In order to improve rib stability,failure criteria and instability mode of a thick coal seam with inter-band rock layer are analysed in this study.A three-dimensional mechanical model is established for the rib by con...In order to improve rib stability,failure criteria and instability mode of a thick coal seam with inter-band rock layer are analysed in this study.A three-dimensional mechanical model is established for the rib by considering the rock layer.A safety factor is defined foy the rib,and it is observed that the safety factor exhibits a positive correlation with the thickness and strength of the inter-band rock.A calculation method for determining critical parameters of the rock layer is presented to ensure the rib stability.It is revealed that incomplete propagation of the fracture at the hard rock constitutes a fundamental prerequisite for ensuring the rib stability.The influence of the position of the inter-band rock in the coal seam on failure mechanism of the rib was thoroughly investigated by developing a series of physical models for the rib at the face area.The best position for the inter-band rock in the coal seam is at a height of 1.5 m away from the roof line,which tends to provide a good stability state for the rib.For different inter-band rock positions,two ways of controlling rib by increasing supports stiffness and flexible grouting reinforcement are proposed.展开更多
The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with differen...The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.展开更多
Spalling is a typical brittle failure phenomenon of hard rock in deep caverns under high geostress.In this study,key issues are systematically studied concerning the spalling failure of deep hard rock caverns.First,th...Spalling is a typical brittle failure phenomenon of hard rock in deep caverns under high geostress.In this study,key issues are systematically studied concerning the spalling failure of deep hard rock caverns.First,the prismatic rock specimens with small thicknesses(i.e.width×thickness×height:20 mm×50 mm×100 mm)are employed in our tests which not only successfully simulate the spalling failure of hard rock in the laboratory but also obtain a reasonable spalling strength similar to that of the rock mass.Then,a series of spalling experiments is carried out to investigate the mechanism of spalling failure of deep hard rock caverns.Our results show that the intermediate principal stress,weak dynamic disturbances,and rock microstructure have significant effects on the spalling failure.The spalling strength is approximately(0.3–0.8)UCS,where UCS is the uniaxial compressive strength of the cylindrical rock sample with a diameter of around 50 mm.The spalling strength increases first and then decreases with increasing intermediate principal stress.Moreover,an empirical spalling strength criterion and a numerical method of spalling failure are proposed.This numerical method can not only simulate the spalling failure zone formed by tangential compressive stress concentration after excavation under different intermediate principal stresses,but also successfully simulate the failure transition from tensile mode to shear mode associated with confinement change in deep hard rock caverns.Furthermore,an acoustic emission-based early warning method using neural network is proposed to predict the spalling failure.Finally,a technical roadmap for preventing and controlling spalling failure of deep hard rock caverns is presented after summarizing the successful experiences in a typical engineering case.展开更多
The Voronoi grain-based breakable block model(VGBBM)based on the combined finite-discrete element method(FDEM)was proposed to explicitly characterize the failure mechanism and predict the deformation behavior of hard-...The Voronoi grain-based breakable block model(VGBBM)based on the combined finite-discrete element method(FDEM)was proposed to explicitly characterize the failure mechanism and predict the deformation behavior of hard-rock mine pillars.The influence of the microscopic parameters on the macroscopic mechanical behavior was investigated using laboratory-scale models.The field-scale pillar models(width-to-height,W/H=1,2 and 3)were calibrated based on the empirically predicted stress-strain curves of Creighton mine pillars.The results indicated that as the W/H ratios increased,the VGBBM effectively predicted the transition from strain-softening to pseudo-ductile behavior in pillars,and explicitly captured the separated rock slabs and the V-shaped damage zones on both sides of pillars and conjugate shear bands in core zones of pillars.The volumetric strain field revealed significant compressional deformation in core zones of pillars.While the peak strains of W/H=1 and 2 pillars were relatively consistent,there were significant differences in the strain energy storage and release mechanism.W/H was the primary factor influencing the deformation and strain energy in the pillar core.The friction coefficient of the structural plane was also an important factor affecting the pillar strength and the weakest discontinuity angle.The fracture surface was controlled by the discontinuity angle and the friction coefficient.This study demonstrated the capability of the VGBBM in predicting the strengths and deformation behavior of hard-rock pillars in deep mine design.展开更多
