A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing e...A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing equations of circular plates.The relation between dimensionless final plastic deformation of circular plates and the new dimensionless number is established based on massive underwater explosion test data.Meanwhile,comparative analysis was discussed with two other published dimensionless parameters which indicated the new dimensionless number proposed in this paper is more effective and extensive to predict the dynamic plastic response of circular plates under underwater explosion condition.展开更多
<strong>OBJECTIVE</strong><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-...<strong>OBJECTIVE</strong><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><strong>:</strong></span></span></span></span><span><span><span><b><span style="font-family:""> </span></b></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;">To compare maternal preoperative and postoperative hemoglobin variation after cord clamping. </span><b><span style="font-family:Verdana;">METHODS: </span></b><span style="font-family:Verdana;">Randomized clinical trial performed in Porto Alegre, RS from January to December 2012. It was included 356 women with habitual risk gestations. In the immediate cord clamping group</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;"> the umbilical cord section was realized between 0 and 60 s (group 1) while in the delayed cord clamping group it was realized >60 s (group 2). </span><b><span style="font-family:Verdana;">RESULTS:</span></b><span style="font-family:Verdana;"> The mean (±standard deviation [SD]) preoperative hemoglobin was 12.13 ± 1.06 in the group 1 and 12.13 ± 1.11 in the group 2. The mean (±SD) postoperative day 2 hemoglobin level was 10.19 ± 1.46 in the group 1 and 10.24 ± 1.42 in the group 2. </span><b><span style="font-family:Verdana;">CONCLUSIONS: </span></b><span style="font-family:Verdana;">Delayed umbilical cord clamping resulted in a similar maternal hemoglobin level reduction at postoperative day 2.</span></span></span></span></span>展开更多
In order to determine the best loading density of tobacco leaf with cage clamp in bulk-curing barns, a curing test was conducted on middle-part tobacco leaves. The results showed that for good appearance quality of cu...In order to determine the best loading density of tobacco leaf with cage clamp in bulk-curing barns, a curing test was conducted on middle-part tobacco leaves. The results showed that for good appearance quality of cured tobacco, the loading density at 59.52 kg/m2 （4 000 kg/barn） was the best, fol owed by 66.96 kg/m2 （4 500 kg/barn） and 74.40 kg/m2 （5 000 kg/barn）. As leaf loading density increased, the contents of leaf nicotine and total nitrogen increased, sugar content had smal changes, the ratio of sugar to nicotine decreased and tended to be balanced and the content of neutral aroma substances was decreasing, but the difference among treatments was not significant. With the increase of loading density, the sensory quality of cured leaf was better. When leaf loading density was 66.96 kg/m2 （4 500 kg/barn）, apperance quality of cured leaf improved considerably, with prominent aro-ma. Therefore, the best loading density of tobacco leaf in cage clamp of bulk-curing barn would be 66.96 kg/m2 （4 500 kg/barn） .展开更多
The paper deduced a calculation formula by the classic control theory on the Reproducibility Error of parts processing in the technology system,the flexible clamp system, with the clamping device on the gas power,and ...The paper deduced a calculation formula by the classic control theory on the Reproducibility Error of parts processing in the technology system,the flexible clamp system, with the clamping device on the gas power,and analyzed its influencing factor with examples,the Reproducibility Error law:\ The larger the diameter of the cylinder,the smaller the error; the slower the tool speed,(k values smaller),the smaller the error.展开更多
The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.B...The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.By fitting the identified nonlinear coefficients under different excitation amplitudes,the nonlinear vibration responses of the system are predicted.The results show that the accuracy of the BWM is higher than that of the CSFM,especially in the non-resonant region.However,the optimization time of the BWM is longer than that of the CSFM.展开更多
Holding an object by clamping force is a fundamental phenomena.Layered or laminated architectures with internal sliding features are essential mechanism in natural and man-made structural system.In this paper,we combi...Holding an object by clamping force is a fundamental phenomena.Layered or laminated architectures with internal sliding features are essential mechanism in natural and man-made structural system.In this paper,we combine the layered architecture and clamping mechanism to form a multilayered clamper and study the clamping force with internal friction.Our investigations show that the clamping force and energy dissipation are very much depend on the number of layers,its geometry and elasticity,as well as internal friction.The central goal of studying the multilayered clamp is not only to predict the clamping force,but also as a representative case to help finding some clue on the universal behaviours of multilayered architectures with internal friction.展开更多
