Fatigue Damage In Structures Research Articles

Assessing the fatigue damage of concrete structures using automatically classified crack severity level information

The aim of this paper is to assess the fatigue damage of concrete structures using automatically classified crack severity level information. To solve the problem that the label data used for the automatic classification of regional complex crack severity levels can only be labeled by intuition, this paper proposes a quantitative index of regional complex crack severity levels that can consider the regional crack width, height, and density information. The testing set F1 score of the Swin Transformer classification model trained by the label data reaches 0.9903. To investigate the feasibility of assessing the concrete structure fatigue damage based on the crack change information, the paper adopted the scanning shooting method to acquire the concrete beam panoramas at different cyclic loading times in the fatigue test, and automatically classified the crack severity levels in different regions of the panoramas using the Swin transformer. The test results show that the information on the change in the number of regions with the same crack severity level on the concrete structure surface can be used to estimate approximately the fatigue life percentage interval that the concrete structure is currently in, which provides a reference for the development of maintenance measures and safety warnings.

A dislocation density-based crystal plasticity damage model for rolling contact fatigue of gradient grained structures

A dislocation density-based crystal plasticity damage model is presented for a numerical study on the spalling behavior of gradient grained structures under rolling contact fatigue loading. The topology of the gradient grained structure is constructed using Voronoi tessellations. The fatigue damage is coupled into a dislocation density-based crystal plasticity model where the evolutions of the dislocation density and fatigue damage are considered. The process of spalling is characterized by the evolution of fatigue damage in the polycrystalline structures. The evolutions of contact pressure, stresses, dislocation density, plastic strain, and fatigue damage of gradient grained structures with regard to rolling cycles are investigated. Moreover, the effect of the gradient form and residual stress on the rolling contact fatigue behavior is studied. The simulation results reveal that the gradient grained structures and the residual stress influence the rolling contact fatigue resistance.

Improvement of Fatigue Crack Propagation Property in Low Carbon Steel by Microstructural Control and an Investigation of its Practical Benefit

The fatigue crack propagation properties of newly-developed SM490 grade steels were investigated in comparison with a conventional steel of the same grade. The fatigue crack propagation rate of the developed steel in Region II of the da/dN-ΔK relationship was suppressed to about 1/2 that of the conventional steel, and its ΔKth value was more than twice as large as in the conventional steel. However, fatigue crack resistance for long crack propagation does not necessarily improve the fatigue life in a condition of increasing ΔK from a small defect, which is usually detected in practical fatigue damage in actual structures in service. The developed steels were subjected to surface crack propagation tests using specimens with artificial small defects to examine their potential under more practical conditions. The fatigue life of the developed steel was about three times longer than that of the conventional steel. A detailed analysis of the surface crack propagation revealed crack propagation below ΔKth only in the developed steels, which suggested the so-called "short crack regime" in a fatigue crack. The crack propagation from a surface defect that deviated from long crack behavior was convincingly explained by the corrected threshold using the R-curve model of a short crack proposed in the previous literature. Based on the experimental fatigue life improvement and its analytical estimation of the propagation resistance in the short crack regime, the effect of the ΔKth value for a long crack in the initial propagation stage just after fatigue crack initiation was discussed.

Research on the Modulus Decay Model under a Three-Dimensional Stress State of Asphalt Mixture during Fatigue Damage

