Fatigue Theory Research Articles

Burning Bright, Not Out! Therapist Well-Being in the Face of What We Face

At a recent conference in Lyon, an American researcher declared that we are all traumatised, all of us including counsellors, clients, workers, lawyers, activists. I was taken aback thinking, “wait a moment!” I am not willing to believe that, in the face of struggle and adversity, we are all mentally ill. Counsellors/therapists form part of a community circle responding to violence, harm, betrayal, grief and heartbreak. We are often inspired by our clients, their survivance, their resistance and the ways they signal injustice. The academic presenter was likely influenced by theories of compassion fatigue and vicarious trauma - ideas that accuse our clients of hurting us. I wonder to what extent these theories hurt us or get us thinking in ways that are individualising and unhelpful.

Bearing life prediction based on critical interface method under multiaxial random loading

The bearing was a key component of the mining machine tire unloader machine and was subjected to random multiaxial stress during operation. Therefore, the life prediction of bearing was of safety guidance. In this paper, a bearing life prediction method based on the critical plane method under multiaxial random loading was proposed. Firstly, a virtual prototype model was built based on the actual working conditions of the tire unloader machine to obtain the time load history of the bearing. Transient dynamic analysis of the bearing was carried out to obtain the triaxial stress-strain time histories at the hazardous locations of the bearing. A new coordinate system was established using the hazard node as the coordinate origin, and the location of the critical plane was searched for based on the critical plane multiaxial fatigue theory, combined with the maximum shear strain amplitude on the critical plane for multi-axial rain flow cycle counting to obtain the damage amount in each direction. At the same time, the life calculated from the maximum damage amount was used as the final life, resulting in a cycle count of the bearing of 268,303 cycles and a duration of 1490.58h. The results of this study could be used as a guide to predict the service life of the bearing in large machinery subjected to multiaxial random stress conditions.

A modified model of Lundberg-Palmgren rolling contact fatigue formula considering the effects of surface treatments

The Lundberg-Palmgren (L-P) fatigue life formula, as a statistical fatigue theory, has been widely used in the industry. However, its direct applicability is limited to the components treated by surface strengthening technologies. Rolling contact fatigue tests and surface integrity measurements of American Iron and Steel Institute (AISI) 9310 rollers with several surface treatments were performed to address this issue. Based on these results, a modified L-P fatigue model was proposed, enabling the consideration of surface modification including surface roughness, residual stress, and hardening introduced by different surface treatments. Compared with the original L-P fatigue formula, its results are more accurate for surface strengthened specimens. Furthermore, this method can assess the contact fatigue life of gears treated by surface strengthening techniques.

Screening of critical dangerous parts of Pi-shaped pipe in the corrosive environment

In order to accurately predict the key dangerous parts of the polygonal pressure pipeline in a corrosive environment, based on the stress fatigue theory, a stainless steel pipeline damage calculation model coupled with the coupling of fatigue and corrosion is established, and the cold and operating conditions are carried out for the polygonal pressure pipeline. The analysis of stress and damage fields shows that the fatigue life of the square-shaped pipeline is reduced from 9225 to 42 years after the influence of the stress concentration factor of pitting corrosion. Based on the results of the damage analysis, by defining the dangerous concentration parameters, it is predicted that the key dangerous parts of the zigzag pressure pipeline are mainly the elbow and the long side abdomen. The greater the dangerous concentration parameter is, the more concentrated the dangerous parts are. When the dangerous concentration parameter is greater than 0.5, the elbow of the pipe shoulder and the long side joint are not critical dangerous parts anymore.

Fatigue determination of the kenaf/PLA composite structure using fatigue specimen (ASTM D7791): a computational analysis

