The relationship between microstructure and tensile behaviors of fatigued AZ31 magnesium alloy was investigated. Axial fatigue tests were performed on PLG-100 fatigue machine at stresses of 50 and 90 MPa. Tensile samp...The relationship between microstructure and tensile behaviors of fatigued AZ31 magnesium alloy was investigated. Axial fatigue tests were performed on PLG-100 fatigue machine at stresses of 50 and 90 MPa. Tensile samples were cut from the fatigued samples, named as L-sample and H-sample respectively, and the O-sample was cut from original rolled AZ31 alloy. The EBSD and TEM were used to characterize the microstructure. It is found that the twinning-detwinning was the main deformation mechanism in high stress fatigue test, while dislocation slipping was dominant in low stress fatigue test. After fatigue tests, the average grain size of the L-sample and H-sample decreased to 4.71 and 5.33 μm, and the tensile and yield strength of the L-sample and H-sample increased slightly. By analyzing SEM images, the ultimate fracture region of the L-sample consisted of dimples, while there were many microvoids in the ultimate fracture region of the H-sample. Consequently, the tensile behaviors of fatigued magnesium have a close relationship with microstructure.展开更多
The dislocation evolution wassimulated by using positiveand negative parallelstraightedgedislocationsrandomly distributing on the primary slip planes astheinitialconditions. Thevein and wallstructuresof dynamicequilib...The dislocation evolution wassimulated by using positiveand negative parallelstraightedgedislocationsrandomly distributing on the primary slip planes astheinitialconditions. Thevein and wallstructuresof dynamicequilibrium have been obtained. Abig dipolestructure wasfound inthesimulation.展开更多
In the present study, flexural behavior of carbon fber reinforced pyrolytic carbon matrix composites （C/C composites） before and after fatigue tests had been studied. The results showed that the residual flexural st...In the present study, flexural behavior of carbon fber reinforced pyrolytic carbon matrix composites （C/C composites） before and after fatigue tests had been studied. The results showed that the residual flexural strengths of the samples had been improved after fatigue tests, and the fracture mechanisms of the original and post-fatigue specimens had some differences. Fracture mechanism of the original specimens could be described as fiber/matrix interfacial de-bonding, and the dominant damage of the post-fatigue specimens could be regarded as pyrolytic carbon sub-layers＇ step-delamination. The degradation of matrix sub-layer interfacial bonding strength was beneficial to improve the mechanical properties of C/C composites.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.展开更多
Under the constant amplitude and pro- grammed loading conditions the fatigued fracture surfaces of 2024-T3 sheet are examined by SEM and TEM.A corrected method,in which the effects of loading sequence are taken into a...Under the constant amplitude and pro- grammed loading conditions the fatigued fracture surfaces of 2024-T3 sheet are examined by SEM and TEM.A corrected method,in which the effects of loading sequence are taken into account,has been developed for the retrieval of effective stress spectrum.The parameters including d,a,C,n,R,α and σ_y are evaluated according to their influences on the retrieved results.Several computer programs have been produced for the fractographic quantita- tive analysis,and the application of image pro- cessing technique in the fractographic analysis is al- so interpreted.展开更多
Ultrafine-grained(UFG)pure titanium was produced by equal channel angular pressing for 4 passes,followed by rotatory swaging at room temperature.The strain-controlled low-cycle fatigue tests of UFG and coarse-grained(...Ultrafine-grained(UFG)pure titanium was produced by equal channel angular pressing for 4 passes,followed by rotatory swaging at room temperature.The strain-controlled low-cycle fatigue tests of UFG and coarse-grained(CG)pure titanium were conducted by Instron electro-hydraulic servo fatigue testing machine in the strain amplitude range of 0.5%—1.1%at room temperature.Transmission electron microscope(TEM)and scanning electron microscope were used to investigate the microstructure and fracture surface of UFG pure titanium after fatigue tests.Results show that UFG pure titanium exhibits a longer low-cycle fatigue life,compared with the CG pure titanium.For example,at a total strain amplitude of 0.5%,UFG and CG pure titanium has fatigue life of 10850 and 4820 cycles,respectively.Significant cyclic softening occurs in UFG pure titanium,except in the case of a total strain amplitude of 0.5%.Hysteresis loop area is increased rapidly with the increase in strain amplitude.The fracture surface shows that the fatigue crack is initiated from the specimen surface.A series of fatigue striations and many microcracks exist in the propagation region.With the increase in strain amplitude,the predominant failure mode is transformed from ductile failure into quasi-cleavage failure.Dislocation slip is the main plastic deformation mechanism of UFG pure titanium during low-cycle fatigue deformation.展开更多
