To reveal the influence of coupled effects of dry-wet cycling and precompression stress(CEDWCPS)on the damage evolution of limestone with horizontal fissure(LHF),a series of degradation and uniaxial compression tests ...To reveal the influence of coupled effects of dry-wet cycling and precompression stress(CEDWCPS)on the damage evolution of limestone with horizontal fissure(LHF),a series of degradation and uniaxial compression tests were conducted,and a corresponding piecewise damage constitutive model(PDCM)was established.We found that both dry-wet cycling and precompression stress deteriorate the physical properties,alter the microscopic characteristics,and reduce the mechanical properties of the LHF.These degradations are particularly pronounced under the CEDWCPS,although the magnitude of these changes gradually diminishes with the progression of dry-wet cycling.Meanwhile,they also reduce the deformation degree,prolong the micropore compaction stage,shorten the unstable crack propagation stage,lower the frequency and intensity of AE events,decrease the high-amplitude and high-frequency AE signals,enlarge crack scales,and shorten the crack initiation time.Among the changes of these indicators,the dry-wet cycling plays a dominant role.The crack types of LHF under the CEDWCPS(LHFCEDWCPS)are predominantly tensile cracks,supplemented by shear cracks.The failure mode can be defined as tensileshear composite failure.Finally,the established PDCM effectively captures the nonlinear deformation of micropore and the linear deformation of the matrix in LHFCEDWCPS,with all corresponding R^(2) consistently exceeding 0.97.展开更多
Molecular dynamics simulations were carried out to study the effect of chemical short-range order(CSRO)on the primary radiation damage in TiVTaNb high-entropy alloys(HEAs).We have performed displacement cascade simula...Molecular dynamics simulations were carried out to study the effect of chemical short-range order(CSRO)on the primary radiation damage in TiVTaNb high-entropy alloys(HEAs).We have performed displacement cascade simulations to explore the CSRO effect on the generation and evolution behaviors of irradiation defects.The results demonstrate that CSRO can suppress the formation of Frenkel pairs in TiVTaNb HEAs,with the suppression effect becoming more pronounced as the degree of CSRO increases.CSRO can change the types of interstitial defects generated during cascade collisions.Specifically,as the degree of CSRO increases,the proportion of Ti-related interstitials shows a marked enhancement,primarily evidenced by a significant rise in Ti–Ti dumbbells accompanied by a corresponding decrease in Ti–V dumbbells.CSRO exhibits negligible influence on defect clustering and the nucleation and evolution of dislocation loops.Regardless of CSRO conditions,TiVTaNb HEAs preserve exceptional radiation tolerance throughout the cascade damage process,suggesting that the intrinsic properties of this multi-principal element system dominate its radiation response.These findings provide fundamental insights into the CSRO effect on defect formation and evolution behaviors in HEAs,which may provide new design strategies for high-entropy alloys.展开更多
Refractory high-entropy alloys(RHEAs)are promising for high-temperature applications due to their ex-ceptional mechanical properties at high temperatures.However,limited studies on their high-temperature fatigue behav...Refractory high-entropy alloys(RHEAs)are promising for high-temperature applications due to their ex-ceptional mechanical properties at high temperatures.However,limited studies on their high-temperature fatigue behavior hinder further development.This study systematically investigates the low-cycle fatigue(LCF)behavior of HfNbTiZr RHEA at room temperature(25℃)and elevated temperatures(350,450,and 600℃)through a combination of experimental analyses and dislocation-based damage-coupled crystal plasticity finite element(CPFE)simulations,to unveil the effects of creep damage on LCF behavior at varying temperatures.The results indicate that the LCF life dramatically decreases at an increased tem-perature,shifting from transgranular fatigue damage at lower temperatures(25-350℃)to a dual damage mechanism involving both intergranular fatigue and creep damage at higher temperatures(450-600℃).At 600℃,creep damage notably contributes to the accumulation of geometrically necessary dislocations(GNDs),crack initiation,and propagation at grain boundaries,and thus accelerates LCF failure.Compara-tive CPFE simulations reveal that creep damage significantly contributes to cyclic softening and reduction in elastic modulus,which also amplifies the strain localization under the LCF loading.The contribution of creep damage to the total stored energy density(SED)representing the overall damage increases with temperatures,accounting for 11%at 600℃.Additionally,CPFE simulations indicate that the creep dam-age notably influences the magnitude of GND density localized at grain boundaries.This study provides critical insights into the fatigue damage mechanisms of RHEAs,offering valuable guidance for their ap-plication in high temperatures.展开更多
Irradiation experiments on p-Ga N gate high-electron-mobility transistors(HEMTs) were conducted using neutrons at Back-streaming White Neutron(Back-n) facility at the China Spallation Neutron Source(CSNS).Two groups o...Irradiation experiments on p-Ga N gate high-electron-mobility transistors(HEMTs) were conducted using neutrons at Back-streaming White Neutron(Back-n) facility at the China Spallation Neutron Source(CSNS).Two groups of devices were float-biased,while one group was ON-biased.Post-irradiation analysis revealed that the electrical performance of the devices exhibited progressive degradation with increasing Back-n fluence,with the ON-biased group demonstrating the most pronounced deterioration.This degradation was primarily characterized by a negative shift in the threshold voltage,a significant increase in reverse gate leakage current,and a slight reduction in forward gate leakage.Further analysis of the gate leakage current and capacitance-voltage characteristics indicated an elevated concentration of two-dimensional electron gas(2DEG),attributed to donor-type defects introduced within the barrier layer by Back-n irradiation.These defects act as hole traps,converting into fixed positive charges that deepen the quantum-well conduction band,thereby enhancing the 2DEG density.Additionally,through the trap-assisted tunneling mechanism,these defects serve as tunneling centers,increasing the probability of electron tunneling and consequently elevating the reverse gate leakage current.展开更多
The emergence of laser technology has led to the gradual integration of laser weapon system(LaWS)into military scene,particularly in the field of anti-unmanned aerial vehicle(UAV),showcasing significant potential.Howe...The emergence of laser technology has led to the gradual integration of laser weapon system(LaWS)into military scene,particularly in the field of anti-unmanned aerial vehicle(UAV),showcasing significant potential.However,A current limitation lies in the absence of a comprehensive quantitative approach to assess the capabilities of LaWS.To address this issue,a damage effectiveness characterization model for LaWS is established,taking into account the properties of laser transmission through the atmosphere and the thermal damage effects.By employing this model,key parameters pertaining to the effectiveness of laser damage are determined.The impact of various spatial positions and atmospheric conditions on the damage effectiveness of LaWS have been examined,employing simulation experiments with diverse parameters.The conclusions indicate that the damage effectiveness of LaWS is contingent upon the spatial position of the target,resulting in a diminished effectiveness to damage on distant,low-altitude targets.Additionally,the damage effectiveness of LaWS is heavily reliant on the atmospheric condition,particularly in complex settings such as midday and low visibility conditions,where the damage effectiveness is substantially reduced.This paper provides an accurate and effective calculation method for the rapid decisionmaking of the operators.展开更多