In this investigation, a kenaf/PLA composite specimen was subjected to the fatigue load, and the results were analyzed numerically. Some of the most significant fatigue tool aspects that were looked into were life expectancy, damage, alternative stress, and biaxiality indication. The static structural tool was utilized in order to predict the numerical analysis, and the calculations were performed with the GoodMan theory of fatigue. The loading was completely reversed so that it was equal to 30 kN. When it was discovered that the system could continue to function even after 1e6 cycles had been completed. After applying the alternative load of 30 kN, the biaxiality indication was found to be 0.425, with a minimum value of 0.9. It has been determined how much damage has occurred. The minimum amount of cycles necessary to reach the maximum damage potential is 1000, while the maximum amount of cycles necessary to reach the maximum damage potential is 1.7662·106. It has been established that there is another stress that is comparable to this one. Based on the findings of the investigation, it was determined that the fillet regions of the specimen were subjected to a maximum alternative stress of 716.4 MPa. The alternative stress cannot drop below 31.276 MPa under any circumstances. It has been determined that 106cycles have been spent living in total by the calculation. It has been found out that there is not going to be any damage regardless of the number of cycles that pass due to the fact that that number is 1. It was found that the alternative stress could reach a maximum value of 716.4 MPa, so that was the value that was used for the alternative stress

Asthenia, mental fatigue and cognitive dysfunction

Conditions associated with asthenia are usually characterized by increased fatigue, impaired activities of daily living and decreased productivity. In clinical practice it is important to distinguish between idiopathic chronic fatigue (primary or functional asthenia) and chronic fatigue syndrome (CFS). Fatigue can also be classified by neuromuscular and/or cognitive and mental fatigue. The article discusses the neuroanatomical basis and focuses on the neurocognitive theory of pathological fatigue. In addition the relationship between mental stress, fatigue and cognitive impairments such as subjective cognitive impairment (SCI) and mild cognitive impairment (MCI) are also discussed. We discuss the rationale that for treatment of asthenic conditions accompanied by cognitive dysfunction it is justified to use combination therapy - fonturacetam and a preparation containing nicotinoyl-GABA and Ginkgo Biloba.

Piezoresistive Fibers with Large Working Factors for Strain Sensing Applications.

Piezoresistive fibers with large working factors remain of great interest for strain sensing applications involving large strains, yet difficult to achieve. Here, we produced strain-sensitive fibers with large working factors by dip-coating nanocomposite piezoresistive inks on surface-modified polyether block amide (PEBA) fibers. Surface modification of neat PEBA fibers was carried out with polydopamine (PDA) while nanocomposite conductive inks consisted of styrene-ethylene-butylene-styrene (SEBS) elastomer and carbon black (CB). As such, the deposition of piezoresistive coatings was enabled through nonconventional hydrogen-bonding interactions. The resultant fibers demonstrated well-defined piezoresistive linear relationships, which increased with CB filler loading in SEBS. In addition, gauge factors decreased with increasing CB mass fractions from ∼15 to ∼7. Furthermore, we used the fatigue theory to predict the endurance limit (Ce) of our fibers toward resistance signal stability. Such a piezoresistive performance allowed us to explore the application of our fibers as strain sensors for monitoring the movement of finger joints.

Passive visual stimulation induces fatigue under conditions of high arousal elicited by auditory tasks.

Theories of cognitive fatigue disagree on whether performance decrement is caused by motivational or functional alterations. Here, drawing inspiration from the habituation and visual adaptation literature, we tested the assumption that keeping neural networks active for an extensive period of time entails consequences at the subjective and objective level-the defining characteristics of fatigue-when confounds such as motivation, boredom, and level of skill are controlled. In Experiment 1, we revealed that passive visual stimulation affected the performance of a subsequent task that was carried out in the same portion of visual space. While under conditions of low cognitive load and arousal, participants improved their performance in the stimulated quadrant; the reverse was observed under high arousal conditions. This latter performance decrement correlated also with the reported subjective level of fatigue and occurred while neural responses to the saturating stimulus remained constant, as assessed through steady-state EEG. In subsequent experiments, we replicated and further characterized this performance deterioration effect, revealing its specificity to the stimulated eye and stimulus orientation. Across the three experiments, the decrease in performance was correlated with pupil-linked arousal, suggesting its mediating effect in this phenomenon. In sum, we show that repeated stimulation of neural networks under high-arousal conditions leads to their altered functional performance, a mechanism which may play a role in the development of global cognitive fatigue. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Dynamic Fatigue Behavior of Hip Joint under Patient Specific Loadings

