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
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
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
The development of substitutable meniscus implants that can effectively protect articular cartilage remains a great challenge.Herein,a polyurethane with chemical crosslinking and sulfobetaine extenders containing hydr...The development of substitutable meniscus implants that can effectively protect articular cartilage remains a great challenge.Herein,a polyurethane with chemical crosslinking and sulfobetaine extenders containing hydrophobic chains(PU-CL-hSB)is developed,which could improve comprehensive properties and long-term stability simultaneously.By regulating the mole ratio of functional groups,PU-CL-hSB with appropriate mechanical properties,excellent tribological properties,and good fatigue resistance is used to prepare substitutable meniscus implant by hot-pressing.Due to the synergistic effect of functional groups,PU-CL-hSB meniscus implant presents comparable or even superior properties to native meniscus.It withstands a maximum force of 26.08 N versus 25.14 N for native meniscus,an energy dissipation from 45.93 to 39.17 N mm compared to 28.83 to 19.11 N mm for native meniscus over 300 cycles,and a friction coefficient from 0.08 to 0.19 compared to 0.11 to 0.26 for native meniscus.This PU-CL-hSB meniscus implant is further implanted into live rabbit knee joints for 8 and 25 weeks by a new approach,and in vivo data indicate that PU-CL-hSB meniscus implant not only protects articular cartilage from severe damage without eliciting inflammatory responses,but also can maintain normal physiological activities in the native state.Our findings present a substitutable meniscus implant that could be applied in vivo and propose evaluation methodologies for meniscus implants.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
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
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
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
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
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
Background:Fatigue,which is commonly observed in Parkinson’s disease(PD),can greatly reduce quality of life and is difficult to treat.We here aimed to investigate the prevalence and characteristics of fatigue among P...Background:Fatigue,which is commonly observed in Parkinson’s disease(PD),can greatly reduce quality of life and is difficult to treat.We here aimed to investigate the prevalence and characteristics of fatigue among PD patients and to explore an effective strategy to treat PD fatigue.Method:This was an observational cross-sectional study conducted in northeastern China.We examined fatigue in 222 PD patients from northeastern China using the Parkinson Fatigue Scale-16(PFS-16).The disease severity,depression,sleep and cognitive functioning were assessed with the Hoehn&Yahr staging(H-Y stage),Unified Parkinson’s Disease Rating Scale(UPDRS),Hamilton Depression Scale(HAMD),Parkinson’s Disease Sleep Scale(PDSS)and Montreal Cognitive Assessment(MoCA)by interview.Results:The frequency of fatigue in PD patients was 59.46%.Fatigued patients had longer disease durations and greater disease severity than nonfatigued patients.Additionally,fatigued PD patients scored significantly higher for all motor symptoms,except for tremor,and had more serious depressive symptoms and sleep disturbances than nonfatigued PD patients did.The sleep disturbance severity was an independent factor for fatigue.Furthermore,43.04% of fatigued patients taking dopaminergic drugs had fatigue remission.Depression severity was identified as an independent factor for dopaminergic drug non-responsive fatigue.Conclusions:PD patients with severe sleep disturbances tend to suffer from fatigue.Levodopa improved fatigue only in PD patients with mild depression or no depression,implying that dopaminergic medication is required,but not sufficient,for fatigue suppression in PD patients with moderate or severe depression.Thus,restoring serotonergic neurotransmission as a combination therapy may offer a better strategy for the treatment of fatigue in these patients.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
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.
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 Special Project for High-tech Industrialization of Science and Technology Cooperation between Jilin Province and Chinese Academy of Sciences(2023SYHZ0042)。
文摘The development of substitutable meniscus implants that can effectively protect articular cartilage remains a great challenge.Herein,a polyurethane with chemical crosslinking and sulfobetaine extenders containing hydrophobic chains(PU-CL-hSB)is developed,which could improve comprehensive properties and long-term stability simultaneously.By regulating the mole ratio of functional groups,PU-CL-hSB with appropriate mechanical properties,excellent tribological properties,and good fatigue resistance is used to prepare substitutable meniscus implant by hot-pressing.Due to the synergistic effect of functional groups,PU-CL-hSB meniscus implant presents comparable or even superior properties to native meniscus.It withstands a maximum force of 26.08 N versus 25.14 N for native meniscus,an energy dissipation from 45.93 to 39.17 N mm compared to 28.83 to 19.11 N mm for native meniscus over 300 cycles,and a friction coefficient from 0.08 to 0.19 compared to 0.11 to 0.26 for native meniscus.This PU-CL-hSB meniscus implant is further implanted into live rabbit knee joints for 8 and 25 weeks by a new approach,and in vivo data indicate that PU-CL-hSB meniscus implant not only protects articular cartilage from severe damage without eliciting inflammatory responses,but also can maintain normal physiological activities in the native state.Our findings present a substitutable meniscus implant that could be applied in vivo and propose evaluation methodologies for meniscus implants.
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 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 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 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.
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This work was funded by the China National Nature Science Fund(no.30973153)Liaoning Doctoral Starting Fund(20071042)the Foundation of the Liaoning Educational Committee(L202013136,L2010560)。
文摘Background:Fatigue,which is commonly observed in Parkinson’s disease(PD),can greatly reduce quality of life and is difficult to treat.We here aimed to investigate the prevalence and characteristics of fatigue among PD patients and to explore an effective strategy to treat PD fatigue.Method:This was an observational cross-sectional study conducted in northeastern China.We examined fatigue in 222 PD patients from northeastern China using the Parkinson Fatigue Scale-16(PFS-16).The disease severity,depression,sleep and cognitive functioning were assessed with the Hoehn&Yahr staging(H-Y stage),Unified Parkinson’s Disease Rating Scale(UPDRS),Hamilton Depression Scale(HAMD),Parkinson’s Disease Sleep Scale(PDSS)and Montreal Cognitive Assessment(MoCA)by interview.Results:The frequency of fatigue in PD patients was 59.46%.Fatigued patients had longer disease durations and greater disease severity than nonfatigued patients.Additionally,fatigued PD patients scored significantly higher for all motor symptoms,except for tremor,and had more serious depressive symptoms and sleep disturbances than nonfatigued PD patients did.The sleep disturbance severity was an independent factor for fatigue.Furthermore,43.04% of fatigued patients taking dopaminergic drugs had fatigue remission.Depression severity was identified as an independent factor for dopaminergic drug non-responsive fatigue.Conclusions:PD patients with severe sleep disturbances tend to suffer from fatigue.Levodopa improved fatigue only in PD patients with mild depression or no depression,implying that dopaminergic medication is required,but not sufficient,for fatigue suppression in PD patients with moderate or severe depression.Thus,restoring serotonergic neurotransmission as a combination therapy may offer a better strategy for the treatment of fatigue in these patients.
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.
