This study explores the dynamic contact response of a viscoelastic functionally graded material(FGM)-coated half-plane under a rigid flat punch subjected to a time-harmonic vertical force.The elastic modulus and mass ...This study explores the dynamic contact response of a viscoelastic functionally graded material(FGM)-coated half-plane under a rigid flat punch subjected to a time-harmonic vertical force.The elastic modulus and mass density of the FGM coating vary exponentially along the thickness direction.The FGM coating and the homogeneous half-plane possess viscoelastic properties,which are described by a linearly hysteretic damping model.By applying the asymptotic method and the Fourier integral transform technique,the contact problem is converted into a Cauchy singular integral equation.The effects of excitation frequency,gradient index,damping factor ratio,and punch width on the vertical impedance and dynamic contact stress are analyzed.The results indicate that adjusting the gradient index of the FGM coating can significantly affect the contact stress and vertical impedance.展开更多
The evolution of the S'precipitate in Al−Cu−Mg alloy was investigated using transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF−STEM),molecular dynam...The evolution of the S'precipitate in Al−Cu−Mg alloy was investigated using transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF−STEM),molecular dynamics(MD)simulations,and other analytical techniques.The precipitation behavior during different aging stages of the supersaturated solid solution formed after rapid cold punching was focused,which induces rapid dissolution of precipitates.The findings reveal that the precipitation sequence is significantly influenced by aging temperature.At higher aging temperatures,which mitigate lattice distortion in the matrix,the precipitation sequence follows the conventional path.Conversely,at lower aging temperatures,where lattice distortion persists,the sequence deviates,suppressing the formation of Guinier−Preston−Bagaryatsky(GPB)zones.MD simulations confirm that the variations in solute atom diffusion rates at different aging temperatures lead to the differences in the S'phase precipitation sequence.展开更多
Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coa...Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coal formations,remains a challenge.The mechanisms underlying permeability improvement in different coal structures need further exploration.Therefore,this paper is focused on the fundamental principles of permeability improvement in soft coal through hydraulic punching,and in hard coal via hydraulic jet fracturing.Firstly,borehole instability results from a dynamic interplay of four factors:in situ stress,coal structure,mechanical properties of coal with fluid,and drilling technology.While borehole instability is inevitable,enhancing drilling tools,drilling media,and drilling processes can mitigate risks associated with buried and stuck drill pipes by ensuring effective discharge of drill cuttings through critical flow velocity and displacement.Secondly,permeability improvement in soft coal through hydraulic punching aims at pressure relief and capacity increase,while in hard coal,hydraulic jet fracturing induces crack formation within the coal seam.Finally,this study illustrates the dynamics of the granular arch in soft coal after hydraulic punching,shedding light on the complex processes involved.展开更多
The study investigates the partial slip contact problem between thermoelectric material and periodic punches including flat and cylindrical punches under various loading conditions,including normal force,energy flux,a...The study investigates the partial slip contact problem between thermoelectric material and periodic punches including flat and cylindrical punches under various loading conditions,including normal force,energy flux,and electric current density.When developing and enhancing thermoelectric devices intended for energy harvesting and temperature regulation,the relationship between punch geometry and thermoelectric material plays a crucial role.The periodic contact problem leads to the formation of a singular integral equation with a Hilbert kernel,distinguishing it from the traditional Cauchy kernel.It delves into the impact of the thermo-electric-mechanical coupling effect on the evolution of stick-slip zone length and contact stress during partial slip.By formulating the current nonlinear problem into a set of singular integral equations,the study identifies primary variables,including normal and tangential contact stresses,as well as slip and stick zones.The partial contact problem is further simplified by applying the Goodman approximation,enabling an iterative approach to determine the stick-slip zone,contact zone size,and stress distribution.Notably,the research reveals that factors such as the shape of the punch,the coefficient of friction,and TE parameters significantly influence stress strength and the characteristics of the stick-slip zone.展开更多
Double-shaft-driven needle punching machine is a specialized equipment designed for processing C/C crucible preforms.Its main needle punching module is operated by two sets of reciprocating crank-slider mechanisms.The...Double-shaft-driven needle punching machine is a specialized equipment designed for processing C/C crucible preforms.Its main needle punching module is operated by two sets of reciprocating crank-slider mechanisms.The intense vibration during needle punching not only generates huge noise,but also substantially reduces the quality of the preform.It is imperative to perform a dynamic analysis and optimization of the entire needle punching machine.In this paper,the three-dimensional(3D)model of the entire double-shaft-driven needle punching machine for C/C crucible preforms is established.Based on the modal analysis theory,the modal characteristics of the needle punching machine under various operating conditions are analyzed and its natural frequencies and vibration modes are determined.The harmonic response analysis is then employed to obtain the amplitude of the needle plate at different frequencies,and the structural weak points of the needle punching machine are identified and improved.The feasibility of the optimized scheme is subsequently reevaluated and verified.The results indicate that the first six natural frequencies of the machine increase,and the maximum amplitude of the needle plate decreases by 70.3%.The enhanced dynamic characteristics of the machine significantly improve its performance,enabling more efficient needle punching of C/C crucible preforms.展开更多
