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A finite element simulation method for fatigue damage calculation and life prediction of pavement structures under the influence of temperature and traffic distribution factors was proposed in this study. Relying on the test cold recycled asphalt pavement structure, the existing distress, pavement structure forms, field monitored temperature and strain were first introduced and analyzed. Then, in constructing the numerical model, the viscoelastic constitutive model was introduced to characterize the effect of temperature and loading conditions on the mechanical response of the hot mix asphalt (HMA) layers and the emulsified asphalt cold recycled (EACR) layer. The damage variables are defined by fatigue equations, and the damage accumulation can be determined by Miner's linear fatigue accumulation theory. To reflect the distribution of traffic volume, the total traffic volume of a year was divided into 144 axle load groups according to the monthly and hourly distribution conditions. Accordingly, based on the monthly maximum and minimum temperature, 12 representative days were selected to represent the climate characteristics of 12 months, respectively. Then, each representative day's measured structural temperature data were extracted every 2 hours and linearly interpolated to obtain 144 representative temperature fields corresponding to 144 axle load groups. Through the above method, simulation calculations were performed for cold recycled asphalt pavement structures with different cement-stabilized aggregate (CSA) base stiffnesses. The results show that the fatigue damage accumulation of the EACR layers reaches its highest value in winter and midday hours, owing to the temperature variation and traffic distribution. Due to the weak fatigue resistance of EACR mixtures, it is not recommended to be paved EACR layers directly on top of the CSA base with poor bearing capacity. Otherwise, fatigue cracking is likely to occur first. For this reason, recommendations for ensuring the durability of the cold recycled pavement structure were also proposed in the study.

It is of significance to reveal the low-cycle fatigue deformation mechanism of titanium alloy with tri-modal microstructure for improving its properties. This work developed a crystal plasticity finite element model based on realistic microstructure to predict the low-cycle fatigue behavior of TA15 titanium alloys with tri-modal microstructure containing primary α (αp), secondary lamellar α (αl) and transformed β (βt). During modelling, plastic strain accumulation (PSA) and energy dissipation were used as the fatigue indicator parameter (FIP) to predict fatigue damage and life. It is found that the fatigue deformation prefers to localize at the interfaces of αp/β, αl/β and at triple junctions, which leads to the initiation of fatigue crack. In addition, the soft geometry of αl will also contribute to the strain localization inside αl grains causing fatigue damage. This is because the local lattice rotation is more prone to occur at these locations due to the tension-compression asymmetry of lattice rotation, which induces the occurrence of the microtexture and aggravates the heterogeneity of the lattice rotation, leading to the localized PSA and the total energy dissipation. And the asymmetry of lattice rotation in each cycle also leads to the tension-compression asymmetry of flow behavior. Both of the two FIPs can effectively predict fatigue life. With the strain amplitude increasing, the PSA-based model shows a relatively higher predictive accuracy of fatigue life than that of the accumulated energy dissipation-based model. The predicted fatigue life is in accordance with the C-M model.

Article Highlights The oscillations of a submarine pipeline subjected to current loads that is varying along the depth are measured in the field (prototype), which is unique and valuable data that is sparsely or seldom available. Using numerical analysis this problem is analysed to replicate the field oscillations due to variable current to enhance the confidence of mathematical models. The high oscillations in the direction of the current can induce damage within the design life of the pipeline and therefore adopt measures to bring down the oscillations to acceptable level by providing external attachments on the pipeline.

Abstract Tread wear and rolling contact fatigue (RCF) damage propagated on railway wheels are the two extremely important focal points as they can tremendously deteriorate wheel/rail interactions and hunting stability and destroy wheel surface materials, and subsequently, cut down the lifetime of the wheels. The on-board anti-slip controllers are of essence aiming to hold back the striking slipping of the powered wheelsets under low-adhesion wheel/rail conditions. This paper intends to investigate the impact of anti-slip control on wheel tread wear and fatigue damage under diverse wheel/rail friction conditions. To this end, a prediction model for wheel wear and fatigue damage evolution on account of a comprehensive vehicle-track interaction model is extended, where the wheel/rail non-Hertzian contact algorithm is used. Furthermore, the effect of frictional wear on the fatigue damage at wheel surface is considered. The simulation results indicate that the wheel/rail contact is full-slip under the low-adhesion conditions with braking effort. The wear amount under the low-adhesion conditions is observably higher than that under the dry condition. It is further suggested that the wheel tread is prone to suffering more serious wear and fatigue damage issues with a higher anti-slip control threshold compared to that with a lower one.

