Search

In recent years, artificial intelligence has played an important role in medicine and disease diagnosis, with many applications to be mentioned, one of which is Medical Visual Question Answering (MedVQA). By combining computer vision and natural language processing, MedVQA systems can assist experts in extracting relevant information from medical image based on a given question and providing precise diagnostic answers. The ImageCLEFmed-MEDVQA-GI-2023 challenge carried out visual question answering task in the gastrointestinal domain, which includes gastroscopy and colonoscopy images. Our team approached Task 1 of the challenge by proposing a multimodal learning method with image enhancement to improve the VQA performance on gastrointestinal images. The multimodal architecture is set up with BERT encoder and different pre-trained vision models based on convolutional neural network (CNN) and Transformer architecture for features extraction from question and endoscopy image. The result of this study highlights the dominance of Transformer-based vision models over the CNNs and demonstrates the effectiveness of the image enhancement process, with six out of the eight vision models achieving better F1-Score. Our best method, which takes advantages of BERT+BEiT fusion and image enhancement, achieves up to 87.25% accuracy and 91.85% F1-Score on the development test set, while also producing good result on the private test set with accuracy of 82.01%., Comment: ImageCLEF2023 published version: https://ceur-ws.org/Vol-3497/paper-129.pdf

Equal channel angular pressing (ECAP) has attracted a lot of interest due to its ability for fabrication of bulk ultrafine-grained materials. With the development of computer skills, the computer-aided methods become very important and useful in understanding the deformation mechanism of ECAP. In this study, the influence of mesh size during finite element simulations of ECAP has been examined based on the plane strain condition assumption. Four different meshes have been compared and these results indicate that Mesh 600 and Mesh 2400 fail to capture the deformation features of ECAP accurately. Large corner gaps develop in these two cases and the simulated strains are smaller than the analytical calculations. Similar results have been obtained between Mesh 6369 and Mesh 12000 and the predicted features of plastic deformation and texture evolution are consistent with the experimental results.

The MMS-2B wear machine was used to study abrasion wear of work rolls in cold rolling by simulating emulsion cooling during the cold rolling process. The work roll materials used were 4%Cr, same as those in industrial production. The surface SEM scanning photographs were taken every 30 minutes until the friction experiment finished, and erosive appearance of emulsion on the work roll surface could be seen in the photos. The corrosive wear of the work roll surface is discussed. Findings show that the main causes of stress corrosion and pitting corrosion are uneven microstructure on the work roll surface and a large number of dislocation accumulations, which form microscopic cells. Water in steel rolling emulsion is the main conductive medium of electrochemistry reaction, and this intensifies the corrosive wear.

The MMS-2B wear machine was used to study abrasion wear of work rolls in cold rolling by simulating emulsion cooling during the cold rolling process. The work roll materials used were 4%Cr, same as those in industrial production. The surface SEM scanning photographs were taken every 30 minutes until the friction experiment finished, and erosive appearance of emulsion on the work roll surface could be seen in the photos. The corrosive wear of the work roll surface is discussed. Findings show that the main causes of stress corrosion and pitting corrosion are uneven microstructure on the work roll surface and a large number of dislocation accumulations, which form microscopic cells. Water in steel rolling emulsion is the main conductive medium of electrochemistry reaction, and this intensifies the corrosive wear.

The MMS-2B wear machine was used to study abrasion wear of work rolls in cold rolling by simulating emulsion cooling during the cold rolling process. The work roll materials used were 4%Cr, same as those in industrial production. The surface SEM scanning photographs were taken every 30 minutes until the friction experiment finished, and erosive appearance of emulsion on the work roll surface could be seen in the photos. The corrosive wear of the work roll surface is discussed. Findings show that the main causes of stress corrosion and pitting corrosion are uneven microstructure on the work roll surface and a large number of dislocation accumulations, which form microscopic cells. Water in steel rolling emulsion is the main conductive medium of electrochemistry reaction, and this intensifies the corrosive wear.

