This article deals with the investigation of the effects of seismic impacts on the design and dimensioning of structures in South Kivu. The starting point is the observation of an ambivalence that can be observed in t...This article deals with the investigation of the effects of seismic impacts on the design and dimensioning of structures in South Kivu. The starting point is the observation of an ambivalence that can be observed in the province, namely the non-consideration of seismic action in the study of structures by both professionals and researchers. The main objective of the study is to show the importance of dynamic analysis of structures in South Kivu. It adopts a meta-analytical approach referring to previous researches on South Kivu and proposes an efficient and optimal method. To arrive at the results, we use Eurocode 7 and 8. In addition, we conducted static analysis using the Coulomb method and dynamic analysis using the Mononobe-Okabe method and compared the results. At Nyabibwe, the results showed that we have a deviation of 24.47% for slip stability, 12.038% for overturning stability and 9.677% for stability against punching through a weight wall.展开更多
In aero-engines,mortise-tenon joint structures are often used to connect the blades to the turbine disk.The disadvantages associated with conventional manufacturing techniques mean that a low-cost,high-efficiency,and ...In aero-engines,mortise-tenon joint structures are often used to connect the blades to the turbine disk.The disadvantages associated with conventional manufacturing techniques mean that a low-cost,high-efficiency,and high-quality nickel-based mortise–tenon joint structure is an urgent requirement in the field of aviation engineering.Electrochemical cutting is a potential machining method for manufacturing these parts,as there is no tool degradation in the cutting process and high-quality surfaces can be obtained.To realize the electrochemical cutting of a mortise-tenon joint structure,a method using a tube electrode with helically distributed jet-flow holes on the side-wall is proposed.During feeding,the tube electrode rotates along its central axis.Flow field simulations show that the rotational speed of the tube electrode determines the direct spraying time of the high-speed electrolyte ejected from the jet-flow holes to the machining area,while the electrolyte pressure determines the flow rate of the electrolyte and the velocity of the electrolyte ejected from the jet-flow holes.The machining results using the proposed method are verified experimentally,and the machining parameters are optimized.Finally,mortise and tenon samples are successfully machined using 20 mm thick Inconel 718 alloy with a feeding rate of 5μm/s.展开更多
Due to the complexity of joint structures and the diversity of disorders in the joints,the diagnosis of joint diseases is challenging.Current clinical diagnostic techniques for evaluating joint diseases,such as arthri...Due to the complexity of joint structures and the diversity of disorders in the joints,the diagnosis of joint diseases is challenging.Current clinical diagnostic techniques for evaluating joint diseases,such as arthritis,have strengths and weaknesses.New imaging techniques need to be developed for the diagnosis or auxiliary diagnosis of arthritis.As an emerging nonintrusive low-cost imaging method,microwave-induced thermoacoustic imaging(TAI)can present tissue morphology while providing the tissue microwave energy absorption density distribution related to dielectric properties.TAI is currently in development to potentially visualize joint anatomic structures and to detect arthritis.Here,we offer a mini review to summarize the status of research on TAI of joints and present an outlook to the future development of TAI in the detection of joint diseases.展开更多
An important consideration when using hot-dip galvanized tubular structures is the uncertainty of the joint behaviour due to the possible reduction in the global joint resistance produced by the vent holes required fo...An important consideration when using hot-dip galvanized tubular structures is the uncertainty of the joint behaviour due to the possible reduction in the global joint resistance produced by the vent holes required for the galvanizing process. This paper assesses the effect on the joint strength of the angle between the brace members and the chord in a K- or N-joints made with rectangular hollow sections. The study is focused on the case when those brace members include characteristic holes required for the hot-dip galvanizing process. To accomplish the objective of the proposed work, some tests on full-scale K- and N-joints, including angles of 35°, 45°, 55° and 90°, were carried out. The experimental work was complemented by a validated numerical simulation in order to give some design recommendations and to extend the research to other joint configurations.展开更多
