Fatigue Analysis Method Research Articles

Fatigue Life Prediction of 2024-T3 Clad Al Alloy Based on an Improved SWT Equation and Machine Learning

The multi-parameter and nonlinear characteristics of the Smith Watson Topper (SWT) equation present considerable challenges for predicting the fatigue life of 2024-T3 clad Al alloy. To overcome these challenges, a novel model integrating traditional fatigue analysis methods with machine learning algorithms is introduced. An improved SWT fatigue life prediction equation is developed by incorporating key factors such as the mean stress effect, stress concentration factor, and surface roughness coefficient. Extreme gradient boosting, Random Forest, and their derived models are used to construct the fatigue life prediction model. The L-BFGS algorithm was then integrated with the established machine learning model to solve for the multi-parameter of the improved SWT equation. Thus, an accurate modified SWT prediction equation for 2024-T3 clad Al alloy was obtained. To further optimize the solution, the deep deterministic policy gradient and deep reinforcement learning algorithms are introduced to dynamically optimize the nonlinear equation, achieving a more efficient and accurate solution. The improved SWT fatigue life prediction equation and its solution method proposed in this study provide new insights for fatigue life prediction of clad metallic materials.

Fatigue Life Prediction and Reliability Assessment of CFRP Adhesively Bonded Joints in Offshore Wind Turbine Blade Applications: A Physics‐Informed Data‐Driven Approach

ABSTRACTAdhesively bonded joints made of carbon fiber reinforced polymer (CFRP) are critical structures of offshore wind turbine blades, yet they are particularly susceptible to fatigue failure influenced by marine environmental factors. Current methodologies for predicting the fatigue life and assessing the reliability of these bonded joints face limitations due to insufficient data, modeling complexities, and inefficiencies. This study introduces a novel, physics‐informed, data‐driven approach to analyze the fatigue performance of CFRP adhesively bonded joints subjected to multi‐environmental stress, thereby improving fatigue life predictions and reliability assessments. Initially, an innovative method that integrates a physics‐informed data‐driven framework for predicting adhesive fatigue life and modeling reliability is proposed, utilizing the cyclic cohesive zone model (CCZM) alongside single‐hidden layer feedforward neural networks (SLFN). Multi‐environmental aging tests were conducted on CFRP‐bonded joints of varying dimensions, leading to the development of a physics‐informed fatigue analysis method based on CCZM. Furthermore, a reliability assessment and sensitivity analysis were performed to evaluate the impact of uncertainty factors. This research provides significant insights for the structural design and safety analysis of bonded structures in offshore wind turbine blades.

Multiscale finite element modelling of dynamic subsea power cables in bending

Abstract This paper proposes a multiscale finite element modelling strategy for dynamic offshore power cables which allows for detailed analysis of individual components. The challenge of modelling the intricate power cores within the cable is addressed by considering a separate repeated unit cell (RUC) of the power core to define its stiffness, where the power cores themselves are then discretised with beam elements in the dynamic cable model. Periodic boundary conditions allowing for geometric non-linearity are employed at both the power core and dynamic cable scale. This means the model size can be reduced to the smallest possible RUC while still permitting non-linear material behaviour. The resulting model is capable of detailed stress analysis of individual components required for fatigue life estimation. The model is validated against existing experimental data showing strong agreement. The proposed multiscale approach may therefore be used to augment existing fatigue analysis methods for dynamic offshore cables where the stress state at individual wires is required.

A Quasi Time-Domain Method for Fatigue Analysis of Reactor Pressure Vessels in Floating Nuclear Power Plants in Marine Environments

The reactor pressure vessel (RPV) in onshore nuclear power plants is typically analysed for fatigue life by considering the temperature, internal pressure, and seismic effects using a simplified time-domain fatigue analysis. In contrast, the frequency-domain fatigue analysis method is commonly employed to assess the fatigue life of ship structures. The RPV of a floating nuclear power plant (FNPP) is subjected to a combination of temperature, internal pressure, and wave loads in the marine environment. Consequently, it is essential to effectively integrate the frequency-domain fatigue analysis method used for hull structures with the time-domain fatigue analysis method for RPVs in FNPPs or, alternatively, to develop a suitable method that effectively accounts for the temperature, internal pressure, and wave loads. In this study, a quasi-time-domain method is proposed for the fatigue analysis of RPVs in FNPPs. In this method, secondary components of marine environmental loads are filtered out using principal component analysis. Subsequently, the stress spectrum induced by waves is transformed into a stress time history. Fatigue stress under the combined influence of temperature, internal pressure, and wave loads is then obtained through a stress component superposition method. Finally, the accuracy of the quasi-time-domain method was validated through three numerical examples. The results indicate that the calculated values obtained by the quasi-time-domain method are slightly higher than those obtained by the traditional time-domain method, with a maximum deviation of no more than 24%. Additionally, the computation time of the quasi-time-domain method is reduced by 98.67% compared to the traditional time-domain method.