This study examined the repeated bout effect(RBE)on muscle damage markers following two bouts of neuromuscular electrical stimulation(NMES)in untrained individuals.Following familiarization,participants received 45 co...This study examined the repeated bout effect(RBE)on muscle damage markers following two bouts of neuromuscular electrical stimulation(NMES)in untrained individuals.Following familiarization,participants received 45 consecutive NMES to the biceps brachii at an intensity that produced low evoked force for the elbow flexors.Muscle damage markers(maximal voluntary isometric contraction[MVIC],elbow range of motion[ROM],muscle soreness via visual analogue scale[VAS]scores,pressure pain threshold[PPT],and muscle thickness)were measured before(PRE),after(POST),1 day after(24 POST),and 2 days after(48 POST)NMES.Following 1 week of rest,procedures were replicated.Separate repeated measures two-way ANOVAs examined each measure.There were no interactions or bout main effects for MVIC or ROM.Time main effects indicated PRE MVIC was greater than POST(p=0.002)and 24-POST(p=0.024),and PRE ROM was greater than POST(p=0.036).There was no interaction for muscle thickness.Respective time and bout main effects indicated muscle thickness at PRE was less than POST(p=0.017),and second-bout muscle thickness(p=0.050)was less compared to the initial-bout.For PPT,there was an interaction(p=0.019).Initial-bout PRE PPT was less than POST(p=0.033).Initial-bout 48-POST PPT was less than second-bout 48-POST(p=0.037).There was a significant interaction for VAS(p=0.009).Initial-bout PRE VAS was less than POST(p=0.033)and 24-POST(p=0.015).Initial-bout POST and 24-POST VAS were greater than second-bout POST(p=0.023)and 24-POST(p=0.006),respectively.The results support RBE on muscle damage markers related to inflammation,but not MVIC and ROM.展开更多
Rock is exposed to the combined effects of the confining pressure and strain rate during the dynamic excavation process in deeply buried high-stress tunnels.Therefore,a constitutive model that considers both the strai...Rock is exposed to the combined effects of the confining pressure and strain rate during the dynamic excavation process in deeply buried high-stress tunnels.Therefore,a constitutive model that considers both the strain rate and the confining pressure effect plays a crucial role in evaluating the disturbance and stability of deeply buried tunnels.Taking mudstone as an example,a series of tests were performed to reveal the combined effect of the strain rate and confining pressure on the mechanical behavior of soft rock,and a novel statistical damage constitutive model was proposed.The confining pressures of 0 MPa,10 MPa,20 MPa,and 30 MPa and strain rates of 10^(-5)s^(-1),10^(-4)s^(-1),10^(-3)s^(-1),and 10^(-2)s^(-1)were investigated.The results show that the rock strength increases with increasing confining pressure and strain rate,and that the contributions of these two factors can be considered independent of each other.However,an increase in the confining pressure reduces the degree of rock damage and increases the ductility of the sample at failure,whereas the strain rate has the opposite effect.Finally,a full deformation process damage model considering strain rate effect is established based on a modified Hoek‒Brown strength criterion considering the strain rate.The model can capture the nonlinear increase in strength and elastic modulus with increasing confining pressure and strain rate,reproducing the brittle‒ductile transition characteristics and the full deformation process.展开更多
The study of the mechanical property and damage state of coal materials under compression is a fundamental area of research in underground mining engineering.Drawing upon the compaction effect and linear energy dissip...The study of the mechanical property and damage state of coal materials under compression is a fundamental area of research in underground mining engineering.Drawing upon the compaction effect and linear energy dissipation(LED)law,a novel compressive damage constitutive model for brittle coal is proposed.Utilizing the energy-defined damage method for mate-rials,the LED law is innovatively introduced to accurately characterize the energy dissipation during the loading process,and a novel formula for characterizing the damage variable of brittle coal is proposed.On this basis,considering that the constitutive model based on the hypothesis of strain equivalence is incapable of accurately describing the compaction effect exhibited by coal material during the compression process,a correction coefficient is proposed and apply it in the novel damage constitutive model.The established conventional monotone loading and single-cyclic loading-unloading uniaxial compression damage constitutive models have been validated using experimental data from cylindrical and cuboid coal specimens.In addition,compared with the constitutive model obtained via the traditional energy calculation method based on the hypothesis that the unloading curve is a straight line,the constitutive model employing LED law can describe the stress-strain state of brittle coal more precisely.This approach introduces a new perspective and enhances the convenience for constructing the constitutive model based on energy theory.展开更多
Understanding how thermal damage accumulates in granites under cyclic thermal loading is crucial for geoengineering design and stability assessment.Two types of granite with different grain sizes were subjected to mul...Understanding how thermal damage accumulates in granites under cyclic thermal loading is crucial for geoengineering design and stability assessment.Two types of granite with different grain sizes were subjected to multiple heating and cooling cycles at identical or increasing target temperatures using a new apparatus.Acoustic emission(AE)and thermal deformation were monitored simultaneously.Ultrasonic velocity,porosity,and permeability measurements,compression tests,and thin-section petrography were conducted to assess the thermal damage and physical and mechanical properties of the treated specimens.The results indicate that the thermal damage progression exhibits cycle-dependent decay at 300℃,and the thermal deformation tends to be elastic.However,the uniaxial compressive strength(UCS)increases after thermal treatment,though the increment decreases with progressive cycles(from 21%to 4%for coarse-grained granite).Progressive temperature cycling induces cumulative damage amplification,manifested by tremendous thermal cracking(the total number of AE hits reaches-170 and 180 times that of the first cycle)and crack density escalation(the crack density reaches-1.6 and 2 times that of the first cycle).AE results reveal that there is a temperature-memory effect in both rock types,and show that thermal stresses are insufficient to generate new thermal damage until the prior exposed temperature is exceeded.Additionally,thermal damage is related to the microstructure of rock:coarse-grained granite with more pre-existing cracks exhibits heating-dominated damage(e.g.94%of the AE energy was generated during heating at 300℃),while fine-grained granite with less inherent damage is more sensitive to cooling(e.g.71%of the AE energy was generated during cooling).Quantitative relationship among P-wave velocity,Young's modulus,and linear crack density provide a good estimation of thermal damage,and can guide assessments of the durability of underground engineering.展开更多
Nuclear DNA, which is essential for the transmission of genetic information, is constantly damaged by external stresses and is subsequently repaired by the removal of the damaged region, followed by resynthesis of the...Nuclear DNA, which is essential for the transmission of genetic information, is constantly damaged by external stresses and is subsequently repaired by the removal of the damaged region, followed by resynthesis of the excised region. Accumulation of DNA damage with failure of repair processes leads to fatal diseases such as cancer. Recent studies have suggested that intra- and extra-nuclear environments play essential roles in DNA damage. However, numerous questions regarding the role of the nuclear mechanical environment in DNA damage remain unanswered. In this study, we investigated the effects of cell confluency (cell crowding) on the morphology of cell nuclei, and cytoskeletal structures, and DNA damage in NIH3T3 skin fibroblasts and HeLa cervical cancer cells. Although nuclear downsizing was observed in both NIH3T3 and HeLa cells with cell crowding, intracellular mechanical changes in the two cell types displayed opposite tendencies. Cell crowding in NIH3T3 cells induced reinforcement of actin filament structures, cell stiffening, and nuclear downsizing, resulting in a significant decrease in endogenous DNA damage, whereas cell crowding in HeLa cells caused partial depolymerization of actin filaments and cell softening, inducing endogenous DNA damage. Ultraviolet (UV) radiation significantly increased DNA damage in NIH3T3;however, this response did not change with cell crowding. In contrast, UV radiation did not cause DNA damage in HeLa cells under either sparse or confluent conditions. These results suggested that cell crowding significantly influenced endogenous DNA damage in cells and was quite different in NIH3T3 and HeLa cells. However, cell crowding did not affect the UV-induced DNA damage in either cell type.展开更多
