The reaction of carbon-free oxide-based(corundum,spinel,zirconia,and mullite)submerged entry nozzle(SEN)lining with rare earth inclusions and its anti-clogging effects under near working conditions were systematically...The reaction of carbon-free oxide-based(corundum,spinel,zirconia,and mullite)submerged entry nozzle(SEN)lining with rare earth inclusions and its anti-clogging effects under near working conditions were systematically studied.A variety of lining composite test methods were innovatively used to ensure the consistency of test conditions.The experimental results showed that the mullite(acidic oxide)has strong reactivity with rare earth inclusions,and the spinel(basic oxide)has stable chemical properties and weak reactivity with rare earth inclusions.Because alumina is one of the main reactants of clogging formation,corundum is not suitable for SEN lining.There are less clogs on the surface of zirconia,but it will be exsoluted and unstable.Therefore,solving the problem of zirconia exsolution will greatly strengthen its application in SEN lining.展开更多
The electrochemical corrosion of ductile pipes(DPs)in drinking water distribution systems(DWDS)has a crucial impact on cement-mortar lining(CML)failure and metal release,potentially leading to drinking water quality d...The electrochemical corrosion of ductile pipes(DPs)in drinking water distribution systems(DWDS)has a crucial impact on cement-mortar lining(CML)failure and metal release,potentially leading to drinking water quality deterioration and posing a risk to public health.An in-situ scanning vibrating electrode technique(SVET)with micron-scale resolution,microscopic scale detection and water quality analysis were used to investigate the corrosion behavior and metal release from DPs throughout the whole CML failure process.Metal pollutants release occurred at three different stages of CML failure process,and there are potential risks of water quality deterioration exceeding the maximum allowable levels set by national standards in the partial failure stage and lining peeling stage.Furthermore,the effects of water chemistry(Cl^(−),SO_(4)^(2−),NO_(3)−,and Ca^(2+))on corrosion scale growth and iron release activity,were investigated during the CML partial failure stage.Results showed that the CML failure process in DPs was accelerated by the autocatalysis of localized corrosion.Cl^(−)was found to damage the uncorroded metal surface,while SO_(4)^(2−)mainly dissolved the corrosion scale surface,increasing iron release.Both the oxidation of NO_(3)−and selective sedimentation of Ca2+were found to enhance the stability of corrosion scales and inhibit iron release.展开更多
To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requir...To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requires immediate investigation.In view of this phenomenon,the durability of unit lining concrete is predicted by analyzing three key indicators:carbonation depth,relative dynamic elastic modulus,and residual quality.This prediction is achieved by integrating the Entropy Weight Method,Grey theory life prediction model and BP artificial neural networks using data from tests and predictions of these indicators.Then,the Entropy Weight-Grey theory-BP Network Model is compared with other methods to analyze the predicted life.Finally,verify the sci-entificity of this model,and the optimum silica fume content of unit concrete lining is verified.The results showed,1)The addition of silica fume will accelerate the carbonization of unit concrete lining,and slow down the freeze-thaw cycle and sulfate erosion.2)The utilization of artificial neural networks is essential for enhancing the realism of the data,as it emphasizes the significance of silica fume content.3)Silica fume content of 10%results in the longest life and is the most suitable for lining construction.4)A comparison between single-factor and multi-factor predictions indicates that the multi-factor approach yields a longer maximum life.This improvement can be attributed to the inclusion of additional factors,such as freeze-thaw cycles and carbonation,which enhance the predicted life when employing these methods.In conclusion,the Entropy Weight-Grey Theory-BP Network life prediction Model is well-suited for tunnel lining in the alpine sulfate area of northwest China.展开更多
The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated t...The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated to assess erosion depth,microstructure,phase migrations,and pore structure in various tunnel lining cement-based materials.Additionally,Ca^(2+)leaching was analyzed,and impact of Ca/Si molar ratio in hydration products on erosion resistance was discussed by thermodynamic calculations.The results indicate that carbonated water erosion caused rough and porous surface on specimens,with reduced portlandite and CaCO_(3) content,increased porosity,and an enlargement of pore size.The thermodynamic calculations indicate that the erosion is spontaneous,driven by physical dissolution and chemical reactions dominated by Gibbs free energy.And the erosion reactions proceed more spontaneously and extensively when Ca/Si molar ratio in hydration products was higher.Therefore,cement-based materials with higher portlandite content exhibit weaker erosion resistance.Model-building concrete,with C-S-H gel and portlandite as primary hydration products,has greater erosion susceptibility than shotcrete with ettringite as main hydration product.Moreover,adding silicon-rich mineral admixtures can enhance the erosion resistance.This research offers theory and tech insights to boost cement-based material resistance against carbonated water erosion in karst tunnel engineering.展开更多
In ground vehicles, the brake is an essential system to ensure the safety of movement. Multiple braking mechanisms have been introduced for use in vehicles. This study explores the potential of using magneto-rheologic...In ground vehicles, the brake is an essential system to ensure the safety of movement. Multiple braking mechanisms have been introduced for use in vehicles. This study explores the potential of using magneto-rheological fluid (MRF) brakes in automotive applications. MRF brakes offer controllable braking force due to a magnetic field, but their use is limited by simulation challenges. In this study, a 7-tooth MRF brake model is proposed. The brake model is simulated in Altair Flux software to analyze magnetic field distribution, braking torque, and its variation under different currents and disc speeds. The simulation conditions also consider both viscous and electromagnetic torque components. Then, the results are analyzed across different brake regions, including rotor, stator, and fluid gap. These results provide valuable insights for designing, manufacturing, installing, and testing MRF brakes for automotive use.展开更多
