Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in- vestigated at 850 and 950℃ and in stress range of 14.7~78.5 MPa.The single phase alloy exhibits typical recovery creep charac...Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in- vestigated at 850 and 950℃ and in stress range of 14.7~78.5 MPa.The single phase alloy exhibits typical recovery creep characteristics,and for the alloy in which M_(23)C_6 carbides densely precipitate at grain boundaries,the creep rate dramatically decreases and creep behav- ior is also significantly different from the single phase alloy.When the carbides precipitate at grain boundaries,the dislocation density are higher and the size of subgrains near grain boundaries are smaller than those of single phase alloy.The creep mechanisms for two grain boundary features have been discussed.展开更多
Warm compression deformation of Fe-13.5%Cr-4.7%Al-2.0%Mo-0.70%Nb-0.40Ta(wt%)(FeCrAl)and Fe-13.5%Cr-4.7%Al-2.0%Mo-0.45%Nb-0.40Ta-0.11Zr(wt%)(FeCrAl-Zr)ferritic stainless steel was performed by a thermal simulation mach...Warm compression deformation of Fe-13.5%Cr-4.7%Al-2.0%Mo-0.70%Nb-0.40Ta(wt%)(FeCrAl)and Fe-13.5%Cr-4.7%Al-2.0%Mo-0.45%Nb-0.40Ta-0.11Zr(wt%)(FeCrAl-Zr)ferritic stainless steel was performed by a thermal simulation machine Gleeble 3800 at 600°C and strain rates of 0.01-10 s^(-1).Before deformation,all the samples were solution-annealed for 2 h at 1150°C for FeCrAl alloy and 1250°C for FeCrAl-Zr alloy.The strain rate has little or no effect on peak stress,and the precipitates in matrix or grain boundary precipitates(GBPs)have no difference in the samples deformed at the strain rate 0.01 s^(-1)and 1 s^(-1)both in FeCrAl and FeCrAl-Zr alloys.The addition of Zr increased the proportion of low-angle grain boundaries(LAGBs).The Laves phase in FeCrAl alloy precipitated uniform in the matrix,while in FeCrAl-Zr alloy Laves phase precipitated at grain boundary and formed GBP.The LAGBs andΣ3 coincident site lattice(CSL)grain boundary both increased in FeCrAl-Zr alloy,which possessed some beneficial properties such as high-temperature creep resistance to the Fe-Cr-Al alloy.More interesting,twins were created by warm deformation,which was difficult in typical bcc ferrite alloy.These results could be expected to provide guidance for subsequent warm working processes for the alloy.展开更多
We address the 3D shape assembly of multiple geometric pieces without overlaps, a scenario often encountered in 3D shape design, field archeology, and robotics. Existing methods depend on strong assumptions on the num...We address the 3D shape assembly of multiple geometric pieces without overlaps, a scenario often encountered in 3D shape design, field archeology, and robotics. Existing methods depend on strong assumptions on the number of shape pieces and coherent geometry or semantics of shape pieces. Despite raising attention to 3D registration with complex or low overlapping patterns, few methods consider shape assembly with rare overlaps. To address this problem, we present a novel framework inspired by solving puzzles, named PuzzleNet, which conducts multi-task learning by leveraging both 3D alignment and boundary information. Specifically, we design an end-to-end neural network based on a point cloud transformer with two-way branches for estimating rigid transformation and predicting boundaries simultaneously. The framework is then naturally extended to reassemble multiple pieces into a full shape by using an iterative greedy approach based on the distance between each pair of candidate-matched pieces. To train and evaluate PuzzleNet, we construct two datasets, named ModelPuzzle and DublinPuzzle, based on a real-world urban scan dataset (DublinCity) and a synthetic CAD dataset (ModelNet40) respectively. Experiments demonstrate our effectiveness in solving 3D shape assembly for multiple pieces with arbitrary geometry and inconsistent semantics. Our method surpasses state-of-the-art algorithms by more than 10 times in rotation metrics and four times in translation metrics.展开更多
Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A...Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O(prismatic-spherical-revolute) is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints' stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.展开更多
文摘Creep behavior of Fe-15Cr-25Ni alloys with different grain boundary features has been in- vestigated at 850 and 950℃ and in stress range of 14.7~78.5 MPa.The single phase alloy exhibits typical recovery creep characteristics,and for the alloy in which M_(23)C_6 carbides densely precipitate at grain boundaries,the creep rate dramatically decreases and creep behav- ior is also significantly different from the single phase alloy.When the carbides precipitate at grain boundaries,the dislocation density are higher and the size of subgrains near grain boundaries are smaller than those of single phase alloy.The creep mechanisms for two grain boundary features have been discussed.