Concrete subjected to fire loads is susceptible to explosive spalling, which can lead to the exposure of reinforcingsteel bars to the fire, substantially jeopardizing the structural safety and stability. The spalling ...Concrete subjected to fire loads is susceptible to explosive spalling, which can lead to the exposure of reinforcingsteel bars to the fire, substantially jeopardizing the structural safety and stability. The spalling of fire-loaded concreteis closely related to the evolution of pore pressure and temperature. Conventional analytical methods involve theresolution of complex, strongly coupled multifield equations, necessitating significant computational efforts. Torapidly and accurately obtain the distributions of pore-pressure and temperature, the Pix2Pix model is adoptedin this work, which is celebrated for its capabilities in image generation. The open-source dataset used hereinfeatures RGB images we generated using a sophisticated coupled model, while the grayscale images encapsulate the15 principal variables influencing spalling. After conducting a series of tests with different layers configurations,activation functions and loss functions, the Pix2Pix model suitable for assessing the spalling risk of fire-loadedconcrete has been meticulously designed and trained. The applicability and reliability of the Pix2Pix model inconcrete parameter prediction are verified by comparing its outcomes with those derived fromthe strong couplingTHC model. Notably, for the practical engineering applications, our findings indicate that utilizing monochromeimages as the initial target for analysis yields more dependable results. This work not only offers valuable insightsfor civil engineers specializing in concrete structures but also establishes a robust methodological approach forresearchers seeking to create similar predictive models.展开更多
The current researches of the wear and spalling behaviors of wheel/rail materials focus on the field investigation rather than the mechanism. However, it is necessary and significant for clarifying the mechanism and r...The current researches of the wear and spalling behaviors of wheel/rail materials focus on the field investigation rather than the mechanism. However, it is necessary and significant for clarifying the mechanism and relationship between the wear and spalling damage of railway wheel to test and reproduce the wheel damages in laboratory. The objective of this paper is to investigate the wear and spalling damage behaviors of railway wheel using a JD-1 wheel/rail simulation facility, which consists of a small wheel serving as rolling stock wheel, and a larger wheel serving as rail. The damage process of wheel roller is explored in terms of the creep ratio, axle load, and carbon content by means of various microscopic examinations. The experimental results show that the wear volume growth of wheel roller is proved to be proportional to the increase of the creep ratio and normal load between simulating wheel and rail. The increase of carbon content of wheel material causes a linear reduction in the wear volume. The microscopic examinations indicate that the rolling wear mechanism transfers from abrasive wear to adhesive and fatigue wear with an increase of tangential friction force, which results in the initiation of fatigue crack, and then aggravates spalling damage on the wheel roller surface. The surface hardness of material depends strongly upon its carbon content. The decrease of the carbon content of wheel material may alleviate spalling damage, but can cause a significant growth in the wear volume of wheel roller. Therefore, there is a competitive relationship between the wear and spalling damage of wheel material. This research proposes an important measure for alleviating or preventing the wear and spalling damage of railway wheel material.展开更多
This paper provides an investigation of the phase transition and spalling characteristic induced during shock loading and unloading in the pure iron and the FeMnNi alloy. The impact for the pure iron is symmetric and ...This paper provides an investigation of the phase transition and spalling characteristic induced during shock loading and unloading in the pure iron and the FeMnNi alloy. The impact for the pure iron is symmetric and with the same-thickness for both the flyer and the target plate. It is found that an abnormal multiple spalling happens in the pure iron sample as the pressure exceeds the α- ε transition threshold of 13 GPa. In the symmetric and same-thickness impact and reverse impact experiments of the FeMnNi alloy, two abnormal tension regions occur when the pressure exceeds the α - ε transition threshold of 6.3 GPa, and the reverse phase transition s - ~ begins below 4.2 GP. The experimental process is simulated successfully from the non-equilibrium mixture phase and Boettger's model. Such abnormal spalling phenomena are believed to relate to the shocked α - ε phase transition. The possible reasons for the abnormal multiple spalling, which occurs during the symmetric and same-thickness impact experiments of pure iron and FeMnNi alloy, are discussed.展开更多
Spalling and mechanical properties of FRHPC subjected to fire were tested on notched beams. The results confirm that the internal vapor pressure is the leading reason for spalling of high-performance concrete (HPC)....Spalling and mechanical properties of FRHPC subjected to fire were tested on notched beams. The results confirm that the internal vapor pressure is the leading reason for spalling of high-performance concrete (HPC). At the same time, the temperature-increasing velocity and constrained conditions of concrete element also play significant roles in spalling. Steel fibers cannot reduce the risk of spalling, although they have obvious beneficial effects on the mechanical properties of concrete before and after exposure to fire. Polypropylene (PP) fibers are very useful in preventing HPC from spalling, however, they have negative effects on the strengths. By using hybrid fibers (steel fibers+PP fibers), both good anti-spalling performance and improved mechanical properties come true, which may provide necessary safe guarantee for the rescue work and structure repair after fire disaster.展开更多