To explore an accurate load spectrum editing method and discover the influence of different types of bench load spectrum on steering knuckle fatigue damage, the verified test field load spectrum was used as the data source and the knuckle endurance specification was simplified. The multi-body dynamics model of the vehicle was verified by the Kinematics Compliance（KC） test of the suspension and virtual iteration method. The bench random spectrum with the features of time and frequency domain was created by the domain editing method. Four-stage bench program spectrum was generated by damge equivalence principle. According to the result of the statistical knuckle’s pseudo damage in all directions and the modal test, the knuckle multi-axis virtual bench was built. The modal stress recovery method is used to compare the fatigue damage under the steering knuckle of the original spectrum, the bench random spectrum, and the bench program spectrum. The result shows that the damage distribution under the three excitations is consistent. The maximum damage ratios of the bench random spectrum and bench program spectrum to the original spectrum were 0.75 and 1.7, the accuracy of the load spectrum editing method and the engineering practicability of the virtual bench are verified. Finally, the load type of the steering knuckle fatigue damage and the road type were determined through the virtual bench transfer matrix, which provides data support for structural improvement.

In order to truly reflect actual stress level borne by equipment, improve inherent reliability of product and reduce maintenance cost of product in the later period, in view of the problem that it is difficult to select test temperature level in the existing climate environment and reliability test standards, this paper analyzes thermal fatigue mechanism of products at measured ambient temperature and proposes a method for constructing test profiles. Through data processing, fatigue damage calculation and fatigue equivalence of the measured temperature data, test profile equivalent to the measured temperature data is finally obtained. Accelerated model is used to accelerate the equivalent test profile to obtain the accelerated test profile. Accelerated test results show that the error between test and computation results is 8.9%,which verifies the effectiveness of the proposed environmental test profile construction method based on measured temperature data.

Autonomous vehicles and truck platooning have become the future in the transportation field. This new strategy has many benefits because it lowers fuel consumption and CO2 emissions, improves safety, optimizes transport by using roads more effectively, and reduces traffic congestion. In this research, the effect of the controlled positioning of autonomous and non-autonomous truck loadings on the long-term performance of pavement was estimated using different variables such as climate, uniform wandering values of distance between trucks, and percentage of autonomous trucks by using MEPDG/AASHTOWare Pavement ME Design software. This was achieved by first computing the strain and stress of the different loading combinations, resulting in the computation of the failures in the pavement infrastructure and the pavement thickness needed to support each combination. The second part of the research consisted of designing a platoon strategy that was developed for a series of autonomous and connected trucks such that the lateral position of the trucks and the spacing between them could be explicitly optimized to minimize flexible pavement damage. The findings revealed that a small percentage of autonomous trucks can be beneficial to pavement life and that truck platooning following a well-studied skeleton can open a whole new world of pavement design. This can be revolutionary in changing roads around the world to improve traffic and infrastructure. [ABSTRACT FROM AUTHOR]

In this paper a joint evaluation method combining the AE technology and nonlinear ultrasonic is proposed for gear service fatigue damage assessment. Firstly, the AE and nonlinear ultrasonic experiment are conducted on 45 steel standard specimen to study the fatigue damage evolution law of 45 steel and link the relationship between relative nonlinear coefficient, material microstructure and fatigue damage state, which lays a theoretical foundation for gear fatigue damage evaluation. Then the ultrasonic nonlinear experiments are carried out on the tooth root and tooth middle of gear after service, the relative nonlinear coefficients of each detection point are calculated. The relative nonlinear coefficients of tooth 2 and tooth 3 are larger than those of other detection points, indicating that the cumulative fatigue damage of these two teeth root is serious. In addition, the relative nonlinear coefficient of tooth root is larger than that of tooth middle under the same service condition showing that the root of gear is prone to fatigue damage, which is consistent with the actual gear service. The experimental results indicate that the fatigue damage state of gear can be effectively evaluated using the joint method, in addition, the early warning information for gear failure accident can be provided to ensure the gear service safety and avoid disaster accidents. [ABSTRACT FROM AUTHOR]