There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions.To the best of our knowledge,little research on the actual constraint of the clamp has been performed...There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions.To the best of our knowledge,little research on the actual constraint of the clamp has been performed.In this paper,according to hysteresis loops of the clamp obtained from experimental test,the simplified bilinear stiffness and damping model is proposed.Then the Finite Element(FE)model of L-type pipeline system with clamps is established using Timoshenko beam theory in combination with aforementioned stiffness-damping model.Both hammering and shaker tests verify the FE model via the comparisons of natural frequencies and vibration responses.The results show that the maximum errors of natural frequencies and vibration responses are about 8.31%and 17.6%,respectively.The proposed model can simulate the dynamic characteristics of the L-type pipeline system with clamps well,which is helpful to provide some guidance for the early design stage of pipeline in aero-engine.展开更多
The violent vibration of hydraulic pipelines in aircraft may cause faults or even an accident,especially for the large aircraft with the multi-pump system because of different vibration sources and complex pipelines s...The violent vibration of hydraulic pipelines in aircraft may cause faults or even an accident,especially for the large aircraft with the multi-pump system because of different vibration sources and complex pipelines system.Aiming to the vibration analysis and control of the multipump system,this paper proposed the clamps’locations optimization to minimize the system impedance at vibration frequencies.Firstly,the models of the flexible clamp and other components in multi-pump system were established,based on which,the system impedance was calculated by using Transfer Matrix Method(TMM);Secondly,the objective function is defined as weighted sum of system impedance at frequencies of different vibration sources.Then,the clamps’locations were altered to change the system impedance.Moreover,The Chaotic Swarm Particle Optimization(CPSO)algorithm was applied to obtain the optimal clamps’locations and the minimum value of objective function which decreased by 36.4%compared to the value of original clamps’locations;Finally,the experiments from vibration and pressure test with original and optimized clamps’locations verified the effectiveness of the system impedance calculation and clamps’locations optimization method.展开更多
The Green quasifunction method is employed to solve the free vibration problem of clamped thin plates.A Green quasifunction is established by using the fundamental solution and boundary equation of the problem.This fu...The Green quasifunction method is employed to solve the free vibration problem of clamped thin plates.A Green quasifunction is established by using the fundamental solution and boundary equation of the problem.This function satisfies the homogeneous boundary condition of the problem.The mode shape differential equation of the free vibration problem of clamped thin plates is reduced to Fredholm integral equation of the second kind by Green formula.Irregularity of the kernel of integral equation is overcome by choosing a suitable form of the normalized boundary equation.Two examples demonstrate the validity of the present method.Comparison with both the series solution and ANSYS finite-element solution shows fine agreement.The present method is a novel and effective mathematical one.展开更多
Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency an...Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency and the shape precision of final spun part. Based on ABAQUS/Explicit nonlinear finite element software, the finite element model of the multi-pass DRCS for the sheet metal is established, and the material model, the contact definition, the mesh generation, the loading trajectory and other key technical problems are solved. The simulations on the multi-pass DRCS of the ordinary Q235A steel cylindrical part with the arc-shaped surface flange are carried out. The effects of number of spinning passes on the production efficiency, the spinning moment, the shape error of the workpiece, and the wall thickness distribution of the final part are obtained. It is indicated definitely that with the increase of the number of spinning passes the geometrical precision of the spun part increases while the production efficiency reduces. Moreover, the variations of the spinning forces and the distributions of the stresses, strains, wall thickness during the multi-pass DRCS process are revealed. It is indicated that during the DRCS process the radical force is the largest, and the whole deformation area shows the tangential tensile strain and the radial compressive strain, while the thickness strain changes along the generatrix directions from the compressive strain on the outer edge of the flange to the tensile strain on the inner edge of the flange. Based on the G-CNC6135 NC lathe, the three-axis linkage computer-controlled experimental device for DRCS which is driven by the AC servo motor is developed. And then using the experimental device, the Q235A cylindrical parts with the arc-shape surface flange are formed by the DRCS. The simulation results of spun parts have good consistency with the experimental results, which verifies the feasibility of DRCS process and the reliability of the finite element model for DRCS.展开更多
Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoptio...Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoption of the amount of reduction upon the given final solidification zone through roll gap adjustments. The synchronization of the clamping cylinders for roll gap adjustments should be very important to the application of soft reduction, including the synchronization of the clamping cylinders adjustments in the same and different segments. The synchronization of clamping cylinders adjustments is mainly affected by the adjustable accuracy of the four position-controlled clamping cylinders mounted in the upper frames of the segments according to a predetermined transformation relationship between the signals of displacement sensors and aimed roll gap, which, however, is also influenced by the installation accuracy, the precision of displacement sensors, the deformation of the segment frames and/or its bearing pedestals. Due to the actual asynchronous adjustments of the four clamping cylinders, the dynamic soft reduction operation is normally applied at non-ideal mechanical conditions. Here 7 possible situations of asynchronous adjustments of the local segments which may induce gap deviation have been presented. The roll gap deviation in the soft reduction region of a slab casting has been studied by a 3-D visco-elastic plastic FEM model, through which the additional inter-roll bulging, the related triangular cracks induced by one kind of the possible asynchronous adjustment situation and the effectiveness of soft reduction have been analyzed. A critical tolerance for the gap adjustments has been proposed for better contribution of soft reduction to the internal quality of slabs.展开更多
In this work, the main reasons for the breakage of 500 kV transmission line are studied. Under low temperature condition, the coverage of the ice results in the disconnection between the aluminum tube and the steel an...In this work, the main reasons for the breakage of 500 kV transmission line are studied. Under low temperature condition, the coverage of the ice results in the disconnection between the aluminum tube and the steel anchor of strain clamp. Using macroscopic analysis, structure stress analysis, force analysis and mechanical property test, the fractured strain clamps are investigated. The crimping of the aluminum tube on the polished rod not on the grooves of the steel anchor leads to the damage of the strain clamps, which is defined as improper crimping. When improper crimping emerges, there will be only friction force between the aluminum tube and the steel anchor without shear force, and the tension of the conductor will be mainly supported by the steel strands which should be supported by both the aluminum tube and steel stands. Therefore, the breaking force of the strain clamp will greatly decrease. The failure analysis helps to promote the proper hydraulic crimping process and the safe operation of the transmission line.展开更多
Associated dynamic performance of the clamping force control valve used in continuously variable transmission(CVT)is optimized.Firstly,the structure and working principle of the valve are analyzed,and then a dynamic m...Associated dynamic performance of the clamping force control valve used in continuously variable transmission(CVT)is optimized.Firstly,the structure and working principle of the valve are analyzed,and then a dynamic model is set up by means of mechanism analysis.For the purpose of checking the validity of the modeling method,a prototype workpiece of the valve is manufactured for comparison test,and its simulation result follows the experimental result quite well.An associated performance index is founded considering the response time,overshoot and saving energy,and five structural parameters are selected to adjust for deriving the optimal associated performance index.The optimization problem is solved by the genetic algorithm(GA)with necessary constraints.Finally,the properties of the optimized valve are compared with those of the prototype workpiece,and the results prove that the dynamic performance indexes of the optimized valve are much better than those of the prototype workpiece.展开更多
A numerical model is established by Abaqus software for superalloy during tungsten inert gas （TIG） welding with welding fixture to simulate the weld temperature filed, stress and strain field, and weld plate＇s hori...A numerical model is established by Abaqus software for superalloy during tungsten inert gas （TIG） welding with welding fixture to simulate the weld temperature filed, stress and strain field, and weld plate＇s horizontal trasnsveral shift. The clamp force perpendicular to the weld plate varying with welding time was analyzed. The maximum clamp force during welding process was calculated. Under the condition of insufficient of clamping force, a half or one third of the maximum clamp force for example, the weld plate＇s horizontal transversal displacement could happen and also be computed.展开更多
This paper deals with the nonlinear forced vibration of FGM rectangular plate with a boundary of two edges clamped opposite and the other two free. The plate is subjected to transversal and in-plane excitations. The p...This paper deals with the nonlinear forced vibration of FGM rectangular plate with a boundary of two edges clamped opposite and the other two free. The plate is subjected to transversal and in-plane excitations. The present research treats the material properties of the FGM plates as temperature-dependent and graded continuously throughout the thickness direction, following the volume fraction of the constituent materials according to the power law. The temperature is assumed to be constant in the plane and varied only in the thickness direction of the plate. In the framework of geometrical nonlinearity the plate is modeled and the equations of motion are obtained on Hamilton＇s principle. With the help of Galerkin discretization, the nonlinear ordinary differential equations describing transverse vibration of the plate are proposed. By the numerical method, the nonlinear dynamical responses of the FGM plate with two clamped opposite and two free edges are analyzed.展开更多
