A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The ...A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The self-locking and virtual work principles were applied to studying the basic self-locking condition of the USM.In order to make the cooperation between the crutch and telescopic mechanism more harmonical,the unlocking time of the USM was calculated.A set of parameters were selected to build a virtual model and fabricate a prototype.Both the simulation and performance experiments were carried out in a pipe with a nominal inside diameter of 160 mm.The results show that USM enables the robot to move quickly in one way,and in the other way it helps the robot get self-locking with the pipe wall.The traction of the inchworm robot can rise to 1.2 kN,beyond the limitation of friction of 0.497 kN.展开更多
ZK60B(Mg-6%Zn-0.6%Zr)alloy joints fabricated by bobbin tool friction stir welding(BTFSW)with various traverse speeds were investigated.The sound joint fabricated by the BTFSW was possible under the appropriate welding...ZK60B(Mg-6%Zn-0.6%Zr)alloy joints fabricated by bobbin tool friction stir welding(BTFSW)with various traverse speeds were investigated.The sound joint fabricated by the BTFSW was possible under the appropriate welding parameters.The severe plastic deformation during BTFSW resulted in dispersion and segregation of the Zr-rich particles within the stirred zone(SZ)followed by evolution of a bimodal grain structure with distributed bands of 0.8-1.7μm ultrafine grains and 4.1-7.1μm equiaxed grains.Micro-hardness of SZ is substantially reduced in contrast to that of parent metal(PM)in spite of the finer grain size owing to dissolution of Mg-Zn based precipitates having hardening effects on alpha-Mg matrix.With the decrease in traverse speed,randomization degree of the plasticized metal flow increases,which is evidenced by the randomized arc line pattern at the low traverse speed.Among all defect-free joints,the 200 mm/min joint exhibits the weakest isotropy of texture within SZ and the best tensile properties,which has reduced ultimate tensile strength and yield strength by 5.4% and by 22.2%,respectively,as compared to the PM.The randomized texture hinders the joint fracturing within SZ at low elongation.Therefore,a relatively high elongation of 10.8% was achieved,which corresponded to 72% of the PM value.展开更多
To investigate the deformation characteristics and instability mechanism of the transportation hub underdownward traversal conditions of the double-track super-large diameter shield tunnel, take the example of Beijing...To investigate the deformation characteristics and instability mechanism of the transportation hub underdownward traversal conditions of the double-track super-large diameter shield tunnel, take the example of BeijingEast Sixth Ring Road into the ground reconstruction project. Using the field experimental monitoring method andnumerical simulation method, after verifying the accuracy of the model, this manuscript begins to unfold theanalysis. The results show that, without any deformation prevention and control measures, The basement raft ofthe underground structure of the transportation hub will produce a deformation difference of 18 mm, and thetensile stress is more than 1.43 MPa, the inhomogeneous deformation and structural cracking will lead tostructural instability and groundwater surges, which seriously affects the safe operation of the transportation hubstation. When control measures are taken, the deformation and stress of the base raft slab of the undergroundstructure of the transportation hub are within the prescribed limits, which can ensure the safe operation of thestation. The displacement of the base slab of the underground structure in the horizontal direction of the crosssection is all pointing to the east, and the overall trend is to shift from the first tunnel to the backward tunnel. Thehorizontal displacement of the base slab in the direction of the tunnel axis all points to the beginning of thecrossing, and the displacement of the slab in the vertical direction is distributed as "rising in the middle andsinking in the surroundings". For a two-lane super-large diameter shield tunnel penetrating an undergroundstructure, there are two mechanical effects: unloading rebound and perimeter rock pressure. The above deformation characteristics are the superposition effect produced by the two, and this fine assessment of the deformation of the raft foundation provides a scientific basis for formulating the deformation control countermeasuresof the crossing project. At the same time, it makes up for the blank of the double-track super-large diameter shieldtunnel down through the transportation hub project.展开更多
基金Project(2007AA04Z256) supported by the National High-Tech Research and Development Program of China
文摘A unilateral self-locking mechanism(USM) was proposed to increase the tractive ability of the inchworm in-pipe robots for pipeline inspection.The USM was basically composed of a cam,a torsional spring and an axis.The self-locking and virtual work principles were applied to studying the basic self-locking condition of the USM.In order to make the cooperation between the crutch and telescopic mechanism more harmonical,the unlocking time of the USM was calculated.A set of parameters were selected to build a virtual model and fabricate a prototype.Both the simulation and performance experiments were carried out in a pipe with a nominal inside diameter of 160 mm.The results show that USM enables the robot to move quickly in one way,and in the other way it helps the robot get self-locking with the pipe wall.The traction of the inchworm robot can rise to 1.2 kN,beyond the limitation of friction of 0.497 kN.