A new electrical toothed band brake is proposed based on the planetary gear shifting transmission.The corresponding mathematical model and the finite element model are established to investigate the braking dynamic ch...A new electrical toothed band brake is proposed based on the planetary gear shifting transmission.The corresponding mathematical model and the finite element model are established to investigate the braking dynamic characteristics and the stress distribution of brake components.According to the structural features and working principle of the brake,the braking process can be divided into a gap elimination stage,a sliding stage,a meshing stage,and a collision stage.The greater the initial speed of brake drum,the higher the impact torque in the collision stage,and the larger the stress of brake components.The ideal range of initial speed is 50-100 r/min,and the ultimate stress is 514 MPa appeared in the right brake band.This study present a wide range of possibilities for further investigation and application of the electrical toothed band brake.展开更多
In this paper,the problem of brake orbits with minimal period estimates are considered for the first-order Hamiltonian systems with anisotropic growth,i.e.,the Hamiltonian functions may have super-quadratic,sub-quadra...In this paper,the problem of brake orbits with minimal period estimates are considered for the first-order Hamiltonian systems with anisotropic growth,i.e.,the Hamiltonian functions may have super-quadratic,sub-quadratic and quadratic behaviors simultaneously in different variable components.展开更多
Brake wear particle(BWP)emissions are considered one of the dominant sources of particulate matter pollution in urban environments.BWP emissions have increased significantly under high-temperature conditions,emerging ...Brake wear particle(BWP)emissions are considered one of the dominant sources of particulate matter pollution in urban environments.BWP emissions have increased significantly under high-temperature conditions,emerging as a focal point of research interest.This study investigates the effect of brake temperatures on BWP emissions.The brake pad materials undergo violent decomposition and oxidation reactions and generate large amounts of incompletely oxidized organic products at temperatures above 475℃.These organic products cause particles below 200 nm to proliferate,and nanoparticles below 40 nm account for the largest contribution of total BWPs.When the friction surface temperature exceeds 475℃,the high-concentration BWPs below 200 nm will agglomerate into larger particles.High temperatures also cause the brake pad surface to delaminate and fragment into particles above 2.5μm.In addition,when the initial brake speed is above 160 km/h,or the brake pressure is above 7 bar,there is a sharp increase in particles below 200 nm.The results suggest that a significant number of nanoparticles below 40 nm are inferred to be generated as the flash temperature of the friction surface reaches the violent reaction temperature.This study provides guidelines for designing low-emission brake pads,as improving the high-temperature resistance of brake pad material components possibly reduces BWP generation.展开更多
The emission of copper-containing particulate matter during braking poses a threat to the natural environment,yet copper plays a crucial role in resin-based brake pads.Developing a copper-free brake pad with high heat...The emission of copper-containing particulate matter during braking poses a threat to the natural environment,yet copper plays a crucial role in resin-based brake pads.Developing a copper-free brake pad with high heat-fade resistance has emerged as a significant current topic.This study employs andalusite-filled resin-based brake pads as a replacement for copper in brake pads.It investigates the effects of andalusite mesh size and content on the physical properties,mechanical properties,and tribological wear performance of the brake pads,and explores the wear mechanism of andalusite-filled copper-free resin-based brake pads.The results indicate that adding andalusite to the brake pads enhances their thermal stability,hardness,impact strength,and density,effectively improving the medium-to-high temperature friction coefficient and heat-fade resistance of the brake pads.As the mesh size of andalusite increases,the hardness of the brake pads also increases,while the impact strength initially increases and then decreases.As the weight content of andalusite increases,the hardness and impact strength of the brake pads gradually increase.When the andalusite mesh size is 320 mesh and the content is 20%,the brake pads exhibit good comprehensive tribological wear performance.The addition of andalusite not only increases the medium-to-high temperature friction coefficient of the brake pads but also strengthens their high-temperature friction surface.This study successfully replaces copper,which is harmful to the environment and costly,with andalusite in brake pads,obtaining a high heat-fade resistance metal-free resin-based brake pad.展开更多
Purpose–For the commonly used concrete mix for railway tunnel linings,concrete model specimens were made,and springback and core drilling tests were conducted at different ages.The springback strength was measured to...Purpose–For the commonly used concrete mix for railway tunnel linings,concrete model specimens were made,and springback and core drilling tests were conducted at different ages.The springback strength was measured to the compressive strength of the core sample with a diameter of 100mm and a height-to-diameter ratio of 1:1.By comparing the measured strength values,the relationship between the measured values under different strength measurement methods was analyzed.Design/methodology/approach–A comparative test of the core drilling method and the rebound method was conducted on the side walls of tunnel linings in some under-construction railways to study the feasibility of the rebound method in engineering quality supervision and inspection.Findings–Tests showed that the rebound strength was positively correlated with the core drill strength.The core drill test strength was significantly higher than the rebound test strength,and the strength still increased after 56 days of age.The rebound method is suitable for the general survey of concrete strength during the construction process and is not suitable for direct supervision and inspection.Originality/value–By studying the correlation of test strength of tunnel lining concrete using two methods,the differences in test results of different methods are proposed to provide a reference for the test and evaluation of tunnel lining strength in railway engineering.展开更多
As a key national project,a newly built plateau railway features a large proportion of tunnels and high construction difficulty.To reduce the voids in the secondary lining of tunnels and address issues such as ineffec...As a key national project,a newly built plateau railway features a large proportion of tunnels and high construction difficulty.To reduce the voids in the secondary lining of tunnels and address issues such as ineffective vibration of the vault,vault voiding,and the inability to monitor the casting status during tunnel lining construction with ordinary lining trolleys,a new smart lining trolley with large clearance that integrates functions such as vibration,automatic casting,and pressure monitoring has been developed.This was achieved by combining the functional design of the new smart lining trolley,comparing traditional construction techniques,and introducing information-based and intelligent design concepts.Through simulation calculations using finite element software modeling,it is verified that the structural stiffness,strength,and other performance parameters of the smart lining trolley meet the technical design requirements.展开更多