In order to investigate the nonlinear characteristics of structural joint,the experimental setup with a jointed mass system is established for dynamic characterization analysis and vibration prediction,and a correspon...In order to investigate the nonlinear characteristics of structural joint,the experimental setup with a jointed mass system is established for dynamic characterization analysis and vibration prediction,and a corresponding nonlinearity identification method is studied.First,the sine-sweep vibration test with different baseexcitation levels areapplied to the structural joint system to study the dominant modal of mass rigid motion.Then,based on t e harmonic balance method principle,t e measured vibration transmissibilities a e utilized for nonlinearity identification using different excitation levels.Experimental results show that nonlinear spring and damping force can be represented by a polynomial order approximation.The identified nonlinear stiffness and damping force can predict the system’s response,and they can reveal t e shifts of resonant frequency or damping due to discontinuity of contact mechanisms within a certain range.展开更多
Components of mechanical product are assembled by structural joints,such as bolting,riveting,welding,etc.Structural joints introduce nonlinearity to some engineering structures,and the nonlinearity need to be modeled ...Components of mechanical product are assembled by structural joints,such as bolting,riveting,welding,etc.Structural joints introduce nonlinearity to some engineering structures,and the nonlinearity need to be modeled precisely.To meet serious quality requirements,it is necessary to detect and identify nonlinearity of mechanical products for structural optimization.Modal test to acquire a dynamic response has been applied for decades,which provides reliable results for finite element(FE)model updating.Here response control vibration test for identification of nonlinearity is presented.A nonlinear system can be regarded as linearity for particular steady state response,and classical linear analysis tool is applicable to extract modal data for particular response.First,its applicability is illustrated by some numerical simulations.Subsequently,it is implemented on experimental setup with structural joints by shaking table.The stiffness and damping function dependent of relative displacement are fitted to describe its inherent nonlinearity.The spring and damping forces are identified by harmonic balance method(HBM)to predict output response.Based on the identified results,the procedure is recommended that it allows a reliable measurement of nonlinearity with a certain accuracy.展开更多
A modified space beam element is presented in this paper to consider the local joint flexibility of T, Y tubular joints subjected to axial forces and in-plane bending moments for analysis of platforms. Two numerical e...A modified space beam element is presented in this paper to consider the local joint flexibility of T, Y tubular joints subjected to axial forces and in-plane bending moments for analysis of platforms. Two numerical examples are shown to verify the efficiency and validity of the method presented here.展开更多
Stress concentration analysis of multiplanar tubular DT joints plays an important role in the fatigue design of offshore platforms. A semi-analytic method for stress analysis under the condition of any loads is briefl...Stress concentration analysis of multiplanar tubular DT joints plays an important role in the fatigue design of offshore platforms. A semi-analytic method for stress analysis under the condition of any loads is briefly introduced in the paper. Nineteen multiplanar tubular DT joints with one of two braces of the same dimension subjected to axial loads and out- of- plane bending moments are computed for parametric stress analysis by using the present method. The influence of geometrical parameters on the stresses of multiplanar tubular DT joints is discussed and compared with corresponding uniplanar T joints. The regression formulae for the stress at hot spot of multiplanar DT joints are found by modification of SCF of corresponding uniplanar T joints. The parametric formulae for the maximum stress by superposition. Finally, the influences of stiffening effect and load-interaction effect on the maximum stress of DT joints are discussed.展开更多
Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine env...Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine environment, random variable amplitude fatigue tests have been carried out on welded plate joints in sea water. The tests have been conducted under the conditions of loading frequency of 0.2 Hz/, stress ratio of -1, seawater temperature of about 20°C and cathodic protection with the potential about -850 mV, SCE. The test results have been compared with the seawater corrosion fatigue life under constant amplitude loading. Miner's linear cumulative damage summation rule has been used to predict the corrosion fatigue life under variable amplitude loading. The predicted life is in good agreement with the test data.展开更多
A two-stage damage detection approach is proposed and experimentally demonstrated on a complicated spatial model structure with a limited number of measurements. In the experiment,five known damage patterns,including ...A two-stage damage detection approach is proposed and experimentally demonstrated on a complicated spatial model structure with a limited number of measurements. In the experiment,five known damage patterns,including 3 brace damage cases and 2 joint damage cases,were simulated by removing braces and weakening beam鈥揷olumn connections in the structure. The limited acceleration response data generated by hammer impact were used for system identification,and modal parameters were extracted by using the eigensystem realization algorithm. In the first stage,the possible damaged locations are determined by using the damage index and the characteristics of the analytical model itself,and the extent of damage for those substructures identified at stage I is estimated in the second stage by using a second-order eigen-sensitivity approximation method. The main contribution of this paper is to test the two-stage method by using the real dynamic data of a complicated spatial model structure with limited sensors. The analysis results indicate that the two-stage approach is ableto detect the location of both damage cases,only the severity of brace damage cases can be assessed,and the reasonable analytical model is critical for successful damage detection.展开更多
