In petroleum extraction,the sealing surfaces of bolted joints are susceptible to damage due to the high-temperature and high-pressure conditions in wellbores.This damage adversely affects sealing performance,consequen...In petroleum extraction,the sealing surfaces of bolted joints are susceptible to damage due to the high-temperature and high-pressure conditions in wellbores.This damage adversely affects sealing performance,consequently leading to the failure and damage of threaded connections.In severe cases,it can result in considerable economic losses and trigger safety accidents.The sealing performance of special bolted joints holds crucial importance for production efficiency,output,equipment lifespan,and cost control.Enhancing the sealing perfor-mance of threaded connections can have a positive impact on industrial production and environmental protection.The existing research on American Petroleum Institute threaded joints has been thorough and has obtained a series of excellent results.However,the research on the sealing damage mechanism of threaded connections under complex well conditions lacks sufficient depth and that on new sealing technology is scarce.This study proposes a half-size evaluation test to address the abovementioned problem.Based on this test,an investigation into the sealing performance of threaded connections under high-temperature,cyclic loading,and high-temperature creep conditions is conducted.This study uses a combined approach of finite element methods and experiments to investigate the impact of different makeup torques on the sealing performance of premium threaded connections(PTCs).The results of the half-size evaluation test indicate that temperature notably influences the sealing performance of threaded connections.The continuous action of high temperatures causes contact pressure and sealing performance to decrease,and sealing contact pressure increases after cooling.Finite element and test results show that for a certain joint A,the greater the torque,the higher the critical sealing pressure of the thread,and the better the sealing performance.The research on the sealing damage mechanism of PTCs provides a scientific basis and theoretical guidance for the further optimization and development of PTCs.展开更多
Simulation of the microstructure evolution during solidifi cation is greatly benefi cial to the control of solidifi cation microstructures. A phase-fi eld method based on the full threaded tree(FTT) for the simulation...Simulation of the microstructure evolution during solidifi cation is greatly benefi cial to the control of solidifi cation microstructures. A phase-fi eld method based on the full threaded tree(FTT) for the simulation of casting solidifi cation microstructure was proposed in this paper, and the structure of the full threaded tree and the mesh refi nement method was discussed. During dendritic growth in solidifi cation, the mesh for simulation is adaptively refi ned at the liquid-solid interface, and coarsened in other areas. The numerical results of a threedimension dendrite growth indicate that the phase-fi eld method based on FTT is suitable for microstructure simulation. Most importantly, the FTT method can increase the spatial and temporal resolutions beyond the limits imposed by the available hardware compared with the conventional uniform mesh. At the simulation time of 0.03 s in this study, the computer memory used for computation is no more than 10 MB with the FTT method, while it is about 50 MB with the uniform mesh method. In addition, the proposed FTT method is more effi cient in computation time when compared with the uniform mesh method. It would take about 20 h for the uniform mesh method, while only 2 h for the FTT method for computation when the solidifi cation time is 0.17 s in this study.展开更多
Selective laser melting(SLM) is a promising technique for additive manufacturing. During SLM of metallic powder, the temperature field and thermal history are important to understand physical phenomena involved. The p...Selective laser melting(SLM) is a promising technique for additive manufacturing. During SLM of metallic powder, the temperature field and thermal history are important to understand physical phenomena involved. The purpose of this study is to simulate the temperature field during the SLM process of a hollow cylinder shape part based on a fully threaded tree(FTT) technique, and to analyze the temperature variation with time in different regions of the part. A revised model for temperature field simulation in the SLM process was employed, which includes the transition of powder-to-dense sub-model and a moving volumetric Gaussian distribution heat source sub-model. The FTT technique is then adopted as an adaptive mesh strategy in the simulation. The simulation result shows that during the SLM process of cylinder part, the temperature of inner powder bed is obviously higher than external one. The temperature at the internal of the molten pool is also higher than external, which may lead to differences in microstructures and other properties between the two regions.展开更多
A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings.The hydrodynamic interactions significantly speed up the diffusion and rela...A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings.The hydrodynamic interactions significantly speed up the diffusion and relaxation of both free and threaded rings.The decoupled diffusion and relaxation dynamics indicate the broken of the Einstein-Stokes relationship.The diffusion of a ring threaded on a flexible chain exhibits a synergism effect compared to that on an axial rod,which originates from the self-diffusion of the ring and the reptation-like motion of the axial chain.Meanwhile,hydrodynamic interactions significantly improve the synergism effect,leading to an enhanced sliding motion of the threaded ring.The faster sliding of threaded rings suggests that the entropic barrier is negligible,which agrees well with the basic assumption of barrier-less confining tube at equilibrium in tube theory.Our results provide a new perspective on analysis of the effects of topology constraints on polymer dynamics.展开更多