In order to explore the characteristics of ultra-high-strength concrete exposed to high temperature,residual mechanical properties and explosive spalling behavior of ultra-high-strength concrete( UHSC) and high streng...In order to explore the characteristics of ultra-high-strength concrete exposed to high temperature,residual mechanical properties and explosive spalling behavior of ultra-high-strength concrete( UHSC) and high strength concrete( HSC) exposed to high temperatures ranging from 20 ℃ to 800 ℃ were determined. The microstructure of the specimens after exposure to elevated temperature was analyzed by means of scanning electron microscope( SEM) and mercury intrusion porosimetry( MIP). The residual compressive strengths of UHSC and HSC were first increased and then decreased as temperature increased. After exposure to 800 ℃,the compressive strengths of UHSC and HSC were 24. 2 % and 22. 3 % of their original strengths at 20 ℃,respectively. The residual splitting tensile strengths of both UHSC and HSC were consistently decreased with the temperature increasing and were approximately 20% of their original strengths after 800 ℃. However,the residual fracture energies of both concretes tended to ascend even at 600 ℃. The explosive spalling of UHSC was more serious than that of HSC. Moisture content of the specimens governs the explosive spalling of both concretes with a positive correlations,and it is more pronounced in UHSC. These results suggest that UHSC suffers a substantial loss in load-bearing capacity and is highly prone to explosive spalling due to high temperature. The changes in compressive strength are due to the changes in the density and the pore structure of concrete. The probability and severity of explosive spalling of UHSC are much higher than those of HSC due to the higher pore volume in HSC.展开更多
In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer (CFRP) sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one...In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer (CFRP) sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.展开更多
The tendency of spalling of the nitrided layer of the hot rolled austenitic steel 4Cr14Ni14W2Mo exhibits close relation to the nitrided surface orientation relative to the rol- led steel rod.It is found that the dislo...The tendency of spalling of the nitrided layer of the hot rolled austenitic steel 4Cr14Ni14W2Mo exhibits close relation to the nitrided surface orientation relative to the rol- led steel rod.It is found that the dislocations in the imperfectly recrystalized steel align as parallel dislocation walls in macroscopic extent,and the thickness of the“white sublayer”in the nitrided layer is much larger at the surface which is parallel to the dislocation walls.On such surface the spalling of the nitrided layer happens often.展开更多
Inner vapor pressure and temperature of vulnerable explosive spalling positions in refractory castables during rapid drying were measured by embedding pressure transmitting pipes and thermocouples during casting. The ...Inner vapor pressure and temperature of vulnerable explosive spalling positions in refractory castables during rapid drying were measured by embedding pressure transmitting pipes and thermocouples during casting. The measured vapor pressure, temperature, and tensile strength of the castables were analyzed and discussed. A hollow sphere shell model was used to analyze the stress induced by the vapor pressure based on the structure of refractory castables. The mechanism of refractory castables explosive spalling caused by vapor-induced pore split was proposed. By comparing the vapor-induced stress and the tensile strength of the castables, the explosive spalling mechanism was validated quantitatively.展开更多
LIRR's Priject of "Research on Spalling Mechanism Due to Rapid Heating-up of Dense Refractory Castables" declared by Wang Zhanmin,vice-president of LIRR,will gain the fund support from National Natural Science Foun...LIRR's Priject of "Research on Spalling Mechanism Due to Rapid Heating-up of Dense Refractory Castables" declared by Wang Zhanmin,vice-president of LIRR,will gain the fund support from National Natural Science Foundation of China in 2011.展开更多
1 Scope This standard specifies the term, definition, classification, labeling, technical requirements, test methods, inspection rules, packing, marking, transportation, storage, and quality certificate of spalling re...1 Scope This standard specifies the term, definition, classification, labeling, technical requirements, test methods, inspection rules, packing, marking, transportation, storage, and quality certificate of spalling resistant bauxite based bricks for cement kiln.展开更多
YB/T 4195-2009 1 Scope This standard specifies the term and definition,classification,technical requirements,test methods,quality appraisal procedures,packing,marking,transportation,storage,and quality certificate of ...YB/T 4195-2009 1 Scope This standard specifies the term and definition,classification,technical requirements,test methods,quality appraisal procedures,packing,marking,transportation,storage,and quality certificate of spalling resistance fast-drying refractory castables.This standard is applicable to spalling resistance fast-drying refractory castables for steel rolling heating furnace and industrial furnace of other industries.2 Normative References展开更多