The purpose of this paper is to present an extended topology optimization method for the stiffeners layout design of aircraft assembled structures. Multi-fastener joint loads and manufacturing constraints are consider...The purpose of this paper is to present an extended topology optimization method for the stiffeners layout design of aircraft assembled structures. Multi-fastener joint loads and manufacturing constraints are considered simultaneously. On one hand, the joint loads are calculated and constrained within a limited value to avoid the failure of fasteners. On the other hand, the manufacturing constraints of the material distribution in the machining directions of stiffeners are implemented by an improved piecewise interpolation based on a beveled cut-surface. It is proven that the objective function is strictly continuous and differentiable with respect to the piecewise interpolation. The effects of the extended method with two different constraints are highlighted by typical numerical examples. Compared with the standard topology optimization, the final designs have clearly shown the layout of stiffeners and the joint loads have been perfectly constrained to a satisfying level.展开更多
Acquisition of accurate channel state information （CSI） at transmitters results in a huge pilot overhead in massive multiple input multiple output （MIMO） systems due to the large number of antennas in the base sta...Acquisition of accurate channel state information （CSI） at transmitters results in a huge pilot overhead in massive multiple input multiple output （MIMO） systems due to the large number of antennas in the base station （BS）. To reduce the overwhelming pilot overhead in such systems, a structured joint channel estimation scheme employing compressed sensing （CS） theory is proposed. Specifically, the channel sparsity in the angular domain due to the practical scattering environment is analyzed, where common sparsity and individual sparsity structures among geographically neighboring users exist in multi-user massive MIMO systems. Then, by equipping each user with multiple antennas, the pilot overhead can be alleviated in the framework of CS and the channel estimation quality can be improved. Moreover, a structured joint matching pursuit （SJMP） algorithm at the BS is proposed to jointly estimate the channel of users with reduced pilot overhead. Furthermore, the probability upper bound of common support recovery and the upper bound of channel estimation quality using the proposed SJMP algorithm are derived. Simulation results demonstrate that the proposed SJMP algorithm can achieve a higher system performance than those of existing algorithms in terms of pilot overhead and achievable rate.展开更多
It＇ s well known welding takes the leading role in development of titanium structures. However, in number of cases technological processes of brazing are more appropriate and, sometimes, being the single possible, in...It＇ s well known welding takes the leading role in development of titanium structures. However, in number of cases technological processes of brazing are more appropriate and, sometimes, being the single possible, in particular, during production of multilayer thin-wall structures. It should be noted that brazing filler metals of Ti-Cu-Ni, Ti-Zr-Cu-Ni, Zr-Ti-Ni and Cu-Zr-Ti systems in a form of plastic foils, as well as in powder form are mainly used in world practice for brazing of titanium alloys. Present work provides the results of complex investigations of brazing filler metals of Ti-Zr-Fe, Ti-Zr-Mn and Ti-Zr-Co systems using differential thermal analysis, light and scanning microscopy, X-ray microspectrum analysis. Data on melting ranges of pilot alloys were obtained, and liquidas su^Caces of given systems using simplex-lattice method were build. Brazing filler metals covering brazing temperature range of current structural titanium materials based on solid solutions as well as intermetallics were proposed. Structure, chemical inhomogeniety and strength characteristics of brazed joints were studied. It is determined that brazing of solid solution based alloys （OT4, VT6 ） using indicated brazing fiUer metals ensures strength characteristics of joints, which are not inferior to that obtained with application of known brazing filler metals even if they are received at lower brazing temperature.展开更多
Forming a joint venture (JV) in China can be a successful endeavor as long as each side’s goals, contributions and responsibilities are mutual and understood. Unfortunately, this is not always the case,
