In the civil and mining industries,bolts are critical components of support systems,playing a vital role in ensuring their stability.Glass fibre reinforced polymer(GFRP)bolts are widely used because they are corrosion...In the civil and mining industries,bolts are critical components of support systems,playing a vital role in ensuring their stability.Glass fibre reinforced polymer(GFRP)bolts are widely used because they are corrosion-resistant and cost-effective.However,the damage mechanisms of GFRP bolts under blasting dynamic loads are still unclear,especially compared to metal bolts.This study investigates the cumulative damage of fully grouted GFRP bolts under blasting dynamic loads.The maximum axial stress at the tails of the bolts is defined as the damage variable,based on the failure characteristics of GFRP bolts.By combining this with Miner's cumulative damage theory,a comprehensive theoretical and numerical model is established to calculate cumulative damage.Field data collected from the Jinchuan No.3 Mining Area,including GFRP bolts parameters and blasting vibration data are used for further analysis of cumulative damage in fully grouted GFRP bolts.Results indicate that with an increasing number of blasts,axial stress increases in all parts of GFRP bolts.The tail exhibits the most significant rise,with stress extending deeper into the anchorage zone.Cumulative damage follows an exponential trend with the number of blasts,although the incremental damage per blast decelerates over time.Higher dynamic load intensities accelerate damage accumulation,leading to an exponential decline in the maximum loading cycles before failure.Additionally,stronger surrounding rock and grout mitigate damage accumulation,with the effect of surrounding rock strength being more pronounced than that of grout.In contrast,the maximum axial stress of metal bolts increases quickly to a certain point and then stabilizes.This shows a clear difference between GFRP and metal bolts.This study presents a new cumulative damage theory that underpins the design of GFRP bolt support systems under blasting conditions,identifies key damage factors,and suggests mitigation measures to enhance system stability.展开更多
The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparat...The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparatus. The blasting test was carried out for ten times at some tunnels of Changba Lead-Zinc Mine. The damage depth of surrounding rock caused by old blasting excavation （0.8-1.2 m） was confirmed. The relation between the cumulative damage degree and blast times was obtained. The results show that the sonic velocity decreases gradually with increasing blast times, hut the damage degree （D） increases. The damage cumulative law is non-linear. The damage degree caused by blast decreases with increasing distance, and damage effects become indistinct. The blasting damage of rock mass is anisotropic. The damage degree of rock mass within charging range is maximal. And the more the charge is, the more severe the damage degree of rock mass is. The test results provide references for researches of mechanical parameters of rock mass and dynamic stability analysis of underground chambers.展开更多
A long-term damage cumulative model for the duration of load effect of structural timber is proposed in this paper, which is economical in analysis as well as involving long-term hygrothermal effect. Based on the Mine...A long-term damage cumulative model for the duration of load effect of structural timber is proposed in this paper, which is economical in analysis as well as involving long-term hygrothermal effect. Based on the Miner linear damage cumulative theory, the cumulative damage model is applied to analyze the annual hygrothermal, daily cyclic thermal and daily cyclic relative humidity＇s effect on load-duration behavior and to calculate the sum of damage in one year. The results indicate that the annual and daily hygrothermal effect should be taken into consideration when calculating the damage accumulation, in which the influence levels from large to small are annual hygrothermal, daily relative humidity and daily thermal effect, Considering both annual and daily hygrothermal variations as external loads the long-term model is determined. Its application to service-life prediction of a historic timber structure verifies the feasibility and high-efficiency of the proposed approach.展开更多
Debris slopes are widely distributed across the Three Gorges Reservoir area in China,and seasonal fluctuations of the water level in the area tend to cause high-frequency microseisms that subsequently induce landslide...Debris slopes are widely distributed across the Three Gorges Reservoir area in China,and seasonal fluctuations of the water level in the area tend to cause high-frequency microseisms that subsequently induce landslides on such debris slopes.In this study,a cumulative damage model of debris slope with varying slope characteristics under the effects of frequent microseisms was established,based on the accurate definition of slope damage variables.The cumulative damage behaviour and the mechanisms of slope instability and sliding under frequent microseisms were thus systematically investigated through a series of shaking table tests and discrete element numerical simulations,and the influences of related parameters such as bedrock,dry density and stone content were discussed.The results showed that the instability mode of a debris slope can be divided into a vibration-compaction stage,a crack generation stage,a crack development stage,and an instability stage.Under the action of frequent microseisms,debris slope undergoes the last three stages cyclically,which causes the accumulation to slide out in layers under the synergistic action of tension and shear,causing the slope to become destabilised.There are two sliding surfaces as well as the parallel tensile surfaces in the final instability of the debris slope.In the process of instability,the development trend of the damage accumulation curve remains similar for debris slopes with different parameters.However,the initial vibration compaction effect in the bedrock-free model is stronger than that in the bedrock model,with the overall cumulative damage degree in the former being lower than that of the latter.The damage degree of the debris slope with high dry density also develops more slowly than that of the debris slope with low dry density.The damage development rate of the debris slope does not always decrease with the increase of stone content.The damage degree growth rate of the debris slope with the optimal stone content is the lowest,and the increase or decrease of the stone content makes the debris slope instability happen earlier.The numerical simulation study also further reveals that the damage in the debris slope mainly develops in the form of crack formation and penetration,in which,shear failure occurs more frequently in the debris slope.展开更多