Fatigue damage can develop within asphalt pavement due to the continuous impact of driving loads and natural elements. Understanding the process of asphalt mixtures’ fatigue damage is crucial for guiding the design, maintenance, and repair of asphalt pavement. This research aims to establish a model that characterizes the mixtures’ modulus decay under a three-dimensional (3-D) stress state. Firstly, asphalt mixes were subjected to direct tensile (DT), indirect tensile (IDT), unconfined compressive (UC) strength and fatigue tests, and the resulting data were analyzed. Then, modulus decay models under DT, IDT, and UC conditions were established, and the modulus decay patterns under the three loading modes were compared and analyzed. Finally, using the fatigue stress strength ratio Δ (a fatigue resistance index for asphalt mixtures that takes into account the impacts of stress state and loading rate), a unified characterization model for asphalt mixes’ modulus decay under a 3-D stress state was created. According to the study’s findings, asphalt mixes’ modulus decay during fatigue damage exhibits obvious nonlinear characteristics. While the asphalt mixes’ modulus decay law with various loading modalities is similar under the same conditions, the decay rate may differ. Essentially, the speed of the modulus decay of a certain asphalt mixture primarily depends on the value of Δ during service. A larger Δ indicates a faster modulus decay. This study offers a theoretical foundation for the conversion from material fatigue damage to structural fatigue damage, which is vital for enhancing the asphalt pavements’ construction quality and longevity.

Floating wind turbines structural details fatigue life assessment

Fatigue damage prediction is essential for safety of contemporary offshore energy industrial projects, like offshore wind turbines, that are to be designed for sufficiently long operational period of time, with minimal operational disruptions. Offshore structures being designed to withstand environmental loadings due to winds and waves. Due to accumulated fatigue damage, offshore wind floating turbines may develop material cracks in their critical locations sooner than expected. Dataset needed for an accurate assessment of fatigue damage may be produced by either extensive numerical modeling, or direct measurements. However, in reality, temporal length of the underlying dataset being typically too short to provide an accurate calculation of direct fatigue damage and fatigue life. Hence, the objective of this work is to contribute to the development of novel fatigue assessment methods, making better use of limited underlying dataset. In this study, in-situ environmental conditions were incorporated to assess offshore FWT tower base stresses; then structural cumulative fatigue damage has been assessed. Novel deconvolution extrapolation method has been introduced in this study, and it was shown to be able to accurately predict long-term fatigue damage. The latter technique was validated, using artificially reduced dataset, and resulted in fatigue damage that was shown to be close to the damage, calculated from the full original underlying dataset. Recommended method has been shown to utilize available dataset much more efficiently, compared to direct fatigue estimation. Accurate fatigue assessment of offshore wind turbine structural characteristics is essential for structural reliability, design, and operational safety.

Investigating the Ice-Induced Fatigue Damage of Offshore Structures by Field Observations

The oil and natural gas resources of the Bohai Sea are mainly marginal oil fields, and there are currently a large number of structures that are approaching or have reached the end of their service life called aging structures. The interactions between ice and offshore structures could lead to significant ice-induced vibration. Ice-induced vibrations may evoke fatigue damage in tubular joints, which results in severe dangers for offshore platforms in the Bohai Sea. Dynamic ice force models and sea ice fatigue environmental parameters have not been well developed in the current design codes. It is not accurate to evaluate the fatigue damage of structures only with numerical simulation. In this paper, a faster method for evaluating fatigue damage on aging structures is proposed. Firstly, the approximate linear relationship between the fatigue hot spot stress and the vibration response of the deck structure has been discovered using dynamic analysis for jacket platform of Bohai Sea. Then, the procedure of the fatigue damage evaluation of the aging structures in the Bohai Sea is established. Finally, the numerical simulation of the structure is carried out considering ice thickness, ice velocity, ice direction, and action height of sea ice. Fatigue damage is calculated by the fatigue hot spot stress and the Palmgren–Miner rule. The measured data on the platform in the Bohai Sea are selected to obtain the fatigue hot spot stress using a mathematical model. The fatigue damage results considering the actual ice conditions of a jacket structure in the Bohai Sea are compared using the proposed method and finite element analysis. The comparison of the results verifies the rationality of the method proposed in this work.

