The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at dif...The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.展开更多
Cross-wedge rolling (CWR) is a metal process of ro ta ry forming. To produce a part, one cylindrical billet should be placed between t wo counterrotating and wedge-shape dies, which move tangentially relative each oth...Cross-wedge rolling (CWR) is a metal process of ro ta ry forming. To produce a part, one cylindrical billet should be placed between t wo counterrotating and wedge-shape dies, which move tangentially relative each other. The billet suffers plastic deformation (essentially, localized compressio n) during its rotation between the rotating dies. Compared to other numerical si mulation methods, the finite element method (FEM) has advantages in solving gene ral problems with complex shapes of the formed parts. In cross-wedge rolling, t here are four stages in the workpiece deformation process, namely knifing, guidi ng, stretching and sizing stage. It is time-consuming and expensive to design t he CWR process by trial and error method. The application of numerical simul ation for the CWR process will help engineers to efficiently improve the process development. Tselikov, Hayama, Jain and Kobayashi, and Higashimo applied the sl ip-line theory in study of CWR process analysis. Zb.pater studied CWR process i ncluding upsetting by upper-bound method. The above numerical simulation were b ased on the two-dimensional plain-strain assumption ignored the metal flow in workpiece axial direction. Therefore, the complex three-dimensional stress and deformation involved in CWR processes were not presented. Compared to other nume rical simulation methods, the finite element method (FEM) has advantages in solv ing general problems with complex shapes of the formed parts. As yet, a few 3-D finite element simulation studies on CWR process have been reported in literatu res. In this paper, the process of cross wedge rolling (CWR) has been simulated and analyzed by 3D rigid-plastic finite element method. Considering the charact eristic of CWR, the static implicit FEM program is selected. The models proposed in this study uses the commercial code DEFORM 3D to simulate the CWR process. T his is an implicit Lagrangian finite element code, which includes many new enhan cements functions. A new method of utilizing multiple processors using the MPI s tandard has been implemented. Automatic switching between the two different defo rmation solvers (Sparse Solver and Conjugate Gradient Solver) has also been impl emented in order to increase the speed of simulations. In this paper, all stages in CWR process are simulated to be able to closely understand and analyze the a ctual CWR process. For simulating all forming stages in CWR process, the dynam ic adaptive remeshing technology for tetrahedral solid elements was applied. T he stress distributions in cross section of forming workpiece are analyzed to in terpret fracture or rarefaction in the center of workpiece. Authors also analyze d the time-torque curve and the laws of load changing.展开更多
The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electr...The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electrical,thermal and mechanical process in the interior ballistic cycle.In this paper present,we first introduced a multi-physical field model of railgun,followed by several examples to investigate the launching process.Especially,we used the explicit finite element method,in which material nonlinearity and geometric nonlinearity were accounted,to investigate the deform behaviors of solid armature.The results show that the dynamic mechanical process of armature is dependent on the armature geometry,material and exciting electric current.By the numerical simulation,the understanding of the fracture mechanism of solid armature was deepened.展开更多
Design of forming dies and whole process of simulation of cold rolling involutes spline can be realized by using of CAD software of PRO-E and CAE software of DEFORM-3D. Software DEFORM-3D provides an automatic and opt...Design of forming dies and whole process of simulation of cold rolling involutes spline can be realized by using of CAD software of PRO-E and CAE software of DEFORM-3D. Software DEFORM-3D provides an automatic and optimized remeshing function, especially for the large deformation. In order to use this function sufficiently, simulation of cold rolling involutes spline can be implemented indirectly. The relationship between die and workpiece, forming force and characteristic of deformation in the forming process of cold rolling involutes spline are analyzed and researched. Meanwhile, reliable proofs for the design of dies and deforming equipment are provided.展开更多