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
Drill string vibration during drilling plays a vital and potentially decisive role in maintaining wellbore stability,as repeated impacts may lead to fatigue and borehole collapse.While drilling through geological laye...Drill string vibration during drilling plays a vital and potentially decisive role in maintaining wellbore stability,as repeated impacts may lead to fatigue and borehole collapse.While drilling through geological layers,a material contrast may act as a localization point for wellbore damage.The hypothesis tested in this paper is that wellbore instability is focused on the boundary between the layers and that mechanical contrasts accelerate the wellbore collapse.In this study,an elastic-plastic damage model was employed to investigate the effects of repeated mechanical impacts on wellbore stability.A 2-dimensional(2D)model of a wellbore surrounded by contrasting materials was developed,and the accumulated damage caused by repeated lateral impacts was monitored.It was found that damage develops not only around the wall of the wellbore but also along the material boundaries.A sensitivity analysis was carried out to identify the impact of contrasts in both elastic(Young's modulus and Poisson's ratio)and plastic(cohesion,friction angle,and dilation angle)parameters between layers.Four damage patterns were identifiedin the simulated models.The results also suggested that the number of impacts required to reach the critical damage was highly affected by the contrast in elastic parameters,while cohesion and friction angle contrasts had a lesser effect.Additionally,increasing the contrast in the dilation angle localized the damage,thus reducing the number of impacts required to trigger wellbore failure.展开更多
Most failures in component operation occur due to cyclic loads.Validation has been performed under quasistatic loads,but the fatigue life of components under dynamic loads should be predicted to prevent failures durin...Most failures in component operation occur due to cyclic loads.Validation has been performed under quasistatic loads,but the fatigue life of components under dynamic loads should be predicted to prevent failures during component service life.Fatigue is a damage accumulation process where loads degrade the material,depending on the characteristics and number of repetitions of the load.Studies on themechanical fatigue of 3D-printedOnyx are limited.In this paper,the strength of 3D-printed Onyx components under dynamic conditions(repetitive loads)is estimated.Fatigue life prediction is influenced bymanufacturing processes,material properties,and applied loads,which can cause scatter in the results due to the interplay of these factors.By utilizing synthetic parameters derived from mechanical properties,the accuracy of fatigue life predictions has been improved significantly,from 23.13%to 98.33%.Additive manufacturing is flexible,but this flexibility generates scatter in the mechanical properties of produced components.This work also proposes the use of synthetic data with a neural network to improve the fatigue life prediction of printedOnyx subjected to tension–tension loads.Experimental uniaxial loads were used to characterize themechanical behaviorofprinted specimens.The experimental datawereused to evaluate thenumerical predictionsobtainedthrough finite element analysis using commercial software and an artificial neural network.The results showed that the use of synthetic data helped improve fatigue life prediction.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
Deep learning and fatigue life prediction remain focal research areas in rail vehicle engineering.This study addresses the vibration fatigue of wheelset lifting lug in Chengdu Metro Line 1 bogies,aiming to develop a f...Deep learning and fatigue life prediction remain focal research areas in rail vehicle engineering.This study addresses the vibration fatigue of wheelset lifting lug in Chengdu Metro Line 1 bogies,aiming to develop a fatigue life prediction method for critical bogie components using deep learning models and measured track load spectra.Extensive field tests on Chengdu Metro Line 1 were conducted to acquire acceleration and stress response data of the wheelset lifting lug,generating training samples for the neural network system.Component stress responses were calculated via time-domain track acceleration and validated against in-situ stress measurements.Results show that neural network-fitted dynamic stress values exhibit excellent consistency with measured data,with errors constrained within 5%.This study validates the proposed small-sample deep learning approach as an effective and accurate solution for fatigue life prediction of critical bogie components under operational load conditions.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
