Fatigue Analysis Research Articles

Polyester mooring system design and evaluation of a semi-platform in south China sea

Polyester rope offers numerous advantages over traditional steel catenary mooring systems and is considered an appealing option for deep-water mooring systems. In this paper, the design and evaluation procedure of the polyester mooring system for a semi-submersible platform located in the South China Sea is presented. A fully coupled numerical model of the semi-submersible platform, including all risers and mooring lines, has been established and calibrated through wave basin testing. To simulate the elongation behavior of polyester, a static-dynamic stiffness model is employed, and the corresponding procedure for mooring evaluation is established to simulate the mooring response under extreme environmental conditions. A comprehensive fatigue analysis is also conducted for the polyester mooring system using time domain dynamic theory. The effects of Vortex-Induced Motion (VIM) on mooring fatigue damage are also considered. The results indicate that the polyester mooring system could be safely operated at the target offshore field throughout its service life. Additionally, model test calibration is a crucial procedure during the entire mooring evaluation process, and the numerical model should be adjusted appropriately to accurately reflect the dynamic behavior of the coupled system. This study also illustrates that the stiffness of the rope plays a crucial role in polyester mooring design and global performance calculations. The proposed evaluation methodology can provide a foundation for the design of polyester mooring systems and for evaluating their safety and reliability in engineering practice.

Influence of connection design and material properties on stress distribution and fatigue lifetime of zygomatic implants: A finite element analysis

Zygomatic implants (ZIs) were developed as a graftless alternative to rehabilitate severely reabsorbed maxillae. This study aims to employ three-dimensional finite element analysis (FEA) to simulate the impact of external hexagonal implant connection (EHC) and internal hexagonal implant connection (IHC) on the stress distribution and fatigue lifetime within the ZI systems using parameters defined in ISO 14801:2016. Two ZI assemblies (Nobel Biocare and Noris Medical) were scanned in a micro-CT scanner and reconstructed using Nrecon software. Three-dimensional models were generated by Simpleware ScanIP Medical software. All models were exported to FEA software (ABAQUS) and subsequently to a fatigue analysis software (Fe-safe). A compressive 150 N load was applied at a 40° angle on the cap surface. A 15 Hz frequency was applied in the in silico cyclic test. The implant components had material properties of commercially pure grade 4 titanium (CPTi) and Titanium-6Aluminum-4Vanadium alloy (Ti64). Von Mises stress data, contour plots, and fatigue limits were collected and analyzed. EHC models exhibited higher peak stresses in implant components for both materials compared to IHC models. However, simulated bone support results showed the opposite trend, with higher stresses on IHCthan EHC models. The fatigue analysis revealed that assemblies with both designs exceeded ISO 14801:2016 number of cycles limits using Ti64, while CPTi groups exhibited comparatively lower worst life-repeats. In conclusion, ZIs with IHC were found to have a more homogeneous and advantageous stress distribution within both materials tested. Ti64 demonstrates a prolonged service life for both design connections.

Structural Integrity Analysis of Marine Dynamic Cables: Water Trees and Fatigue

Abstract Offshore power cables are typically designed to have a service life of around 25 years. A pattern is emerging where these cables only last 10 years or even as little as two. The main consensus as to why the service life is so short is due to a combination of fatigue and fretting/wear damages of the copper conductors and water treeing in the insulation material. This study presents a method that can be used to analyze the structural integrity of dynamic subsea power cables and estimate their service life determined by the factors above. The numerical simulation models developed and used to carry out global and local fatigue analyses of dynamic subsea power cables are presented, together with methods and models for assessing fretting, wear, and growth of water tree defects. A methodology for structural integrity assessment that includes all these factors is proposed. A dynamic subsea power cable connected to a wave energy converter is used as the case study for comparison of the service life when these factors are considered compared to when, e.g., the growth of water trees is excluded. A numerical sensitivity analysis demonstrates that the value of the seawater's electrical conductivity and the insulation material's threshold stress-intensity factor greatly influence the cable's service life.