The aim of this paper is to determine the fatigue damage of structures subject to random vibrations generated by Qualmark chamber. In real life, structures are generally subjected to complex multiaxial random load. To determine their fatigue life, many criteria have been elaborated, mostly in time domain. To minimize the computing time, the fatigue damage analysis should be done in the frequency domain. Tests that lead to the failure of the structures are commonly used to determine their weakness. But these tests are sometimes costly. To this end, in this paper an original new numerical model of the Qualmark chamber that leads us to determine the generated excitation at each point of its table is proposed. This model is validated using experimental measurement where adjustment process is proposed. Then, we develop a numerical strategy that leads to determine the multiaxial fatigue damage of structure under random vibrations using Matsubara's criterion developed in the frequency domain of structures tested with Qualmark chamber. A numerical application of a PCB tested with Qualmark chamber is presented at the end of this paper where fatigue damage is determined at each point using the developed strategy. Boundaries condition of the PCB is then determined using the proposed Qualmark table model. [ABSTRACT FROM AUTHOR]

A finite element simulation method for fatigue damage calculation and life prediction of pavement structures under the influence of temperature and traffic distribution factors was proposed in this study. Relying on the test cold recycled asphalt pavement structure, the existing distress, pavement structure forms, field monitored temperature and strain were first introduced and analyzed. Then, in constructing the numerical model, the viscoelastic constitutive model was introduced to characterize the effect of temperature and loading conditions on the mechanical response of the hot mix asphalt (HMA) layers and the emulsified asphalt cold recycled (EACR) layer. The damage variables are defined by fatigue equations, and the damage accumulation can be determined by Miner's linear fatigue accumulation theory. To reflect the distribution of traffic volume, the total traffic volume of a year was divided into 144 axle load groups according to the monthly and hourly distribution conditions. Accordingly, based on the monthly maximum and minimum temperature, 12 representative days were selected to represent the climate characteristics of 12 months, respectively. Then, each representative day's measured structural temperature data were extracted every 2 hours and linearly interpolated to obtain 144 representative temperature fields corresponding to 144 axle load groups. Through the above method, simulation calculations were performed for cold recycled asphalt pavement structures with different cement-stabilized aggregate (CSA) base stiffnesses. The results show that the fatigue damage accumulation of the EACR layers reaches its highest value in winter and midday hours, owing to the temperature variation and traffic distribution. Due to the weak fatigue resistance of EACR mixtures, it is not recommended to be paved EACR layers directly on top of the CSA base with poor bearing capacity. Otherwise, fatigue cracking is likely to occur first. For this reason, recommendations for ensuring the durability of the cold recycled pavement structure were also proposed in the study. [ABSTRACT FROM AUTHOR]

In drilling engineering, the cost of drilling tool fracture is enormous, and studying the fatigue failure process of drilling tools has practical significance. This paper uses metal magnetic memory detection technology to design and conduct fatigue damage tests on typical drilling tool material 42CrMo specimens under tensile, torsional, compressive, tensile, compressive, and torsional dynamic loading conditions. By analyzing the changes in the tangential component Hp(x) and gradient value K of the magnetic memory signal under different load conditions with the number of loading times, the process of fatigue failure of the specimens and the trend of changes in the magnetic memory signal in local stress concentration areas are explored. The characteristic parameters of fatigue damage based on magnetic memory detection were extracted and the critical point at which fatigue damage leads to crack initiation was inferred. This confirms that metal magnetic memory testing technology is an effective means of analyzing the fatigue damage process of drilling tools and provides a certain reference for formulating judgment standards for drilling tool maintenance on site. [ABSTRACT FROM AUTHOR]