A Combined Cycle Fatigue(CCF)life prediction model considering the effect of load sequence was proposed.To account for the interaction of high and low cycle fatigue,the CCF load was divided into two different loading ...A Combined Cycle Fatigue(CCF)life prediction model considering the effect of load sequence was proposed.To account for the interaction of high and low cycle fatigue,the CCF load was divided into two different loading paths of variable stress amplitude and stress ratio.Based on the iso-damage curves,a CCF life prediction model independent of fitting parameters was proposed,agreeing well with the experimental results.Finally,the effect of load sequence on CCF was discussed according to the fracture morphology of designed blade-like specimen.The results showed that the predicted CCF life was almost located in three-fold dispersion band for the LCF-HCF(LH)and HCF-LCF(HL)loading paths,especially for the average results of both.Compared with other models,the proposed model had better predictive and generalization abilities for multiple materials and variable experimental conditions.展开更多
Aiming at addressing the issues of unclear dynamic response mechanisms and insufficient quantification of temperature coupling effects in building structures under long-duration blast loads,this study investigates typ...Aiming at addressing the issues of unclear dynamic response mechanisms and insufficient quantification of temperature coupling effects in building structures under long-duration blast loads,this study investigates typical composite beam-slab structures through integrated blast shock tube experiments and multiscale numerical simulations using Voronoi-coupled Finite-Discrete Element Method(VoroFDEM).The research systematically reveals the dynamic response mechanisms and damage evolution patterns of composite beam-slab structures subjected to prolonged blast loading.An environmenttemperature-coupled P-I curve damage assessment system is established,and a rapid evaluation method based on image crack characteristics is proposed,achieving innovative transition from traditional mechanical indicators to intelligent recognition paradigms.Results demonstrate that composite beam-slab structures exhibit three-phase failure modes:elastic vibration,plastic hinge formation,and global collapse.Numerical simulations identify the brittle-to-ductile transition temperature threshold at-10℃,and establish a temperature-dependent piecewise function-based P-I curve prediction model,whose overpressure asymptote displays nonlinear temperature sensitivity within-50-30℃.A novel dual-mode evaluation methodology integrating Voro-FDEM numerical simulations with image-based damage feature recognition is developed,enabling quantitative mapping between crack area and destruction levels.These findings provide theoretical foundations and technical pathways for rapid blast damage assessment and protective engineering design.展开更多
The low porosity and low permeability of shale remain the primary challenges in shale gas exploitation.Traditional single permeability enhancement techniques have shown limited efficacy,failing to effectively address ...The low porosity and low permeability of shale remain the primary challenges in shale gas exploitation.Traditional single permeability enhancement techniques have shown limited efficacy,failing to effectively address these technical bottlenecks.This study investigates the synergistic effects of perforationinduced permeability enhancement and acidizing operations on the mechanical properties and micropore structure of shale.The improved Split Hopkinson Pressure Bar(SHPB)technique was employed to simulate dynamic impact damage under triaxial stress conditions.Damaged and undamaged rock specimens were immersed in a 15%hydrochloric acid solution to fabricate combined-damage specimens and acid-etched specimens with varying damage states.Uniaxial compression tests,X-ray diffraction(XRD)analysis,and scanning electron microscopy(SEM)were conducted on these specimens.SEM images were binarized,and combined with low-temperature nitrogen adsorption tests,the effects of different damage states on the mechanical behavior,energy dissipation,micro-morphology,and pore characteristics of shale were systematically evaluated.Results demonstrate that the peak stress and elastic modulus of shale exhibit a negative correlation with acid-etching duration.The mechanical properties of combined-damage specimens are inferior to those of pure acid-etched specimens,with the minimum peak stress reaching 147.10 MPa—a 43.53%reduction compared to untreated specimens.The energy dissipation ratio significantly increases,with a maximum value of 34.74%.XRD analysis reveals that prolonged acid immersion effectively reduces the carbonate content in specimens,while composite treatment accelerates the reaction between rock matrix and acid solution.Microstructural characterization indicates that acid etching enhances the porosity of shale,particularly the area of mesopores and macropores,with more pronounced pore development and a fragmented interface structure.These findings deepen the understanding of physical mechanisms during shale gas extraction and provide critical theoretical support for optimizing integrated permeability enhancement technologies.展开更多
AIM:To investigate the effects of adenosine triphosphate(ATP)and melatonin,which have antioxidant and antiinflammatory activities,on potential 5-fluorouracil(5-FU)-induced optic nerve damage in rats.METHODS:Twenty-fou...AIM:To investigate the effects of adenosine triphosphate(ATP)and melatonin,which have antioxidant and antiinflammatory activities,on potential 5-fluorouracil(5-FU)-induced optic nerve damage in rats.METHODS:Twenty-four rats were categorized into four groups of six rats:healthy(HG),5-FU(FUG),ATP+5-FU(AFU),and melatonin+5-FU(MFU).ATP(4 mg/kg)and melatonin(10 mg/kg)were administered intraperitoneally and orally,respectively.One hour after ATP and melatonin administration,rats in the AFU,MFU,and FUG were intraperitoneally injected with 5-FU(100 mg/kg).ATP and melatonin were administered once daily for 10d.5-FU was administered at a single dose on days 1,3,and 5 of the experiment.After 10d,the rats were euthanized and optic nerve tissues were extracted.Optic nerve tissues were biochemically and histopathologically examined.RESULTS:ATP and melatonin treatments inhibited the increase in malondialdehyde(MDA)and interleukin-6(IL-6)levels,which were elevated in the FUG.The treatments also prevented the decrease in total glutathione(tGSH)levels and the superoxide dismutase(SOD)and catalase(CAT)activities(P<0.001).This inhibition was higher in the ATP group than in the melatonin group(P<0.001).ATP prevented histopathological damage better than melatonin(P<0.05).CONCLUSION:ATP and melatonin have the potential to be used in alleviating 5-FU-induced optic nerve damage.In addition,ATP treatment shows better protective effects than melatonin.展开更多
Investigation techniques,such as uniaxial compression tests,acoustic emission,digital image correlation monitoring,and scanning electron microscopy,were used from macroscopic and microscopic perspectives to investigat...Investigation techniques,such as uniaxial compression tests,acoustic emission,digital image correlation monitoring,and scanning electron microscopy,were used from macroscopic and microscopic perspectives to investigate the effects of gangue particle-size gradation on the damage characteristics of cemented backfill.The peak strength,acoustic emission characteristics,and failure modes of cemented backfills with different gangue size gradations were examined.Test results indicated that with an increase in the gradation coefficient,the compressive strength of the gangue-cemented backfill first increased and then decreased.When the gradation coefficient is 0.5,the maximum compressive strength of the backfill is 4.28 MPa.The acoustic emission counts during the loading of gangue-cemented fills with different gradation coefficients passed through three phases:rising,active,and significantly active.The number of internal pores and cracks,as well as the uneven distribution of their locations,cause differences in acoustic emission characteristics at the same stage and variations in the strength of the backfill due to the different gangue particle-size gradations in the filler sample.展开更多
As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stabilit...As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications.Based on the pre-peak and post-peak stages of the rock stress-strain curve,this study constructed a brittleness index BI^(*).The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage.Another index,BII,was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy.This index reflects the essential properties of rock failure by revealing the energy evolution mechanism.Furthermore,by defining a damage variable from the energy dissipation over the entire deformation process,an index B_(D)was introduced to evaluate brittleness from the perspective of internal damage development.Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index.The influences of confining pressure and lithology on rock brittleness were analyzed,along with the sensitivity analysis of various brittleness index parameters.The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures.Meanwhile,different brittleness indices were affected by confining pressure and lithology to different degrees.The post-peak softening stage of rock played a particularly significant role in brittleness analysis.A brittleness classification system under different confining pressures and lithologies was established.The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.展开更多
