Fatigue Conditions Research Articles

Research on the Influence of Operator Fatigue Factors on Port Service Capability Based on Discrete System Simulation

With the continuous and stable development of the global economy, ports play a vital role as cargo transhipment hubs. Among them, the human factor of the operators in the port plays a decisive role in the port service ability. In order to explore the specific effects of different fatigue states of the quay bridge, yard bridge, and internal truck operators in the traditional container terminal on the port’s service capacity, seven test schemes are proposed, and computer simulation methods are used to build a simulation model of the terminal. Through a large number of simulation tests, it is concluded that the fatigue of different equipment operators has different effects on the operation efficiency of the terminal. If the three operators are fatigued at the same time, the operation efficiency of the terminal will be reduced by 17.27%, which will have a very negative impact on the overall operation of the terminal. Therefore, optimizing the scheduling of operators and avoiding fatigue operations will improve the port’s service capacity.

Study on the influence of spring helix angle increase on stress distribution and fatigue life of the operating mechanism

The spring operating mechanism is the key component of the high-voltage circuit breaker, and its split-closing power comes from the self-energy storage of the split-closing spring, so the performance mechanism and fatigue state of the split-closing spring has a great impact on the operation process and dynamic response of the operating mechanism. In this paper, by increasing the coil angle of the spring, changing the spring design material, classifying and modeling the spring, and applying finite element analysis aim to analyze the static structure. The influence of the change of different spring coil angles and materials on the stress distribution of the spring is explored, and the finite element calculation results are imported into the life analysis module to evaluate the life of springs with different helix angles and materials. The results show that under the action of 9 kN working load, after the helix angle is increased by 0.6°, the spring life decreases by 7.23%, the spring life continues to increase by 0.7°, and the overall life of the spring decreases by 12.3%, compared with the initial state. The life decline curve shows an inverse proportional trend.

Effect of maximum applied cyclic stress on fretting fatigue stress distribution of flat-on-flat modified 9Cr-1Mo steel contact: Finite element analysis

Fretting fatigue experiments were conducted on a modified 9Cr-1Mo (P91) steel under flat-on-flat contact with maximum applied cyclic stress (σmax) levels of 450 MPa, 500 MPa and 550 MPa at a stress ratio of 0.3 and a contact pressure of 100 MPa. A decrease in the cyclic life was observed with an increase in σmax. Chaboche model with isotropic and kinematic hardening was employed in finite element analysis to evaluate the stress distribution near the contact pad and along the contact surface under fretting fatigue conditions. In addition, the contact-related parameters such as contact pressure, contact shear stress and relative tangential motion were also assessed. The relative tangential motion was found to increase with increasing σmax. Besides, the peak values of normal stress (parallel to the applied loading direction) and maximum principal stress were observed around the leading and trailing edges of the contact pad at the σmax. The amplitude of relative tangential motion and slip zone increases with σmax. The orientations of the principal plane and shear plane to the applied cyclic loading direction are −89.5° and −134.5°, irrespective of the σmax. The fracture surface of the failed specimen revealed that the direction of the crack was nearly perpendicular to the applied stress. Smith-Watson-Topper parameter was used for estimating the crack initiation life with σmax. It has been noticed that the fraction and dominance of crack initiation or propagation phase depend on the imposed cyclic condition for the steel.

Analyzing Multi-Mode Fatigue Information from Speech and Gaze Data from Air Traffic Controllers

In order to determine the fatigue state of air traffic controllers from air talk, an algorithm is proposed for discriminating the fatigue state of controllers based on applying multi-speech feature fusion to voice data using a Fuzzy Support Vector Machine (FSVM). To supplement the basis for discrimination, we also extracted eye-fatigue-state discrimination features based on Percentage of Eyelid Closure Duration (PERCLOS) eye data. To merge the two classes of discrimination results, a new controller fatigue-state evaluation index based on the entropy weight method is proposed, based on a decision-level fusion of fatigue discrimination results for speech and the eyes. The experimental results show that the fatigue-state recognition accuracy rate was 86.0% for the fatigue state evaluation index, which was 3.5% and 2.2%higher than those for speech and eye assessments, respectively. The comprehensive fatigue evaluation index provides important reference values for controller scheduling and mental-state evaluations.