In the present work, a finite element model with standard Charnley’s implant of hip joint is considered for investigation under different patient-specific dynamic activities obtained in vivo. The application of forces occurred due to human movement, which ultimately generates dynamic stress over the prosthesis. Anatomical loading constraints are more clinically relevant than ISO standards. The performance of different materials for each suitable gait pattern is analyzed using commercial finite element code. A liner isotropic material Ti-6Al-4V and PMMA material is utilized for an implant and bone cement, respectively. However, cortical and cancellous bone are treated as non-isotropic in nature. Clinically obtained dynamic forces and torque are being used for the present investigation. Additionally, Goodman, Solderberg, Gerber and ASME elliptic fatigue theories were considered to obtain the fatigue life of the implant. The most strenuous activity in terms of stress and strain are, going downstairs followed by going upstairs, walking, standing up and sitting down, which have been found in good agreement with the safety factor for every activity. Additionally, the life expectancy of the implant was a minimum of 23 years under every dynamic motion. The present work exhibits the greater relevance in terms of the life expectancy of implant for the pre-surgical analysis before implanted in vivo.

Electromechanical Properties and Resistance Signal Fatigue of Piezoresistive Fiber-Based Strain Gauges

Piezoresistive nanocomposite fibers are essential elements for smart wearables and have recently become a research hotspot because of their high sensitivities at large deformations in the plastic regime. However, little attention has been paid to the electromechanical properties of such fibers at low strains where the resistance–strain (R–ε) relationship is reliably linear. In addition, prediction of the resistance signal stability for these materials during cyclic loading remains unreported. Here, we studied these two aspects using wet-spun piezoresistive nanocomposite fibers from polyether block amide (PEBA) composed of a hybrid conductive filler network of carbon black (CB) and carbon nanotubes (CNTs) in which the CB loading in the PEBA matrix was varied at a constant volume fraction of CNTs. We found the R–ε linear relationship (working factor, W) to increase with CB filler loading from 0.01 to 0.058. In addition, the gauge factors of these fibers varied inversely with W from 16.89 to 3.81. Using fatigue theory, we predicted the endurance limit of PEBA/CB-CNT fibers in the elastic regime to be ∼34.9 cycles. Although our fibers were extremely deformable, up to 500% strain, as is the case for most piezoresistive nanocomposite fibers, this work reveals the working range to be actually very small, comparable to rigid conventional strain gauges. We believe with PEBA/CB-CNT fibers’ robust mechanical properties and the ease with which the electromechanical signal can be quantified with the fatigue model, they would be ideal materials to be integrated into textiles to perform as tough, finely tuned strain sensors for a range of rigorous bodily monitoring such as low-strain impacts and joint movements.

Basic mechanical and fatigue properties of rubber materials and components for railway vehicles: A literature survey

Abstract Rubber material is widely used in railway vehicles due to its superior damping performance. The testing methods, fatigue, and aging theories of rubber materials are of great significance to improve the design, manufacture, and application of rubber components for railway vehicles. This work systematically introduces the constitutive theory, mechanical testing standards, and testing methods of rubber materials. Then, the aging mechanism is described and the research progress of rubber fatigue properties is reviewed from the perspectives of fatigue crack initiation and fatigue crack propagation. Moreover, the reinforcement methods of rubber materials are presented. Finally, according to the working conditions of rubber components in railway vehicle, the technical difficulties and future research trends of fatigue characteristics analysis of rubber materials and components are pointed out.

Fatigue reliability of wind turbines: historical perspectives, recent developments and future prospects

Wind, as a sustainable and affordable energy source, represents a strong alternative to traditional energy sources. However, wind power is only one of the options, together with other renewable energy sources. Consequently, the core concerns for wind turbine manufacturers and operators are to increase its reliability and decrease costs, therefore enhancing commercial competitiveness. Among typical failure modes of wind turbines, fatigue is a common and critical source. Given the significance of fatigue reliability in wind turbine structural integrity, reliable probabilistic fatigue theories are necessary for design scheme optimization. By reducing the expenses on manufacturing, operation, and maintenance in reliability- and cost-optimal ways, the cost of energy can be significantly reduced. This study systematically reviews the state-of-the-art technology for fatigue reliability of wind turbines, and elaborates on the evolution of methodology in wind load uncertainty modelling. In addition, fatigue reliability assessment techniques on four typical components are summarized. Finally, discussions and conclusions are presented, intending to provide direct insights into future theoretical development and methodological innovation in this field.