Coupled critical plane-pseudo excitation method for multiaxial fatigue analysis of structures under random vibration

This study proposes a coupled critical plane–pseudo excitation method for assessing multiaxial fatigue damage in mechanical structures subjected to random loads. Within the modal coordinate framework, we derive an expression for the spectral moment of the structural stress response using the pseudo excitation method, which facilitates the decoupling of spatial characteristics from frequency domain properties. For the input power spectral density, represented as an integer power function, we employ eigenvalue decomposition and the residue theorem to derive an analytical expression for the spectral moment of the modal displacement response. By constructing equivalent stress modes based on the maximum shear stress and normal stress criteria, we obtain an expression for the equivalent stress variance. Intelligent optimization algorithms are utilized to determine the critical plane position and the corresponding equivalent stress spectral moments, followed by the application of the Dirlik method for fatigue assessment. A numerical example involving random vibration multiaxial fatigue analysis of an L-shaped thin-walled plate demonstrates the effectiveness of the proposed coupled critical plane–pseudo excitation method in comparison to the traditional critical plane method that relies on the stress covariance matrix for calculating equivalent variance. The results confirm the accuracy and efficiency of our approach, and we further explore the impact of different forms of the excitation power spectral density and the damping ratios on the computational outcomes.

Research on satellite unidirectional random vibration test method based on vibration fatigue equivalence

Abstract This article studies the unidirectional random vibration testing method based on vibration fatigue equivalence for batch production satellites, aiming to optimize the mechanical testing project of batch production satellites and reduce satellite development costs. This article first starts from the frequency domain vibration fatigue analysis method and constructs a relationship model between the number of acceleration cycles and the test duration. Then, based on the model of the relationship between the number of acceleration cycles and the duration of the experiment, the response of the satellite in various directions during the noise test was taken as a reference. The random vibration test and the noise test were analyzed for the number of acceleration cycles and the duration of the experiment. Finally, a unidirectional random vibration test method for batch production satellites was obtained.

Fatigue Analysis of PTO Gearboxes in Paddy Power Chassis Using Measured Loads

This study aims to analyze the fatigue life of a PTO (power take-off) gearbox used in a paddy field power chassis. The analysis considers factors such as stress concentration, dimensions, surface quality, and load characteristics affecting fatigue life. A finite element simulation was conducted using the Ansys 2022 software to identify the critical point of the PTO shell. The modified nominal stress fatigue analysis method, incorporating a stress adjustment coefficient, was employed to derive the modified S-N curve. Combined with the measured load data of the PTO bench operation, the load data and the 3D model of the PTO shell were imported into the fatigue analysis software n-code to analyze the fatigue life of the PTO gearbox of a paddy field power chassis and compare it with the prediction results from the traditional stress field strength method. The findings indicate that the optimized stress adjustment coefficient method predicts a fatigue life (31,699 h) closer to the actual operational life (20,000 h) compared to the traditional method (39,151 h). This research contributes to the advancement of the analytical techniques for predicting fatigue life in critical components of agricultural machinery.

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.

Evaluation of the accuracy and efficiency of the modified maximum variance method for multiaxial fatigue analysis under constant amplitude loading

An optimized version of the Maximum Variance Method (MVM) is employed to determine maximum shear stress amplitudes in high-cycle multiaxial fatigue analysis using the critical plane approach, increasing accuracy and reducing computational burden. This refined approach posits that the MVM assumes that the critical plane is the one subjected to the maximum variance of the shear stress history. Comprehensive statistical analyses, including Analysis of Variance (ANOVA) and multiple comparison techniques such as Tukey’s HSD and Bonferroni correction, were conducted to systematically investigate the impact of critical factors on fatigue resistance, such as mean stress, phase, synchrony, failure criteria, and the strategy for calculating maximum shear stress amplitude. These analyses highlighted significant effects of mean stress and phase on the accuracy of fatigue strength predictions, underscoring the effectiveness of the enhanced MVM in managing complex loading scenarios. The results demonstrate that the proposed methodology performs equal to or better than conventional methods, with significantly lower computational costs.