NMR is becoming increasingly popular for the investigation of building materials as it is a non-invasive technology that does not require any sample preparation nor causes damage to the material.Depending on the speci...NMR is becoming increasingly popular for the investigation of building materials as it is a non-invasive technology that does not require any sample preparation nor causes damage to the material.Depending on the specific application it can offer insights into properties like porosity and spatial saturation degree as well as pore structure.Moreover it enables the determination of moisture transport properties and the(re-)distribution of internal moisture into different reservoirs or chemical phases upon damage and curing.However,as yet most investigations were carried out using devices originally either designed for geophysical applications or the analysis of rather homogeneous small scale(<10 mL)samples.This paper describes the capabilities of an NMR tomograph,which has been specifically optimized for the investigation of larger,heterogeneous building material samples(diameters of up to 72 mm,length of up to 700 mm)with a high flexibility due to interchangeable coils allowing for a high SNR and short echo times(50-80 ms).展开更多
Rock mechanics plays a critical role in the design and construction of hydroelectric projects including large caverns under high in situ stress,deep tunnels with overburden more than 2500 m,and excavated rock slopes o...Rock mechanics plays a critical role in the design and construction of hydroelectric projects including large caverns under high in situ stress,deep tunnels with overburden more than 2500 m,and excavated rock slopes of 700 m in height.For this,this paper conducts a review on the rock mechanics contributions to recent hydroelectric developments in China.It includes the development of new testing facilities,mechanical models,recognition methods for mechanical parameters of rock masses,design flowchart and modeling approaches,cracking-restraint method,governing flowchart of rock engineering risk factors enabling the development of risk-reduced design and risk-reduced construction,and initial and dynamic design methods.As an example,the optimal design of underground powerhouses at the Baihetan hydroelectric plant,China,is given.This includes determination of in situ stresses,prediction of deformation and failure depth of surrounding rock masses,development of the optimal excavation scheme and support design.In situ monitoring results of the displacements and excavation damaged zones(EDZs)have verified the rationality of the design methodology.展开更多
To analyze and predict the mechanical behaviors of deep hard rocks,some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed.First,a series of apparatuses and methods have been ...To analyze and predict the mechanical behaviors of deep hard rocks,some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed.First,a series of apparatuses and methods have been developed to test the mechanical properties and fracturing behaviors of hard rocks under high true triaxial stress paths.Evolution mechanisms of stress-induced disasters in deep hard rock excavations,such as spalling,deep cracking,massive roof collapse,large deformation and rockbursts,have been recognized.The analytical theory for the fracturing process of hard rock masses,including the three-dimensional failure criterion,stress-induced mechanical model,fracturing degree index,energy release index and numerical method,has been established.The cracking-restraint method is developed for mitigating or controlling rock spalling,deep cracking and massive collapse of deep hard rocks.An energy-controlled method is also proposed for the prevention of rockbursts.Finally,two typical cases are used to illustrate the application of the proposed methodology in the Baihetan caverns and Bayu tunnels of China.展开更多
During the construction of an underground excavation, damage occurs in the surrounding rock mass due in large part to stress changes. While the predicted damage extent impacts profile selection and support design, the...During the construction of an underground excavation, damage occurs in the surrounding rock mass due in large part to stress changes. While the predicted damage extent impacts profile selection and support design, the depth of damage is a critical aspect for the design of permeability sensitive excavations, such as a deep geological repository(DGR) for nuclear waste. Review of literature regarding the depth of excavation damage zones(EDZs) indicates three zones are common and typically related to stress induced damage. Based on past developments related to brittle damage prediction using continuum modelling, the depth of the EDZs has been examined numerically. One method to capture stress induced damage in conventional engineering software is the damage initiation and spalling limit(DISL) approach. The variability of depths predicted using the DISL approach has been evaluated and guidelines are suggested for determining the depth of the EDZs around circular excavations in brittle rock masses. Of the inputs evaluated, it was found that the tensile strength produces the greatest variation in the depth of the EDZs. The results were evaluated statistically to determine the best fit relation between the model inputs and the depth of the EDZs. The best correlation and least variation were found for the outer EDZ and the highly damaged zone(HDZ) showed the greatest variation. Predictive equations for different EDZs have been suggested and the maximum numerical EDZ depths, represented by the 68% prediction interval, agreed well with the empirical evidence. This suggests that the numerical limits can be used for preliminary depth prediction of the EDZs in brittle rock for circular excavations.展开更多