Fatigue Analysis of Composite Leaf Springs - A Review

The purpose of this paper is to provide a review of work that has been carried out in analyzing composite leaf springs. Leaf springs made of fibre reinforced composites exhibit much more advantages when compared with steel leaf springs. Most importantly, polymer composites increase the performances of vehicles by decreasing the weight of the leaf spring and also by providing corrosion resistance. This paper summarizes the fatigue analysis of composite leaf springs by considering the results obtained by some of the research works.

Fatigue and Autofrettage Analysis of Steel Sleeve Based on Precision Fit under Ultra High Pressure

Abstract In order to ensure precision fit between steel sleeve and plunger, copper sleeve and the other parts of the ultra high pressure plunger pump, as well as increase the fatigue life of steel sleeve, this paper made the analysis of work process and fatigue life of ultra high pressure autofrettage steel sleeve of plunger pump based on both analytical method and FEM. The elastic-plastic boundary radius, radial stress and plastic zone displacement were obtained based on the elastic-plastic mechanics analysis of ultra high pressure steel sleeve. The functional relationship built related to precision fit among autofrettage pressure, inner diameter expectation and displacement could ensure the machining dimension of inner diameter of steel sleeve and realize the precise control of inner diameter of steel sleeve. The analytical method and FEM for calculating fatigue life was also proposed, which are verified by experiment. The research shows that machining dimension is determined by inner diameter expectation in the autofrettage process to ensure precision fit; autofrettage treatment can reduce the working stress level of the steel sleeve and extend the fatigue life remarkably. These conclusions contribute to guide the design of steel sleeve.

Low cycle fatigue analysis of welded joints considering material cycling behavior

In order to describe the local cyclic behavior of welds during low cycle fatigue of welded structures, so as to effectively assess the low cycle fatigue of structures, a structural strain numerical method is proposed. Based on the plate and shell theory and elastic-plastic theory, the numerical method of equivalent structural strain parameter is derived, and the UMAT subroutine of ABAQUS software is used to solve the structural strain parameters directly. The fatigue life of the welded specimens of different materials was evaluated, and the predicted life was basically the same as the test life, among which the maximum error of the predicted life of structural steel was 12%, the maximum error of the predicted life of aluminum alloy was 15.7%, and the maximum error of the predicted life of titanium alloy was 7.3%. The fatigue data of different materials were analyzed by using the master E-N curve, and the results showed that all the evaluated fatigue data were distributed in the same narrow band of the master E-N curve, which proved the effectiveness of the equivalent structural strain range for the evaluation of low cycle fatigue of welded specimens.

Virtual vibration test rig for fatigue analysis of dozer push arms

AbstractTo obtain accurate fatigue life results for construction machinery components, acquiring load spectra is crucial, as their authenticity and validity directly determine the precision of the analysis. In working conditions, component attitudes change continuously, but they remain static on the vibration test rig (VTR), so the acquired target signals should match with the actual component attitudes in the driving signal generation. This paper proposes an efficient and economical simulation‐based virtual VTR for fatigue analysis of dozers. First, the relationship between the push arm rotation angle and the cylinder stroke is established, since the cylinder strokes can be measured easily in data acquisition experiments. Second, load decomposition is used to determine the attitude relationship between virtual VTR conditions and actual conditions, and target signals are calculated based on this attitude relationship and measured data. According to the system's frequency response function, the driving signals are iterated until the system's response signals converge with the target signals. Finally, the iteratively obtained load spectra are utilized for fatigue life analysis. The results show that the virtual VTR can effectively and accurately obtain the results of fatigue analysis and has engineering application significance.