In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the pr...In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.展开更多
Railgun launcher design relies on appropriate models. A multi-field coupled model of railgun launcher was presented in this paper. The 3D transient multi-field was composed of electromagnetic field, thermal field and ...Railgun launcher design relies on appropriate models. A multi-field coupled model of railgun launcher was presented in this paper. The 3D transient multi-field was composed of electromagnetic field, thermal field and structural field. The magnetic diffusion equations were solved by a finite-element boundary-element coupling method. The thermal diffusion equations and structural equations were solved by a finite element method. A coupled calculation was achieved by the transfer data from the electromagnetic field to the thermal and structural fields. Some characteristics of railgun shot, such as velocity skin effect, melt-wave erosion and magnetic sawing, which are generated under the condition of large-current and high-speed sliding electrical contact, were demonstrated by numerical simulation.展开更多
Determination of ballistic performance of an armor solution is a complicated task and evolved significantly with the application of finite element methods(FEM) in this research field.The traditional armor design studi...Determination of ballistic performance of an armor solution is a complicated task and evolved significantly with the application of finite element methods(FEM) in this research field.The traditional armor design studies performed with FEM requires sophisticated procedures and intensive computational effort,therefore simpler and accurate numerical approaches are always worthwhile to decrease armor development time.This study aims to apply a hybrid method using FEM simulation and artificial neural network(ANN) analysis to approximate ballistic limit thickness for armor steels.To achieve this objective,a predictive model based on the artificial neural networks is developed to determine ballistic resistance of high hardness armor steels against 7.62 mm armor piercing ammunition.In this methodology,the FEM simulations are used to create training cases for Multilayer Perceptron(MLP) three layer networks.In order to validate FE simulation methodology,ballistic shot tests on 20 mm thickness target were performed according to standard Stanag 4569.Afterwards,the successfully trained ANN(s) is used to predict the ballistic limit thickness of 500 HB high hardness steel armor.Results show that even with limited number of data,FEM-ANN approach can be used to predict ballistic penetration depth with adequate accuracy.展开更多
Being aimed at the inside wall wrinkling and sinking phenomenon of palladium-yttrium alloy thin wall spiral tube used for preparation of high purity hydrogen, extraction of hydrogen isotope, and purification and separ...Being aimed at the inside wall wrinkling and sinking phenomenon of palladium-yttrium alloy thin wall spiral tube used for preparation of high purity hydrogen, extraction of hydrogen isotope, and purification and separation of hydrogen in the winding process, this article analyzed the reasons for above phenomena, established a numerical simulation model of winding process of above tube, using elastic-plastic Finite Element method analyzed the max. tensile stress and max. compression stress and their locations, thereby provides a theory base for the control of working forming course of thin wall spiral tube.展开更多
In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity ve...In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.展开更多
近年来,部分特高压换流变压器在运行中相继发生电弧短路故障并引发爆炸、起火事故,严重威胁直流系统安全稳定运行。充油设备故障冲击下的结构失效机制尚不明确,且缺乏成熟的数值计算方法,制约故障防爆技术的发展。基于此,该文提出一套...近年来,部分特高压换流变压器在运行中相继发生电弧短路故障并引发爆炸、起火事故,严重威胁直流系统安全稳定运行。充油设备故障冲击下的结构失效机制尚不明确,且缺乏成熟的数值计算方法,制约故障防爆技术的发展。基于此,该文提出一套适用于高能电弧故障冲击的结构失效仿真计算方法。首先,建立有限腔体内油中电弧能量持续注入的气泡动力学模型,准确描述故障气泡的脉动膨胀行为;其次,提出自适应有限元-光滑粒子流体动力学(finite element method-smoothed particle hydrodynamics,FEM-SPH)耦合方法,利用SPH粒子继承失效前的物理信息参与FEM计算;进行不同能量、不同位置的电弧故障仿真计算,获得换流变压器结构的薄弱区域及其破裂行为,复现了油箱结构失效行为。研究发现,油箱顶盖两侧及侧壁转角接缝位置容易发生应力集中现象。一旦结构出现裂缝,将在极短时间内沿着应力集中方向快速发展,最终导致壁面整体撕裂。可知,该方法揭示的结构失效行为可为改进变压器设计和提高设备安全性提供依据。展开更多