As a vulnerable part of diesel engine, cylinder head is periodically subjected to the thermo-mechanical coupling loads. While due to the restriction of complex structures and working conditions, it makes the damage mechanism of thermo-mechanical coupling still unclear. In this research, thermo-mechanical responses are predicted successfully by load spectrums and the Sehitoglu theory. Then the effects of working loads on classified damage characteristics are analyzed with the equivalent cylinder head model. The results show that the deviations of temperature and stress are, respectively, within 10°C and 30 MPa, and it verifies the effectiveness of simulated component. Operating speed takes the greatest effect on the thermo-mechanical characteristics, and bolt force and gas pressure are negatively correlated with the responses of stress and strain. Fatigue life and damage are determined by the values of working loads. The effect of temperature load is the most dominant, MechDam and OxidDam increase substantially when operating speed exceeds 3500 r/min. The research will provide a theoretical reference for engineering design and optimization of cylinder head. [ABSTRACT FROM AUTHOR]

Online monitoring of the fatigue damage process of A7N01 aluminum alloy base metal and weld seam was conducted based on acoustic emission (AE) and digital microscopic imaging technology. The AE signals were recorded during the fatigue tests and analyzed using the AE characteristic parameter method. Fatigue fracture was observed using scanning electron microscopy (SEM) to analyze the source mechanism of AE. The AE results show that the AE count and rise time can effectively predict the initiation of fatigue microcracks in A7N01 aluminum alloy. The digital image monitoring results of a notch tip verified the prediction of fatigue microcracks using the AE characteristic parameters. In addition, the AE characteristics of the A7N01 aluminum alloy under different fatigue parameters were studied, and the relationships between the AE characteristic values of the base metal and weld seam and the crack propagation rate were calculated using the seven-point recurrence polynomial method. These provide a basis for predicting the remaining fatigue damage in the A7N01 aluminum alloy. The present work indicates that AE technology can be used to monitor the fatigue damage evolution of welded aluminum alloy structures. [ABSTRACT FROM AUTHOR]

In this paper, the research on the fatigue damage mechanism of tire rubber materials is the core, from designing fatigue experimental methods and building a visual fatigue analysis and testing platform with variable temperature to fatigue experimental research and theoretical modeling. Finally, the fatigue life of tire rubber materials is accurately predicted by using numerical simulation technology, forming a relatively complete set of rubber fatigue evaluation means. The main research is as follows: (1) Mullins effect experiment and tensile speed experiment are carried out to explore the standard of the static tensile test, and the tensile speed of 50 mm/min is determined as the speed standard of plane tensile, and the appearance of 1 mm visible crack is regarded as the standard of fatigue failure. (2) The crack propagation experiments were carried out on rubber specimens, and the crack propagation equations under different conditions were constructed, and the relationship between temperature and tearing energy was found out from the perspective of functional relations and images, and the analytical relationship between fatigue life and temperature and tearing energy was established. Thomas model and thermo-mechanical coupling model were used to predict the life of plane tensile specimens at 50 °C, and the predicted results were 8.315 × 105 and 6.588 × 105, respectively, and the experimental results were 6.42 × 105, with errors of 29.5% and 2.6%, thus verifying the accuracy of thermo-mechanical coupling model. [ABSTRACT FROM AUTHOR]

The interface bonding layer is usually adopted to connect the asphalt surfacing and steel deck plate; however, the effect of interface bonding conditions on fatigue performance of rib-deck welds still remains unclear. In this study, comprehensive finite element analysis was carried out to clarify the effect of interface bonding conditions. Parametric analysis was conducted to investigate the effect of Poisson's ratio and elastic modulus of asphalt surfacing, and the interface bonding condition on fatigue performance of rib-deck welds, so is the coupled effect of elastic modulus and interface bonding condition. Taking into account the time-variant temperature and traffic volume, the accumulated fatigue damages in rib-deck welds were compared and analysed. Results show that the simulation of the interface bonding condition is reliable, as convinced by bending tests. The interface bonding condition and the elastic modulus of asphalt surfacing, which are both sensitive to the temperature, considerably affect the fatigue performance of rib-deck welds. The fatigue damage of rib-deck welds is underestimated if the interface bonding behaviour is not considered. [ABSTRACT FROM AUTHOR]

