Mechanical Fatigue Research Articles

Investigation of pad radius effects on multiaxial fretting fatigue behavior of al2024 alloy

Fretting fatigue, a critical phenomenon prevalent in engineering applications, occurs at the interface of contacting surfaces under cyclic loading, presenting significant challenges. The advent of Finite Element Analysis (FEA) has transformed the investigation of fretting fatigue by offering detailed insights into stress distributions and fatigue damage mechanisms. This study delves into the impact of pad radius on the fretting fatigue behavior of Al2024 alloy using FEA, with a focus on hot spot analysis and the Smith-Watson-Topper (SWT) criterion. The analysis aims to validate numerical results against analytical findings and explore the role of pad radius in determining contact behavior, fatigue life, and hot spot locations. By incorporating "fe-safe" software, computations are streamlined, facilitating efficient comparison of different fatigue initiation criteria. The results demonstrate that variations in pad radius significantly influence fretting fatigue behavior. Larger pad radii tend to distribute stresses more uniformly across the contact interface, resulting in reduced fatigue damage and longer fatigue life compared to smaller pad radii. Hot spot analysis reveals that smaller pad radii concentrate stresses at specific regions, accelerating fatigue damage initiation. The findings contribute to a deeper understanding of fretting fatigue mechanisms, shedding light on the importance of pad radius in designing more durable engineering components. Through professional scientific methodology, this study provides valuable insights into optimizing pad design to mitigate fretting fatigue and enhance the reliability of mechanical systems.

Review on Environmentally Assisted Static and Fatigue Cracking of Al-Mg-Si-(Cu) Alloys

This paper reviews the relevant literature and covers the main aspects of the environmentally assisted cracking of Al-Mg-Si-(Cu) alloys. Apart from a brief overview of the major microstructural and mechanical properties, it presents research results on the corrosion sensitivity and stress corrosion susceptibility of Al-Mg-Si alloys. Possible mechanisms of stress corrosion cracking and corrosion fatigue in aluminum alloys, such as anodic dissolution and/or interaction with hydrogen, are considered. A number of factors, including atmospheric or solution conditions, applied stress, and material properties, can affect these mechanisms, leading to environmentally assisted cracking. Specific attention is given to Al-Mg-Si alloys with copper, which may increase the sensitivity to intergranular corrosion. The susceptibility to both intergranular corrosion and stress corrosion cracking of Cu-containing Al-Mg-Si alloys is mostly associated with a very thin layer (segregation) of Cu on the grain boundaries. However, the effect of Cu on the corrosion fatigue and fatigue crack growth rate of Al-Mg-Si alloys has received limited attention in the literature. At the current state of the research, it has not yet been holistically assessed, although a few studies have shown that a certain content of copper can improve the resistance of aluminum alloys to the environment with regard to corrosion fatigue. Furthermore, considerations of the synergistic actions of various factors remain essential for further studying environmentally assisted cracking phenomena in aluminum alloys.

Polymer time crystal: Mechanical activation of reversible bonds by low-amplitude high frequency excitations.

Reversible supramolecular bonds play an important role in materials science and in biological systems. The equilibrium between open and closed bonds and the association rate can be controlled thermally, chemically, by mechanical pulling, by ultrasound, or by catalysts. In practice, these intrinsic equilibrium methods either suffer from a limited range of tunability or may damage the material. Here, we present a nonequilibrium strategy that exploits the dissipative properties of the system to control and change the dynamic properties of sacrificial and reversible networks. We show theoretically and numerically how high-frequency mechanical oscillations of very low amplitude can open or close bonds. This mechanism indicates how reversible bonds could alleviate mechanical fatigue of materials especially at low temperatures where they are fragile. In another area, it suggests that the system can be actively modified by the application of ultrasound to induce gel-fluid transitions and to activate or deactivate adhesion properties.