基金financial support from the National Key Research and Development Program of China (No.2023YFC2907501)the National Natural Science Foundation of China (No.52374106)the Fundamental Research Funds for the Central Universities (No.2023ZKPYNY01)。
文摘In order to improve rib stability,failure criteria and instability mode of a thick coal seam with inter-band rock layer are analysed in this study.A three-dimensional mechanical model is established for the rib by considering the rock layer.A safety factor is defined foy the rib,and it is observed that the safety factor exhibits a positive correlation with the thickness and strength of the inter-band rock.A calculation method for determining critical parameters of the rock layer is presented to ensure the rib stability.It is revealed that incomplete propagation of the fracture at the hard rock constitutes a fundamental prerequisite for ensuring the rib stability.The influence of the position of the inter-band rock in the coal seam on failure mechanism of the rib was thoroughly investigated by developing a series of physical models for the rib at the face area.The best position for the inter-band rock in the coal seam is at a height of 1.5 m away from the roof line,which tends to provide a good stability state for the rib.For different inter-band rock positions,two ways of controlling rib by increasing supports stiffness and flexible grouting reinforcement are proposed.
基金supported by the Beijing Natural Science Foundation,China(Grant No.JQ20039)National Natural Science Foundation of China(Grant No.12172019).
文摘The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.
基金The authors greatly gratefully acknowledge the financial support from the National Natural Science Foundation of China(Grant Nos.52169021 and 51869003)the Interdisciplinary Scientific Research Foundation of Guangxi University,China(Grant No.2022JCA004).
文摘Spalling is a typical brittle failure phenomenon of hard rock in deep caverns under high geostress.In this study,key issues are systematically studied concerning the spalling failure of deep hard rock caverns.First,the prismatic rock specimens with small thicknesses(i.e.width×thickness×height:20 mm×50 mm×100 mm)are employed in our tests which not only successfully simulate the spalling failure of hard rock in the laboratory but also obtain a reasonable spalling strength similar to that of the rock mass.Then,a series of spalling experiments is carried out to investigate the mechanism of spalling failure of deep hard rock caverns.Our results show that the intermediate principal stress,weak dynamic disturbances,and rock microstructure have significant effects on the spalling failure.The spalling strength is approximately(0.3–0.8)UCS,where UCS is the uniaxial compressive strength of the cylindrical rock sample with a diameter of around 50 mm.The spalling strength increases first and then decreases with increasing intermediate principal stress.Moreover,an empirical spalling strength criterion and a numerical method of spalling failure are proposed.This numerical method can not only simulate the spalling failure zone formed by tangential compressive stress concentration after excavation under different intermediate principal stresses,but also successfully simulate the failure transition from tensile mode to shear mode associated with confinement change in deep hard rock caverns.Furthermore,an acoustic emission-based early warning method using neural network is proposed to predict the spalling failure.Finally,a technical roadmap for preventing and controlling spalling failure of deep hard rock caverns is presented after summarizing the successful experiences in a typical engineering case.
基金the National Natural Science Foundation of China(No.42377172)the National Key Research and Development Plan Project of China(No.2023YFC2907204).
文摘The Voronoi grain-based breakable block model(VGBBM)based on the combined finite-discrete element method(FDEM)was proposed to explicitly characterize the failure mechanism and predict the deformation behavior of hard-rock mine pillars.The influence of the microscopic parameters on the macroscopic mechanical behavior was investigated using laboratory-scale models.The field-scale pillar models(width-to-height,W/H=1,2 and 3)were calibrated based on the empirically predicted stress-strain curves of Creighton mine pillars.The results indicated that as the W/H ratios increased,the VGBBM effectively predicted the transition from strain-softening to pseudo-ductile behavior in pillars,and explicitly captured the separated rock slabs and the V-shaped damage zones on both sides of pillars and conjugate shear bands in core zones of pillars.The volumetric strain field revealed significant compressional deformation in core zones of pillars.While the peak strains of W/H=1 and 2 pillars were relatively consistent,there were significant differences in the strain energy storage and release mechanism.W/H was the primary factor influencing the deformation and strain energy in the pillar core.The friction coefficient of the structural plane was also an important factor affecting the pillar strength and the weakest discontinuity angle.The fracture surface was controlled by the discontinuity angle and the friction coefficient.This study demonstrated the capability of the VGBBM in predicting the strengths and deformation behavior of hard-rock pillars in deep mine design.