Structural strength and fatigue analyses of large-scale underwater compressed hydrogen energy storage accumulator

Underwater compressed hydrogen energy storage (UWCHES) is a potential solution for offshore energy storage. By taking advantage of the hydrostatic pressure of deep seawater, the compressed hydrogen can be isobarically stored in underwater artificial energy storage accumulators. The accumulator should withstand high pressure and large buoyancy and possess reliable anchoring to the seabed. In this study, the structural strength analysis and fatigue life of the large-scale accumulator is conducted employing the finite element method (FEM). The dimensionless stress prediction model and dimensionless fatigue life prediction model are developed through dimensional analysis and multivariate regression analysis. The performance of the accumulator with operating water depth of 100∼300 m, gas storage volume of 1081∼10128 m³, and concrete wall thickness of 0.1∼0.63 m is investigated. The results show that with an operating water depth of 100 m, gas storage capacity of 10,128 m3, and concrete wall thickness of 0.63 m, the maximum compressive stress is 1.43 MPa (yield strength is 60 MPa) and the maximum tensile stress of the accumulator is 2.55 MPa (yield strength is 6 MPa). The design fatigue life is 106 cycles which is larger than the expected service life of 104 cycles. Therefore, the accumulator structure meets the static strength and fatigue life. As the operating water depth increases with a consistent gas storage capacity, a transition in the stress state shifts from primarily tensile stress to predominantly compressive stress. The accuracy of the dimensionless stress prediction model and the dimensionless fatigue life prediction model were verified, with maximum deviations of 10.3 % and 13.7 %, respectively. Furthermore, the anchoring factor of safety of 1.12 is achieved.

Discovery of white etching areas in high nitrogen bearing steel X30CrMoN15-1: A novel finding in rolling contact fatigue analysis

White etching areas (WEA) and white etching cracks (WEC) are frequently linked to premature bearing failure in conventional high carbon bearing steels like 100Cr6 (SAE 52100). In contrast, no WEA/WEC has yet been reported for the high nitrogen bearing steel X30CrMoN15-1 (SAE AMS 5898). Thus, the present study proves for the first time that X30CrMoN15-1 is also susceptible to develop WEA/WEC under rolling contact fatigue (RCF) when pre-charged with hydrogen. RCF tests conducted in parallel without hydrogen pre-charging resulted in RCF damage only, which identifies hydrogen as an active agent for WEA/WEC formation in X30CrMoN15-1. These findings correspond to the fact that hydrogen diffusion during RCF is often considered to cause or accelerate the formation of WEA/WEC. Additionally, it is observed that the M2(C, N) and M23C6 precipitates of the martensitic microstructure of the X30CrMoN15-1 do not entirely decompose during the WEA formation process as observed for M3C precipitates in 100Cr6. In conclusion, the results for X30CrMoN15-1 strongly suggest that the formation of WEA is driven by a hydrogen-activated local severe plastic deformation process, which initiates continuous dynamic recrystallisation, leading to the characteristic nano-ferritic grains observed in WEA. Also, the highly stable and self-regenerating passive chromium-oxide layer of X30CrMoN15-1 mitigates the risk of WEA/WEC failure during typical RCF operation by hindering the formation and adsorption of ionic hydrogen. Hence, this study emphasises the importance of protecting the base material against hydrogen ingress to delay WEA/WEC formation.

A New Critical Plane Multiaxial Fatigue Criterion with an Exponent to Account for High Mean Stress Effect

The mean stress effect remains a critical aspect in multiaxial fatigue analysis. This work presents a new criterion that, based on the classical Findley criterion, applies a material-dependent exponent to the mean normal stress term and includes the ultimate tensile stress as a fitting parameter. This way of considering the non-linear effect of the mean stress, with a material-dependent rather than a fixed exponent, is totally innovative among the multiaxial fatigue criteria found in the literature. In order to verify its accuracy, the new criterion has been checked against an extended version of the Papuga database of multiaxial experimental tests with 485 results, and compared with the criteria by Findley, Robert, and Papuga. The new criterion provides outstanding results for pure uniaxial cases, with multiaxial performance similar to the Robert criterion with a smaller range of error and a conservative trend, even surpassing the popular Papuga method in several relevant loading scenarios. These features enhance the applicability and versatility of the criterion for its use in the fatigue design of structural components.

