Fatigue Damage Assessment Research Articles

Master S-N curve method to fatigue damage assessment of the high-ply cutter body

AbstractAt present, the cutting fabric thickness of the high-ply cutter can reach 100 mm, which requires high vacuum pressure resistance performance, and the fatigue reliability of the cutter body is an important indicator of cutting performance. In this paper, the cutter body was analyzed by finite element simulation, the equivalent structural stress and Von Mises stress at key positions were calculated separately. Then, the master S-N curve method and traditional method were used to evaluate fatigue damages at key locations of the cutter body, which are compared and analyzed with the fatigue damage of measured dynamic stress. The results show that the maximum fatigue damage calculated by the master S-N curve method is 0.223, which is the safest. it verifies the effectiveness and reliability of the master S-N curve method in evaluating the fatigue damage of the cutter body. Meanwhile, the fatigue damage of the three measuring points calculated by the three methods is all below 0.5, and it indicates that the design of the cutter body is reasonable. In addition, the master S-N curve method and equivalent structural stress method were first applied to the fatigue damage assessment of high-ply cutter body, which provides an efficient and high-precision approach for the anti-fatigue design of cutter body.

A novel framework for fatigue hotspot localization and damage assessment of multi-defect marine structures under random vibration

In ocean engineering, assessing vibration-induced fatigue under random loads is critical, particularly for ocean structures with multiple defects, as fatigue is highly sensitive to local structural flaws. Recently, incorporating structural dynamic characteristics into vibration fatigue assessments has emerged as a significant trend and formidable challenge, involving three key obstacles: precise localization of fatigue hotspots, extraction of key modes, and determination and integration of modal damage contributions. This paper introduces a novel framework for fatigue hotspot localization and damage assessment in the context of random vibration fatigue in ocean structures. By initially identifying fatigue hotspots and hot regions using stress mode shapes, refining the finite element mesh in hot regions, and conducting reanalysis, the exact locations of fatigue hotspots can be determined, enabling structural dimensionality reduction. The introduction of a modal damage contribution factor allows for the evaluation of each mode's damage contribution and the identification of key modes, further facilitating modal reduction. For the precisely localized fatigue hotspots, the proposed method combines the damage contributions of key modes, enabling rapid and accurate assessment of fatigue damage under random vibration loads. Finite element case studies and vibration fatigue test results demonstrate that the proposed framework effectively addresses the challenges of random vibration fatigue evaluation, achieving structural and modal reduction while significantly enhancing the efficiency of damage assessment without compromising accuracy.

Buffeting induced fatigue damage assessment of long-span bridge decks under uncertain turbulence conditions

Fatigue in wind-sensitive structures is influenced by the mean wind speed and the turbulence characteristics. This study investigates the importance of uncertainty in the turbulence characteristics of buffeting-induced fatigue damage of flexible wind-sensitive structures, focusing on long-span bridges. We address the importance of the variability of uncertainty in the wind field by using a probabilistic wind field model, including uncertain turbulence parameters for calculating the accumulated fatigue damage throughout the structure’s design life. However, it has been demonstrated that a high computational load accompanies this approach. A new method is proposed that significantly reduces the computational effort through surrogate modelling. This is achieved through a sequentially updating Gaussian Process surrogate modelling approach, which integrates new simulation points into the training dataset and reduces the number of buffeting calculations required for the surrogate to converge to the true solution, thereby reducing the computational cost by almost 95%. The efficiency of the algorithm is demonstrated by using it to compute the fatigue damage accumulation through the design life for a long-span bridge girder, resulting in the increase of damage by several orders of magnitude in comparison to the conventional method of treating the turbulence parameters as deterministic and uncorrelated.

