Fatigue Strength Research Articles

Ultrasonic Resonance Fatigue Testing of 6082 Aluminum Alloy

This study explores the fatigue properties of EN AW-6082-T6 aluminum alloy in the gigacycle range (106–109 cycles), using ultrasonic resonance fatigue testing at 20 kHz in a push–pull mode with a symmetric load cycle (R = −1). A custom-built ultrasonic fatigue machine, developed at TU-Varna, comprising a generator, ultrasonic train (including a high-power transducer, booster, custom-made sonotrode, and specimen), monitoring, data logging systems, and an air-cooling capability, was used for the experiments conducted. A Bezier curve sonotrode, with an amplification ratio of 1:6, was designed and produced for the test. Hourglass-shaped specimens were designed on the base of the dynamic Young’s modulus E = 71.3 GPa, determined through the impulse resonance method (ASTM E1876-01), and validated with FEM analysis for resonance length and stress amplitude. The fatigue testing revealed a fatigue strength reduction of approximately 60 MPa between 106 and 109 cycles. The percentile of failure curves based on a Cactillo–Canteli model fits well with the experimental data and gives a fatigue limit at 109 cycles σl = 104 MPa and “endurance strength” σw = 84 MPa. Surface crack initiation was consistently observed with predominately cleavage transgranular fractures in the fatigue zone. The present research highlights the utility of ultrasonic testing for examining fatigue behavior in the gigacycle regime.

An Anatomy of Ethnic Gangsterism and Militant Nationalism in Kenya: The Case of Nairobi, 1940-1963

Towards the end of the 1940s, Nairobi was characterized by momentous political conflict. A large proportion of Africans were said to be living outside the confines of colonial supervision, a situation that resulted in gangsterism and serious anarchy. Extensive research has been carried out on various dimensions of this episode, revealing that militarism and anarchy were deeply rooted in unresolved issues revolving around economic deprivation and the political exclusion of Africans by the colonial authorities. Some aspects of this violent agitation however remain unexplored. It’s demonstrated in this study that the urban poor in post-1945 Nairobi, pushed to the limits of human endurance, created their own alternative society in clandestine opposition to the forces of law and order. Examining the anarchy, however, reveals a nexus between anti-colonial militancy and ethnic acrimony. The study reveals that tribalism remained an important influence on daily life and political allegiances in the African locations. Armed with various weapons, Kikuyu gangs roamed the streets, terrorizing people of other communities. The spate of militant activity in Nairobi alienated the non-Kikuyu elements in the African population. Anti-colonial militarism thus had far-reaching implications on inter-ethnic relations in Nairobi. The ethnic question remained critical in political transitions that took place in Nairobi city in the post-Mau Mau period. The study was carried out in Nairobi County, particularly in the colonial ‘African locations’ of Pumwani and Shauri Moyo. It entailed the collection and analysis of data from both primary and secondary sources. Primary data was collected from oral informants and the Kenya National Archives while secondary data came from newspapers, books, magazines and dissertations. Data was then corroborated and both context and content analysis were done to guarantee consistency, reliability and validity of the information. A historical research design based on qualitative procedures was employed. Interpretation was done within the Marxist theoretical framework. Marxists hold that social and political behaviour can be reduced to economic motives, and ethnicity is an important force in political behaviour.

Physiology mechanisms of exercise for PTSD: a narrative review

In at-risk societies, the population of post-traumatic stress disorder (PTSD) incidence is gradually expanding from veterans to the general public. In the face of the high incidence of PTSD, exercise therapy, as an economical and maneuverable treatment, has not received the attention it deserves. In this paper, the literature on PTSD symptom improvement through comb-climbing exercise interventions found that performing long-term exercise can achieve significant improvement in PTSD symptoms by modulating the central nervous system, autonomic nervous system, and immune system at the physiological level. Aerobic exercise (running, walking) is beneficial to the central nervous system and immune system; anaerobic exercise positively affects the autonomic nervous system, including resistance or strength endurance training; yoga, which focuses on flexibility and balance training, has a positive effect on the immune system. Future research should explore the neutral and negative effects and mechanisms of exercise on PTSD interventions. Expand more empirical studies in special occupational populations. And implement longitudinal intervention studies with PTSD patients to gain an in-depth understanding of PTSD intervention effects.