Sacred breath: Ohio nurses respond to COVID-19

In the fall of 2021, the Wick Poetry Center, a recognized international leader in creative writing interventions, launched the website Sacred Breath: Voices of Ohio Nurses in Response to COVID-19 (sacredbreathproject.com) with funding from the Ohio Nurses Foundation. The purpose of the website was to offer Ohio nurses an accessible platform to reflect on their personal and professional lived experiences as caregivers during an historic time of pandemic, sacrifice, uncertainty, and scarcity, and to share their voice with others. What resulted was 204 submissions over a three-month period with participant responses touching on widespread sentiments including grief, fatigue, anger, and resilience. It was from the gap in the current literature on pandemic narratives that the researchers of this study began a basic qualitative thematic analysis of the Sacred Breath project website (SBP) responses to gain a better understanding of how nurses, nurse educators, and nursing students made sense of and gave voice to their personal and professional lived experiences during the ongoing COVID-19 pandemic.While stories of nursing during the Covid-19 pandemic have been widely available and disseminated by popular media, academic studies have been slower to utilize qualitative and experimental methods to specifically address pandemic narratives and the resulting discourses by nurses working in and around clinical settings. The Wick Poetry Center at Kent State University has spent nearly forty years working in the community to address urgent social needs using expressive writing methods that are often overlooked by traditional social and arts outreach. The Wick Poetry Center engaged local academic networks and community health partners to invite nurses, nursing students, and nurse educators the Sacred Breath Project By evaluating responses to the intervention website, this qualitative study is aimed to fill this gap in the current literature as well as begin to understand how nurses made sense of their work lives during the ongoing Covid-19 pandemic.What does this paper contribute to the wider global clinical community?What is already known:•The COVID-19 pandemic resulted in substantial increases of alarm fatigue, moral distress, and dysfunctional coping mechanisms among clinical nurses.•Art interventions positively impact mental health conditions in nurses.What this paper adds:•This review of the Sacred Breath thematic analysis broadens the understanding of how nurses made sense of their work lives during the Covid-19 pandemic.•This review creates a new discourse about the nursing profession in times of crisis—one cocreated by practitioners, educators, students, and creative intervention participants.

High-cycle folding fatigue mechanics of a bistable composite tape-spring

A bistable composite tape-spring (CTS) is a thin-walled open slit tube, which can be coiled or folded into two stable configurations. The CTS has been applied to roll-out-solar-array and successfully launched to space station and micro-satellites based on their one-time deployment performance. There is growing interest on CTS to be applied in reversible deployable structures and foldable mechanical hinges; however, its high-cycle fatigue under large shape folding is still unknown. Here, we device a novel folding fatigue setup to investigate the folding-unfolding cyclic behaviour of the CTS. This is achieved by using a bespoke folding fatigue rig, where both the tape ends of the CTS were clamped separately on rotatable shafts to enable folding under cyclic axial displacements. Since stress concentration is more significant in the snapping fold region, analysis is focused on the peak fatigue stress. It is found that the folding peak stress decreases with the folding cycle: although progressive local damage is observed during 3000 to 100,000 cycles, the CTS is still functional and tends to be stablised after 300,000 folding cycles. The Basquin’s law is applied to predict the fatigue life of the CTS, indicating a fatigue life of 1.4E11 folding cycles with a 40% decrease in peak folding stress. These findings are expected to facilitate the structural designs and applications of the CTS to flexible composite hinges.

More severe surface relief but stronger fatigue resistance at small scales: Vacancy-assisted fatigue damage mechanism

Surface relief in forms of extrusions and intrusions as the substantial feature of early fatigue damage is one of the most important phenomena studied in metal fatigue. The most common surface relief models in bulk metals are agreed to be correlated with the formation of typical dislocation patterns as persistent slip bands (PSBs), while little is known about the fundamental mechanisms at submicron and even nanometer scales where dislocation pattern formation is fully inhibited. Here, as exampled with thin Au films, the underlying fatigue damage mechanism at small scales is investigated through the quantitative characterization of fatigue damages. Continuous generation and migration of vacancies is found to be crucial for the shape of extrusion/intrusions and kinetics of their growth at submicron and even nanometer scales. Due to the degraded dislocation interaction and intensified vacancy diffusion, the delayed vacancy accumulation in the small-scale metal interior suppresses the extrusion and interface void formation in thinner films, which finally leads to the superior ability to support tremendous surface relief and strong fatigue resistance. The finding of the vacancy-dominated fatigue mechanism at small scales extends our understanding of the metal fatigue mechanisms down to the submicron and even nanometer scales and suggests a novel interface engineering strategy by vacancy behavior modulation for fatigue-tolerance material design.

