The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstru...The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.展开更多
Statistical distribution of residual fatigue life(RFL)of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters.Experimental data f...Statistical distribution of residual fatigue life(RFL)of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters.Experimental data for the EA4T railway axle steel,the loading spectrum,the press fit loading and the residual stress induced by surface hardening were considered in the crack propagation simulations.Usually,the material properties measured by tensile tests are considered to be the most informative source of material data.Under fatigue loading,however,the crack growth rates near the threshold are the most critical data.Two important influencing factors on these crack growth rates are presented:first,the air humidity and,second,the near-surface residual stress.The typical variation of these parameters in operation may change the RFL by one or two orders of magnitude.Experimentally obtained crack growth thresholds and residual stress profiles are highly affected by the used methodology.Therefore,the obtained input data may be located anywhere within a large scatter,while the experimenters are completely unaware of it.This can lead to dangerously non-conservative situations,e.g.when the thresholds are measured in a laboratory under humid air conditions and then applied to predictions of RFLs of axles operated in winter in low air humidity.This is significant for the topic of inspection interval optimisation.The results of experiments done on real 1:1 railway axles were close to the most frequent value found in the histogram of the numerically computed RFLs.展开更多
Numerous sectors,such as education,the IT sector,and corporate organizations,transitioned to virtual meetings after the COVID-19 crisis.Organizations now seek to assess participants’fatigue levels in online meetings ...Numerous sectors,such as education,the IT sector,and corporate organizations,transitioned to virtual meetings after the COVID-19 crisis.Organizations now seek to assess participants’fatigue levels in online meetings to remain competitive.Instructors cannot effectively monitor every individual in a virtual environment,which raises significant concerns about participant fatigue.Our proposed system monitors fatigue,identifying attentive and drowsy individuals throughout the online session.We leverage Dlib’s pre-trained facial landmark detector and focus on the eye landmarks only,offering a more detailed analysis for predicting eye opening and closing of the eyes,rather than focusing on the entire face.We introduce an Eye Polygon Area(EPA)formula,which computes eye activity from Dlib eye landmarks by measuring the polygonal area of the eye opening.Unlike the Eye Aspect Ratio(EAR),which relies on a single distance ratio,EPA adapts to different eye shapes(round,narrow,or wide),providing a more reliable measure for fatigue detection.The VMFD system issues a warning if a participant remains in a fatigued condition for 36 consecutive frames.The proposed technology is tested under multiple scenarios,including low-to high-lighting conditions(50-1400 lux)and both with and without glasses.This study builds an OpenCV application in Python,evaluated using the iBUG 300-W dataset,achieving 97.5%accuracy in detecting active participants.We compare VMFD with conventional methods relying on the EAR and show that the EPA technique performs significantly better.展开更多
Accurately predicting fatigue life under multiaxial fatigue damage conditions is essential for ensuring the safety of critical components in service.However,due to the complexity of fatigue failure mechanisms,achievin...Accurately predicting fatigue life under multiaxial fatigue damage conditions is essential for ensuring the safety of critical components in service.However,due to the complexity of fatigue failure mechanisms,achieving accurate multiaxial fatigue life predictions remains challenging.Traditional multiaxial fatigue prediction models are often limited by specific material properties and loading conditions,making it difficult to maintain reliable life prediction results beyond these constraints.This paper presents a study on the impact of seven key feature quantities on multiaxial fatigue life,using Convolutional Neural Networks(CNN),Long Short-Term Memory Networks(LSTM),and Fully Connected Neural Networks(FCNN)within a deep learning framework.Fatigue test results from eight metal specimens were analyzed to identify these feature quantities,which were then extracted as critical time-series features.Using a CNN-LSTM network,these features were combined to form a feature matrix,which was subsequently input into an FCNN to predict metal fatigue life.A comparison of the fatigue life prediction results from the STFAN model with those from traditional prediction models—namely,the equivalent strain method,the maximum shear strain method,and the critical plane method—shows that the majority of predictions for the five metal materials and various loading conditions based on the STFAN model fall within an error band of 1.5 times.Additionally,all data points are within an error band of 2 times.These findings indicate that the STFAN model provides superior prediction accuracy compared to the traditional models,highlighting its broad applicability and high precision.展开更多
High-performance magnesium alloys are in great demand to meet the lightweight design requirements of aircraft.Grain size has long been recognized as a key factor influencing the mechanical properties of alloys.This st...High-performance magnesium alloys are in great demand to meet the lightweight design requirements of aircraft.Grain size has long been recognized as a key factor influencing the mechanical properties of alloys.This study investigates the effect of grain size,controlled by Zr addition,on the fatigue behavior of a recently developed low-cost Mg-2.6Nd-0.35Zn alloy,through systematic characterization and analysis of stress-life(S-N)curves,fatigue crack propagation,fracture surface morphology,stress intensity factor,and crack propagation threshold.The results show that after heat treatment(solution at 525±5℃ for 8 h and water quenching at 60-80℃,followed by aging at 250±5℃for 14 h and then air cooling),coarse-grained specimens(average grain size approximately 596μm)containing 0.12wt.%Zr exhibit greater resistance to fatigue crack propagation than fine-grained specimens(average grain size approximately 94μm)containing 0.46wt.%Zr.Coarse grains promote intergranular fracture,while fine grains favor transgranular fracture.In addition,coarse grains reduce the sensitivity of the crack tip to stress concentration.Furthermore,fine-grained samples demonstrate a longer total fatigue life,owing to their superior resistance to crack initiation,which significantly prolongs the crack initiation stage.These findings highlight the importance of optimizing grain size to achieve the best possible fatigue resistance in Mg-Nd-Zn-Zr alloys for practical engineering applications.展开更多