Flow-induced vibration fatigue damage of two unequal-diameter flexible cylinders in side-by-side and tandem arrangements

Flow-induced vibrations (FIVs) are the indispensable factor causing the fatigue damage and failure for multi-cylindrical structures in offshore engineering. Mutual interferences between unequal-diameter cylinders complicate the fatigue behaviors. In this paper, an experiment was conducted on two flexible cylinders with a diameter ratio d/D of 0.5 (d and D denote the diameter of small and large cylinders) in uniform flow to investigate their fatigue damage characteristics. Two typical arrangements of side-by-side arrangement and tandem arrangement with a center-to-center spacing ratio P/d = 6.0 (P refers to the center-to-center distance between two cylinders) were examined. The results indicate that the fatigue damage is considerably affected by the arrangement and the diameter ratio. For the side-by-side arrangement, the small cylinder suffers from more serious fatigue damage in the CF direction due to the continuous impingement of the stable biased gap flow. However, the fatigue of the large cylinder is insensitive to the presence of the small cylinder. In a tandem arrangement, the wake shielding effect of the large cylinder located upstream is pronounced, resulting in a significant alleviation in the fatigue damage of the small cylinder. The wake inhibitory effect of the large cylinder is more prominent compared with that of two identical cylinders. The upstream large cylinder behaves analogously to the isolated cylinder. However, its CF fatigue damage is restrained in a few cases of 16.28 ≤ Vr ≤ 18.79 because the vortex shedding frequency is suppressed by the downstream small cylinder. On the other hand, when the small cylinder is located upstream, the wake shielding effect somewhat reduces the IL vibration of the large cylinder. The upstream small cylinder in this unequal-diameter experiment undergoes similar fatigue damage to the cylinder in the equal-diameter experiment.

A probabilistic framework for fatigue damage of lift based wave energy converters

Wave cycloidal rotors are lift based wave energy devices that have shown great potential to harness the energy of the waves through the use of submerged hydrofoils. Although the lift force of the foils can be controlled passively or actively to maximise power extraction, the foils of the rotor are subject to variable loading which can expose these components to premature mechanical failure. Therefore, it is important to develop novel fatigue analysis tools that help predicting the lifetime of this type of lift based devices. In this paper, we test the hypothesis that when cyclorotor operates at constant rotational velocity in irregular waves, the fatigue damage of the hydrofoil stress hot spot can be computed through a probabilistic approach. We compare our results to the fatigue damage computed with well established deterministic methods. We find that for both narrow and broad band stress energy spectra, the probabilistic method works well at high probability sea states, when the range of stresses does not exceed the inflection point of a double slope SN curve. This is a promising outlook since it confirms that the fatigue damage of these versatile lift based wave devices can be treated in a similar fashion to the fatigue damage of conventional offshore structures.

Nonlinear FE analysis of RC slabs strengthened with prestressed EB CFRP strips under high-cyclic fatigue loading

A significant issue in structural health monitoring is identifying fatigue damage in concrete structures that have been retrofitted with externally bonded Carbon Fiber Reinforced Polymer (EB-CFRP). Although the finite element method has significantly contributed to modeling the damage mechanisms of concrete, reinforcement, and CFRP, further research is still needed in this area. For instance, RC slabs reinforced with EB-CFRP technology must be evaluated and predicted for high-cyclic fatigue and progressive damage. Therefore, this research aimed to develop intricate numerical models that could be utilized to analyze the dynamics of fatigued RC slabs and find damage in slabs that have prestressed EB-CFRP reinforcement. It was discovered that prestressed EB-CFRP-reinforced RC slabs can significantly affect the vibration response of specimens. When the prestressing and fatigue loads were high, the prestressing altered the damage distribution at the CFRP-concrete interface, leading to debonding of the CFRP near the ends of the RC slabs. Additionally, for high-cyclic fatigue progressive damage, the mixed damage mode—steel yielding and CFRP debonding—was the primary failure mechanism of RC slabs reinforced with prestressed EB-CFRP.