High pressure torsion (HPT) is an efficient technique of producing ultrafine grained materials with exceptional small grain size. In this study, a crystal plasticity finite element method (CPFEM) model has been developed to investigate the plastic deformation behavior of pure aluminum single crystal during the HPT process. The simulation results show that, the distribution and evolution of the macroscopic plastic strain and the accumulative shear strain are similar. The value increases with the increase of the distance from the center as well as the number of revolution. The simulation is capable of reflecting the anisotropic characteristics of HPT deformation, a non-homogenous deformation along the circumference of the sample could be observed. At the early stage of HPT deformation, the critical resolved shear stress (CRSS) along the radial direction presents a rapid increase, followed by a moderate increase and then reaches the near-saturate state. As the HPT deformation proceeds, there is a relatively weak increase in the quasi-saturate value and the near-steady region expands gradually towards the sample center. The orientation changes during the HPT process with increasing applied strain predicted by the developed CPFEM model are also presented.

The MMS-2B wear machine was used to study abrasion wear of work rolls in cold rolling by simulating emulsion cooling during the cold rolling process. The work roll materials used were 4%Cr, same as those in industrial production. The surface SEM scanning photographs were taken every 30 minutes until the friction experiment finished, and erosive appearance of emulsion on the work roll surface could be seen in the photos. The corrosive wear of the work roll surface is discussed. Findings show that the main causes of stress corrosion and pitting corrosion are uneven microstructure on the work roll surface and a large number of dislocation accumulations, which form microscopic cells. Water in steel rolling emulsion is the main conductive medium of electrochemistry reaction, and this intensifies the corrosive wear.

Equal channel angular pressing (ECAP) has attracted a lot of interest due to its ability for fabrication of bulk ultrafine-grained materials. With the development of computer skills, the computer-aided methods become very important and useful in understanding the deformation mechanism of ECAP. In this study, the influence of mesh size during finite element simulations of ECAP has been examined based on the plane strain condition assumption. Four different meshes have been compared and these results indicate that Mesh 600 and Mesh 2400 fail to capture the deformation features of ECAP accurately. Large corner gaps develop in these two cases and the simulated strains are smaller than the analytical calculations. Similar results have been obtained between Mesh 6369 and Mesh 12000 and the predicted features of plastic deformation and texture evolution are consistent with the experimental results.

In this paper, a solid lubricant has been applied to the warm rolling process of interstitial free (IF) steel and its effect has been studied compared with dry condition. The solid lubricant effectively reduced the rolling force. The surface quality and microstructure of strips were improved by solid lubricant during warm rolling process. The high temperature behaviour of the solid lubricant has been in situ observed in a high temperature laser scanning confocal microscope. A series of pin on disc tests with different temperatures and lubrication conditions were carried out to study the contact behaviour of this solid lubricant in contact area. The results show that the solid lubricant can effectively eliminate the surface defect and reduce the wear and oxidation in the contact zone compared with the dry sliding condition. The contact surface under solid lubricant condition presents a lower friction coefficient compared to the dry condition.

Equal channel angular pressing (ECAP), or equal channel angular extrusion (ECAE), is a very promising severe plastic deformation technique for producing ultra-fine grained (UFG) materials. Up to now, many works have been contributed to understand the influence of die geometry, frictional condition and back-pressure during the ECAP process. Most of them only focused on a specific sample size, and very few investigations about the sample size effect have been reported. Therefore, the present investigation was designed specifically to provide systematical information on the influence of sample size on the deformation heterogeneity and texture development after ECAP. To the authors' knowledge, this is the first attempt to consider the sample dimension influence on the texture evolution of ECAP processed aluminum single crystals. Study has been successfully conducted using crystal plasticity finite element model for four different samples having widths between 2 mm and 40 mm. For each of sample, the simulated effective plastic strain is close to the theoretical value. The calculated shear strength and stress decreased slightly with the sample width, but show very little change at larger samples. Simulation results revealed similar deformation heterogeneity during the process as the reference. The predicted {1 1 1} pole figures and activity of slip systems indicate that the texture evolution is independent of the sample dimension. Simulation results are consistent with the experimental observations when the same initial crystallographic orientation and sample size have been used. The present work offers a good suggestion for the scaling up of the ECAP process for the industrial application from the views of both deformation pattern and evolution of texture. © 2013 Elsevier B.V. All rights reserved.