Detecting Voice Fatigue With Artificial Intelligence

Voice fatigue (VF) has many symptoms and can occur after extended or brief voice use, depending on the presence or absence of voice pathology, and other factors. However, fatigue is difficult to detect and quantify through current approaches. This study explores the use of artificial intelligence (AI) in the automatic detection and analysis of voice fatigue, presenting a novel approach to detect and monitor the condition. ObjectiveThis study aims to create an AI-based system for detecting voice fatigue. The AI model’s performance is evaluated against traditional methods of assessment conducted by speech-language pathologists (SLPs). MethodsVoice samples were collected from individuals experiencing varying levels of voice fatigue. To validate these samples, we calculated fo, increases which have been shown to be correlated with voice fatigue, at the beginning and end of the recordings. The samples were processed using a machine learning model trained to recognize patterns associated with voice fatigue. To build the model, we extracted embeddings from an ECAPA-TDNN model that has been shown to capture changes in the voice characteristics of a speaker over time and used a convolutional neural network for classification. To validate the model, the model’s accuracy in detecting voice fatigue was compared to assessments from SLPs. ResultsWe achieved an accuracy score of 93% on our dataset of English academic lectures and podcasts. As further validation, we asked 3 experienced SLPs to classify audio segments from our dataset and compared their responses to the classifications from our model, and achieved an accuracy of 86% as compared to their ratings. ConclusionThe application of AI in the detection of voice fatigue shows a generalizable approach for the analysis of voice fatigue. Future research will incorporate patient data to validate further the models that we created.

Assessing the influence of image capture frequency and asynchronicity on the accuracy of digital image correlation for fatigue analysis

Efficiency of Digital Image Correlation (DIC) technique for fatigue analysis can be significantly increased by capturing images at periodic intervals for correlation. However, the scarcity of images to capture the history of deformation can cause inaccuracies in full-field measurements. In this study, a comprehensive analysis is conducted to quantitatively assess this error by considering various scenarios. These include skipping of frames within every cycle and across cycles, as well as deviations between intended and captured frames. DIC measurements based on a high density of frames in every cycle is assumed to be true solution to evaluate error for all the cases. Analysis indicates that the skipping frames within every cycle introduces error in full-field strain, which increases with the propagation of crack. Interestingly, magnitude of error for periodic skipping of frames across cycles is observed to be more than skipping of frames within cycle. Furthermore, error shows an increasing trend as the gap between periodic frames becomes larger. Analysis also shows that random deviations disturbing periodicity of skipped frames for DIC can further increase the error in full-field strains. Overall, accuracy of the accelerated approach is seen to strongly depend on presence of discontinuous features and local gradients in response.

Structural integrity assessment of an offshore platform using RB-FEA

PurposeThe paper aims to analyze the structural integrity of an existing offshore platform located in the Northern Adriatic Sea, followed by the topside decommissioning and the re-utilization of the jacket as a wind turbine support. The structural integrity assessment against the in-place and the long-term actions is accomplished by using a reduced basis finite element method (RB-FEA) software program assessing the capability of the jacket to be used as a support for wind turbines at the end of its life cycle as oil and gas (O&G) platform.Design/methodology/approachThe project starts by modeling the jacket, and subsequently, the structural analyses for the in-place loads in operative and extreme conditions are performed. Then, the fatigue analysis is carried out in order to define the cumulative damage necessary to evaluate the possibility to use the jacket as a wind turbine support.FindingsThe results show that the jacket, at the end of the service life as O&G platform, is able to withstand the loads produced by the installation of the wind turbine since the analyses are satisfied even with the conservative approach used which overestimates the thickness loss assuming a linear increasing value during the service life.Research limitations/implicationsBecause of the chosen approach, the study presents some limitations, especially concerning the real state of the platform which has been defined considering the thickness loss only. Additionally, a 1D model was used to perform the analyses, and hence, a 3D model could help in evaluating the critical points with higher precision.Practical implicationsThe assessment of the structure could be improved by modeling a digital twin of the asset allowing a real-time monitoring which, however, involves a huge amount of data to be processed, so a suitable simulation technology must be used.Originality/valueThe RB-FEA proposed by Akselos is suitable to perform the analyses speeding up the processing of the data even in real time.