With the continuous advancement of aerospace technology,ensuring the reliability of aerospace engines after testing is critical.While various methods exist for assessing fatigue life,non-destructive prediction based o...With the continuous advancement of aerospace technology,ensuring the reliability of aerospace engines after testing is critical.While various methods exist for assessing fatigue life,non-destructive prediction based on insitu X-ray diffraction(XRD)residual stress analysis remains underexplored—particularly for low-cycle fatigue in welded joints.This study proposes a novel approach that uses in-situ XRD to monitor residual stress evolution under fatigue and creep loading in gas tungsten arc welding(GTAW)joints of aerospace-grade austenitic stainless steel SUS321.Through metallographic observation,scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),and in-situ XRD measurements,we demonstrate a strong correlation between longitudinal residual stress at the weld center and fatigue life.Under fatigue loading at 60%of the ultimate tensile strength(UTS),longitudinal residual stress transitions from tensile to compressive with increasing cycles,and fatigue fracture occurs once residual stress approaches base metal levels(∼0 MPa).In contrast,under creep loading,no clear trend in Y-direction residual stress was observed,limiting its utility for creep life prediction.This work establishes a reliable,non-destructive framework for evaluating the service life of welded aerospace components,offering a new methodology beyond conventional practices.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
Background:Cupping therapy(CT),an ancient practice revived in modern sports medicine,offers potential benefits for athlete recovery and performance.Distinctions between wet CT(WCT)and dry CT(DCT)in sports science focu...Background:Cupping therapy(CT),an ancient practice revived in modern sports medicine,offers potential benefits for athlete recovery and performance.Distinctions between wet CT(WCT)and dry CT(DCT)in sports science focus on their effects on recovery metrics,particularly how they influence sleep quality,perceived wellness,and athletic performance.Despite anecdotal evidence of its efficacy,rigorous comparative studies are scarce.Objective:This study aimed to evaluates and compare the effects of WCT and DCT on endurance,perceived wellness,exertion levels,and sleep quality among young,active males,addressing the gap in the literature regarding CT's efficacy in sports performance and recovery.Methods:Thirty-two amateur runners were randomly divided into two groups:one followed WCT sessions and the other followed DCT sessions.The study assessed the interventions'impacts on endurance performance(Yo-Yo intermittent recovery test),sleep quality(Pittsburgh Sleep Quality Index),and perceived exertion(Borg CR10 Scale).Heart rate was measured using a Polar H10 sensor to gauge physiological responses during physical tests.Results:Significant improvements were observed in the WCT group for sleep latency(%change=-82.31%;interaction group×time p=0.006;Cohen's d=0.74)and sleep disturbance(%change=-68.70%;interaction group×time p<0.001;Cohen's d=1.09),suggesting enhanced sleep quality(global score;%change=-52.81;interaction group×time p=0.004;Cohen's d=0.77).However,no significant differences were found in direct performance metrics(distance,maximal heart rate,maximal oxygen uptake)between WCT and DCT groups.These findings highlight WCT's potential as a recovery aid,particularly through improved sleep,without directly influencing endurance performance outcomes.Conclusion:WCT may serve as an effective ergogenic aid for athletes by potentially improving sleep quality and reducing perceived exertion,thus contributing indirectly to performance through enhanced recovery.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
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
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
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
基金Projects(51271208,51071183,50890170)supported by the National Natural Science Foundation of ChinaProject(2010CB631004)supported by the National Basic Research Program of China
文摘The relationship between microstructure and tensile behaviors of fatigued AZ31 magnesium alloy was investigated. Axial fatigue tests were performed on PLG-100 fatigue machine at stresses of 50 and 90 MPa. Tensile samples were cut from the fatigued samples, named as L-sample and H-sample respectively, and the O-sample was cut from original rolled AZ31 alloy. The EBSD and TEM were used to characterize the microstructure. It is found that the twinning-detwinning was the main deformation mechanism in high stress fatigue test, while dislocation slipping was dominant in low stress fatigue test. After fatigue tests, the average grain size of the L-sample and H-sample decreased to 4.71 and 5.33 μm, and the tensile and yield strength of the L-sample and H-sample increased slightly. By analyzing SEM images, the ultimate fracture region of the L-sample consisted of dimples, while there were many microvoids in the ultimate fracture region of the H-sample. Consequently, the tensile behaviors of fatigued magnesium have a close relationship with microstructure.
文摘The dislocation evolution wassimulated by using positiveand negative parallelstraightedgedislocationsrandomly distributing on the primary slip planes astheinitialconditions. Thevein and wallstructuresof dynamicequilibrium have been obtained. Abig dipolestructure wasfound inthesimulation.