Analysis on Vibroacoustic Fatigue Life of Empennage in a Hypersonic Vehicle

In this study, the fatigue life prediction in hypersonic vehicle noise environment is researched under the structural vibration caused by the engine jet noise and the aerodynamic noise. A finite element analysis model is first established, and then natural frequency and vibration mode are obtained. According to the modal analysis, the vibroacoustic coupling calculation is finished in the dynamic analysis software. Modal participation factor, modal displacement, and the power spectral density of the stress response on the coupled surface are acquired. The finite element, border component, and vibrating stress analytical techniques are also employed in this research to predict the acoustical fatigue performance of the tail fins of a specific type of spacecraft. On the basis of vibration fatigue theory, identified material S–N curve, and linear cumulative damage theory, the Dirlik model in the frequency domain method for vibration fatigue is used to predict the fatigue life of empennage. According to the characteristics of the acoustic load, effects of the load characteristics, and damping ratios on the fatigue conditions, the design of the antifatigue design is put forward.

Developing fatigue test machine for composite material

This paper’s goal is to introduce the third step of the EFOP-3.6.1-16-2016-00014. project on the Faculty of Engineering, University of Szeged. In this period the production technology of composite material was chosen and a fatigue test machine was developed and tested. The paper shortly describes the composite materials and summarizes the theory of fatigue than it presents the process of the development with several prototypes of fatigue test machine, some of which were manufactured and tested. Initially a shaker played the key role in the first two conceptions and finally a crank mechanism became as the best solution. The main solved problems during the development were selection of bearings and solving the partly dynamic balancing of the moving parts.

Identifying the Mental Health Profiles of Black Adolescents Who Experience School Policing and School Discipline: A Person-Centered Approach.

Educational environments that are structured by race perpetuate poor mental health for Black adolescents. This empirical relationship is pronounced when it is examined through Racial Battle Fatigue theory, which provides a framework that links educational environments and poor psychological health of Black students. School police have a major effect on Black adolescents' educational and health experiences and trajectories. The purpose of this person-centered study was to assess the risk of Black students' depressive symptoms who were stopped by school police, saw other students stopped by school police, or experienced school discipline. Data on Black student youths from the Fragile Families Study Year 15 wave (N= 1,601) were used to conduct a latent class analysis to identify subgroups of school policing (ie, being stopped by school police, seeing other students stopped by school police) and school discipline on the distal outcome of depressive symptoms. Covariates included demographic and school attachment. We identified 4 distinct Black student subgroups: (1) unscathed [no school policing or discipline reported]; (2) school disciplined; (3) combined school policing; and (4) school policed [arrested by police]. Each subgroup had an incremental increase in mean depressive symptom scores. Compared to the unscathed subgroup, each subgroup also had lower school attachment. This study disrupts the notion that education environments are a social determinant of health and a great equalizer. This study critically exposes how educational institutions complicit with school policing are associated with racism-related mental health conditions of Black youths.

Study on safety evaluation and design method of union joint thread for Ultra-high pressure fracturing manifold

Ultra-high pressure fracturing technology has become more and more important in China's deep Shale Gas extraction. In recent years, fracturing manifold failure accidents have happened frequently and service life has shortened drastically. There are more than 94% of failure accidents that are caused by vibration fatigue of the union joint. In this paper, it was established as a 3d finite element model of the union joint based on finite element theory and fatigue theory. The author proposed a safety evaluation method based on fatigue life, and compared it with that based on strength. The results show that vibration is the key factor affecting fatigue life, and the fatigue life-based safety evaluation method is more suitable to describe the union joint safety. Therefore, set fatigue life as optimization goal and the key parameters of the union joint thread are optimized by orthogonal optimization method. The optimal results are obtained from the study range, namely that the thread turns 8, the pitch is 10.47 mm, the bearing surface angle is 24.5°, and the guide surface angle is 24.5°. In comparison to the initial union joint, the fatigue life of the optimized union joint is increased by two orders of magnitude. These studies improve the fatigue performance of the union joint and have important guiding significance for improving the safety evaluation level of the fracturing manifold system in this paper.