高位滑坡对建筑集群的冲击破坏时常导致严重的人员伤亡,基于光滑粒子流体动力学-离散元法-有限元法(smoothed particle hydrodynamics-discrete element method-finite element method,SPH-DEM-FEM)耦合的数值模型,开展了高位滑坡对框...高位滑坡对建筑集群的冲击破坏时常导致严重的人员伤亡,基于光滑粒子流体动力学-离散元法-有限元法(smoothed particle hydrodynamics-discrete element method-finite element method,SPH-DEM-FEM)耦合的数值模型,开展了高位滑坡对框架结构建筑群的冲击过程、建筑结构破坏机理、冲击力时程与框架柱关键点应力和弯矩等动力机制研究。研究结果表明:SPH-DEM-FEM耦合数值方法能够有效地模拟碎石土滑坡中土(SPH)石(DEM)混合物的抛射弹跳、爬高绕流冲击运动过程。考虑了常规建筑垂直、平行于滑坡流向的三排建筑组合布局,位于滑坡近端的纵向排列建筑表现为连续性倾倒破坏,横向排列的建筑则呈现整体倾倒破坏;因前排建筑群对滑坡冲击能量的耗散及滑坡自身摩擦耗能,位于滑坡后端建筑表现为引流面墙体和前排柱发生局部破坏,结构保持稳定,损毁程度依次为上游无建筑缓冲耗能的建筑>有横向排列的建筑>有纵向排列的建筑;纵向、横向排列的建筑冲击力衰减幅度分别31%、21%。横向框架建筑整体倾倒的损毁机制表现为框架柱的直接剪断或节点塑形铰链失效;纵向框架建筑连续性倾倒的损毁机制表现为前排框架柱的失效引起后排框架柱轴向压力和极限弯矩增加,持续冲击荷载超过其极限弯矩致使后排框架柱发生弯曲破坏,最终结构倾倒。系统能量在动能、内能和摩擦耗能间转化,其中摩擦耗能占65.5%,结构耗能占23.6%,动能快速下降与内能急剧增加是建筑破坏的关键特征。展开更多
For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-p...For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.展开更多
In order to obtain satisfactory mechanical properties for the cam used in high-power ship diesel engines, a new quenching technology was proposed by designing a two-stage quenching process with an alkaline bath as the...In order to obtain satisfactory mechanical properties for the cam used in high-power ship diesel engines, a new quenching technology was proposed by designing a two-stage quenching process with an alkaline bath as the quenching medium. To demonstrate the effectiveness of the proposed new quenching technology, both numerical analysis and experimental study were performed. The new quenching technology was analyzed using finite element method. The combined effects of the temperature, stress and microstructure fields were investigated considering nonlinear material properties. Finally, an experimental study was performed to verify the effectiveness of the proposed new quenching technology. The numerical results show that internal stress is affected by both thermal stress and transformation stress. In addition, the direction of the internal stress is changed several times due to thermal interaction and microstructure evolution during the quenching process. The experimental results show that the proposed new quenching technology significantly improves the mechanical properties and microstructures of the cam. The tensile strength, the impact resistance and the hardness value of the cam by the proposed new quenching technology are improved by 4.3%, 8.9% and 3.5% compared with those by the traditional quenching technology. Moreover, the residual stress and cam shape deformation are reduced by 40.0% and 48.9% respectively for the cam manufactured by the new quenching technology.展开更多
To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liqu...To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar(SHPB).The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy.Simulations of the machining process were carried out using the Deform-3D finite element software.The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature.The increase in the cutting speed and feed caused the cutting temperature to rise sharply,whereas the influence of the cutting amount on the cutting temperature was weak.Because of the presence of chip nodules,there was extremum in the cutting force vs cutting speed curves.The increase in the feed and cutting depth increased the cutting area Ac,so the cutting force also increased.The simulation results were verified by experiments.The simulation predictions were in good agreement with the test values,and the cutting force and temperature variations with the cutting parameters were the same.Thus,the correctness of the 7A09 aluminum alloy finite element model was verified.展开更多
In order to investigate the temperature distribution, a three-dimensional finite element model （FEM） was developed to simulate the temperature regime in the channels of double-loop inductor, and the simulated result...In order to investigate the temperature distribution, a three-dimensional finite element model （FEM） was developed to simulate the temperature regime in the channels of double-loop inductor, and the simulated results were compared with experimental data from low load trials of a 400 kW inductor. The results of numerical simulations, such as the temperature and Joule heating rate, show reasonable correlation with experimental data. The results indicate that Joule heating rate and the temperature reach the maximum at the comers and the minimum at the centre of the cross-section area. The temperature difference between the inlet and outlet is in an inverse proportion to mass transport. Joule heating rate and the temperature are directly proportional to power frequency. It is concluded that mass transport and power frequency play a critical role in determining the temperature regime and Joule heating rate, the relative permeability of the magnetic core shows no significant influence on temperature regime and Joule heating rate, when the relative permeability varies from 5 000 to 10 000.展开更多
文摘The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.