In order to improve the efficiency of grain refinement, a study on the modified process (called Non-equal channel angular pressing) from the conventional equal channel angular pressing has been conducted. The deformation behavior of aluminum alloy AA1050 deformed by the Non-equal channel angular pressing which has a smaller width in the exit channel than the entry channel was examined based on the finite element simulations. The results revealed that a smaller ratio of dE and dI (dE/dI) leads to a larger equivalent plastic strain. It is not only beneficial to enhance the plastic deformation but also very helpful to get rid of the development of dead zone in the outer corner of die by decreasing the exit channel width by comparing with the conventional process. © (2013) Trans Tech Publications, Switzerland.

Severe plastic deformation (SPD) techniques have attracted significant attention in the last two decades due to its capacity of producing bulk ultra-fine grained (UFG) or nanostructured materials, by imposing very high plastic strain. Equal channel angular pressing (ECAP), or equal channel angular extrusion (ECAE), is one of the most widely used SPD techniques. During ECAP, a sample is pressed through a die which consists of two channels with equal cross-section intersecting at an angle varying from 60 degrees to 150 degrees. Since the cross-section geometry of the sample remains nearly unchanged, the materials can be deformed to a very high strain by repeating the process. The deformation mechanism of ECAP is very complicated and it is dependent on the die geometry and material properties. It has been assumed as simple shear on the intersecting plane of two channels at ideal conditions, such as frictionless, perfectly plastic material and very sharp outer corner. However, from the view of texture evolutions, many experimental results have revealed the deviation from the ideal simple shear. Therefore, an insight into the deformation mechanism and orientation changes in the real ECAP case is still essential. In the present work, a comprehensive study based on the crystal plasticity finite element model (CPFEM) has been conducted to investigate the stress state, plastic strain, required load and crystallographic orientation development history of aluminum single crystals subjected to ECAP. The influence factors such as ECAP die geometry, frictional conditions and initial crystallographic orientations have been studied in detail. 2013 AIP Publishing LLC.

1050/6061 laminated composite sheets have been fabricated by the accumulative roll bonding (ARB) using commercial 1050 and 6061 aluminium alloys. Through-thickness hardness and tensile testes have been conducted to examine the mechanical properties of the laminated composites. It has been found that the strength of the composite materials is between the strengths of 6061 and 1050 primary materials. The average hardness of the 6061 layer is almost twice of the average value of the 1050 layer for both one and two-cycle processed composites. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used to evaluate the microstructure of the composites. Grain refinement has been observed for both the 1050 and 6061 layers. The 1050 layer showed coarser and more equiaxed microstructure than the 6061 layer after the second ARB cycle.

Severe plastic deformation (SPD) techniques have attracted significant attention in the last two decades due to its capacity of producing bulk ultra-fine grained (UFG) or nanostructured materials, by imposing very high plastic strain. Equal channel angular pressing (ECAP), or equal channel angular extrusion (ECAE), is one of the most widely used SPD techniques. During ECAP, a sample is pressed through a die which consists of two channels with equal cross-section intersecting at an angle varying from 60 degrees to 150 degrees. Since the cross-section geometry of the sample remains nearly unchanged, the materials can be deformed to a very high strain by repeating the process. The deformation mechanism of ECAP is very complicated and it is dependent on the die geometry and material properties. It has been assumed as simple shear on the intersecting plane of two channels at ideal conditions, such as frictionless, perfectly plastic material and very sharp outer corner. However, from the view of texture evolutions, many experimental results have revealed the deviation from the ideal simple shear. Therefore, an insight into the deformation mechanism and orientation changes in the real ECAP case is still essential. In the present work, a comprehensive study based on the crystal plasticity finite element model (CPFEM) has been conducted to investigate the stress state, plastic strain, required load and crystallographic orientation development history of aluminum single crystals subjected to ECAP. The influence factors such as ECAP die geometry, frictional conditions and initial crystallographic orientations have been studied in detail. 2013 AIP Publishing LLC.

