Fatigue Life Research Articles

Combined Proxies for Heart Rate Variability as a Global Tool to Assess and Monitor Autonomic Dysregulation in Fibromyalgia and Disease-Related Impairments

Background: Heart rate variability (HRV) provides both linear and nonlinear autonomic proxies that can be informative of health status in fibromyalgia (FM), where sympatho-vagal abnormalities are common. This retrospective observational study aims to: 1. detect differences in correlation dimension (D2) between FM patients and healthy controls (HCs); 2. correlate D2 with standard HRV parameters; 3. correlate the degree of HRV changes using a global composite parameter called HRV grade, derived from three linear indices (SDNN = intervals between normal sinus beats; RMSSD = mean square of successive differences; total power), with FM clinical outcomes; 4. correlate all linear and nonlinear HRV parameters with clinical variables in patients. Methods: N = 85 patients were considered for the analysis and compared to 35 healthy subjects. According to standard diagnostic protocol, they underwent a systematic HRV protocol with a 5-min paced breathing task. Disease duration, pain intensity, mood, sleep, fatigue, and quality of life were assessed. Non-parametric tests for independent samples and pairwise correlations were performed using JMP (all p < 0.001). Results: Mann-Whitney U found a significant difference in D2 values between FM patients and HCs (p < 0.001). In patients, D2 was associated with all HRV standard indices (all p < 0.001) and FM impairment (FIQ = −0.4567; p < 0.001). HRV grade was also associated with FM impairment (FIQ = 0.5058; p < 0.001). Conclusion: Combining different HRV measurements may help understand the correlates of autonomic dysregulation in FM. Specifically, clinical protocols could benefit from the inclusion and validation of D2 and HRV parameters to target FM severity and related dysautonomia.

STRENGTHENING Ti-15-3: DISCOVERING THE FATIGUE-BOOSTING WONDERS OF LASER SHOCK PEENING

Laser shock peening (LSP) is a promising surface modification technique used to enhance the surface properties of material. This study investigates the impact of laser shock peening without a protective coating (LPwC) on the fatigue behavior of the duplex-aged (DA) Ti-15-3 alloy with a power density of 9[Formula: see text]GW/cm2 power density and a wavelength of 1064[Formula: see text]nm. The application of laser shock peening without Coating (LPwC) resulted in the development of a titanium oxide layer on the surface of the material, a change that was not seen in the untreated samples and is linked to the high-energy nature of the laser treatment. The untreated DA specimens displayed a compressive residual stress (CRS) of −198 MPa at the surface, which shifted to tensile stress at a depth of 100[Formula: see text][Formula: see text]m. In comparison, the samples subjected to laser peening exhibited a significant increase in CRS, reaching [Formula: see text] MPa at the same depth. Furthermore, the hardness of the surface rose from 350[Formula: see text]HV in the untreated samples to 546[Formula: see text]HV in those that underwent laser peening, emphasizing the work hardening induced by the treatment. Results from axial fatigue testing demonstrated that LPwC markedly improved the fatigue life of the Ti-15-3 alloy, attributed to the combined effects of CRSs, work hardening, and changes in microstructure. These findings highlight the substantial promise of LPwC as a surface treatment method for enhancing the fatigue resistance of DA Ti-15-3 alloy, which is crucial for applications in aerospace and defense. The insights gained can serve as a basis for refining laser peening parameters to further enhance the material’s performance.

Research on fracture failure mechanism of steering knuckle arms of a heavy-duty vehicle during accelerated life test on proving ground

ABSTRACT To research the fracture failure behavior of steering knuckle arms (SKAs) of a heavy-duty vehicle during the reliability validation test on the proving ground (PG), the failure mode of the SKAs was detected in detail combined with the process assembly and the metallographic structure of metal materials. According to the hysteresis loop curves equation of the cyclic stress-strain at the notch root and Neuber’s rule, the tested nominal stress was converted into the local stress-strain response of the crack site, and the fatigue life and damage of the SKAs were calculated using Morrow’s mean stress correction equation. The testing and calculation results show that the material properties of the SKAs meet the requirements for technical parameters, while the process assembly conicity and cone surface roughness fail to meet the design parameters, the assembly contact area between the SKAs and the steering knuckles (SKs) was only about 30%, and the multiple ‘small steps’ were left by the machining tool marks at the fracture and crack source, during the accelerated life test of the heavy-duty vehicle, the SKAs were subjected to local highly concentrated stress, finally resulting in bending low-cycle fatigue fracture.