On the basis of the statistical characteristics of fatigue cumulative damageand its critical value, a new dynamic interference model for reliability analysis is presented. Because the nonlinearity of fatigue damage ac...On the basis of the statistical characteristics of fatigue cumulative damageand its critical value, a new dynamic interference model for reliability analysis is presented. Because the nonlinearity of fatigue damage accumulation is taken into account,this model is able to predict the fatigue reliability for random spectrum loadingconveniently. To verify the predicted results, a special fatigue expenment, in which thenumber of specimen is up to 101, is conducted using a fighter spectrum loading. It isshown that the new model is reliable, practicable and better than existing models.展开更多
Frequent aftershocks often follow a strong mainshock.They can significantly increase cumulative damage to a structure.A model of a five-story reinforced concrete frame structure was designed and a nonlinear mathematic...Frequent aftershocks often follow a strong mainshock.They can significantly increase cumulative damage to a structure.A model of a five-story reinforced concrete frame structure was designed and a nonlinear mathematical model of the structure was developed to investigate the damage states resulting from different mainshock-aftershock sequences.Mainshock-aftershock sequences consisting of one of three recorded mainshocks combined with one of five recorded aftershocks were created for input to the mathematical model.Inelastic energy dissipation and the Park-Ang damage index were used as measures of cumulative damage to the structure.The results demonstrate that consideration of only the single mainshock ground motion in seismic building design can result in the design and construction of unsafe buildings.Total cumulative damage to a structure is caused by the combination of damage states resulting from the mainshock and the aftershock(s).展开更多
Fatigue failure of mechanical part is treated as a random event.the fatigue reliablility problem can be solved through researching the random event.A new definition δb that measures fatigue damage quantity in a cycle...Fatigue failure of mechanical part is treated as a random event.the fatigue reliablility problem can be solved through researching the random event.A new definition δb that measures fatigue damage quantity in a cycle under cyclic stress is put forward. According to δ.the paper presents two new definitions K and D is fatigue damage strength.D is overall fatigue damage quantity.Using K and D to describe the fatigue failure of the parts,the paper puts forward a new fatigue cumulative damage probabilistic model of the mechanical parts.The model can be used to solve reliability fatigue problem.展开更多
The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm×100mm×100mm specimens of ordinary strength c...The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm×100mm×100mm specimens of ordinary strength concrete were tested with constant-or variable-amplitude cyclic compression and lateral confinement pressure in two orthogonal directions. A fatigue equation was gained by modifying the classical Aas-Jakobsen S-N equation and used for taking into account the effect of the confined stress on fatigue strength of plain concrete. The present study indicates that the fatigue failure is greatly influenced by the sequence of applied variable-amplitude fatigue loading, and Miner’s rule is inapplicable to predict the residual fatigue life, especially in the sequence of low to high. The present research also shows that the exponent d of the Corten-Dolan’s damage formula is a constant depending on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. The residual fatigue lives predicted by Corten-Dolan’s damage formula are found to be in good agreement with the results of the experiments.展开更多
Aim To study the theory and method for the prediction of service life of solid rocket propellant grain. Methods With the aid of discontiguous diagnostic technology and method of accumulated damage using accelerated...Aim To study the theory and method for the prediction of service life of solid rocket propellant grain. Methods With the aid of discontiguous diagnostic technology and method of accumulated damage using accelerated aging or heat air oven, the aging isotherms for void content versus aging time were determined. According to the principle of time temperature equivalence the viscoelastic master curve for the prediction of service life were obtained. Results and Conclusion The service life of HMX CMDB solid rocket propellant grain were obtained. Because the critical storage life is measured, the accuracy of predicting the service life of the grain has been increased greatly.展开更多
Raveling is a common distress of asphalt pavements,defined as the removal of stones from the pavement surface.To predict and assess raveling quantitatively,a cumulative damage model based on an energy dissipation appr...Raveling is a common distress of asphalt pavements,defined as the removal of stones from the pavement surface.To predict and assess raveling quantitatively,a cumulative damage model based on an energy dissipation approach has been developed at the meso level.To construct the model,a new test method,the pendulum impact test,was employed to determine the fracture energy of the stone-mastic-stone meso-unit,while digital image analysis and dynamic shear rheometer test were used to acquire the strain rate of specimens and the rheology property of mastic,respectively.Analysis of the model reveals that when the material properties remain constant,the cumulative damage is directly correlated with loading time,loading amplitude,and loading frequency.Specifically,damage increases with superimposed linear and cosine variations over time.A higher stress amplitude results in a more rapidly increasing rate of damage,while a lower load frequency leads to more severe damage within the same loading time.Moreover,an example of the application of the model has been presented,showing that the model can be utilized to estimate failure life due to raveling.The model is able to offer a theoretical foundation for the design and maintenance of anti-raveling asphalt pavements.展开更多