Based on the stability criteria of workpiece-fixture system, quantitative optimization of clamping forces during precise machining process for thin walled part is studied considering the contact condition between wokp...Based on the stability criteria of workpiece-fixture system, quantitative optimization of clamping forces during precise machining process for thin walled part is studied considering the contact condition between wokpiece and locator, the contact mechanical model is achieved, which is further been used to calculate the entire passive forces acting on the statically undetermined workpiece by means of the force screw theory as well as minimum norm force principle. Furthermore, a new methodology to optimize clamping forces is put forward, on the criteria of keeping the stability of workpiece during cutting process. By this way, the intensity of clamping forces is decreased dramatically, which will be most beneficial for improving the machining quality of thin-walled parts. Finally, a case study is used to support and validate the proposed model.展开更多
Two kinds of clamping in micro/nano scale experiments are investigated in this paper, one based on electron-beam-induced deposition, and the other on the van der Waals interaction. The clamping strength and mechanism ...Two kinds of clamping in micro/nano scale experiments are investigated in this paper, one based on electron-beam-induced deposition, and the other on the van der Waals interaction. The clamping strength and mechanism are analyzed both theoretically and experimentally. The influence of relative humidity on the micro/nano clamping and the method of electrostatic clamping are discussed. The clamping strength and performance of different clamping methods are compared considering the size and material of the clamped objects, and the application environments.展开更多
In this paper the method of the reciprocal theorem (MRT) is extended to solve the steady state responses of rectangular plater under harmonic disturbing forces. A series of the closed solutions of rectangular plates w...In this paper the method of the reciprocal theorem (MRT) is extended to solve the steady state responses of rectangular plater under harmonic disturbing forces. A series of the closed solutions of rectangular plates with various boundary conditions are given and the tables and figures which have practical value are provided.MRT is a simple, convenient and general method for solving the steady stale responses of rectangular plates under various harmonic disturbing forces.The paper contains three parts: (I) rectangular plates with four damped edges and with three clamped edges; (II) rectangular plates with two adjacent clamped edges; (III) cantilever plates.We arc going to publish them one after another.展开更多
基金supported by the National Natural Science Foundation of China(12402444)。
文摘A new dimensionless number is proposed for dynamic plastic deformation analysis of clamped circular plates under underwater explosion loads by introducing dimensional analysis method to the basic dynamical governing equations of circular plates.The relation between dimensionless final plastic deformation of circular plates and the new dimensionless number is established based on massive underwater explosion test data.Meanwhile,comparative analysis was discussed with two other published dimensionless parameters which indicated the new dimensionless number proposed in this paper is more effective and extensive to predict the dynamic plastic response of circular plates under underwater explosion condition.
文摘<strong>OBJECTIVE</strong><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><strong>:</strong></span></span></span></span><span><span><span><b><span style="font-family:""> </span></b></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;">To compare maternal preoperative and postoperative hemoglobin variation after cord clamping. </span><b><span style="font-family:Verdana;">METHODS: </span></b><span style="font-family:Verdana;">Randomized clinical trial performed in Porto Alegre, RS from January to December 2012. It was included 356 women with habitual risk gestations. In the immediate cord clamping group</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;"> the umbilical cord section was realized between 0 and 60 s (group 1) while in the delayed cord clamping group it was realized >60 s (group 2). </span><b><span style="font-family:Verdana;">RESULTS:</span></b><span style="font-family:Verdana;"> The mean (±standard deviation [SD]) preoperative hemoglobin was 12.13 ± 1.06 in the group 1 and 12.13 ± 1.11 in the group 2. The mean (±SD) postoperative day 2 hemoglobin level was 10.19 ± 1.46 in the group 1 and 10.24 ± 1.42 in the group 2. </span><b><span style="font-family:Verdana;">CONCLUSIONS: </span></b><span style="font-family:Verdana;">Delayed umbilical cord clamping resulted in a similar maternal hemoglobin level reduction at postoperative day 2.</span></span></span></span></span>
文摘In order to determine the best loading density of tobacco leaf with cage clamp in bulk-curing barns, a curing test was conducted on middle-part tobacco leaves. The results showed that for good appearance quality of cured tobacco, the loading density at 59.52 kg/m2 （4 000 kg/barn） was the best, fol owed by 66.96 kg/m2 （4 500 kg/barn） and 74.40 kg/m2 （5 000 kg/barn）. As leaf loading density increased, the contents of leaf nicotine and total nitrogen increased, sugar content had smal changes, the ratio of sugar to nicotine decreased and tended to be balanced and the content of neutral aroma substances was decreasing, but the difference among treatments was not significant. With the increase of loading density, the sensory quality of cured leaf was better. When leaf loading density was 66.96 kg/m2 （4 500 kg/barn）, apperance quality of cured leaf improved considerably, with prominent aro-ma. Therefore, the best loading density of tobacco leaf in cage clamp of bulk-curing barn would be 66.96 kg/m2 （4 500 kg/barn） .