Reinforced concrete buildings may experience partial damage after earthquakes or some human-induced actions.A decision about the future of those buildings requires detailed analyses,while determining the dynamic chara...Reinforced concrete buildings may experience partial damage after earthquakes or some human-induced actions.A decision about the future of those buildings requires detailed analyses,while determining the dynamic characteristics of a real building in its pre-and post-event situations can guide the analysis.Hence,this study was planned to monitor the dynamic response of an existing six-story,reinforced concrete building with regard to structural damage.The modal characteristics of the original building were initially determined by the use of operational modal analysis.Next,three steps of progressive structural damage were applied to the building.The first damage level peeled off the clear cover of a beam and three columns on a corner of the building’s ground floor.whereas the second and third levels completely razed the damaged columns.Operational modal analysis was repeated at each damage stage to extract the frequencies and detailed mode shapes.Moreover,numerical models based on the finite element method were constructed to confirm the obtained experimental findings.The well-agreed experimental and numerical findings revealed the damage sensitivity of the building’s dynamic response.The quantified amount of frequency change favored a retrofit of the partially damaged buildings rather than their replacement.展开更多
Thermomechanical Fatigue (TMF) is one of the most dangerous failure modes of high-temperature structures. The effect of coarsened and rafted microstructures on the TMF behavior of Nickel-Base Single Crystal Superalloy...Thermomechanical Fatigue (TMF) is one of the most dangerous failure modes of high-temperature structures. The effect of coarsened and rafted microstructures on the TMF behavior of Nickel-Base Single Crystal Superalloys (NBSX) was experimentally studied. TMF tests under In-Phase (IP) and Out-of-Phase (OP) paths revealed significant variations in TMF life reduction. Cyclic deformation behaviors of alloys with different microstructures were compared. The effect of microstructure on TMF damage mechanisms was unveiled from characterizations of fracture surfaces and longitudinal sections by scanning electronic microscope and optical microscope. A transition from mode-I to crystallographic fracture in the coarsened alloy during IP-TMF was observed and discussed. Due to the degraded microstructure, the dispersed distribution of crystal slips was distinguished in the coarsened and rafted alloys. The competitive or synergetic interactions among oxidation-assisted mode-I opening, casting pore-related mode-I creep and crystallographic slipping were discussed. This study underscores the complex interplay among microstructure, deformation behaviors and damage mechanisms, offering valuable insights into alloy performance under TMF conditions.展开更多
The service life of refractory brick in the slag tapping hole of gasifiers is a significant concern for long-term and stable operation.This study examined the damage mechanism of high chromia refractory of four commer...The service life of refractory brick in the slag tapping hole of gasifiers is a significant concern for long-term and stable operation.This study examined the damage mechanism of high chromia refractory of four commercial coal-water slurry gasifiers with their corresponding gasification coal samples and the corroded refractory bricks in the slag tapping hole of the gasifier.The slag characteristic,including crystallization and viscosity-temperature of four gasification coal samples were analyzed.The results revealed that the low viscosity slag could lead to more severe damage to refractory bricks.Given the risk of slag crystallization,it is recommended to establish a safe slag tapping temperature range should be set as tICT(initial crystallization temperature)−t_(2.5) when tICT is higher than t_(25).Upon examining interior morphology of these corroded refractory bricks,some cracks were observed within them.The chemical composition of molten slag was analyzed using SEM-EDS.However,XRD results found no spinel containing zirconium in these cracks.This suggests that the emergence of these cracks are mainly attributed to the molten slag penetration and the subsequent reaction with the refractory material.The difference in thermal expansion between the newly formed substances and refractory material is critical in forming these cracks.Furthermore,SEM-EDS analysis was also conducted on the slag-aggregate and the slag-matrix interface.The results reveal that the reduction in Cr_(2)O_(3) content is the earliest characteristic of damage in high chromia refractories.A proposed damage mechanism of refractory brick suggests that the matrix and aggregate of high chromia refractory are initially compromised because of the reduced Cr_(2)O_(3) content.Subsequently,the molten slag penetrates the interior of the refractory brick,forming new substances,leading to damage caused by the difference in thermal expansion between the new substances and the refractory brick.Understanding and preventing the reduction of Cr_(2)O_(3) content is vital to prolonging the service life of refractory brick in the slag tapping hole of the gasifier based on this damage mechanism.展开更多
Prolonged cyclic water intrusion has progressively developed joints in the hydro-fluctuation belt,elevating the instability risk of reservoir bank slopes.To investigate its impact on joint shear damage evolution,joint...Prolonged cyclic water intrusion has progressively developed joints in the hydro-fluctuation belt,elevating the instability risk of reservoir bank slopes.To investigate its impact on joint shear damage evolution,joint samples were prepared using three representative roughness curves and subjected to direct shear testing following cyclic water intrusion.A shear damage constitutive model considering the coupling effect of cyclic water intrusion and load was developed based on macroscopic phenomenological damage mechanics and micro-statistical theory.Results indicate:(1)All critical shear mechanical parameters(including peak shear strength,shear stiffness,basic friction angle,and joint compressive strength)exhibit progressive deterioration with increasing water intrusion cycles;(2)Model validation through experimental curve comparisons confirms its reliability.The model demonstrates that intensified water intrusion cycles reduce key mechanical indices,inducing a brittle-to-ductile transition in joint surface deformation—a behavior consistent with experimental observations;(3)Damage under cyclic water intrusion and load coupling follows an S-shaped trend,divided into stabilization(water-dominated stage),development(load-dominated stage),and completion stages.The research provides valuable insights for stability studies,such as similar model experiments for reservoir bank slopes and other water-related projects.展开更多
基金supported by the Yunnan Province Science and Technology Plan Project(No.202403AA080001-4)the Key Research and Development Project of Guangxi,China(No.guikeAB24010144)the National Key Research and Development Project of China(Nos.2021YFB3901402 and 2018YFC1504802)。
文摘To reveal the influence of coupled effects of dry-wet cycling and precompression stress(CEDWCPS)on the damage evolution of limestone with horizontal fissure(LHF),a series of degradation and uniaxial compression tests were conducted,and a corresponding piecewise damage constitutive model(PDCM)was established.We found that both dry-wet cycling and precompression stress deteriorate the physical properties,alter the microscopic characteristics,and reduce the mechanical properties of the LHF.These degradations are particularly pronounced under the CEDWCPS,although the magnitude of these changes gradually diminishes with the progression of dry-wet cycling.Meanwhile,they also reduce the deformation degree,prolong the micropore compaction stage,shorten the unstable crack propagation stage,lower the frequency and intensity of AE events,decrease the high-amplitude and high-frequency AE signals,enlarge crack scales,and shorten the crack initiation time.Among the changes of these indicators,the dry-wet cycling plays a dominant role.The crack types of LHF under the CEDWCPS(LHFCEDWCPS)are predominantly tensile cracks,supplemented by shear cracks.The failure mode can be defined as tensileshear composite failure.Finally,the established PDCM effectively captures the nonlinear deformation of micropore and the linear deformation of the matrix in LHFCEDWCPS,with all corresponding R^(2) consistently exceeding 0.97.