To effectively address the challenge where the speed of tunnel lining construction struggles to match that of tunnel face and inverted arch construction,and to enhance the quality of secondary lining,a new type of ske...To effectively address the challenge where the speed of tunnel lining construction struggles to match that of tunnel face and inverted arch construction,and to enhance the quality of secondary lining,a new type of skeleton-free,traversing secondary lining trolley has been developed.This trolley features a set of gantries paired with two sets of formwork.The formwork adopts a multi-segment hinged and strengthened design,ensuring its own strength can meet the requirements of secondary lining concrete pouring without relying on the support of the gantries.When retracted,the formwork can be transported by the gantries through another set of formwork in the supporting state,enabling early formwork support,effectively accelerating the construction progress of the tunnel’s secondary lining,and extending the maintenance time of the secondary lining with the formwork.Finite element software modeling was used for simulation calculations,and the results indicate that the structural strength,stiffness,and other performance parameters of the new secondary lining trolley meet the design requirements,verifying the rationality of the design.展开更多
To improve braking performance and achieve lightweight in transport equipment,it is necessary to implement overall plastic forming manufacturing of the brake pad baseboard(BPB),which is the core safety component of th...To improve braking performance and achieve lightweight in transport equipment,it is necessary to implement overall plastic forming manufacturing of the brake pad baseboard(BPB),which is the core safety component of the brake system.This study presents an innovative multi-DOF envelope forming(MDFEF)process to realize the plastic forming of BPB with thin skin and high reinforcing ribs.The MDFEF principle for BPB,and the design methods for the envelope mold are first presented.Through FE simulations,the behavior of metal flow,uneven growth pattern of reinforcing ribs,evolution of equivalent strain and evolution of forming force in MDFEF of BPB are investigated.To realize MDFEF,an innovative MDFEF equipment driven by parallel linkages is exploited.The force states of linkages in MDFEF are calculated,and the reasonable mold position is determined to reduce the maximum force on the linkages and improve the service performance of MDFEF equipment.The MDFEF experiments of BPB are conducted and qualified BPB is obtained,which demonstrates that the presented MDFEF process and equipment are applicable to manufacture BPB with thin skin and high reinforcing ribs.展开更多
Currently,chemical furnaces play an important role in the chemical industry.It is necessary to ensure their quality and operation performance,so as to guarantee the efficiency of chemical production.Compared with othe...Currently,chemical furnaces play an important role in the chemical industry.It is necessary to ensure their quality and operation performance,so as to guarantee the efficiency of chemical production.Compared with other furnaces,chemical furnaces have strong particularity,which puts forward higher requirements for the thermal shock resistance of the refractories of furnace linings.This paper studied the thermal shock resistance of the refractories for chemical furnace linings,and proposed measures for improvement,providing experience and technical support for the safe production of chemical enterprises.展开更多
When constructing water conveyance shield tunnels under high internal pressure,composite linings are preferred over single-layer segmental linings due to the superior water tightness and load-bearing capacity.A triple...When constructing water conveyance shield tunnels under high internal pressure,composite linings are preferred over single-layer segmental linings due to the superior water tightness and load-bearing capacity.A triple-layer composite lining,consisting of an outer segmental lining,internal steel tube,and self-compacting concrete(SCC)filling,has recently been applied in a large-scale water conveyance tunnel project in China.However,its structural behavior under external overburden and internal water pressures remains poorly understood.This study investigates the mechanical behavior of the triple-layer composite lining through full-scale loading tests using a novel platform that simulates external and internal pressures.Results show that the composite lining remains highly elastic under combined loads with an internal pressure of 0.4 MPa.When the internal pressure increases to 0.6 MPa,cracks first appear in the SCC layer near segment joints,propagating uniformly and leading to stress redistribution.Studs on the steel tube-SCC interface strengthen bonding,reducing debonding at this interface while slightly increasing debonding at the SCC-segment interface.Despite localized SCC damage,the lining maintains excellent serviceability under cyclic pressure fluctuations.This study offers valuable insights for the design and construction of water conveyance shield tunnels with triple-layer composite linings,particularly in high-pressure environments.展开更多
The lining materials for blast furnaces have evolved from brick masonry to monolithic refractory materials.Monolithic castables are widely used in various industrial furnaces.The rapid development of silica sol materi...The lining materials for blast furnaces have evolved from brick masonry to monolithic refractory materials.Monolithic castables are widely used in various industrial furnaces.The rapid development of silica sol materials,combined with the commonly used construction methods of casting and spraying,offers greater flexibility,efficiency,environmental friendliness,and a longer lifespan.Typical monolithic refractory technologies,such as the integral casting technique for the furnace hearth,the pre-applied slag coating technique for the furnace belly and waist,and the inner lining gunning technique,are grounded in scientific theory and practice,thereby advancing the development of refractory materials and enhancing the operational quality of blast furnaces.展开更多