Assessment of longitudinal load spectrum characteristics and structural fatigue damage of metro vehicle body in service

Aiming at the structural integrity requirements of service vehicles, there is an urgent need to construct a set of analytical methods based on service load characterization to realize the life assessment of the critical weak regions of the vehicle body. This study measured the longitudinal load spectrum of a metro vehicle body under a typical service line using a calibrated coupler and traction bar. Based on the signal characteristics of the longitudinal loads, a dynamic load feature decomposition method is proposed to decompose the longitudinal load features into trend and fluctuation signals to reflect the overall and local laws. The longitudinal load transfer characteristics of the vehicle body under traction, braking, linear, and curved conditions are innovatively analyzed, and a longitudinal load distribution ratio coefficient with generality is proposed as the input of effective service load. The service stress spectrum of the vital points of the vehicle body is constructed, which can more comprehensively and realistically respond to the service stress state of the vehicle body compared with the standard design loads, which further improves the accuracy of the structural integrity assessment.

A Review on the Recent Process of Lazy Wave Risers

Lazy wave risers (LWRs) are designed with equidistant buoyancy blocks attached in the lower half of the riser, allowing the riser to take on an arch shape under the buoyancy forces provided by buoyancy blocks. This arch configuration can provide flexibility to the LWR arrangement and effectively isolate the dynamic responses between the offshore floating structure and the riser’s touchdown zone (TDZ). Its design and application aim to address the issues of dynamic response and fatigue damage that traditional steel catenary risers (SCRs) face in deep water and complex marine environments. Given that research on the LWRs in the field of ocean engineering is not sufficiently abundant, the structural characteristics, hydrodynamic loads, global responses, fatigue damage assessment, and structural optimization progress of LWRs are systematically reviewed in this paper to provide references for researchers in related fields. Among these topics, the global response of LWRs is the main point of this review. This section details the theoretical analysis and numerical modeling methods employed in the study of LWRs’ global response, explores the research advancements in the vortex-induced vibration (VIV) related to LWRs, and discusses corresponding experimental studies. Finally, the installation, transfer, and repair processes of LWRs are investigated. Additionally, the importance of leveraging advanced technologies from other fields and combining them with current advanced algorithms is emphasized in efforts to assess fatigue damage and optimize the structures of LWRs, ultimately achieving complementary advantages.

Fatigue Damage and Reliability Assessment of Wind Turbine Structure During Service Utilizing Real-Time Monitoring Data

Under the action of wind load, a wind turbine tower will produce alternating stress, which leads to fatigue failure. According to the mean wind speed at the wind turbine impeller collected from the SCADA system, the mean wind speed of the simulation point is calculated by using the wind speed exponential model formula. Davenport spectra are used to simulate the pulsating wind speed time series. The wind spectrum is obtained using the harmonic superposition method. Subsequently, the wind speed time series and wind load time series at the simulation point are calculated. Structural modeling of a 5 MW wind turbine tower is performed in ABAQUS 2021. The modal shape and natural frequency are obtained by modal analysis to verify the rationality of the model. Subsequently, wind loads are applied to the model, and structural stress time history is obtained by transient modal dynamics analysis. The stress time history of the maximum stress area of the tower structure is extracted, and the rain flow counting method is applied to it to obtain the stress spectrum. The Weibull distribution of the stress spectrum is fitted, the mean and variance of the total damage in one day are calculated, and the fatigue reliability analysis of the maximum stress area of the tower structure is carried out. And the nonlinear fatigue cumulative damage analysis of the region is carried out. This work has implications for fatigue reliability studies for approximate operating conditions.

Research on the electromagnetic ultrasonic detection method of initiation crack based on multi-acoustic coefficients fusion

Abstract The traditional single acoustic coefficient cannot judge the different degrees of fatigue damage such as initiation crack and crack extension. Based on the law between the structural evolution of dislocation pile-up initiating crack and acoustic coefficients, a multi-acoustic coefficients fusion feature-fatigue damage stage detection method is proposed. By extracting the nonlinear features as well as linear features of the multi-point detection signals for a single fatigue-damaged aluminum plate, achieves the fatigue damage state. Experiments verified multi-acoustic coefficients with different features corresponding to different fatigue stages such as initiation crack and crack extension.The peak points of the acoustic nonlinear coefficients are used for the judgment of the initiation crack stage, and the peak-to-peak amplitude of the acoustic linear coefficients are used for the judgment of the crack extension stage. Comparing and analyzing the results of electromagnetic ultrasonic detection and microscopic observation of different fatigue damage stages, the proposed method provides early warning of the initiation crack and crack extension by studying the characteristics of acoustic coefficients of different fatigue damage stages. This study provides theoretical and experimental basis for the application of electromagnetic ultrasonic assessment of fatigue damage in metallic materials.