The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted...The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted circumferential joint during the entire bearing process.Simplified analytical algorithms for four stress stages are established to describe the bearing behaviors of the joint under a compressive bending load.A height adjustment coefficient,α,for the outer concrete compression zone is introduced into a simplified analytical model.Factors affectingαare determined,and the degree of influence of these factors is investigated via orthogonal numerical simulations.The numerical results show thatαcan be specified as approximately 0.2 for most metro shield tunnels in China.Subsequently,a case study is performed to verify the rationality of the simplified theoretical analysis for the segment joint via numerical simulations and experiments.Using the proposed simplified analytical algorithms,a parametric investigation is conducted to discuss the factors affecting the ultimate compressive bending capacity of the joint.The method for optimizing the joint flexural stiffness is clarified.The results of this study can provide a theoretical basis for optimizing the design and prediciting the damage of bolted segment joints in shield tunnels.展开更多
Composite-metal joints with a metal insert are one kind of connecting structure.In this paper,tensile experimental tests were carried out to investigate tensile properties of a compositemetal joint with a novel metal ...Composite-metal joints with a metal insert are one kind of connecting structure.In this paper,tensile experimental tests were carried out to investigate tensile properties of a compositemetal joint with a novel metal insert design.Finite element models of the joint were established,and strain distribution and tensile strength were analyzed.The numerical results are in good agreement with the experimental results.Results show that the joint failure is dominated by shear properties of the resin layer.Increasing the resin layer thickness in a certain range will improve the tensile strength of the joint,while increasing the radius of the fillet on the ending side of the metal insert will decrease the joint strength.Increasing the resin layer plasticity will improve the joint strength.The effect of the embedded depth of the metal insert can be ignored.展开更多
Naturally optimized successful synovial joints with lightweight,high load-carrying,ultra-low friction and wear have attracted tribological communities to constantly imitate and replicate.Despite impressive advances in...Naturally optimized successful synovial joints with lightweight,high load-carrying,ultra-low friction and wear have attracted tribological communities to constantly imitate and replicate.Despite impressive advances in cartilage lubrication,extending such extraordinary performance advantages to macroscale solid lubrication remains a challenge.Herein,inspired by the fascinating interplay of synovial joints,a novel kind of trans-scale hierarchical structured ceramic-based composite was developed.Intro-ducing microscale Ag microspheres(AgMs)“cartilage”layer and nanoscale Ag quantum dots/MXene(AgQDs/MXene)“synovial fluid”into the interior and exterior of printed macroscale SiOC“hard bone”realistically restores the gradient structure of synovial joint prototype.The resulted composite with ideal compressive strength(70.44 MPa)can achieve a 60.53%friction reduction and a low wear rate(2.05×10^(−6)mm 3 N^(−1)m^(−1))in dry tribo-contact for 3600 sliding cycles,while also maintaining considerable low friction(∼0.11)over 10,000 sliding cycles and long-term stable lubrication(∼0.13)for up to 50,000 re-ciprocating cycles.Such extraordinary performance can be explained by the division of macro contacts,full loading of AgMs and AgQDs/MXene,abrasive debris capture and removal,as well as the shear rolling effect induced by friction process.This work opens a new avenue to develop structural lubricating mate-rials for complex engineering applications.展开更多
When investing in China’s restricted in- dustries, it is essential to have a joint venture (JV) partner. Often the maximum percent- age of equity allowed in foreign ownership can only be 50 percent. So what options a...When investing in China’s restricted in- dustries, it is essential to have a joint venture (JV) partner. Often the maximum percent- age of equity allowed in foreign ownership can only be 50 percent. So what options are available to the foreign investor to mitigate the risk of not owning, on paper, a展开更多
文摘This article deals with the investigation of the effects of seismic impacts on the design and dimensioning of structures in South Kivu. The starting point is the observation of an ambivalence that can be observed in the province, namely the non-consideration of seismic action in the study of structures by both professionals and researchers. The main objective of the study is to show the importance of dynamic analysis of structures in South Kivu. It adopts a meta-analytical approach referring to previous researches on South Kivu and proposes an efficient and optimal method. To arrive at the results, we use Eurocode 7 and 8. In addition, we conducted static analysis using the Coulomb method and dynamic analysis using the Mononobe-Okabe method and compared the results. At Nyabibwe, the results showed that we have a deviation of 24.47% for slip stability, 12.038% for overturning stability and 9.677% for stability against punching through a weight wall.