Impact of a Light Volleyball Intervention Among Older Chinese Adult Women

Modified sports offer a strategic approach to promoting health in older adults. Light volleyball, which uses a larger, lighter ball than traditional volleyball, is more accessible for this population. This study investigated the effects of a 16-week light volleyball program on the functional fitness of older adults in Hong Kong. A total of 275 participants aged 60 years or older were recruited and randomly assigned to three groups: a light volleyball intervention group, a Tai Chi group, and a control group. Functional fitness was assessed at the pretest, posttest, and 6-month follow-up. Results revealed that the light volleyball group exhibited more significant improvements in lower and upper limb strength, agility, dynamic balance, and aerobic endurance than did the Tai Chi and control groups. This study highlights the effectiveness of light volleyball as a newly emerging, group-based sport physical activity for promoting healthy aging in older adult women. The use of light volleyball in future health promotion initiatives is highly recommended.

EXPERIMENTAL STUDY ON NOTCH SHAPE AND LIQUID CARBONITRIDING SPECIMENS UNDER BENDING LOADING

The current work includes studying the effect of heat treatment using liquid carbon nitriding technology on steel notched (Mechanical testing is part of the process; include tests for surface microhardness, fatigue before and after treatment,tensile testing and chemical analysis of the material. Before treatments, fatigue testing was done on the notched specimens at room temperature under full reverse bending stress. Obusirved that V-notching the specimen reduced strength and fatigue life of steel. The results showed that heat treatments significantly increased strength and fatigue life; in comparison to untreated samples, heat treatments increased fatigue life by 12.5% and 20%, respectively. Finding that the carbonitriding method of hardening produced a surface hardness of 868.71HV, which was 73% higher than the non-hardened samples.The fatigue strength increased to 338.55 MPa and 455.56 MPa at 30° and 90 °, respectively, at the highest temperature due to saturation of the surface with carbon and nitrogen atoms.

AoI-Minimal Task Assignment and Trajectory Optimization in Multi-UAV-Assisted Wireless Powered IoT Networks

This paper investigates the energy transfer and data collection problem of multiple unmanned aerial vehicle (UAV)-assisted wireless-powered Internet of Things (IoT) networks. To ensure information freshness for IoT devices and reduce UAVs’ energy consumption, we minimize the average Age of Information (AoI) of IoT devices by jointly optimizing the energy harvesting (EH) and data collection time for IoT devices, the selection of data collection points (DCPs), DCP-IoT associations, and task assignment, flight speed, and trajectories of UAVs, subject to the limited endurance of UAVs. As this problem is nonconvex, we propose a novel DCP association and trajectory-planning scheme that seeks age-optimal solutions through an iterative three-step process. First, we calculate the EH and data collection time for IoT devices using Karush–Kuhn–Tucker (KKT) conditions. Then, we introduce an optimal hovering time allocation-based affinity propagation (OHTAP) clustering algorithm to determine optimal DCP locations and establish DCP-IoT associations. Finally, we develop two algorithms to optimize UAVs’ trajectories: an improved partheno-genetic algorithm with enhancement mechanisms (EIPGA) and a hybrid algorithm that combines improved MinMax k-means clustering with EIPGA. Numerical results confirm that our scheme consistently outperforms benchmark schemes in AoI performance and solution stability across diverse scenarios.

Improvement of induction equipment for differentiated heat treatment of welded joints of rails.