In order to improve the accuracy of threaded hole object detection,combining a dual camera vision system with the Hough transform circle detection,we propose an object detection method of artifact threaded hole based ...In order to improve the accuracy of threaded hole object detection,combining a dual camera vision system with the Hough transform circle detection,we propose an object detection method of artifact threaded hole based on Faster region-ased convolutional neural network(Faster R-CNN).First,a dual camera image acquisition system is established.One industrial camera placed at a high position is responsible for collecting the whole image of the workpiece,and the suspected screw hole position on the workpiece can be preliminarily selected by Hough transform detection algorithm.Then,the other industrial camera is responsible for collecting the local images of the suspected screw holes that have been detected by Hough transform one by one.After that,ResNet50-based Faster R-CNN object detection model is trained on the self-built screw hole data set.Finally,the local image of the threaded hole is input into the trained Faster R-CNN object detection model for further identification and location.The experimental results show that the proposed method can effectively avoid small object detection of threaded holes,and compared with the method that only uses Hough transform or Faster RCNN object detection alone,it has high recognition and positioning accuracy.展开更多
Threaded fasteners are one of the most commonly used connection methods for mechanical structures.Its primary function is to generate appropriate clamping forces and fasten the connected parts.An inappropriate preload...Threaded fasteners are one of the most commonly used connection methods for mechanical structures.Its primary function is to generate appropriate clamping forces and fasten the connected parts.An inappropriate preload can cause loosening,fatigue fracture,and other problems.This will affect the safety and reliability of mechanical equipment.The precise control of the preload has become a critical issue in mechanical assembly processes.Over the past few decades,various tightening measures and methods have been proposed to address this issue.However,many problems continue to exist with practical applications that have not been reviewed comprehensively and systematically.First,various control methods were summarized systematically,and their advantages and disadvantages in engineering applications were analyzed.Torque control is the most widely used tightening method owing to its simple operation and low cost.Therefore,the research on the torque control method was summarized systematically from three aspects:the torque-preload correlation formula,effective friction radius,and friction characteristics during tightening.In addition,the special circumstances that may increase preload uncertainty were discussed.Finally,based on a summary of the current research status,the prospects for future research were discussed.This study would aid researchers in extensively understanding the problems in preload control.展开更多
Threaded aluminum nitride （A1N） whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering...Threaded aluminum nitride （A1N） whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering, scanning electron microscopy, transmission electron microscopy and photoluminescence. The analysis shows that the whiskers are single-crystalline, wurtzite AIN. The threaded A1N whiskers are 0.5 μm^100 μm in diameter and several millimeters in length in the fiber direction, and have lots of tiny sawteeth on the surface. The morphology of this threaded A1N whisker is beneficial for bonding when the whisker is used in composite. The growth of the whiskers is dominated by the vapor-solid （VS） mechanism, and the particular morphology might result from an oscillating condition produced in the radio-frequency induction heating furnace.展开更多
Experimental investigation on the pull-out behaviour,including the withdrawal capacity,slip stiffness and inter-facial shear stress,of axially loaded screwed-in threaded rod embedded in cross laminated timber(CLT)was ...Experimental investigation on the pull-out behaviour,including the withdrawal capacity,slip stiffness and inter-facial shear stress,of axially loaded screwed-in threaded rod embedded in cross laminated timber(CLT)was con-ducted.Specimens with varying embedment length and different number of threaded rods were tested in this study.To prevent premature splitting failure of timber,some specimens were reinforced in the direction perpen-dicular to the timber grain with self-tapping screws.Test results showed that the screwed-in threaded rod con-nections exhibited good pull-out behaviour with high withdrawal capacity and slip stiffness.Within a certain range,the withdrawal capacity increases considerably with the increase of embedment length,while the average interfacial shear stress shows the opposite tendency.The self-tapping screws played an important role on reducing the splitting of the timber and improving the withdrawal capacity and slip stiffness of the screwed-in threaded rod.Additionally,for the specimens with self-tapping screw reinforcements,the improvement of withdrawal capacity and stiffness when increasing the number of threaded rods are much more obvious than that of the speci-mens without the self-tapping screws,due to the change of failure modes.展开更多
We are developing a speed reducer that can be considered a transformation of a worm gear reducer: the worm is replaced by an inverted roller screw, and the gear is replaced by a threaded chain drive. This configuratio...We are developing a speed reducer that can be considered a transformation of a worm gear reducer: the worm is replaced by an inverted roller screw, and the gear is replaced by a threaded chain drive. This configuration lessens wear, increases load capacity, and improves efficiency. The threaded chain consists of nut-shaped links. This paper presents the results of tests carried out on a prototype with a reduction ratio of 46.展开更多
One of the design methods for closing the end of a pressure cylinder is to screw down a screw plug on the threaded end of the cylinder. In this case, there is the problem of stress concentration in the threaded end of...One of the design methods for closing the end of a pressure cylinder is to screw down a screw plug on the threaded end of the cylinder. In this case, there is the problem of stress concentration in the threaded end of the pressure cylinder. To solve the problem, it is necessary to know accurately the load distribution on the threaded end of the cylinder. To find the load distribution on the threaded end of the pressure cylinder engaged with the screw plug, the following experiments are carried out. Applying the tensile load between the screw plug and the pressure cylinder and regarding the situation above as equivalent to the situation in which the internal pressure is applied, the load distribution is measured with the strain gauge. The influence of thread pitch on the load distribution on the threaded end of the cylinder is presented and an optimum pitch for design is discussed.展开更多