The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weld...The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.展开更多
To enhance the efficiency and cost-effectiveness of coal seam gas extraction in coal mines,this study introduces an integrated approach combining drilling,hydraulic punching,and fracturing technologies.This method opt...To enhance the efficiency and cost-effectiveness of coal seam gas extraction in coal mines,this study introduces an integrated approach combining drilling,hydraulic punching,and fracturing technologies.This method optimizes drilling media tailored to specific coal seams and fine-tunes technical parameters during drilling and permeability improvement processes.Furthermore,it clarifies the relationships among the coal breaking rate,discharge of drill cuttings,jet velocity,rotation speed,and displacement.This ensures precise and effective permeability improvement in both soft and hard coal formations.To implement this technology,a set of high-performance drilling tool with a large inner diameter,high pressure resistance,and superior sealing capabilities has been developed.Consisting of a water braid,drill pipe and hydraulic ejector,this tool meets the requirements of substantial displacement and high pump pressure.Field test results demonstrate remarkable enhancements in borehole formation,coal breaking and slagging efficiency.Specifically,the operation time is reduced by 60%–80%,the coal output is increased by 1–1.5 times,the pure coal seam gas extraction yield is increased by 1–2 times,and the extraction radius expands by more than 100%.These results highlight significant advancements in operational efficiency and permeability improvement effects,paving the way for efficient and economical coal seam gas extraction practices.展开更多
目的比较采用毛囊单位钻取术(follicular unit excision,FUE)喇叭口针和锐针钻取毛囊的临床效果。方法回顾性分析自2024年10月至2025年5月,南方医科大学南方医院进行毛发移植49例患者的临床资料。采用FUE喇叭口针钻取毛囊的患者25例,采...目的比较采用毛囊单位钻取术(follicular unit excision,FUE)喇叭口针和锐针钻取毛囊的临床效果。方法回顾性分析自2024年10月至2025年5月,南方医科大学南方医院进行毛发移植49例患者的临床资料。采用FUE喇叭口针钻取毛囊的患者25例,采用FUE锐针钻取毛囊患者24例。通过查询每例患者供区毛囊钻取情况(包括毛囊钻取时间、毛囊钻取总量及毛囊离断率等)、随访期间供区恢复和并发症情况等,综合分析采用FUE喇叭口针和FUE锐针钻取毛囊的临床效果。结果FUE喇叭口针和FUE锐针组患者中,毛囊的平均钻取总量分别为(5380±237)根毛囊和(5540±204)根毛囊,平均钻取时间分别为(89±23)min和(93±28)min,差异均无统计学意义(P>0.05);平均离断率分别为(4.37±0.31)%和(7.02±0.39)%,差异有统计学意义(P<0.05)。FUE喇叭口针组和FUE锐针组患者供区术后恢复时间均为(3±1)d,并发症发生率差异无统计学意义(P>0.05),术后两组间毛发生长情况无明显差异。结论FUE喇叭口针钻取毛囊具有离断率较低的特点,能够减少毛囊损伤,值得临床推广。展开更多
To accurately describe the mechanical properties of aluminium alloy sheet during deformation, an inverse identification was presented to deal with material parameters from the popular punch stretch test. In the identi...To accurately describe the mechanical properties of aluminium alloy sheet during deformation, an inverse identification was presented to deal with material parameters from the popular punch stretch test. In the identification procedure, the optimization strategy combines finite element method （FEM）, Latin hypercube sampling （LHS）, Kriging model and multi-island genetic algorithm （MIGA）. The proposed approach is used on material parameter identification of aluminium alloy sheet 2D12. The anisotropic yield criterion Hill’90 is discussed. The results show that the Hill’90 anisotropic yield criterion with identified anisotropic material parameters has a good potential in describing the anisotropic behaviours. It provides a way to obtain the material parameters for FE simulations of sheet metal forming.展开更多
Based on a new semi empirical analytical method, namely equivalent doping transformation, the breakdown voltage and the peak field of the epitaxial diffused punch through junction have been obtained. The basic prin...Based on a new semi empirical analytical method, namely equivalent doping transformation, the breakdown voltage and the peak field of the epitaxial diffused punch through junction have been obtained. The basic principle of this method is introduced and a set of breakdown voltage and peak field plots are provided for the optimum design of the low voltage power devices. It shows that the analytical results coincide with the previous numerical simulation well.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.12021002,12192212,and 12462007)。
文摘This study explores the dynamic contact response of a viscoelastic functionally graded material(FGM)-coated half-plane under a rigid flat punch subjected to a time-harmonic vertical force.The elastic modulus and mass density of the FGM coating vary exponentially along the thickness direction.The FGM coating and the homogeneous half-plane possess viscoelastic properties,which are described by a linearly hysteretic damping model.By applying the asymptotic method and the Fourier integral transform technique,the contact problem is converted into a Cauchy singular integral equation.The effects of excitation frequency,gradient index,damping factor ratio,and punch width on the vertical impedance and dynamic contact stress are analyzed.The results indicate that adjusting the gradient index of the FGM coating can significantly affect the contact stress and vertical impedance.
