The subsection linear torsional model of hydrodynamic torque converter was established and further simplified. According to the identification theory, the frequency characteristic was achieved with the Matlab/ Ident ...The subsection linear torsional model of hydrodynamic torque converter was established and further simplified. According to the identification theory, the frequency characteristic was achieved with the Matlab/ Ident toolbox. Then parametric model was established by adopting the subsection linearization method, and the damp value was estimated. The curve and function of damp changing with speed ratio was also established by fitting. In order to validate the identification results, the experimental output was compared with the output of the model in which torque was chosen as input signal and speed as output signal in Matlab/Ident toolbox. It was shown that model output is in good agreement with experimental output.展开更多
The influence of free-end torsion on compressive behavior of an extruded AZ31 rod at various temperatures was studied.Pre-torsion generates a high density of dislocations and a large number of{1012}twins in the matrix...The influence of free-end torsion on compressive behavior of an extruded AZ31 rod at various temperatures was studied.Pre-torsion generates a high density of dislocations and a large number of{1012}twins in the matrix,which can largely enhance the compressive yield strength at RT and 100℃.However,with increasing temperature,hardening effect via pre-torsion gradually decreases.When the compressive temperature reaches 300℃,pre-torsion reduces the compressive yield strength.Moreover,initial dislocations and twins via torsion help to refine the sub-structure and accelerate the continuous dynamic recrystallization during compression at 200℃.Thus,twisted sample exhibits more rapid flow softening behavior than the as-extruded sample at 200℃.When compressed at 300℃,the twins and dislocations via torsion were largely eliminated during the holding time,and the discontinuous dynamic recrystallization was enhanced.It is found that the compression curves of twisted sample and as-extruded sample tended to be coincident at 300℃.Related mechanisms were discussed in detail.展开更多
Objective： In pedicle screw fixation, the heads of monoaxial screws need to be directed in the same straight line to accommodate the rod placement by backing out during operation, which decreases the insertional torq...Objective： In pedicle screw fixation, the heads of monoaxial screws need to be directed in the same straight line to accommodate the rod placement by backing out during operation, which decreases the insertional torque and internal fixation strength. While polyaxial screws facilitate the assembly of the connecting rod, but its ball-in-cup locking mechanism reduces the static compressive bending yield strength as compared with monoaxial screws. Our study aimed to assess the mechanical performance of a modified pedicle screw. Methods： In this study, the tail of the screw body of the modified pedicle screw was designed to be a cylindershaped structure that well matched the inner wall of the screw head and the screw head only rotated around the cyclinder. Monoaxial screws, modified screws and polyaxial screws were respectively assembled into 3 groups ofvertebrectomy models simulated by ultra high molecular weight polyethylene （UHMWPE） blocks. This model was developed according to a standard for destructive mechanical testing published by the American Society for Testing Materials （ASTM F1717-04）. Each screw design had 6 subgroups, including 3 for static tension, load compression and torsion tests, and the rest for dynamic compression tests. In dynamic tests, the cyclic loads were 25%, 50%, and 75% of the compressive bending ultimate loads respectively. Yield load, yield ultimate load, yield stiffness, torsional stiffness, cycles to failure and modes of failure for the 3 types of screws were recorded. The results of modified screws were compared with those ofmonoaxial and polyaxial screws. Results： In static tests, results of bending stiffness, yield load, yield torque and torsional stiffness indicated no significant differences between the modified and monoaxial screws （P〉0.05）, but both differed significantly from those ofpolyaxial screws （P〈0.05）. In dynamic compression tests, both modified and monoaxial screws showed failures that occurred at the insertion point of screw body into the UHMWPE block, while the polyaxial screw group showed screw body swung up and down the screw head because of loosening of the ball-in-cup mechanism. Conclusions： The modified screw is well-designed and biomechanically improved. And it can provide sufficient stability for segment fixation as monoaxial screws.展开更多
文摘The subsection linear torsional model of hydrodynamic torque converter was established and further simplified. According to the identification theory, the frequency characteristic was achieved with the Matlab/ Ident toolbox. Then parametric model was established by adopting the subsection linearization method, and the damp value was estimated. The curve and function of damp changing with speed ratio was also established by fitting. In order to validate the identification results, the experimental output was compared with the output of the model in which torque was chosen as input signal and speed as output signal in Matlab/Ident toolbox. It was shown that model output is in good agreement with experimental output.
基金the National Natural Science Foundation of China(No.51601154)Southwest University Undergraduate Innovation Project(No.zsm2021026).
文摘The influence of free-end torsion on compressive behavior of an extruded AZ31 rod at various temperatures was studied.Pre-torsion generates a high density of dislocations and a large number of{1012}twins in the matrix,which can largely enhance the compressive yield strength at RT and 100℃.However,with increasing temperature,hardening effect via pre-torsion gradually decreases.When the compressive temperature reaches 300℃,pre-torsion reduces the compressive yield strength.Moreover,initial dislocations and twins via torsion help to refine the sub-structure and accelerate the continuous dynamic recrystallization during compression at 200℃.Thus,twisted sample exhibits more rapid flow softening behavior than the as-extruded sample at 200℃.When compressed at 300℃,the twins and dislocations via torsion were largely eliminated during the holding time,and the discontinuous dynamic recrystallization was enhanced.It is found that the compression curves of twisted sample and as-extruded sample tended to be coincident at 300℃.Related mechanisms were discussed in detail.
文摘Objective： In pedicle screw fixation, the heads of monoaxial screws need to be directed in the same straight line to accommodate the rod placement by backing out during operation, which decreases the insertional torque and internal fixation strength. While polyaxial screws facilitate the assembly of the connecting rod, but its ball-in-cup locking mechanism reduces the static compressive bending yield strength as compared with monoaxial screws. Our study aimed to assess the mechanical performance of a modified pedicle screw. Methods： In this study, the tail of the screw body of the modified pedicle screw was designed to be a cylindershaped structure that well matched the inner wall of the screw head and the screw head only rotated around the cyclinder. Monoaxial screws, modified screws and polyaxial screws were respectively assembled into 3 groups ofvertebrectomy models simulated by ultra high molecular weight polyethylene （UHMWPE） blocks. This model was developed according to a standard for destructive mechanical testing published by the American Society for Testing Materials （ASTM F1717-04）. Each screw design had 6 subgroups, including 3 for static tension, load compression and torsion tests, and the rest for dynamic compression tests. In dynamic tests, the cyclic loads were 25%, 50%, and 75% of the compressive bending ultimate loads respectively. Yield load, yield ultimate load, yield stiffness, torsional stiffness, cycles to failure and modes of failure for the 3 types of screws were recorded. The results of modified screws were compared with those ofmonoaxial and polyaxial screws. Results： In static tests, results of bending stiffness, yield load, yield torque and torsional stiffness indicated no significant differences between the modified and monoaxial screws （P〉0.05）, but both differed significantly from those ofpolyaxial screws （P〈0.05）. In dynamic compression tests, both modified and monoaxial screws showed failures that occurred at the insertion point of screw body into the UHMWPE block, while the polyaxial screw group showed screw body swung up and down the screw head because of loosening of the ball-in-cup mechanism. Conclusions： The modified screw is well-designed and biomechanically improved. And it can provide sufficient stability for segment fixation as monoaxial screws.