The analysis for fatigue caused by vibration of railway composite beam considering time-dependent effect

The time-dependent effects in steel-concrete composite beam bridges can intensify track irregularities, subsequently leading to amplified train-bridge coupling vibrations. This phenomenon may increase the stress amplitudes in the bridge steel, thereby impacting the fatigue performance of the composite structures. This paper employs multiple rigid body dynamics to construct a high-speed train model and utilizes the finite element method to develop a steel-concrete composite beam element model that accounts for time-dependent effects, interfacial slip, and shear hysteresis. This approach enables the computational analysis of the train-bridge coupling system, facilitating an investigation into the influence of concrete’s time-dependent effects on the fatigue performance of railway steel-concrete composite bridges. Focusing on a 40-m simply supported composite bridge, the train-bridge coupling dynamic responses were computed for each operational year within a decade of the completion of construction. Applying the P-M linear fatigue damage accumulation theory, statistical analysis of stress history data across various operational periods was conducted to quantify the fatigue damage induced by a single eight-car high-speed train on the lower flange of the mid-span steel beam and the beam-end studs. The findings reveal that the beam-end studs sustain greater damage than the mid-span steel beam. Moreover, the detrimental impact of time-dependent effects diminishes with the increase of operational years. Notably, compared to the initial year, the fatigue damage to the lower flange of the mid-span steel beam by an eight-car train in the tenth year has surged by 39.3%. Conversely, the damage to the beam-end studs has decreased by 47.5%.

Fatigue analysis of selective laser melting Inconel 718 and the mechanism of ductile–brittle continuous alternating steps during fatigue process

In this paper, Inconel 718 powber fabricated by selective laser melting were studied to explore the mechanical characteristics and microstructures. The results of microstructure show that the material exhibits the columnar, honeycomb, and mixed crystal structures. The microhardness is very uniform, with a average value of 317 HV. Tensile test shows the ultimate tensile strength of 785Mpa, elongation of 4.93%, which is high stress brittle fracture. The fatigue strength of 180 MPa was obtained from the fatigue test. The fatigue life was sensitive to the effect of stress. In the scanning electron microscope observation, small crack propagation was found in the fracture, and a large number of step-like fracture characteristics of repeated transformation of toughness and brittleness were found. The mechanism analysis of the step-like ductile–brittle fracture is carried out, which is divided into four stages. Mathematically analyzing the tough-brittle fracture of the step type, where the crack is subjected to both the stress field around the pore and the stress field at the crack tip on the way to extension, a stress field model for crack propagation around the pore and a fracture toughness formula for transverse and longitudinal propagation of tough-brittle steps applicable to this paper are proposed.

Fatigue Analysis of Woven Intraply Carbon/Kevlar Hybrid Composite Below Ambient Temperature

Fatigue Analysis of Woven Intraply Carbon/Kevlar Hybrid Composite Below Ambient Temperature

Internet of things and ensemble learning-based mental and physical fatigue monitoring for smart construction sites