The paper analyzes the current state of the problem of crumpling welded joints of rails on the Russian railway network. In order to radically solve the problem of improving the quality of the joint, reducing structural heterogeneity and creating uniformity in hardness along the entire length of welded rails, comprehensive research has been carried out and the fundamental principles of manufacturing technology for welded rail lashes by continuous sequential volumetric induction heating with compressed air cooling have been developed. It is shown that compressed air with controlled humidity can be used to create a controlled cooling rate system. The development of the fundamental principles for the manufacture of welded rail lashes during heat treatment along the entire length is an urgent scientific and practical task. The description of modern air-cooled induction equipment used both in Russia and in other countries is presented. The equipment used in the Russian Federation is studied in detail – an induction heating installation (UIN) and a sprayer used in it for one-way supply of compressed air. The induction equipment for differentiated heat treatment of welded joints of rails has been improved with the introduction of a modified compressed air cooling spray. The in-troduction of a two-way joint cooling system on an upgraded installation ensures an increase in hardness in the joint on both sides and the formation of a favorable diagram of internal residual stresses (compressing in the head and sole and compensating stretching in the neck), which will positively affect the fatigue strength of the rail in the area of the weld-ed joint. Such a stress diagram best corresponds to the loading of the joint in operation. To confirm this assumption, the installation was tested and the data obtained were analyzed after local heat treatment with one-sided and two-sided cooling schemes. Together with the research laboratory of PJSC “CHMK”, Chelyabinsk, a modernized induction installation of the UIN type was tested at the Rail Welding Enterprise No. 13 in Chelyabinsk-001-100/RT-C with a two-way cooling circuit.

New developments and guideline updates for HFMI treatment for improving the fatigue strength of welded joints

Abstract High-frequency mechanical impact (HFMI) has established itself as a reliable, effective, and user-friendly method for a post-weld fatigue strength improvement technique for welded structures. HFMI can be implemented as an important element of lightweight design for new structures and as a tool for the rehabilitation of structures in service. The first IIW recommendations for HFMI treatment were developed over several years and published in 2016. An abundance of new research and test data confirms the important elements of that guideline. However, it also demonstrated that certain portions of those recommendations need to be clarified, expanded, and improved. These include: The scope of the guidelines for steels with yield strengths from 960 to 1300 MPa Relaxing the fatigue geometry requirement of the weld profile prior to HFMI treatment and the groove dimension following treatment Presenting fatigue strength modification factors also numerically as an alternative to modifying the fatigue class Incorporating the updated thickness correction factors from the newest IIW Fatigue Design Recommendations Adding a series of tables that summarize the rules for defining the appropriate fatigue strength for different combinations of material strength, load ratio, stress range, and assessment method Provide guidelines on HFMI treatment of prefatigued structures Present a methodology for verifying the effectiveness of HFMI devices based on documentation and experimental data This paper presents details of this new information that is being incorporated into a revised IIW recommendations for HFMI treatment for improving the fatigue strength of welded joints.

Thermal stress behavior of monolithic zirconia crowns with different thicknesses.

This study was aimed at investigating the thermal stresses in monolithic zirconia crowns (MZC) of various thicknesses and elucidating their thermal behavior under cooling or heating changes in the oral cavity. Additionally, the clinical availability and potential issues of MZC were examined by comparing them with other crown materials. Finite element models comprising MZC (0.5-, 1.0-, and 1.5-mm thick), cement layers, and abutment teeth were subjected to thermal changes from 37 to 5 °C or 60 °C. Using a thermal distribution at 5 s, the thermal stress was calculated and compared with those of gold alloy and resin composite crowns. The loads corresponding to the thermal stresses were also estimated by comparing them with the stresses induced by vertical loading on the occlusal surface. Tensile stress occurred primarily in the crowns and cement during cooling, whereas compressive stress was generated during heating. Thermal stresses increased from 16.0 to 27.2 MPa with decreasing crown thickness from 1.5 to 0.5 mm and varied with different materials. Although the MZC exhibited the highest thermal stress, the estimated load (200 N) corresponding to the thermal stress was smaller than that of the resin composite (1280 N). Thinner crowns exhibited higher thermal stress, suggesting an increased risk of failure owing to thermal changes. Despite the higher thermal stress in thinner MZC, the stresses were below the fatigue strength of the material, indicating sufficient resistance to thermal changes in the oral cavity.

Quantitative Review of Critical Plane Criteria and Stress Analysis Approaches for Multiaxial Fatigue of Welded Joints

ABSTRACTThis quantitative review evaluates the effectiveness of stress‐based critical plane criteria, specifically Findley's criterion, the approach due to Carpinteri–Spagnoli (CS), and the Modified Wöhler Curve Method (MWCM), in assessing fatigue strength in aluminum and steel welded joints subjected to constant amplitude (CA) and variable amplitude (VA) multiaxial loading. These criteria were analyzed alongside stress analysis approaches, including nominal stress (NS), hot‐spot stress (HSS), effective notch stress (ENS), and the Theory of Critical Distances–Point Method (TCD PM). Results confirm that all criteria effectively estimate fatigue life for steel welded joints under CA loading, with MWCM combined with HSS proving most accurate. For aluminum joints, estimations showed greater conservatism and scatter, highlighting the need for further experimental data to improve accuracy. Experimentally calibrated constants significantly enhanced prediction reliability. Future research should refine these criteria for diverse aluminum grades and thicknesses, ensuring accurate estimations and robust alternatives to established codes.