Deep gated recurrent unit networks for time-domain long-term fatigue analysis of mooring lines considering wave directionality

Mooring lines are a crucial component of offshore mooring systems, and long-term fatigue damage assessment is a challenging task in mooring line design and structural health monitoring. Traditional methods require a large number of structural time-domain simulations. Because the sea state varies over time, the variations in wave parameters (e.g., wave heights, periods, and directions) must be considered in long-term fatigue damage assessment. Wave directions have usually been ignored in previous studies, while the wave direction sensitive analysis conducted in this study showed that the wave directions could not be neglected in the long-term fatigue damage assessment of mooring lines. Recent deep neural network (DNN) methods have shown great potential in mooring line/riser response prediction for offshore structures. However, the utilization of float responses as input data in these DNNs restricts their applicability during the structure design phase. To address this issue, a gated recurrent unit (GRU) network is proposed for mooring line tension modeling. The proposed GRU network surrogate models are capable of accurately predicting the mooring line tension using wave elevation components or float motion responses. The rain-flow counting algorithm, T-N approach, and Miner's rule were employed to estimate the structural fatigue damage. The results showed that the proposed method could replace the heavy cost numerical computation, assess the long-term fatigue damage with high accuracy and alleviate the data dependency of DNN methods.

A spectral method for accurate evaluation of fatigue damage induced by wide-band non-Gaussian random processes

Evaluating the fatigue damage of marine structures subjected to random environmental loadings is of great practical significance at the design stage. In many situations, the structural responses of marine structures exhibit wide-band non-Gaussian properties. This study presents the fatigue damage assessment of wide-band softening non-Gaussian random processes by a spectral method proposed by Benasciutti and Tovo (2005b). Following this spectral method, the rainflow fatigue damage is approximated by a linear combination of its upper and lower bounds. A refined formulation of the weighting factor is proposed, which depends on the bandwidth parameters, slope parameter of the S‒N curve, and skewness and kurtosis of non-Gaussian processes. By introducing a suitable transformation function, the simulated non-Gaussian process is generated from its underlying Gaussian process. Through case studies, the effectiveness and accuracy of the present method for wide-band non-Gaussian processes are verified by comparisons with the results from the time-domain rainflow counting method and the other existing spectral methods.

Development and Validation of a Low-Cost Device for Real-Time Detection of Fatigue Damage of Structures Subjected to Vibrations.

This paper presents the development and validation of a low-cost device for real-time detection of fatigue damage of structures subjected to vibrations. The device consists of an hardware and signal processing algorithm to detect and monitor variations in the structural response due to damage accumulation. The effectiveness of the device is demonstrated through experimental validation on a simple Y-shaped specimen subjected to fatigue loading. The results show that the device can accurately detect structural damage and provide real-time feedback on the health status of the structure. The low-cost and easy-to-implement nature of the device makes it promising for use in structural health monitoring applications in various industrial sectors.

A new frequency-domain method for fatigue prediction of offshore structures under wideband random loadings

The frequency-domain methods used to predict fatigue damage in offshore structure are widely employed in practice due to their simple algorithms and fast computation speed. While reliable accuracy can be achieved with current prediction methods for narrowband stress processes, actual offshore fields often exhibit wideband stress responses, resulting in more complex relations between the rainflow stress distribution, power spectral density, and fatigue damage. This study proposes a novel fatigue prediction method for wideband stress processes that utilizes Monte Carlo simulation for designed standard spectra. An empirical formula is derived to calculate the expected damage rate, considering material properties, spectral moments, and rainflow range distribution moments. To verify the accuracy of the model, 3-month onsite measured stress data from a semi-submersible platform are used, and the proposed method is compared with several typical prediction methods with explicit expressions. The results indicate that the expected damage rate is determined by the spectral moments of power spectral density, assuming fixed material properties. The proposed method shows good prediction accuracy for the field data and has a significant improvement of fatigue damage prediction for various bandwidth processes.