Objectives:The aim of this study was to provide a comprehensive understanding of the nonthermal plasma(NTP)-induced inactivated behaviors on a multiple antibiotic-resistant(MAR)Staphylococcus aureus(S.aureus).Material...Objectives:The aim of this study was to provide a comprehensive understanding of the nonthermal plasma(NTP)-induced inactivated behaviors on a multiple antibiotic-resistant(MAR)Staphylococcus aureus(S.aureus).Materials and Methods:A dielectric barrier discharge(DBD)NTP system was employed for the inactivation of a MAR S.aureus under various applied powers of 35,45,and 55 W,and gas distances of 4,6,and 8 mm.The inactivation kinetics of S.aureus were estimated with linear and nonlinear predictive models.In addition,degradation of carotenoid pigment,peroxidation of fatty acids,oxidation of nucleic acids and proteins,and alteration in gene expression were analyzed after NTP treatment.Results and Discussion:The computationally simulated results indicated that the densities of various reactive species increased with enhanced applied powers and decreased discharge distances.These species were further transformed into reactive oxidative and nitrogen species in the gas-liquid interphase and liquid phase.The oxidative and nitrosative stress of NTP resulted in severe damage to cellular components and the morphological structure of S.aureus.On the other hand,the plasma reactive species could also induce the sublethal injury of S.aureus through upregulating the general stress response,antioxidative and antinitrosative defensive systems.Once the cumulative damages overrode the stress tolerance of S.aureus,the completed cell death was finally achieved by NTP.Conclusions:This work infers the possible risk of inducing the repair and resistant capacity of pathogens when the applied NTP parameters are inappropriate,which helps the optimization of NTP process to achieve sufficient inactivation.展开更多
Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic load...Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic loading was proposed. The specimens of aluminum alloy LY12-CZ soaked in corrosive liquid for different times were tested under the constant amplitude cyclic loading to obtain S-N curves. The test was carried out to verify the proposed cumulative fatigue damage rule under the different combinations among corrosion time, loading level, and the cycle numbers. It was shown that the predicted residual fatigue lives showed a good agreement with the experimental results and the proposed rule was simple and can be easily adopted.展开更多
Cyclic impact induces ongoing fatigue damage and performance degradation in anchoring structures,ser-ving as a critical factor leading to the instability of deep roadways.This paper takes the intrinsic spatio-temporal...Cyclic impact induces ongoing fatigue damage and performance degradation in anchoring structures,ser-ving as a critical factor leading to the instability of deep roadways.This paper takes the intrinsic spatio-temporal relationship of macro-microscopic cumulative damage in anchoring structures as the main thread,revealing the mechanism of bearing capacity degradation and progressive instability of anchoring structure under cyclic impact.Firstly,a set of impact test devices and methods for the prestressed solid anchor bolt anchoring structure were developed,effectively replicating the cyclic impact stress paths in situ.Secondly,cyclic impact anchoring structure tests and simulations were conducted,which clarifies the damage evolution mechanism of the anchoring structure.Prestress loss follows a cubic decay func-tion as the number of impacts increases.Under the same impact energy and pretension force,the impact resistance cycles of extended anchoring and full-length anchoring were increased by 186.7%and 280%,respectively,compared to end anchoring.The rate of internal damage accumulation is positively corre-lated with impact energy and negatively correlated with anchorage length.Internal tensile cracks account for approximately 85%.Stress transmission follows a fluctuating pattern.Compared to the extended anchoring,the maximum vibration velocity of the exposed end particles in the full-length anchoring was reduced by 59.31%.Damage evolution exhibits a pronounced cumulative mutation effect.Then,a three-media,two-interface mechanical model of the anchoring structure was constructed.It has been clarified that the compressive stress,tensile stress,and oscillation effect arising from rapid transi-tions between compression and tension are the primary internal factors responsible for the degradation of the anchoring structure’s bearing capacity.Finally,the progressive instability mechanism of the anchoring structure under cyclic impact was elucidated.The mutual feedback and superposition of media rupture,interface debonding,and bearing capacity degradation result in overall failure.The failure pro-cess involves stages dominated by oscillation-compression,tensile stress,and compression failure.A tar-geted control strategy was further proposed.This provides a reference for maintaining the long-term stability of deep roadways under dynamic impact loads.展开更多
This paper conducts a comparative study on seismic damage to reinforced concrete(RC)bridges,using three damage models:Park and Ang,Hindi and Sexsmith,and input energy-based damage(IEBD)indices,and presents a global cu...This paper conducts a comparative study on seismic damage to reinforced concrete(RC)bridges,using three damage models:Park and Ang,Hindi and Sexsmith,and input energy-based damage(IEBD)indices,and presents a global cumulative damage model based on the IEBD index to establish a practical damage assessment of an overall bridge system.A series of RC bridges are studied under seismic loadings,and to compare the efficiency and reliability of the damage indices,damage curves of RC piers are developed,and damage levels of piers are calculated at design basis earthquake(DBE)and maximum considered earthquake(MCE)levels.The global cumulative damage index is calculated for bridge models regarding damage values of components.The results indicate that the IEBD index shows a gradual progression of damage and provides reasonable values for different damage levels of piers compared to two other damage indices.Moreover,the global cumulative damage index shows the impact of induced damage to a certain component regarding the damage level of the overall bridge system.Moreover,this new approach is a relatively simple and practical tool for seismic damage assessment of RC bridge systems,which can be implemented in finite element models,particularly in the absence of experimental data.展开更多