A comprehensive full-sieve-hole grading correction method was used to adjust aggregate gradings.The fatigue properties of recycled concrete aggregate(RCA)asphalt mixtures were investigated using an improved indirect t...A comprehensive full-sieve-hole grading correction method was used to adjust aggregate gradings.The fatigue properties of recycled concrete aggregate(RCA)asphalt mixtures were investigated using an improved indirect tensile fatigue test under temperature-humidity coupling based on 20-year meteorological data of Beijing,and the degeneration mechanism was further explored by scanning electron microscopy and energy-dispersive spectroscopy.The experimental results indicate that replacing 5-20 mm coarse limestone aggregate(LA)with RCA at a 50% substitution volume can mitigate the impact of RCA variations on the asphalt mixture proportioning design.All RCA asphalt mixtures have lower initial fatigue properties than the LA asphalt mixture.However,under temperature-humidity coupling,the long-term fatigue property of an RCA asphalt mixture with a low proportion of recycled brick exceeds that of the LA asphalt mixture,and the fatigue life decline rate of the RCA asphalt mixture during 10-year service decreases by approximately 25%.This is due to the penetration of the asphalt mortar into the RCA through the pores and cracks on the RCA surface.It forms an interfacial transition zone composed of asphalt mortar and cement mortar and further reduces the mixture damage caused by the water and freeze-thaw conditions.展开更多
The axle box bearings of high-speed trains often operate in extremely harsh environments,bearing loads from different directions.Long-term operation and frequent changes in working conditions can easily lead to axle b...The axle box bearings of high-speed trains often operate in extremely harsh environments,bearing loads from different directions.Long-term operation and frequent changes in working conditions can easily lead to axle box bearing failures.Therefore,it is extremely important to study the mechanism of axle box bearings.Firstly,the medium of thermal deformation establishes a coupling relationship between the system dynamics model and the thermal grid model,and then obtains the thermal force coupling model of the high-speed train axle box bearing.The coupling model is validated from the perspectives of system dynamics response and temperature response,proving its effectiveness in system dynamics response and temperature characteristic response.Comparing the coupling model with the dynamics model,it is found that thermal deformation complicates the dynamic re-sponse.Finally,using the Lundberg-Palmgren(L-P)bearing fatigue calculation method and damage accumu-lation theory,the bearing fatigue life is calculated,and it is found that thermal deformation deteriorates the bearing operating environment,reducing the bearing fatigue life.Finally,by comparing the bearing fatigue life under different working conditions,it is concluded that the faster the vehicle speed,the greater the load,and the smaller the initial radial clearance of the bearing,the fatigue life of the bearing is reduced.The shorter the lifespan.展开更多
BACKGROUND Parkinson’s disease(PD)is a common neurodegenerative disorder in the elderly population.Non-motor symptoms such as anxiety and depression are often subtle,hindering early detection and intervention,yet the...BACKGROUND Parkinson’s disease(PD)is a common neurodegenerative disorder in the elderly population.Non-motor symptoms such as anxiety and depression are often subtle,hindering early detection and intervention,yet they markedly affect quality of life and clinical outcomes.AIM To investigate the prevalence of anxiety and depression in elderly PD patients,identify associated risk factors,and assess their relationship with fatigue severity.METHODS A cross-sectional analysis was conducted in 123 elderly PD patients treated at The Second Rehabilitation Hospital of Shanghai between January 2023 and December 2024.Demographic and clinical data were obtained using standardized questionnaires.Anxiety,depression,and fatigue were assessed using the Beck Anxiety Inventory(BAI),Geriatric Depression Scale(GDS),and Fatigue Scale-14(FS-14),respectively.Binary logistic regression identified risk factors for anxiety and depression,whereas Spearman’s correlation assessed associations with fatigue.RESULTS Anxiety and depression prevalence rates were 64.2%(mean BAI score:19.59±10.92)and 56.1%(mean GDS score:12.82±6.37),respectively.The mean FS-14 total score was 9.46±1.89,comprising physical(5.77±1.51)and mental(3.69±1.20)fatigue components.Significant positive correlations were observed between fatigue scores(total,physical,and mental)and both anxiety and depression(all P<0.05).Univariate analysis revealed statistically significant associations between anxiety/depression and monthly income,disease duration,and disease severity(all P<0.05).Multivariate logistic regression indicated higher anxiety risk in patients with lower monthly income,prolonged disease duration,advanced disease severity,or multimorbidity.Depression risk was elevated in patients with lower monthly income and severe disease,whereas longer disease duration unexpectedly served as a protective factor.CONCLUSION Elderly PD patients show high rates of anxiety and depression,both of which are significantly correlated with fatigue severity.These findings highlight the importance of psychological monitoring and targeted mental health interventions in PD management among the elderly.展开更多
Myalgic encephalomyelitis/chronic fatigue syndrome-an insidious disease:The recent COVID-19 pandemic has brought substantial attention to the overlapping symptoms between long COVID and myalgic encephalomyelitis/chron...Myalgic encephalomyelitis/chronic fatigue syndrome-an insidious disease:The recent COVID-19 pandemic has brought substantial attention to the overlapping symptoms between long COVID and myalgic encephalomyelitis/chronic fatigue syndrome(ME/CFS),a chronic and poorly understood neurological disorder(Shankar et al.,2024).展开更多