基金supported by the National Natural Science Foundation of China(No.91960204)the Natural Science Foundation of Jiangsu Province(No.BK20191279)+1 种基金the Aeronautical Science Foundation of China(No.201907052002)the National Natural Science Foundation of China for Creative Research Groups(No.51921003)。
文摘In aero-engines,mortise-tenon joint structures are often used to connect the blades to the turbine disk.The disadvantages associated with conventional manufacturing techniques mean that a low-cost,high-efficiency,and high-quality nickel-based mortise–tenon joint structure is an urgent requirement in the field of aviation engineering.Electrochemical cutting is a potential machining method for manufacturing these parts,as there is no tool degradation in the cutting process and high-quality surfaces can be obtained.To realize the electrochemical cutting of a mortise-tenon joint structure,a method using a tube electrode with helically distributed jet-flow holes on the side-wall is proposed.During feeding,the tube electrode rotates along its central axis.Flow field simulations show that the rotational speed of the tube electrode determines the direct spraying time of the high-speed electrolyte ejected from the jet-flow holes to the machining area,while the electrolyte pressure determines the flow rate of the electrolyte and the velocity of the electrolyte ejected from the jet-flow holes.The machining results using the proposed method are verified experimentally,and the machining parameters are optimized.Finally,mortise and tenon samples are successfully machined using 20 mm thick Inconel 718 alloy with a feeding rate of 5μm/s.
基金supported by the National Natural Science Foundation of China under Grant No.62001075the Chinese Postdoctoral Science Foundation under Grant No.2022MD723722+1 种基金the Chongqing Postdoctoral Research Project under Grant No.2021XM2026the Scientific and Technological Research Program of Chongqing Municipal Education Commission under Grant No.KJQN202000610.
文摘Due to the complexity of joint structures and the diversity of disorders in the joints,the diagnosis of joint diseases is challenging.Current clinical diagnostic techniques for evaluating joint diseases,such as arthritis,have strengths and weaknesses.New imaging techniques need to be developed for the diagnosis or auxiliary diagnosis of arthritis.As an emerging nonintrusive low-cost imaging method,microwave-induced thermoacoustic imaging(TAI)can present tissue morphology while providing the tissue microwave energy absorption density distribution related to dielectric properties.TAI is currently in development to potentially visualize joint anatomic structures and to detect arthritis.Here,we offer a mini review to summarize the status of research on TAI of joints and present an outlook to the future development of TAI in the detection of joint diseases.
文摘An important consideration when using hot-dip galvanized tubular structures is the uncertainty of the joint behaviour due to the possible reduction in the global joint resistance produced by the vent holes required for the galvanizing process. This paper assesses the effect on the joint strength of the angle between the brace members and the chord in a K- or N-joints made with rectangular hollow sections. The study is focused on the case when those brace members include characteristic holes required for the hot-dip galvanizing process. To accomplish the objective of the proposed work, some tests on full-scale K- and N-joints, including angles of 35°, 45°, 55° and 90°, were carried out. The experimental work was complemented by a validated numerical simulation in order to give some design recommendations and to extend the research to other joint configurations.