基金Tianjin Nature Science Date(08JCYBJC 11700) "CAD System of Fixture on New Fixture Design Theory of Accuracy Design"
文摘The paper deduced a calculation formula by the classic control theory on the Reproducibility Error of parts processing in the technology system,the flexible clamp system, with the clamping device on the gas power,and analyzed its influencing factor with examples,the Reproducibility Error law:\ The larger the diameter of the cylinder,the smaller the error; the slower the tool speed,(k values smaller),the smaller the error.
文摘The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.By fitting the identified nonlinear coefficients under different excitation amplitudes,the nonlinear vibration responses of the system are predicted.The results show that the accuracy of the BWM is higher than that of the CSFM,especially in the non-resonant region.However,the optimization time of the BWM is longer than that of the CSFM.
基金This work was supported by Xi’an University of Architecture and Technology(No.002/2040221134).
文摘Holding an object by clamping force is a fundamental phenomena.Layered or laminated architectures with internal sliding features are essential mechanism in natural and man-made structural system.In this paper,we combine the layered architecture and clamping mechanism to form a multilayered clamper and study the clamping force with internal friction.Our investigations show that the clamping force and energy dissipation are very much depend on the number of layers,its geometry and elasticity,as well as internal friction.The central goal of studying the multilayered clamp is not only to predict the clamping force,but also as a representative case to help finding some clue on the universal behaviours of multilayered architectures with internal friction.
基金supported by National Natural Science Foundation of China(No.11772089)Fundamental Research Funds for the Central Universities(Nos.N170308028,N170306004 and N180708009)Program for the Innovative Talents of Higher Learning Institutions of Liaoning(LR2017035)。
文摘There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions.To the best of our knowledge,little research on the actual constraint of the clamp has been performed.In this paper,according to hysteresis loops of the clamp obtained from experimental test,the simplified bilinear stiffness and damping model is proposed.Then the Finite Element(FE)model of L-type pipeline system with clamps is established using Timoshenko beam theory in combination with aforementioned stiffness-damping model.Both hammering and shaker tests verify the FE model via the comparisons of natural frequencies and vibration responses.The results show that the maximum errors of natural frequencies and vibration responses are about 8.31%and 17.6%,respectively.The proposed model can simulate the dynamic characteristics of the L-type pipeline system with clamps well,which is helpful to provide some guidance for the early design stage of pipeline in aero-engine.
基金supported by the National Natural Science Foundation of China (No. 51775004)
文摘The violent vibration of hydraulic pipelines in aircraft may cause faults or even an accident,especially for the large aircraft with the multi-pump system because of different vibration sources and complex pipelines system.Aiming to the vibration analysis and control of the multipump system,this paper proposed the clamps’locations optimization to minimize the system impedance at vibration frequencies.Firstly,the models of the flexible clamp and other components in multi-pump system were established,based on which,the system impedance was calculated by using Transfer Matrix Method(TMM);Secondly,the objective function is defined as weighted sum of system impedance at frequencies of different vibration sources.Then,the clamps’locations were altered to change the system impedance.Moreover,The Chaotic Swarm Particle Optimization(CPSO)algorithm was applied to obtain the optimal clamps’locations and the minimum value of objective function which decreased by 36.4%compared to the value of original clamps’locations;Finally,the experiments from vibration and pressure test with original and optimized clamps’locations verified the effectiveness of the system impedance calculation and clamps’locations optimization method.