To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tes...To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tests were conducted for the damaged samples.Besides,coupling modeling technology of finite difference method(FDM)—discrete element method(DEM)was used to carry out the numerical investigation.The results show that after multiple impacts,more white patches appear on the surface,and some microcracks,macro-fractures as well as pulverized grains are found by optical microscopic.The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample.The interaction between grains in the damaged sample becomes intense in the subsequent static loading process,causing a relatively large strain.The volume of the fragments falling off around the loading points becomes larger as impact number increases.As the dynamic damage increases,the absorbed energy of sample during the static loading first decreases and then tends to be stable.Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.展开更多
A class of lifetime distributions, new better than equilibrium in expectation （NBEE）, and its dual, new worse than equilibrium in expectation （NWEE）, are studied based on the comparison of the expectations of life...A class of lifetime distributions, new better than equilibrium in expectation （NBEE）, and its dual, new worse than equilibrium in expectation （NWEE）, are studied based on the comparison of the expectations of lifetime X and its equilibrium Xo. The relationships of the NBEE （NWEE） and other lifetime distribution classes are discussed. It is proved that the NBEE is very large, and increasing failure rate （IFR）, new better than used （NBU） and the L class are its subclasses. The closure properties under two kinds of reliability operations, namely, convolution and mixture, are investigated. Furthermore, a Poisson shock model and a special cumulative model are also studied, in which the necessary and sufficient conditions for the NBEE （NWEE） lifetime distribution of the systems are established. In the homogenous Poisson shock model, the system lifetime belongs to NBEE（NWEE） if and only if the corresponding discrete failure distribution belongs to the discrete NBEE（NWEE）. While in the cumulative model, the system has an NBEE lifetime if and only if the stochastic threshold of accumulated damage is NBEE.展开更多
Flange joint part is the weak link of wind turbine tower.In view of the special structure,complex stress and easy failure of the connecting bolt of the wind turbine tower flange,the relationship between the external l...Flange joint part is the weak link of wind turbine tower.In view of the special structure,complex stress and easy failure of the connecting bolt of the wind turbine tower flange,the relationship between the external load of the tower section and the internal stress of the bolt is established by the finite element method,and the time series internal stress of the bolt is calculated by the Schmidt-Neuper algorithm.The S-N curve which is suitable for the connecting bolt material of the tower flange is selected by the GL2010 specification.On the basis of Miner’s fatigue cumulative damage theory and rain flow counting method,the fatigue strength of the whole ring bolt is roughly calculated,and the most dangerous part is determined.The axial symmetry model of screw connection is used for accurately calculating the fatigue cumulative damage of the bolt at the dangerous part.The results show that the fatigue life of the bolts in the most dangerous position can meet the requirements,the engineering algorithm has advantages in determining the dangerous part of the whole ring bolt,and the finite element method has high accuracy in predicting the fatigue life of the bolts in the dangerous part.The proposed method is feasible and effective in predicting the fatigue life of the flange joint bolts of the tower.展开更多
Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the inves...Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.展开更多
The performance degradation rates of the missile tank are generally time-varying functions uneasily evaluated by general classical evaluation methods. This paper develops a segmented nonlinear accelerated degradation ...The performance degradation rates of the missile tank are generally time-varying functions uneasily evaluated by general classical evaluation methods. This paper develops a segmented nonlinear accelerated degradation model （SNADM） based on the equivalent method of accumulative damage theory, which tackles the problem that product life is difficult to be determined with degradation rate being a function of the variable of time. A segmented expression of the function of population accumulative degradation is derived. And combined with nonlinear function, an accelerated degradation function, i.e., SNADM is obtained. The parameters of the SNADM are identified by numerical iteration, and the statistical function of degradation track is extrapolated. The reliability function is determined through the type of random process of the degradation distribution. Then an evaluation of product storage life is undertaken by combining the statistical function of degradation track, reliability function and threshold. An example of a missile tank undergoes a step-down stress accelerated degradation test （SDSADT）, in which the results with the SNADM and the classical method are evaluated and compared. The technology introduced is validated with the resultant coincidence of both evaluated and field storage lives.展开更多
To research the approach of predicting composites fatigue life,the cumulative fatigue damage of fiber-reinforced plastic laminates(FRP) was investigated,and based on the complex exponential function,the residual stren...To research the approach of predicting composites fatigue life,the cumulative fatigue damage of fiber-reinforced plastic laminates(FRP) was investigated,and based on the complex exponential function,the residual strength model was obtained. This model can accurately describe the propagation of cumulative fatigue damage of FRP in three stages,especially in the initial stage and the ceasing stage. Applying this model in the experiment with two loading cycles,it can be found that the prediction result has good coincidence with experimental data. So a reliable residual strength model can be provided for studying the cumulative fatigue damage of FRP.展开更多
基金funded by the National Natural Science Foundation of China(No.51974206)the Hubei Province Safety Production Special Fund Science and Technology Project(No.KJZX202007007).