基金supported by the National Natural Science Foundation of China (Nos. 51472203 and 51521061)the “111” Project (No. B08040)the Research Fund of State Key Laboratory of Solidification Processing (NWPU), China (No. 142-TZ-2016)
文摘In the present study, flexural behavior of carbon fber reinforced pyrolytic carbon matrix composites （C/C composites） before and after fatigue tests had been studied. The results showed that the residual flexural strengths of the samples had been improved after fatigue tests, and the fracture mechanisms of the original and post-fatigue specimens had some differences. Fracture mechanism of the original specimens could be described as fiber/matrix interfacial de-bonding, and the dominant damage of the post-fatigue specimens could be regarded as pyrolytic carbon sub-layers＇ step-delamination. The degradation of matrix sub-layer interfacial bonding strength was beneficial to improve the mechanical properties of C/C composites.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.
文摘Under the constant amplitude and pro- grammed loading conditions the fatigued fracture surfaces of 2024-T3 sheet are examined by SEM and TEM.A corrected method,in which the effects of loading sequence are taken into account,has been developed for the retrieval of effective stress spectrum.The parameters including d,a,C,n,R,α and σ_y are evaluated according to their influences on the retrieved results.Several computer programs have been produced for the fractographic quantita- tive analysis,and the application of image pro- cessing technique in the fractographic analysis is al- so interpreted.
基金Natural Science Foundation of Shaanxi Province (2023-JC-YB-312)。
文摘Ultrafine-grained(UFG)pure titanium was produced by equal channel angular pressing for 4 passes,followed by rotatory swaging at room temperature.The strain-controlled low-cycle fatigue tests of UFG and coarse-grained(CG)pure titanium were conducted by Instron electro-hydraulic servo fatigue testing machine in the strain amplitude range of 0.5%—1.1%at room temperature.Transmission electron microscope(TEM)and scanning electron microscope were used to investigate the microstructure and fracture surface of UFG pure titanium after fatigue tests.Results show that UFG pure titanium exhibits a longer low-cycle fatigue life,compared with the CG pure titanium.For example,at a total strain amplitude of 0.5%,UFG and CG pure titanium has fatigue life of 10850 and 4820 cycles,respectively.Significant cyclic softening occurs in UFG pure titanium,except in the case of a total strain amplitude of 0.5%.Hysteresis loop area is increased rapidly with the increase in strain amplitude.The fracture surface shows that the fatigue crack is initiated from the specimen surface.A series of fatigue striations and many microcracks exist in the propagation region.With the increase in strain amplitude,the predominant failure mode is transformed from ductile failure into quasi-cleavage failure.Dislocation slip is the main plastic deformation mechanism of UFG pure titanium during low-cycle fatigue deformation.
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support from the Research Council of Norway,Equinor,and Sekal with NFR project(Grant No.308826).
文摘Drill string vibration during drilling plays a vital and potentially decisive role in maintaining wellbore stability,as repeated impacts may lead to fatigue and borehole collapse.While drilling through geological layers,a material contrast may act as a localization point for wellbore damage.The hypothesis tested in this paper is that wellbore instability is focused on the boundary between the layers and that mechanical contrasts accelerate the wellbore collapse.In this study,an elastic-plastic damage model was employed to investigate the effects of repeated mechanical impacts on wellbore stability.A 2-dimensional(2D)model of a wellbore surrounded by contrasting materials was developed,and the accumulated damage caused by repeated lateral impacts was monitored.It was found that damage develops not only around the wall of the wellbore but also along the material boundaries.A sensitivity analysis was carried out to identify the impact of contrasts in both elastic(Young's modulus and Poisson's ratio)and plastic(cohesion,friction angle,and dilation angle)parameters between layers.Four damage patterns were identifiedin the simulated models.The results also suggested that the number of impacts required to reach the critical damage was highly affected by the contrast in elastic parameters,while cohesion and friction angle contrasts had a lesser effect.Additionally,increasing the contrast in the dilation angle localized the damage,thus reducing the number of impacts required to trigger wellbore failure.
文摘Most failures in component operation occur due to cyclic loads.Validation has been performed under quasistatic loads,but the fatigue life of components under dynamic loads should be predicted to prevent failures during component service life.Fatigue is a damage accumulation process where loads degrade the material,depending on the characteristics and number of repetitions of the load.Studies on themechanical fatigue of 3D-printedOnyx are limited.In this paper,the strength of 3D-printed Onyx components under dynamic conditions(repetitive loads)is estimated.Fatigue life prediction is influenced bymanufacturing processes,material properties,and applied loads,which can cause scatter in the results due to the interplay of these factors.By utilizing synthetic parameters derived from mechanical properties,the accuracy of fatigue life predictions has been improved significantly,from 23.13%to 98.33%.Additive manufacturing is flexible,but this flexibility generates scatter in the mechanical properties of produced components.This work also proposes the use of synthetic data with a neural network to improve the fatigue life prediction of printedOnyx subjected to tension–tension loads.Experimental uniaxial loads were used to characterize themechanical behaviorofprinted specimens.The experimental datawereused to evaluate thenumerical predictionsobtainedthrough finite element analysis using commercial software and an artificial neural network.The results showed that the use of synthetic data helped improve fatigue life prediction.