文摘Cross-wedge rolling (CWR) is a metal process of ro ta ry forming. To produce a part, one cylindrical billet should be placed between t wo counterrotating and wedge-shape dies, which move tangentially relative each other. The billet suffers plastic deformation (essentially, localized compressio n) during its rotation between the rotating dies. Compared to other numerical si mulation methods, the finite element method (FEM) has advantages in solving gene ral problems with complex shapes of the formed parts. In cross-wedge rolling, t here are four stages in the workpiece deformation process, namely knifing, guidi ng, stretching and sizing stage. It is time-consuming and expensive to design t he CWR process by trial and error method. The application of numerical simul ation for the CWR process will help engineers to efficiently improve the process development. Tselikov, Hayama, Jain and Kobayashi, and Higashimo applied the sl ip-line theory in study of CWR process analysis. Zb.pater studied CWR process i ncluding upsetting by upper-bound method. The above numerical simulation were b ased on the two-dimensional plain-strain assumption ignored the metal flow in workpiece axial direction. Therefore, the complex three-dimensional stress and deformation involved in CWR processes were not presented. Compared to other nume rical simulation methods, the finite element method (FEM) has advantages in solv ing general problems with complex shapes of the formed parts. As yet, a few 3-D finite element simulation studies on CWR process have been reported in literatu res. In this paper, the process of cross wedge rolling (CWR) has been simulated and analyzed by 3D rigid-plastic finite element method. Considering the charact eristic of CWR, the static implicit FEM program is selected. The models proposed in this study uses the commercial code DEFORM 3D to simulate the CWR process. T his is an implicit Lagrangian finite element code, which includes many new enhan cements functions. A new method of utilizing multiple processors using the MPI s tandard has been implemented. Automatic switching between the two different defo rmation solvers (Sparse Solver and Conjugate Gradient Solver) has also been impl emented in order to increase the speed of simulations. In this paper, all stages in CWR process are simulated to be able to closely understand and analyze the a ctual CWR process. For simulating all forming stages in CWR process, the dynam ic adaptive remeshing technology for tetrahedral solid elements was applied. T he stress distributions in cross section of forming workpiece are analyzed to in terpret fracture or rarefaction in the center of workpiece. Authors also analyze d the time-torque curve and the laws of load changing.
文摘The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electrical,thermal and mechanical process in the interior ballistic cycle.In this paper present,we first introduced a multi-physical field model of railgun,followed by several examples to investigate the launching process.Especially,we used the explicit finite element method,in which material nonlinearity and geometric nonlinearity were accounted,to investigate the deform behaviors of solid armature.The results show that the dynamic mechanical process of armature is dependent on the armature geometry,material and exciting electric current.By the numerical simulation,the understanding of the fracture mechanism of solid armature was deepened.
文摘Design of forming dies and whole process of simulation of cold rolling involutes spline can be realized by using of CAD software of PRO-E and CAE software of DEFORM-3D. Software DEFORM-3D provides an automatic and optimized remeshing function, especially for the large deformation. In order to use this function sufficiently, simulation of cold rolling involutes spline can be implemented indirectly. The relationship between die and workpiece, forming force and characteristic of deformation in the forming process of cold rolling involutes spline are analyzed and researched. Meanwhile, reliable proofs for the design of dies and deforming equipment are provided.
基金Project(50175034) supported by the National Natural Science Foundation of China
文摘In order to investigate the process of incremental sheet forming (ISF) through both experimental and numerical approaches, a three-dimensional elasto-plastic finite element model (FEM) was developed to simulate the process and the simulated results were compared with those of experiment. The results of numerical simulations, such as the strain history and distribution, the stress state and distribution, sheet thickness distribution, etc, were discussed in details, and the influences of process parameters on these results were also analyzed. The simulated results of the radial strain and the thickness distribution are in good agreement with experimental results. The simulations reveal that the deformation is localized around the tool and constantly remains close to a plane strain state. With decreasing depth step, increasing tool diameter and wall inclination angle, the axial stress reduces, leading to less thinning and more homogeneous plastic strain and thickness distribution. During ISF, the plastic strain increases stepwise under the action of the tool. Each increase in plastic strain is accompanied by hydrostatic pressure, which explains why obtainable deformation using ISF exceeds the forming limits of conventional sheet forming.