The construction industry substantially contributes to the economic growth of a country. However, it records a large number of workplace injuries and fatalities annually due to its hesitant adoption of automated safety monitoring systems. To address this critical concern, this study presents a real-time monitoring approach that uses the Internet of Things and ensemble learning. This study leverages wearable sensor technology, such as photoplethysmography and electroencephalography sensors, to continuously track the physiological parameters of construction workers. The sensor data is processed using an ensemble learning approach called the ChronoEnsemble Fatigue Analysis System (CEFAS), comprising deep autoregressive and temporal fusion transformer models, to accurately predict potential physical and mental fatigue. Comprehensive evaluation metrics, including mean square error, mean absolute scaled error, and symmetric mean absolute percentage error, demonstrated the superior prediction accuracy and reliability of the proposed model compared to standalone models. The ensemble learning model exhibited remarkable precision in predicting physical and mental fatigue, as evidenced by the mean square errors of 0.0008 and 0.0033, respectively. The proposed model promptly recognizes potential hazards and irregularities, considerably enhancing worker safety and reducing on-site risks.

Fatigue analysis of spherulitic semi‐crystalline polymers: Unveiling the effects of microstructure and defect

AbstractA micromechanical model considering the spherulite structure of semi‐crystalline polymers was established in this study. The micro stress–strain histories were captured by combining the constitutive equations and multi‐axial fatigue criterion. The continuous damage theory was employed to describe the degradation of material properties during cycle loading. Based on the proposed model, the effects of microstructure features, such as grain anisotropy, defects, and crystallinity, on the fatigue performance was examined under multi‐axial loading condition. The local material degradation and damage accumulation were then focused on to understand the underlying fatigue mechanisms with various microstructures. Meanwhile, the crack initiation site was precisely predicted and discussed. This research provides theoretical support for understanding the failure mechanisms of spherulitic semi‐crystalline polymers, deepening the understanding of associated microstructural characteristics and strengthening the anti‐fatigue design of semi‐crystalline polymers.

Redesign of workstations guitar product to minimize musculoskeletal disorders for workers

The production process of acoustic guitars in Indonesia involves 4 workstations and 17 distinct activities. Due to the nature of the work—8-hour shifts in seated positions with frequent bending, squatting, and repetitive movements—workers are at risk of musculoskeletal disorders (MSDs), particularly in the neck, shoulders, back, arms, and wrists. This study aimed to identify and analyze body posture conditions using the Nordic Body Map (NBM) and Muscle Fatigue Analysis (MFA) methods. The NBM method was used to record pain complaints across various body parts, while the MFA assessed muscle fatigue by considering the level of effort, work duration, and movement frequency. Results from the NBM showed that among the workers, 2 were at high risk, 3 at medium risk, and 7 at low risk for MSDs. The MFA further identified 3 workers with very high to high-priority fatigue concerns, specifically affecting the neck, back, shoulders, right arm, wrist, and legs. To address these issues, the study recommended redesigning work facilities and layouts using the SolidWorks application, along with implementing regular muscle stretching and exercise routines to minimize the risk of MSDs and improve worker well-being.

Effect of Suspension Preload on Fatigue Life of Two Wheeler Frame

A suspension unit is a significant component in a vehicle. It provides a smooth ride, improves traction, maintains ride geometry and facilitates better handling. A typical suspension setup in a two-wheeler consists of a front and rear suspension setup working independently to achieve the desired function. It connects the wheel to the chassis of the vehicle, transferring road load and hence affecting the durability of the structural members. This research work focuses on the durability aspect of the suspension unit with its preload as the control parameter. A rear suspension with seven preload settings was chosen for this study. The provision requirements of preload settings in suspension were experimentally analyzed using static measurements. The vehicle was instrumented with transducers (strain gauges, accelerometers, linear displacement sensors, and Global Positioning System (GPS) sensors), and dynamic road load data was acquired at different rear suspension preload settings by changing from the minimum, i.e., the 1st setting, to the maximum, i.e., the 7th setting, while keeping other parameters constant. Statistical analysis and fatigue analysis were utilized to study the dynamic effects. It was observed and quantified that increasing the preload for higher static load conditions or rough road conditions provides a smoother ride and improved life due to lower bump stopper engagement and full bump conditions owing to increased compression stroke availability. Keywords: Suspension, Fatigue Life, Stiffness, Riding, Strain Gauges