Block-flexure toppling constitutes the predominant form of toppling failure in rock slopes.Although it has been extensively studied,the current theoretical models are often oversimplified by treating rock layers as ri...Block-flexure toppling constitutes the predominant form of toppling failure in rock slopes.Although it has been extensively studied,the current theoretical models are often oversimplified by treating rock layers as rigid bodies that diverge from actual conditions.The proposed Equivalent Deformation Compatibility Method(EDCM)offers a fresh approach to assess the stability of rock slopes prone to block-flexure toppling.EDCM posits that blocky rock layers,with their inability to withstand significant bending and role in merely transferring forces,can be modeled as intact layers with a reduced modulus.The method simplifies the complex issue of analyzing discrete and continuous rock layers to the study of layered soft and hard rock,establishing deformation compatibility equations subsequently.Validation of the EDCM was achieved through numerical models,physical model testing,and application to an actual slope.The factor of safety(FS)for slopes corresponds with the results from both models and the actual slope,demonstrating the method's applicability for evaluating susceptibility to block-flexure toppling.When applying the EDCM,it is advised to set the elastic modulus reduction coefficient for blocky layers at a value below 0.1.展开更多
The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel.The different bainite contents(18–53 vol.%)in polygonal ferrite and bainite(PF+B)dual phase steel were o...The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel.The different bainite contents(18–53 vol.%)in polygonal ferrite and bainite(PF+B)dual phase steel were obtained by controlling the relaxation finish temperature during the rolling process.The effect of bainite volume fraction on the tensile deformability was systematically investigated via experiments and crystal plasticity finite element model(CPFEM)simulation.The experimental results showed that the steel showed optimal strain hardenability and strength–plasticity matching when the bainite reached 35%.The 3D-CPFEM models with the same grain size and texture characters were established to clarify the influence of stress/strain distribution on PF+B dual phase steel with different bainite contents.The simulation results indicated that an appropriate increase in the bainite content(18%–35%)did not affect the interphase strain difference,but increased the stress distribution in both phases,as a result of enhancing the coordinated deformability of two phases and improving the strength–plasticity matching.When the bainite content increased to 53%,the stress/strain difference between the two phases was greatly increased,and plastic damage between the two phases was caused by the reduction of the coordinated deformability.展开更多
The deformation compatibility equations and the torque balance equations of star gearing with three branches have been found based on the characteristic that the system composes a closed-loop of power flow. In conside...The deformation compatibility equations and the torque balance equations of star gearing with three branches have been found based on the characteristic that the system composes a closed-loop of power flow. In consideration of the parts manufacturing errors, assembly errors, bearing stiffness and float, the power splitting rate of each star gear and the system were calculated by using the theory of equivalent mesh error. The effects of the errors, float and the bearing stiffness on power splitting were studied. The study provides a useful theoretical guideline for the design of star gearing.展开更多
The Mg-8.5Li-6.6Zn-1.5Y(wt%)as-cast alloy exhibits a(β+a)duplex phase structure.Interspersed eutectics,primarily reticularⅠ-phase,predominantly form along phase and grain boundaries,enhancing the strength but leadin...The Mg-8.5Li-6.6Zn-1.5Y(wt%)as-cast alloy exhibits a(β+a)duplex phase structure.Interspersed eutectics,primarily reticularⅠ-phase,predominantly form along phase and grain boundaries,enhancing the strength but leading to a reduction in ductility due to the brittle nature of theⅠ-phase.This study focuses on modifying the alloy's microstructure through heat treatment to simultaneously improve both strength and ductility.Heating the alloy at 450℃/6 h results in the dissolution of continuous reticular Iphase and the massive a-Mg.Subsequent slow cooling facilitates the reintroduction of a-Mg,with the cooling rate directly impacting the mean size of the a-Mg phase.The slower the cooling,the larger the aMg phase.The strength and ductility of LZW861 alloy are simultaneously enhanced by heat treatment,particularly in the air-cooled(450℃/6 h-AC)alloy,while the yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)increases from 147 MPa,189 MPa,and 17.8%to 192 MPa,242 MPa,and 22.3%,respectively,compared to the as-cast state.This increase in strength can be attributed partly to the precipitation of fine needle-like a-Mg uniformly dispersed in theβ-Li matrix.Additionally,the increase in dispersed(Li,Mg)3Zn nanoparticles contributes to matrix strengthening.The enhancement of ductility after 450℃/6 h-AC heat treatment is ascribed to the dissolution of reticulated I-phase and the refinement of a-Mg phase,which enhance interphase deformation compatibility and weaken crack initiation at dispersedβ/a interface.展开更多