基金financially supported by the National Natural Science Foundation of China(No.51365014)the Industrial Support Key Project of Jiangxi Province,China(No.20161BBE50072)
基金The Major National Science and Technology Project(No.2012ZX04002032,2013ZX04012032)Graduate Scientific Research Innovation Project of Jiangsu Province(No.KYLX-0096)
文摘In order to investigate the nonlinear characteristics of structural joint,the experimental setup with a jointed mass system is established for dynamic characterization analysis and vibration prediction,and a corresponding nonlinearity identification method is studied.First,the sine-sweep vibration test with different baseexcitation levels areapplied to the structural joint system to study the dominant modal of mass rigid motion.Then,based on t e harmonic balance method principle,t e measured vibration transmissibilities a e utilized for nonlinearity identification using different excitation levels.Experimental results show that nonlinear spring and damping force can be represented by a polynomial order approximation.The identified nonlinear stiffness and damping force can predict the system’s response,and they can reveal t e shifts of resonant frequency or damping due to discontinuity of contact mechanisms within a certain range.
文摘Components of mechanical product are assembled by structural joints,such as bolting,riveting,welding,etc.Structural joints introduce nonlinearity to some engineering structures,and the nonlinearity need to be modeled precisely.To meet serious quality requirements,it is necessary to detect and identify nonlinearity of mechanical products for structural optimization.Modal test to acquire a dynamic response has been applied for decades,which provides reliable results for finite element(FE)model updating.Here response control vibration test for identification of nonlinearity is presented.A nonlinear system can be regarded as linearity for particular steady state response,and classical linear analysis tool is applicable to extract modal data for particular response.First,its applicability is illustrated by some numerical simulations.Subsequently,it is implemented on experimental setup with structural joints by shaking table.The stiffness and damping function dependent of relative displacement are fitted to describe its inherent nonlinearity.The spring and damping forces are identified by harmonic balance method(HBM)to predict output response.Based on the identified results,the procedure is recommended that it allows a reliable measurement of nonlinearity with a certain accuracy.
文摘A modified space beam element is presented in this paper to consider the local joint flexibility of T, Y tubular joints subjected to axial forces and in-plane bending moments for analysis of platforms. Two numerical examples are shown to verify the efficiency and validity of the method presented here.
文摘Stress concentration analysis of multiplanar tubular DT joints plays an important role in the fatigue design of offshore platforms. A semi-analytic method for stress analysis under the condition of any loads is briefly introduced in the paper. Nineteen multiplanar tubular DT joints with one of two braces of the same dimension subjected to axial loads and out- of- plane bending moments are computed for parametric stress analysis by using the present method. The influence of geometrical parameters on the stresses of multiplanar tubular DT joints is discussed and compared with corresponding uniplanar T joints. The regression formulae for the stress at hot spot of multiplanar DT joints are found by modification of SCF of corresponding uniplanar T joints. The parametric formulae for the maximum stress by superposition. Finally, the influences of stiffening effect and load-interaction effect on the maximum stress of DT joints are discussed.
文摘Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine environment, random variable amplitude fatigue tests have been carried out on welded plate joints in sea water. The tests have been conducted under the conditions of loading frequency of 0.2 Hz/, stress ratio of -1, seawater temperature of about 20°C and cathodic protection with the potential about -850 mV, SCE. The test results have been compared with the seawater corrosion fatigue life under constant amplitude loading. Miner's linear cumulative damage summation rule has been used to predict the corrosion fatigue life under variable amplitude loading. The predicted life is in good agreement with the test data.
基金supported by the National Natural Science Foundation of China (90815025, 90715032 and 50808013)
文摘A two-stage damage detection approach is proposed and experimentally demonstrated on a complicated spatial model structure with a limited number of measurements. In the experiment,five known damage patterns,including 3 brace damage cases and 2 joint damage cases,were simulated by removing braces and weakening beam鈥揷olumn connections in the structure. The limited acceleration response data generated by hammer impact were used for system identification,and modal parameters were extracted by using the eigensystem realization algorithm. In the first stage,the possible damaged locations are determined by using the damage index and the characteristics of the analytical model itself,and the extent of damage for those substructures identified at stage I is estimated in the second stage by using a second-order eigen-sensitivity approximation method. The main contribution of this paper is to test the two-stage method by using the real dynamic data of a complicated spatial model structure with limited sensors. The analysis results indicate that the two-stage approach is ableto detect the location of both damage cases,only the severity of brace damage cases can be assessed,and the reasonable analytical model is critical for successful damage detection.