This study investigates the influence of loading frequency on the fatigue behavior of ballastless track concrete for high-speed railways,aiming to support the development of concrete capable of withstanding higher ope...This study investigates the influence of loading frequency on the fatigue behavior of ballastless track concrete for high-speed railways,aiming to support the development of concrete capable of withstanding higher operational speeds.Fatigue tests were conducted at loading frequencies ranging from 5 to 40 Hz,with a focus on fatigue life,damage evolution,energy dissipation,and residual fatigue strain in the concrete.The results indicate that between 5 and 15 Hz,the fatigue life and energy dissipation remain relatively stable,with minimal damage evolution and small residual strains.As the frequency increases to 15-20 Hz,the fatigue life and energy dissipation gradually decrease,while damage accumulation and residual strain increase.Beyond 20 Hz,both fatigue life and energy dissipation decrease rapidly,damage accumulation becomes more pronounced,and residual strain continues to rise.These phenomena are primarily attributed to the increased strain rate and load change rate at higher frequencies,which affect the microstructure evolution and lead to reduced fatigue performance.展开更多
The effects of three corrosion inhibitors on Mg-Zn-Y-Nd alloy corrosion fatigue were investigated.Salicylic acid(SA)induces uniform but rapid corrosion,limiting fatigue life improvement.2,6-pyridinedicarboxylic acid(2...The effects of three corrosion inhibitors on Mg-Zn-Y-Nd alloy corrosion fatigue were investigated.Salicylic acid(SA)induces uniform but rapid corrosion,limiting fatigue life improvement.2,6-pyridinedicarboxylic acid(2,6-PDCA)delays crack initiation under low stress yet fails to fully suppress localized corrosion.Paeonol condensed cysteine Schiff base(PCCys)significantly inhibits both uniform corrosion and localized attacks,enhancing corrosion fatigue life.Localized corrosion behavior,rather than isolated corrosion rate metrics,critically determines mechanical performance under combined corrosive-dynamic stress conditions.A multi-parameter evaluation framework integrating localized corrosion,corrosion rate,and stress effects is proposed for practical screening of corrosion inhibitors for magnesium alloys.展开更多
This study aims to explore the impact of fatigue induced by different limb exercises on cerebral cortical oxygenation levels and functional connectivity strength using functional near-infrared spectroscopy(fNIRS).Fati...This study aims to explore the impact of fatigue induced by different limb exercises on cerebral cortical oxygenation levels and functional connectivity strength using functional near-infrared spectroscopy(fNIRS).Fatigue was induced using an upper limb ergometer or a lower limb ergometer,with the load increasing gradually each minute.fNIRS covering the prefrontal cortex and motor cortex were used to collect data during the resting state,both before and after fatigue induction.A two-way ANOVA was conducted to examine differences in oxyhemoglobin(HbO_(2))and functional connectivity before and after fatigue induction in both groups,with the significance level set at 0.05.Exercise-induced fatigue in both the upper and lower limbs leads to a significant decrease in cerebral cortical oxygenation levels.Upper limb fatigue leads to a significant reduction in functional connectivity,there were significant decreases in connectivity within the motor cortex,between the motor cortex and frontal regions,and between the right ventrolateral prefrontal cortex and other frontal regions.Conversely,no significant changes were observed before and after lower limb fatigue.Future studies should focus on examining the extent to which how changes in the cerebral cortex,induced by exercise fatigue,are linked to exercise-and/or performance-related outcomes.展开更多
The interrupted fatigue test method was utilized to investigate the damage evolution mechanism of the notch high-cycle fatigue(NHCF)in Ti-55531 alloy with a multilevel lamellar microstructure.The results reveal that s...The interrupted fatigue test method was utilized to investigate the damage evolution mechanism of the notch high-cycle fatigue(NHCF)in Ti-55531 alloy with a multilevel lamellar microstructure.The results reveal that significant microvoids and microcracks predominantly initiate at α/β interfaces under various notch root radii(R).Notably,even under larger R(0.75 mm),mutual interactions of stacking faults(SFs)−deformation twins,twins−twins,and SFs−SFs are observed.Furthermore,with decreasing R(0.34 and 0.14 mm),the volume fraction of SFs escalates significantly and twins are almost absent.Moreover,activated prismatic slip system decreases with a decrease in Schmidt factor and with the further decrease in R.Finally,strain localization near α/β interfaces contributes to the initiation of fatigue microcracks.展开更多
Aviation aluminum alloys,primarily from the Al-Cu,Al-Zn-Mg-(Cu),and Al-Li series,have been widely applied over six decades,greatly advancing the aviation industry.However,their Corrosion Fatigue(CF)properties impede f...Aviation aluminum alloys,primarily from the Al-Cu,Al-Zn-Mg-(Cu),and Al-Li series,have been widely applied over six decades,greatly advancing the aviation industry.However,their Corrosion Fatigue(CF)properties impede further advancements,prompting extensive research into their CF behaviors and underlying mechanisms.This review comprehensively evaluates previous studies on their development history,CF mechanisms,and key influencing factors.First,the historical evolution of aerospace aluminum alloys is summarized.Then,the currently recognized four crack initiation mechanisms and three crack propagation mechanisms are concluded,and the effects of external and internal factors on CF performance are discussed.The paper also reviews three methods and CF life prediction models for characterizing the CF behavior of aerospace aluminum alloys.Most existing studies on the CF behavior of aluminum alloys are based on the single corrosive environment,neglecting the fact that aircrafts experience multiple corrosive environments during service.However,the most critical scientific challenge is how to enhance their CF properties under increasingly demanding service conditions.For the purpose,this paper introduces advanced forming techniques based on the microstructural control,such as Equal Channel Angular Pressing(ECAP)and High-Pressure Torsion(HPT),aimed at laying the theoretical foundation for improving CF properties through microstructural regulation.展开更多
Accurate detection of driver fatigue is essential for improving road safety.This study investigates the effectiveness of using multimodal physiological signals for fatigue detection while incorporating uncertainty qua...Accurate detection of driver fatigue is essential for improving road safety.This study investigates the effectiveness of using multimodal physiological signals for fatigue detection while incorporating uncertainty quantification to enhance the reliability of predictions.Physiological signals,including Electrocardiogram(ECG),Galvanic Skin Response(GSR),and Electroencephalogram(EEG),were transformed into image representations and analyzed using pretrained deep neu-ral networks.The extracted features were classified through a feedforward neural network,and prediction reliability was assessed using uncertainty quantification techniques such as Monte Carlo Dropout(MCD),model ensembles,and combined approaches.Evaluation metrics included standard measures(sensitivity,specificity,precision,and accuracy)along with uncertainty-aware metrics such as uncertainty sensitivity and uncertainty precision.Across all evaluations,ECG-based models consistently demonstrated strong performance.The findings indicate that combining multimodal physi-ological signals,Transfer Learning(TL),and uncertainty quantification can significantly improve both the accuracy and trustworthiness of fatigue detection systems.This approach supports the development of more reliable driver assistance technologies aimed at preventing fatigue-related accidents.展开更多