A novel high-speed parallel kinematic machine （PKM） named Delta-S parallel manipulator is proposed, which consists of a fixed base connected to a moving platform through three limbs with identical topology. Each lim...A novel high-speed parallel kinematic machine （PKM） named Delta-S parallel manipulator is proposed, which consists of a fixed base connected to a moving platform through three limbs with identical topology. Each limb is composed of one driving ann and one follower arm, herein, the latter includes two strings and one middle rod, all located in a same plane. Compared with similar manipulators with uniform parameters, the novel and unique topology as well as the addition of two strings of Delta-S manipulator can remove the clearance of the spherical joints, reduce the inertial load of components further, improve the positioning accuracy and dynamic performance, and so on. In order to formulate the kineto-static model of Delta-S manipulator, the kineto-static analyses and models of the driving arm, the generalized follower and the moving platform can be carried out by the D＇ALEMBERT principle. For the sake of obtaining the force analytic results of strings, the deformation compatibility condition of strings and the middle rod are determined. Furthermore, in virtue of the assumption of small deformation and the linear superposition principle, the minimal pre-tightening force of the strings is calculated. The main results include that the loads of the strings and the middle rod must be larger than ＂zero＂ and the pre-tightening force over the workspace must be larger than the minimal pre-tightening force at any time within the workspace, which lay the foundation for the dynamic analysis and the prototype manufacture of the Delta-S manipulator.展开更多
Mg-Li alloys with high lithium concentrations possess a lightweight body-centered cubic(BCC)matrix structure(β-Li).Interspersed eutectics(primarily the reticulated I-phase)often form along phase boundaries(PBs)and gr...Mg-Li alloys with high lithium concentrations possess a lightweight body-centered cubic(BCC)matrix structure(β-Li).Interspersed eutectics(primarily the reticulated I-phase)often form along phase boundaries(PBs)and grain boundaries(GBs)which strengthen the alloy but cause the loss of ductility due to the brittle behavior of I-phase.By modifying the Li content,we fabricated the(β+α)biphase Mg-Li alloy in which theα-Mg phase with a hexagonal close-packed structure(HCP)is embedded inβ-Li matrix,significantly increasing interface density.The high-density interfaces mitigate the distribution and dimension of the I-phase along GBs and PBs.The alloy exhibits enhanced ductility(elongation(EL)=17.8%)compared with the alloy without theα-Mg phase(EL=5.1%).Structural characterizations unveil the strengthening mechanism of the nanoscale B2(Li,Mg)3Zn-type precipitates in conjunction with the microscale I-phase.The(Li,Mg)3Zn nanophases augment the yield and ultimate tensile strength of the alloy without a discernible compromise in ductility,predominantly due to gliding dislocations cutting through the precipitates.In contrast,the microscale I-phase presents a formidable barrier to dislocation motion,facilitating dislocation pileups at interfaces and culminating in diminished ductility across the interface.In-situ stretching techniques were employed to scrutinize the microstructural evolution of alloys during tensile deformation,elucidating that the deformation compatibility of alloys correlates with the average size of the I-phase and their distribution along GBs and PBs.Corresponding to the orientation relationship(OR)between theα-Mg andβ-Li phases{110}Li//{0001}Mg and<ˉ111>Li//<11ˉ20>Mg,the slip continuity betweenα-Mg andβ-Li on plane pairs of{123}Li-{11ˉ22}Mg and{112}Li-{11ˉ22}Mg assures the deformation compatibility through facilitating the deformation across interfaces.Simultaneously,during the stretching process,the dispersed I-phase instigates the emergence of sporadic microcracks,indicating gradual damage evolution.These discoveries offer novel insights into achieving exceptional strength-ductility amalgamations in Mg-Li alloys through microstructural adjustments.展开更多