Fatigue damage assessment of a large rail-cum-road steel truss-arch bridge using structural health monitoring dynamic data

Structural health monitoring (SHM) system provides valuable information for the fatigue assessment of existing rail-cum-road bridges. This paper aims to develop an effective fatigue assessment approach for the rail-cum-road bridge, Jiujiang Yangtze River Bridge, by utilising the SHM data, focusing on dynamic modal analysis, finite element model updating and fatigue assessment. First, the traffic load spectrum and modal characteristics of the bridge are investigated from the SHM data. A three-dimensional finite element model is constructed and then updated by using the measured modal data through the proposed regularised model updating method. Then, the updated numerical model is verified with the measured dynamic response data, which can be utilised for calculating stress response at critical structural components of the rail-cum-road bridge. Finally, an improved Corten-Dolan’s model is proposed to analyse the fatigue damage and structural reliability of the critical structural components of the bridge, taking into account the combined effects of train and highway vehicle loads. The results demonstrate that the proposed fatigue assessment method provides more reliable results for the rail-cum-road bridge by considering the combined effect of multi-level traffic loads and the non-linear fatigue damage accumulation. It is concluded that the short H-shaped suspender is identified as the most vulnerable structural member of the rail-cum-road bridge, and the remaining fatigue service life of the typical components of the bridge should meet the design requirement.

A framework for rapid fatigue hotspot localization and damage assessment of plate with multiple holes based on the fatigue damage response spectrum method

AbstractThis paper proposes a novel framework for the random vibration fatigue assessment of thin‐walled plate with multiple holes based on the fatigue damage response spectrum method. Compared with other frequency‐domain evaluation methods, this framework fully exploits the dynamic characteristics of complex structures, decoupling the external excitation characteristics from the spatial characteristics of the structural response. This approach significantly enhances evaluation efficiency by avoiding the complex calculations associated with stress response spectral moments. The proposed method is employed to evaluate the contribution of each mode to the overall damage, additionally, the stress mode shapes are used to identify and refine the mesh around fatigue hotspots. Modal damage contribution factors are proposed to identify the key modes. By leveraging both structural dimension reduction and modal reduction techniques, the proposed framework can swiftly and accurately locate fatigue hotspots within complex structures and conduct precise fatigue assessments using the Absolute Sum ‐ Square Root of the Sum of Squares hybrid method. Finite element simulation analysis is conducted on a single‐lap structure containing numerous circular openings, validating the accuracy and efficiency of the proposed stochastic vibration fatigue assessment.

A CFD-DEM-FEM coupling method for the ice-induced fatigue damage assessment of ships in brash ice channels

Polar transport ships frequently traverse in the brash ice channel opened by icebreakers. Although the substantial ice resistance caused by direct collisions with the level ice is avoided, the hull still encounters collisions with the brash ice, leading to periodic damage and exacerbating the fatigue issues of the hull structure. To address the fatigue challenges faced by ships sailing in the brash ice channels, this paper proposes an ice-induced fatigue damage assessment method based on the CFD-DEM-FEM. Referring to the brash ice model test conducted at the Hamburg Ship Model Basin (HSVA), a discrete element ice model and a numerical brash ice tank are established using the CFD-DEM coupling method. The simulated ship-ice interaction is compared with HSVA’s experimental results to validate the reliability of the numerical brash ice tank and ice load. The ice load time history resulting from the ship-brash ice collision is applied to the hull, and the hot spot stress time history under each fatigue sub-condition is calculated using the FEM. The improved rain-flow counting method is employed to determine the stress level of the hot spot stress time history, and the S-N curve method based on the linear cumulative damage criterion is used to calculate the total fatigue damage of hot spots. Finally, the results of the proposed method are compared with those of the LR method. This study can serve as a valuable reference for the ice-induced fatigue assessment of ships navigating in brash ice channels.