The high-cycle fatigue fracture characteristics and damage mechanism of nickel-based single crystal superalloys at 850℃ was investigated.The results indicate that high-cycle fatigue cracks in single crystal superallo...The high-cycle fatigue fracture characteristics and damage mechanism of nickel-based single crystal superalloys at 850℃ was investigated.The results indicate that high-cycle fatigue cracks in single crystal superalloys generally originate from defect locations on the subsurface or interior of the specimen at 850℃.Under the condition of stress ratio R=0.05,as the fatigue load decreases,the high-cycle fatigue life gradually increases.The high-cycle fatigue fracture is mainly characterized by octahedral slip mechanism.At high stress and low lifespan,the fracture exhibits single or multiple slip surface features.Some fractures originate along a vertical small plane and then propagate along the{111}slip surface.At low stress and high lifespan,the fracture surface tend to alternate and expand along multiple slip planes after originating from subsurface or internal sources,exhibiting characteristics of multiple slip planes.Through electron backscatter diffraction and transmission electron microscope analysis,there is obvious oxidation behavior on the surface of the high-cycle fatigue fracture,and the fracture section is composed of oxidation layer,distortion layer,and matrix layer from the outside to the inside.Among them,the main components of the oxidation layer are oxides of Ni and Co.The distortion layer is mainly distributed in the form of elongated or short rod-shaped oxides of Al,Ta,and W.The matrix layer is a single crystal layer.Crack initiation and propagation mechanism were obtained by systematical analysis of a large number of highcycle fatigue fractures.In addition,the stress ratio of 0.05 is closer to the vibration mode of turbine blades during actual service,providing effective guidance for the study of failure and fracture mechanisms of turbine blades.展开更多
The crack initiation and early propagation are of great significance to the overall fatigue life of material.In order to investigate the anisotropic fracture behavior of laser metal deposited Ti-6Al-4V alloy(LMD Ti64)...The crack initiation and early propagation are of great significance to the overall fatigue life of material.In order to investigate the anisotropic fracture behavior of laser metal deposited Ti-6Al-4V alloy(LMD Ti64)during the early stage,the fourpoint bending fatigue test was carried out on specimens of three different directions,as well as the forged specimens.The results indicate the anisotropic crack initiation and early propagation of LMD Ti64.The direction perpendicular to the deposition direction exhibits a better fatigue resistance than the other two.The crack initiation position and propagation path are dominated by the microstructure in the vicinity of U-notch.LMD Ti64 has a typical small crack effect,and the early crack propagation velocities in three directions are similar.Affected by the slip system of LMD Ti64,secondary cracks frequently occur,which are often found to have an angle of 60°to the main crack.The electron backscatter diffraction analysis indicates that LMD Ti64 has preferred orientations,i.e.,strong 0001//Z texture and 001//Z texture.Their crystallographic orientation will change as the direction of columnarβgrains turns over,resulting in the fatigue anisotropy of LMD Ti64 in crack initiation and early crack propagation process.展开更多
Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fa...Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms.The study demonstrated that the faceted primaryα nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests.Slip trace analysis revealed that faceted cracking occurred at(0001)basal plane with the maximum Schmid factor value through a special cracking mode referred to as(0001)twist boundary cracking.Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations,which well identify candidates for(0001)twist boundary crack nucleation.It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface(0001)twist-boundary crack initiation,and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking.Based on this,phenomeno-logical models are proposed to explain the surface(0001)twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.展开更多
Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads.Furthermore,the incorporation of recycled aggregates in their construction may ...Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads.Furthermore,the incorporation of recycled aggregates in their construction may exacerbate these limitations.To address these issues,this study introduced a novel cement-stabilized permeable recycled aggregate material.A total of 162 beam specimens prepared with nine different levels of cement-aggregate ratio were tested to evaluate their permeability,bending load,and bending fatigue life.The experimental results indicate that increasing the content of recycled aggregates led to a reduction in both permeability and bending load.Additionally,the inclusion of recycled aggregates diminished the energy dissipation capacity of the specimens.These findings were used to establish a robust relationship between the initial damage in cement-stabilized permeable recycled aggregate material specimens and their fatigue life,and to propose a predictive model for their fatigue performance.Further,a method for assessing fatigue damage based on the evolution of fatigue-induced strain and energy dissipation was developed.The findings of this study provide valuable insights into the mechanical behavior and fatigue performance of cement-stabilized permeable recycled aggregate materials,offering guidance for the design of low-carbon-emission,permeable,and durable roadways incorporating recycled aggregates.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
基金National Key Research and Development Program of China(2024YFB4610803)。
文摘The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.
基金financially supported by the Czech Science Foundation in the frame of the project No.22-28283Sby the Technology Agency of the Czech Republic through the project No.CK03000060.