When only a portion of the shield lining structures in a full-line tunnel are overloaded,their bearing and failure characteristics are significantly different from those in the full-line overloaded case.In existing st...When only a portion of the shield lining structures in a full-line tunnel are overloaded,their bearing and failure characteristics are significantly different from those in the full-line overloaded case.In existing studies,one or several segmental lining rings have been studied,with overload applied to selected lining rings to analyze the performance evolution of the lining structures;however,this approach fails to reveal the bearing and failure characteristics of shield lining rings under localized overload.To address this research gap,we employ 3D finite element modeling to investigate the mechanical performance and failure mechanisms of shield segmental linings under localized overload conditions,and compare the results with full-line overload scenarios.Additionally,the impact of reinforcing shield segmental linings with steel rings is studied to address issues arising from localized overloads.The results indicate that localized overloads lead to significant ring joint dislocation and higher stress on longitudinal bolts,potentially causing longitudinal bolt failure.Furthermore,the overall deformation of lining rings,segmental joint opening,and stress in circumferential bolts and steel bars is lower compared to full-line overloads.For the same overload level,the convergence deformation of the lining under full-line overload is 1.5 to 2.0 times higher than that under localized overload.For localized overload situations,a reinforcement scheme with steel rings spanning across two adjacent lining rings is more effective than installing steel rings within individual lining rings.This spanning ring reinforcement strategy not only enhances the structural rigidity of each ring,but also limits joint dislocation and reduces stress on longitudinal bolts,with the reduction in maximum ring joint dislocation ranging from 70%to 82%and the reduction in maximum longitudinal bolt stress ranging from 19%to 57%compared to reinforcement within rings.展开更多
The current research of master cylinder pressure estimation mainly relies on hydraulic characteristic or vehicle dynamics.But they are not independently applicable to any environment and have their own scope of applic...The current research of master cylinder pressure estimation mainly relies on hydraulic characteristic or vehicle dynamics.But they are not independently applicable to any environment and have their own scope of application.In addition,about the master cylinder pressure control,there are few studies that can simultaneously balance pressure building accuracy,speed,and prevent pressure overshoot and jitter.In this paper,an adaptative fusion method based on electro-hydraulic characteristic and vehicle mode is proposed to estimate the master cylinder pressure.The fusion strategy is mainly based on the prediction performance of two algorithms under different vehicle speeds,pressures,and ABS states.Apart from this,this article also includes real-time prediction of the friction model based on RLS to improve the accuracy of the electro-hydraulic mode.In order to simultaneously balance pressure control accuracy,response speed,and prevent overshoot and jitter,this article proposes an adaptative LQR controller for MC pressure control which uses fuzzy-logic controller to adjust the weights of LQR controller based on target pressure and difference compared with actual pressure.Through mode-in-loop and hardware-in-loop tests in ramp,step and sinusoidal response,the whole estimation and control system is verified based on real hydraulic system and the performance is satisfactory under these scenes.This research proposes an adaptative pressure estimation and control architecture for integrated electro-hydraulic brake system which could eliminate pressure sensors in typical scenarios and ensure the comprehensive performance of pressure control.展开更多
This study aims to assess the comprehensive strengthening effect of a steel-ultra high performance concrete(UHPC)composite strengthening method.The axial force-moment interaction curve(N-M curve)was calculated in a no...This study aims to assess the comprehensive strengthening effect of a steel-ultra high performance concrete(UHPC)composite strengthening method.The axial force-moment interaction curve(N-M curve)was calculated in a novel way,using cross-sectional strains at ultimate states as well as real-time stress measurements for each material.The enclosed area of the N-M curve was defined as a comprehensive performance index for the system.We validate our approach with comparisons to numerical modeling and full-scale four-point bending experiments.Additionally,strengthening effects were compared for different sagging and hogging moments based on material stress responses,and the impact of various strengthening parameters was analyzed.We find that the N-M curve of the strengthened cross-section envelops that of the un-strengthened cross-section.Notably,improvements in flexural capacity are greater under sagging moments during the large eccentric failure stage,and greater under hogging moments during the small eccentric failure stage.This discrepancy is attributed to the strength utilization of strengthening materials.These findings provide a reference for understanding the strengthening effects and parameters of steel-UHPC composite.展开更多
Detecting internal defects,particularly voids behind linings,is critical for ensuring the structural integrity of aging high-speed rail(HSR)tunnel networks.While ground-penetrating radar(GPR)is widely employed,systema...Detecting internal defects,particularly voids behind linings,is critical for ensuring the structural integrity of aging high-speed rail(HSR)tunnel networks.While ground-penetrating radar(GPR)is widely employed,systematic quantification of performance boundaries for air-coupled(A-CGPR)and ground-coupled(G-CGPR)systems within the complex electromagnetic environment of multilayer reinforced HSR tunnels remains limited.This study establishes physics-based quantitative performance limits for A-CGPR and G-CGPR through rigorously validated GPRMax finite-difference time-domain(FDTD)simulations and comprehensive field validation over a 300 m operational HSR tunnel section.Key performance metrics were quantified as functions of:(a)detection distance(A-CGPR:2.0–4.5 m;G-CGPR:≤0.1 m),(b)antenna frequency(A-CGPR:300 MHz;G-CGPR:400/900 MHz),(c)reinforcement configuration(unreinforced,single-layer,multilayer rebar),and(d)void geometry(axial length:0.1–1.0 m;radial depth:0.1–0.5 m).Key findings demonstrate:a.A-CGPR(300 MHz):Reliably detects axial voids≥0.3 m at distances≤3 m in minimally reinforced(single-layer rebar)linings(field R2=0.89).Performance degrades significantly at distances>3 m(>60%signal attenuation at 4.5 m)or under multilayer rebar interference,causing 25%–40%accuracy loss for voids<0.3 m.Optimal distance:2.0–2.5 m.b.G-CGPR(900 MHz):Achieves<5%size measurement error for axial voids≥0.1 m and radial voids≥0.2 m in unreinforced linings.Resolution degrades under multilayer reinforcement due to severe signal attenuation,increasing axial void detection error to 10%–20%for voids≥0.3 m and constraining radial size measurement.c.Synergistic Framework:A hybrid inspection protocol is proposed,integrating A-CGPR(20 km/h)for rapid large-area screening and targeted G-CGPR(3 km/h)for high-resolution verification of identified anomalies.This framework enhances NDT efficiency while reducing estimated lifecycle inspection costs by 34%compared to G-CGPR alone.This research provides the first physics-derived quantitative detection thresholds for A-CGPR and G-CGPR in multi-rebar HSR tunnels,validated through field-correlated simulations.Future work will focus on multi-frequency antenna arrays and deep learning algorithms to mitigate reinforcement interference.The established performance boundaries and hybrid framework offer critical guidance for optimizing tunnel lining inspection strategies in extensive HSR networks.展开更多
基金supported by the National Outstanding Youth Science Fund Project of National Natural Science Foundation of China(52302031)National Natural Science Foundation of China(51932008 and 51772277)Central China Thousand Talents Project(204200510011).