This paper presents the application of four nonlinear methods of feature extraction in slewing bearing condition monitoring and prognosis: these are largest Lyapunov exponent, fractal dimension, correlation dimension, and approximate entropy methods. Although correlation dimension and approximate entropy methods have been used previously, the largest Lyapunov exponent and fractal dimension methods have not been used in vibration condition monitoring to date. The vibration data of the laboratory slewing bearing test-rig run at 1 rpm was acquired daily from February to August 2007 (138 days). As time progressed, a more accurate observation of the alteration of bearing condition from normal to faulty was obtained using nonlinear features extraction. These findings suggest that these methods provide superior descriptive information about bearing condition than time-domain features extraction, such as root mean square (RMS), variance, skewness and kurtosis.

1050/6061 laminated composite sheets have been fabricated by the accumulative roll bonding (ARB) using commercial 1050 and 6061 aluminium alloys. Through-thickness hardness and tensile testes have been conducted to examine the mechanical properties of the laminated composites. It has been found that the strength of the composite materials is between the strengths of 6061 and 1050 primary materials. The average hardness of the 6061 layer is almost twice of the average value of the 1050 layer for both one and two-cycle processed composites. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used to evaluate the microstructure of the composites. Grain refinement has been observed for both the 1050 and 6061 layers. The 1050 layer showed coarser and more equiaxed microstructure than the 6061 layer after the second ARB cycle.

Severe plastic deformation (SPD) techniques have attracted significant attention in the last two decades due to its capacity of producing bulk ultra-fine grained (UFG) or nanostructured materials, by imposing very high plastic strain. Equal channel angular pressing (ECAP), or equal channel angular extrusion (ECAE), is one of the most widely used SPD techniques. During ECAP, a sample is pressed through a die which consists of two channels with equal cross-section intersecting at an angle varying from 60 degrees to 150 degrees. Since the cross-section geometry of the sample remains nearly unchanged, the materials can be deformed to a very high strain by repeating the process. The deformation mechanism of ECAP is very complicated and it is dependent on the die geometry and material properties. It has been assumed as simple shear on the intersecting plane of two channels at ideal conditions, such as frictionless, perfectly plastic material and very sharp outer corner. However, from the view of texture evolutions, many experimental results have revealed the deviation from the ideal simple shear. Therefore, an insight into the deformation mechanism and orientation changes in the real ECAP case is still essential. In the present work, a comprehensive study based on the crystal plasticity finite element model (CPFEM) has been conducted to investigate the stress state, plastic strain, required load and crystallographic orientation development history of aluminum single crystals subjected to ECAP. The influence factors such as ECAP die geometry, frictional conditions and initial crystallographic orientations have been studied in detail. 2013 AIP Publishing LLC.

This paper presents the application of four nonlinear methods of feature extraction in slewing bearing condition monitoring and prognosis: these are largest Lyapunov exponent, fractal dimension, correlation dimension, and approximate entropy methods. Although correlation dimension and approximate entropy methods have been used previously, the largest Lyapunov exponent and fractal dimension methods have not been used in vibration condition monitoring to date. The vibration data of the laboratory slewing bearing test-rig run at 1 rpm was acquired daily from February to August 2007 (138 days). As time progressed, a more accurate observation of the alteration of bearing condition from normal to faulty was obtained using nonlinear features extraction. These findings suggest that these methods provide superior descriptive information about bearing condition than time-domain features extraction, such as root mean square (RMS), variance, skewness and kurtosis.

This paper presents the application of four nonlinear methods of feature extraction in slewing bearing condition monitoring and prognosis: these are largest Lyapunov exponent, fractal dimension, correlation dimension, and approximate entropy methods. Although correlation dimension and approximate entropy methods have been used previously, the largest Lyapunov exponent and fractal dimension methods have not been used in vibration condition monitoring to date. The vibration data of the laboratory slewing bearing test-rig run at 1 rpm was acquired daily from February to August 2007 (138 days). As time progressed, a more accurate observation of the alteration of bearing condition from normal to faulty was obtained using nonlinear features extraction. These findings suggest that these methods provide superior descriptive information about bearing condition than time-domain features extraction, such as root mean square (RMS), variance, skewness and kurtosis.