Estimation Method of Wind-Induced Fatigue of Metal Roof Claddings under Typhoon: Numerical Analysis and Experimental Comparison

Equivalent load cycle sequence (ELCS) is important basic information to know that affects the reliability of the evaluation of wind-induced fatigue on metal roof claddings. In this study, an estimation method of wind-induced fatigue of metal roof claddings is proposed. Based on the measured wind pressure–time history data of the roof claddings on a full-scale low-rise building located along the coast of South China during a typhoon, a new ELCS (NELCS) that reflects typhoon and actual structure wind pressure characteristics in China’s coastal areas is obtained by using the rainflow counting method. The locations of fatigue hot spots of metal roof panels are analyzed by using the finite element analysis method, and the relationship between hot spot stress and wind pressure is obtained. The fatigue damage accumulation of metal roof claddings under the ELCS of a typhoon process is counted by the linear cumulative fatigue theory, commonly known as Miner’s rule. The fatigue damage accumulation of roof claddings with different purlin distances and design wind loads is analyzed using this method and then compared with the results from the dynamic loading test of an air chamber. Results show that the physical test findings are close to the numerical calculation results, which proves that the numerical calculation method has high accuracy and reliability. The comparison between NELCS in this study and the Australian standard low-high-low (LHL) sequence shows that the LHL loading sequence is conservative.

Study of Quenched Crankshaft High-Cycle Bending Fatigue Based on a Local Sub Model and the Theory of Multi-Axial Fatigue

For critical steel engine parts, such as crankshafts, the fatigue strength under the critical working condition is usually improved by the electromagnetic induction quenching technique. In a previous study, the strengthening effect of this approach was always evaluated by a constant, which may result in some errors with the change of the technological parameters. In this paper, a type of steel crankshaft is selected to study the strengthening effect of this approach; first a local sub model composed of the crankpin is built to simulate the magnetic–thermal coupling process, then, the residual stress field is determined by simulating the whole course of fabrication. Finally, the prediction of the fatigue limit load is proposed based on the residual stress and the strength parameters of the material. The experimental verification shows that, when compared to the general means of modification models, the modified McDiarmid multi-axial fatigue model is more suitable to be applied to analyze the fatigue property of this quenched crankshaft due to the markedly higher accuracy. Based on this study, a new fatigue-limit load-prediction approach of this kind of crankshaft can be proposed for engineering applications.

Non-ordinary state-based peridynamic fatigue modelling of composite laminates with arbitrary fibre orientation

For the safe application of carbon fibre-reinforced polymer (CFRP) materials in engineering structures, fatigue life prediction and failure modelling are essential. In this paper, an application of a nonordinary state-based peridynamics (NOSB-PD) approach for the fatigue failure prediction of multilayer CFRP was presented. To characterize the structure of composite laminates, matrix and fibre bonds were introduced within the plies, and normal and shear bonds were introduced between the plies. The fatigue simulation model of composite materials was established by combining the fatigue theory of peridynamics and Paris-Erdogan law, and a method to obtain model parameters was proposed. To demonstrate the accuracy of the model, tension and fatigue experiments were conducted. By comparing the results of tensile and fatigue experiments, it was shown that the model developed in this paper can accurately predict the failure process of multidirectional CFRP laminate under the action of tensile or fatigue loading. The crack initiation and propagation for different laminae during the tensile and fatigue processes can be obtained from the proposed model.

Computational fatigue failure analysis of magnesium alloy core structure inside the metal sandwich panels under constant spectrum loadings

This paper presents the delamination effect on the metal sandwich panel of AR500 with magnesium alloy of AZ31B as main core under constant spectrum loading. Recent sandwich panel mostly dealt with static loading, with least research under constant cyclic loading while also having cavity element on its structure, which made them exposed to the catastrophic failure under consistent loading. The metal sandwich panel were simulated using three types of core design for Magnesium alloy; smooth surface, rounded dimple and hemispherical dimple smooth under static and constant cyclic loading. Two types of conditions are applied to the simulation model; with and without pre-stress loads with varying load ratios. Gerber and Goodman stress life fatigue theory was used as a corrective model. Result shows that sandwich panel with dimple core design obtained up to 5% better fatigue life value compared to solid core panel, with and without pre-stress. This study is important as it can improve sandwich panel’s bonding strength and reduces the risk of early delamination, especially when it is use for real world application such as protection panel for military purposes.