In order to analyze the sealing performance of a new designed premium threaded connection,this paper studies the sealing reliability and sensitivity of the premium threaded connection at its most dangerous load condit...In order to analyze the sealing performance of a new designed premium threaded connection,this paper studies the sealing reliability and sensitivity of the premium threaded connection at its most dangerous load condition based on Kriging model.The load condition of premium threaded connection in deep well is so complex that the most dangerous load point of premium threaded connection under the typical series loads is studied by finite element analysis(FEA) method firstly.Since the FEA of the premium threaded connection is too time-consuming,Kriging model which is accurate and efficient for multidimensional and highly nonlinear problems is built to calculate the sealing reliability of the premium threaded connection at the most dangerous load point.Finally,the sealing sensitivity analysis of the premium threaded connection is performed by the method of variance-based global sensitivity analysis.The work in this paper could contribute for the analysis and further improvement of the premium threaded connection.展开更多
Using premium casing connections instead of API ones is one of the mosteffective technique to prevent casing failure. The factors contribute to the strength of premiumcasing connections are studied with FEA and full-s...Using premium casing connections instead of API ones is one of the mosteffective technique to prevent casing failure. The factors contribute to the strength of premiumcasing connections are studied with FEA and full-scale test. The criterions are presented thatensure the connection's strength higher than the pipe. At the same time, the method is given todecrease the peak stress of the connection so as to improve its anticorruption property. At last,full-scale tests are done to test the strength of the connections designed with the methoddescribed, the results show that the connection's strength is higher than the pipe. This indicatedthat the method described is effective in designing premium casing connection.展开更多
Analytical method for the distributions of axial-load and stress is based on elastic assumption,but the threaded connections are often in plastic deformation stage in practice.Meanwhile the strain in the threaded conn...Analytical method for the distributions of axial-load and stress is based on elastic assumption,but the threaded connections are often in plastic deformation stage in practice.Meanwhile the strain in the threaded connection is difficult to measure.So it is necessary to study the reliable numerical method.At present neither the convergence analysis of the computational results nor the elastic-plastic analysis in the loading-unloading process are studied.In this paper,von Mises plasticity and kinematic hardening model is used to describe the material response.A new convergence criterion for nonlinear finite element analysis of the loading-unloading process is proposed.An axisymmetric finite element model according to the proposed convergence criterion is developed and used to analyze the distributions of axial-load and stress.It can be conclude that the stress distribution analysis is more dependent on the mesh density than the axial-load distribution analysis.The stress distribution result indicates that with increasing of applied load,the engaged threads close to the nut-bearing surface become plastic firstly.The axial-load distribution result reveals that the load percentage carried by single thread depends on the position of thread and load intensity.When the load is relatively small,the applied load is mainly carried by the engaged threads near the nut-bearing surface,when the load is larger,the differences of percentages for all threads become small.The proposed convergence analyzing procedure is applicable for other nonlinear analyses.The obtained distributions of axial-load and stress can be a reference of engineering application.展开更多
Bioelectrical stimulation is a powerful technique used to promote tissue regeneration,but it can be hindered by an“electrical overload”phenomenon in the core region of stimulation.We develop a threaded microneedle e...Bioelectrical stimulation is a powerful technique used to promote tissue regeneration,but it can be hindered by an“electrical overload”phenomenon in the core region of stimulation.We develop a threaded microneedle electrode system that protects against“electrical overload”by delivering medicinal hydrogel microspheres into the core regions.The threaded needle body is coated with polydopamine and chitosan to enhance the adhesion of microspheres,which are loaded into the threaded grooves,allowing for their stereoscopic release in the core regions.After the electrode is inserted,the microspheres can be delivered three-dimensionally through physical swelling and the shear-thinning effect of chitosan,mitigating the electrical damage.Microspheres are designed to release alkylated vitamin B12 and vitamin E,providing antioxidant and cell protection effects upon in-situ activation,reducing reactive oxygen species(ROS)by 72.8%and cell death by 59.5%.In the model of peripheral nerve injury,the electrode system improves the overall antioxidant capacity by 78.5%and protects the surrounding cells.Additionally,it leads to an improved nerve conduction velocity ratio of 41.9%and sciatic nerve function index of 12.1%,indicating enhanced neuroregeneration.The threaded microneedle electrode system offers a promising approach for nerve repair by inhibiting“electrical overload”,potentially improving outcomes for tissue regeneration.展开更多
Loosening of threaded fasteners is a key failure mode,which is mainly caused by the slippage and friction behaviors on the thread and bearing surfaces,and will affect the integrity and reliability of products.Numerous...Loosening of threaded fasteners is a key failure mode,which is mainly caused by the slippage and friction behaviors on the thread and bearing surfaces,and will affect the integrity and reliability of products.Numerous scholars have conducted research on the loosening of threaded fasteners;however,comprehensive reviews on the loosening of threaded fasteners have been scarce.In this review article,we define loosening as a loss of preload and divide it into non-rotational and rotational loosening.The causes and mechanisms of non-rotational and rotational loosening are summarised.Some essential topics regarding loosening under transverse vibration have also attracted significant attention and have been investigated widely,including the loosening curve,critical condition of loosening,and influencing factors of loosening.The research carried out on these three topics is also summarised in this review.It is believed that our work will not only help new researchers quickly understand the state-of-the-art research on loosening,but also increase the knowledge of engineers on this critical subject.In the future,it is important to conduct more quantitative research on local slippage accumulation,and the relationship between local slippage accumulation and rotational loosening,which will have the potential to comprehensively unravel the loosening mechanism,and effectively guide the anti-loosening design of threaded fasteners.展开更多