文摘The Green quasifunction method is employed to solve the free vibration problem of clamped thin plates.A Green quasifunction is established by using the fundamental solution and boundary equation of the problem.This function satisfies the homogeneous boundary condition of the problem.The mode shape differential equation of the free vibration problem of clamped thin plates is reduced to Fredholm integral equation of the second kind by Green formula.Irregularity of the kernel of integral equation is overcome by choosing a suitable form of the normalized boundary equation.Two examples demonstrate the validity of the present method.Comparison with both the series solution and ANSYS finite-element solution shows fine agreement.The present method is a novel and effective mathematical one.
基金supported by National Natural Science Foundation of China(Grant Nos.50905137,50975222)China Postdoctoral Science Foundation(Grant No.2012M521757)Natural Science Foundation of Shaanxi for Youths,China(Grant No.2012JQ7032)
文摘Compared with the conventional single-roller spinning process, the double-roller clamping spinning（DRCS） process can effectively prevent the sheet metal surface wrinkling and improve the the production efficiency and the shape precision of final spun part. Based on ABAQUS/Explicit nonlinear finite element software, the finite element model of the multi-pass DRCS for the sheet metal is established, and the material model, the contact definition, the mesh generation, the loading trajectory and other key technical problems are solved. The simulations on the multi-pass DRCS of the ordinary Q235A steel cylindrical part with the arc-shaped surface flange are carried out. The effects of number of spinning passes on the production efficiency, the spinning moment, the shape error of the workpiece, and the wall thickness distribution of the final part are obtained. It is indicated definitely that with the increase of the number of spinning passes the geometrical precision of the spun part increases while the production efficiency reduces. Moreover, the variations of the spinning forces and the distributions of the stresses, strains, wall thickness during the multi-pass DRCS process are revealed. It is indicated that during the DRCS process the radical force is the largest, and the whole deformation area shows the tangential tensile strain and the radial compressive strain, while the thickness strain changes along the generatrix directions from the compressive strain on the outer edge of the flange to the tensile strain on the inner edge of the flange. Based on the G-CNC6135 NC lathe, the three-axis linkage computer-controlled experimental device for DRCS which is driven by the AC servo motor is developed. And then using the experimental device, the Q235A cylindrical parts with the arc-shape surface flange are formed by the DRCS. The simulation results of spun parts have good consistency with the experimental results, which verifies the feasibility of DRCS process and the reliability of the finite element model for DRCS.
文摘Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoption of the amount of reduction upon the given final solidification zone through roll gap adjustments. The synchronization of the clamping cylinders for roll gap adjustments should be very important to the application of soft reduction, including the synchronization of the clamping cylinders adjustments in the same and different segments. The synchronization of clamping cylinders adjustments is mainly affected by the adjustable accuracy of the four position-controlled clamping cylinders mounted in the upper frames of the segments according to a predetermined transformation relationship between the signals of displacement sensors and aimed roll gap, which, however, is also influenced by the installation accuracy, the precision of displacement sensors, the deformation of the segment frames and/or its bearing pedestals. Due to the actual asynchronous adjustments of the four clamping cylinders, the dynamic soft reduction operation is normally applied at non-ideal mechanical conditions. Here 7 possible situations of asynchronous adjustments of the local segments which may induce gap deviation have been presented. The roll gap deviation in the soft reduction region of a slab casting has been studied by a 3-D visco-elastic plastic FEM model, through which the additional inter-roll bulging, the related triangular cracks induced by one kind of the possible asynchronous adjustment situation and the effectiveness of soft reduction have been analyzed. A critical tolerance for the gap adjustments has been proposed for better contribution of soft reduction to the internal quality of slabs.
文摘In this work, the main reasons for the breakage of 500 kV transmission line are studied. Under low temperature condition, the coverage of the ice results in the disconnection between the aluminum tube and the steel anchor of strain clamp. Using macroscopic analysis, structure stress analysis, force analysis and mechanical property test, the fractured strain clamps are investigated. The crimping of the aluminum tube on the polished rod not on the grooves of the steel anchor leads to the damage of the strain clamps, which is defined as improper crimping. When improper crimping emerges, there will be only friction force between the aluminum tube and the steel anchor without shear force, and the tension of the conductor will be mainly supported by the steel strands which should be supported by both the aluminum tube and steel stands. Therefore, the breaking force of the strain clamp will greatly decrease. The failure analysis helps to promote the proper hydraulic crimping process and the safe operation of the transmission line.