Effects of Auricular Acupressure on Fatigue, Sleep Quality, Physical Activity, and Quality of Life in Pancreatic Cancer Patients Undergoing Chemotherapy: A Randomized Controlled Trial.

Patients with pancreatic cancer exhibit various symptoms and numerous physiological and psychological complications. Therefore, designing intervention measures to alleviate symptoms is crucial. This study explored the effectiveness of a 4-week auricular acupressure intervention for reducing fatigue and improving quality of life, sleep quality, and physical activity in patients receiving chemotherapy for pancreatic cancer. This randomized controlled trial was conducted at a medical center in northern Taiwan. The study participants comprised 80 patients undergoing chemotherapy for pancreatic cancer. The experimental group received auricular acupressure therapy for 4 weeks, which targeted the shenmen (TF4), sympathetic (AH6), liver (CO12), spleen (CO13), and subcortex (AT4) acupoints, and the control group received routine care. The European Organization for Research and Treatment of Cancer Quality of Life Group Core Questionnaire-C30, European Organization for Research and Treatment of Cancer Quality of Life Group Core Questionnaire-PAN26, Brief Fatigue Inventory-Taiwanese version, Pittsburgh Sleep Quality Index, and 3-day Physical Activity Record were used for assessment. After auricular acupressure therapy for 4 weeks, the experimental group exhibited significant improvements in insomnia symptoms during weeks 1 to 4, as measured using the European Organization for Research and Treatment of Cancer Quality of Life Group Core Questionnaire-C30 (all P < .01), and improvements in sleep quality by week 4, as measured using the Pittsburgh Sleep Quality Index ( P < .036). After auricular acupressure therapy for 4 weeks, significant improvements were observed in patients' sleep quality and quality of life in terms of insomnia. Auricular acupressure can improve sleep quality and other aspects of quality of life among patients undergoing chemotherapy for pancreatic cancer. The study findings indicate the potential of auricular acupressure as an adjunctive cancer care treatment.

Study on ultrasonic evaluation of connection state and service performance of resistance projection welding joints

Fatigue failure of welded joints is a performance factor of structural parts under dynamic load, and the effective evaluation of its life is always the key to the service ability of structures. The fatigue failure process of welded joints is complicated because of the non-uniformity of microstructure and asymmetry of structure. This study utilized ultrasonic C-scan imaging for non-destructive testing of the internal connection states of resistance projection welding (RPW). The connection state of RPW before, during and after fatigue test and the characteristic change of ultrasonic detection image were compared. With the occurrence of fatigue failure behavior, the area representing the fusion connection region in the ultrasonic C-scan image changes. The area of the molten connection zone in the ultrasonic images can quantitatively evaluate the fatigue limit of stainless steel RPW joints, providing an effective method for assessing fatigue life in practical engineering applications.

A robust methodology for dataset preparation and algorithm performance assessment in machine learning prediction of the fatigue life of additive manufactured components

A robust methodology for dataset preparation and algorithm performance assessment in machine learning prediction of the fatigue life of additive manufactured components

Experimental and numerical investigation of the evolution of residual stresses under cyclic mechanical loading

Forming-induced residual stresses highly influence the performance of metallic engineering components. They offer great potential particularly for increasing fatigue life by targeted introduction of compressive residual stresses in failure-critical areas. However, this only holds true if one can understand and predict the change of residual stresses under cyclic mechanical loading and thus ensure their stability. In the present paper, we introduce a combined experimental and numerical approach for the investigation of residual stress evolution under cyclic mechanical loading. Therefore, a suitable experiment is conceptualized and realized using a 4-point bending setup. The initial plastic deformation of each specimen is followed by a certain number of load cycles and experimental residual stress analyses. From this, a course of residual stresses over the fatigue life is constructed. In order to simulate the determined change in residual stresses, a cyclic plasticity model is proposed that takes into account the nonlinear kinematics due to the large deflection of the beam. A parametrization algorithm is presented, which employs a global optimization strategy using uniaxial stress–strain data from various parametrization experiments. The final comparison of experimental and numerical results shows a qualitative agreement. Their stabilization level after a few thousand load cycles can be predicted.