文摘Statistical distribution of residual fatigue life(RFL)of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters.Experimental data for the EA4T railway axle steel,the loading spectrum,the press fit loading and the residual stress induced by surface hardening were considered in the crack propagation simulations.Usually,the material properties measured by tensile tests are considered to be the most informative source of material data.Under fatigue loading,however,the crack growth rates near the threshold are the most critical data.Two important influencing factors on these crack growth rates are presented:first,the air humidity and,second,the near-surface residual stress.The typical variation of these parameters in operation may change the RFL by one or two orders of magnitude.Experimentally obtained crack growth thresholds and residual stress profiles are highly affected by the used methodology.Therefore,the obtained input data may be located anywhere within a large scatter,while the experimenters are completely unaware of it.This can lead to dangerously non-conservative situations,e.g.when the thresholds are measured in a laboratory under humid air conditions and then applied to predictions of RFLs of axles operated in winter in low air humidity.This is significant for the topic of inspection interval optimisation.The results of experiments done on real 1:1 railway axles were close to the most frequent value found in the histogram of the numerically computed RFLs.
文摘Numerous sectors,such as education,the IT sector,and corporate organizations,transitioned to virtual meetings after the COVID-19 crisis.Organizations now seek to assess participants’fatigue levels in online meetings to remain competitive.Instructors cannot effectively monitor every individual in a virtual environment,which raises significant concerns about participant fatigue.Our proposed system monitors fatigue,identifying attentive and drowsy individuals throughout the online session.We leverage Dlib’s pre-trained facial landmark detector and focus on the eye landmarks only,offering a more detailed analysis for predicting eye opening and closing of the eyes,rather than focusing on the entire face.We introduce an Eye Polygon Area(EPA)formula,which computes eye activity from Dlib eye landmarks by measuring the polygonal area of the eye opening.Unlike the Eye Aspect Ratio(EAR),which relies on a single distance ratio,EPA adapts to different eye shapes(round,narrow,or wide),providing a more reliable measure for fatigue detection.The VMFD system issues a warning if a participant remains in a fatigued condition for 36 consecutive frames.The proposed technology is tested under multiple scenarios,including low-to high-lighting conditions(50-1400 lux)and both with and without glasses.This study builds an OpenCV application in Python,evaluated using the iBUG 300-W dataset,achieving 97.5%accuracy in detecting active participants.We compare VMFD with conventional methods relying on the EAR and show that the EPA technique performs significantly better.
基金supported by Key Program of National Natural Science Foundation of China(U2368215)the Science and Technology Research and Development Program Project of China Railway Group Co.,Ltd.(N2023J056).
文摘Accurately predicting fatigue life under multiaxial fatigue damage conditions is essential for ensuring the safety of critical components in service.However,due to the complexity of fatigue failure mechanisms,achieving accurate multiaxial fatigue life predictions remains challenging.Traditional multiaxial fatigue prediction models are often limited by specific material properties and loading conditions,making it difficult to maintain reliable life prediction results beyond these constraints.This paper presents a study on the impact of seven key feature quantities on multiaxial fatigue life,using Convolutional Neural Networks(CNN),Long Short-Term Memory Networks(LSTM),and Fully Connected Neural Networks(FCNN)within a deep learning framework.Fatigue test results from eight metal specimens were analyzed to identify these feature quantities,which were then extracted as critical time-series features.Using a CNN-LSTM network,these features were combined to form a feature matrix,which was subsequently input into an FCNN to predict metal fatigue life.A comparison of the fatigue life prediction results from the STFAN model with those from traditional prediction models—namely,the equivalent strain method,the maximum shear strain method,and the critical plane method—shows that the majority of predictions for the five metal materials and various loading conditions based on the STFAN model fall within an error band of 1.5 times.Additionally,all data points are within an error band of 2 times.These findings indicate that the STFAN model provides superior prediction accuracy compared to the traditional models,highlighting its broad applicability and high precision.
文摘High-performance magnesium alloys are in great demand to meet the lightweight design requirements of aircraft.Grain size has long been recognized as a key factor influencing the mechanical properties of alloys.This study investigates the effect of grain size,controlled by Zr addition,on the fatigue behavior of a recently developed low-cost Mg-2.6Nd-0.35Zn alloy,through systematic characterization and analysis of stress-life(S-N)curves,fatigue crack propagation,fracture surface morphology,stress intensity factor,and crack propagation threshold.The results show that after heat treatment(solution at 525±5℃ for 8 h and water quenching at 60-80℃,followed by aging at 250±5℃for 14 h and then air cooling),coarse-grained specimens(average grain size approximately 596μm)containing 0.12wt.%Zr exhibit greater resistance to fatigue crack propagation than fine-grained specimens(average grain size approximately 94μm)containing 0.46wt.%Zr.Coarse grains promote intergranular fracture,while fine grains favor transgranular fracture.In addition,coarse grains reduce the sensitivity of the crack tip to stress concentration.Furthermore,fine-grained samples demonstrate a longer total fatigue life,owing to their superior resistance to crack initiation,which significantly prolongs the crack initiation stage.These findings highlight the importance of optimizing grain size to achieve the best possible fatigue resistance in Mg-Nd-Zn-Zr alloys for practical engineering applications.
