Fatigue Life Of Structures Research Articles

Numerical Appraisal of Reinforced Concrete Dapped-End Girder Under High-Fatigue Fixed Pulsating and Moving Loads

This paper presents the numerical evaluation of structural response and fatigue life of a Reinforced Concrete Dapped-End Girder (RCDEB) and associated fatigue life under fixed pulsating and moving loads. For that, a finite element (FE) model of RCDEB is developed using a three-dimensional FE analysis code, Concrete Model of 3-Dimensions (COM3D), and analyzes the FE model under high-fatigue loads by adopting a certain percentage of verified maximum static capacity of the girder. The COM3D system is activated with a multidirectional active crack approach which considers the space averaging of stress–strain in an element. The experimental validation of the numerical analysis is also performed in the laboratory using a small-scale model of the RCDEB under the fixed pulsating load. The experimental validation demonstrates good agreement with the FE analysis. However, the moving load is not considered in the experimental scheme because of the limitation in the testing facility. Finally, it is found from the FE analysis that the moving load, as compared with the fixed pulsating load, has the greatest effect on fatigue performance of the girder, causing about a three-order reduction in fatigue life at the same percentage static capacity of the girder. An increase in the fatigue life of approximately one order is also recorded in the analysis under the static midpoint load of 350 kN as compared with the moving load. Moreover, it is also observed that the reentrant corner of the RCDEB is more vulnerable to fatigue, implying that the hanger bars close to this corner resisted the stresses after the concrete cracked. As a result, strengthening the reentrant zone is recommended.

A Review on Fatigue Performance of Concrete Structures Part I: Loading Parameters, Current Prediction Models and Design Approaches

Abstract This review paper highlights the most fundamental state of knowledge regarding the fatigue of concrete that is available through the literature over the last decades and reveals the areas that are needed for further investigation. The loading factors influencing the fatigue performance and the fatigue life estimation of concrete structures are taken into consideration. This review explores the impact of eight loading parameters on the fatigue life of concrete structures, and we aimed to be succinct in our investigation. Besides, we present a review on the deterministic and probabilistic approaches for fatigue life prediction. For example, in more recent studies, the utilization of machine learning techniques has been shown to outperform the traditional methods. The review gives adequate insight into the approach of some of the main current design codes for fatigue life prediction of concrete.

Dynamic resilient modulus of heavy-haul subgrade silt subjected to freeze-thaw cycles: Experimental investigation and evolution analysis

To investigate dynamic resilient modulus (MR) of heavy-haul subgrade silt, especially in seasonal frozen regions, a series of dynamic triaxial tests were performed after various freeze-thaw (FT) cycles. The specifically designed loading sequence was proposed for determining MR, which reflected the stress characteristics of subgrade induced by heavy-haul traffic load. Furthermore, the effects of numbers of FT cycles, initial moisture content, freezing temperature, deviator stress and confining stress were comprehensively considered as state variables. The results revealed that MR showed a decreasing trend with increase of numbers of FT cycles, where the attenuation stages for dynamic resilient modulus were divided into three stages, namely, rapid attenuation, slow attenuation and gradual cessation of attenuation. Then, the increase of initial moisture content and decrease of freezing temperature led to a decrease in MR, where the higher initial moisture content was, the more obvious deterioration effect was. Meanwhile, when the freezing temperature decreased to −15 °C, the appearance of the freeze shrinkage effect inhibited the damage to the soil skeleton, and the attenuation trend of MR was alleviated. The ensuing discoveries were that confining stress and deviator stress had hardening and softening effects on the thawed silt, respectively, leading to the increase and decrease in MR. In particular, when the initial water content was higher, the softening effect caused by deviator stress was more significant. To enhance the practicability, the predicted model for determining MR was proposed that included the coupled effects of the above variables. Furthermore, the fatigue life of typical asphalt pavement structures was calculated considering the damaged dynamic resilient modulus of silt subgrade duo to the freeze-thaw cycles. The outcomes illustrated that fatigue life of pavement structures with semi-rigid and flexible base reduced by 17.5% and 22.5%, respectively, via adopting the dynamic resilient modulus values under maximum attenuation state. This study could supply meaningful reference for safe and sustainable design of heavy-haul subgrade and asphalt pavement in seasonal frozen regions.