Multiaxial low-cycle fatigue life model for notched specimens considering small sample characteristics

PurposeSufficient sample data are the necessary condition to ensure high reliability; however, there are relatively poor fatigue test data in the engineering, which affects fatigue life's prediction accuracy. Based on this, this research intends to analyze the fatigue data with small sample characteristics, and then realize the life assessment under different stress levels.Design/methodology/approachFirstly, the Bootstrap method and the principle of fatigue life percentile consistency are used to realize sample aggregation and information fusion. Secondly, the classical outlier detection algorithm (DBSCAN) is used to check the sample data. Then, based on the stress field intensity method, the influence of the non-uniform stress field near the notch root on the fatigue life is analyzed, and the calculation methods of the fatigue damage zone radius and the weighting function are revised. Finally, combined with Weibull distribution, a framework for assessing multiaxial low-cycle fatigue life has been developed.FindingsThe experimental data of Q355(D) material verified the model and compared it with the Yao’s stress field intensity method. The results show that the predictions of the model put forward in this research are all located within the double dispersion zone, with better prediction accuracies than the Yao’s stress field intensity method.Originality/valueAiming at the fatigue test data with small sample characteristics, this research has presented a new method of notch fatigue analysis based on the stress field intensity method, which is combined with the Weibull distribution to construct a low-cycle fatigue life analysis framework, to promote the development of multiaxial fatigue from experimental studies to practical engineering applications.

Application of a new method for probabilistic fatigue analysis from strain measurements on bridges

Increasing loads, ageing of materials as well as environmental change make the issue of fatigue damage critical on bridges, especially in the case of old steel or iron structures. The assessment of the fatigue loads on specific elements of these assets can be carried out from on-field strain measurements with the application of classical methods involving rainflow cycle counting and the use of Palmgren-Miner's rule. However, such a fatigue assessment suffers of significant uncertainties about the real fatigue damage ratio and the consecutive residual fatigue life. A new probabilistic method for the fatigue assessment is proposed, as the result of a joint research by OSMOS Group and the Ecole des Ponts. The theoretical background of the method is described, involving a probabilistic formulation of Miner's rule and the use of a Weibull-Basquin model to describe the health of structural elements. Real field case studies are presented, on two historical iron truss road bridges in France, with a dataset of more than 18 months of continuous strain measurements used for the fitting of the probabilistic model of fatigue loads. The incidence of the quantity of data and of the number of sensors used for the analysis is discussed, along with the conclusive results concerning the probabilistic description of the residual fatigue life.

Redesign of workstations to minimize musculoskeletal disorders for guitar workers in Indonesia

This study aims to determine and analyze body parts that experience musculoskeletal disorders (MSDs) and muscles that experience fatigue in guitar-making workers. The method used is the Nordic Body Map (NBM) to determine MSDs complaints, including complaints of pain in 28 parts of the worker's body, and the Muscle Fatigue Analysis (MFA) method to determine muscle fatigue that occurs in each part of the body by determining the level of effort, duration of work, and frequency of work movements. The results of research using NBM were 2 workers with high risk, 3 workers with medium risk, and 7 workers with low risk. The results of the MFA method were that 3 workers experienced muscle fatigue in the very high category with priority in the neck, back, shoulders, right arm, wrist and feet. Efforts to minimize the risk of MSDs by redesigning work facilities using SolidWorks software and reducing the risk of muscle fatigue by improving work facilities, improving the layout of the production floor, and encouraging workers to stretch their muscles and exercise regularly.

An experimental investigation of ship propulsion system fatigue damage during crash astern maneuver

Marine propulsion shafts are exposed to fatigue due to various maneuvers. Among them, crash astern is considered to induce a high level of torsional stress on the shaft. Torsional stress is a dominant factor in shaft fatigue damage; however, there has been limited discussion on how much this maneuver impacts shaft fatigue life. So, this study aims to calculate fractional fatigue damage resulting from crash astern maneuvers, obtaining numerical results through a marine shaft fatigue analysis method. Firstly, shaft fatigue criteria were defined to establish S-N curves. Then, crash astern maneuvers were conducted to measure torsional stress as a loading history. Raw data were analyzed to apply alternating stress values to the S-N curve, enabling the calculation of cumulative fractional damage. The crash astern maneuver was executed under two different drafts: full laden and normal ballast, allowing for a comparison of shaft fatigue levels based on draft. Torsional stress was higher in the ballast condition than in full laden. Additionally, fatigue damage in ballast is approximately 1.7 times higher than in the other condition. The results suggest that the shaft is more affected by fatigue when sailing in shallow water than when sailing in deep sea.