文摘Railgun launcher design relies on appropriate models. A multi-field coupled model of railgun launcher was presented in this paper. The 3D transient multi-field was composed of electromagnetic field, thermal field and structural field. The magnetic diffusion equations were solved by a finite-element boundary-element coupling method. The thermal diffusion equations and structural equations were solved by a finite element method. A coupled calculation was achieved by the transfer data from the electromagnetic field to the thermal and structural fields. Some characteristics of railgun shot, such as velocity skin effect, melt-wave erosion and magnetic sawing, which are generated under the condition of large-current and high-speed sliding electrical contact, were demonstrated by numerical simulation.
基金Otokar Otomotiv ve Savunma Sanayi A.S. for the financial support
文摘Determination of ballistic performance of an armor solution is a complicated task and evolved significantly with the application of finite element methods(FEM) in this research field.The traditional armor design studies performed with FEM requires sophisticated procedures and intensive computational effort,therefore simpler and accurate numerical approaches are always worthwhile to decrease armor development time.This study aims to apply a hybrid method using FEM simulation and artificial neural network(ANN) analysis to approximate ballistic limit thickness for armor steels.To achieve this objective,a predictive model based on the artificial neural networks is developed to determine ballistic resistance of high hardness armor steels against 7.62 mm armor piercing ammunition.In this methodology,the FEM simulations are used to create training cases for Multilayer Perceptron(MLP) three layer networks.In order to validate FE simulation methodology,ballistic shot tests on 20 mm thickness target were performed according to standard Stanag 4569.Afterwards,the successfully trained ANN(s) is used to predict the ballistic limit thickness of 500 HB high hardness steel armor.Results show that even with limited number of data,FEM-ANN approach can be used to predict ballistic penetration depth with adequate accuracy.
文摘Being aimed at the inside wall wrinkling and sinking phenomenon of palladium-yttrium alloy thin wall spiral tube used for preparation of high purity hydrogen, extraction of hydrogen isotope, and purification and separation of hydrogen in the winding process, this article analyzed the reasons for above phenomena, established a numerical simulation model of winding process of above tube, using elastic-plastic Finite Element method analyzed the max. tensile stress and max. compression stress and their locations, thereby provides a theory base for the control of working forming course of thin wall spiral tube.
文摘In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.
文摘近年来,部分特高压换流变压器在运行中相继发生电弧短路故障并引发爆炸、起火事故,严重威胁直流系统安全稳定运行。充油设备故障冲击下的结构失效机制尚不明确,且缺乏成熟的数值计算方法,制约故障防爆技术的发展。基于此,该文提出一套适用于高能电弧故障冲击的结构失效仿真计算方法。首先,建立有限腔体内油中电弧能量持续注入的气泡动力学模型,准确描述故障气泡的脉动膨胀行为;其次,提出自适应有限元-光滑粒子流体动力学(finite element method-smoothed particle hydrodynamics,FEM-SPH)耦合方法,利用SPH粒子继承失效前的物理信息参与FEM计算;进行不同能量、不同位置的电弧故障仿真计算,获得换流变压器结构的薄弱区域及其破裂行为,复现了油箱结构失效行为。研究发现,油箱顶盖两侧及侧壁转角接缝位置容易发生应力集中现象。一旦结构出现裂缝,将在极短时间内沿着应力集中方向快速发展,最终导致壁面整体撕裂。可知,该方法揭示的结构失效行为可为改进变压器设计和提高设备安全性提供依据。
文摘高位滑坡对建筑集群的冲击破坏时常导致严重的人员伤亡,基于光滑粒子流体动力学-离散元法-有限元法(smoothed particle hydrodynamics-discrete element method-finite element method,SPH-DEM-FEM)耦合的数值模型,开展了高位滑坡对框架结构建筑群的冲击过程、建筑结构破坏机理、冲击力时程与框架柱关键点应力和弯矩等动力机制研究。研究结果表明:SPH-DEM-FEM耦合数值方法能够有效地模拟碎石土滑坡中土(SPH)石(DEM)混合物的抛射弹跳、爬高绕流冲击运动过程。考虑了常规建筑垂直、平行于滑坡流向的三排建筑组合布局,位于滑坡近端的纵向排列建筑表现为连续性倾倒破坏,横向排列的建筑则呈现整体倾倒破坏;因前排建筑群对滑坡冲击能量的耗散及滑坡自身摩擦耗能,位于滑坡后端建筑表现为引流面墙体和前排柱发生局部破坏,结构保持稳定,损毁程度依次为上游无建筑缓冲耗能的建筑>有横向排列的建筑>有纵向排列的建筑;纵向、横向排列的建筑冲击力衰减幅度分别31%、21%。横向框架建筑整体倾倒的损毁机制表现为框架柱的直接剪断或节点塑形铰链失效;纵向框架建筑连续性倾倒的损毁机制表现为前排框架柱的失效引起后排框架柱轴向压力和极限弯矩增加,持续冲击荷载超过其极限弯矩致使后排框架柱发生弯曲破坏,最终结构倾倒。系统能量在动能、内能和摩擦耗能间转化,其中摩擦耗能占65.5%,结构耗能占23.6%,动能快速下降与内能急剧增加是建筑破坏的关键特征。
基金Project(51164030)supported by the National Natural Science Foundation of China
文摘For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.