Alzheimer’s disease is a multi-amyloidosis disease characterized by amyloid-βdeposits in brain blood vessels,microaneurysms,and senile plaques.How amyloid-βdeposition affects axon pathology has not been examined ex...Alzheimer’s disease is a multi-amyloidosis disease characterized by amyloid-βdeposits in brain blood vessels,microaneurysms,and senile plaques.How amyloid-βdeposition affects axon pathology has not been examined extensively.We used immunohistochemistry and immunofluorescence staining to analyze the forebrain tissue slices of Alzheimer’s disease patients.Widespread axonal amyloidosis with distinctive axonal enlargement was observed in patients with Alzheimer’s disease.On average,amyloid-β-positive axon diameters in Alzheimer’s disease brains were 1.72 times those of control brain axons.Furthermore,axonal amyloidosis was associated with microtubule-associated protein 2 reduction,tau phosphorylation,lysosome destabilization,and several blood-related markers,such as apolipoprotein E,alpha-hemoglobin,glycosylated hemoglobin type A1C,and hemin.Lysosome destabilization in Alzheimer’s disease was also clearly identified in the neuronal soma,where it was associated with the co-expression of amyloid-β,Cathepsin D,alpha-hemoglobin,actin alpha 2,and collagen type IV.This suggests that exogenous hemorrhagic protein intake influences neural lysosome stability.Additionally,the data showed that amyloid-β-containing lysosomes were 2.23 times larger than control lysosomes.Furthermore,under rare conditions,axonal breakages were observed,which likely resulted in Wallerian degeneration.In summary,axonal enlargement associated with amyloidosis,micro-bleeding,and lysosome destabilization is a major defect in patients with Alzheimer’s disease.This finding suggests that,in addition to the well-documented neural soma and synaptic damage,axonal damage is a key component of neuronal defects in Alzheimer’s disease.展开更多
E-commerce has transformed Caoxian into a hub of traditional Chinese attire.STEPPING inside Caoxian’s Youai Cloud Warehouse,a livestreaming base dedicated to hanfu(traditional clothing),it feels less like a clothing ...E-commerce has transformed Caoxian into a hub of traditional Chinese attire.STEPPING inside Caoxian’s Youai Cloud Warehouse,a livestreaming base dedicated to hanfu(traditional clothing),it feels less like a clothing warehouse and more like a time capsule.Thousands of intricately embroidered garments line the racks-from elegant horse-face skirts to modernised editions of traditional Chinese clothing.展开更多
Archives of threaded discussions generated by users in online forums and discussion boards contain valuable knowledge on various topics. However, not all threads are useful because of deliberate abuses, such as trolli...Archives of threaded discussions generated by users in online forums and discussion boards contain valuable knowledge on various topics. However, not all threads are useful because of deliberate abuses, such as trolling and flaming, that are commonly observed in online conversations. The existence of various users with different levels of expertise also makes it difficult to assume that every discussion thread stored online contains high-quality contents. Although finding high-quality threads automatically can help both users and search engines sift through a huge amount of thread archives and make use of these potentially useful resources effectively, no previous work to our knowledge has performed a study on such task. In this paper, we propose an automatic method for distinguishing high-quality threads from low-quality ones in online discussion sites. We first suggest four different artificial measures for inducing overall quality of a thread based on ratings of its posts. We then propose two tasks involving prediction of thread quality without using post rating information. We adopt a popular machine learning framework to solve the two prediction tasks. Experimental results on a real world forum archive demonstrate that our method can significantly improve the prediction performance across all four measures of thread quality on both tasks. We also compare how different types of features derived from various aspects of threads contribute to the overall performance and investigate key features that play a crucial role in discovering high-quality threads in online discussion sites.展开更多
Earth observation data are typically compressed using general-purpose single-threaded compression algorithms that operate at a fraction of the bandwidth of modern storage and processing systems.We present evidence tha...Earth observation data are typically compressed using general-purpose single-threaded compression algorithms that operate at a fraction of the bandwidth of modern storage and processing systems.We present evidence that recently developed multi-threaded compression codecs offer substantial benefits over widely used single-threaded codecs in terms of compression efficiency when applied to a selection of moderate resolution imaging spectroradiometer(MODIS)datasets stored in the HDF5 format.Compression codecs from the LZ77 and Rice families are shown to vary in efficacy when applied to different MODIS data products,highlighting the need for compression strategies to be tailored to different classes of data.We also introduce LPC-Rice,a new multi-threaded codec,that performs particularly well when applied to time-series data.展开更多
This paper focuses on the effect of welding parameters on microstructure and tensile strength of joints welded by friction-stir welding(FSW).The effects of pin profile(threaded conical,non-threaded conical and triangu...This paper focuses on the effect of welding parameters on microstructure and tensile strength of joints welded by friction-stir welding(FSW).The effects of pin profile(threaded conical,non-threaded conical and triangular pin),tool rotational speed(800,1000,1250 and 1600 r·min^(-1))and welding speed(63,80,100 and 125 mm·min^(-1))on the mechanical and microstructural properties of joints welded in 5-mm 7075-T6 were investigated.The results depict that the pin profile has a major role in the shape and grain size of the weld nugget zone(WNZ).In other words,a wider weld nugget and a finer grain size by threaded conical pin are obtained in WNZ.The attained data of tensile tests show that the maximum ultimate tensile strength(UTS)belongs to the threaded conical pin which is attributed to a finer grain size generated in the weld nugget zone.Additionally,it is found that the tensile strength increases with the welding speed increasing,whereas rotational speed has a bilateral effect on the tensile strength.The microhardness tests show that the minimum hardness is obtained in the heat-affected zone(HAZ).展开更多