1050/6061 laminated composite sheets have been fabricated by the accumulative roll bonding (ARB) using commercial 1050 and 6061 aluminium alloys. Through-thickness hardness and tensile testes have been conducted to examine the mechanical properties of the laminated composites. It has been found that the strength of the composite materials is between the strengths of 6061 and 1050 primary materials. The average hardness of the 6061 layer is almost twice of the average value of the 1050 layer for both one and two-cycle processed composites. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used to evaluate the microstructure of the composites. Grain refinement has been observed for both the 1050 and 6061 layers. The 1050 layer showed coarser and more equiaxed microstructure than the 6061 layer after the second ARB cycle.

1050/6061 laminated composite sheets have been fabricated by the accumulative roll bonding (ARB) using commercial 1050 and 6061 aluminium alloys. Through-thickness hardness and tensile testes have been conducted to examine the mechanical properties of the laminated composites. It has been found that the strength of the composite materials is between the strengths of 6061 and 1050 primary materials. The average hardness of the 6061 layer is almost twice of the average value of the 1050 layer for both one and two-cycle processed composites. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used to evaluate the microstructure of the composites. Grain refinement has been observed for both the 1050 and 6061 layers. The 1050 layer showed coarser and more equiaxed microstructure than the 6061 layer after the second ARB cycle.

1050/6061 laminated composite sheets have been fabricated by the accumulative roll bonding (ARB) using commercial 1050 and 6061 aluminium alloys. Through-thickness hardness and tensile testes have been conducted to examine the mechanical properties of the laminated composites. It has been found that the strength of the composite materials is between the strengths of 6061 and 1050 primary materials. The average hardness of the 6061 layer is almost twice of the average value of the 1050 layer for both one and two-cycle processed composites. Optical microscopy, scanning electron microscopy and transmission electron microscopy were used to evaluate the microstructure of the composites. Grain refinement has been observed for both the 1050 and 6061 layers. The 1050 layer showed coarser and more equiaxed microstructure than the 6061 layer after the second ARB cycle.

In this paper, a solid lubricant has been applied to the warm rolling process of interstitial free (IF) steel and its effect has been studied compared with dry condition. The solid lubricant effectively reduced the rolling force. The surface quality and microstructure of strips were improved by solid lubricant during warm rolling process. The high temperature behaviour of the solid lubricant has been in situ observed in a high temperature laser scanning confocal microscope. A series of pin on disc tests with different temperatures and lubrication conditions were carried out to study the contact behaviour of this solid lubricant in contact area. The results show that the solid lubricant can effectively eliminate the surface defect and reduce the wear and oxidation in the contact zone compared with the dry sliding condition. The contact surface under solid lubricant condition presents a lower friction coefficient compared to the dry condition.

Severe plastic deformation (SPD) techniques have attracted significant attention in the last two decades due to its capacity of producing bulk ultra-fine grained (UFG) or nanostructured materials, by imposing very high plastic strain. Equal channel angular pressing (ECAP), or equal channel angular extrusion (ECAE), is one of the most widely used SPD techniques. During ECAP, a sample is pressed through a die which consists of two channels with equal cross-section intersecting at an angle varying from 60 degrees to 150 degrees. Since the cross-section geometry of the sample remains nearly unchanged, the materials can be deformed to a very high strain by repeating the process. The deformation mechanism of ECAP is very complicated and it is dependent on the die geometry and material properties. It has been assumed as simple shear on the intersecting plane of two channels at ideal conditions, such as frictionless, perfectly plastic material and very sharp outer corner. However, from the view of texture evolutions, many experimental results have revealed the deviation from the ideal simple shear. Therefore, an insight into the deformation mechanism and orientation changes in the real ECAP case is still essential. In the present work, a comprehensive study based on the crystal plasticity finite element model (CPFEM) has been conducted to investigate the stress state, plastic strain, required load and crystallographic orientation development history of aluminum single crystals subjected to ECAP. The influence factors such as ECAP die geometry, frictional conditions and initial crystallographic orientations have been studied in detail. 2013 AIP Publishing LLC.