Assessment of thermal fatigue damage in square tubes using second harmonic generation of longitudinal waves

Assessment of thermal fatigue damage in square tubes using second harmonic generation of longitudinal waves

Quantitative characterization of fatigue damage in plate structures based on FSOM

For the problem of fatigue damage detection and damage degree assessment of plate structures, a quantitative damage assessment method based on the fast self-organizing feature mapping (FSOM) algorithm is proposed in this paper. The damage detection problem is transformed into a binary classification problem by extracting multidimensional damage features of the Lamb wave signal in plate to be detected and selecting damage sensitive features. Then, the FSOM network is used to identify the health state of the plate to be inspected, and the damage index is obtained by fusing the damage sensitive features using FSOM to quantitatively evaluate the damage level of the plate to be inspected. Simulation and experimental results show this method has a good dynamic tracking capability for the fatigue damage evolution of aluminum and composite plates, and can achieve quantitative assessment of fatigue damage of plate structures.

Fatigue damage identification based on Kullback-Leibler relative entropy for raw acoustic emission waveform

Acoustic emission (AE) as a non-destructive testing technique is used to identify structural fatigue damage through the evolution of AE characteristic parameters, aiming to prevent significant economic losses and catastrophic consequences caused by fatigue failure. Traditional AE characteristic parameters (counts, hit rate, duration, rise time) are susceptible to the influence of threshold and user-defined acquisition parameters (PDT, HDT, HLT). Inaccurate parameter settings can miss the AE signals of the structural damage, resulting in inaccurate assessment. To reduce the dependency on threshold and other user-defined parameters, the Kullback-Leibler relative entropy (KLRE) is proposed as a feature parameter for identifying structural fatigue damage and performing fatigue life analysis. The effectiveness and feasibility of KLRE were verified through the fatigue tension–compression test on medium carbon steel (MCS) 1045 V-notch specimens. Based on different waveform recording methods, KLRE is divided into the hit KLRE (HKLRE) and waveform stream KLRE (SKLRE). Experimental results demonstrate that:(1) SKLRE outperforms the traditional AE time–frequency domain features in assessing fatigue damage, exhibiting an inflection point in its evolution trend before reaching fatigue critical failure. (2) Node-independent wavelet packet denoising method improves the initial instability of SKLRE caused by work hardening and crack face friction. (3) Amplitude attenuation does not affect the evolution trends of Shannon entropy (SE) and SKLRE. (4) The evolution trend of HKLRE is similar to traditional AE time–frequency domain features, necessitating the use of multiple features together to reduce uncertainty.

An efficient active learning Kriging approach for expected fatigue damage assessment applied to wind turbine structures

Estimating fatigue damage in wind turbine structures over their lifetime is a time-demanding task, necessitating simulations encompassing all the wind and wave conditions. Typically, this involves expending several thousand hours in simulation efforts. Given formidable computational demand, this study proposes an efficient active learning Kriging approach named ALK-EFDA for estimating expected fatigue damage in wind turbines. The ALK-EFDA framework leverages a Kriging surrogate model to predict fatigue damage levels across various wind-wave scenarios, and a learning function is designed to reduce Kriging prediction error in the high probability of occurrences of wind-wave cases. An active learning approach is proposed to estimate the expected fatigue damage efficiently. To validate the effectiveness of this approach, we applied it to a 15 MW Semi-submersible floating wind turbine model. The proposed approach estimates the expected short-term fatigue damage of the wind turbine tower and mooring lines. Our findings demonstrate that the ALK-EFDA method efficiently and accurately estimates fatigue damage in wind turbine structures. Compared to simulation methods, the proposed ALK-EFDA approach significantly reduces computational expenses by over 30 times. Furthermore, the absolute error, when compared to simulated results, remains at approximately 1%. This method will be a useful tool for offshore wind turbine designers.