文摘The reaction of carbon-free oxide-based(corundum,spinel,zirconia,and mullite)submerged entry nozzle(SEN)lining with rare earth inclusions and its anti-clogging effects under near working conditions were systematically studied.A variety of lining composite test methods were innovatively used to ensure the consistency of test conditions.The experimental results showed that the mullite(acidic oxide)has strong reactivity with rare earth inclusions,and the spinel(basic oxide)has stable chemical properties and weak reactivity with rare earth inclusions.Because alumina is one of the main reactants of clogging formation,corundum is not suitable for SEN lining.There are less clogs on the surface of zirconia,but it will be exsoluted and unstable.Therefore,solving the problem of zirconia exsolution will greatly strengthen its application in SEN lining.
基金supported by the National Natural Science Foundation of China(Nos.51808158,52170101,and 52200116)Tianjin Natural Science Foundation(No.23JCYBJC00640).
文摘The electrochemical corrosion of ductile pipes(DPs)in drinking water distribution systems(DWDS)has a crucial impact on cement-mortar lining(CML)failure and metal release,potentially leading to drinking water quality deterioration and posing a risk to public health.An in-situ scanning vibrating electrode technique(SVET)with micron-scale resolution,microscopic scale detection and water quality analysis were used to investigate the corrosion behavior and metal release from DPs throughout the whole CML failure process.Metal pollutants release occurred at three different stages of CML failure process,and there are potential risks of water quality deterioration exceeding the maximum allowable levels set by national standards in the partial failure stage and lining peeling stage.Furthermore,the effects of water chemistry(Cl^(−),SO_(4)^(2−),NO_(3)−,and Ca^(2+))on corrosion scale growth and iron release activity,were investigated during the CML partial failure stage.Results showed that the CML failure process in DPs was accelerated by the autocatalysis of localized corrosion.Cl^(−)was found to damage the uncorroded metal surface,while SO_(4)^(2−)mainly dissolved the corrosion scale surface,increasing iron release.Both the oxidation of NO_(3)−and selective sedimentation of Ca2+were found to enhance the stability of corrosion scales and inhibit iron release.
基金funded by the Technology Funding Scheme of China Construction Second Engineering Bureau LTD(2020ZX150002)the National Natural Science Foundation Project of China(12262018).
文摘To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requires immediate investigation.In view of this phenomenon,the durability of unit lining concrete is predicted by analyzing three key indicators:carbonation depth,relative dynamic elastic modulus,and residual quality.This prediction is achieved by integrating the Entropy Weight Method,Grey theory life prediction model and BP artificial neural networks using data from tests and predictions of these indicators.Then,the Entropy Weight-Grey theory-BP Network Model is compared with other methods to analyze the predicted life.Finally,verify the sci-entificity of this model,and the optimum silica fume content of unit concrete lining is verified.The results showed,1)The addition of silica fume will accelerate the carbonization of unit concrete lining,and slow down the freeze-thaw cycle and sulfate erosion.2)The utilization of artificial neural networks is essential for enhancing the realism of the data,as it emphasizes the significance of silica fume content.3)Silica fume content of 10%results in the longest life and is the most suitable for lining construction.4)A comparison between single-factor and multi-factor predictions indicates that the multi-factor approach yields a longer maximum life.This improvement can be attributed to the inclusion of additional factors,such as freeze-thaw cycles and carbonation,which enhance the predicted life when employing these methods.In conclusion,the Entropy Weight-Grey Theory-BP Network life prediction Model is well-suited for tunnel lining in the alpine sulfate area of northwest China.
基金Project(2021YJ059)supported by the Research Project of China Academy of Railway Sciences。
文摘The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated to assess erosion depth,microstructure,phase migrations,and pore structure in various tunnel lining cement-based materials.Additionally,Ca^(2+)leaching was analyzed,and impact of Ca/Si molar ratio in hydration products on erosion resistance was discussed by thermodynamic calculations.The results indicate that carbonated water erosion caused rough and porous surface on specimens,with reduced portlandite and CaCO_(3) content,increased porosity,and an enlargement of pore size.The thermodynamic calculations indicate that the erosion is spontaneous,driven by physical dissolution and chemical reactions dominated by Gibbs free energy.And the erosion reactions proceed more spontaneously and extensively when Ca/Si molar ratio in hydration products was higher.Therefore,cement-based materials with higher portlandite content exhibit weaker erosion resistance.Model-building concrete,with C-S-H gel and portlandite as primary hydration products,has greater erosion susceptibility than shotcrete with ettringite as main hydration product.Moreover,adding silicon-rich mineral admixtures can enhance the erosion resistance.This research offers theory and tech insights to boost cement-based material resistance against carbonated water erosion in karst tunnel engineering.
文摘In ground vehicles, the brake is an essential system to ensure the safety of movement. Multiple braking mechanisms have been introduced for use in vehicles. This study explores the potential of using magneto-rheological fluid (MRF) brakes in automotive applications. MRF brakes offer controllable braking force due to a magnetic field, but their use is limited by simulation challenges. In this study, a 7-tooth MRF brake model is proposed. The brake model is simulated in Altair Flux software to analyze magnetic field distribution, braking torque, and its variation under different currents and disc speeds. The simulation conditions also consider both viscous and electromagnetic torque components. Then, the results are analyzed across different brake regions, including rotor, stator, and fluid gap. These results provide valuable insights for designing, manufacturing, installing, and testing MRF brakes for automotive use.