Composite probability distribution for fatigue life prediction of API X65 steel via Vickers hardness

Accurate prediction of the fatigue life of API X65 steel is crucial in various applications. However, the traditional bootstrap method has inherent limitations, such as a tendency to deviate from the true distribution with insufficient sample sizes, difficulty in identifying extreme statistics, and an inability to generate distributions closer to the original sample. These deficiencies lead to overly conservative S-N curve designs and pose challenges in data collection, particularly for small samples. To address these issues, we propose an improved bootstrap method using a composite probability distribution. This method enhances the sampling range and improves prediction accuracy for parameter uncertainty ranges by considering both small samples and extended virtual samples’ probability distribution. Comparative analysis through Monte Carlo simulation demonstrates the superior parameter estimation of our method for small samples. Our case analysis further explores the relationships between Vickers hardness, tensile strength, surface roughness factor, and intercept constant. The findings led to a novel method for estimating the S-N curve confidence interval of API X65 steel from Vickers hardness. Analysis of fatigue life test data for API X65 steel yielded favorable results, confirming the effectiveness and feasibility of our improved method.

Biomimetic Seal Whisker Sensors for High-Sensitivity Wake Detection and Localization.

Pinnipeds, with highly sensitive whiskers, can detect instantaneous spatial hydrodynamic disturbances, crucial for tracking wakes and their sources. However, no existing engineering solution replica tes this for intelligent passive flow perception. To bridge this gap, we propose a low -cost, whisker-inspired sensor designed for use in arrays for underwater sensing and tracking. The sensor integrates metal foil strain gages within a polydimethylsiloxane (PDMS) soft base, coupled with a 3D-printed biomimetic seal whisker model. It exhibits low self-noise in undisturbed flow and high sensitivity in wake detection, identifying flow speeds as low as 0.5 mm/s-comparable to biological whiskers (~0.25 mm/s). The dual strain gage design, placed on adjacent perpendicular sides, allows precise measurement of whisker bending amplitude and direction. The sensor shows excellent linearity, repeatability, fatigue life, short response time and superior dynamic performance in the low-frequency range (≤35 Hz). Despite its high performance, it is cost-effective and easy to fabricate, requiring no specialized facilities or extensive training, making it ideal for large-scale array deployment. To demonstrate its potential, we t ested a nine-sensor array capable of predicting dipole source locations using an artificial neural network model. This work demonstrates the feasibility of whisker-inspired sensing for robust spatial flow perception in underwater environments.&#xD.

A Novel Approach to Predict the Location and Fatigue Life of Intervertebral Disc Degeneration

This study presents a novel approach for predicting the location and fatigue life of degenerative intervertebral discs (IVDs) under cyclic loading conditions, aiming to improve the understanding of disc degeneration mechanisms. Based on mechanical theories linking IVD degeneration to stress imbalance and water loss, a finite element (FE) model of the L4–L5 lumbar spine was developed, combining probability-weighted anatomical structures, inverse dynamics, and cumulative fatigue mechanics. By quantifying stress variations and calculating cumulative damage across disc regions, stress-concentration areas prone to degeneration were identified, and validation via a case study of a retired weightlifter diagnosed with intervertebral disc disease (IVDD) demonstrated that the predicted degeneration location correlated well with affected areas observed in CT scan images. These findings suggest that prolonged, abnormal stress imbalances within the disc may contribute significantly to degeneration, offering potential clinical applications in preventive assessment and targeted treatment for spine health.