Application of an active learning method for cumulative fatigue damage assessment of floating wind turbine mooring lines

Long-term cumulative fatigue damage of mooring lines is crucial for the design of floating wind turbine structures (FWTs). Although many efforts are carried out for the offshore floating platforms, there still needs to be an efficient approach for assessing the long-term fatigue damage of the floating wind turbine mooring lines due to the complex loading in FWTs. An active learning approach named AK-DA (Adaptive Kriging Damage Assessment) was recently proposed for the cumulative fatigue damage assessment of wind turbine structures. However, in the original work, the AK-DA approach was only tested on fatigue damage assessment of a 5MW wind turbine tower with monopile support structures. It is unclear whether it is applicable to other parts of the wind turbine system, especially considering the complex loading of FWTs. Therefore, in this work, the AK-DA approach is used to assess the cumulative fatigue damage of mooring lines. The Gaussian process regression (Kriging) model is used to predict the fatigue damage of the mooring line under different wind-wave cases. The cumulative fatigue damage of the mooring lines in the IEA 15MW semi-submersible wind turbines is assessed with the AK-DA approach. The numerical simulation results show that the AK-DA approach can efficiently and accurately estimate the cumulative fatigue damage of the mooring lines. Compared to the traditional simulation approach, the AK-DA approach can increase efficiency by more than 45 times, and the absolute error is less than 1%. This active learning approach could serve as a helpful tool for offshore mooring system designers, facilitating the cumulative fatigue damage assessment during the design process.

Time-domain fatigue damage assessment for wind turbine tower bolts under yaw optimization control at offshore wind farm

Yaw optimization control is recognized as the most effective active wake control strategy for enhancing the overall power generation of wind farms. However, the potential adverse effects of yaw optimization control on the fatigue life of wind turbines remain unclear. This study examined the effect of yaw optimization control on the fatigue life of offshore wind turbines using tower bolts. Initially, the yaw misalignment of the wind turbines was optimized using the open-source FLORIS package to maximize wind farm power generation. Subsequently, the time-varying load of the wind turbines was obtained through the OpenFAST software, using the optimal yaw misalignment, wind speed, and turbulence intensity at the hub height as inputs. The fatigue life of the wind turbines was then calculated by integrating the Schmidt–Neuper engineering stress algorithm, rain flow counting method, and Miner-Palmgren fatigue damage accumulation theory. Finally, a case study of the Horns Rev I large-scale offshore wind farm, comprising 80 wind turbines, revealed that yaw optimization control could significantly enhance the annual power generation of the wind farm by approximately 1.818%. However, optimization comes at the cost of reducing the fatigue life of wind turbine tower bolts by approximately 3–9 years.

A critical review of wheel/rail high frequency vibration-induced vibration fatigue of railway bogie in China

PurposeThis review aims to give a critical view of the wheel/rail high frequency vibration-induced vibration fatigue in railway bogie.Design/methodology/approachVibration fatigue of railway bogie arising from the wheel/rail high frequency vibration has become the main concern of railway operators. Previous reviews usually focused on the formation mechanism of wheel/rail high frequency vibration. This paper thus gives a critical review of the vibration fatigue of railway bogie owing to the short-pitch irregularities-induced high frequency vibration, including a brief introduction of short-pitch irregularities, associated high frequency vibration in railway bogie, typical vibration fatigue failure cases of railway bogie and methodologies used for the assessment of vibration fatigue and research gaps.FindingsThe results showed that the resulting excitation frequencies of short-pitch irregularity vary substantially due to different track types and formation mechanisms. The axle box-mounted components are much more vulnerable to vibration fatigue compared with other components. The wheel polygonal wear and rail corrugation-induced high frequency vibration is the main driving force of fatigue failure, and the fatigue crack usually initiates from the defect of the weld seam. Vibration spectrum for attachments of railway bogie defined in the standard underestimates the vibration level arising from the short-pitch irregularities. The current investigations on vibration fatigue mainly focus on the methods to improve the accuracy of fatigue damage assessment, and a systematical design method for vibration fatigue remains a huge gap to improve the survival probability when the rail vehicle is subjected to vibration fatigue.Originality/valueThe research can facilitate the development of a new methodology to improve the fatigue life of railway vehicles when subjected to wheel/rail high frequency vibration.