Mechanical deformation in lithium-ion battery electrodes: modelling and experiment

Abstract Models that can accurately describe deformation and stress in lithium-ion batteries are required to inform new device designs that can better withstand mechanical fatigue. Developing such models is particularly challenging because (i) there is a need to capture several different materials including, active materials, binders, current collectors and separators, and (ii) the length scales of interest are highly disparate (ranging from a few microns, relevant to active material particles, up to centimeters, relevant to whole devices). In this study we present a continuum mechanical model that resolves individual active material particles of a nickel-manganese-cobalt-oxide cathode, and predicts the mechanical response of the cathode coating as a whole. The model is validated by comparison with experimental tests which mimic industrial-scale electrode calendaring, and then a parametric study is conducted to provide insight into the roles of the material and geometric properties of the electrode's constituents on the cathode's overall behavior.

Recent Advances in the Deposition of Aluminide Coatings on Nickel-Based Superalloys: A Synthetic Review (2019–2023)

Thermal barrier coatings (TBCs) are widely used to improve the oxidation resistance and high-temperature performance of nickel-based superalloys operating in aggressive environments. Among the TBCs, aluminide coatings (ACs) are commonly utilized to protect the structural parts of jet engines against high-temperature oxidation and corrosion. They can be deposited by different techniques, including pack cementation (PC), slurry aluminizing or chemical vapor deposition (CVD). Although the mentioned deposition techniques have been known for years, the constant developments in materials sciences and processing stimulates progress in terms of ACs. Therefore, this review paper aims to summarize recent advances in the AC field that have been reported between 2019 and 2023. The review focuses on recent advances involving improved corrosion resistance in salty environments as well as against high temperatures ranging between 1000 °C and 1200 °C under both continuous isothermal high-temperature exposure for up to 1000 h and cyclic oxidation resulting from AC application. Additionally, the beneficial effects of enhanced mechanical properties, including hardness, fatigue performance and wear, are discussed.

Failure analysis of the suspender fracture in a railway self-anchored suspension bridge: Damage identification, fatigue mechanism and remaining life prediction

A suspender fracture accident was reported in a railway self-anchored suspension bridge, arousing intensive concern to fatigue issue in the suspender end connector area which is exposed to complex stress states and cyclic traffic loads. Some critical issues involving the fatigue mechanism, the damage identification, and the remaining life prediction were investigated on the basis of on-site and lab tests, numerical simulations, and theoretical analyses. It was found that the root of an ear-plate screw with threads becomes the fatigue-prone detail since action of stress concentration and the unexpected cyclic bending. Also, an effective crack identification scheme by the ultrasonic phased array inspection as well as a verified prediction method for remaining life were proposed. Short suspenders in the main span are significantly affected by the cyclic bending, resulting in the extremely lower fatigue life than that of a long or side-span suspender. Suggestions for a classified disposal plan are provided based on fatigue risk for individual suspender.

Lysine-Triggered Polymeric Hydrogels with Self-Adhesion, Stretchability, and Supportive Properties.