文摘In the civil and mining industries,bolts are critical components of support systems,playing a vital role in ensuring their stability.Glass fibre reinforced polymer(GFRP)bolts are widely used because they are corrosion-resistant and cost-effective.However,the damage mechanisms of GFRP bolts under blasting dynamic loads are still unclear,especially compared to metal bolts.This study investigates the cumulative damage of fully grouted GFRP bolts under blasting dynamic loads.The maximum axial stress at the tails of the bolts is defined as the damage variable,based on the failure characteristics of GFRP bolts.By combining this with Miner's cumulative damage theory,a comprehensive theoretical and numerical model is established to calculate cumulative damage.Field data collected from the Jinchuan No.3 Mining Area,including GFRP bolts parameters and blasting vibration data are used for further analysis of cumulative damage in fully grouted GFRP bolts.Results indicate that with an increasing number of blasts,axial stress increases in all parts of GFRP bolts.The tail exhibits the most significant rise,with stress extending deeper into the anchorage zone.Cumulative damage follows an exponential trend with the number of blasts,although the incremental damage per blast decelerates over time.Higher dynamic load intensities accelerate damage accumulation,leading to an exponential decline in the maximum loading cycles before failure.Additionally,stronger surrounding rock and grout mitigate damage accumulation,with the effect of surrounding rock strength being more pronounced than that of grout.In contrast,the maximum axial stress of metal bolts increases quickly to a certain point and then stabilizes.This shows a clear difference between GFRP and metal bolts.This study presents a new cumulative damage theory that underpins the design of GFRP bolt support systems under blasting conditions,identifies key damage factors,and suggests mitigation measures to enhance system stability.
基金Project (50490272) supported by the National Natural Science Foundation of ChinaProject(040109) supported by the Doctor Degree Paper Innovation Engineering of Central South University
文摘The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparatus. The blasting test was carried out for ten times at some tunnels of Changba Lead-Zinc Mine. The damage depth of surrounding rock caused by old blasting excavation （0.8-1.2 m） was confirmed. The relation between the cumulative damage degree and blast times was obtained. The results show that the sonic velocity decreases gradually with increasing blast times, hut the damage degree （D） increases. The damage cumulative law is non-linear. The damage degree caused by blast decreases with increasing distance, and damage effects become indistinct. The blasting damage of rock mass is anisotropic. The damage degree of rock mass within charging range is maximal. And the more the charge is, the more severe the damage degree of rock mass is. The test results provide references for researches of mechanical parameters of rock mass and dynamic stability analysis of underground chambers.
基金Supported by the National Natural Science Foundation of China (50708083)
文摘A long-term damage cumulative model for the duration of load effect of structural timber is proposed in this paper, which is economical in analysis as well as involving long-term hygrothermal effect. Based on the Miner linear damage cumulative theory, the cumulative damage model is applied to analyze the annual hygrothermal, daily cyclic thermal and daily cyclic relative humidity＇s effect on load-duration behavior and to calculate the sum of damage in one year. The results indicate that the annual and daily hygrothermal effect should be taken into consideration when calculating the damage accumulation, in which the influence levels from large to small are annual hygrothermal, daily relative humidity and daily thermal effect, Considering both annual and daily hygrothermal variations as external loads the long-term model is determined. Its application to service-life prediction of a historic timber structure verifies the feasibility and high-efficiency of the proposed approach.
基金funded by the Natural Science Foundation of Chongqing municipality(Grant No.CSTC2021JCYJMSXMX0558)the National Key R&D Program of China(Grant No.2018YFC1504802)the Fundamental Research Funds for the Central Universities(Project No.2019CDCG0013)。
文摘Debris slopes are widely distributed across the Three Gorges Reservoir area in China,and seasonal fluctuations of the water level in the area tend to cause high-frequency microseisms that subsequently induce landslides on such debris slopes.In this study,a cumulative damage model of debris slope with varying slope characteristics under the effects of frequent microseisms was established,based on the accurate definition of slope damage variables.The cumulative damage behaviour and the mechanisms of slope instability and sliding under frequent microseisms were thus systematically investigated through a series of shaking table tests and discrete element numerical simulations,and the influences of related parameters such as bedrock,dry density and stone content were discussed.The results showed that the instability mode of a debris slope can be divided into a vibration-compaction stage,a crack generation stage,a crack development stage,and an instability stage.Under the action of frequent microseisms,debris slope undergoes the last three stages cyclically,which causes the accumulation to slide out in layers under the synergistic action of tension and shear,causing the slope to become destabilised.There are two sliding surfaces as well as the parallel tensile surfaces in the final instability of the debris slope.In the process of instability,the development trend of the damage accumulation curve remains similar for debris slopes with different parameters.However,the initial vibration compaction effect in the bedrock-free model is stronger than that in the bedrock model,with the overall cumulative damage degree in the former being lower than that of the latter.The damage degree of the debris slope with high dry density also develops more slowly than that of the debris slope with low dry density.The damage development rate of the debris slope does not always decrease with the increase of stone content.The damage degree growth rate of the debris slope with the optimal stone content is the lowest,and the increase or decrease of the stone content makes the debris slope instability happen earlier.The numerical simulation study also further reveals that the damage in the debris slope mainly develops in the form of crack formation and penetration,in which,shear failure occurs more frequently in the debris slope.