基金the National Natural Science Foundation of China(NSFC)(52178324).
文摘Concrete subjected to fire loads is susceptible to explosive spalling, which can lead to the exposure of reinforcingsteel bars to the fire, substantially jeopardizing the structural safety and stability. The spalling of fire-loaded concreteis closely related to the evolution of pore pressure and temperature. Conventional analytical methods involve theresolution of complex, strongly coupled multifield equations, necessitating significant computational efforts. Torapidly and accurately obtain the distributions of pore-pressure and temperature, the Pix2Pix model is adoptedin this work, which is celebrated for its capabilities in image generation. The open-source dataset used hereinfeatures RGB images we generated using a sophisticated coupled model, while the grayscale images encapsulate the15 principal variables influencing spalling. After conducting a series of tests with different layers configurations,activation functions and loss functions, the Pix2Pix model suitable for assessing the spalling risk of fire-loadedconcrete has been meticulously designed and trained. The applicability and reliability of the Pix2Pix model inconcrete parameter prediction are verified by comparing its outcomes with those derived fromthe strong couplingTHC model. Notably, for the practical engineering applications, our findings indicate that utilizing monochromeimages as the initial target for analysis yields more dependable results. This work not only offers valuable insightsfor civil engineers specializing in concrete structures but also establishes a robust methodological approach forresearchers seeking to create similar predictive models.
基金supported by National Natural Science Foundation of China(Grant No.51174282)Innovative Research Teams in Universities of China(Grant No.IRT1178)Autonomous Research Project of State Key Laboratory of China(Grant No.TPL1301)
文摘The current researches of the wear and spalling behaviors of wheel/rail materials focus on the field investigation rather than the mechanism. However, it is necessary and significant for clarifying the mechanism and relationship between the wear and spalling damage of railway wheel to test and reproduce the wheel damages in laboratory. The objective of this paper is to investigate the wear and spalling damage behaviors of railway wheel using a JD-1 wheel/rail simulation facility, which consists of a small wheel serving as rolling stock wheel, and a larger wheel serving as rail. The damage process of wheel roller is explored in terms of the creep ratio, axle load, and carbon content by means of various microscopic examinations. The experimental results show that the wear volume growth of wheel roller is proved to be proportional to the increase of the creep ratio and normal load between simulating wheel and rail. The increase of carbon content of wheel material causes a linear reduction in the wear volume. The microscopic examinations indicate that the rolling wear mechanism transfers from abrasive wear to adhesive and fatigue wear with an increase of tangential friction force, which results in the initiation of fatigue crack, and then aggravates spalling damage on the wheel roller surface. The surface hardness of material depends strongly upon its carbon content. The decrease of the carbon content of wheel material may alleviate spalling damage, but can cause a significant growth in the wear volume of wheel roller. Therefore, there is a competitive relationship between the wear and spalling damage of wheel material. This research proposes an important measure for alleviating or preventing the wear and spalling damage of railway wheel material.
基金Project supported by the National Science Foundations of China (Grant Nos. 10776032 and 10902102)Science Foundation of China Academy of Engineering Physics (Grant Nos. 20060104 and 2009B0201014)
文摘This paper provides an investigation of the phase transition and spalling characteristic induced during shock loading and unloading in the pure iron and the FeMnNi alloy. The impact for the pure iron is symmetric and with the same-thickness for both the flyer and the target plate. It is found that an abnormal multiple spalling happens in the pure iron sample as the pressure exceeds the α- ε transition threshold of 13 GPa. In the symmetric and same-thickness impact and reverse impact experiments of the FeMnNi alloy, two abnormal tension regions occur when the pressure exceeds the α - ε transition threshold of 6.3 GPa, and the reverse phase transition s - ~ begins below 4.2 GP. The experimental process is simulated successfully from the non-equilibrium mixture phase and Boettger's model. Such abnormal spalling phenomena are believed to relate to the shocked α - ε phase transition. The possible reasons for the abnormal multiple spalling, which occurs during the symmetric and same-thickness impact experiments of pure iron and FeMnNi alloy, are discussed.