Use of subject-specific models to detect fatigue-related changes in running biomechanics: a random forest approach.

Running biomechanics are affected by fatiguing or prolonged runs. However, no evidence to date has conclusively linked this effect to running-related injury (RRI) development or performance implications. Previous investigations using subject-specific models in running have demonstrated higher accuracy than group-based models, however, this has been infrequently applied to fatigue. In this study, two experiments were conducted to determine whether subject-specific models outperformed group-based models to classify running biomechanics during non-fatigued and fatigued conditions. In the first experiment, 16 participants performed four treadmill runs at or around the maximal lactate steady state. In the second experiment, nine participants performed five prolonged runs using commercial wearable devices. For each experiment, two segments were extracted from each trial from early and late in the run. For each participant, a random forest model was applied with a leave-one-run-out cross-validation to classify between the early (non-fatigued) and late (fatigued) segments. Additionally, group-based classifiers with a leave-one-subject-out cross validation were constructed. For experiment 1, mean classification accuracies for the single-subject and group-based classifiers were 68.2 ± 8.2% and 57.0 ± 8.9%, respectively. For experiment 2, mean classification accuracies for the single-subject and group-based classifiers were 68.9 ± 17.1% and 61.5 ± 11.7%, respectively. Variable importance rankings were consistent within participants, but these rankings differed from each participant to those of the group. Although the classification accuracies were relatively low, these findings highlight the advantage of subject-specific classifiers to detect changes in running biomechanics with fatigue and indicate the potential of using big data and wearable technology approaches in future research to determine possible connections between biomechanics and RRI.

Task reallocation of human-robot collaborative production workshop based on a dynamic human fatigue model

As collaborative robots become more popular in industry, they are used to collaborate with human workers and free human workers from repeated and heavy work and reduce the risk of physical injuries. However, human workers need to finish tasks that require high cognitive abilities, which increases the risk of mental fatigue. Fatigue can negatively impact workers and even threaten the safety of workers. Currently, the dynamics of human fatigue model are rarely considered. Hence, it is crucial to develop a dynamic allocation method for human-robot collaborative tasks that considers dynamic human fatigue to ensure efficient and safe human-robot collaboration. This paper proposes a task reallocation method for human-robot collaborative production workshop based on a dynamic human fatigue model. A fatigue feature extraction method from multimodal data and a fatigue evaluation network are proposed to evaluate the current fatigue status of human workers. Based on the evaluation results, the human fatigue model is dynamically updated. If the worker’s fatigue state changes, a task reallocation scheme is generated by an improved genetic algorithm based on reinforcement learning and the dynamic human fatigue model. The experimental results show that the proposed model and algorithm are effective and efficient, and can provide innovative insights for realizing a human-centered manufacturing workshop.

Predicting fracture behavior (mixed‐modes I/III) of cement asphalt mortar under fatigue and static loading conditions using response surface method

AbstractStatic and cyclic fracture properties (Modes I, III, and I/III) of cement emulsified asphalt mortar at three frequencies were investigated in terms of the fracture energy and fatigue life, respectively. For this to achieve, 576 edge notched disk bend specimens with 16 haphazard mix designs including, disparate bitumen‐to‐cement (B/C), water‐to‐cement (W/C) ratios, and cement contents (C) were tested. By developing statistical models (at the 5% significance level, p value < 0.05), the findings revealed that under static loading, the fracture energy got highest in tearing mode and lowest in opening mode. In all fracture modes, the fracture energy decreased with an increase of C and decrease of B/C while the mortar's fatigue life augmented due to a rise in C and B/C. Moreover, the fatigue life gained an increase with the increase in the fracture energy, loading frequency, and Me in the nonlinear trend. The utmost variation of fatigue life was explained with the increase of fracture energy which had the greatest effect in mode‐III loading.