基金supported by National Natural Science Foundation of China (Nos. 11432011, 11620101002)National key research and development program of China (No. 2017YFB1102800)Key Research and Development Program of Shaanxi, China (No. S2017-ZDYF-ZDXM-GY-0035)
文摘The purpose of this paper is to present an extended topology optimization method for the stiffeners layout design of aircraft assembled structures. Multi-fastener joint loads and manufacturing constraints are considered simultaneously. On one hand, the joint loads are calculated and constrained within a limited value to avoid the failure of fasteners. On the other hand, the manufacturing constraints of the material distribution in the machining directions of stiffeners are implemented by an improved piecewise interpolation based on a beveled cut-surface. It is proven that the objective function is strictly continuous and differentiable with respect to the piecewise interpolation. The effects of the extended method with two different constraints are highlighted by typical numerical examples. Compared with the standard topology optimization, the final designs have clearly shown the layout of stiffeners and the joint loads have been perfectly constrained to a satisfying level.
基金Project supported by the Fundamental Research Funds for the Cen- tral Universities （No. HIT.MKSTISP.2016 13） and the National Natural Science Foundation of China （No. 61671176）
文摘Acquisition of accurate channel state information （CSI） at transmitters results in a huge pilot overhead in massive multiple input multiple output （MIMO） systems due to the large number of antennas in the base station （BS）. To reduce the overwhelming pilot overhead in such systems, a structured joint channel estimation scheme employing compressed sensing （CS） theory is proposed. Specifically, the channel sparsity in the angular domain due to the practical scattering environment is analyzed, where common sparsity and individual sparsity structures among geographically neighboring users exist in multi-user massive MIMO systems. Then, by equipping each user with multiple antennas, the pilot overhead can be alleviated in the framework of CS and the channel estimation quality can be improved. Moreover, a structured joint matching pursuit （SJMP） algorithm at the BS is proposed to jointly estimate the channel of users with reduced pilot overhead. Furthermore, the probability upper bound of common support recovery and the upper bound of channel estimation quality using the proposed SJMP algorithm are derived. Simulation results demonstrate that the proposed SJMP algorithm can achieve a higher system performance than those of existing algorithms in terms of pilot overhead and achievable rate.
文摘It＇ s well known welding takes the leading role in development of titanium structures. However, in number of cases technological processes of brazing are more appropriate and, sometimes, being the single possible, in particular, during production of multilayer thin-wall structures. It should be noted that brazing filler metals of Ti-Cu-Ni, Ti-Zr-Cu-Ni, Zr-Ti-Ni and Cu-Zr-Ti systems in a form of plastic foils, as well as in powder form are mainly used in world practice for brazing of titanium alloys. Present work provides the results of complex investigations of brazing filler metals of Ti-Zr-Fe, Ti-Zr-Mn and Ti-Zr-Co systems using differential thermal analysis, light and scanning microscopy, X-ray microspectrum analysis. Data on melting ranges of pilot alloys were obtained, and liquidas su^Caces of given systems using simplex-lattice method were build. Brazing filler metals covering brazing temperature range of current structural titanium materials based on solid solutions as well as intermetallics were proposed. Structure, chemical inhomogeniety and strength characteristics of brazed joints were studied. It is determined that brazing of solid solution based alloys （OT4, VT6 ） using indicated brazing fiUer metals ensures strength characteristics of joints, which are not inferior to that obtained with application of known brazing filler metals even if they are received at lower brazing temperature.