基金the National Natural Science Foundation of China (No. 50278013)
文摘Spalling and mechanical properties of FRHPC subjected to fire were tested on notched beams. The results confirm that the internal vapor pressure is the leading reason for spalling of high-performance concrete (HPC). At the same time, the temperature-increasing velocity and constrained conditions of concrete element also play significant roles in spalling. Steel fibers cannot reduce the risk of spalling, although they have obvious beneficial effects on the mechanical properties of concrete before and after exposure to fire. Polypropylene (PP) fibers are very useful in preventing HPC from spalling, however, they have negative effects on the strengths. By using hybrid fibers (steel fibers+PP fibers), both good anti-spalling performance and improved mechanical properties come true, which may provide necessary safe guarantee for the rescue work and structure repair after fire disaster.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51278048)the Fundamental Research Funds for the Central Universities of China(Grant No.C11JB00720)
文摘In order to explore the characteristics of ultra-high-strength concrete exposed to high temperature,residual mechanical properties and explosive spalling behavior of ultra-high-strength concrete( UHSC) and high strength concrete( HSC) exposed to high temperatures ranging from 20 ℃ to 800 ℃ were determined. The microstructure of the specimens after exposure to elevated temperature was analyzed by means of scanning electron microscope( SEM) and mercury intrusion porosimetry( MIP). The residual compressive strengths of UHSC and HSC were first increased and then decreased as temperature increased. After exposure to 800 ℃,the compressive strengths of UHSC and HSC were 24. 2 % and 22. 3 % of their original strengths at 20 ℃,respectively. The residual splitting tensile strengths of both UHSC and HSC were consistently decreased with the temperature increasing and were approximately 20% of their original strengths after 800 ℃. However,the residual fracture energies of both concretes tended to ascend even at 600 ℃. The explosive spalling of UHSC was more serious than that of HSC. Moisture content of the specimens governs the explosive spalling of both concretes with a positive correlations,and it is more pronounced in UHSC. These results suggest that UHSC suffers a substantial loss in load-bearing capacity and is highly prone to explosive spalling due to high temperature. The changes in compressive strength are due to the changes in the density and the pore structure of concrete. The probability and severity of explosive spalling of UHSC are much higher than those of HSC due to the higher pore volume in HSC.
基金supported by the Scheme of Science and Technology of Guangdong Province,China(2005B32801002)
文摘In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer (CFRP) sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.
文摘The tendency of spalling of the nitrided layer of the hot rolled austenitic steel 4Cr14Ni14W2Mo exhibits close relation to the nitrided surface orientation relative to the rol- led steel rod.It is found that the dislocations in the imperfectly recrystalized steel align as parallel dislocation walls in macroscopic extent,and the thickness of the“white sublayer”in the nitrided layer is much larger at the surface which is parallel to the dislocation walls.On such surface the spalling of the nitrided layer happens often.
文摘Inner vapor pressure and temperature of vulnerable explosive spalling positions in refractory castables during rapid drying were measured by embedding pressure transmitting pipes and thermocouples during casting. The measured vapor pressure, temperature, and tensile strength of the castables were analyzed and discussed. A hollow sphere shell model was used to analyze the stress induced by the vapor pressure based on the structure of refractory castables. The mechanism of refractory castables explosive spalling caused by vapor-induced pore split was proposed. By comparing the vapor-induced stress and the tensile strength of the castables, the explosive spalling mechanism was validated quantitatively.
文摘LIRR's Priject of "Research on Spalling Mechanism Due to Rapid Heating-up of Dense Refractory Castables" declared by Wang Zhanmin,vice-president of LIRR,will gain the fund support from National Natural Science Foundation of China in 2011.
文摘1 Scope This standard specifies the term, definition, classification, labeling, technical requirements, test methods, inspection rules, packing, marking, transportation, storage, and quality certificate of spalling resistant bauxite based bricks for cement kiln.