Thermomechanical Constitutive Modeling of the Kirigami-Inspired Shape Memory Alloy

Abstract Shape Memory Alloys (SMAs) are unique materials capable of recovering predefined shapes through reversible phase transformations between austenite and martensite phases. This behavior enables SMAs to exhibit the shape memory effect and pseudoelasticity, allowing for the recovery of large strains and the generation of significant forces. These properties make SMAs highly desirable for applications in actuation, sensing, and other engineering domains. Conventional SMA actuator designs, while effective, often face limitations such as slow response times, non-uniform stress distribution, and reduced fatigue life under cyclic loading.&amp;#xD;Integrating Kirigami-inspired techniques into SMA actuator design addresses these challenges by introducing precise cut patterns that transform 2D SMA materials into complex 3D structures. Kirigami-based SMA structures offer enhanced stroke lengths, improved heat dissipation, and uniform load distribution, reducing stress concentrations and extending actuator lifespan. This approach enables the creation of versatile and efficient actuators with tailored mechanical properties, overcoming traditional design constraints.&amp;#xD;This paper presents a constitutive model for Kirigami-based SMA structures, coupling mechanical deformation and thermal response modeling to capture in-plane and out-of-plane deformations. The proposed framework provides a detailed understanding of the unique thermomechanical behavior of Kirigami-inspired SMA actuators, offering insights into their performance under varying operational conditions. The findings highlight the potential of Kirigami-based SMA structures for advancing actuator technologies across a range of applications.

Assessment of Fatigue Life in Grouted Polyurethane Composites for Pavement Maintenance

Polyurethane grouting technology is widely employed to maintain critical transportation infrastructure, including pavements, airports, and railways. After injection, foamed polyurethane bonds with surrounding aggregates to form a polyurethane–aggregate composite material (PACM). The gradation of aggregates in PACM, stress levels, and loading frequencies significantly influence fatigue performance under cyclic traffic loading. This study investigates the fatigue behavior of three distinct PACM gradation types through three-point bending fatigue tests under varying stress levels and loading frequencies. Results reveal that the finer gradations of PACM tend to exhibit higher flexural stiffness and longer fatigue life but also greater sensitivity to stress levels. Conversely, coarser gradations show lower stiffness but improved energy dissipation characteristics. Additionally, the flexural stiffness modulus, fatigue life, and cumulative dissipated energy decrease with increasing stress levels, while they grow with higher loading frequencies. In contrast, the dissipated angle follows an opposite trend. Additionally, mathematical models were developed to describe the evolution of dissipated energy, uncovering a three-stage pattern dominated by a prolonged plateau phase accounting for over 80% of the fatigue process. Based on this characteristic plateau, fatigue life prediction models were established for each gradation type, achieving high prediction accuracy with relative errors below 10%. These findings not only highlight the significant impact of aggregate gradation on PACM fatigue performance but also provide practical tools for optimizing material design in pavement maintenance.

Rolling Contact Fatigue Behavior of Pitch Bearing Raceway in Offshore Wind Turbines

As critical components in offshore wind turbine (OWT) systems, pitch bearings require exceptional fatigue resistance to ensure the extended operational lifespan and structural reliability demanded by marine environments. Failure of these bearings due to rolling contact fatigue (RCF) can severely affect the economic efficiency of offshore wind turbines and potentially lead to safety accidents involving both humans and machinery. A simulation model for pitch bearings used in a 3 MW OWT is established to study the RCF behavior under operational conditions based on continuum damage mechanics. Both the elastic and plastic damage are considered in the damage process through a Python script. A user subroutine UMAT is programmed to depict the gradual deterioration of mechanical properties. The results indicate that the fatigue damage of the raceway exhibits significant nonlinear characteristics, with elastic damage playing a predominant role in determining its fatigue life under operational conditions.

A comprehensive approach to characterize flexural behaviour and fatigue life in aggregates stabilized with different cementitious stabilizers

ABSTRACT Flexural fatigue characterisation entails evaluating the material's response to repeated bending to dynamic loads and measuring its resilience to cyclic stresses. It is the ability to resist damage and deformation over time, thus being a crucial factor in advancing understanding of stabilised layer design and performance. Traditional methods often lack sensitivity to factors such as variations in cementitious stabilisers, curing period and stress ratio when it comes to flexural characterisation, be it stiffness or fatigue damage. The present study highlights the development of flexural stiffness characterisation with respect to flexural strength, curing period and stress ratio by investigating five distinct stabiliser combinations involving cement, fly ash, ground granulated blast furnace steel slag (GGBS), and two chemical stabilisers on aggregates. Stress-dependent flexural modulus models were developed, which predicted close to the actual data determined in the laboratory setup. The study also demonstrated the development of stress-dependent flexural fatigue models with different stabiliser combinations with a high degree of accuracy (R2 – 0.89–0.93). The findings from the study are expected to enhance the understanding of the flexural behaviour of stabilised layers within the composite pavement systems and the influence of different cementitious stabiliser combinations in improving its performance.