Combined loading effect on high cycle fatigue fracture behaviors of a stainless steel welded structure of elbow and socket

In welded structures with complicated geometries and combined loading state, it is crucial to establish the criteria for fatigue failure. High cycle fatigue tests under combined loading states were performed using stainless steel sheets and welded specimens of elbow pipe and socket in this work. The cyclic stress–strain curve of the parent sheet were applied to the characteristics analysis of the welded specimens. Mode I or Mode I + III fatigue fracture occurred at the stress concentration part of the weld, and the crack starting point was different depending on the loading mode. The applied load was divided into bending and torsion for analysis, and the crack initiation was found on the side with the higher equivalent stress converted according to the Gough-Pollard failure criterion. The crack grew almost perpendicularly to the surface of the elbow pipe, and exhibited the appearance of a transgranular fracture. The fatigue limit based on the stress intensity factor (SIF) amplitude calculated by the proposed method using the strain energy release rate remained nearly constant even though the measured surface strain differed greatly. It is possible to predict the fatigue limit and life of similar structures by simplified models.

Load response and fatigue life of cement-stabilized macadam base structure considering dynamic and static load differences and tension-compression modulus differences

The conventional semi-rigid base asphalt pavement (SRBAP) construction is designed with the classical theory of linear elastic mechanics. There is a significant discrepancy between the calculation results of the pavement structure load response and the measured results, which leads to inaccurate structural resistance and load response calculations. For this reason, this work depended on the actual structure of the SRBAP, took the linear elasticity theory as a contrast, and considered the difference between dynamic and static loads or the difference between the compressive and tensile modulus of pavement materials. Thus, the pavement structure response to load under three conditions is calculated, and five mechanical indexes are selected for comparative analysis. Furthermore, based on the calculated mechanical response, the structural fatigue life of the cement-stabilized macadam (CSMB) was then calculated, replacing the design index in the fatigue cracking model with the underside tensile stress or equivalent stress. The results demonstrated 20–30% variations between the calculated mechanical responses to dynamic and static stresses. Additionally, there is a substantial discrepancy between the strain computed using the bimodulus theory and the traditional linear elasticity theory, with a maximum divergence of 40%. In the meantime, the fatigue life of the CSMB produced using various design indices is noticeably different, and the fatigue life achieved using equivalent stress as the design index is significantly higher than that obtained using underside course tensile stress. Following is a relationship between the CSMB's fatigue life calculated by underside course tensile stress: viscoelastic theory (dynamic load) > bimodulus theory (tension–compression modulus difference) > classical linear elastic theory; The relationship of fatigue life represented by equivalent stress is as follows: viscoelastic theory > classical linear elastic theory > bimodulus theory.

Random vibration-based virtual fatigue test for large-scale welded structures using frequency-domain structural stress method and its application to traction transformers

PurposeThis paper aims to present an engineering computational method for fatigue life evaluation of welded structures on large-scale equipment under random vibration load.Design/methodology/approachBased on a case study of the traction transformers, virtual fatigue test (VFT) was proposed via numerical simulation approach. Static analysis was conducted to identify the risky zone and then dynamic response of the risky welds under random vibration load was calculated based on frequency-domain structural stress method (FDSSM) theory, life distribution and associated survivability at various locations of the structure were obtained. Structural modification was finally performed according to the evaluation results. Moreover, experimental test was carried out and compared with the virtual test result.FindingsBy applying the virtual test, fatigue life of the complex welded structures on large-scale equipment can be accurately and efficiently obtained considering dynamic effect under random vibration load. Meanwhile, risky welds can be directly determined and targeted modification scheme can be accordingly concluded. Validity of the VFT result was proved by comparing with the experimental test.Originality/valueThe proposed method can help obtain equivalent structural stress and fatigue life distribution of the welded structure at any position with various survivability and make quantitative evaluation on the life-extending effect of the structural modification. This method shows significant cost and efficiency advantages over experimental test during design stage of the large-scale structures in numerous manufacturing industries.

Interfacial thermal damage and fatigue between auxetic honeycomb sandwich and underneath substrate

A general model to evaluate the interfacial thermal damage and predict the fatigue life of the auxetic honeycomb-substrate structure (H-SS) is built. To improve the accuracy, all material parameters in the model are temperature-dependent. The transient temperature field and the associated thermal stresses associated with the temperature changes in the structure are determined by the finite difference method. The interfacial thermal stress intensity factor is employed to characterize the stress concentration behavior. Based on the stress field and the stress concentrations at the interface, interfacial thermal damage evolution and fatigue life prediction of the structure are made. The results show that the auxetic property can significantly enhance the fatigue life of the structure. The fatigue life will be undervalued when the effect of temperature-dependent material properties (TDMPs) is neglected. Furthermore, the influence of TDMPs on the fatigue life of the structure will increase as the absolute value of the internal cell angle increases. This paper provides a comprehensive assessment of the thermal damage and fatigue life of auxetic H-SSs and can serve as a solid theoretical foundation for future applications of related structures in extreme temperature environments.