文摘On the basis of the statistical characteristics of fatigue cumulative damageand its critical value, a new dynamic interference model for reliability analysis is presented. Because the nonlinearity of fatigue damage accumulation is taken into account,this model is able to predict the fatigue reliability for random spectrum loadingconveniently. To verify the predicted results, a special fatigue expenment, in which thenumber of specimen is up to 101, is conducted using a fighter spectrum loading. It isshown that the new model is reliable, practicable and better than existing models.
基金The research was funded by the Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration(No.2019A01)the Nation Key R&D Program of China(No.2018YFC1504602)the Heilongjiang Touyan Innovation Team Program.
文摘Frequent aftershocks often follow a strong mainshock.They can significantly increase cumulative damage to a structure.A model of a five-story reinforced concrete frame structure was designed and a nonlinear mathematical model of the structure was developed to investigate the damage states resulting from different mainshock-aftershock sequences.Mainshock-aftershock sequences consisting of one of three recorded mainshocks combined with one of five recorded aftershocks were created for input to the mathematical model.Inelastic energy dissipation and the Park-Ang damage index were used as measures of cumulative damage to the structure.The results demonstrate that consideration of only the single mainshock ground motion in seismic building design can result in the design and construction of unsafe buildings.Total cumulative damage to a structure is caused by the combination of damage states resulting from the mainshock and the aftershock(s).
文摘Fatigue failure of mechanical part is treated as a random event.the fatigue reliablility problem can be solved through researching the random event.A new definition δb that measures fatigue damage quantity in a cycle under cyclic stress is put forward. According to δ.the paper presents two new definitions K and D is fatigue damage strength.D is overall fatigue damage quantity.Using K and D to describe the fatigue failure of the parts,the paper puts forward a new fatigue cumulative damage probabilistic model of the mechanical parts.The model can be used to solve reliability fatigue problem.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50078010).
文摘The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm×100mm×100mm specimens of ordinary strength concrete were tested with constant-or variable-amplitude cyclic compression and lateral confinement pressure in two orthogonal directions. A fatigue equation was gained by modifying the classical Aas-Jakobsen S-N equation and used for taking into account the effect of the confined stress on fatigue strength of plain concrete. The present study indicates that the fatigue failure is greatly influenced by the sequence of applied variable-amplitude fatigue loading, and Miner’s rule is inapplicable to predict the residual fatigue life, especially in the sequence of low to high. The present research also shows that the exponent d of the Corten-Dolan’s damage formula is a constant depending on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. The residual fatigue lives predicted by Corten-Dolan’s damage formula are found to be in good agreement with the results of the experiments.
文摘Aim To study the theory and method for the prediction of service life of solid rocket propellant grain. Methods With the aid of discontiguous diagnostic technology and method of accumulated damage using accelerated aging or heat air oven, the aging isotherms for void content versus aging time were determined. According to the principle of time temperature equivalence the viscoelastic master curve for the prediction of service life were obtained. Results and Conclusion The service life of HMX CMDB solid rocket propellant grain were obtained. Because the critical storage life is measured, the accuracy of predicting the service life of the grain has been increased greatly.
基金The authors gratefully acknowledge the financial supports by the National Natural Science Foundation of China(Grant No.51278203)the Natural Science Fund of Guangdong Province(No.2019A1515011965).
文摘Raveling is a common distress of asphalt pavements,defined as the removal of stones from the pavement surface.To predict and assess raveling quantitatively,a cumulative damage model based on an energy dissipation approach has been developed at the meso level.To construct the model,a new test method,the pendulum impact test,was employed to determine the fracture energy of the stone-mastic-stone meso-unit,while digital image analysis and dynamic shear rheometer test were used to acquire the strain rate of specimens and the rheology property of mastic,respectively.Analysis of the model reveals that when the material properties remain constant,the cumulative damage is directly correlated with loading time,loading amplitude,and loading frequency.Specifically,damage increases with superimposed linear and cosine variations over time.A higher stress amplitude results in a more rapidly increasing rate of damage,while a lower load frequency leads to more severe damage within the same loading time.Moreover,an example of the application of the model has been presented,showing that the model can be utilized to estimate failure life due to raveling.The model is able to offer a theoretical foundation for the design and maintenance of anti-raveling asphalt pavements.