基金Project(50875268) supported by the National Natural Science Foundation of China Project(CSTC2008AB3057) supported by Foundation of Chongqing Science and Technology Commission, China+1 种基金 Project(108107) supported by the Key Project of Ministry of Education of China Project(50925518) supported by the National Science Fund for Distinguished Young Scholars
文摘In order to obtain satisfactory mechanical properties for the cam used in high-power ship diesel engines, a new quenching technology was proposed by designing a two-stage quenching process with an alkaline bath as the quenching medium. To demonstrate the effectiveness of the proposed new quenching technology, both numerical analysis and experimental study were performed. The new quenching technology was analyzed using finite element method. The combined effects of the temperature, stress and microstructure fields were investigated considering nonlinear material properties. Finally, an experimental study was performed to verify the effectiveness of the proposed new quenching technology. The numerical results show that internal stress is affected by both thermal stress and transformation stress. In addition, the direction of the internal stress is changed several times due to thermal interaction and microstructure evolution during the quenching process. The experimental results show that the proposed new quenching technology significantly improves the mechanical properties and microstructures of the cam. The tensile strength, the impact resistance and the hardness value of the cam by the proposed new quenching technology are improved by 4.3%, 8.9% and 3.5% compared with those by the traditional quenching technology. Moreover, the residual stress and cam shape deformation are reduced by 40.0% and 48.9% respectively for the cam manufactured by the new quenching technology.
基金Projects(51575289,51705270)supported by the National Natural Science Foundation of ChinaProject(2019GHY112068)supported by the Key Research and Development of Shandong,China
文摘To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar(SHPB).The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy.Simulations of the machining process were carried out using the Deform-3D finite element software.The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature.The increase in the cutting speed and feed caused the cutting temperature to rise sharply,whereas the influence of the cutting amount on the cutting temperature was weak.Because of the presence of chip nodules,there was extremum in the cutting force vs cutting speed curves.The increase in the feed and cutting depth increased the cutting area Ac,so the cutting force also increased.The simulation results were verified by experiments.The simulation predictions were in good agreement with the test values,and the cutting force and temperature variations with the cutting parameters were the same.Thus,the correctness of the 7A09 aluminum alloy finite element model was verified.
基金Project(50876116) supported by the National Natural Science Foundation of ChinaProject(2007CK3077) supported by the Innovative Program of Hunan Science and Technology Agency, ChinaProject(1343-77225) supported by the Graduate School of Central South University, China
文摘In order to investigate the temperature distribution, a three-dimensional finite element model （FEM） was developed to simulate the temperature regime in the channels of double-loop inductor, and the simulated results were compared with experimental data from low load trials of a 400 kW inductor. The results of numerical simulations, such as the temperature and Joule heating rate, show reasonable correlation with experimental data. The results indicate that Joule heating rate and the temperature reach the maximum at the comers and the minimum at the centre of the cross-section area. The temperature difference between the inlet and outlet is in an inverse proportion to mass transport. Joule heating rate and the temperature are directly proportional to power frequency. It is concluded that mass transport and power frequency play a critical role in determining the temperature regime and Joule heating rate, the relative permeability of the magnetic core shows no significant influence on temperature regime and Joule heating rate, when the relative permeability varies from 5 000 to 10 000.