Mechanical properties of Sn–Pb based solder joints and fatigue life prediction of PBGA package structure

Solder joints are generally the weakest part in electronic packaging structure whose fatigue life depends to a large extent on the durability of solder joints. In pursuit of a balance between environmental protection and soldering performance, commonly used Sn–Pb solder should be modified by adding other chemical elements to reduce Pb content. This work aims to investigate the performance of different solder materials and explore the impact of different electronic package structures. Firstly, tensile experiments are performed on three kinds of solders (Sn–Pb, Sn–Pb–In, Sn–Pb–Bi) to obtain their mechanical behavior, and then the constitutive laws of them are calibrated by Anand model. Additionally, finite element method (FEM) is used simulate the response of plastic ball grid array (PBGA) package structure under thermal cycles, and mechanical variables including deformation, equivalent stress, and equivalent strain are analyzed. Finally, Coffin-Manson and Engelmaier equations are adopted to predict the fatigue life of package structures and the effects of various factors such as solder materials, dimensions of components, and welding quality are further investigated. Results reveal that adding Bi into Sn–Pb solder can make the solder joints have better performance. From the perspective of optimum fatigue life, the plastic package thickness is recommended in the range of 0.8 mm–0.9 mm, the chip thickness is recommended as 0.35 mm, the substrate thickness is recommended to be less than 0.34 mm, and the ratio of stand-off height to solder ball diameter should be controlled between 0.6 and 0.7. According to the prediction, the solder ball diameter is suggested to be 0.54 mm so that fatigue life could reach 194 cycles, and the stand-off height for this package structure is suggested to be 0.36 mm so that fatigue life could reach 123 cycles.

Effect of bolt tightening torque on fatigue life of multi-bolted composite structure

Bolt tightening torque has an influence on the fatigue life of the multi-bolted joints which cannot be ignored, but there are few methods to predict the fatigue life of the multi-bolted composite structure by considering the bolt tightening torque. A fatigue life prediction method of the multi-bolted composite structure by considering the bolt tightening torque is proposed. It can take into account the various damages of bolts and laminates and accurately calculate fatigue life and damage evolution of multi-bolted composite structure. The multi-bolted composite structure being composed of T300/BMP-316 composite laminates and TC4 titanium alloy bolts is used to verify the present method. The logarithmic error between the predicted fatigue life and the experimental is 4.36%, and the failure mode is consistent with the experimental. Through the present method, the influence of the bolt tightening torque is explored, in which it is found that with the increasing of bolt tightening torque, the fatigue life increases firstly and decreases, and there is an optimal tightening torque. By observing the damage evolution diagram, it is found that when the tightening torque is below the optimal tightening torque, the damage propagation cannot be effectively restrained, which will lead to the reduction of fatigue life. On the contrary, when the tightening torque is more than the optimal tightening torque, it will cause the initial damage to the test piece, which will also lead to the reduction of fatigue life. In engineering, to choose the best tightening torque of the structure for assembly can effectively improve the fatigue life of the structure.

Fatigue life of unified riveted superstructures designed by Transmostproject with the introduction of increased axle loads

The article presents a study of the residual fatigue life of superstructures during the introduction of trains with increased axial loads on bridges with riveted superstructures, designed in the fifties of the last century. Unified metal superstructures have been in relatively heavy duty conditions for more than 60 years. During lcontinuous operation, processes occur in elements and joints that lead to the appearance and development of various damages and varying degree failures of hazard, so it is necessary to decide on the further operation of old bridge spans and their replacement. When determining the fatigue life, the linear addition hypothesis of fatigue damage accumulation was used, taking into account the increase in stresses with the introduction of increased axial loads. As a critical measure of damage, providing a given reliability, the value obtained from the calculation results of several hundred cracks in riveted superstructures of older design standards was adopted. The increase in load from the installation of a ballastless bridge floor is taken into account. To determine the residual fatigue life, fatigue data is used depending on the concentration of stresses magnitude in the attachments of the main truss elements. For a more accurate determination of the rivet joints operation stage, the author carried out a wear-out calculation through operation period. The introduction of heavier train loads will lead to an increase in the accumulation of fatigue damage in the elements. If weak rivets in attachments are found during inspection, they must be replaced with high-strength bolts to increase fatigue life. The author obtained that the residual fatigue life of the span structures designed by Transmostproekt has not yet been fully exhausted even with the introduction of heavy trains with a wagon axle load of 27–30 tons.