Hydrogels, recognized for their flexibility and diverse characteristics, are extensively used in medical fields such as wearable sensors and soft robotics. However, many hydrogel sensors derived from biomaterials lack mechanical strength and fatigue resistance, emphasizing the necessity for enhanced formulations. In this work, we utilized acrylamide and polyacrylamide as the primary polymer network, incorporated chemically modified poly(ethylene glycol) (DF-PEG) as a physical crosslinker, and introduced varying amounts of methacrylated lysine (LysMA) to prepare a series of hydrogels. This formulation was labeled as poly(acrylamide)-DF-PEG-LysMA, abbreviated as pADLx, with x denoting the weight/volume percentage of LysMA. We observed that when the hydrogel contained 2.5% w/v LysMA (pADL2.5), compared to hydrogels without LysMA (pADL0), its stress increased by 642 ± 76%, strain increased by 1790 ± 95%, and toughness increased by 2037 ± 320%. Our speculation regarding the enhanced mechanical performance of the pADL2.5 hydrogel revolves around the synergistic effects arising from the co-polymerization of LysMA with acrylamide and the formation of multiple intermolecular hydrogen bonds within the network structures. Moreover, the acid, amine, and amide groups present in the LysMA molecules have proven to be instrumental contributors to the self-adhesion capability of the hydrogel. The validation of the pADL2.5 hydrogel's exceptional mechanical properties through rigorous tensile tests further underscores its suitability for use in strain sensors. The outstanding stretchability, adhesive strength, and fatigue resistance demonstrated by this hydrogel affirm its potential as a key component in the development of robust and reliable strain sensors that fulfill practical requirements.

Nanofiber derived MXene composite paper for electromagnetic shielding and thermal management

Despite the urgent demands in protecting wearable electronics from electromagnetic interference (EMI) in various conditions, it remains challenging to attain mechanically robust and flexible materials with both excellent EMI shielding and thermal managing performance. Herein, we report MXene composite paper that can provide multifunction with superior mechanical properties. To construct a hierarchical composite with 2D/0D reinforcements, the MXene paper is fabricated by hot pressing of electrospun Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers incorporated with MXene nanosheets and carbon black nanoparticles. Due to the laminated structure connected by nanoparticles, the flexible composite paper shows remarkable mechanical strength and fatigue resistance that can provide stable EMI shielding effectiveness of 500 dB/mm even after 10000th cyclic rolling. Moreover, the high in-plane electrical conductivity and out-of-plane thermal conductivity allow a fast electrothermal heating and cooling behavior, which qualifies the MXene paper as multifunctional surface for wearable electronics.

A short linear glucan nanocomposite hydrogel formed by in situ self-assembly with highly elastic, fatigue-resistant and self-recovery

Polyacrylamide (PAM) hydrogels are widely used in wide-ranging applications in biology, medicine, pharmaceuticals and environmental sectors. However, achieving the requisite mechanical properties, fatigue resistance, self-recovery, biocompatibility, and biodegradability remains a challenge. Herein, we present a facile method to construct a nanocomposite hydrogel by integrating short linear glucan (SLG), obtained by debranching waxy corn starch, into a PAM network through self-assembly. The resulting composite hydrogel with 10 % SLG content exhibited satisfactory stretchability (withstanding over 1200 % strain), along with maximum compressive and shear strengths of about 490 kPa and 39 kPa at 90 % deformation, respectively. The hydrogel demonstrated remarkable resilience and could endure repeated compression and stretching. Notably, the nanocomposite hydrogel with 10 % SLG content exhibited full stress recovery at 90 % compression deformation after 20 s, without requiring specific environmental conditions, achieving an energy dissipation recovery rate of 98 %. Meanwhile, these hydrogels exhibited strong adhesion to various soft and hard substrates, including skin, glasses and metals. Furthermore, they maintain solid integrity at both 37 °C and 50 °C after swelling equilibrium, unlike traditional PAM hydrogels, which exhibited softening under similar conditions. We hope that this PAM-SLG hydrogel will open up new avenues for the development of multifunctional electronic devices, offering enhanced performance and versatility.

Damage accumulation and its effect during thermal- and stress-induced cycling martensite transformation of laser powder bed fused (LPBF) NiTi alloy

Nitinol (NiTi) alloys produced via laser powder bed fusion (LPBF) exhibit promising potential across diverse applications, yet their suitability for devices necessitating repetitive actuation confronts uncertainties regarding microstructural evolution and functional fatigue behavior during cyclic operation. Our investigation unveils that damage accumulation during thermal cycling stems from geometrically necessary dislocations formed through finite-scale incoherent interface motion, contrasting earlier hypotheses attributing LPBF-induced dislocation activity as the primary contributor. Damage accumulation during mechanical cycling is characterized by notable multiplication of cyclic dislocations via dislocation twinning interactions, rather than severe martensitic plasticity. These newborn cycling dislocations inherit martensite's crystallographic characteristics, exerting a distinct influence mechanism on martensite transformation and deformation behavior, diverging from conventional studies on function fatigue in traditional NiTi alloys. This study sheds light on the distinctive damage accumulation traits observed during thermal/mechanical cycling of LPBF-fabricated NiTi alloys, offering valuable insights for probing their functional fatigue mechanisms.