基金Project supported by the Youth Program of the National Natural Science Foundation of China(Grant No.12405324)the CNNC Science Fund for Talented Young Scholars(Grant No.24940)the CNNC Basic Science Fund(Grant No.24851)。
文摘Molecular dynamics simulations were carried out to study the effect of chemical short-range order(CSRO)on the primary radiation damage in TiVTaNb high-entropy alloys(HEAs).We have performed displacement cascade simulations to explore the CSRO effect on the generation and evolution behaviors of irradiation defects.The results demonstrate that CSRO can suppress the formation of Frenkel pairs in TiVTaNb HEAs,with the suppression effect becoming more pronounced as the degree of CSRO increases.CSRO can change the types of interstitial defects generated during cascade collisions.Specifically,as the degree of CSRO increases,the proportion of Ti-related interstitials shows a marked enhancement,primarily evidenced by a significant rise in Ti–Ti dumbbells accompanied by a corresponding decrease in Ti–V dumbbells.CSRO exhibits negligible influence on defect clustering and the nucleation and evolution of dislocation loops.Regardless of CSRO conditions,TiVTaNb HEAs preserve exceptional radiation tolerance throughout the cascade damage process,suggesting that the intrinsic properties of this multi-principal element system dominate its radiation response.These findings provide fundamental insights into the CSRO effect on defect formation and evolution behaviors in HEAs,which may provide new design strategies for high-entropy alloys.
基金National Science Foundation of China(Nos.52401212 and52401214)the National Science Foundation of Jiangsu Province(No.BK20241020)+1 种基金the Avi-ation Foundation(No.2023Z0530S6004)the Jiangsu Province University Collaborative Innovation Centre(High-Tech Ships)Pro-gram(No.XTCX202401).
文摘Refractory high-entropy alloys(RHEAs)are promising for high-temperature applications due to their ex-ceptional mechanical properties at high temperatures.However,limited studies on their high-temperature fatigue behavior hinder further development.This study systematically investigates the low-cycle fatigue(LCF)behavior of HfNbTiZr RHEA at room temperature(25℃)and elevated temperatures(350,450,and 600℃)through a combination of experimental analyses and dislocation-based damage-coupled crystal plasticity finite element(CPFE)simulations,to unveil the effects of creep damage on LCF behavior at varying temperatures.The results indicate that the LCF life dramatically decreases at an increased tem-perature,shifting from transgranular fatigue damage at lower temperatures(25-350℃)to a dual damage mechanism involving both intergranular fatigue and creep damage at higher temperatures(450-600℃).At 600℃,creep damage notably contributes to the accumulation of geometrically necessary dislocations(GNDs),crack initiation,and propagation at grain boundaries,and thus accelerates LCF failure.Compara-tive CPFE simulations reveal that creep damage significantly contributes to cyclic softening and reduction in elastic modulus,which also amplifies the strain localization under the LCF loading.The contribution of creep damage to the total stored energy density(SED)representing the overall damage increases with temperatures,accounting for 11%at 600℃.Additionally,CPFE simulations indicate that the creep dam-age notably influences the magnitude of GND density localized at grain boundaries.This study provides critical insights into the fatigue damage mechanisms of RHEAs,offering valuable guidance for their ap-plication in high temperatures.
基金supported by the National Natural Science Foundation of China (Grant Nos.12120101005,U2030104,12175174,11975174,and 12105229)State Key Laboratory Foundation of Laser Interaction with Matter (Grant Nos.SKLLIM1807 and SKLLIM2106)+1 种基金the Postdoctoral Fellowship Program of CPSF (Grant No.GZC20241372)National Key Laboratory of Intense Pulsed Radiation Simulation and Effect (Grant No.NKLIPR2419)。
文摘Irradiation experiments on p-Ga N gate high-electron-mobility transistors(HEMTs) were conducted using neutrons at Back-streaming White Neutron(Back-n) facility at the China Spallation Neutron Source(CSNS).Two groups of devices were float-biased,while one group was ON-biased.Post-irradiation analysis revealed that the electrical performance of the devices exhibited progressive degradation with increasing Back-n fluence,with the ON-biased group demonstrating the most pronounced deterioration.This degradation was primarily characterized by a negative shift in the threshold voltage,a significant increase in reverse gate leakage current,and a slight reduction in forward gate leakage.Further analysis of the gate leakage current and capacitance-voltage characteristics indicated an elevated concentration of two-dimensional electron gas(2DEG),attributed to donor-type defects introduced within the barrier layer by Back-n irradiation.These defects act as hole traps,converting into fixed positive charges that deepen the quantum-well conduction band,thereby enhancing the 2DEG density.Additionally,through the trap-assisted tunneling mechanism,these defects serve as tunneling centers,increasing the probability of electron tunneling and consequently elevating the reverse gate leakage current.
基金supported by the National Social Science Foundation of China(2022-SKJJ-C-037)the National Natural Science Foundation of China General Program(72071209).
文摘The emergence of laser technology has led to the gradual integration of laser weapon system(LaWS)into military scene,particularly in the field of anti-unmanned aerial vehicle(UAV),showcasing significant potential.However,A current limitation lies in the absence of a comprehensive quantitative approach to assess the capabilities of LaWS.To address this issue,a damage effectiveness characterization model for LaWS is established,taking into account the properties of laser transmission through the atmosphere and the thermal damage effects.By employing this model,key parameters pertaining to the effectiveness of laser damage are determined.The impact of various spatial positions and atmospheric conditions on the damage effectiveness of LaWS have been examined,employing simulation experiments with diverse parameters.The conclusions indicate that the damage effectiveness of LaWS is contingent upon the spatial position of the target,resulting in a diminished effectiveness to damage on distant,low-altitude targets.Additionally,the damage effectiveness of LaWS is heavily reliant on the atmospheric condition,particularly in complex settings such as midday and low visibility conditions,where the damage effectiveness is substantially reduced.This paper provides an accurate and effective calculation method for the rapid decisionmaking of the operators.