文摘In petroleum extraction,the sealing surfaces of bolted joints are susceptible to damage due to the high-temperature and high-pressure conditions in wellbores.This damage adversely affects sealing performance,consequently leading to the failure and damage of threaded connections.In severe cases,it can result in considerable economic losses and trigger safety accidents.The sealing performance of special bolted joints holds crucial importance for production efficiency,output,equipment lifespan,and cost control.Enhancing the sealing perfor-mance of threaded connections can have a positive impact on industrial production and environmental protection.The existing research on American Petroleum Institute threaded joints has been thorough and has obtained a series of excellent results.However,the research on the sealing damage mechanism of threaded connections under complex well conditions lacks sufficient depth and that on new sealing technology is scarce.This study proposes a half-size evaluation test to address the abovementioned problem.Based on this test,an investigation into the sealing performance of threaded connections under high-temperature,cyclic loading,and high-temperature creep conditions is conducted.This study uses a combined approach of finite element methods and experiments to investigate the impact of different makeup torques on the sealing performance of premium threaded connections(PTCs).The results of the half-size evaluation test indicate that temperature notably influences the sealing performance of threaded connections.The continuous action of high temperatures causes contact pressure and sealing performance to decrease,and sealing contact pressure increases after cooling.Finite element and test results show that for a certain joint A,the greater the torque,the higher the critical sealing pressure of the thread,and the better the sealing performance.The research on the sealing damage mechanism of PTCs provides a scientific basis and theoretical guidance for the further optimization and development of PTCs.
基金financially supported by Program for New Century Excellent Talents in University(No.NCET-090396)the Foundation for Innovative Research Groups of the Natural Science Foundation of Hubei Province,China(2010CDA067)State Major Science and Technology Special Project Foundation for High-end Numerical Machine and Basic Manufacturing Equipment(2011ZX04014-052,2012ZX04012-011)
文摘Simulation of the microstructure evolution during solidifi cation is greatly benefi cial to the control of solidifi cation microstructures. A phase-fi eld method based on the full threaded tree(FTT) for the simulation of casting solidifi cation microstructure was proposed in this paper, and the structure of the full threaded tree and the mesh refi nement method was discussed. During dendritic growth in solidifi cation, the mesh for simulation is adaptively refi ned at the liquid-solid interface, and coarsened in other areas. The numerical results of a threedimension dendrite growth indicate that the phase-fi eld method based on FTT is suitable for microstructure simulation. Most importantly, the FTT method can increase the spatial and temporal resolutions beyond the limits imposed by the available hardware compared with the conventional uniform mesh. At the simulation time of 0.03 s in this study, the computer memory used for computation is no more than 10 MB with the FTT method, while it is about 50 MB with the uniform mesh method. In addition, the proposed FTT method is more effi cient in computation time when compared with the uniform mesh method. It would take about 20 h for the uniform mesh method, while only 2 h for the FTT method for computation when the solidifi cation time is 0.17 s in this study.
基金supported by the Horrizon 2020"Efficient Manufacturing for Aerospace Components Using Additive Manufacturing,Net Shape HIP and Investment Casting(EMUSIC)"the State Key Laboratory of Materials Processing and Die&Mould Technology Research Project,China(2015-2017)
文摘Selective laser melting(SLM) is a promising technique for additive manufacturing. During SLM of metallic powder, the temperature field and thermal history are important to understand physical phenomena involved. The purpose of this study is to simulate the temperature field during the SLM process of a hollow cylinder shape part based on a fully threaded tree(FTT) technique, and to analyze the temperature variation with time in different regions of the part. A revised model for temperature field simulation in the SLM process was employed, which includes the transition of powder-to-dense sub-model and a moving volumetric Gaussian distribution heat source sub-model. The FTT technique is then adopted as an adaptive mesh strategy in the simulation. The simulation result shows that during the SLM process of cylinder part, the temperature of inner powder bed is obviously higher than external one. The temperature at the internal of the molten pool is also higher than external, which may lead to differences in microstructures and other properties between the two regions.
基金supported by the Science Challenge Project(No.TZ2018004)the National Natural Science Foundation of China(Nos.21790340 and 21674113)+2 种基金Jilin Scientific and Technological Development Program(No.20180519001JH)the Programs of Chinese Academy of Sciences(Nos.QYZDY SSW-SLH027 and YJKYYQ20190084)Y.L.acknowledges the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2016204)for financial support.
文摘A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings.The hydrodynamic interactions significantly speed up the diffusion and relaxation of both free and threaded rings.The decoupled diffusion and relaxation dynamics indicate the broken of the Einstein-Stokes relationship.The diffusion of a ring threaded on a flexible chain exhibits a synergism effect compared to that on an axial rod,which originates from the self-diffusion of the ring and the reptation-like motion of the axial chain.Meanwhile,hydrodynamic interactions significantly improve the synergism effect,leading to an enhanced sliding motion of the threaded ring.The faster sliding of threaded rings suggests that the entropic barrier is negligible,which agrees well with the basic assumption of barrier-less confining tube at equilibrium in tube theory.Our results provide a new perspective on analysis of the effects of topology constraints on polymer dynamics.