Analysis of the relationship between age-related erythrocyte dysfunction and fatigue.

With the declining birth rates and aging societies in developed countries, the average age of the working population is increasing. Older people tend to get tired more easily, so prevention of fatigue is important to improve the quality of life for older workers. This study aimed to assess the mechanism of fatigue in older people, especially focused on relation between dysfunction of erythrocyte and fatigue. Total power (TP), which is the value of autonomic nerve activity, was measured as a value of fatigue and significantly decreased in workers with aging. As properties of senescent erythrocytes, the erythrocyte sedimentation rate and damaged erythrocytes population increased with aging and correlated with TP. These results suggested that the accumulation of damaged erythrocytes contributes to fatigue. Recent studies revealed that senescence-associated secretory phenotype (SASP), a phenomenon in which senescent cells secrete a variety of cytokines, affected hematopoiesis in bone marrow. We analyzed the effects of SASP factors on erythropoiesis and found that Interleukin -1α (IL-1α) suppressed erythrocyte differentiation of hematopoietic stem cells in vitro. We also showed that IL-1α levels in human blood and saliva increase with aging, suggesting the possibility that IL-1α level in saliva can be used to predict the decline in hematopoietic function.

Disuse-Induced Muscle Fatigue: Facts and Assumptions.

Skeletal muscle unloading occurs during a wide range of conditions, from space flight to bed rest. The unloaded muscle undergoes negative functional changes, which include increased fatigue. The mechanisms of unloading-induced fatigue are far from complete understanding and cannot be explained by muscle atrophy only. In this review, we summarize the data concerning unloading-induced fatigue in different muscles and different unloading models and provide several potential mechanisms of unloading-induced fatigue based on recent experimental data. The unloading-induced changes leading to increased fatigue include both neurobiological and intramuscular processes. The development of intramuscular fatigue seems to be mainly contributed by the transformation of soleus muscle fibers from a fatigue-resistant, "oxidative" "slow" phenotype to a "fast" "glycolytic" one. This process includes slow-to-fast fiber-type shift and mitochondrial density decline, as well as the disruption of activating signaling interconnections between slow-type myosin expression and mitochondrial biogenesis. A vast pool of relevant literature suggests that these events are triggered by the inactivation of muscle fibers in the early stages of muscle unloading, leading to the accumulation of high-energy phosphates and calcium ions in the myoplasm, as well as NO decrease. Disturbance of these secondary messengers leads to structural changes in muscles that, in turn, cause increased fatigue.

Impact of Rheology-Based Optimum Parameters on Enhancing the Mechanical Properties and Fatigue of Additively Manufactured Acrylonitrile-Butadiene-Styrene/Graphene Nanoplatelet Composites.

This study investigates the interaction between static and fatigue strength and the rheological properties of acrylonitrile-butadiene-styrene (ABS) polymer reinforced with graphene nanoplatelets (GNPs) in both filament and 3D-printed forms. Specifically focusing on the effects of 1.0 wt.% GNPs, the study examines their influence on static/fatigue responses. The rheological behaviour of pure ABS polymer and ABS/GNPs nanocomposite samples, fabricated through material extrusion, is evaluated. The results indicated that the addition of 1.0 wt.% GNPs to the ABS matrix improved the elastic modulus of the nanocomposite filaments by up to about 34%, while reducing their ductility by approximately 60%. Observations revealed that the static and fatigue responses of the composite filament materials and 3D-printed parts were not solely attributed to differences in mechanical properties, but were also influenced by extrusion-related process parameters. The shark-skin effect, directly related to the material's rheological properties, had a major impact on static strength and fatigue life. The proposed method involved adjusting the temperature of the heating zones of the extruder during filament production to enhance the static response of the filament and using a higher nozzle temperature (270 °C) to improve the fatigue life of the 3D-printed samples. The findings reveal that the proposed parameter optimisation led to filaments with minimised shark-skin effects, resulting in an improvement in ultimate tensile strength compared to pure ABS. Moreover, the 3D-printed samples produced with a higher nozzle temperature exhibited increased fatigue lives compared to those manufactured under identical conditions as pure ABS.