基金This work was financially supported by the National Natural Science Foundation of China(No.U1867201)the Key Project of Nuclear Safety and Advanced Nuclear Technology(No.2019YFB1901002)"the Project supported by State Key Laboratory of Powder Metallurgy",Central South University,Changsha.China.
文摘Warm compression deformation of Fe-13.5%Cr-4.7%Al-2.0%Mo-0.70%Nb-0.40Ta(wt%)(FeCrAl)and Fe-13.5%Cr-4.7%Al-2.0%Mo-0.45%Nb-0.40Ta-0.11Zr(wt%)(FeCrAl-Zr)ferritic stainless steel was performed by a thermal simulation machine Gleeble 3800 at 600°C and strain rates of 0.01-10 s^(-1).Before deformation,all the samples were solution-annealed for 2 h at 1150°C for FeCrAl alloy and 1250°C for FeCrAl-Zr alloy.The strain rate has little or no effect on peak stress,and the precipitates in matrix or grain boundary precipitates(GBPs)have no difference in the samples deformed at the strain rate 0.01 s^(-1)and 1 s^(-1)both in FeCrAl and FeCrAl-Zr alloys.The addition of Zr increased the proportion of low-angle grain boundaries(LAGBs).The Laves phase in FeCrAl alloy precipitated uniform in the matrix,while in FeCrAl-Zr alloy Laves phase precipitated at grain boundary and formed GBP.The LAGBs andΣ3 coincident site lattice(CSL)grain boundary both increased in FeCrAl-Zr alloy,which possessed some beneficial properties such as high-temperature creep resistance to the Fe-Cr-Al alloy.More interesting,twins were created by warm deformation,which was difficult in typical bcc ferrite alloy.These results could be expected to provide guidance for subsequent warm working processes for the alloy.
基金supported by the National Natural Science Foundation of China under Grant Nos.U22B2034,62172416,U21A20515,62172415,62271467the Youth Innovation Promotion Association of the Chinese Academy of Sciences under Grant No.2022131.
文摘We address the 3D shape assembly of multiple geometric pieces without overlaps, a scenario often encountered in 3D shape design, field archeology, and robotics. Existing methods depend on strong assumptions on the number of shape pieces and coherent geometry or semantics of shape pieces. Despite raising attention to 3D registration with complex or low overlapping patterns, few methods consider shape assembly with rare overlaps. To address this problem, we present a novel framework inspired by solving puzzles, named PuzzleNet, which conducts multi-task learning by leveraging both 3D alignment and boundary information. Specifically, we design an end-to-end neural network based on a point cloud transformer with two-way branches for estimating rigid transformation and predicting boundaries simultaneously. The framework is then naturally extended to reassemble multiple pieces into a full shape by using an iterative greedy approach based on the distance between each pair of candidate-matched pieces. To train and evaluate PuzzleNet, we construct two datasets, named ModelPuzzle and DublinPuzzle, based on a real-world urban scan dataset (DublinCity) and a synthetic CAD dataset (ModelNet40) respectively. Experiments demonstrate our effectiveness in solving 3D shape assembly for multiple pieces with arbitrary geometry and inconsistent semantics. Our method surpasses state-of-the-art algorithms by more than 10 times in rotation metrics and four times in translation metrics.
基金Supported by National Natural Science Foundation of China(Grant No.51221004)National Hi-tech Research and Development Program of China(863 Program,Grant No.2012AA040605)
文摘Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O(prismatic-spherical-revolute) is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints' stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.