Acute intermittent hypoxia in spinal cord injury gait rehabilitation: a systematic review of randomized trials.

Gait impairments are one of the popular consequences of spinal cord injury (SCI). Acute intermittent hypoxia (AIH) is an innovative treatment that has recently been used to enhance motor function in patients with neurological conditions. This review aims to examine the effects of AIH on gait post-SCI, verify who most likely would benefit from the treatment, and recognize the best treatment protocol, if possible. The search was conducted in "PubMed, MEDLINE, The Cochrane Library, Scopus, PEDro, and Web of Science" databases from inception to October 2024. This review included randomized trials involving individuals with SCI who received AIH, alone or in combination with other interventions, compared with active or passive comparators, and evaluated at least one outcome related to gait ability. The quality of the included studies was measured using the "Physiotherapy Evidence Database (PEDro)". Nine studies met the eligibility criteria. In total, 158 individuals with SCI (mean age 44.45 years; 86% male) were involved in this analysis. The included studies' PEDro scores ranged from 5 to 10, with a median of 8. The main findings showed that AIH improves gait speed, walking endurance, dynamic balance, and plantar flexor strength in individuals with SCI. AIH is a safe intervention for individuals with SCI. This review underscores the potential benefits of AIH for improving gait abilities in SCI with motor-incomplete injuries (ASIA grades C and D) at cervical, thoracic, and lumbar levels. Further studies are recommended to verify our findings.

Forecasting High Cycle and Very High Cycle Fatigue Through Enhanced Strain-Energy Based Fatigue Life Prediction

Abstract This study applies a novel strain-energy based fatigue life prediction method to low cycle fatigue (LCF) data additive manufactured (AM) Inconel 718 round dog-bones, specifically focusing on cycles to failure less than 105. The objective is to forecast high cycle fatigue (HCF, 106–107) and very high cycle fatigue (VHCF >107), aiming to approximate stress versus cycles to failure (SN) behavior and the inherent variability in the fatigue life of the material system. This tool is motivated by the need to characterize an expanding and diverse array of materials produced by additive manufacturing methods, process parameter modifications, and optimizations, which can significantly impact fatigue life and overall structural reliability. The fatigue life prediction method achieves this by generating a fatigue life distribution as a function of stress amplitude. Bayesian statistical inference and stochastic sampling techniques are employed iteratively for each test data point, incorporating stress, cycles to failure, and total strain-energy dissipated leading to fatigue failure. Experimental LCF fatigue data are acquired using a standard axial servohydraulic load frame equipped with an axial extensometer for strain and strain-energy data collection. HCF and VHCF data is generated utilizing an ultrasonic fatigue test frame capable of cycling at 20 kHz. The fatigue data obtained from both servohydraulic and ultrasonic fatigue testing are presented and compared. The energy-based fatigue life prediction framework, utilizing only LCF data, is deployed to forecast HCF and VHCF fatigue behavior for AM Inconel 718 fatigue. The HCF and VHCF data generated are then used to validate the forecasts generated from the novel energy-based fatigue life prediction method. Comparisons are made against Random Fatigue Limit curve estimations to assess the effectiveness and accuracy of the proposed methodology.