基金supported by the China Scholarship Council (CSC) Local Cooperation Program (No. 202308430176)the National Natural Science Foundation of China (No. 52271177)the Hunan Provincial Natural Science Foundation Regional Joint Fund, China (No. 2023JJ50173)。
文摘The evolution of the S'precipitate in Al−Cu−Mg alloy was investigated using transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF−STEM),molecular dynamics(MD)simulations,and other analytical techniques.The precipitation behavior during different aging stages of the supersaturated solid solution formed after rapid cold punching was focused,which induces rapid dissolution of precipitates.The findings reveal that the precipitation sequence is significantly influenced by aging temperature.At higher aging temperatures,which mitigate lattice distortion in the matrix,the precipitation sequence follows the conventional path.Conversely,at lower aging temperatures,where lattice distortion persists,the sequence deviates,suppressing the formation of Guinier−Preston−Bagaryatsky(GPB)zones.MD simulations confirm that the variations in solute atom diffusion rates at different aging temperatures lead to the differences in the S'phase precipitation sequence.
基金supported by the National Natural Science Foundation of China(42072193,42230804,Xianbo Su)the National Overseas Top Talents Program of China(JXRSB02001,Zhenjiang You).
文摘Coal seams in China are typically characterized by high coal seam gas content and low permeability,posing challenges for efficient coal seam gas extraction.However,achieving successful boreholes,especially in soft coal formations,remains a challenge.The mechanisms underlying permeability improvement in different coal structures need further exploration.Therefore,this paper is focused on the fundamental principles of permeability improvement in soft coal through hydraulic punching,and in hard coal via hydraulic jet fracturing.Firstly,borehole instability results from a dynamic interplay of four factors:in situ stress,coal structure,mechanical properties of coal with fluid,and drilling technology.While borehole instability is inevitable,enhancing drilling tools,drilling media,and drilling processes can mitigate risks associated with buried and stuck drill pipes by ensuring effective discharge of drill cuttings through critical flow velocity and displacement.Secondly,permeability improvement in soft coal through hydraulic punching aims at pressure relief and capacity increase,while in hard coal,hydraulic jet fracturing induces crack formation within the coal seam.Finally,this study illustrates the dynamics of the granular arch in soft coal after hydraulic punching,shedding light on the complex processes involved.
基金supported by the National Natural Science Foundation of China(Grant Nos.12262033,12272269,12062021,and 12062022)the Ningxia Hui Autonomous Region Science and Technology Innovation Leading Talent Training Project of China(Grant Nos.2020GKLRLX01 and 2022GKLRLX04)+1 种基金the Natural Science Foundation of Ningxia(Grant No.2023AAC02003)the Shanghai Pilot Program for Basic Research,and Shanghai Gaofeng Project for University Academic Program Development.
文摘The study investigates the partial slip contact problem between thermoelectric material and periodic punches including flat and cylindrical punches under various loading conditions,including normal force,energy flux,and electric current density.When developing and enhancing thermoelectric devices intended for energy harvesting and temperature regulation,the relationship between punch geometry and thermoelectric material plays a crucial role.The periodic contact problem leads to the formation of a singular integral equation with a Hilbert kernel,distinguishing it from the traditional Cauchy kernel.It delves into the impact of the thermo-electric-mechanical coupling effect on the evolution of stick-slip zone length and contact stress during partial slip.By formulating the current nonlinear problem into a set of singular integral equations,the study identifies primary variables,including normal and tangential contact stresses,as well as slip and stick zones.The partial contact problem is further simplified by applying the Goodman approximation,enabling an iterative approach to determine the stick-slip zone,contact zone size,and stress distribution.Notably,the research reveals that factors such as the shape of the punch,the coefficient of friction,and TE parameters significantly influence stress strength and the characteristics of the stick-slip zone.