文摘YB/T 4195-2009 1 Scope This standard specifies the term and definition,classification,technical requirements,test methods,quality appraisal procedures,packing,marking,transportation,storage,and quality certificate of spalling resistance fast-drying refractory castables.This standard is applicable to spalling resistance fast-drying refractory castables for steel rolling heating furnace and industrial furnace of other industries.2 Normative References
文摘NMR is becoming increasingly popular for the investigation of building materials as it is a non-invasive technology that does not require any sample preparation nor causes damage to the material.Depending on the specific application it can offer insights into properties like porosity and spatial saturation degree as well as pore structure.Moreover it enables the determination of moisture transport properties and the(re-)distribution of internal moisture into different reservoirs or chemical phases upon damage and curing.However,as yet most investigations were carried out using devices originally either designed for geophysical applications or the analysis of rather homogeneous small scale(<10 mL)samples.This paper describes the capabilities of an NMR tomograph,which has been specifically optimized for the investigation of larger,heterogeneous building material samples(diameters of up to 72 mm,length of up to 700 mm)with a high flexibility due to interchangeable coils allowing for a high SNR and short echo times(50-80 ms).
基金financial support from the National Natural Science Foundation of China (Grant No. 51621006)
文摘Rock mechanics plays a critical role in the design and construction of hydroelectric projects including large caverns under high in situ stress,deep tunnels with overburden more than 2500 m,and excavated rock slopes of 700 m in height.For this,this paper conducts a review on the rock mechanics contributions to recent hydroelectric developments in China.It includes the development of new testing facilities,mechanical models,recognition methods for mechanical parameters of rock masses,design flowchart and modeling approaches,cracking-restraint method,governing flowchart of rock engineering risk factors enabling the development of risk-reduced design and risk-reduced construction,and initial and dynamic design methods.As an example,the optimal design of underground powerhouses at the Baihetan hydroelectric plant,China,is given.This includes determination of in situ stresses,prediction of deformation and failure depth of surrounding rock masses,development of the optimal excavation scheme and support design.In situ monitoring results of the displacements and excavation damaged zones(EDZs)have verified the rationality of the design methodology.
基金financial support from the National Natural Science Foundation of China(Grant Nos.51839003 and 41827806)Liaoning Revitalization Talents Program of China(Grant No.XLYCYSZX1902)。
文摘To analyze and predict the mechanical behaviors of deep hard rocks,some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed.First,a series of apparatuses and methods have been developed to test the mechanical properties and fracturing behaviors of hard rocks under high true triaxial stress paths.Evolution mechanisms of stress-induced disasters in deep hard rock excavations,such as spalling,deep cracking,massive roof collapse,large deformation and rockbursts,have been recognized.The analytical theory for the fracturing process of hard rock masses,including the three-dimensional failure criterion,stress-induced mechanical model,fracturing degree index,energy release index and numerical method,has been established.The cracking-restraint method is developed for mitigating or controlling rock spalling,deep cracking and massive collapse of deep hard rocks.An energy-controlled method is also proposed for the prevention of rockbursts.Finally,two typical cases are used to illustrate the application of the proposed methodology in the Baihetan caverns and Bayu tunnels of China.
基金funded by the Natural Sciences and Engineering Research Council of Canadaby the Nuclear Waste Management Organization(NWMO)of Canada
文摘During the construction of an underground excavation, damage occurs in the surrounding rock mass due in large part to stress changes. While the predicted damage extent impacts profile selection and support design, the depth of damage is a critical aspect for the design of permeability sensitive excavations, such as a deep geological repository(DGR) for nuclear waste. Review of literature regarding the depth of excavation damage zones(EDZs) indicates three zones are common and typically related to stress induced damage. Based on past developments related to brittle damage prediction using continuum modelling, the depth of the EDZs has been examined numerically. One method to capture stress induced damage in conventional engineering software is the damage initiation and spalling limit(DISL) approach. The variability of depths predicted using the DISL approach has been evaluated and guidelines are suggested for determining the depth of the EDZs around circular excavations in brittle rock masses. Of the inputs evaluated, it was found that the tensile strength produces the greatest variation in the depth of the EDZs. The results were evaluated statistically to determine the best fit relation between the model inputs and the depth of the EDZs. The best correlation and least variation were found for the outer EDZ and the highly damaged zone(HDZ) showed the greatest variation. Predictive equations for different EDZs have been suggested and the maximum numerical EDZ depths, represented by the 68% prediction interval, agreed well with the empirical evidence. This suggests that the numerical limits can be used for preliminary depth prediction of the EDZs in brittle rock for circular excavations.