文摘In order to improve the accuracy of threaded hole object detection,combining a dual camera vision system with the Hough transform circle detection,we propose an object detection method of artifact threaded hole based on Faster region-ased convolutional neural network(Faster R-CNN).First,a dual camera image acquisition system is established.One industrial camera placed at a high position is responsible for collecting the whole image of the workpiece,and the suspected screw hole position on the workpiece can be preliminarily selected by Hough transform detection algorithm.Then,the other industrial camera is responsible for collecting the local images of the suspected screw holes that have been detected by Hough transform one by one.After that,ResNet50-based Faster R-CNN object detection model is trained on the self-built screw hole data set.Finally,the local image of the threaded hole is input into the trained Faster R-CNN object detection model for further identification and location.The experimental results show that the proposed method can effectively avoid small object detection of threaded holes,and compared with the method that only uses Hough transform or Faster RCNN object detection alone,it has high recognition and positioning accuracy.
基金Supported by National Natural Science Foundation of China(Grant Nos.U23B20104,52075012 and 52205510).
文摘Threaded fasteners are one of the most commonly used connection methods for mechanical structures.Its primary function is to generate appropriate clamping forces and fasten the connected parts.An inappropriate preload can cause loosening,fatigue fracture,and other problems.This will affect the safety and reliability of mechanical equipment.The precise control of the preload has become a critical issue in mechanical assembly processes.Over the past few decades,various tightening measures and methods have been proposed to address this issue.However,many problems continue to exist with practical applications that have not been reviewed comprehensively and systematically.First,various control methods were summarized systematically,and their advantages and disadvantages in engineering applications were analyzed.Torque control is the most widely used tightening method owing to its simple operation and low cost.Therefore,the research on the torque control method was summarized systematically from three aspects:the torque-preload correlation formula,effective friction radius,and friction characteristics during tightening.In addition,the special circumstances that may increase preload uncertainty were discussed.Finally,based on a summary of the current research status,the prospects for future research were discussed.This study would aid researchers in extensively understanding the problems in preload control.
基金Project supported by the National Basic Research Program of China(Grant No.2013CB932901)the National Natural Science Foundation of China(Grant Nos.51210105026 and 51172270)the Funds from the Chinese Academy of Sciences
文摘Threaded aluminum nitride （A1N） whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering, scanning electron microscopy, transmission electron microscopy and photoluminescence. The analysis shows that the whiskers are single-crystalline, wurtzite AIN. The threaded A1N whiskers are 0.5 μm^100 μm in diameter and several millimeters in length in the fiber direction, and have lots of tiny sawteeth on the surface. The morphology of this threaded A1N whisker is beneficial for bonding when the whisker is used in composite. The growth of the whiskers is dominated by the vapor-solid （VS） mechanism, and the particular morphology might result from an oscillating condition produced in the radio-frequency induction heating furnace.
基金This research was sponsored by the National Natural Science Foundation of China(Grant Nos.51878344 and 51578284).
文摘Experimental investigation on the pull-out behaviour,including the withdrawal capacity,slip stiffness and inter-facial shear stress,of axially loaded screwed-in threaded rod embedded in cross laminated timber(CLT)was con-ducted.Specimens with varying embedment length and different number of threaded rods were tested in this study.To prevent premature splitting failure of timber,some specimens were reinforced in the direction perpen-dicular to the timber grain with self-tapping screws.Test results showed that the screwed-in threaded rod con-nections exhibited good pull-out behaviour with high withdrawal capacity and slip stiffness.Within a certain range,the withdrawal capacity increases considerably with the increase of embedment length,while the average interfacial shear stress shows the opposite tendency.The self-tapping screws played an important role on reducing the splitting of the timber and improving the withdrawal capacity and slip stiffness of the screwed-in threaded rod.Additionally,for the specimens with self-tapping screw reinforcements,the improvement of withdrawal capacity and stiffness when increasing the number of threaded rods are much more obvious than that of the speci-mens without the self-tapping screws,due to the change of failure modes.
文摘We are developing a speed reducer that can be considered a transformation of a worm gear reducer: the worm is replaced by an inverted roller screw, and the gear is replaced by a threaded chain drive. This configuration lessens wear, increases load capacity, and improves efficiency. The threaded chain consists of nut-shaped links. This paper presents the results of tests carried out on a prototype with a reduction ratio of 46.
文摘One of the design methods for closing the end of a pressure cylinder is to screw down a screw plug on the threaded end of the cylinder. In this case, there is the problem of stress concentration in the threaded end of the pressure cylinder. To solve the problem, it is necessary to know accurately the load distribution on the threaded end of the cylinder. To find the load distribution on the threaded end of the pressure cylinder engaged with the screw plug, the following experiments are carried out. Applying the tensile load between the screw plug and the pressure cylinder and regarding the situation above as equivalent to the situation in which the internal pressure is applied, the load distribution is measured with the strain gauge. The influence of thread pitch on the load distribution on the threaded end of the cylinder is presented and an optimum pitch for design is discussed.