Fatigue assessment of historic retrofitted through-truss riveted railway bridge

Fatigue damage has been the most common reason for failure in riveted bridges, with the stringer-to-floor-beams connections being identified as the most prone-fatigue locations by several studies. When assessing fatigue damage of historic riveted railway bridges, the analysis usually considers the structure in its current configuration, disregarding any retrofitting the bridge has experienced during its lifetime. This paper presents a fatigue analysis of a one-century-old riveted through-truss railway bridge, part of the Chilean North-South railway line, considering all interventions made to the superstructure since its construction. To perform the analysis, a detailed train loading spectrum is defined considering historical and current data of freight trains and traffic to generate a realistic loading model for the bridge. FE models are generated for the bridge in all configurations (initial and after each retrofitting), and the fatigue damage is evaluated through S-N curves from the Eurocode. The accumulated fatigue damage obtained by this sequence is then compared with a fatigue analysis of the structure in its current configuration. The comparison shows that the fatigue damage is significantly underestimated when assessing the bridge considering only its current configuration and that the retrofitting can substantially change the structural response at the stringer-to-floor beam connections.

Extreme load extrapolation and long-term fatigue assessment of offshore wind turbine tower based on monitoring data

Extreme load and fatigue damage are important parameters in the structural design of offshore wind turbines (OWTs). The purpose of this study is to obtain extreme loads and long-term fatigue damage assessment of OWT structures based on measured data. In the present study, a utility-scale OWT was monitored with a dynamic response monitoring system and long-term strains of the OWT tower were collected. Based on the monitoring strain and the operational conditions of the OWT, the load and fatigue characteristics of the OWT tower were discussed. Furthermore, statistical extrapolation of the extreme load of the OWT tower was performed and the applicability of different statistical extrapolation methods was studied. The results indicate that the same probability distribution model does not apply to all wind speeds. The maximum extreme load is extrapolated in the vicinity of the rated wind speed. Finally, the relationship between short-term fatigue damage and long-term fatigue damage of the OWT structure was discussed. Superimposing fatigue from a short calculation period underestimates the long-term fatigue of OWT structures due to significant calculation period impact. Therefore, an evaluation method for OWT structures' long-term fatigue was established to improve the accuracy of long-term fatigue calculation by superimposing short calculation periods.

Weld Fatigue Damage Assessment of Rail Track Maintenance Equipment: Regulatory Compliance and Practical Insights

<div>The use of appropriate loads and regulations is of great importance in weld fatigue assessment of rail on-track maintenance equipment and similar vehicles for optimized design. The regulations and available loads, however, are often generalized for several categories, which proves to be overly conservative for some specific categories of machines. EN (European Norm) and AAR (Association of American Railroads) regulations play a pivotal role in determining the applicable loads and acceptance criteria within this study. The availability of track-induced fatigue load data for the cumulative damage approach in track maintenance machines is often limited. Consequently, the FEA-based validation of rail track maintenance equipment often resorts to the infinite life approach rather than cumulative damage approach for track-induced travel loads, resulting in overly conservative designs. The work presented in this article evaluates and compares the weld fatigue damage of track maintenance equipment for EN loads using infinite life approach and AAR loads using cumulative damage approach and highlights the need of having distinct category for track maintenance machines in regulations based on its usage and application to have close representative loads for the endurance limit approach or suitable loads for the cumulative damage approach. Additionally, the study utilizes the BS7608 regulation to determine weld class and predict weld fatigue damage. Both nominal and hot-spot stress approaches are employed to thoroughly investigate and calculate fatigue damage, providing a comprehensive analysis of weld fatigue in rail maintenance equipment.</div>