基金supported by the National Natural Science Foundation of China(No.31772079).
文摘Objectives:The aim of this study was to provide a comprehensive understanding of the nonthermal plasma(NTP)-induced inactivated behaviors on a multiple antibiotic-resistant(MAR)Staphylococcus aureus(S.aureus).Materials and Methods:A dielectric barrier discharge(DBD)NTP system was employed for the inactivation of a MAR S.aureus under various applied powers of 35,45,and 55 W,and gas distances of 4,6,and 8 mm.The inactivation kinetics of S.aureus were estimated with linear and nonlinear predictive models.In addition,degradation of carotenoid pigment,peroxidation of fatty acids,oxidation of nucleic acids and proteins,and alteration in gene expression were analyzed after NTP treatment.Results and Discussion:The computationally simulated results indicated that the densities of various reactive species increased with enhanced applied powers and decreased discharge distances.These species were further transformed into reactive oxidative and nitrogen species in the gas-liquid interphase and liquid phase.The oxidative and nitrosative stress of NTP resulted in severe damage to cellular components and the morphological structure of S.aureus.On the other hand,the plasma reactive species could also induce the sublethal injury of S.aureus through upregulating the general stress response,antioxidative and antinitrosative defensive systems.Once the cumulative damages overrode the stress tolerance of S.aureus,the completed cell death was finally achieved by NTP.Conclusions:This work infers the possible risk of inducing the repair and resistant capacity of pathogens when the applied NTP parameters are inappropriate,which helps the optimization of NTP process to achieve sufficient inactivation.
基金supported by the National Natural Science Foundation of China(No.10377007)
文摘Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic loading was proposed. The specimens of aluminum alloy LY12-CZ soaked in corrosive liquid for different times were tested under the constant amplitude cyclic loading to obtain S-N curves. The test was carried out to verify the proposed cumulative fatigue damage rule under the different combinations among corrosion time, loading level, and the cycle numbers. It was shown that the predicted residual fatigue lives showed a good agreement with the experimental results and the proposed rule was simple and can be easily adopted.
基金supported by National Key Research and Development Program of China(No.2023YFC2907600)the National Natural Science Foundation of China(Nos.52074263,52274145 and 52034007)+1 种基金the Postdoctoral Fellowship Program(Grade C)of China Postdoctoral Science Foundation(No.GZC20241925)the Fundamental Research Funds for the Central Universities(No.2024QN11002).
文摘Cyclic impact induces ongoing fatigue damage and performance degradation in anchoring structures,ser-ving as a critical factor leading to the instability of deep roadways.This paper takes the intrinsic spatio-temporal relationship of macro-microscopic cumulative damage in anchoring structures as the main thread,revealing the mechanism of bearing capacity degradation and progressive instability of anchoring structure under cyclic impact.Firstly,a set of impact test devices and methods for the prestressed solid anchor bolt anchoring structure were developed,effectively replicating the cyclic impact stress paths in situ.Secondly,cyclic impact anchoring structure tests and simulations were conducted,which clarifies the damage evolution mechanism of the anchoring structure.Prestress loss follows a cubic decay func-tion as the number of impacts increases.Under the same impact energy and pretension force,the impact resistance cycles of extended anchoring and full-length anchoring were increased by 186.7%and 280%,respectively,compared to end anchoring.The rate of internal damage accumulation is positively corre-lated with impact energy and negatively correlated with anchorage length.Internal tensile cracks account for approximately 85%.Stress transmission follows a fluctuating pattern.Compared to the extended anchoring,the maximum vibration velocity of the exposed end particles in the full-length anchoring was reduced by 59.31%.Damage evolution exhibits a pronounced cumulative mutation effect.Then,a three-media,two-interface mechanical model of the anchoring structure was constructed.It has been clarified that the compressive stress,tensile stress,and oscillation effect arising from rapid transi-tions between compression and tension are the primary internal factors responsible for the degradation of the anchoring structure’s bearing capacity.Finally,the progressive instability mechanism of the anchoring structure under cyclic impact was elucidated.The mutual feedback and superposition of media rupture,interface debonding,and bearing capacity degradation result in overall failure.The failure pro-cess involves stages dominated by oscillation-compression,tensile stress,and compression failure.A tar-geted control strategy was further proposed.This provides a reference for maintaining the long-term stability of deep roadways under dynamic impact loads.
文摘This paper conducts a comparative study on seismic damage to reinforced concrete(RC)bridges,using three damage models:Park and Ang,Hindi and Sexsmith,and input energy-based damage(IEBD)indices,and presents a global cumulative damage model based on the IEBD index to establish a practical damage assessment of an overall bridge system.A series of RC bridges are studied under seismic loadings,and to compare the efficiency and reliability of the damage indices,damage curves of RC piers are developed,and damage levels of piers are calculated at design basis earthquake(DBE)and maximum considered earthquake(MCE)levels.The global cumulative damage index is calculated for bridge models regarding damage values of components.The results indicate that the IEBD index shows a gradual progression of damage and provides reasonable values for different damage levels of piers compared to two other damage indices.Moreover,the global cumulative damage index shows the impact of induced damage to a certain component regarding the damage level of the overall bridge system.Moreover,this new approach is a relatively simple and practical tool for seismic damage assessment of RC bridge systems,which can be implemented in finite element models,particularly in the absence of experimental data.