The influence of biological sex on the relationship between inorganic phosphates, hydrogen ions, and the peripheral component of neuromuscular fatigue

Background: In males, the relationship between peripheral fatigue development and intramuscular inorganic phosphate (Pi) accumulation is more robust than that with hydrogen ion (H+) accumulation. Based on previous findings of greater peripheral fatigability during exercise in males vs females (as pre-post %changes in twitch force, Qtw) and thus the potential for sex differences in the mechanisms of fatigue, we aimed to: 1) establish whether the relationship between peripheral fatigue development and Pi accumulation is more robust than that with H+ accumulation in females, and 2) determine whether females and males differ in the development of peripheral fatigue for a given Pi or H+ accumulation. Methods: Eleven recreationally active, healthy, young individuals (5 females) performed two consecutive (interspersed by 5-min of rest) intermittent isometric single-leg knee-extensor trials (60 maximal voluntary contractions; 3-s contraction, 2-s relaxation). Throughout both trials, quadriceps intramuscular [Pi] and [H+] were quantified using phosphorus magnetic resonance spectroscopy (31P-MRS), and quadriceps Qtw was measured using electrical femoral nerve stimulation. Peripheral fatigue was quantified as the exercise-induced decrease in Qtw. The relationships between Qtw and [Pi] and [H+] were analyzed using linear mixed-effects models for the portion of exercise where peripheral fatigue was developing ( i.e., decreasing Qtw). The results are presented as the Z-score β coeffcients and p-values. Results: The exercise-induced reduction in Qtw (thus peripheral fatigue) was larger in males compared to females (-65±16 vs -43±21%; p<0.05). During both trials, the decrease in Qtw for a given increase in [Pi] was not different between sexes, and these relationships were not altered from Trial 1 to Trial 2 (Female slope Trial 1: -1.5 vs Trial 2: -1.4; Male slope Trial 1: -1.7 vs Trial 2: -1.6, all p>0.3). The decrease in Qtw for a given increase in [H+] was greater for men compared to women in both trials (both p<0.01), and these relationships were not altered from Trial 1 to Trial 2 (both p>0.4) (Female slope Trial 1: -0.8 vs Trial 2: -0.9; Male slope Trial 1: -1.2 vs Trial 2: -1.3). The overall relationship ( i.e., y-intercept) between Qtw and [Pi] did not shift up or down across the consecutive trials for either sex (Females y-intercept Trial 1: -1.0 vs Trial 2: -1.3; Males y-intercept Trial 1: 0.8 vs Trial 2: 0.7, both p>0.2). In contrast, the overall relationship ( i.e., y-intercept) between Qtw and [H+] shifted down from Trial 1 to Trial 2 for both sexes (Females y-intercept Trial 1: 0.2 vs Trial 2: -0.3; Males y-intercept Trial 1: 0.3 vs Trial 2: -0.2, both p<0.01). Conclusions: In males and females, the relationship between the magnitude of Qtw and Pi is more robust compared to the relationship between the magnitude of Qtw and H+, suggesting Pi accumulation as the stronger mediator of peripheral fatigue in both sexes. Furthermore, the susceptibility of Qtw to decrease in response to a given increase in Pi was not different between sexes. The difference in peripheral fatigability between males and females are therefore likely due to differences in [Pi] and factors determining the magnitude of its accumulation ( e.g., force output, muscle fiber type distribution, or O2 transport and utilization). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Prediction of mechanical properties and fatigue life of nanosilver slurry in chip interconnection