Study on low-cycle fatigue life of nickel-based superalloy GH4586 at various temperatures

Abstract The nickel-based superalloy GH4586 has been more widely used as the main material for the preparation of aerospace turbine components. However, with the development of reusable rocket engine technology, a more profound understanding of the low-cycle fatigue performance of the material under cyclic loading is required. In this study, the same specification of GH4586 used in the turbine disk of an engine is used to prepare test specimens, the fatigue performance at different strain levels of 0.5, 0.7, 0.9 and 1% is investigated, and fatigue tests are carried out at six temperatures from room temperature to 1,173 K. The fatigue σ–N curves of the material are obtained. In this study, the cyclic hardening/softening transformation mechanism of GH4586 alloy and its influence on the life of turbine components are systematically revealed through low-cycle fatigue tests with multiple temperature points (room temperature to 1,173 K) and multiple strain amplitudes (0.5–1%). The study shows that optimizing the strain amplitude below 900 K can improve the component life by more than 20%, which provides a quantitative basis for the strain–temperature coupling design of reusable rocket engine turbine.

An Investigation of the Fatigue Behavior and Dislocation Substructures of Friction-Stir-Welded SSM 6063 Aluminum Alloy

In this study, we examine the evolution of dislocation substructures influenced by the fatigue behavior of SSM 6063 aluminum alloy processed through friction stir welding (FSW). The findings indicate that dislocation substructures have a significant impact on fatigue life. Cyclic loading induced recrystallization in the stir zone (SZ), the advancing-side thermomechanically affected zone (AS-TMAZ), and the retreating-side thermomechanically affected zone (RS-TMAZ). The transformation of the α-primary aluminum matrix phase into an S/S’ structure and the precipitation of Al5FeSi intermetallic compounds into the T-phase were observed. Furthermore, the precipitation of Si and Mg, the primary alloying elements, was observed in the Guinier–Preston (GP) zone within the SZ. Transmission electron microscopy (TEM) analysis revealed small rod-like particles in the T-phase, measuring approximately 10–20 nm in width and 20–30 nm in length in the SZ. In the AS-TMAZ, these rod-like structures ranged from 10 to 120 nm in width and 20 to 180 nm in length, whereas in the RS-TMAZ, they varied between 10 and 70 nm in width and from 20 to 110 nm in length. The dislocation substructures influenced the stress amplitude, which was 42.46 MPa in the base metal (BM) and 33.12 MPa in the FSW-processed SSM 6063 aluminum alloy after undergoing more than 2 × 106 loading cycles. The endurance limit was 42.50 MPa for BM and 32.40 MPa for FSW. Fractographic analysis of the FSW samples revealed distinct laminar crack zones and shear fracture surface zones, differing from those of other regions. Both brittle and ductile fracture characteristics were identified.

Fatigue Prediction of 50% Short Fiber‐Reinforced Polyphthalamide Using Equivalent Stress Criteria and Critical Distance Methods

AbstractAccurately predicting the fatigue lifetime of short fiber‐reinforced polymers (SFRPs) remains a significant challenge in the automotive industry, especially in the presence of sharp geometric discontinuities. This study presents a practical approach for estimating the fatigue life of injection‐molded notched SFRP specimens, considering material anisotropy and load ratio dependency. Micro‐computed tomography was used to analyze fiber orientation in critical areas for simulating anisotropic behavior. The Point Method, based on the Theory of Critical Distances, was applied to calculate matrix equivalent stresses near the notch root. Both von Mises and Beltrami equivalent stresses were evaluated at the matrix level, highlighting distinct behaviors across specimens and enabling the development of a master SN curve. Additionally, a modified constant life diagram was created to account for load ratio effects, offering a generalized fatigue prediction method. This approach provides a balanced solution between prediction accuracy and computational efficiency.