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 CRRC Original Technology TenYear Cultivation Program(Grant No.2022CYY007)。
文摘Deep learning and fatigue life prediction remain focal research areas in rail vehicle engineering.This study addresses the vibration fatigue of wheelset lifting lug in Chengdu Metro Line 1 bogies,aiming to develop a fatigue life prediction method for critical bogie components using deep learning models and measured track load spectra.Extensive field tests on Chengdu Metro Line 1 were conducted to acquire acceleration and stress response data of the wheelset lifting lug,generating training samples for the neural network system.Component stress responses were calculated via time-domain track acceleration and validated against in-situ stress measurements.Results show that neural network-fitted dynamic stress values exhibit excellent consistency with measured data,with errors constrained within 5%.This study validates the proposed small-sample deep learning approach as an effective and accurate solution for fatigue life prediction of critical bogie components under operational load conditions.
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supported by the Fundamental Research Funds for the Central Universities,the Institute of Marine Equipment,the Shanghai Rising-Star Program of Science and Technology Commission of Shanghai Municipality(Grant No.23QA1404700)National Natural Science Foundation of China(Grant Nos.52475384,52505409)China Postdoctoral Science Foundation(Grant No.2024M761963).
文摘With the continuous advancement of aerospace technology,ensuring the reliability of aerospace engines after testing is critical.While various methods exist for assessing fatigue life,non-destructive prediction based on insitu X-ray diffraction(XRD)residual stress analysis remains underexplored—particularly for low-cycle fatigue in welded joints.This study proposes a novel approach that uses in-situ XRD to monitor residual stress evolution under fatigue and creep loading in gas tungsten arc welding(GTAW)joints of aerospace-grade austenitic stainless steel SUS321.Through metallographic observation,scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),and in-situ XRD measurements,we demonstrate a strong correlation between longitudinal residual stress at the weld center and fatigue life.Under fatigue loading at 60%of the ultimate tensile strength(UTS),longitudinal residual stress transitions from tensile to compressive with increasing cycles,and fatigue fracture occurs once residual stress approaches base metal levels(∼0 MPa).In contrast,under creep loading,no clear trend in Y-direction residual stress was observed,limiting its utility for creep life prediction.This work establishes a reliable,non-destructive framework for evaluating the service life of welded aerospace components,offering a new methodology beyond conventional practices.
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.
文摘Background:Cupping therapy(CT),an ancient practice revived in modern sports medicine,offers potential benefits for athlete recovery and performance.Distinctions between wet CT(WCT)and dry CT(DCT)in sports science focus on their effects on recovery metrics,particularly how they influence sleep quality,perceived wellness,and athletic performance.Despite anecdotal evidence of its efficacy,rigorous comparative studies are scarce.Objective:This study aimed to evaluates and compare the effects of WCT and DCT on endurance,perceived wellness,exertion levels,and sleep quality among young,active males,addressing the gap in the literature regarding CT's efficacy in sports performance and recovery.Methods:Thirty-two amateur runners were randomly divided into two groups:one followed WCT sessions and the other followed DCT sessions.The study assessed the interventions'impacts on endurance performance(Yo-Yo intermittent recovery test),sleep quality(Pittsburgh Sleep Quality Index),and perceived exertion(Borg CR10 Scale).Heart rate was measured using a Polar H10 sensor to gauge physiological responses during physical tests.Results:Significant improvements were observed in the WCT group for sleep latency(%change=-82.31%;interaction group×time p=0.006;Cohen's d=0.74)and sleep disturbance(%change=-68.70%;interaction group×time p<0.001;Cohen's d=1.09),suggesting enhanced sleep quality(global score;%change=-52.81;interaction group×time p=0.004;Cohen's d=0.77).However,no significant differences were found in direct performance metrics(distance,maximal heart rate,maximal oxygen uptake)between WCT and DCT groups.These findings highlight WCT's potential as a recovery aid,particularly through improved sleep,without directly influencing endurance performance outcomes.Conclusion:WCT may serve as an effective ergogenic aid for athletes by potentially improving sleep quality and reducing perceived exertion,thus contributing indirectly to performance through enhanced recovery.
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.
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.