Influence of Fatigue Damage on Criticality Cell Ultimate Load Capacity of Steel–Concrete Composite Section

In order to investigate the impact of fatigue damage on the ultimate load capacity of criticality cells in steel–concrete composite segments and to address the complex design challenges associated with bridge steel–concrete composite segments in practical engineering, this study designs two scaled criticality cell specimens with a scale ratio of 1:2 and performs ultimate load capacity tests after fatigue cyclic loading. By analyzing the stress distribution of each component and the force transmission ratio and combining the results from finite element model calculations, this study introduces the degree of structural fatigue damage and proposes a predictive model for the ultimate load capacity of steel–concrete composite segment criticality cells that is easy to apply. This model is compared with the finite element calculation results and experimental values, and the results are found to be in good agreement. Additionally, the number of shear connection members in the model is optimized based on the calculation results. The research findings indicate that the main failure mode of criticality cells is inclined compression failure. The strength of each part decreases in the following order: steel–concrete composite segment, steel structure segment, and concrete segment. Furthermore, fatigue damage has a significant impact on criticality cells. The optimized model exhibits similar stress performance and force transmission ratio to the original model and provides a reference for the design of practical engineering.

Flow-induced vibration modeling of bluff bodies with data assimilation

Vortex-induced vibration (VIV) and galloping are two typical flow-induced vibration (FIV) problems of bluff bodies, which often cause fatigue damage or destruction of structures. Therefore, the accurate and effective FIV prediction has become a requirement of the industry in order to prevent structural damage and guide design. Although the semi-empirical model (such as the wake oscillator model) is an efficient FIV prediction tool, the precision ability of existing models is constrained due to empirical parameters and unideal mathematical equations. Generally, the numerical simulation and wind tunnel experiments are relatively accurate methods, but for complex fluid–structure interaction problems, their cost is too high. As a result, a data-driven FIV prediction model is proposed to accomplish effective and high-precision prediction in this study. The Ensemble Kalman filter (ENKF) data assimilation (DA) technique is used to combine the experimental data with a semi-empirical model. First, the sensitivity of empirical parameters is analyzed, and the most sensitive ones are selected as the target parameters for data assimilation. The mean deviation of ensemble (MDE) is proposed to represent the sensitivity of parameters. Then DA-based model is used to predict the galloping and VIV of a rectangular cylinder. The results indicate that the accuracy of the DA-based model is up to 10 times greater than that of the initial semi-empirical model. With the data-driven technology, the typical ‘quasi-steady’ theory of galloping has been improved for low Scruton number values. For the wake oscillator model, assimilating the parameters of the acceleration and velocity coupled terms can improve the prediction accuracy of VIV. Also, this modeling procedure can be regarded as a new parameter identification method from forced and free vibration.

Fatigue strengthening of damaged steel members using wire arc additive manufacturing

In this study, a directed energy deposition (DED) process called wire arc additive manufacturing (WAAM) is employed for the fatigue strengthening of damaged steel members. Three steel specimens with central cracks were tested under a high-cycle fatigue loading (HCF) regime: (1) the reference specimen; (2) the WAAM-repaired specimen with an as-deposited profile, and (3) the WAAM-repaired specimen machined to reduce stress concentration factors (SCF). The corresponding finite element (FE) simulation of the WAAM process was calibrated using static experimental results, which revealed the main mechanism. The process was found to introduce compressive residual stresses at the crack tip owing to the thermal contraction of the repair. The FE results also revealed that stress concentration exists at the root of the as-deposited WAAM; this stress concentration can be mitigated by machining the WAAM to a pyramid-like shape. The fractography analysis indicated that the cracks were initiated at the WAAM-steel interface, and microscopic observations revealed that the microcracks were arrested by the porosities in the melted interface. The results of this pioneering study suggest that WAAM repair is a promising technique for combating fatigue damage in steel structures.

Extreme structural response prediction and fatigue damage evaluation for large-scale monopile offshore wind turbines subject to typhoon conditions

Offshore wind is becoming the way forward for green energy harnessing worldwide. However, frequent typhoons are a major constraint for the development of offshore wind power for some regions in Asia and North America. Typhoons may pose a huge challenge to offshore wind farm development in southern China. In this paper, a fully-coupled analysis was carried out for a 10 MW large-scale monopile offshore wind turbine (OWT) using SIMO-Riflex-Aerodyn (SRA) code. The response characteristics of the OWTs in different typhoon regions are investigated based on the measured typhoon conditions in China. The effect of aerodynamic damping on the response and the load effect is analyzed in detail. Two different distribution methods are used to statistically extrapolate the response value and get the short-term extreme response. Cumulative linear fatigue damage is evaluated by the rain-flow counting method to explore the possible failure modes of large wind turbines during typhoons. The results show that aerodynamic loads play an important role in large monopile OWTs during high wind speeds in parked conditions. The extreme response and fatigue analyses from this study indicate that fatigue is a dominant failure mode for the large OWT tower during typhoons, while buckling is unlikely.