Research and engineering application of DED laser cladding repair for steam turbine XM-25 alloy LP blades

High-strength martensitic precipitation-hardening stainless steel XM-25, characterised by its high strength, high hardness, and good workability, has been utilised in engineering as the low-pressure last stage blade of steam turbines. However, it is beset by the issue of water erosion. This paper focuses on the restoration of large blade workpieces made of XM-25 material, employing directed energy deposition (DED) laser cladding with parent material powder. The parameters for laser cladding include laser power of 1300 W, movement speed of 500 mm/min, and powder feed rate of 15 g/min. The performance of the XM-25 alloy after laser cladding restoration is evaluated through non-destructive testing (PT, RT), tensile testing, hardness testing, metallographic analysis, fracture morphology analysis, residual stress measurement, and high-cycle fatigue testing. Results indicate that the material after laser cladding exhibits an ultimate tensile strength exceeding 1200 MPa, a yield strength above 1050 MPa, microhardness above 415 HBW, residual stress at approximately 30% of the base material, and a fatigue limit of 586.25 MPa – 95% higher than the base material. These findings confirm the effectiveness of the proposed DED laser cladding method for restoring XM-25 turbine blades, offering a viable engineering solution for mitigating and repairing water erosion in steam turbine components.

Effect of Eight-Week Transcranial Direct-Current Stimulation Combined with Lat Pull-Down Resistance Training on Improving Pull-Up Performance for Male College Students.

The aim of this study was to investigate the effects and potential mechanisms of 8-week transcranial direct-current stimulation (tDCS) combined with resistance training (RT) on pull-up performance in male college students. Twenty-five male college students were randomly assigned to either RT combined with anodal tDCS stimulation (RT + tDCS) or RT alone (RT). Participants of both groups engaged in lat pull-down training programs for 8 weeks, with the RT + tDCS group receiving 20 min tDCS before each RT session. Pre- and post-intervention tests included pull-up endurance (number of repetitions), flexed arm circumference (FAC), and lat pull-down maximal voluntary isometric contraction (MVIC) peak force. During the pull-up endurance test, surface electromyography (sEMG) was recorded for the bicep brachii (BB), tricep brachii (TB), brachioradialis (BR), anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), pectoralis major (PM), and latissimus dorsi (LD) muscles. Both groups demonstrated significant improvements in pull-up endurance and lat pull-down MVIC peak force after training, but no significant difference between the two groups was observed in the post-training test. Additionally, muscle activation of BR, PD, and PM decreased significantly in both groups, while the RT + tDCS group also demonstrated a significant reduction in TB coactivation after training. These findings suggest that eight weeks of tDCS combined with lat pull-down training and lat pull-down training alone can both significantly improve pull-up performance, which may be attributed to enhanced muscle contraction capacity. Although no significant training gains were found between the two training groups, the RT + tDCS group showed a significant decrease in TB coactivation and the enhancement of elbow flexion muscle contraction efficiency after training.

Internal Curing of Concrete Pavements and Overlays

Internal curing is an innovative technology to improve the mechanical properties and performance of concrete. The internal water was supplied by fine saturated lightweight aggregate particles (LWA) in this study. The LWA was used to replace a portion of the conventional fine aggregate in the mixture. An internal curing effect has also been observed when comparing concrete made with low and moderate absorption coarse aggregate. Because concrete pavements have large surface to volume ratios and are exposed to the environment, it is particularly difficult to achieve proper curing. However, proper curing of pavements is important because it reduces early age cracking tendencies and shrinkage and improves concrete fatigue strength. Cracking risk also influences the joint saw cutting window. These considerations are also valid, and probably more important, for thin overlays, whether bonded concrete or ultra-thin/ thin whitetopping overlays. Internal curing is a tool that can increase strength and reduce cracking tendency of concrete, under some circumstances. Splitting tensile and flexural strength are increased, without a corresponding increase in modulus of elasticity.

Fatigue life evaluation of bulk cement tank trailer frame based on hot spot stress approach using the combined fe/mbd method

The bulk cement tanker trailer frame is the main load-bearing component, and it is manufactured by the welding method. Therefore, it is necessary to evaluate the fatigue strength of the trailer frame. In this study, the fatigue stress of this structure is determined by using the hot spot stress approach. First, a combined method of finite element (FE) analysis and multi-body dynamics (MBD) simulation is used to analyse the structural stress. Considering the factors of speed and road surface class in operating conditions in Vietnam, MBD simulation is used to determine the dynamic load acting on the trailer frame when the trailer is excited by an uneven road surface. The nodal stress in the time domain is determined by structural dynamic analysis of the trailer frame with this dynamic load. The linear extrapolation of stress at the reference points is then used to determine the structural hot spot stress of the critical locations. Finally, the selected fatigue curve that corresponds to the related fatigue class (FAT) is used to calculate the fatigue life. In the fatigue analysis model, the cumulative fatigue damage value is chosen taking into account the durability degradation due to the thermal influence of the welded structures