基金funded by the National Natural Science Foundation of China(Nos.52205047,52175037)China Postdoctoral Science Foundation(No.2021M700422)Beijing Key Laboratory Foundation(No.KF20212223201).
文摘A new electrical toothed band brake is proposed based on the planetary gear shifting transmission.The corresponding mathematical model and the finite element model are established to investigate the braking dynamic characteristics and the stress distribution of brake components.According to the structural features and working principle of the brake,the braking process can be divided into a gap elimination stage,a sliding stage,a meshing stage,and a collision stage.The greater the initial speed of brake drum,the higher the impact torque in the collision stage,and the larger the stress of brake components.The ideal range of initial speed is 50-100 r/min,and the ultimate stress is 514 MPa appeared in the right brake band.This study present a wide range of possibilities for further investigation and application of the electrical toothed band brake.
基金supported by the NSFC(12301138)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2021L377)+1 种基金the Doctoral Scientific Research Foundation of Shanxi Datong University(2018-B-15)The second author’s work was supported by the NSFC(12171108).
文摘In this paper,the problem of brake orbits with minimal period estimates are considered for the first-order Hamiltonian systems with anisotropic growth,i.e.,the Hamiltonian functions may have super-quadratic,sub-quadratic and quadratic behaviors simultaneously in different variable components.
基金supported by the National Natural Science Foundation of China(Nos.52172337 and 52272342)the Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(No.GZB20240352)the Shuimu Tsinghua Scholar Program of Tsinghua University(No.2023SM230)。
文摘Brake wear particle(BWP)emissions are considered one of the dominant sources of particulate matter pollution in urban environments.BWP emissions have increased significantly under high-temperature conditions,emerging as a focal point of research interest.This study investigates the effect of brake temperatures on BWP emissions.The brake pad materials undergo violent decomposition and oxidation reactions and generate large amounts of incompletely oxidized organic products at temperatures above 475℃.These organic products cause particles below 200 nm to proliferate,and nanoparticles below 40 nm account for the largest contribution of total BWPs.When the friction surface temperature exceeds 475℃,the high-concentration BWPs below 200 nm will agglomerate into larger particles.High temperatures also cause the brake pad surface to delaminate and fragment into particles above 2.5μm.In addition,when the initial brake speed is above 160 km/h,or the brake pressure is above 7 bar,there is a sharp increase in particles below 200 nm.The results suggest that a significant number of nanoparticles below 40 nm are inferred to be generated as the flash temperature of the friction surface reaches the violent reaction temperature.This study provides guidelines for designing low-emission brake pads,as improving the high-temperature resistance of brake pad material components possibly reduces BWP generation.
基金Supported by National Natural Science Foundation of China(Grant No.52275178)the Fuzhou Municipal Science and Technology Plan Project(Grant No.2024-Y-004)the Liaoning Provincial Key Laboratory of Aero-engine Materials Tribology(Grant No.LKLAMTF202502).
文摘The emission of copper-containing particulate matter during braking poses a threat to the natural environment,yet copper plays a crucial role in resin-based brake pads.Developing a copper-free brake pad with high heat-fade resistance has emerged as a significant current topic.This study employs andalusite-filled resin-based brake pads as a replacement for copper in brake pads.It investigates the effects of andalusite mesh size and content on the physical properties,mechanical properties,and tribological wear performance of the brake pads,and explores the wear mechanism of andalusite-filled copper-free resin-based brake pads.The results indicate that adding andalusite to the brake pads enhances their thermal stability,hardness,impact strength,and density,effectively improving the medium-to-high temperature friction coefficient and heat-fade resistance of the brake pads.As the mesh size of andalusite increases,the hardness of the brake pads also increases,while the impact strength initially increases and then decreases.As the weight content of andalusite increases,the hardness and impact strength of the brake pads gradually increase.When the andalusite mesh size is 320 mesh and the content is 20%,the brake pads exhibit good comprehensive tribological wear performance.The addition of andalusite not only increases the medium-to-high temperature friction coefficient of the brake pads but also strengthens their high-temperature friction surface.This study successfully replaces copper,which is harmful to the environment and costly,with andalusite in brake pads,obtaining a high heat-fade resistance metal-free resin-based brake pad.
文摘Purpose–For the commonly used concrete mix for railway tunnel linings,concrete model specimens were made,and springback and core drilling tests were conducted at different ages.The springback strength was measured to the compressive strength of the core sample with a diameter of 100mm and a height-to-diameter ratio of 1:1.By comparing the measured strength values,the relationship between the measured values under different strength measurement methods was analyzed.Design/methodology/approach–A comparative test of the core drilling method and the rebound method was conducted on the side walls of tunnel linings in some under-construction railways to study the feasibility of the rebound method in engineering quality supervision and inspection.Findings–Tests showed that the rebound strength was positively correlated with the core drill strength.The core drill test strength was significantly higher than the rebound test strength,and the strength still increased after 56 days of age.The rebound method is suitable for the general survey of concrete strength during the construction process and is not suitable for direct supervision and inspection.Originality/value–By studying the correlation of test strength of tunnel lining concrete using two methods,the differences in test results of different methods are proposed to provide a reference for the test and evaluation of tunnel lining strength in railway engineering.