Self-powered vibration sensor based on the coupling of dual-mode triboelectric nanogenerator and non-contact electromagnetic generator

Random vibration of mechanical equipment will lead to structural fatigue damage, while strong and sustained vibration will lead to the overall performance decline of the equipment. Vibration sensors can be used to monitor the stability of mechanical operation. However, in some complex unattended environments, it is still a significant challenge to realize real-time equipment monitoring and early warning. Therefore, we propose a self-powered multifunctional vibration sensor based on coupling a dual-mode triboelectric nanogenerator and a non-contact electromagnetic generator (M-HNG) for automatic condition monitoring. The dual-mode triboelectric nanogenerator and non-contact electromagnetic generator can work together to realize real-time self-powered vibration monitoring. We established the prototype model of the vibration sensor, simulated the working principle of each part of the sensor, and fitted the functional relationship between the vibration amplitude and speed of the sensor and the output electrical signal. The results show that the short-circuit current of the sensor is very sensitive to the change in external vibration speed and has good stability in its detection range. Using a non-contact electromagnetic generator can effectively improve the service life of the vibration sensor. The system can continuously monitor the vibration signals generated by machinery during operation and provide an effective way for structural health monitoring, especially in extreme environments or unattended conditions.

A review on fatigue monitoring of structures

PurposeThe purpose of this study is to review the existing fatigue and vibration-based structural health monitoring techniques and highlight the advantages of combining both approaches.Design/methodology/approachFatigue monitoring requires a fatigue model of the material, the stresses at specific points of the structure, a cycle counting technique and a fatigue damage criterion. Firstly, this paper reviews existing structural health monitoring (SHM) techniques, addresses their principal classifications and presents the main characteristics of each technique, with a particular emphasis on modal-based methodologies. Automated modal analysis, damage detection and localisation techniques are also reviewed. Fatigue monitoring is an SHM technique which evaluate the structural fatigue damage in real time. Stress estimation techniques and damage accumulation models based on the S-N field and the Miner rule are also reviewed in this paper.FindingsA vast amount of research has been carried out in the field of SHM. The literature about fatigue calculation, fatigue testing, fatigue modelling and remaining fatigue life is also extensive. However, the number of publications related to monitor the fatigue process is scarce. A methodology to perform real-time structural fatigue monitoring, in both time and frequency domains, is presented.Originality/valueFatigue monitoring can be combined (applied simultaneously) with other vibration-based SHM techniques, which might significantly increase the reliability of the monitoring techniques.

New indicator for damage localization in a thick adhesive joint of a composite material used in a wind turbine blade

In this paper, a new indicator to localize fatigue damage in a fibre glass composite structure, i.e. spar cap to shear web thick adhesive joint of a wind turbine blade, is presented. This indicator is based on the effect of damping on the phase of the mode shapes of the structure. When fatigue damage occurs, damping increases in the defective area and this leads to an increase in the local energy dissipation. This non-uniformity in the energy dissipation throughout the structure causes the structure to vibrate with mode shapes whose structural elements no longer have the same phase creating complex mode shapes. A visco-elastic finite element (FE) vibration model is developed for a thick adhesive joint of a wind turbine blade. The mass, stiffness, and damping matrix extracted from the FE model are used to determine the complex mode shapes. The results show that the damaged area is located where the spatial derivative of the phase of the components of the mode shapes is minimum. Changes in the phase of mode shapes of the structural elements are strongly dependent on the location of damage. In the locations where the strain modal energy is greater, the change in the phase is also higher.