During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a chang...During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a change of the shape and dimension of deformation zone located in the gap of forming rolls is found. It has a significant effect on metal flow and the forming quality of deformed ring. So the size effect of forming rolls on cold ring rolling was investigated by three-dimensional dynamic explicit FEM under ABAQUS environment. The obtained results thoroughly reveal the influence laws of the sizes of forming rolls on the average spread, fishtail coefficient, degree of inhomogeneous deformation and force and power parameters etc not only provide an important basis for design of the forming rolls and optimization of cold ring rolling process, but also reveal the plastic deformation mechanism of cold ring rolling.展开更多
Recently, research strives to apply Ultra High Performance Concrete (UHPC) to large-sized structures owing to its remarkable mechanical performance and durability compared to normal concrete. The Korea Institute of Co...Recently, research strives to apply Ultra High Performance Concrete (UHPC) to large-sized structures owing to its remarkable mechanical performance and durability compared to normal concrete. The Korea Institute of Construction Technology proposed SuperBridge800, an edge girder type UHPC cable stayed bridge with central span of 800 m, through its detailed design. The bridge is designed to be erected through the connection of precast UHPC segments. The precast UHPC segment is monolithically composed of one ribbed deck slab and edge girders at each side. The connection between the precast segments is achieved by steel bars at the edge girders and by UHPC cast-in-place wet joint at the slab. Despite of the outstanding mechanical performance of UHPC, the fabrication of large-sized members is a difficult task since UHPC hardens faster than normal concrete and requires a special curing process. Therefore, the constructability of large-sized UHPC segment should be secured to achieve SuperBridge800. Besides, the performance of the connection between segments should also be guaranteed, especially in terms of the fatigue performance of the UHPC cast-in-place joint, which constitutes a weak point. To that goal, two half-scaled UHPC segments are manufactured and the constructability is examined by fabricating a large-sized UHPC member connected with respect to the design conditions. This study conducts rolling fatigue test on the so-fabricated large-sized UHPC member. Rolling fatigue test is carried out up to 2 million cycles considering actual vehicle load at each center and quarter points of the member. The test results confirm that the service limit state is satisfied.展开更多
For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection o...For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection of hot-rolling control parameters was studied for microalloy steel by following the neural network principle. An experimental scheme was first worked out for acquisition of sample data, in which a gleeble-1500 thermal simolator was used to obtain rolling temperature, strain, stain rate, and stress-strain curves. And consequently the aust enite grain sizes was obtained through microscopic observation. The experimental data was then processed through regression. By using the training network of BP algorithm, the mapping relationship between the hotrooling control parameters (rolling temperature, stain, and strain rate) and the microstructural paramete rs (austenite grain in size and flow stress) of microalloy steel was function appro ached for the establishment of a neural network-based model of the austeuite grain size and flow stress of microalloy steel. From the results of estimation made with the neural network based model, the hot-rolling control parameters can be effectively predicted.展开更多
滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,...滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,利用金相显微镜、扫描电子显微镜对不同旋转速度增材试件宏观形貌、微观组织进行了表征。结果表明:(1)沉积层组织致密,无夹杂、裂纹等缺陷、相邻两沉积层之间形成良好的冶金结合。(2)沉积层呈现细小的轴晶粒组织,随着旋转速度升高,晶粒尺寸呈下降趋势。(3)沉积层第二相粒子呈现点片状分布于Al基体上,随着转速增大,第二相粒子趋向于细化与均匀。展开更多
The hollow parts formed with cross-wedge rolling (CWR) have a wide application in many fields, such as architecture and automobile, etc. But the finished configuration of part’s cross section was always ellipse and i...The hollow parts formed with cross-wedge rolling (CWR) have a wide application in many fields, such as architecture and automobile, etc. But the finished configuration of part’s cross section was always ellipse and it was hard to make it satisfied with traditional forming process. This paper proposed a FEM model of hollow workpiece of CWR in the sizing process, and simulated the deformation condition using the ANSYS program. Three kinds of parts with different wall thickness were calculated. Some stress and strain fields of the deformed hollow parts at various conditions are gained. The influence of wall thickness on the distribution of stress and strain was analyzed. The paper also found two phenomena, which never have been seen at traditional experiment, and author tried to give some explanations. The ANSYS program provided the relationship between the tolerance of the deformed workpiece and the deforming parameter. It is helpful to design the sizing dies of a new precise forming process of hollow parts on the CWR. The new process that designed through the information of FEM improved the accuracy of hollow parts on CWR. It proved the validity and practicability of numerical simulation.展开更多
In the shaping process of cross wedge rolling(CWR), metal undergoes a complex microstructural evolution, which affects the quality and mechanical properties of the product. Through secondary development of the DEFOR...In the shaping process of cross wedge rolling(CWR), metal undergoes a complex microstructural evolution, which affects the quality and mechanical properties of the product. Through secondary development of the DEFORM-3D software, we developed a rigid plastic finite element model for a CWR-processed rear axle tube, coupled with thermomechanical and microstructural aspects of workpieces. Using the developed model, we investigated the microstructural evolution of the CWR process. Also, the influence of numerous parameters, including the initial temperature of workpieces, the roll speed, the forming angle, and the spreading angle, on the grain size and the grain-size uniformity of the rolled workpieces was analyzed. The numerical simulation was verified through rolling and metallographic experiments. Good agreement was obtained between the calculated and experimental results, which demonstrated the reliability of the model constructed in this work.展开更多
Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking...Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.展开更多
基金Prqject(50335060) supported by the National Natural Science Foundation for Key Program of China Project (50225518) supported by the National Science Found of China for Distinguished Young Scholars
文摘During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a change of the shape and dimension of deformation zone located in the gap of forming rolls is found. It has a significant effect on metal flow and the forming quality of deformed ring. So the size effect of forming rolls on cold ring rolling was investigated by three-dimensional dynamic explicit FEM under ABAQUS environment. The obtained results thoroughly reveal the influence laws of the sizes of forming rolls on the average spread, fishtail coefficient, degree of inhomogeneous deformation and force and power parameters etc not only provide an important basis for design of the forming rolls and optimization of cold ring rolling process, but also reveal the plastic deformation mechanism of cold ring rolling.