基金sponsored by the National Science and Technology Major Project(No.2017ZX04005001)the Key Research and Development program of Shandong(No.2018GGX103053)。
文摘ZK60B(Mg-6%Zn-0.6%Zr)alloy joints fabricated by bobbin tool friction stir welding(BTFSW)with various traverse speeds were investigated.The sound joint fabricated by the BTFSW was possible under the appropriate welding parameters.The severe plastic deformation during BTFSW resulted in dispersion and segregation of the Zr-rich particles within the stirred zone(SZ)followed by evolution of a bimodal grain structure with distributed bands of 0.8-1.7μm ultrafine grains and 4.1-7.1μm equiaxed grains.Micro-hardness of SZ is substantially reduced in contrast to that of parent metal(PM)in spite of the finer grain size owing to dissolution of Mg-Zn based precipitates having hardening effects on alpha-Mg matrix.With the decrease in traverse speed,randomization degree of the plasticized metal flow increases,which is evidenced by the randomized arc line pattern at the low traverse speed.Among all defect-free joints,the 200 mm/min joint exhibits the weakest isotropy of texture within SZ and the best tensile properties,which has reduced ultimate tensile strength and yield strength by 5.4% and by 22.2%,respectively,as compared to the PM.The randomized texture hinders the joint fracturing within SZ at low elongation.Therefore,a relatively high elongation of 10.8% was achieved,which corresponded to 72% of the PM value.
文摘To investigate the deformation characteristics and instability mechanism of the transportation hub underdownward traversal conditions of the double-track super-large diameter shield tunnel, take the example of BeijingEast Sixth Ring Road into the ground reconstruction project. Using the field experimental monitoring method andnumerical simulation method, after verifying the accuracy of the model, this manuscript begins to unfold theanalysis. The results show that, without any deformation prevention and control measures, The basement raft ofthe underground structure of the transportation hub will produce a deformation difference of 18 mm, and thetensile stress is more than 1.43 MPa, the inhomogeneous deformation and structural cracking will lead tostructural instability and groundwater surges, which seriously affects the safe operation of the transportation hubstation. When control measures are taken, the deformation and stress of the base raft slab of the undergroundstructure of the transportation hub are within the prescribed limits, which can ensure the safe operation of thestation. The displacement of the base slab of the underground structure in the horizontal direction of the crosssection is all pointing to the east, and the overall trend is to shift from the first tunnel to the backward tunnel. Thehorizontal displacement of the base slab in the direction of the tunnel axis all points to the beginning of thecrossing, and the displacement of the slab in the vertical direction is distributed as "rising in the middle andsinking in the surroundings". For a two-lane super-large diameter shield tunnel penetrating an undergroundstructure, there are two mechanical effects: unloading rebound and perimeter rock pressure. The above deformation characteristics are the superposition effect produced by the two, and this fine assessment of the deformation of the raft foundation provides a scientific basis for formulating the deformation control countermeasuresof the crossing project. At the same time, it makes up for the blank of the double-track super-large diameter shieldtunnel down through the transportation hub project.