基金Funded by"Green Construction and Maintenance of Road Engineering"the Belt and Road Joint Laboratory,International(Hong Kong,Macao and Taiwan)Science and Technology Cooperation Project(No.Z251100007125040)the National Key R&D Program of China(No.2022YFC3803403)+3 种基金the Project of Construction and Support for High-level Innovative Teams of Beijing Municipal Institutions(No.BPHR20220109)the Cultivation Project Funds for Beijing University of Civil Engineering and Architecture(No.X24013)the BUCEA Doctor Graduate Scientific Research Ability Improvement Project(No.DG2024016)the China Scholarship Council(No.202408110091)。
文摘A comprehensive full-sieve-hole grading correction method was used to adjust aggregate gradings.The fatigue properties of recycled concrete aggregate(RCA)asphalt mixtures were investigated using an improved indirect tensile fatigue test under temperature-humidity coupling based on 20-year meteorological data of Beijing,and the degeneration mechanism was further explored by scanning electron microscopy and energy-dispersive spectroscopy.The experimental results indicate that replacing 5-20 mm coarse limestone aggregate(LA)with RCA at a 50% substitution volume can mitigate the impact of RCA variations on the asphalt mixture proportioning design.All RCA asphalt mixtures have lower initial fatigue properties than the LA asphalt mixture.However,under temperature-humidity coupling,the long-term fatigue property of an RCA asphalt mixture with a low proportion of recycled brick exceeds that of the LA asphalt mixture,and the fatigue life decline rate of the RCA asphalt mixture during 10-year service decreases by approximately 25%.This is due to the penetration of the asphalt mortar into the RCA through the pores and cracks on the RCA surface.It forms an interfacial transition zone composed of asphalt mortar and cement mortar and further reduces the mixture damage caused by the water and freeze-thaw conditions.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12393780,12032017,12302067)College Education Scientific Research Project of Hebei Province(Grant No.JZX2024006)Hebei Provincial S&T Program(Grant No.21567622 H).
文摘The axle box bearings of high-speed trains often operate in extremely harsh environments,bearing loads from different directions.Long-term operation and frequent changes in working conditions can easily lead to axle box bearing failures.Therefore,it is extremely important to study the mechanism of axle box bearings.Firstly,the medium of thermal deformation establishes a coupling relationship between the system dynamics model and the thermal grid model,and then obtains the thermal force coupling model of the high-speed train axle box bearing.The coupling model is validated from the perspectives of system dynamics response and temperature response,proving its effectiveness in system dynamics response and temperature characteristic response.Comparing the coupling model with the dynamics model,it is found that thermal deformation complicates the dynamic re-sponse.Finally,using the Lundberg-Palmgren(L-P)bearing fatigue calculation method and damage accumu-lation theory,the bearing fatigue life is calculated,and it is found that thermal deformation deteriorates the bearing operating environment,reducing the bearing fatigue life.Finally,by comparing the bearing fatigue life under different working conditions,it is concluded that the faster the vehicle speed,the greater the load,and the smaller the initial radial clearance of the bearing,the fatigue life of the bearing is reduced.The shorter the lifespan.
基金Supported by Foundation of Shanghai Baoshan Science and Technology Commission,No.2024-E-66Shanghai Nursing Association Scientific Research Project,No.2024MS-B02.
文摘BACKGROUND Parkinson’s disease(PD)is a common neurodegenerative disorder in the elderly population.Non-motor symptoms such as anxiety and depression are often subtle,hindering early detection and intervention,yet they markedly affect quality of life and clinical outcomes.AIM To investigate the prevalence of anxiety and depression in elderly PD patients,identify associated risk factors,and assess their relationship with fatigue severity.METHODS A cross-sectional analysis was conducted in 123 elderly PD patients treated at The Second Rehabilitation Hospital of Shanghai between January 2023 and December 2024.Demographic and clinical data were obtained using standardized questionnaires.Anxiety,depression,and fatigue were assessed using the Beck Anxiety Inventory(BAI),Geriatric Depression Scale(GDS),and Fatigue Scale-14(FS-14),respectively.Binary logistic regression identified risk factors for anxiety and depression,whereas Spearman’s correlation assessed associations with fatigue.RESULTS Anxiety and depression prevalence rates were 64.2%(mean BAI score:19.59±10.92)and 56.1%(mean GDS score:12.82±6.37),respectively.The mean FS-14 total score was 9.46±1.89,comprising physical(5.77±1.51)and mental(3.69±1.20)fatigue components.Significant positive correlations were observed between fatigue scores(total,physical,and mental)and both anxiety and depression(all P<0.05).Univariate analysis revealed statistically significant associations between anxiety/depression and monthly income,disease duration,and disease severity(all P<0.05).Multivariate logistic regression indicated higher anxiety risk in patients with lower monthly income,prolonged disease duration,advanced disease severity,or multimorbidity.Depression risk was elevated in patients with lower monthly income and severe disease,whereas longer disease duration unexpectedly served as a protective factor.CONCLUSION Elderly PD patients show high rates of anxiety and depression,both of which are significantly correlated with fatigue severity.These findings highlight the importance of psychological monitoring and targeted mental health interventions in PD management among the elderly.
基金supported by the Judith Jane Mason and Harold Stannett Williams Memorial Foundation National Medical Program(#Mason2210)to JX。
文摘Myalgic encephalomyelitis/chronic fatigue syndrome-an insidious disease:The recent COVID-19 pandemic has brought substantial attention to the overlapping symptoms between long COVID and myalgic encephalomyelitis/chronic fatigue syndrome(ME/CFS),a chronic and poorly understood neurological disorder(Shankar et al.,2024).