Components Design of Cube Cutter for Fruit and Meat: Strength Analyses Under Static and Fatigue Conditions

Food preparation is one of the longest and the most time consuming part in cooking a food. In the preparation phase, the food ingredients are often needed to be cut into cube shape or stick shape. Besides that, most of the small food industry needs to serve a lot of customers while having limited number of workers, causing the workers to be tired even before the cooking process begin. For this reason, this paper proposes a design idea of a cutting tool that can cut food ingredients into cube and stick shape. This design is also completed with the strength analysis to evaluate the components’ safety for applied force of 50N. Furthermore, the strength analysis was done by a theoretical approach of static and fatigue loading. According to the analysis, the cutting tool has a safety of more than 3.7 for static loading and 2.14 for fatigue loading. In addition, this paper is expected to be used as a reference to create a cutting tool that can help workers in Indonesia

Numerical and Experimental Analysis of Strength Loss of 1.2709 Maraging Steel Produced by Selective Laser Melting (SLM) under Thermo-Mechanical Fatigue Conditions.

The result of the development of additive manufacturing (AM) methods is the increasing use of the selective laser melting (SLM) method as a technique for producing tooling for injection moulds and die casting pressure moulds from maraging steel powders. The mould components are subjected to varying thermo-mechanical loads during these operations. This paper presents a numerical model that is used to predict the fatigue life of a material that is loaded with a time-varying temperature field according to the classic and modified Coffin test. Using a computational model, the temperature changes in the resistance-heated specimen and the stress and strain fields that are caused by this phenomenon were determined. Using three different multiaxial fatigue criteria, the fatigue life of SLM steel was determined. Numerical calculations were verified using experimental thermal fatigue tests on 1.2709 SLM steel that was aged at 490 °C as well as via metallographic tests. The numerical model was used to predict the durability of the same steel aged at 540 °C. The effect of specimen clamping conditions on the fatigue life of SLM steel was determined numerically. The value of the decrease in strength of SLM steel as a result of the increasing number of cycles of temperature changes was determined experimentally; a great influence of ageing temperature on fatigue life was found. Changes in the structure of steel occurring during cyclic changes in temperature are presented.

Microstructure analysis and life prediction of DD6 superalloy under 760 °C combined high and low cycle fatigue conditions

The impact of high and low cycle combined loads on the fatigue performance of DD6 alloy was investigated in this work. Specifically, the combined high- and low-cycle fatigue response of DD6 alloy was examined at a temperature of 760 °C under different low cycle stress amplitudes (960, 1000, and 1040 MPa). The findings revealed that higher low cycle stress amplitudes result in shorter combined high and low cycle fatigue life and less dispersion in life. Correlations between the microstructural features (crystal plane distribution, fracture elevation difference, and the area proportion of crack propagation zone) and fatigue performance were accurately established, demonstrating a linear relationship between these microstructural features and the logarithm of fatigue life. The study also uncovered the evolution rule of microstructural features in high- and low-cycle combined fatigue. Furthermore, the fracture mechanism was analyzed and the distribution of high and low cycle combined fatigue life of DD6 alloy at 760 °C was statistically validated using the dual-parameter Weibull distribution theory. Building upon the crystal plasticity theory, a fatigue life prediction model was developed, and the combined cycle fatigue lifespan under various low cycle stress amplitudes was compared. The comparison between the predicted life and actual fatigue life indicated that the predicted lifespan falls in three times the scatter band.

A pilot study on the immune cell proteome of long COVID patients shows changes to physiological pathways similar to those in myalgic encephalomyelitis/chronic fatigue syndrome

Of those infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), ~ 10% develop the chronic post-viral debilitating condition, long COVID (LC). Although LC is a heterogeneous condition, about half of cases have typical post-viral fatigue with onset and symptoms that are very similar to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). A key question is whether these conditions are closely related. ME/CFS is a post-stressor fatigue condition that arises from multiple triggers. To investigate the pathophysiology of LC, a pilot study of patients (n = 6) and healthy controls (n = 5) has used quantitative proteomics to discover changes in peripheral blood mononuclear cell (PBMC) proteins. A principal component analysis separated all long COVID patients from healthy controls. Analysis of 3131 proteins identified 162 proteins differentially regulated, of which 37 were related to immune functions, and 21 to mitochondrial functions. Markov cluster analysis identified clusters involved in immune system processes, and two aspects of gene expression-spliceosome and transcription. These results were compared with an earlier dataset of 346 differentially regulated proteins in PBMC’s from ME/CFS patients (n = 9) analysed by the same methodology. There were overlapping protein clusters and enriched molecular pathways particularly in immune functions, suggesting the two conditions have similar immune pathophysiology as a prominent feature, and mitochondrial functions involved in energy production were affected in both conditions.