基金financial support of the International Science and Technology Cooperation Plan of Jiangsu Province,China(No.BZ2020066)the National Natural Science Foundation of China(Nos.52179118,42077240 and 52074269)。
文摘To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tests were conducted for the damaged samples.Besides,coupling modeling technology of finite difference method(FDM)—discrete element method(DEM)was used to carry out the numerical investigation.The results show that after multiple impacts,more white patches appear on the surface,and some microcracks,macro-fractures as well as pulverized grains are found by optical microscopic.The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample.The interaction between grains in the damaged sample becomes intense in the subsequent static loading process,causing a relatively large strain.The volume of the fragments falling off around the loading points becomes larger as impact number increases.As the dynamic damage increases,the absorbed energy of sample during the static loading first decreases and then tends to be stable.Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.
基金The National Natural Science Foundation of China(No. 10801032)
文摘A class of lifetime distributions, new better than equilibrium in expectation （NBEE）, and its dual, new worse than equilibrium in expectation （NWEE）, are studied based on the comparison of the expectations of lifetime X and its equilibrium Xo. The relationships of the NBEE （NWEE） and other lifetime distribution classes are discussed. It is proved that the NBEE is very large, and increasing failure rate （IFR）, new better than used （NBU） and the L class are its subclasses. The closure properties under two kinds of reliability operations, namely, convolution and mixture, are investigated. Furthermore, a Poisson shock model and a special cumulative model are also studied, in which the necessary and sufficient conditions for the NBEE （NWEE） lifetime distribution of the systems are established. In the homogenous Poisson shock model, the system lifetime belongs to NBEE（NWEE） if and only if the corresponding discrete failure distribution belongs to the discrete NBEE（NWEE）. While in the cumulative model, the system has an NBEE lifetime if and only if the stochastic threshold of accumulated damage is NBEE.
基金the Special Research Fund for the Natural Science Foundation of Inner Mongolia Autonomous Region(No.2019MS05070)。
文摘Flange joint part is the weak link of wind turbine tower.In view of the special structure,complex stress and easy failure of the connecting bolt of the wind turbine tower flange,the relationship between the external load of the tower section and the internal stress of the bolt is established by the finite element method,and the time series internal stress of the bolt is calculated by the Schmidt-Neuper algorithm.The S-N curve which is suitable for the connecting bolt material of the tower flange is selected by the GL2010 specification.On the basis of Miner’s fatigue cumulative damage theory and rain flow counting method,the fatigue strength of the whole ring bolt is roughly calculated,and the most dangerous part is determined.The axial symmetry model of screw connection is used for accurately calculating the fatigue cumulative damage of the bolt at the dangerous part.The results show that the fatigue life of the bolts in the most dangerous position can meet the requirements,the engineering algorithm has advantages in determining the dangerous part of the whole ring bolt,and the finite element method has high accuracy in predicting the fatigue life of the bolts in the dangerous part.The proposed method is feasible and effective in predicting the fatigue life of the flange joint bolts of the tower.
基金This paper is financially supported by the National Natural Science Foundation of China(Grant Nos.52074263 and 52034007)the Postgraduate Research and Practice Innovation Program of Jiangsu Province(Grant No.KYCX21_2332).
文摘Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.
文摘The performance degradation rates of the missile tank are generally time-varying functions uneasily evaluated by general classical evaluation methods. This paper develops a segmented nonlinear accelerated degradation model （SNADM） based on the equivalent method of accumulative damage theory, which tackles the problem that product life is difficult to be determined with degradation rate being a function of the variable of time. A segmented expression of the function of population accumulative degradation is derived. And combined with nonlinear function, an accelerated degradation function, i.e., SNADM is obtained. The parameters of the SNADM are identified by numerical iteration, and the statistical function of degradation track is extrapolated. The reliability function is determined through the type of random process of the degradation distribution. Then an evaluation of product storage life is undertaken by combining the statistical function of degradation track, reliability function and threshold. An example of a missile tank undergoes a step-down stress accelerated degradation test （SDSADT）, in which the results with the SNADM and the classical method are evaluated and compared. The technology introduced is validated with the resultant coincidence of both evaluated and field storage lives.
基金Sponsored by the National Basic Research Development Program of China (973 Program)(Grant No. 61379)
文摘To research the approach of predicting composites fatigue life,the cumulative fatigue damage of fiber-reinforced plastic laminates(FRP) was investigated,and based on the complex exponential function,the residual strength model was obtained. This model can accurately describe the propagation of cumulative fatigue damage of FRP in three stages,especially in the initial stage and the ceasing stage. Applying this model in the experiment with two loading cycles,it can be found that the prediction result has good coincidence with experimental data. So a reliable residual strength model can be provided for studying the cumulative fatigue damage of FRP.