基金sponsored by the National Natural Science Foundation of China(Grant No.52438002)the New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘This study investigates the influence of loading frequency on the fatigue behavior of ballastless track concrete for high-speed railways,aiming to support the development of concrete capable of withstanding higher operational speeds.Fatigue tests were conducted at loading frequencies ranging from 5 to 40 Hz,with a focus on fatigue life,damage evolution,energy dissipation,and residual fatigue strain in the concrete.The results indicate that between 5 and 15 Hz,the fatigue life and energy dissipation remain relatively stable,with minimal damage evolution and small residual strains.As the frequency increases to 15-20 Hz,the fatigue life and energy dissipation gradually decrease,while damage accumulation and residual strain increase.Beyond 20 Hz,both fatigue life and energy dissipation decrease rapidly,damage accumulation becomes more pronounced,and residual strain continues to rise.These phenomena are primarily attributed to the increased strain rate and load change rate at higher frequencies,which affect the microstructure evolution and lead to reduced fatigue performance.
基金support from the National Natural Science Foundation of China(52301107,52571107)the Joint Fund Project of Henan Provincial Science and Technology Research and Development Plan(242301420036)supported by the Training Program for Young Backbone Teachers in Higher Education Institutions of Zhengzhou University.
文摘The effects of three corrosion inhibitors on Mg-Zn-Y-Nd alloy corrosion fatigue were investigated.Salicylic acid(SA)induces uniform but rapid corrosion,limiting fatigue life improvement.2,6-pyridinedicarboxylic acid(2,6-PDCA)delays crack initiation under low stress yet fails to fully suppress localized corrosion.Paeonol condensed cysteine Schiff base(PCCys)significantly inhibits both uniform corrosion and localized attacks,enhancing corrosion fatigue life.Localized corrosion behavior,rather than isolated corrosion rate metrics,critically determines mechanical performance under combined corrosive-dynamic stress conditions.A multi-parameter evaluation framework integrating localized corrosion,corrosion rate,and stress effects is proposed for practical screening of corrosion inhibitors for magnesium alloys.
基金supported by National Natural Science Foundation of China[NO.11932013].
文摘This study aims to explore the impact of fatigue induced by different limb exercises on cerebral cortical oxygenation levels and functional connectivity strength using functional near-infrared spectroscopy(fNIRS).Fatigue was induced using an upper limb ergometer or a lower limb ergometer,with the load increasing gradually each minute.fNIRS covering the prefrontal cortex and motor cortex were used to collect data during the resting state,both before and after fatigue induction.A two-way ANOVA was conducted to examine differences in oxyhemoglobin(HbO_(2))and functional connectivity before and after fatigue induction in both groups,with the significance level set at 0.05.Exercise-induced fatigue in both the upper and lower limbs leads to a significant decrease in cerebral cortical oxygenation levels.Upper limb fatigue leads to a significant reduction in functional connectivity,there were significant decreases in connectivity within the motor cortex,between the motor cortex and frontal regions,and between the right ventrolateral prefrontal cortex and other frontal regions.Conversely,no significant changes were observed before and after lower limb fatigue.Future studies should focus on examining the extent to which how changes in the cerebral cortex,induced by exercise fatigue,are linked to exercise-and/or performance-related outcomes.
基金supported by the National Natural Science Foundation of China(Nos.52061005,52261025)the Science and Technology Programs of Guizhou Province,China(Nos.YQK[2023]009,CXTD[2023]009)the Technology Innovation Leading Program of Shaanxi Province,China(No.2024ZCYYDP92)。
文摘The interrupted fatigue test method was utilized to investigate the damage evolution mechanism of the notch high-cycle fatigue(NHCF)in Ti-55531 alloy with a multilevel lamellar microstructure.The results reveal that significant microvoids and microcracks predominantly initiate at α/β interfaces under various notch root radii(R).Notably,even under larger R(0.75 mm),mutual interactions of stacking faults(SFs)−deformation twins,twins−twins,and SFs−SFs are observed.Furthermore,with decreasing R(0.34 and 0.14 mm),the volume fraction of SFs escalates significantly and twins are almost absent.Moreover,activated prismatic slip system decreases with a decrease in Schmidt factor and with the further decrease in R.Finally,strain localization near α/β interfaces contributes to the initiation of fatigue microcracks.
基金co-supported by the National Natural Science Foundation of China(Nos 52475346 and U21A20130)the Natural Science Foundation of Hunan Province,China(No.2023JJ10019)+1 种基金China Postdoctoral Science Foundation(No.2022M712642)Hunan Science and Technology Innovation Plan,China(2023RC1068)。
文摘Aviation aluminum alloys,primarily from the Al-Cu,Al-Zn-Mg-(Cu),and Al-Li series,have been widely applied over six decades,greatly advancing the aviation industry.However,their Corrosion Fatigue(CF)properties impede further advancements,prompting extensive research into their CF behaviors and underlying mechanisms.This review comprehensively evaluates previous studies on their development history,CF mechanisms,and key influencing factors.First,the historical evolution of aerospace aluminum alloys is summarized.Then,the currently recognized four crack initiation mechanisms and three crack propagation mechanisms are concluded,and the effects of external and internal factors on CF performance are discussed.The paper also reviews three methods and CF life prediction models for characterizing the CF behavior of aerospace aluminum alloys.Most existing studies on the CF behavior of aluminum alloys are based on the single corrosive environment,neglecting the fact that aircrafts experience multiple corrosive environments during service.However,the most critical scientific challenge is how to enhance their CF properties under increasingly demanding service conditions.For the purpose,this paper introduces advanced forming techniques based on the microstructural control,such as Equal Channel Angular Pressing(ECAP)and High-Pressure Torsion(HPT),aimed at laying the theoretical foundation for improving CF properties through microstructural regulation.
基金the Australian Research Council Discovery Projects funding scheme(DP190102181,DP210101465).