An Investigation on the Effect of Watertightness Criteria on the Structural Assessment of Prestressed Concrete Substructures of Floating Wind Turbines

The effect of watertightness criteria on structural assessment was investigated in this study through the design of a semi-submersible floater for a 10 MW wind turbine. A structural assessment was carried out for the ultimate, fatigue, and serviceability limit states, where six cases of combinations of the loading conditions and structural requirements were assumed for the assessment of watertightness. The different assessment conditions for watertightness resulted in different designs of prestressing tension, which also caused differences in the design margins for the ultimate limit states as well as the SN diagram used for the assessment of the fatigue limit states. The maximum stress acting on the member of the floating wind turbine differed by about 7.6 to 16.2% for the 50-year and 1-year environmental conditions. The small difference between the stresses for the two return periods can be attributed to the large component of the wind turbine thrust in the variable loads. When the partial load factor of 1.0 was used, the structural requirement in the prestressing design caused larger differences compared to the return period of the loading conditions in the watertightness assessment. The use of the partial load factor of 0.5 for the prestressing design also caused a large difference in the results of the structural assessment, indicating the necessity of further investigation of the determination of the partial load factor for floating offshore wind turbines.

Biological Aspects of Fatigue: A Narrative Review

Introduction: Fatigue is among the most common symptoms in Primary Health-Care and it can be caused by several factors. It is prevailing in the general population and the aggravated condition of fatigue is named Chronic Fatigue Syndrome. This syndrome has a negative impact on the individual’s quality of life and it can lead to functional incapacity. Despite decades of research, Chronic Fatigue Syndrome remains a mysterious disease that needs to be highlighted.
 Objective: To describe biological aspects of fatigue regarding its definition, biological origin, the main etiologies of Chronic Fatigue Syndrome and its relation with the circadian cycle, as well as the main methods for measurement, diagnosis, complementary tests and treatment.
 Method: It is a narrative review, performed from 2019 to 2022, using the PubMed/MEDLINE database and a manual search for studies referred in selected articles from authors with notorious knowledge and specialized groups in the area. It was performed a combination of several search terms added to Fatigue and Fatigue Syndrome, Chronic through Boolean Operators AND, OR and NOT. Scientific articles that involved studies in humans were included in the research. The articles were available in full version for free, in Portuguese, English and Spanish, with no restriction related to the period of publication. The articles were selected by reading of titles and abstracts. The ones that did not fit the aim of this study were excluded. The remaining articles were read in full and selected according to their relevance and contribution to the topic.
 Results: Fatigue can be considered peripheral, physical, mental, intellectual and emotional, but there is no consensus regarding its definition. Its main biological origin is related to cytokines, however, fatigue’s measurement is still mostly conducted by self-reports of affected patients. There is no objective marker consistently associated to fatigue. Regarding Chronic Fatigue Syndrome, its etiology is still not very well-established, but it was observed that genetic, epigenetic, immunological, infectious, psychosocial, psychiatric and neurological factors can contribute to it. Since fatigue is multidimensional and multifactorial, it is important to associate multiple instruments for its investigation. A potent strategy for the measurement of fatigue is using instruments adapted to the realities, extensively tested in different populations considering socio-economic-cultural aspects. These instruments assess the cognitive function in order to measure several variables and when associated they can increase the accuracy of the investigative instruments. The treatments available include cognitive-behavioral therapy, gradual exercises, immunological treatment, corticosteroids and antidepressants, but they do not guarantee a full remission of symptoms in an isolated way. 
 Conclusion: Even though there are well-defined biological factors it still lacks a precise marker for the measurement of fatigue. Considering fatigue as multidimensional and multifactorial, it is important to associate several instruments for its investigation. The treatments available have shown effectiveness, but they do not guarantee a full remission of symptoms in an isolated way. For this reason, it is necessary a bio-psycho-social care for these patients.