Physics-assisted reduced-order modeling for identifying dominant features of transonic buffet

Transonic buffet is a flow instability phenomenon that arises from the interaction between the shock wave and the separated boundary layer. This flow phenomenon is considered to be highly detrimental during flight and poses a significant risk to the structural strength and fatigue life of aircraft. Up to now, there has been a lack of an accurate, efficient, and intuitive metric to predict buffet and impose a feasible constraint on aerodynamic design. In this paper, a Physics-Assisted Variational Autoencoder is proposed to identify dominant features of transonic buffet, which combines unsupervised reduced-order modeling with additional physical information embedded via a buffet classifier. Specifically, four models with various weights adjusting the contribution of the classifier are trained so as to investigate the impact of buffet information on the latent space. Statistical results reveal that the buffet state can be determined exactly with just one latent space when a proper weight of classifier is chosen. The dominant latent space further reveals a strong relevance with the key flow features located in the boundary layers downstream of shock. Based on this identification, the displacement thickness at 80% chordwise location is proposed as a metric for buffet prediction. This metric achieves an accuracy of 98.5% in buffet state classification, which is more reliable than the existing separation metric used in design. The proposed method integrates the benefits of feature extraction, flow reconstruction, and buffet prediction into a unified framework, demonstrating its potential in low-dimensional representations of high-dimensional flow data and interpreting the “black box” neural network.

Investigation on fatigue failure of split-sleeve cold expansion holes of 7075-T651 aluminum alloy

7075-T6 is widely used in the manufacture of aircraft structural components, the majority of which are joined and assembled through hole structures. However, the geometric discontinuity near the fastener holes facilitates stress concentration and makes the joints susceptible to crack nucleation and fatigue failure. It is essential to improve the fatigue resistance of the hole structure. In this paper, the factors affecting the split-sleeve cold expansion on the fatigue behavior of fastener holes of 7075-T651 are investigated based on the compressive residual stress, microstructure, surface roughness, and fatigue fracture. Results revealed that cold expansion causes sub-grain refinement near the hole wall, which increases the surface micro-hardness and favors inhibition of crack growth. Grain refinement, plastic deformation on the surface of the holes, and residual compressive stress produced by the cold expansion process all work together to extend the fatigue life of the hole structure. The constituent particles and microstructure after expansion are important factors affecting fatigue performance, higher level of Fe content could result in the formation of a large number of iron-bearing particles leading to the acceleration of the failure of the workpiece.

Fretting Fatigue Life Prediction of Dovetail Structure Based on Plastic Effect and Sensitivity Analysis of Influencing Factors.

Micro relative sliding exists on the contact surface of the main primary equipment's surface structures, resulting in serious fretting fatigue. The plastic effect causes serious fatigue to the structure under alternating loads. Existing fatigue life prediction models fail to fully consider the shortcomings of fretting and plastic effects, which causes the prediction results to be significantly different to real-lifeworld in engineering situations. Therefore, it is urgent to establish a fretting damage fatigue life prediction model of contact structures which considers plastic effects. In this study, a plastic fretting fatigue life prediction model was established according to the standard structural contact theory. The location of dangerous points was evaluated according to a finite element simulation. The cyclic load maximum stress value was compared with the fretting fatigue test data to confirm the error value, and the error between the proposed fretting fatigue life model and the test value was within 15%. Concurrently, we combined this with mass data analysis and research, as it is known that the contact zone parameters have an impact on fretting fatigue and affect the structural lifespan. With the help of ABAQUS, the fretting numerical calculation of the dovetail tenon model was carried out to analyze the sensitive factors affecting the fretting fatigue life of the dovetail tenon structure. By keeping the fretting load unchanged, the contact area parameters such as contact surface form, contact area width and friction coefficient were changed in order to calculate the fretting stress value, σfretting and the dovetail structure was improved to extend its fretting fatigue life. Finally, it was concluded that fretting fatigue was most sensitive to the width and contact form of the contact area. In actual engineering design, multiple factors should be considered comprehensively to determine a more accurate and suitable width and form of the contact area. For the selection of friction coefficient, on the premise of saving costs and meeting the structural strength requirements, the friction coefficient should be as small as possible, and the problem can also be solved through lubrication during processing.