The composite structure with the dielectric elastomer and soft materials is the main form of theactuators in soft robots. However, the theoretical model is hard to obtain due to the nonlinear large deformationof mater...The composite structure with the dielectric elastomer and soft materials is the main form of theactuators in soft robots. However, the theoretical model is hard to obtain due to the nonlinear large deformationof materials. In this paper, a new composite element model is established based on the absolute nodal coordinateformulation. The consistent deformation conditions at the contact interface between two thin plates are deduced.The hyperelastic constitutive model and the dielectric elastomer constitutive model are introduced for the twothin plates. Then the dynamic model is established to study the dynamic behaviors of the composite flexiblestructure with various parameters. The results show that the nonlinear deformation appears obviously whenthe flexible composite plate structure is driven by various voltages, and the warping deformation becomes moreobvious with the increase of the voltage. The width and thickness of the driven thin plate influence the stabilityof the whole structure. With the decrease of the width or thickness, the deformation of the structure is moreconsistent with obvious periodicity, and the control performance is improved. Finally, the structural parametersof the composite structures are optimized to improve the control performance based on the dynamic performance.Additionally, smaller width and thickness parameters are preferred to obtain better performance in the design offlexible actuator of soft robot.展开更多
基金financially supported by Youth Innovation Promotion Association,CAS(Grant No.2022333)Knowledge Innovation Program of Wuhan e Basic Research(Grant No.2022010801010161)Natural Science Foundation of Hubei Province,China(Grant No.2023AFD219).
文摘Block-flexure toppling constitutes the predominant form of toppling failure in rock slopes.Although it has been extensively studied,the current theoretical models are often oversimplified by treating rock layers as rigid bodies that diverge from actual conditions.The proposed Equivalent Deformation Compatibility Method(EDCM)offers a fresh approach to assess the stability of rock slopes prone to block-flexure toppling.EDCM posits that blocky rock layers,with their inability to withstand significant bending and role in merely transferring forces,can be modeled as intact layers with a reduced modulus.The method simplifies the complex issue of analyzing discrete and continuous rock layers to the study of layered soft and hard rock,establishing deformation compatibility equations subsequently.Validation of the EDCM was achieved through numerical models,physical model testing,and application to an actual slope.The factor of safety(FS)for slopes corresponds with the results from both models and the actual slope,demonstrating the method's applicability for evaluating susceptibility to block-flexure toppling.When applying the EDCM,it is advised to set the elastic modulus reduction coefficient for blocky layers at a value below 0.1.
基金supported by the Project of Liaoning Marine Economic Development(Development of high strength pipeline steel for submarine oil and gas transmission)State Key Laboratory of Metal Material for Marine Equipment and Application Funding(No.SKLMEA-K202205).
文摘The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel.The different bainite contents(18–53 vol.%)in polygonal ferrite and bainite(PF+B)dual phase steel were obtained by controlling the relaxation finish temperature during the rolling process.The effect of bainite volume fraction on the tensile deformability was systematically investigated via experiments and crystal plasticity finite element model(CPFEM)simulation.The experimental results showed that the steel showed optimal strain hardenability and strength–plasticity matching when the bainite reached 35%.The 3D-CPFEM models with the same grain size and texture characters were established to clarify the influence of stress/strain distribution on PF+B dual phase steel with different bainite contents.The simulation results indicated that an appropriate increase in the bainite content(18%–35%)did not affect the interphase strain difference,but increased the stress distribution in both phases,as a result of enhancing the coordinated deformability of two phases and improving the strength–plasticity matching.When the bainite content increased to 53%,the stress/strain difference between the two phases was greatly increased,and plastic damage between the two phases was caused by the reduction of the coordinated deformability.