Equal channel angular pressing (ECAP), or equal channel angular extrusion (ECAE), is a very promising severe plastic deformation technique for producing ultra-fine grained (UFG) materials. Up to now, many works have been contributed to understand the influence of die geometry, frictional condition and back-pressure during the ECAP process. Most of them only focused on a specific sample size, and very few investigations about the sample size effect have been reported. Therefore, the present investigation was designed specifically to provide systematical information on the influence of sample size on the deformation heterogeneity and texture development after ECAP. To the authors' knowledge, this is the first attempt to consider the sample dimension influence on the texture evolution of ECAP processed aluminum single crystals. Study has been successfully conducted using crystal plasticity finite element model for four different samples having widths between 2 mm and 40 mm. For each of sample, the simulated effective plastic strain is close to the theoretical value. The calculated shear strength and stress decreased slightly with the sample width, but show very little change at larger samples. Simulation results revealed similar deformation heterogeneity during the process as the reference. The predicted {1 1 1} pole figures and activity of slip systems indicate that the texture evolution is independent of the sample dimension. Simulation results are consistent with the experimental observations when the same initial crystallographic orientation and sample size have been used. The present work offers a good suggestion for the scaling up of the ECAP process for the industrial application from the views of both deformation pattern and evolution of texture. © 2013 Elsevier B.V. All rights reserved.

In order to improve the efficiency of grain refinement, a study on the modified process (called Non-equal channel angular pressing) from the conventional equal channel angular pressing has been conducted. The deformation behavior of aluminum alloy AA1050 deformed by the Non-equal channel angular pressing which has a smaller width in the exit channel than the entry channel was examined based on the finite element simulations. The results revealed that a smaller ratio of dE and dI (dE/dI) leads to a larger equivalent plastic strain. It is not only beneficial to enhance the plastic deformation but also very helpful to get rid of the development of dead zone in the outer corner of die by decreasing the exit channel width by comparing with the conventional process. © (2013) Trans Tech Publications, Switzerland.

This paper presents the application of four nonlinear methods of feature extraction in slewing bearing condition monitoring and prognosis: these are largest Lyapunov exponent, fractal dimension, correlation dimension, and approximate entropy methods. Although correlation dimension and approximate entropy methods have been used previously, the largest Lyapunov exponent and fractal dimension methods have not been used in vibration condition monitoring to date. The vibration data of the laboratory slewing bearing test-rig run at 1 rpm was acquired daily from February to August 2007 (138 days). As time progressed, a more accurate observation of the alteration of bearing condition from normal to faulty was obtained using nonlinear features extraction. These findings suggest that these methods provide superior descriptive information about bearing condition than time-domain features extraction, such as root mean square (RMS), variance, skewness and kurtosis.

This paper is part of a larger study to understand the wear of hot rolling rolls. A significant cost of the hot rolling process is associated with the consumption of rolls, which is why a comprehensive understanding of the wear of the roll material is important. Given that the surface of the rolls is covered by an oxide layer, it is important to know the tribological and mechanical properties of the oxides. Research in this area concentrates mainly on the morphologies and microstructures of the oxide layers. Previously published works give very little, if any, information of the mechanical properties of the layers on high speed steel. This paper presents a methodology to study the mechanical properties of the oxide layer formed on the surface of a high speed steel roll using combined nanoindentation tests and finite element simulations. Mechanical properties such as the elastic modulus (E), hardness (H), yield strength (sigma(y)), and Poisson's ratio (nu), have been determined, and the work has revealed a variation of microstructure, porosity (f), and mechanical properties of the oxide layer across its thickness. The outer sub-layer has a higher E and H than the inner sub-layer. This variation of mechanical properties in the oxide layer was consistent with variations in the porosity and grain sizes in the two sub-layers. (C) 2012 Elsevier B.V. All rights reserved.

"Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes.It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size.Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation.Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process.The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies.The CT-ECAPed samples had a higher fraction of monovacancies and divacancies.These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples.A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.(c) 2012 Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved."