文摘Forming a joint venture (JV) in China can be a successful endeavor as long as each side’s goals, contributions and responsibilities are mutual and understood. Unfortunately, this is not always the case,
基金This study was supported by the National Natural Science Foundation of China (Grant Nos. 51978019 and 52278382)the Natural Science Foundation of Beijing Municipality (No. 8222004).
文摘The integrity and bearing capacity of segment joints in shield tunnels are associated closely with the mechanical properties of the joints.This study focuses on the mechanical characteristics and mechanism of a bolted circumferential joint during the entire bearing process.Simplified analytical algorithms for four stress stages are established to describe the bearing behaviors of the joint under a compressive bending load.A height adjustment coefficient,α,for the outer concrete compression zone is introduced into a simplified analytical model.Factors affectingαare determined,and the degree of influence of these factors is investigated via orthogonal numerical simulations.The numerical results show thatαcan be specified as approximately 0.2 for most metro shield tunnels in China.Subsequently,a case study is performed to verify the rationality of the simplified theoretical analysis for the segment joint via numerical simulations and experiments.Using the proposed simplified analytical algorithms,a parametric investigation is conducted to discuss the factors affecting the ultimate compressive bending capacity of the joint.The method for optimizing the joint flexural stiffness is clarified.The results of this study can provide a theoretical basis for optimizing the design and prediciting the damage of bolted segment joints in shield tunnels.
基金the National Natural Science Foundation of China(No.11472024)for financial support
文摘Composite-metal joints with a metal insert are one kind of connecting structure.In this paper,tensile experimental tests were carried out to investigate tensile properties of a compositemetal joint with a novel metal insert design.Finite element models of the joint were established,and strain distribution and tensile strength were analyzed.The numerical results are in good agreement with the experimental results.Results show that the joint failure is dominated by shear properties of the resin layer.Increasing the resin layer thickness in a certain range will improve the tensile strength of the joint,while increasing the radius of the fillet on the ending side of the metal insert will decrease the joint strength.Increasing the resin layer plasticity will improve the joint strength.The effect of the embedded depth of the metal insert can be ignored.
基金supported by the National Key R&D Program of China(No.2021YFB3701500)the National Natural Science Founda-tion of China(No.52072306)+2 种基金the National Defense Basic Scientific Research Program of China(No.JCKYS2019607001)the Fundamen-tal Research Funds for the Central Universities(Nos.3102019PJ008 and 3102018JCC002)the National Program for Support of Top-notch Young Professionals(No.W02070161).
文摘Naturally optimized successful synovial joints with lightweight,high load-carrying,ultra-low friction and wear have attracted tribological communities to constantly imitate and replicate.Despite impressive advances in cartilage lubrication,extending such extraordinary performance advantages to macroscale solid lubrication remains a challenge.Herein,inspired by the fascinating interplay of synovial joints,a novel kind of trans-scale hierarchical structured ceramic-based composite was developed.Intro-ducing microscale Ag microspheres(AgMs)“cartilage”layer and nanoscale Ag quantum dots/MXene(AgQDs/MXene)“synovial fluid”into the interior and exterior of printed macroscale SiOC“hard bone”realistically restores the gradient structure of synovial joint prototype.The resulted composite with ideal compressive strength(70.44 MPa)can achieve a 60.53%friction reduction and a low wear rate(2.05×10^(−6)mm 3 N^(−1)m^(−1))in dry tribo-contact for 3600 sliding cycles,while also maintaining considerable low friction(∼0.11)over 10,000 sliding cycles and long-term stable lubrication(∼0.13)for up to 50,000 re-ciprocating cycles.Such extraordinary performance can be explained by the division of macro contacts,full loading of AgMs and AgQDs/MXene,abrasive debris capture and removal,as well as the shear rolling effect induced by friction process.This work opens a new avenue to develop structural lubricating mate-rials for complex engineering applications.
文摘When investing in China’s restricted in- dustries, it is essential to have a joint venture (JV) partner. Often the maximum percent- age of equity allowed in foreign ownership can only be 50 percent. So what options are available to the foreign investor to mitigate the risk of not owning, on paper, a