Fatigue life prediction of aircraft gun cabin structure under impact

The aircraft gun firing will cause serious impact on airframe structure. According to the gun firing principle, the muzzle blast wave is simulated by chemical explosion. ALE method is used to deal with the fluid-structure interaction between high-pressure flowing air and the surface of the cabin. Then the expression model of the impact load is established. The numerical calculation is completed to analyse the dynamic response of the cabin structure under the impact load. The parameters of load and cabin model are modified by using the experiment results. Comparing the calculated dynamic response with the experiment results, the error is within acceptable range. Multiaxial stress equivalence and rain-flow counting method are used to process the simulation impact response data to estimate the impact fatigue life. In conclusion, the paper provides a feasible method for analysing dynamic response and fatigue life of gun cabin structure.

Effect of curtailment scenarios on the loads and lifetime of offshore wind turbine generator support structures

Curtailment is a known phenomenon for wind turbine operators of both onshore and offshore wind turbine generators (WTG). Curtailment refers to the situation in which the power output of all WTG’s within a windfarm is forced below the expected power output at the occurring environmental conditions. A direct consequence of curtailment is the loss of power production. In the present contribution further consequences of curtailment of an offshore wind farm (OWF) are studied from the perspective of the support structure, in specific the foundation. In relation to curtailment a couple of potentially critical operational conditions impacting the fatigue consumption of the support structure can be identified. Besides the standstill during operational windspeed conditions, in specific damaging for the +7MW generation WTG’s, curtailment introduces repeated transitions between operational conditions. Since transitions between operational conditions of a WTG are known to be a cause of high fatigue loads in the structural components of the WTG, their increased occurrence due to curtailment might also have an impact on the fatigue consumption of the support structure. With the growing interest of the industry to quantify and potentially optimize the structural lifetime consumption in view of potential lifetime extension of OWF assets, any potential fatigue damaging operational condition is to be investigated. The present work focusses on the investigation of the impact these transitional load cycles may have on the structural lifetime of the WTG foundation. To assess the impact on lifetime, the assessment of the damage equivalent loads (DEL) derived from structural health monitoring (SHM) data are used as a data-driven alternative for model-based load simulations. In the present work such data-driven lifetime assessment studies the impact of curtailment regimes with different frequency of stop and start cycles on the structural lifetime. The study is performed based on 1 year of SHM data collected from two OWF’s. The assessment demonstrates that the impact of additional transitional load cycles on the structural fatigue life consumption is to be considered when defining a long-term curtailment strategy for an OWF.

From Gaussian Distribution to Weibull Distribution

The Gaussian distribution is one of the most widely used statistical distributions, but there are a lot of data that do not conform to Gaussian distribution. For example, structural fatigue life is mostly in accordance with the Weibull distribution rather than the Gaussian distribution, and the Weibull distribution is in a sense a more general full state distribution than the Gaussian distribution. However, the biggest obstacle affecting the application of the Weibull distribution is the complexity of the Weibull distribution, especially the estimation of its three parameters is relatively difficult. In order to avoid this difficulty, people used to solve this problem by taking the logarithm to make the data appear to be more consistent with the Gaussian distribution. But in fact, this approach is problematic, because from the physical point of view, the structure of the data has changed and the physical meaning has changed, so it is not appropriate to use logarithmic Gaussian distribution to fit the original data after logarithm. The author thinks that Z.T. Gao method can give the estimation of three parameters of Weibull distribution conveniently, which lays a solid mathematical foundation for Weibull distribution to directly fit the original data.

Analytical model for near-crack debonding in fiber-reinforced polymer composite-overlaid metallic plates with a central crack

Extensive research has been undertaken on the use of fiber-reinforced polymer (FRP) in the strengthening of fatigue-damaged and fatigue-prone civil engineering metallic structures. Evaluation of the static load-bearing capacity and fatigue life of the so-strengthened structures necessitates the accurate prediction of the stress intensity factor (SIF) for an FRP-overlaid crack in a metallic structure. This paper first presents a new analytical model for predicting the near-crack interfacial debonding process and its effect on the SIF of a centrally cracked metallic plate that is bonded on both sides with an FRP overlay. The stress distributions in both the overlays and the metallic plate, the interfacial shear stress distribution, the crack opening displacement profile, and the SIF can all be found without the need for any a priori assumption of the near-crack interfacial debonding process/pattern. The accuracy of the analytical model is evaluated with both finite element predictions and experimental data. The analytical model is then used to advance our understanding of the mechanisms of near-crack interfacial debonding, including both the initiation and propagation of debonding, as well as the effect of near-crack debonding on the SIF. It should be noted that while the study was conducted with explicit reference to metallic plates bonded with FRP overlays, the analytical model is applicable to combinations of other materials as long as the substrate plate material is isotropic, and both components remain linear-elastic during the loading process.