This article investigates the failure mode and mechanism of copper pillar solder joints in temperature cycling experiments, focusing on a Cu/nano Ag/Cu solder joint structure. The hot pressing bonding condition at 300 °C with insulation for 10 s is chosen for the experiments. Based on the life test results, the thermal cycling fatigue life of the nanosilver solder joint is determined to be 2050 cycles. To gain further insights, finite element software ANSYS is employed to simulate nanosilver solder joints in flip chips, revealing the stress–strain distribution within the solder joints. The simulation utilizes the Anand viscoplastic constitutive model for the solder joint, providing a reasonable representation of the stress–strain behavior under thermal cycling load. Notably, the simulation highlights that the maximum stress and strain occur in the contact area between the solder joint and the copper column. To enhance accuracy, the calculation equation is refined using relevant experience, resulting in a prediction of the thermal fatigue life of nanosilver solder joints. This prediction aligns closely with the experimental results. The research outcomes not only contribute valuable insights into the behavior of nanosilver solder but also serve as a reference for its application in electronic packaging.

Improved low cycle fatigue property of Ti–6Al–4V alloy by trace Fe addition

The low-cycle fatigue properties of titanium alloys suffering cyclic loading determines the safety in service for their components used in submarine shells. It has been reported that tensile property could be improved by making use of Fe alloying element partitioning effect. However, the fatigue property and mechanism of titanium alloys with Fe addition remain unknown. In this study, the low-cycle fatigue property and cyclic deformation mechanism of Ti–6Al–4V-0.55Fe and Ti–6Al–4V ELI with a duplex microstructure were systematically investigated. With the addition of Fe element, Ti–6Al–4V-0.55Fe with longer lasting cyclic hardening behavior and lower cyclic softening rate, showed higher fatigue life under selected strain amplitudes. Under low strain amplitude, effect of Fe on dislocation motion, interface resistance, lattice distortion, and micro strain were responsible for the enhanced fatigue life. While under high strain amplitude, Fe brought out the pinning effect on interface. Besides, Fe addition also limited the fatigue crack propagation.

The Effects of Anchoring a Fatiguing Forearm Flexion Task to a High vs. Low Rating of Perceived Exertion on Torque and Neuromuscular Responses.

Ortega, DG, Housh, TJ, Smith, RW, Arnett, JE, Neltner, TJ, Schmidt, RJ, and Johnson, GO. The effects of anchoring a fatiguing forearm flexion task to a high versus low rating of perceived exertion on torque and neuromuscular responses. J Strength Cond Res 38(5): e219-e225, 2024-This study examined the torque and neuromuscular responses following sustained, isometric, forearm flexion tasks anchored to 2 ratings of perceived exertion (RPE). Nine men (mean ± SD: age = 21.0 ± 2.4 years; height = 179.5 ± 5.1 cm; body mass = 79.6 ± 11.4 kg) completed maximal voluntary isometric contractions (MVIC) before and after sustained, isometric, forearm flexion tasks to failure anchored to RPE = 2 and RPE = 8. The amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) signal were recorded from the biceps brachii. Normalized torque was divided by normalized EMG AMP to calculate neuromuscular efficiency (NME). A dependent t-test was used to assess the mean difference for time to task failure (TTF). Repeated-measures analysis of variances was used to compare mean differences for MVIC and normalized neuromuscular parameters. There was no significant difference in TTF between RPE = 2 and RPE = 8 (p = 0.713). The MVIC decreased from pretest to posttest at RPE = 2 (p = 0.009) and RPE = 8 (p = 0.003), and posttest MVIC at RPE = 8 was less than that at RPE = 2 (p < 0.001). In addition, NME decreased from pretest to posttest (p = 0.008). There was no change in normalized EMG AMP or EMG MPF (p > 0.05). The current findings indicated that torque responses were intensity specific, but TTF and neuromuscular responses were not. Furthermore, normalized EMG AMP and EMG MPF remained unchanged but NME decreased, likely due to peripheral fatigue and excitation-contraction coupling failure. Thus, this study provides information regarding the neuromuscular responses and mechanisms of fatigue associated with tasks anchored to RPE, which adds to the foundational understanding of the relationship between resistance exercise and the perception of fatigue.