In this paper, finite element model is used to carry out thermal analysis of bead-on-plate welding. The model followed the proposed five step strategies which were then built into a model to obtain temperature history at the positions of thermocouples. Temperature field was also evaluated by comparing predicted weld bead with the actual weld bead. Using these proposed strategies, well matched temperature histories and temperature field have been obtained.

"Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes.It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size.Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation.Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process.The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies.The CT-ECAPed samples had a higher fraction of monovacancies and divacancies.These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples.A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.(c) 2012 Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved."

In this paper, finite element model is used to carry out thermal analysis of bead-on-plate welding. The model followed the proposed five step strategies which were then built into a model to obtain temperature history at the positions of thermocouples. Temperature field was also evaluated by comparing predicted weld bead with the actual weld bead. Using these proposed strategies, well matched temperature histories and temperature field have been obtained.

"Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes.It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size.Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation.Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process.The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies.The CT-ECAPed samples had a higher fraction of monovacancies and divacancies.These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples.A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.(c) 2012 Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved."

In this paper, finite element model is used to carry out thermal analysis of bead-on-plate welding. The model followed the proposed five step strategies which were then built into a model to obtain temperature history at the positions of thermocouples. Temperature field was also evaluated by comparing predicted weld bead with the actual weld bead. Using these proposed strategies, well matched temperature histories and temperature field have been obtained.

Different types of defects can be introduced into graphene during material synthesis, and significantly influence the properties of graphene. In this work, we investigated the effects of structural defects, edge functionalisation and reconstruction on the fracture strength and morphology of graphene by molecular dynamics simulations. The minimum energy path analysis was conducted to investigate the formation of Stone-Wales defects. We also employed out-of-plane perturbation and energy minimization principle to study the possi-ble morphology of graphene nanoribbons with edge-termination. Our numerical results show that the fracture strength of graphene is dependent on defects and environmental temperature. However, pre-existing defects may be healed, resulting in strength recovery. Edge functionalization can induce compressive stress and ripples in the edge areas of gra-phene nanoribbons. On the other hand, edge reconstruction contributed to the tensile stress and curved shape in the graphene nanoribbons.

This work is motivated by the need to efficiently machine the edges of ophthalmic polymer lenses for mounting in spectacle or instrument frames. The polymer materials used are required to have suitable optical characteristics such high refractive index and Abbe number, combined with low density and high scratch and impact resistance. Edge surface finish is an important aesthetic consideration; its quality is governed by the material removal operation and the physical properties of the material being processed. The wear behaviour of polymer materials is not as straightforward as for other materials due to their molecular and structural complexity, not to mention their time-dependent properties. Four commercial ophthalmic polymers have been studied in this work using nanoindentation techniques which are evaluated as tools for probing surface mechanical properties in order to better understand the grinding response of polymer materials.

TiN monolayer and TiN/Ti multilayer thin films were deposited on commercially pure Ti substrates using a filtered arc deposition system (FADS). Surface topography and chemical composition have been characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. Fracture properties of coatings induced by nanoindentation have been investigated. Focused ion beam (FIB) and transmission electron microscopy (TEM) were used to identify the fracture modes. It was found that the TiN/Ti multilayer coating exhibited a higher pop-in force, which indicated good film ductility. Transmission electron microscope (TEM) observation showed that the small bending crack was the dominant crack in the TiN/Ti multilayer coating. The Ti layer shows that it could efficiently suppress the crack propagation, which was responsible for the improved ductility of the TiN/Ti multilayer coating.

This paper is part of a larger study to understand the wear of hot rolling rolls. A significant cost of the hot rolling process is associated with the consumption of rolls, which is why a comprehensive understanding of the wear of the roll material is important. Given that the surface of the rolls is covered by an oxide layer, it is important to know the tribological and mechanical properties of the oxides. Research in this area concentrates mainly on the morphologies and microstructures of the oxide layers. Previously published works give very little, if any, information of the mechanical properties of the layers on high speed steel. This paper presents a methodology to study the mechanical properties of the oxide layer formed on the surface of a high speed steel roll using combined nanoindentation tests and finite element simulations. Mechanical properties such as the elastic modulus (E), hardness (H), yield strength (sigma(y)), and Poisson's ratio (nu), have been determined, and the work has revealed a variation of microstructure, porosity (f), and mechanical properties of the oxide layer across its thickness. The outer sub-layer has a higher E and H than the inner sub-layer. This variation of mechanical properties in the oxide layer was consistent with variations in the porosity and grain sizes in the two sub-layers. (C) 2012 Elsevier B.V. All rights reserved.

"Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes.It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size.Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation.Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process.The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies.The CT-ECAPed samples had a higher fraction of monovacancies and divacancies.These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples.A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.(c) 2012 Acta Materialia Inc.Published by Elsevier Ltd.All rights reserved."

In this paper, finite element model is used to carry out thermal analysis of bead-on-plate welding. The model followed the proposed five step strategies which were then built into a model to obtain temperature history at the positions of thermocouples. Temperature field was also evaluated by comparing predicted weld bead with the actual weld bead. Using these proposed strategies, well matched temperature histories and temperature field have been obtained.

Bulk metals deformed by severe plastic deformation have some unusual phenomenon such as hardening by low temperature annealing. Commercial purity aluminum processed by equal channel angular pressing has been used to investigate the deformation mechanism during further annealing of the severed plastic deformed materials. It has been found that vacancy-type defects induced by severe plastic deformation are responsible for some unusual phenomena, such as hardening by annealing and softening by slight deformation in nanostructured metals. It is anticipated that the effective control of vacancy-type defects during SPD and consequent annealing process will be combined to attain an optimum combination of strength and ductility in nanostructured metals.

Characteristics of the oxide scale formed on a high-speed steel (HSS) material in the temperature range 550–650 °C were examined. The surface morphologies of oxidised sample indicate that the temperature has a significant influence on the oxidation behaviour of the HSS samples. Differential oxidation is expected to occur due to high-alloyed components in the material. The carbide-free matrix has a good oxidation resistance due to the dissolved chromium; while vanadium rich carbide (MC) regions were oxidised heavily because of high free energy at the carbide/matrix interface and low thermal stability of the MC carbides. FIB/TEM cross-section observation shows that the oxide scale formed on the surface has a duplex-layer structure with vanadium oxides covering the top of the scale.

In order to develop the relationship between surface roughness, friction and texture in the uniaxial planar compression, Al 6061 samples are compressed in a channel-die to conduct plane-strain compression experiments. Molly bond is selected as a lubricant in a group of samples. The other group of samples is compressed without lubrication. The tool is polished smoothly; all the samples are prepared with the same method to retain the same surface roughness. Finite element modelling of the surface asperity flattening is carried out with ABAQUS under the same experimental conditions, original random textures are employed in the two dimensional model. The same surface roughness (Ra) obtained from the experiment is also employed on the top surface of the sample. The constitutive model and time-integration procedure have been implemented into the implicit finite element code ABAQUS using user material subroutine UMAT. Both the calculated results and the experimental results show a same tendency: the lubrication can constrain the process of surface asperity flattening. When the reduction is less than 10%, the effect of lubrication on surface asperity flattening is not significant. If the reduction is 10–40%, the lubrication plays a satisfactory role during the compression. With an increase of reduction, the lubrication will be damaged, and then the sample compressed with and without lubrication keeps a similar tendency of change.

A crystal plasticity finite element method (CPFEM) model has been developed to investigate the texture evolution and heterogeneity during equal channel angular pressing (ECAP) of an aluminum single crystal. The developed model has been validated by comparison with experimental observations. The simulation results show that the lattices rotate predominantly around the Z axis (transverse direction) during ECAP. After deformation the billet is subdivided into three matrix bands along the thickness by the Z-axis rotation. The Z-axis rotation angles within three matrix bands are about 60°, 0° and 90°, respectively. It has been found that the die geometry plays a very important role on the texture evolution and heterogeneity in ECAP. In the large strain gradient region, multi-slip can be activated and the material rotation induced by slips is negligible. The lattices must rotate to accommodate the whole material rotation required by deformation. When the strain gradient is small, the single dominant slip is the main slip mechanism. The material remains roughly at the initial orientation after deformation. There is a rigid-rotation region in the lower part of the die corner where the lattices rotate by the die angle