The influence of water vapor on the structural response of asphalt pavement

Abstract A series of water damage phenomena of asphalt pavement during service show that water is very important. To comprehensively analyze the influence of water vapor factors on the response of pavement structure, this article first tests the water vapor diffusion coefficient of asphalt pavement materials at different temperatures establishes the water vapor concentration field model of the pavement structure, and analyzes the actual water vapor distribution of the pavement structure; then, the relationship between viscoelastic parameters of the mixture and water vapor concentration is established. Based on this, the finite element model of the pavement structure considering the water vapor factor is established, and the influence of the water vapor factor on the pavement structure response and fatigue life is quantified. It is found that water vapor has an important influence on the mechanical response. On the hottest days in summer, the attenuation of surface modulus caused by water vapor has the greatest impact on the upper layer of the pavement structure. Under the influence of water vapor, the position just below the wheel of the upper layer at the bottom of the horizontal tension strain increases by 108.26%, and the horizontal tension strain of the other layers increases by about 5%, increasing the risk of upper layer cracking. At the same time, water vapor reduces the stress that can be borne by the surface layer, while the rest of the stress is borne by the base. Compared with the fatigue life calculation method in the specification, the actual non-uniform water vapor concentration field reduces the fatigue life of the surface layer by 12.246%. This shows that the current structural calculation does not consider the water vapor factor, which makes the pavement structure more dangerous, and the influence of the water vapor factor should be fully considered.

Parametrically upscaled crack nucleation model (PUCNM) for fatigue nucleation in titanium alloys containing micro-texture regions (MTR)

Micro-texture regions (MTRs), delineated as the clusters of grains with similar crystallographic orientations in the polycrystalline microstructure, play a significant role in fatigue crack nucleation and life of structures of Ti alloys. This paper develops a parametrically upscaled constitutive and crack nucleation modeling (PUCM/PUCNM) platform for predicting structural-scale fatigue crack nucleation in α/β Ti–6Al–4V alloys, whose polycrystalline microstructures contain MTRs. The PUCM/PUCNM platform bridges micro and macro scales through thermodynamically consistent incorporation of representative aggregated microstructural parameters (RAMPs) in macroscopic constitutive relations. A novel RAMP kMTRθc that captures both the MTR size and contrast in the overall texture is proposed to quantitatively represent the MTR intensity in the microstructure. Geometric analysis and comparison with experimental data establish the effectiveness of kMTRθc in characterizing the MTR distributions. The impact of MTR characteristics on fatigue crack nucleation is evaluated through the support vector regression (SVR)-aided Sobol analysis, based on data from crystal plasticity FE simulations of polycrystalline microstructure volumes with a grain-scale crack nucleation model. The PUCNM is uniquely suitable for the incorporation of the MTR RAMP kMTRθc in its probabilistic framework. A novel functional form is derived using the genetic programming-based symbolic regression (GPSR). The PUCM/PUCNM tool is used to simulate an engine blade under dwell loading conditions. Results exhibit the reduction of nucleation life with a higher level of MTR intensity, despite the same overall textures.

Fatigue Life Convergence of Offshore Wind Turbine Support Structure According to Wind Measurement Period

This paper investigated the fatigue life of offshore wind turbine (OWT) support structures. For this purpose, a 3 MW-capacity typical wind turbine is investigated using time-domain finite element simulations. In numerical simulations, different stochastic wind models corresponding to different accumulation periods are applied. Then, the stress-based fatigue life is estimated following the rain-flow counting algorithm and Palmgren-Miner linearly cumulative damage rule. The study also addresses the joint distribution of loads at the site of interest. Generally, the study emphasizes the significance of the long-term distribution of the applied environment loads and its influence on the fatigue life of OWT’s substructures. The results imply that the wind measurement period is directly linked to the fatigue life of offshore wind turbine support structures. Accordingly, its fatigue life is significantly reduced at the 25-year accumulative period of wind. Therefore, this study recommends that a sufficient number of accumulative periods of wind and other environmental loads should be considered appropriately.