基金Open Project of Shanghai Key Laboratory of Lightweight Composite,China(No.2232021A4-04)。
文摘Double-shaft-driven needle punching machine is a specialized equipment designed for processing C/C crucible preforms.Its main needle punching module is operated by two sets of reciprocating crank-slider mechanisms.The intense vibration during needle punching not only generates huge noise,but also substantially reduces the quality of the preform.It is imperative to perform a dynamic analysis and optimization of the entire needle punching machine.In this paper,the three-dimensional(3D)model of the entire double-shaft-driven needle punching machine for C/C crucible preforms is established.Based on the modal analysis theory,the modal characteristics of the needle punching machine under various operating conditions are analyzed and its natural frequencies and vibration modes are determined.The harmonic response analysis is then employed to obtain the amplitude of the needle plate at different frequencies,and the structural weak points of the needle punching machine are identified and improved.The feasibility of the optimized scheme is subsequently reevaluated and verified.The results indicate that the first six natural frequencies of the machine increase,and the maximum amplitude of the needle plate decreases by 70.3%.The enhanced dynamic characteristics of the machine significantly improve its performance,enabling more efficient needle punching of C/C crucible preforms.
基金supports provided by the National Natural Science Foundation of China(No.52372330).
文摘The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.
基金supported by the National Natural Science Foundation of China(42230804,42072193,Xianbo Su)the National Overseas Top Talents Program of China(JXRSB02001,Zhenjiang You).
文摘To enhance the efficiency and cost-effectiveness of coal seam gas extraction in coal mines,this study introduces an integrated approach combining drilling,hydraulic punching,and fracturing technologies.This method optimizes drilling media tailored to specific coal seams and fine-tunes technical parameters during drilling and permeability improvement processes.Furthermore,it clarifies the relationships among the coal breaking rate,discharge of drill cuttings,jet velocity,rotation speed,and displacement.This ensures precise and effective permeability improvement in both soft and hard coal formations.To implement this technology,a set of high-performance drilling tool with a large inner diameter,high pressure resistance,and superior sealing capabilities has been developed.Consisting of a water braid,drill pipe and hydraulic ejector,this tool meets the requirements of substantial displacement and high pump pressure.Field test results demonstrate remarkable enhancements in borehole formation,coal breaking and slagging efficiency.Specifically,the operation time is reduced by 60%–80%,the coal output is increased by 1–1.5 times,the pure coal seam gas extraction yield is increased by 1–2 times,and the extraction radius expands by more than 100%.These results highlight significant advancements in operational efficiency and permeability improvement effects,paving the way for efficient and economical coal seam gas extraction practices.
文摘目的比较采用毛囊单位钻取术(follicular unit excision,FUE)喇叭口针和锐针钻取毛囊的临床效果。方法回顾性分析自2024年10月至2025年5月,南方医科大学南方医院进行毛发移植49例患者的临床资料。采用FUE喇叭口针钻取毛囊的患者25例,采用FUE锐针钻取毛囊患者24例。通过查询每例患者供区毛囊钻取情况(包括毛囊钻取时间、毛囊钻取总量及毛囊离断率等)、随访期间供区恢复和并发症情况等,综合分析采用FUE喇叭口针和FUE锐针钻取毛囊的临床效果。结果FUE喇叭口针和FUE锐针组患者中,毛囊的平均钻取总量分别为(5380±237)根毛囊和(5540±204)根毛囊,平均钻取时间分别为(89±23)min和(93±28)min,差异均无统计学意义(P>0.05);平均离断率分别为(4.37±0.31)%和(7.02±0.39)%,差异有统计学意义(P<0.05)。FUE喇叭口针组和FUE锐针组患者供区术后恢复时间均为(3±1)d,并发症发生率差异无统计学意义(P>0.05),术后两组间毛发生长情况无明显差异。结论FUE喇叭口针钻取毛囊具有离断率较低的特点,能够减少毛囊损伤,值得临床推广。
基金Project(2011YSKF01)supported by the Henan Key Laboratory of Advanced Non-ferrous Metals,ChinaProject(50905008)supported by the National Natural Science Foundation of China
文摘To accurately describe the mechanical properties of aluminium alloy sheet during deformation, an inverse identification was presented to deal with material parameters from the popular punch stretch test. In the identification procedure, the optimization strategy combines finite element method （FEM）, Latin hypercube sampling （LHS）, Kriging model and multi-island genetic algorithm （MIGA）. The proposed approach is used on material parameter identification of aluminium alloy sheet 2D12. The anisotropic yield criterion Hill’90 is discussed. The results show that the Hill’90 anisotropic yield criterion with identified anisotropic material parameters has a good potential in describing the anisotropic behaviours. It provides a way to obtain the material parameters for FE simulations of sheet metal forming.
文摘Based on a new semi empirical analytical method, namely equivalent doping transformation, the breakdown voltage and the peak field of the epitaxial diffused punch through junction have been obtained. The basic principle of this method is introduced and a set of breakdown voltage and peak field plots are provided for the optimum design of the low voltage power devices. It shows that the analytical results coincide with the previous numerical simulation well.