文摘This study examined the repeated bout effect(RBE)on muscle damage markers following two bouts of neuromuscular electrical stimulation(NMES)in untrained individuals.Following familiarization,participants received 45 consecutive NMES to the biceps brachii at an intensity that produced low evoked force for the elbow flexors.Muscle damage markers(maximal voluntary isometric contraction[MVIC],elbow range of motion[ROM],muscle soreness via visual analogue scale[VAS]scores,pressure pain threshold[PPT],and muscle thickness)were measured before(PRE),after(POST),1 day after(24 POST),and 2 days after(48 POST)NMES.Following 1 week of rest,procedures were replicated.Separate repeated measures two-way ANOVAs examined each measure.There were no interactions or bout main effects for MVIC or ROM.Time main effects indicated PRE MVIC was greater than POST(p=0.002)and 24-POST(p=0.024),and PRE ROM was greater than POST(p=0.036).There was no interaction for muscle thickness.Respective time and bout main effects indicated muscle thickness at PRE was less than POST(p=0.017),and second-bout muscle thickness(p=0.050)was less compared to the initial-bout.For PPT,there was an interaction(p=0.019).Initial-bout PRE PPT was less than POST(p=0.033).Initial-bout 48-POST PPT was less than second-bout 48-POST(p=0.037).There was a significant interaction for VAS(p=0.009).Initial-bout PRE VAS was less than POST(p=0.033)and 24-POST(p=0.015).Initial-bout POST and 24-POST VAS were greater than second-bout POST(p=0.023)and 24-POST(p=0.006),respectively.The results support RBE on muscle damage markers related to inflammation,but not MVIC and ROM.
基金financed by the Key Technology R&D Plan of Yunnan Provincial Department of Science and Technology(Grant No.202303AA080003)the Shanghai Rising-Star Program(Grant No.23QB1404800).
文摘Rock is exposed to the combined effects of the confining pressure and strain rate during the dynamic excavation process in deeply buried high-stress tunnels.Therefore,a constitutive model that considers both the strain rate and the confining pressure effect plays a crucial role in evaluating the disturbance and stability of deeply buried tunnels.Taking mudstone as an example,a series of tests were performed to reveal the combined effect of the strain rate and confining pressure on the mechanical behavior of soft rock,and a novel statistical damage constitutive model was proposed.The confining pressures of 0 MPa,10 MPa,20 MPa,and 30 MPa and strain rates of 10^(-5)s^(-1),10^(-4)s^(-1),10^(-3)s^(-1),and 10^(-2)s^(-1)were investigated.The results show that the rock strength increases with increasing confining pressure and strain rate,and that the contributions of these two factors can be considered independent of each other.However,an increase in the confining pressure reduces the degree of rock damage and increases the ductility of the sample at failure,whereas the strain rate has the opposite effect.Finally,a full deformation process damage model considering strain rate effect is established based on a modified Hoek‒Brown strength criterion considering the strain rate.The model can capture the nonlinear increase in strength and elastic modulus with increasing confining pressure and strain rate,reproducing the brittle‒ductile transition characteristics and the full deformation process.
基金supported by the National Science Fund for Distinguished Young Scholars(52225403)the National Natural Science Foundation of China(42077244).
文摘The study of the mechanical property and damage state of coal materials under compression is a fundamental area of research in underground mining engineering.Drawing upon the compaction effect and linear energy dissipation(LED)law,a novel compressive damage constitutive model for brittle coal is proposed.Utilizing the energy-defined damage method for mate-rials,the LED law is innovatively introduced to accurately characterize the energy dissipation during the loading process,and a novel formula for characterizing the damage variable of brittle coal is proposed.On this basis,considering that the constitutive model based on the hypothesis of strain equivalence is incapable of accurately describing the compaction effect exhibited by coal material during the compression process,a correction coefficient is proposed and apply it in the novel damage constitutive model.The established conventional monotone loading and single-cyclic loading-unloading uniaxial compression damage constitutive models have been validated using experimental data from cylindrical and cuboid coal specimens.In addition,compared with the constitutive model obtained via the traditional energy calculation method based on the hypothesis that the unloading curve is a straight line,the constitutive model employing LED law can describe the stress-strain state of brittle coal more precisely.This approach introduces a new perspective and enhances the convenience for constructing the constitutive model based on energy theory.
基金support from the National Natural Science Foundation of China under Grant No.51879135supported by the Taishan Scholars Program(Grant No.ZR2021ME099)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Grant No.SKLGME023003。
文摘Understanding how thermal damage accumulates in granites under cyclic thermal loading is crucial for geoengineering design and stability assessment.Two types of granite with different grain sizes were subjected to multiple heating and cooling cycles at identical or increasing target temperatures using a new apparatus.Acoustic emission(AE)and thermal deformation were monitored simultaneously.Ultrasonic velocity,porosity,and permeability measurements,compression tests,and thin-section petrography were conducted to assess the thermal damage and physical and mechanical properties of the treated specimens.The results indicate that the thermal damage progression exhibits cycle-dependent decay at 300℃,and the thermal deformation tends to be elastic.However,the uniaxial compressive strength(UCS)increases after thermal treatment,though the increment decreases with progressive cycles(from 21%to 4%for coarse-grained granite).Progressive temperature cycling induces cumulative damage amplification,manifested by tremendous thermal cracking(the total number of AE hits reaches-170 and 180 times that of the first cycle)and crack density escalation(the crack density reaches-1.6 and 2 times that of the first cycle).AE results reveal that there is a temperature-memory effect in both rock types,and show that thermal stresses are insufficient to generate new thermal damage until the prior exposed temperature is exceeded.Additionally,thermal damage is related to the microstructure of rock:coarse-grained granite with more pre-existing cracks exhibits heating-dominated damage(e.g.94%of the AE energy was generated during heating at 300℃),while fine-grained granite with less inherent damage is more sensitive to cooling(e.g.71%of the AE energy was generated during cooling).Quantitative relationship among P-wave velocity,Young's modulus,and linear crack density provide a good estimation of thermal damage,and can guide assessments of the durability of underground engineering.
文摘Nuclear DNA, which is essential for the transmission of genetic information, is constantly damaged by external stresses and is subsequently repaired by the removal of the damaged region, followed by resynthesis of the excised region. Accumulation of DNA damage with failure of repair processes leads to fatal diseases such as cancer. Recent studies have suggested that intra- and extra-nuclear environments play essential roles in DNA damage. However, numerous questions regarding the role of the nuclear mechanical environment in DNA damage remain unanswered. In this study, we investigated the effects of cell confluency (cell crowding) on the morphology of cell nuclei, and cytoskeletal structures, and DNA damage in NIH3T3 skin fibroblasts and HeLa cervical cancer cells. Although nuclear downsizing was observed in both NIH3T3 and HeLa cells with cell crowding, intracellular mechanical changes in the two cell types displayed opposite tendencies. Cell crowding in NIH3T3 cells induced reinforcement of actin filament structures, cell stiffening, and nuclear downsizing, resulting in a significant decrease in endogenous DNA damage, whereas cell crowding in HeLa cells caused partial depolymerization of actin filaments and cell softening, inducing endogenous DNA damage. Ultraviolet (UV) radiation significantly increased DNA damage in NIH3T3;however, this response did not change with cell crowding. In contrast, UV radiation did not cause DNA damage in HeLa cells under either sparse or confluent conditions. These results suggested that cell crowding significantly influenced endogenous DNA damage in cells and was quite different in NIH3T3 and HeLa cells. However, cell crowding did not affect the UV-induced DNA damage in either cell type.
