeline designers in making appropriate recommendations regarding the properties required of the pipeline materials. The paper also describes a preliminary experiment designed carried out to validate the CFD simulations. More detailed experiments are under way.