Notch and Fracture Mechanics‐Based Assessment of Multiaxial Fatigue Thresholds of Defects and Sharp Notches in Metallic Materials

ABSTRACTThis investigation focuses on the constant amplitude (CA) multiaxial fatigue limit of components made of metallic materials weakened by defects, cracks, and sharp U‐ and/or V‐notches. To estimate the multiaxial fatigue thresholds of plain, sharply notched, and cracked materials and defects, a novel theoretical framework based on the well‐known averaged strain energy density (SED) criterion is proposed, which extends the Atzori–Lazzarin–Meneghetti (ALM) diagram to multiaxial loading. The proposed design equations are validated against 128 experimental multiaxial fatigue limits, taken from the literature.

Mechanical properties and microbial assessment of additively manufactured diamond and gyroid Ti-6Al-4V ELI scaffolds for interbody fusion cages applications

Abstract This study investigates the mechanical behaviour and microbial assessment of additively manufactured porous titanium scaffolds for interbody fusion cages applications. This study is meticulously designed to focus on both the mechanical and microbial assessments. Two types of cubic porous structure scaffolds were manufactured. The type 1 scaffold was designed with a diamond structure, featuring a pore size of 500 microns and 65% porosity. Similarly, the type 2 scaffold was designed with a gyroid structure, having a pore size of 500 microns and 65% porosity. Both the types of scaffolds were manufactured using direct selective laser sintering technique. Both the group of scaffolds tested for quasi static compression testing, fatigue compression testing, compression torsional testing and corrosion testing for mechanical properties evaluation. For microbial evaluation, bio burden tests, total organic carbon and total hydrocarbon tests were conducted on the both type of scaffolds. Static compression testing results reported that there is no significant effect on the compression strength properties. Diamond scaffolds had higher yield force value than gyroid scaffolds. Fatigue compression and compression - torsional results reported the higher endurance strength of diamond scaffolds over the gyroid scaffolds. There was no significant difference reported for corrosion behavior of both scaffolds. In the present study, both types of scaffolds demonstrated an almost negligible biological burden. The total organic carbon and hydrocarbons values reported were also under permissible limit as per ISO 19227.Results demonstrated several advantages such as higher endurance strength of diamond scaffolds over gyroid scaffolds, highly corrosion resistance and negligible bio burden limits.

Fatigue Strength Plateau Induced by Primary Alpha Phase Size in TC11 Alloy

Enhancing the fatigue strength of materials by increasing their tensile strength is generally considered as an effective strategy. This study observed a fatigue strength plateau in TC11 alloy: despite significant variations in tensile strength, the fatigue strength of TC11 alloy demonstrates remarkable stability. It is determined that this anomalous behavior is governed by a unique fatigue cracking mechanism associated with the primary α phase (αp) in dual‐phase titanium alloys due to the pilling‐up of dislocations and consequent cleavage (pillingup‐cleavage). Under this mechanism, the critical cracking stress is predominantly influenced by the pilling‐up distance of dislocations (reflected in the size of αp phase) and is relatively independent of the lattice frictional resistance (expressed in the nanoindentation hardness of αp phase). This leads to the occurrence of fatigue strength plateau in TC11 alloy in this study.

Assessing the Very High Cycle Fatigue Behavior and Frequency Effect of Structural Steel Welds

ABSTRACTThe very high cycle fatigue behavior of S275J2+N flux‐core arc welded joints was investigated using the ultrasonic fatigue testing method at a loading frequency of 20 kHz. A bespoke specimen design featuring the weld toe was employed to more suitably represent in‐service welded joints than typical ultrasonic fatigue testing specimens. This revealed that fracture occurs above 10 million cycles, beyond the classically accepted fatigue limit. Additionally, comparative fatigue tests were performed at 10 Hz to investigate the frequency effect on the fatigue behavior. A 35% increase in fatigue strength was measured at 20 kHz when compared to 10 Hz, indicating that a correction must be considered in the use of ultrasonic fatigue testing data for design purposes. Fracture surfaces for both test frequencies showed similar morphologies and typical characteristics for fatigue failures of ductile metals.