基金funding by National Natural Science Foundation of China(No.52105137)the National Science and Technology Major Project,China(No.2017-IV0012-0049)the Beijing Natural Science Foundation,China(No.3244033)。
文摘A Combined Cycle Fatigue(CCF)life prediction model considering the effect of load sequence was proposed.To account for the interaction of high and low cycle fatigue,the CCF load was divided into two different loading paths of variable stress amplitude and stress ratio.Based on the iso-damage curves,a CCF life prediction model independent of fitting parameters was proposed,agreeing well with the experimental results.Finally,the effect of load sequence on CCF was discussed according to the fracture morphology of designed blade-like specimen.The results showed that the predicted CCF life was almost located in three-fold dispersion band for the LCF-HCF(LH)and HCF-LCF(HL)loading paths,especially for the average results of both.Compared with other models,the proposed model had better predictive and generalization abilities for multiple materials and variable experimental conditions.
基金supported by Open Research Fund of State Key Laboratory of Target Vulnerability Assessment,Defense Engineering Institute,AMS,PLA(Grant No.YSX2024KFPG002)。
文摘Aiming at addressing the issues of unclear dynamic response mechanisms and insufficient quantification of temperature coupling effects in building structures under long-duration blast loads,this study investigates typical composite beam-slab structures through integrated blast shock tube experiments and multiscale numerical simulations using Voronoi-coupled Finite-Discrete Element Method(VoroFDEM).The research systematically reveals the dynamic response mechanisms and damage evolution patterns of composite beam-slab structures subjected to prolonged blast loading.An environmenttemperature-coupled P-I curve damage assessment system is established,and a rapid evaluation method based on image crack characteristics is proposed,achieving innovative transition from traditional mechanical indicators to intelligent recognition paradigms.Results demonstrate that composite beam-slab structures exhibit three-phase failure modes:elastic vibration,plastic hinge formation,and global collapse.Numerical simulations identify the brittle-to-ductile transition temperature threshold at-10℃,and establish a temperature-dependent piecewise function-based P-I curve prediction model,whose overpressure asymptote displays nonlinear temperature sensitivity within-50-30℃.A novel dual-mode evaluation methodology integrating Voro-FDEM numerical simulations with image-based damage feature recognition is developed,enabling quantitative mapping between crack area and destruction levels.These findings provide theoretical foundations and technical pathways for rapid blast damage assessment and protective engineering design.
文摘The low porosity and low permeability of shale remain the primary challenges in shale gas exploitation.Traditional single permeability enhancement techniques have shown limited efficacy,failing to effectively address these technical bottlenecks.This study investigates the synergistic effects of perforationinduced permeability enhancement and acidizing operations on the mechanical properties and micropore structure of shale.The improved Split Hopkinson Pressure Bar(SHPB)technique was employed to simulate dynamic impact damage under triaxial stress conditions.Damaged and undamaged rock specimens were immersed in a 15%hydrochloric acid solution to fabricate combined-damage specimens and acid-etched specimens with varying damage states.Uniaxial compression tests,X-ray diffraction(XRD)analysis,and scanning electron microscopy(SEM)were conducted on these specimens.SEM images were binarized,and combined with low-temperature nitrogen adsorption tests,the effects of different damage states on the mechanical behavior,energy dissipation,micro-morphology,and pore characteristics of shale were systematically evaluated.Results demonstrate that the peak stress and elastic modulus of shale exhibit a negative correlation with acid-etching duration.The mechanical properties of combined-damage specimens are inferior to those of pure acid-etched specimens,with the minimum peak stress reaching 147.10 MPa—a 43.53%reduction compared to untreated specimens.The energy dissipation ratio significantly increases,with a maximum value of 34.74%.XRD analysis reveals that prolonged acid immersion effectively reduces the carbonate content in specimens,while composite treatment accelerates the reaction between rock matrix and acid solution.Microstructural characterization indicates that acid etching enhances the porosity of shale,particularly the area of mesopores and macropores,with more pronounced pore development and a fragmented interface structure.These findings deepen the understanding of physical mechanisms during shale gas extraction and provide critical theoretical support for optimizing integrated permeability enhancement technologies.
文摘AIM:To investigate the effects of adenosine triphosphate(ATP)and melatonin,which have antioxidant and antiinflammatory activities,on potential 5-fluorouracil(5-FU)-induced optic nerve damage in rats.METHODS:Twenty-four rats were categorized into four groups of six rats:healthy(HG),5-FU(FUG),ATP+5-FU(AFU),and melatonin+5-FU(MFU).ATP(4 mg/kg)and melatonin(10 mg/kg)were administered intraperitoneally and orally,respectively.One hour after ATP and melatonin administration,rats in the AFU,MFU,and FUG were intraperitoneally injected with 5-FU(100 mg/kg).ATP and melatonin were administered once daily for 10d.5-FU was administered at a single dose on days 1,3,and 5 of the experiment.After 10d,the rats were euthanized and optic nerve tissues were extracted.Optic nerve tissues were biochemically and histopathologically examined.RESULTS:ATP and melatonin treatments inhibited the increase in malondialdehyde(MDA)and interleukin-6(IL-6)levels,which were elevated in the FUG.The treatments also prevented the decrease in total glutathione(tGSH)levels and the superoxide dismutase(SOD)and catalase(CAT)activities(P<0.001).This inhibition was higher in the ATP group than in the melatonin group(P<0.001).ATP prevented histopathological damage better than melatonin(P<0.05).CONCLUSION:ATP and melatonin have the potential to be used in alleviating 5-FU-induced optic nerve damage.In addition,ATP treatment shows better protective effects than melatonin.
基金financially supported by the National Natural Science Foundation of China(Nos.52174095 and51804310)。
文摘Investigation techniques,such as uniaxial compression tests,acoustic emission,digital image correlation monitoring,and scanning electron microscopy,were used from macroscopic and microscopic perspectives to investigate the effects of gangue particle-size gradation on the damage characteristics of cemented backfill.The peak strength,acoustic emission characteristics,and failure modes of cemented backfills with different gangue size gradations were examined.Test results indicated that with an increase in the gradation coefficient,the compressive strength of the gangue-cemented backfill first increased and then decreased.When the gradation coefficient is 0.5,the maximum compressive strength of the backfill is 4.28 MPa.The acoustic emission counts during the loading of gangue-cemented fills with different gradation coefficients passed through three phases:rising,active,and significantly active.The number of internal pores and cracks,as well as the uneven distribution of their locations,cause differences in acoustic emission characteristics at the same stage and variations in the strength of the backfill due to the different gangue particle-size gradations in the filler sample.
基金support from the National Natural Science Foundation of China(Grant Nos.12072102 and 12102129).