文摘As a key national project,a newly built plateau railway features a large proportion of tunnels and high construction difficulty.To reduce the voids in the secondary lining of tunnels and address issues such as ineffective vibration of the vault,vault voiding,and the inability to monitor the casting status during tunnel lining construction with ordinary lining trolleys,a new smart lining trolley with large clearance that integrates functions such as vibration,automatic casting,and pressure monitoring has been developed.This was achieved by combining the functional design of the new smart lining trolley,comparing traditional construction techniques,and introducing information-based and intelligent design concepts.Through simulation calculations using finite element software modeling,it is verified that the structural stiffness,strength,and other performance parameters of the smart lining trolley meet the technical design requirements.
文摘To effectively address the challenge where the speed of tunnel lining construction struggles to match that of tunnel face and inverted arch construction,and to enhance the quality of secondary lining,a new type of skeleton-free,traversing secondary lining trolley has been developed.This trolley features a set of gantries paired with two sets of formwork.The formwork adopts a multi-segment hinged and strengthened design,ensuring its own strength can meet the requirements of secondary lining concrete pouring without relying on the support of the gantries.When retracted,the formwork can be transported by the gantries through another set of formwork in the supporting state,enabling early formwork support,effectively accelerating the construction progress of the tunnel’s secondary lining,and extending the maintenance time of the secondary lining with the formwork.Finite element software modeling was used for simulation calculations,and the results indicate that the structural strength,stiffness,and other performance parameters of the new secondary lining trolley meet the design requirements,verifying the rationality of the design.
基金Supported by National Natural Science Foundation of China(Grant No.U21A20131)Innovative Research Team Development Program of Ministry of Education of China(Grant No.IRT17R83)111 Project(Grant No.B17034)。
文摘To improve braking performance and achieve lightweight in transport equipment,it is necessary to implement overall plastic forming manufacturing of the brake pad baseboard(BPB),which is the core safety component of the brake system.This study presents an innovative multi-DOF envelope forming(MDFEF)process to realize the plastic forming of BPB with thin skin and high reinforcing ribs.The MDFEF principle for BPB,and the design methods for the envelope mold are first presented.Through FE simulations,the behavior of metal flow,uneven growth pattern of reinforcing ribs,evolution of equivalent strain and evolution of forming force in MDFEF of BPB are investigated.To realize MDFEF,an innovative MDFEF equipment driven by parallel linkages is exploited.The force states of linkages in MDFEF are calculated,and the reasonable mold position is determined to reduce the maximum force on the linkages and improve the service performance of MDFEF equipment.The MDFEF experiments of BPB are conducted and qualified BPB is obtained,which demonstrates that the presented MDFEF process and equipment are applicable to manufacture BPB with thin skin and high reinforcing ribs.
文摘Currently,chemical furnaces play an important role in the chemical industry.It is necessary to ensure their quality and operation performance,so as to guarantee the efficiency of chemical production.Compared with other furnaces,chemical furnaces have strong particularity,which puts forward higher requirements for the thermal shock resistance of the refractories of furnace linings.This paper studied the thermal shock resistance of the refractories for chemical furnace linings,and proposed measures for improvement,providing experience and technical support for the safe production of chemical enterprises.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.42225702 and 42077235)Special Research Foundation on Water Resources Allocation Project in the Pearl River Delta(Grant No.CD88-QT01-2022-0085).
文摘When constructing water conveyance shield tunnels under high internal pressure,composite linings are preferred over single-layer segmental linings due to the superior water tightness and load-bearing capacity.A triple-layer composite lining,consisting of an outer segmental lining,internal steel tube,and self-compacting concrete(SCC)filling,has recently been applied in a large-scale water conveyance tunnel project in China.However,its structural behavior under external overburden and internal water pressures remains poorly understood.This study investigates the mechanical behavior of the triple-layer composite lining through full-scale loading tests using a novel platform that simulates external and internal pressures.Results show that the composite lining remains highly elastic under combined loads with an internal pressure of 0.4 MPa.When the internal pressure increases to 0.6 MPa,cracks first appear in the SCC layer near segment joints,propagating uniformly and leading to stress redistribution.Studs on the steel tube-SCC interface strengthen bonding,reducing debonding at this interface while slightly increasing debonding at the SCC-segment interface.Despite localized SCC damage,the lining maintains excellent serviceability under cyclic pressure fluctuations.This study offers valuable insights for the design and construction of water conveyance shield tunnels with triple-layer composite linings,particularly in high-pressure environments.
文摘The lining materials for blast furnaces have evolved from brick masonry to monolithic refractory materials.Monolithic castables are widely used in various industrial furnaces.The rapid development of silica sol materials,combined with the commonly used construction methods of casting and spraying,offers greater flexibility,efficiency,environmental friendliness,and a longer lifespan.Typical monolithic refractory technologies,such as the integral casting technique for the furnace hearth,the pre-applied slag coating technique for the furnace belly and waist,and the inner lining gunning technique,are grounded in scientific theory and practice,thereby advancing the development of refractory materials and enhancing the operational quality of blast furnaces.
基金supported by the National Natural Science Foundation of China(No.52008308).
文摘When only a portion of the shield lining structures in a full-line tunnel are overloaded,their bearing and failure characteristics are significantly different from those in the full-line overloaded case.In existing studies,one or several segmental lining rings have been studied,with overload applied to selected lining rings to analyze the performance evolution of the lining structures;however,this approach fails to reveal the bearing and failure characteristics of shield lining rings under localized overload.To address this research gap,we employ 3D finite element modeling to investigate the mechanical performance and failure mechanisms of shield segmental linings under localized overload conditions,and compare the results with full-line overload scenarios.Additionally,the impact of reinforcing shield segmental linings with steel rings is studied to address issues arising from localized overloads.The results indicate that localized overloads lead to significant ring joint dislocation and higher stress on longitudinal bolts,potentially causing longitudinal bolt failure.Furthermore,the overall deformation of lining rings,segmental joint opening,and stress in circumferential bolts and steel bars is lower compared to full-line overloads.For the same overload level,the convergence deformation of the lining under full-line overload is 1.5 to 2.0 times higher than that under localized overload.For localized overload situations,a reinforcement scheme with steel rings spanning across two adjacent lining rings is more effective than installing steel rings within individual lining rings.This spanning ring reinforcement strategy not only enhances the structural rigidity of each ring,but also limits joint dislocation and reduces stress on longitudinal bolts,with the reduction in maximum ring joint dislocation ranging from 70%to 82%and the reduction in maximum longitudinal bolt stress ranging from 19%to 57%compared to reinforcement within rings.