基金Key Science-Technology Foundation of Hunan Province,China(No.05GK2007).
文摘Associated dynamic performance of the clamping force control valve used in continuously variable transmission(CVT)is optimized.Firstly,the structure and working principle of the valve are analyzed,and then a dynamic model is set up by means of mechanism analysis.For the purpose of checking the validity of the modeling method,a prototype workpiece of the valve is manufactured for comparison test,and its simulation result follows the experimental result quite well.An associated performance index is founded considering the response time,overshoot and saving energy,and five structural parameters are selected to adjust for deriving the optimal associated performance index.The optimization problem is solved by the genetic algorithm(GA)with necessary constraints.Finally,the properties of the optimized valve are compared with those of the prototype workpiece,and the results prove that the dynamic performance indexes of the optimized valve are much better than those of the prototype workpiece.
基金supported by the National Natural Science Foundation of China(Grant No.51275496)
文摘A numerical model is established by Abaqus software for superalloy during tungsten inert gas （TIG） welding with welding fixture to simulate the weld temperature filed, stress and strain field, and weld plate＇s horizontal trasnsveral shift. The clamp force perpendicular to the weld plate varying with welding time was analyzed. The maximum clamp force during welding process was calculated. Under the condition of insufficient of clamping force, a half or one third of the maximum clamp force for example, the weld plate＇s horizontal transversal displacement could happen and also be computed.
基金supported by the National Natural Science Foundation of China(NNSFC)(Nos.10972026,11272063,11072008 and 11290152)the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality(PHRIHLB)the Science Foundation of Beijing Municipal Education Commission(No.cit&tcd201304112)
文摘This paper deals with the nonlinear forced vibration of FGM rectangular plate with a boundary of two edges clamped opposite and the other two free. The plate is subjected to transversal and in-plane excitations. The present research treats the material properties of the FGM plates as temperature-dependent and graded continuously throughout the thickness direction, following the volume fraction of the constituent materials according to the power law. The temperature is assumed to be constant in the plane and varied only in the thickness direction of the plate. In the framework of geometrical nonlinearity the plate is modeled and the equations of motion are obtained on Hamilton＇s principle. With the help of Galerkin discretization, the nonlinear ordinary differential equations describing transverse vibration of the plate are proposed. By the numerical method, the nonlinear dynamical responses of the FGM plate with two clamped opposite and two free edges are analyzed.
基金Beijing Municipal Commission of Education Project(XK100070530)
文摘Based on the stability criteria of workpiece-fixture system, quantitative optimization of clamping forces during precise machining process for thin walled part is studied considering the contact condition between wokpiece and locator, the contact mechanical model is achieved, which is further been used to calculate the entire passive forces acting on the statically undetermined workpiece by means of the force screw theory as well as minimum norm force principle. Furthermore, a new methodology to optimize clamping forces is put forward, on the criteria of keeping the stability of workpiece during cutting process. By this way, the intensity of clamping forces is decreased dramatically, which will be most beneficial for improving the machining quality of thin-walled parts. Finally, a case study is used to support and validate the proposed model.
基金supported by the NSFC (Nos10972113,10572071 and 10732080)the National Basic Research Program of China (Nos2007CB936803 and 2010CB631005)the SRFDP (No20070003053) and the Central Laboratory of Strength and Vibration of Tsinghua University
文摘Two kinds of clamping in micro/nano scale experiments are investigated in this paper, one based on electron-beam-induced deposition, and the other on the van der Waals interaction. The clamping strength and mechanism are analyzed both theoretically and experimentally. The influence of relative humidity on the micro/nano clamping and the method of electrostatic clamping are discussed. The clamping strength and performance of different clamping methods are compared considering the size and material of the clamped objects, and the application environments.
文摘In this paper the method of the reciprocal theorem (MRT) is extended to solve the steady state responses of rectangular plater under harmonic disturbing forces. A series of the closed solutions of rectangular plates with various boundary conditions are given and the tables and figures which have practical value are provided.MRT is a simple, convenient and general method for solving the steady stale responses of rectangular plates under various harmonic disturbing forces.The paper contains three parts: (I) rectangular plates with four damped edges and with three clamped edges; (II) rectangular plates with two adjacent clamped edges; (III) cantilever plates.We arc going to publish them one after another.