基金supported by the Natural Science Foundation of China (51175423)
文摘The deformation compatibility equations and the torque balance equations of star gearing with three branches have been found based on the characteristic that the system composes a closed-loop of power flow. In consideration of the parts manufacturing errors, assembly errors, bearing stiffness and float, the power splitting rate of each star gear and the system were calculated by using the theory of equivalent mesh error. The effects of the errors, float and the bearing stiffness on power splitting were studied. The study provides a useful theoretical guideline for the design of star gearing.
基金Project supported by the Jiangxi Province Key Laboratory of Light Alloy(2024SSY05031)the National Key Research and Development Program of China(2021YFB3501001,2022YFC2905204)the National Natural Science Foundation of China(52061028,52061039)。
文摘The Mg-8.5Li-6.6Zn-1.5Y(wt%)as-cast alloy exhibits a(β+a)duplex phase structure.Interspersed eutectics,primarily reticularⅠ-phase,predominantly form along phase and grain boundaries,enhancing the strength but leading to a reduction in ductility due to the brittle nature of theⅠ-phase.This study focuses on modifying the alloy's microstructure through heat treatment to simultaneously improve both strength and ductility.Heating the alloy at 450℃/6 h results in the dissolution of continuous reticular Iphase and the massive a-Mg.Subsequent slow cooling facilitates the reintroduction of a-Mg,with the cooling rate directly impacting the mean size of the a-Mg phase.The slower the cooling,the larger the aMg phase.The strength and ductility of LZW861 alloy are simultaneously enhanced by heat treatment,particularly in the air-cooled(450℃/6 h-AC)alloy,while the yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)increases from 147 MPa,189 MPa,and 17.8%to 192 MPa,242 MPa,and 22.3%,respectively,compared to the as-cast state.This increase in strength can be attributed partly to the precipitation of fine needle-like a-Mg uniformly dispersed in theβ-Li matrix.Additionally,the increase in dispersed(Li,Mg)3Zn nanoparticles contributes to matrix strengthening.The enhancement of ductility after 450℃/6 h-AC heat treatment is ascribed to the dissolution of reticulated I-phase and the refinement of a-Mg phase,which enhance interphase deformation compatibility and weaken crack initiation at dispersedβ/a interface.
基金Projects(50175295,50675151) supported by the National Natural Science Foundation of ChinaProject(11JCZDJC22700) supported by Tianjin Science and Technology Program,ChinaProject(2007AA042001) supported by the National High Technology Research and Development Program of China
文摘A novel high-speed parallel kinematic machine （PKM） named Delta-S parallel manipulator is proposed, which consists of a fixed base connected to a moving platform through three limbs with identical topology. Each limb is composed of one driving ann and one follower arm, herein, the latter includes two strings and one middle rod, all located in a same plane. Compared with similar manipulators with uniform parameters, the novel and unique topology as well as the addition of two strings of Delta-S manipulator can remove the clearance of the spherical joints, reduce the inertial load of components further, improve the positioning accuracy and dynamic performance, and so on. In order to formulate the kineto-static model of Delta-S manipulator, the kineto-static analyses and models of the driving arm, the generalized follower and the moving platform can be carried out by the D＇ALEMBERT principle. For the sake of obtaining the force analytic results of strings, the deformation compatibility condition of strings and the middle rod are determined. Furthermore, in virtue of the assumption of small deformation and the linear superposition principle, the minimal pre-tightening force of the strings is calculated. The main results include that the loads of the strings and the middle rod must be larger than ＂zero＂ and the pre-tightening force over the workspace must be larger than the minimal pre-tightening force at any time within the workspace, which lay the foundation for the dynamic analysis and the prototype manufacture of the Delta-S manipulator.