基金Supported by National Natural Science Foundation of China(Grant Nos.52202494,52202495)Chongqing Special Project for Technological Innovation and Application Development(Grant No.CSTB2022TIAD-DEX0014).
文摘The current research of master cylinder pressure estimation mainly relies on hydraulic characteristic or vehicle dynamics.But they are not independently applicable to any environment and have their own scope of application.In addition,about the master cylinder pressure control,there are few studies that can simultaneously balance pressure building accuracy,speed,and prevent pressure overshoot and jitter.In this paper,an adaptative fusion method based on electro-hydraulic characteristic and vehicle mode is proposed to estimate the master cylinder pressure.The fusion strategy is mainly based on the prediction performance of two algorithms under different vehicle speeds,pressures,and ABS states.Apart from this,this article also includes real-time prediction of the friction model based on RLS to improve the accuracy of the electro-hydraulic mode.In order to simultaneously balance pressure control accuracy,response speed,and prevent overshoot and jitter,this article proposes an adaptative LQR controller for MC pressure control which uses fuzzy-logic controller to adjust the weights of LQR controller based on target pressure and difference compared with actual pressure.Through mode-in-loop and hardware-in-loop tests in ramp,step and sinusoidal response,the whole estimation and control system is verified based on real hydraulic system and the performance is satisfactory under these scenes.This research proposes an adaptative pressure estimation and control architecture for integrated electro-hydraulic brake system which could eliminate pressure sensors in typical scenarios and ensure the comprehensive performance of pressure control.
基金supported by the National Natural Science Foundation of China(Nos.51938005,52090082,and 52378395)the National Key Research and Development Program of China(No.2023YFB2604402).
文摘This study aims to assess the comprehensive strengthening effect of a steel-ultra high performance concrete(UHPC)composite strengthening method.The axial force-moment interaction curve(N-M curve)was calculated in a novel way,using cross-sectional strains at ultimate states as well as real-time stress measurements for each material.The enclosed area of the N-M curve was defined as a comprehensive performance index for the system.We validate our approach with comparisons to numerical modeling and full-scale four-point bending experiments.Additionally,strengthening effects were compared for different sagging and hogging moments based on material stress responses,and the impact of various strengthening parameters was analyzed.We find that the N-M curve of the strengthened cross-section envelops that of the un-strengthened cross-section.Notably,improvements in flexural capacity are greater under sagging moments during the large eccentric failure stage,and greater under hogging moments during the small eccentric failure stage.This discrepancy is attributed to the strength utilization of strengthening materials.These findings provide a reference for understanding the strengthening effects and parameters of steel-UHPC composite.
基金funded by the Key Project of Science&Technology Research ofChina Academy of Railway Sciences,grant number 2023YJ022.
文摘Detecting internal defects,particularly voids behind linings,is critical for ensuring the structural integrity of aging high-speed rail(HSR)tunnel networks.While ground-penetrating radar(GPR)is widely employed,systematic quantification of performance boundaries for air-coupled(A-CGPR)and ground-coupled(G-CGPR)systems within the complex electromagnetic environment of multilayer reinforced HSR tunnels remains limited.This study establishes physics-based quantitative performance limits for A-CGPR and G-CGPR through rigorously validated GPRMax finite-difference time-domain(FDTD)simulations and comprehensive field validation over a 300 m operational HSR tunnel section.Key performance metrics were quantified as functions of:(a)detection distance(A-CGPR:2.0–4.5 m;G-CGPR:≤0.1 m),(b)antenna frequency(A-CGPR:300 MHz;G-CGPR:400/900 MHz),(c)reinforcement configuration(unreinforced,single-layer,multilayer rebar),and(d)void geometry(axial length:0.1–1.0 m;radial depth:0.1–0.5 m).Key findings demonstrate:a.A-CGPR(300 MHz):Reliably detects axial voids≥0.3 m at distances≤3 m in minimally reinforced(single-layer rebar)linings(field R2=0.89).Performance degrades significantly at distances>3 m(>60%signal attenuation at 4.5 m)or under multilayer rebar interference,causing 25%–40%accuracy loss for voids<0.3 m.Optimal distance:2.0–2.5 m.b.G-CGPR(900 MHz):Achieves<5%size measurement error for axial voids≥0.1 m and radial voids≥0.2 m in unreinforced linings.Resolution degrades under multilayer reinforcement due to severe signal attenuation,increasing axial void detection error to 10%–20%for voids≥0.3 m and constraining radial size measurement.c.Synergistic Framework:A hybrid inspection protocol is proposed,integrating A-CGPR(20 km/h)for rapid large-area screening and targeted G-CGPR(3 km/h)for high-resolution verification of identified anomalies.This framework enhances NDT efficiency while reducing estimated lifecycle inspection costs by 34%compared to G-CGPR alone.This research provides the first physics-derived quantitative detection thresholds for A-CGPR and G-CGPR in multi-rebar HSR tunnels,validated through field-correlated simulations.Future work will focus on multi-frequency antenna arrays and deep learning algorithms to mitigate reinforcement interference.The established performance boundaries and hybrid framework offer critical guidance for optimizing tunnel lining inspection strategies in extensive HSR networks.