文摘As a critical mechanical characteristic of rock,brittleness significantly influences fracture modes and damage evolution processes.Accurate quantitative evaluation of brittleness is essential for ensuring the stability of various engineering applications.Based on the pre-peak and post-peak stages of the rock stress-strain curve,this study constructed a brittleness index BI^(*).The index quantifies the ability of rock to resist plastic deformation during the pre-peak crack growth stage and evaluates the intensity of strength drop during the post-peak softening stage.Another index,BII,was established based on the degree of pre-peak elastic energy accumulation and the instability characteristics of post-peak dissipated energy.This index reflects the essential properties of rock failure by revealing the energy evolution mechanism.Furthermore,by defining a damage variable from the energy dissipation over the entire deformation process,an index B_(D)was introduced to evaluate brittleness from the perspective of internal damage development.Triaxial compression and cyclic loading tests were conducted on rocks of different lithologies to evaluate the new index.The influences of confining pressure and lithology on rock brittleness were analyzed,along with the sensitivity analysis of various brittleness index parameters.The results indicated that the proposed brittleness indices accurately distinguish the brittleness differences among various lithologies and show effective consistency with the failure modes of specimens under different confining pressures.Meanwhile,different brittleness indices were affected by confining pressure and lithology to different degrees.The post-peak softening stage of rock played a particularly significant role in brittleness analysis.A brittleness classification system under different confining pressures and lithologies was established.The research results contribute to the enhancement and refinement of the rock brittleness evaluation system.
基金supported by the Scientific and Technological Research Council of Türkiye(TUBITAK)under Research Grant 116M254.
文摘Reinforced concrete buildings may experience partial damage after earthquakes or some human-induced actions.A decision about the future of those buildings requires detailed analyses,while determining the dynamic characteristics of a real building in its pre-and post-event situations can guide the analysis.Hence,this study was planned to monitor the dynamic response of an existing six-story,reinforced concrete building with regard to structural damage.The modal characteristics of the original building were initially determined by the use of operational modal analysis.Next,three steps of progressive structural damage were applied to the building.The first damage level peeled off the clear cover of a beam and three columns on a corner of the building’s ground floor.whereas the second and third levels completely razed the damaged columns.Operational modal analysis was repeated at each damage stage to extract the frequencies and detailed mode shapes.Moreover,numerical models based on the finite element method were constructed to confirm the obtained experimental findings.The well-agreed experimental and numerical findings revealed the damage sensitivity of the building’s dynamic response.The quantified amount of frequency change favored a retrofit of the partially damaged buildings rather than their replacement.
基金financed by the National Natural Science Foundation of China(Nos.12402071,92160204)the China Postdoctoral Science Foundation(No.2024M751635)+1 种基金the Postdoctoral Fellowship Program of CPSF,China(No.GZB20240365)the National Science and Technology Major Projects of China(No.J2019-IV-0011-0079).
文摘Thermomechanical Fatigue (TMF) is one of the most dangerous failure modes of high-temperature structures. The effect of coarsened and rafted microstructures on the TMF behavior of Nickel-Base Single Crystal Superalloys (NBSX) was experimentally studied. TMF tests under In-Phase (IP) and Out-of-Phase (OP) paths revealed significant variations in TMF life reduction. Cyclic deformation behaviors of alloys with different microstructures were compared. The effect of microstructure on TMF damage mechanisms was unveiled from characterizations of fracture surfaces and longitudinal sections by scanning electronic microscope and optical microscope. A transition from mode-I to crystallographic fracture in the coarsened alloy during IP-TMF was observed and discussed. Due to the degraded microstructure, the dispersed distribution of crystal slips was distinguished in the coarsened and rafted alloys. The competitive or synergetic interactions among oxidation-assisted mode-I opening, casting pore-related mode-I creep and crystallographic slipping were discussed. This study underscores the complex interplay among microstructure, deformation behaviors and damage mechanisms, offering valuable insights into alloy performance under TMF conditions.
基金Supported by Carbon Neutrality and Energy System Transformation (CNEST) ProgramScience and Technology Innovation Project of CHN Energy (GJNY-24-26)。
文摘The service life of refractory brick in the slag tapping hole of gasifiers is a significant concern for long-term and stable operation.This study examined the damage mechanism of high chromia refractory of four commercial coal-water slurry gasifiers with their corresponding gasification coal samples and the corroded refractory bricks in the slag tapping hole of the gasifier.The slag characteristic,including crystallization and viscosity-temperature of four gasification coal samples were analyzed.The results revealed that the low viscosity slag could lead to more severe damage to refractory bricks.Given the risk of slag crystallization,it is recommended to establish a safe slag tapping temperature range should be set as tICT(initial crystallization temperature)−t_(2.5) when tICT is higher than t_(25).Upon examining interior morphology of these corroded refractory bricks,some cracks were observed within them.The chemical composition of molten slag was analyzed using SEM-EDS.However,XRD results found no spinel containing zirconium in these cracks.This suggests that the emergence of these cracks are mainly attributed to the molten slag penetration and the subsequent reaction with the refractory material.The difference in thermal expansion between the newly formed substances and refractory material is critical in forming these cracks.Furthermore,SEM-EDS analysis was also conducted on the slag-aggregate and the slag-matrix interface.The results reveal that the reduction in Cr_(2)O_(3) content is the earliest characteristic of damage in high chromia refractories.A proposed damage mechanism of refractory brick suggests that the matrix and aggregate of high chromia refractory are initially compromised because of the reduced Cr_(2)O_(3) content.Subsequently,the molten slag penetrates the interior of the refractory brick,forming new substances,leading to damage caused by the difference in thermal expansion between the new substances and the refractory brick.Understanding and preventing the reduction of Cr_(2)O_(3) content is vital to prolonging the service life of refractory brick in the slag tapping hole of the gasifier based on this damage mechanism.
基金supported by Shandong Provincial Colleges and Universities Youth Innovation Technol ogy Support Program(No.2023KJ092)Natural Science Foundation of Shandong Province(No.ZR2024ME060)Key Laboratory of Geological Safety of Coastal Urban Underground Space,Ministry of Natural Resources(No.BHKF2024Z06)。
文摘Prolonged cyclic water intrusion has progressively developed joints in the hydro-fluctuation belt,elevating the instability risk of reservoir bank slopes.To investigate its impact on joint shear damage evolution,joint samples were prepared using three representative roughness curves and subjected to direct shear testing following cyclic water intrusion.A shear damage constitutive model considering the coupling effect of cyclic water intrusion and load was developed based on macroscopic phenomenological damage mechanics and micro-statistical theory.Results indicate:(1)All critical shear mechanical parameters(including peak shear strength,shear stiffness,basic friction angle,and joint compressive strength)exhibit progressive deterioration with increasing water intrusion cycles;(2)Model validation through experimental curve comparisons confirms its reliability.The model demonstrates that intensified water intrusion cycles reduce key mechanical indices,inducing a brittle-to-ductile transition in joint surface deformation—a behavior consistent with experimental observations;(3)Damage under cyclic water intrusion and load coupling follows an S-shaped trend,divided into stabilization(water-dominated stage),development(load-dominated stage),and completion stages.The research provides valuable insights for stability studies,such as similar model experiments for reservoir bank slopes and other water-related projects.