文摘In order to analyze the sealing performance of a new designed premium threaded connection,this paper studies the sealing reliability and sensitivity of the premium threaded connection at its most dangerous load condition based on Kriging model.The load condition of premium threaded connection in deep well is so complex that the most dangerous load point of premium threaded connection under the typical series loads is studied by finite element analysis(FEA) method firstly.Since the FEA of the premium threaded connection is too time-consuming,Kriging model which is accurate and efficient for multidimensional and highly nonlinear problems is built to calculate the sealing reliability of the premium threaded connection at the most dangerous load point.Finally,the sealing sensitivity analysis of the premium threaded connection is performed by the method of variance-based global sensitivity analysis.The work in this paper could contribute for the analysis and further improvement of the premium threaded connection.
文摘Using premium casing connections instead of API ones is one of the mosteffective technique to prevent casing failure. The factors contribute to the strength of premiumcasing connections are studied with FEA and full-scale test. The criterions are presented thatensure the connection's strength higher than the pipe. At the same time, the method is given todecrease the peak stress of the connection so as to improve its anticorruption property. At last,full-scale tests are done to test the strength of the connections designed with the methoddescribed, the results show that the connection's strength is higher than the pipe. This indicatedthat the method described is effective in designing premium casing connection.
基金supported by Vehicular Diesel Engine Development Program of China(Grant No.DEDP0202)
文摘Analytical method for the distributions of axial-load and stress is based on elastic assumption,but the threaded connections are often in plastic deformation stage in practice.Meanwhile the strain in the threaded connection is difficult to measure.So it is necessary to study the reliable numerical method.At present neither the convergence analysis of the computational results nor the elastic-plastic analysis in the loading-unloading process are studied.In this paper,von Mises plasticity and kinematic hardening model is used to describe the material response.A new convergence criterion for nonlinear finite element analysis of the loading-unloading process is proposed.An axisymmetric finite element model according to the proposed convergence criterion is developed and used to analyze the distributions of axial-load and stress.It can be conclude that the stress distribution analysis is more dependent on the mesh density than the axial-load distribution analysis.The stress distribution result indicates that with increasing of applied load,the engaged threads close to the nut-bearing surface become plastic firstly.The axial-load distribution result reveals that the load percentage carried by single thread depends on the position of thread and load intensity.When the load is relatively small,the applied load is mainly carried by the engaged threads near the nut-bearing surface,when the load is larger,the differences of percentages for all threads become small.The proposed convergence analyzing procedure is applicable for other nonlinear analyses.The obtained distributions of axial-load and stress can be a reference of engineering application.
基金supported by various grants,including the National Key Research and Development Program of China(2020YFA0908200)National Natural Science Foundation of China General Program(81930051,82205244)China Postdoctoral Science Foundation(2022M712135).
文摘Bioelectrical stimulation is a powerful technique used to promote tissue regeneration,but it can be hindered by an“electrical overload”phenomenon in the core region of stimulation.We develop a threaded microneedle electrode system that protects against“electrical overload”by delivering medicinal hydrogel microspheres into the core regions.The threaded needle body is coated with polydopamine and chitosan to enhance the adhesion of microspheres,which are loaded into the threaded grooves,allowing for their stereoscopic release in the core regions.After the electrode is inserted,the microspheres can be delivered three-dimensionally through physical swelling and the shear-thinning effect of chitosan,mitigating the electrical damage.Microspheres are designed to release alkylated vitamin B12 and vitamin E,providing antioxidant and cell protection effects upon in-situ activation,reducing reactive oxygen species(ROS)by 72.8%and cell death by 59.5%.In the model of peripheral nerve injury,the electrode system improves the overall antioxidant capacity by 78.5%and protects the surrounding cells.Additionally,it leads to an improved nerve conduction velocity ratio of 41.9%and sciatic nerve function index of 12.1%,indicating enhanced neuroregeneration.The threaded microneedle electrode system offers a promising approach for nerve repair by inhibiting“electrical overload”,potentially improving outcomes for tissue regeneration.
基金The authors are grateful for support by the National Natural Science Foundation of China(Nos.51935003 and 51675050)the National Defense Fundamental Research Foundation of China(No.JCKY2016204B201)。
文摘Loosening of threaded fasteners is a key failure mode,which is mainly caused by the slippage and friction behaviors on the thread and bearing surfaces,and will affect the integrity and reliability of products.Numerous scholars have conducted research on the loosening of threaded fasteners;however,comprehensive reviews on the loosening of threaded fasteners have been scarce.In this review article,we define loosening as a loss of preload and divide it into non-rotational and rotational loosening.The causes and mechanisms of non-rotational and rotational loosening are summarised.Some essential topics regarding loosening under transverse vibration have also attracted significant attention and have been investigated widely,including the loosening curve,critical condition of loosening,and influencing factors of loosening.The research carried out on these three topics is also summarised in this review.It is believed that our work will not only help new researchers quickly understand the state-of-the-art research on loosening,but also increase the knowledge of engineers on this critical subject.In the future,it is important to conduct more quantitative research on local slippage accumulation,and the relationship between local slippage accumulation and rotational loosening,which will have the potential to comprehensively unravel the loosening mechanism,and effectively guide the anti-loosening design of threaded fasteners.