文摘Accurate detection of driver fatigue is essential for improving road safety.This study investigates the effectiveness of using multimodal physiological signals for fatigue detection while incorporating uncertainty quantification to enhance the reliability of predictions.Physiological signals,including Electrocardiogram(ECG),Galvanic Skin Response(GSR),and Electroencephalogram(EEG),were transformed into image representations and analyzed using pretrained deep neu-ral networks.The extracted features were classified through a feedforward neural network,and prediction reliability was assessed using uncertainty quantification techniques such as Monte Carlo Dropout(MCD),model ensembles,and combined approaches.Evaluation metrics included standard measures(sensitivity,specificity,precision,and accuracy)along with uncertainty-aware metrics such as uncertainty sensitivity and uncertainty precision.Across all evaluations,ECG-based models consistently demonstrated strong performance.The findings indicate that combining multimodal physi-ological signals,Transfer Learning(TL),and uncertainty quantification can significantly improve both the accuracy and trustworthiness of fatigue detection systems.This approach supports the development of more reliable driver assistance technologies aimed at preventing fatigue-related accidents.
基金National Science and Technology Major Project(J2019-VI-0022-0138)。
文摘The high-cycle fatigue fracture characteristics and damage mechanism of nickel-based single crystal superalloys at 850℃ was investigated.The results indicate that high-cycle fatigue cracks in single crystal superalloys generally originate from defect locations on the subsurface or interior of the specimen at 850℃.Under the condition of stress ratio R=0.05,as the fatigue load decreases,the high-cycle fatigue life gradually increases.The high-cycle fatigue fracture is mainly characterized by octahedral slip mechanism.At high stress and low lifespan,the fracture exhibits single or multiple slip surface features.Some fractures originate along a vertical small plane and then propagate along the{111}slip surface.At low stress and high lifespan,the fracture surface tend to alternate and expand along multiple slip planes after originating from subsurface or internal sources,exhibiting characteristics of multiple slip planes.Through electron backscatter diffraction and transmission electron microscope analysis,there is obvious oxidation behavior on the surface of the high-cycle fatigue fracture,and the fracture section is composed of oxidation layer,distortion layer,and matrix layer from the outside to the inside.Among them,the main components of the oxidation layer are oxides of Ni and Co.The distortion layer is mainly distributed in the form of elongated or short rod-shaped oxides of Al,Ta,and W.The matrix layer is a single crystal layer.Crack initiation and propagation mechanism were obtained by systematical analysis of a large number of highcycle fatigue fractures.In addition,the stress ratio of 0.05 is closer to the vibration mode of turbine blades during actual service,providing effective guidance for the study of failure and fracture mechanisms of turbine blades.
基金National Natural Science Foundation of China(12172292,12072287)。
文摘The crack initiation and early propagation are of great significance to the overall fatigue life of material.In order to investigate the anisotropic fracture behavior of laser metal deposited Ti-6Al-4V alloy(LMD Ti64)during the early stage,the fourpoint bending fatigue test was carried out on specimens of three different directions,as well as the forged specimens.The results indicate the anisotropic crack initiation and early propagation of LMD Ti64.The direction perpendicular to the deposition direction exhibits a better fatigue resistance than the other two.The crack initiation position and propagation path are dominated by the microstructure in the vicinity of U-notch.LMD Ti64 has a typical small crack effect,and the early crack propagation velocities in three directions are similar.Affected by the slip system of LMD Ti64,secondary cracks frequently occur,which are often found to have an angle of 60°to the main crack.The electron backscatter diffraction analysis indicates that LMD Ti64 has preferred orientations,i.e.,strong 0001//Z texture and 001//Z texture.Their crystallographic orientation will change as the direction of columnarβgrains turns over,resulting in the fatigue anisotropy of LMD Ti64 in crack initiation and early crack propagation process.
基金supported by the National Natural Science Foundation of China(Nos.52074231,52274396 and 52001258)the Chongqing Natural Science Foundation(No.cstc2020jcyj-msxmX1056).
文摘Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect,and it is not completely understood yet.This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms.The study demonstrated that the faceted primaryα nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests.Slip trace analysis revealed that faceted cracking occurred at(0001)basal plane with the maximum Schmid factor value through a special cracking mode referred to as(0001)twist boundary cracking.Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations,which well identify candidates for(0001)twist boundary crack nucleation.It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface(0001)twist-boundary crack initiation,and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking.Based on this,phenomeno-logical models are proposed to explain the surface(0001)twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.
基金Project(2024JJ2073)supported by the Science Fund for Distinguished Young Scholars of Hunan Province,ChinaProjects(2023YFC3807205,2019YFC1904704)+4 种基金supported by the National Key R&D Program of ChinaProject(52178443)supported by the National Natural Science Foundation of ChinaProject(2024ZZTS0109)supported by Fundamental Research Funds for the Central Universities of Central South University,China。
文摘Permeable roads generally exhibit inferior mechanical properties and shorter service life than traditional dense-graded/impermeable roads.Furthermore,the incorporation of recycled aggregates in their construction may exacerbate these limitations.To address these issues,this study introduced a novel cement-stabilized permeable recycled aggregate material.A total of 162 beam specimens prepared with nine different levels of cement-aggregate ratio were tested to evaluate their permeability,bending load,and bending fatigue life.The experimental results indicate that increasing the content of recycled aggregates led to a reduction in both permeability and bending load.Additionally,the inclusion of recycled aggregates diminished the energy dissipation capacity of the specimens.These findings were used to establish a robust relationship between the initial damage in cement-stabilized permeable recycled aggregate material specimens and their fatigue life,and to propose a predictive model for their fatigue performance.Further,a method for assessing fatigue damage based on the evolution of fatigue-induced strain and energy dissipation was developed.The findings of this study provide valuable insights into the mechanical behavior and fatigue performance of cement-stabilized permeable recycled aggregate materials,offering guidance for the design of low-carbon-emission,permeable,and durable roadways incorporating recycled aggregates.
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.