基金National Key Research and Development Program of China(Nos.2021YFB3501001)financial support from the National Natural Science Foundation of China(Nos.52061028,U21A2049,and 52061039)+2 种基金Natural Science Foundation of Jiangxi Province(Nos.20212BAB204049)Interdisciplinary Innovation Fund of Nanchang University(IIFNCU)China(No.9166-27060003-ZD05)。
文摘Mg-Li alloys with high lithium concentrations possess a lightweight body-centered cubic(BCC)matrix structure(β-Li).Interspersed eutectics(primarily the reticulated I-phase)often form along phase boundaries(PBs)and grain boundaries(GBs)which strengthen the alloy but cause the loss of ductility due to the brittle behavior of I-phase.By modifying the Li content,we fabricated the(β+α)biphase Mg-Li alloy in which theα-Mg phase with a hexagonal close-packed structure(HCP)is embedded inβ-Li matrix,significantly increasing interface density.The high-density interfaces mitigate the distribution and dimension of the I-phase along GBs and PBs.The alloy exhibits enhanced ductility(elongation(EL)=17.8%)compared with the alloy without theα-Mg phase(EL=5.1%).Structural characterizations unveil the strengthening mechanism of the nanoscale B2(Li,Mg)3Zn-type precipitates in conjunction with the microscale I-phase.The(Li,Mg)3Zn nanophases augment the yield and ultimate tensile strength of the alloy without a discernible compromise in ductility,predominantly due to gliding dislocations cutting through the precipitates.In contrast,the microscale I-phase presents a formidable barrier to dislocation motion,facilitating dislocation pileups at interfaces and culminating in diminished ductility across the interface.In-situ stretching techniques were employed to scrutinize the microstructural evolution of alloys during tensile deformation,elucidating that the deformation compatibility of alloys correlates with the average size of the I-phase and their distribution along GBs and PBs.Corresponding to the orientation relationship(OR)between theα-Mg andβ-Li phases{110}Li//{0001}Mg and<ˉ111>Li//<11ˉ20>Mg,the slip continuity betweenα-Mg andβ-Li on plane pairs of{123}Li-{11ˉ22}Mg and{112}Li-{11ˉ22}Mg assures the deformation compatibility through facilitating the deformation across interfaces.Simultaneously,during the stretching process,the dispersed I-phase instigates the emergence of sporadic microcracks,indicating gradual damage evolution.These discoveries offer novel insights into achieving exceptional strength-ductility amalgamations in Mg-Li alloys through microstructural adjustments.
基金the National Natural Science Foundation of China(No.51775345)。
文摘The composite structure with the dielectric elastomer and soft materials is the main form of theactuators in soft robots. However, the theoretical model is hard to obtain due to the nonlinear large deformationof materials. In this paper, a new composite element model is established based on the absolute nodal coordinateformulation. The consistent deformation conditions at the contact interface between two thin plates are deduced.The hyperelastic constitutive model and the dielectric elastomer constitutive model are introduced for the twothin plates. Then the dynamic model is established to study the dynamic behaviors of the composite flexiblestructure with various parameters. The results show that the nonlinear deformation appears obviously whenthe flexible composite plate structure is driven by various voltages, and the warping deformation becomes moreobvious with the increase of the voltage. The width and thickness of the driven thin plate influence the stabilityof the whole structure. With the decrease of the width or thickness, the deformation of the structure is moreconsistent with obvious periodicity, and the control performance is improved. Finally, the structural parametersof the composite structures are optimized to improve the control performance based on the dynamic performance.Additionally, smaller width and thickness parameters are preferred to obtain better performance in the design offlexible actuator of soft robot.