基金supported by the National Natural Science Foundation of China,No.81472235(to HF)the Shanghai Jiao Tong University Medical and Engineering Project,Nos.YG2021QN53(to HF),YG2017MS71(to HF)+1 种基金the International Cooperation Project of the National Natural Science Foundation of China,No.82020108017(to DC)the Innovation Group Project of the National Natural Science Foundation of China,No.81921002(to DC).
文摘Alzheimer’s disease is a multi-amyloidosis disease characterized by amyloid-βdeposits in brain blood vessels,microaneurysms,and senile plaques.How amyloid-βdeposition affects axon pathology has not been examined extensively.We used immunohistochemistry and immunofluorescence staining to analyze the forebrain tissue slices of Alzheimer’s disease patients.Widespread axonal amyloidosis with distinctive axonal enlargement was observed in patients with Alzheimer’s disease.On average,amyloid-β-positive axon diameters in Alzheimer’s disease brains were 1.72 times those of control brain axons.Furthermore,axonal amyloidosis was associated with microtubule-associated protein 2 reduction,tau phosphorylation,lysosome destabilization,and several blood-related markers,such as apolipoprotein E,alpha-hemoglobin,glycosylated hemoglobin type A1C,and hemin.Lysosome destabilization in Alzheimer’s disease was also clearly identified in the neuronal soma,where it was associated with the co-expression of amyloid-β,Cathepsin D,alpha-hemoglobin,actin alpha 2,and collagen type IV.This suggests that exogenous hemorrhagic protein intake influences neural lysosome stability.Additionally,the data showed that amyloid-β-containing lysosomes were 2.23 times larger than control lysosomes.Furthermore,under rare conditions,axonal breakages were observed,which likely resulted in Wallerian degeneration.In summary,axonal enlargement associated with amyloidosis,micro-bleeding,and lysosome destabilization is a major defect in patients with Alzheimer’s disease.This finding suggests that,in addition to the well-documented neural soma and synaptic damage,axonal damage is a key component of neuronal defects in Alzheimer’s disease.
文摘E-commerce has transformed Caoxian into a hub of traditional Chinese attire.STEPPING inside Caoxian’s Youai Cloud Warehouse,a livestreaming base dedicated to hanfu(traditional clothing),it feels less like a clothing warehouse and more like a time capsule.Thousands of intricately embroidered garments line the racks-from elegant horse-face skirts to modernised editions of traditional Chinese clothing.
基金supported by the Ministry of Knowledge Economy(MKE),KoreaMicrosoft Research through the IT/SW Creative Research Program supervised by the National IT Industry Promotion Agency(NIPA)of Korea under Grant No.NIPA2012-H0503-12-1012the Next-Generation Information Computing Development Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT&Future Planning of Korea under Grant No.NRF-2012M3C4A7033344
文摘Archives of threaded discussions generated by users in online forums and discussion boards contain valuable knowledge on various topics. However, not all threads are useful because of deliberate abuses, such as trolling and flaming, that are commonly observed in online conversations. The existence of various users with different levels of expertise also makes it difficult to assume that every discussion thread stored online contains high-quality contents. Although finding high-quality threads automatically can help both users and search engines sift through a huge amount of thread archives and make use of these potentially useful resources effectively, no previous work to our knowledge has performed a study on such task. In this paper, we propose an automatic method for distinguishing high-quality threads from low-quality ones in online discussion sites. We first suggest four different artificial measures for inducing overall quality of a thread based on ratings of its posts. We then propose two tasks involving prediction of thread quality without using post rating information. We adopt a popular machine learning framework to solve the two prediction tasks. Experimental results on a real world forum archive demonstrate that our method can significantly improve the prediction performance across all four measures of thread quality on both tasks. We also compare how different types of features derived from various aspects of threads contribute to the overall performance and investigate key features that play a crucial role in discovering high-quality threads in online discussion sites.
文摘Earth observation data are typically compressed using general-purpose single-threaded compression algorithms that operate at a fraction of the bandwidth of modern storage and processing systems.We present evidence that recently developed multi-threaded compression codecs offer substantial benefits over widely used single-threaded codecs in terms of compression efficiency when applied to a selection of moderate resolution imaging spectroradiometer(MODIS)datasets stored in the HDF5 format.Compression codecs from the LZ77 and Rice families are shown to vary in efficacy when applied to different MODIS data products,highlighting the need for compression strategies to be tailored to different classes of data.We also introduce LPC-Rice,a new multi-threaded codec,that performs particularly well when applied to time-series data.
文摘This paper focuses on the effect of welding parameters on microstructure and tensile strength of joints welded by friction-stir welding(FSW).The effects of pin profile(threaded conical,non-threaded conical and triangular pin),tool rotational speed(800,1000,1250 and 1600 r·min^(-1))and welding speed(63,80,100 and 125 mm·min^(-1))on the mechanical and microstructural properties of joints welded in 5-mm 7075-T6 were investigated.The results depict that the pin profile has a major role in the shape and grain size of the weld nugget zone(WNZ).In other words,a wider weld nugget and a finer grain size by threaded conical pin are obtained in WNZ.The attained data of tensile tests show that the maximum ultimate tensile strength(UTS)belongs to the threaded conical pin which is attributed to a finer grain size generated in the weld nugget zone.Additionally,it is found that the tensile strength increases with the welding speed increasing,whereas rotational speed has a bilateral effect on the tensile strength.The microhardness tests show that the minimum hardness is obtained in the heat-affected zone(HAZ).