Fatigue life evaluation method for multi-joint robot-like boom structure of concrete pump truck

Concrete pump trucks are widely used in engineering construction. The fatigue life of the multi-joint robot-like boom structure, being the most crucial part of a concrete pump truck, significantly impacts the safe operation and maintenance of the truck. A novel approach to generate fatigue load spectra and evaluate the fatigue life for the multi-joint robot-like boom structure of a concrete pump truck is proposed. Initially, the typical operating posture of a concrete pump truck is defined through big data analysis of the boom inclination and included angle. Subsequently, load information is collected and pre-processed corresponding to the determined typical operating posture. Finally, a parametric method is employed to estimate and extrapolate the amplitude distribution of the load spectra and then strengthened to reduce the test period. The reliability and practicability of the proposed method were validated through 120 pump trucks. The relative deviation of fatigue cycles between test and actual external feedback is 1.37%, which illustrates the effectiveness of the proposed method.

Performance Evaluation of Porous Asphalt Mixture Reinforced with Waste Cellulose Acetate Fibers

Cellulose acetate fiber (CAF), a typical waste product derived from cigarette filters, has attracted growing attention for its potential reuse in asphalt materials. However, its application in porous asphalt (PA) mixtures remains underexplored. This study investigates the effects of CAF on the performance of asphalt binders and PA-13 mixtures through a series of laboratory tests. The results demonstrate that CAF significantly enhances the high-temperature rheological performance of asphalt binders. A 1% CAF content improved the low-temperature rheological performance of asphalt binder, while a higher CAF content resulted in performance degradation. A fatigue life analysis revealed a parabolic relationship with CAF content with the optimal Nf50 observed at a 1% CAF-a 4.3% increase over the original binder. Compared to 3% lignin fiber (LF)-modified binders, 3% CAF-modified binders exhibited reduced temperature sensitivity in high-temperature performance, at least a 4.6% improvement in low-temperature performance and an 8.4% increase in the fatigue life. As for PA-13 mixtures, the incorporation of CAF progressively improved rutting, moisture and stripping resistance with increasing CAF content, achieving the highest dynamic stability, highest tensile strength ratio and lowest mass loss rate at 5% CAF. The low-temperature performance and fatigue life (S = 0.45) of PA-13 mixtures exhibited a parabolic trend, peaking at 3% CAF. Moreover, the 3% CAF-modified PA-13 mixture demonstrated improved low-temperature performance and fatigue resistance, while exhibiting a slight decrease in high-temperature stability, water resistance and resistance to disintegration. Overall, CAF is a viable alternative to LF for improving the durability and service life of asphalt pavements.

Failure Analysis of the Threaded Connection of the Top Inlet Pipe for the High-pressure Polyethylene Reactor

Abstract To investigate the thread failure issue of the top inlet pipe end of a high-pressure polyethylene reactor, a fluid-structure interaction (FSI) numerical model was developed for the reactor?s top inlet pipe. Bidirectional FSI analysis revealed that, although fluid pressure pulsations are the primary cause of pipeline vibrations, asymmetric secondary flow at the double elbows induces out-of-plane structural vibrations, causing the crack locations at the threaded pipe end to deviate out of plane. A localized numerical model of the straight pipe segment with threads was established, and the reaction forces and moments at the fixed end of the pipe segment were directly applied based on results from the FSI analysis to assess the very high cycle fatigue (VHCF) life of the structure. A parametric analysis was performed by replacing the real threads with a virtual thread structure, and the simulation results were corrected to explore optimized reinforcement strategies for the inlet pipe segment. The results indicate that adding support at the end of the inlet elbow increases fatigue life by 4.35 times compared to the original structure. Fractographic analysis using scanning electron microscopy revealed the presence of shallow non-metallic inclusions at the crack initiation site, characterized by atypical ‘fish-eye’ features. Based on a high-strength steel VHCF life prediction model, recommendations were proposed to enhance the fatigue life of the pipe segment by controlling the size of non-metallic inclusions.