Automated crack extension measurement method for fracture and fatigue analysis using digital image correlation

A novel Automated Crack Extension Measurement (ACEM) method based on combining decorrelation in strain field and a threshold near maximum of full-field strain obtained from digital image correlation, is developed in this work. A manual method for measuring crack extension from images of the specimen surface and ImageJ, was utilized to validate the accuracy of the proposed method. Initially, ACEM method was validated for crack extension under mode-I fracture of single edge notch specimens with different initial notch sizes. A satisfactory agreement was obtained from this analysis along with limits on the different parameter values used in ACEM. The method was then applied to low-cycle fatigue specimens with different initial notch lengths. Comparison of crack extension between ACEM and manual method reveals satisfactory agreement reinforcing the fidelity of the developed method for fracture and fatigue analysis. Fracture resistance and fatigue crack growth rate curves were also obtained for the different specimens.

CCZM‐based fatigue analysis and reliability assessment for wind turbine blade adhesive joints considering parameter uncertainties

AbstractWind turbine blades are complex structures composed of multiple bonded components. The fatigue performance of these adhesive joints is crucial for ensuring operational safety over the blade's lifespan. Traditional structural fatigue analysis methods are inadequate for evaluating the fatigue properties of these joints due to the unique characteristics of adhesive materials. Variations in material and dimensional parameters, as well as fluctuating operational loads, further complicate the fatigue analysis of adhesive joints in wind turbine blades. To tackle this issue, this study introduces a fatigue analysis and reliability assessment method for the adhesive joints of wind turbine blades, employing the Cyclic Cohesive Zone Model (CCZM) and accounting for parameter uncertainties. Specifically, a novel methodology for fatigue analysis based on the CCZM is presented. The methodology is programmatically implemented to obtain a fatigue life dataset through multiple simulations, considering uncertainties in material parameters, adhesive dimensions, and loads. Subsequently, a fatigue reliability model is formulated to evaluate the fatigue reliability of adhesive joints in wind turbine blades under different parameter conditions, and the sensitivity of fatigue reliability to each parameter is investigated. The findings offer valuable insights for improving the safety and reliability of adhesive structures in wind turbine blades.

A method for the fatigue-life assessment of subsea wellhead connectors considering riser wave-induced vibration

During drilling operations, strong non-linear environmental loads are applied to the riser, which can generate powerful fatigue loads, resulting in safety hazards. This paper deals with the problem of the 330 m subsea wellhead connector in the Liu-hua 11–1, which is subjected to long-term non-linear fatigue loading in drilling conditions. Examining the fatigue response law of the subsea wellhead connector ensures the safe operation of offshore oil and gas wells. First, fatigue tests were performed on key components to obtain the stress-fatigue life curve. The F22 strain fatigue life curve was constructed based on the Neuber stress-strain relationship theory and Manson-Coffin strain-life equation. Then, the overall drilling platform - riser - subsea wellhead - soil model was established, and the bending moment-stress data of the subsea wellhead connector was obtained via finite element analysis. Then, the fatigue load spectrum was determined via the MATLAB program using the rainflow counting theory. The response characteristics of the wellhead connector fatigue damage were also compared based on four fatigue damage accumulation theories. A set of fatigue calculation and analysis methods for subsea wellhead connectors was finally developed. This method can provide reference and guidance for subsequent studies.

Dynamics optimization of small branch pipes in nuclear power plants based on machine learning algorithms

Vibration fatigue failure of small branch pipes poses a great threat to the safe operation of nuclear power plants. However, the transient and wide-band vibration problems are not adequately considered in ASME and RCC-M code, resulting in repeated fatigue failures. In addition, the current research mainly focuses on vibration test methods and fatigue analysis methods, neglecting the study of pipeline vibration characteristics. Therefore, innovative approaches were essential for effectively managing complex dynamic loads. In this study, an innovative approach combining backpropagation artificial neural networks (BP-ANN) and non-dominated sorting Genetic Algorithm II (NSGA-II) was proposed to optimize the vibration of these pipes. The goal was mitigating vibration-induced failures by enhancing operational stability. The methodology progressed through several key stages. Firstly, BP-ANN was utilized for regression analysis, correlating pipe characteristics to vibration effects. Through regression analysis, the complex interrelationships governing the pipes' dynamic behavior was revealed. Subsequently, based on the regression model, NSGA-II was used to derive an optimal combination of design parameters to minimize the vibration response. The proposed technique was validated on an L-shaped cantilevered pipe via finite element simulations and physical experiments. The analysis case shows that the BP-ANN model demonstrated excellent accuracy in predicting vibration responses. Meanwhile, NSGA-II successfully revealed the trade-offs between conflicting objectives, generating a Pareto-optimal set balancing stability under different excitation directions. This study highlights the potential of machine learning methods for dynamic optimization of small branch pipes in nuclear power plants, and verifies the accuracy and effectiveness of the method through experiments. The research results provide a new idea for small branch pipe design and vibration control of nuclear power plant, which contributes to enhancing the safety and reliability of small branch pipes.