文摘Recently, research strives to apply Ultra High Performance Concrete (UHPC) to large-sized structures owing to its remarkable mechanical performance and durability compared to normal concrete. The Korea Institute of Construction Technology proposed SuperBridge800, an edge girder type UHPC cable stayed bridge with central span of 800 m, through its detailed design. The bridge is designed to be erected through the connection of precast UHPC segments. The precast UHPC segment is monolithically composed of one ribbed deck slab and edge girders at each side. The connection between the precast segments is achieved by steel bars at the edge girders and by UHPC cast-in-place wet joint at the slab. Despite of the outstanding mechanical performance of UHPC, the fabrication of large-sized members is a difficult task since UHPC hardens faster than normal concrete and requires a special curing process. Therefore, the constructability of large-sized UHPC segment should be secured to achieve SuperBridge800. Besides, the performance of the connection between segments should also be guaranteed, especially in terms of the fatigue performance of the UHPC cast-in-place joint, which constitutes a weak point. To that goal, two half-scaled UHPC segments are manufactured and the constructability is examined by fabricating a large-sized UHPC member connected with respect to the design conditions. This study conducts rolling fatigue test on the so-fabricated large-sized UHPC member. Rolling fatigue test is carried out up to 2 million cycles considering actual vehicle load at each center and quarter points of the member. The test results confirm that the service limit state is satisfied.
文摘For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection of hot-rolling control parameters was studied for microalloy steel by following the neural network principle. An experimental scheme was first worked out for acquisition of sample data, in which a gleeble-1500 thermal simolator was used to obtain rolling temperature, strain, stain rate, and stress-strain curves. And consequently the aust enite grain sizes was obtained through microscopic observation. The experimental data was then processed through regression. By using the training network of BP algorithm, the mapping relationship between the hotrooling control parameters (rolling temperature, stain, and strain rate) and the microstructural paramete rs (austenite grain in size and flow stress) of microalloy steel was function appro ached for the establishment of a neural network-based model of the austeuite grain size and flow stress of microalloy steel. From the results of estimation made with the neural network based model, the hot-rolling control parameters can be effectively predicted.
文摘滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,利用金相显微镜、扫描电子显微镜对不同旋转速度增材试件宏观形貌、微观组织进行了表征。结果表明:(1)沉积层组织致密,无夹杂、裂纹等缺陷、相邻两沉积层之间形成良好的冶金结合。(2)沉积层呈现细小的轴晶粒组织,随着旋转速度升高,晶粒尺寸呈下降趋势。(3)沉积层第二相粒子呈现点片状分布于Al基体上,随着转速增大,第二相粒子趋向于细化与均匀。
文摘The hollow parts formed with cross-wedge rolling (CWR) have a wide application in many fields, such as architecture and automobile, etc. But the finished configuration of part’s cross section was always ellipse and it was hard to make it satisfied with traditional forming process. This paper proposed a FEM model of hollow workpiece of CWR in the sizing process, and simulated the deformation condition using the ANSYS program. Three kinds of parts with different wall thickness were calculated. Some stress and strain fields of the deformed hollow parts at various conditions are gained. The influence of wall thickness on the distribution of stress and strain was analyzed. The paper also found two phenomena, which never have been seen at traditional experiment, and author tried to give some explanations. The ANSYS program provided the relationship between the tolerance of the deformed workpiece and the deforming parameter. It is helpful to design the sizing dies of a new precise forming process of hollow parts on the CWR. The new process that designed through the information of FEM improved the accuracy of hollow parts on CWR. It proved the validity and practicability of numerical simulation.
基金support given by the National Natural Science Foundation of China (No.51505026)
文摘In the shaping process of cross wedge rolling(CWR), metal undergoes a complex microstructural evolution, which affects the quality and mechanical properties of the product. Through secondary development of the DEFORM-3D software, we developed a rigid plastic finite element model for a CWR-processed rear axle tube, coupled with thermomechanical and microstructural aspects of workpieces. Using the developed model, we investigated the microstructural evolution of the CWR process. Also, the influence of numerous parameters, including the initial temperature of workpieces, the roll speed, the forming angle, and the spreading angle, on the grain size and the grain-size uniformity of the rolled workpieces was analyzed. The numerical simulation was verified through rolling and metallographic experiments. Good agreement was obtained between the calculated and experimental results, which demonstrated the reliability of the model constructed in this work.
基金finically supported by the National Natural Science Foundation of China (No. 51474127)the Chinese Scholar Council (No. 201408210289)the Key Laboratory Open Project of Liaoning Province (USTLKFSY201504)
文摘Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.