Life prediction and failure analysis in laser powder bed fused TiC/Ti6Al4V titanium matrix composite under high cycle and very high cycle fatigue conditions

This study investigates the failure behavior of a TiC-reinforced titanium matrix composite (TMC) manufactured by laser powder bed fusion (L-PBF) through fully reversed and pulsating tension fatigue tests in both high-cycle and very-high-cycle regimes. Inhomogeneous hardening zone (IHZ) and un-melted TiC zone (UMTZ) resulting from TiC agglomeration, along with pore and lack of fusion (LOF) generated during the L-PBF process, play a crucial role in inducing fatigue failure and influencing the variability of fatigue life. Advanced microscopy techniques, including optical microscopy, scanning electron microscopy, and electron backscatter diffraction, were employed to elucidate four failure modes: LOF-assisted IHZ cracking, IHZ cracking, pore cracking, and UMTZ cracking. IHZ cracking originates from stress concentration caused by the mechanical property mismatch between IHZ and Ti matrix, leading to brittle fracture of α'-grains within the IHZ. This constitutes the predominant failure mode. The presence of LOF near IHZ further exacerbates stress concentration, diminishing the material's load-carrying capacity and significantly reducing fatigue life. Considering the fatigue cracking mechanism, microstructural characteristics and the influence of defect location and stress concentration, a crack nucleation life prediction model is developed. The agreement between experimental and predicted data is satisfactory.

Effects of cognitive load and different exercise intensities on perceived effort in sedentary university students: a follow up of the Cubo Fitness Test validation.

Work and intellectually fatiguing environments can significantly influence the health of individuals, which is strictly bound to motor efficiency. In particular, desk workers and university students may have a sedentary lifestyle and a condition of mental fatigue caused by daily routine, which could impair motor efficiency. The assessment is a starting point for enhancing awareness of the individual's psychophysical condition through the perception of one's body motor efficiency, motivating to move towards improvement. This way, a submaximal test based on perceived exertion was developed (Cubo Fitness Test, CFT) and validated in previous studies. Hence, two further studies were employed to enhance the consistency and accuracy of this instrument in different conditions. The first study investigated the internal responsiveness of CFT, evaluating if mental fatigue could affect motor efficiency. The second study investigated which perceived intensity (weak, moderate, strong, or absolute maximum) could be more reliable for applying the CFT (as previous research focused the investigation only on moderate intensity). In the first investigation, participants assessed two stimuli (mental fatigue induced with a Stroop color-word task and a neutral condition based on the vision of a documentary) lasting 60 min each. The quality of psychophysical recovery (total quality recovery) and the mood state (Italian Mood State questionnaire) were evaluated before the stimuli. After the fatiguing or the neutral task, the mood state was newly assessed, together with the evaluation of the workload's characteristics (Nasa TLX) and the CFT motor efficiency. In the second investigation, participants had to perform CFT twice for each at different intensities of Borg's Scale of perceived exertion. Researchers successfully requested to fill out the NASA TLX questionnaire regarding the perceived workload characteristics of CFT, and the reliability of each intensity was assessed. Results seem to enhance the consistency and the accuracy of the instrument. Indeed, findings evidenced that CFT is not influenced by mental fatigue conditions typical of the intellectual work of desk workers and university students for which this test was specifically conceived. Moreover, moderate and strong perceived intensity are the most adequate conditions to assess motor efficiency in these populations.

Fatigue and Fracture Evaluations in Ti-10V-2Fe-3Al (Ti 10-2-3)

A mechanical assessment was conducted to characterise the near β titanium alloy Ti-10V-2Fe-3Al (Ti 10-2-3), which was heat-treated to provide two strength variants. Low cycle fatigue and crack propagation tests were performed under standard laboratory air plus a salt fog environment. The differences in static strength were also demonstrated under fatigue conditions utilising plain specimens. However, the alloy was essentially insensitive to the test environment when comparing LCF performance in air and salt fog. Salt fog also provided no effect on crack growth behaviour. A double edge notch specimen geometry was employed to measure free initiation and the growth of cracks from a stress-raising feature. The current data now supplement previous studies aimed at expanding the mechanical database for Ti 10-2-3 component design and in-service life predictions.