An enhanced stress field intensity approach for fatigue life assessment combining notch and size effect

The notch characteristics of engineering components significantly impact their fatigue lives. Accurately analyzing the notch effect and size effect is of great significance for structural integrity evaluation, which provides insights into the extent of fatigue failure in engineering structures. In this paper, a new method is proposed for determining the fatigue failure region based on actual elastic–plastic stress distribution under various notch geometries and applied loads. It considers the complex mechanical behavior of the plastic effect and stress relaxation near the notch root. Furthermore, a novel weight function is employed to consider the relative stress gradient at all points within the fatigue failure region. Finally, an enhanced stress field intensity approach is developed to predict notch specimens fatigue lives utilizing experimental lives of smooth specimens. Additionally, the effectiveness of the proposed method is analyzed by predicting the fatigue lives of three distinct materials notched specimens with varying geometries and applied loads. The prediction absolute errors of the proposed approach are compared with those of the other traditional notched fatigue analysis methods. The comparative results indicated that the performance of the proposed method outperforms the other methods.

Investigating the fatigue performance of conventional reinforced concrete CRTS III ballastless track structures using a fatigue damage constitutive model

Compared to prestressed track structures, the mechanisms underlying fatigue degradation in conventional reinforced concrete track structures under high-cycle train loads remain elusive. This paper introduces a finite element model for CRTS (China Railway Track System) III slab ballastless track. In this model, fatigue damage constitutive relationships for both concrete and reinforcement are incorporated as material subroutines. The study focuses on investigating the fatigue characteristics of composite plate structures, which consist of track slabs and self-compacting concrete (SCC). An accelerated calculation method for high-cycle fatigue issues is utilized. Several key findings emerge from this study. First, the onset of fatigue cracks is observed on the lower surface of the SCC, directly beneath the applied load. These cracks tend to propagate laterally from the most critical location toward the slab edge. Second, a significant interrelationship exists between material fatigue degradation and stress redistribution. Traditional decoupled fatigue analysis methods are likely to overestimate the rate of fatigue evolution at critical points. Third, increasing the stiffness of geotextiles can partially optimize stress distribution within the track structures, thereby extending the time to initial cracking.

An Out-of-Plane Bending Fatigue Assessment Approach for Offshore Mooring Chains Considering the Real-Time Updating of Interlink Bending Stiffness

Fatigue failure caused by frequent tension and bending loads is a crucial safety concern for mooring chains used on floating structures in the oil and gas industry. The bending effect for a chain’s fatigue is usually not considered by existing fatigue analysis methods, and even if it is considered, existing commercial software can only calculate the constant interlink bending stiffness without consideration of the stiffness variations due to tension and friction. To address this issue, this study develops an in-plane bending (IPB)/out-of-plane bending (OPB) fatigue assessment approach for offshore mooring chains considering the time-varying nonlinear interlink bending stiffness. Initially, the mooring tension and IPB/OPB angles are calculated by an in-house code MeCAP (multi-element coupled analysis program), considering the time-varying interlink stiffness between the chain links. The fatigue life of mooring chains for pure tension–tension (TT) and OPB combined fatigue at different hotspot locations (A, B, and C) is calculated by MeCAP-fatigue, a newly-developed module in MeCAP. Based on the analysis model, a comparative study is implemented to investigate the effects of interlink stiffness on fatigue damage. The differences and advantages of the combined fatigue calculation method over the pure TT fatigue assessment method are discussed. The results illustrate that combined fatigue would be underestimated significantly if zero interlink stiffness (hinge joint assumption) is applied or even constant interlink stiffness (calculated by mooring pretension), while pure TT fatigue will be largely unaffected. Moreover, compared to pure TT fatigue, the OPB combined fatigue assessment method, considering the effects of OPB/IPB and the time-varying properties of the connection between chain links, could evaluate fatigue life more comprehensively.