Numerical Determination of the Life of Steel Exposed To Low Cycle Fatigue

In the paper, based on the results of the experimental research of high-strength low-alloy steel (HSLA), Nionicral 70 (NN-70), under conditions of low-cycle fatigue (LCF), a numerical analysis of stress and determination of the life of steel samples was performed. Experimental testing of the behavior of the samples were performed with controlled and fully reversible strain (/2 = const, R = min/max = -1), according to the standard ISO 12106:2003 (E). For computational analyses, the following were used: the method of least squares and the method of finite elements (FEM). On the basis of the analysis of the results of the stress-deformation state and the determination of the life span through the isolines of the life span and comparison with the results of experimental tests, a graphic representation is given. The analysis justified the effort to numerically solve the estimation of the lifespan of steel under low cycle fatigue (LCF).

Experimental evaluation of fatigue in wind turbine blades with wake effects

Large investments in the implementation of wind turbines were made in the last decades, which increased the importance of this source in the national electricity systems. The management of this asset can strongly benefit from the development of cost effective monitoring strategies. These may contribute to the extension of the lifespan of existing wind turbines, to the reduction of insurance costs by reducing the operation risk and to the optimization of the design, leading to an increase in the competitiveness of this energy source. This paper is dedicated to the implementation and validation of tools to assess the fatigue condition of wind turbine blades from strains measurements with a set of fiber optic strain gages installed at the blade roots. It describes the data processing needed to obtain accurate experimental estimations of the bending moments applied to the blade roots and the procedure to obtain the accumulated fatigue damage. The instrumentation of two wind turbine rotors aligned with the most frequent wind direction allowed quantifying the interaction between neighboring wind turbines and its effect on fatigue life consumption. The paper presents unique experimental data simultaneously collected in two 1.8 MW wind turbines of an onshore wind farm during 14 months that permitted a very clear illustration of wake effects on fatigue consumption.

EEG-based detection of driving fatigue using a novel electrode

In view of the serious harm caused by driving fatigue, this paper investigated driving fatigue detection based on electroencephalogram (EEG) features, designed a novel semi-dry electrode for acquisitioning drivers' EEG signals, and performed refined composite multiscale fluctuation dispersion entropy (RCMFDE) feature extraction of the θ and β bands rhythm signals in the acquisitioned EEG signals. The research results showed that the novel semi-dry electrode designed in this paper had the advantages of convenient replenishment of conductive liquid, early warning of insufficient conductive liquid, comfortable to wear compared with the traditional wet and dry electrodes under the premise of being able to collect EEG signals with qualified quality. And compared with traditional methods such as multiscale sample entropy (MSE), multiscale permutation entropy (MPE), multiscale symbolic dynamic entropy (MSDE), multiscale dispersion entropy (MDE), and refined composite multiscale dispersion entropy (RCMDE), the EEG features extracted by the RCMFDE method in this paper have a more obvious fatigue feature tendency, and thus can identify the driving fatigue state more effectively.

Small-strain, non-linear elastic Winkler models for uniaxial loading of suction caisson foundations

Soils exhibit non-linear stress–strain behaviour, even at relatively low strain levels. Existing Winkler models for suction caisson foundations cannot capture this small-strain, non-linear soil behaviour. To address this issue, this paper describes a new non-linear elastic Winkler model for the uniaxial loading of suction caissons. The soil reaction curves employed in the model are formulated as scaled versions of the soil response as observed in standard laboratory tests (e.g. triaxial or simple shear tests). The scaling relationships needed to map the observed soil-element behaviour onto the soil reaction curves employed in the Winkler model are determined from an extensive numerical study employing three-dimensional finite-element analysis. Key features of the proposed Winkler model include: computational efficiency, wide applicability (it can be used for caisson design in clay, silt or sand) and design convenience (the required soil reaction curves can be determined straightforwardly from standard laboratory test results). The proposed model is suitable for small and intermediate caisson displacements (corresponding to fatigue and serviceability limit state conditions) but it is not applicable to ultimate limit state analyses.