New materials and structures with complex microstructural distributions are being rapidly developed using advanced manufacturing approaches, such as Additive Manufacturing (AM). For example, it is possible to fabricate metals using AM processes, such as Direct Metal Laser Sintering (DMLS), with spatial variations at sub-millimeter scales in textured grain structures, residual porosity, and precipitate morphologies at sub-millimeter scales. This poses new challenges for characterizing the corresponding variation in material behavior, particularly fatigue, for which conventional techniques were not designed. Therefore, new techniques are needed to quickly and accurately quantify these spatial variations. To this end, a method was developed for locally characterizing the fatigue behavior of materials, particularly metals and metal-matrix composites, by extending indentation methods to fatigue characterization using cyclic instrumented testing to measure the localized stiffness, which degrades due to the accumulation of fatigue damage under the indenter. A high frequency electro mechanical load frame equipped with an indenter was used to characterize three different metals: 4340 steel, 9310 steel, and brass. The S-N curve was then generated by applying a linear transformation to convert the measured stiffness to an equivalent alternating stress. The results correlated well with those obtained using conventional fatigue characterization techniques, including capturing the endurance limits. Finite element analysis with fatigue damage modeling was also used to quantify the evolution of stresses near the indenter due to the fatigue damage, while optical microscopy provided validation of the observed accumulation of plastic deformation associated with cyclic indentation loading. [ABSTRACT FROM AUTHOR]

This paper investigates the reliability of composite laminates with various lay-ups under fatigue loading. The prediction of failure probability of composite laminates subjected to different loads involves many uncertainties associated with mechanical properties, loading, and boundary conditions. Failure in the composite material is truly hard to trace because there are individual faults in each ply, and we face a stochastic process due to the scatter in the mechanical properties. The continuum damage mechanics (CDM), as a powerful approach, is applied to model the damage of fiber, matrix, and fiber/matrix debonding. This method defines criteria for damage detection and determines safe zones. The material constitutive equations are executed using a subroutine in Abaqus. The first-order reliability method and second-order reliability method have been applied to examine the reliability of laminated composites. The results are compared with those of the Monte Carlo simulation. Different composite laminates under different stress levels are considered for the failure probability investigation. The limit state functions and random variables have been determined based on the CDM model. Finally, the effects of the number of cycles, applied stress, and stacking sequence of the laminate on the reliability and fatigue life in fiber-reinforced laminated composites are assessed. [ABSTRACT FROM AUTHOR]

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Railway infrastructures play a pivotal role in developing the national transportation system. Recently, the strategy of the railway engineer has been significantly shifted; along with the development of new assets, they tend to pay increasing attention to the operation and management of existing railway assets. In this regard, this paper proposes a Digital Twin (DT) model to improve fatigue assessment efficiency in the operational processes of railway steel bridges (RSBs). The DT concept mainly lies in the federation and interaction of a Fatigue Analysis System (FAS), which is based on Eurocodes principles, and a model in Building Information Modeling (BIM). Along with the proposed DT concept, a prototyping system for a real bridge is initiated and curated. The FAS is validated in good-agreement results with the ambient vibration test of the bridge (about 1.6% variation between numerical and experimental values), and close values were found between numerical and experimental stresses, the latter obtained by installing strain gauges on the bridge. The BIM model provides access to the numerical values of fatigue state results in a given bridge connection detail but also automatically represents that information in a 3D environment using a color-scale-based visualization process. Furthermore, a simulation model with the main input variables being the traffic and geometric conditions of the bridge is continuously updated for timely re-evaluation of the damage state, which shows promise for the lifecycle management of the bridge. [ABSTRACT FROM AUTHOR]

This paper examines the potential of using additive manufacturing (AM) technology to create nature-inspired designs with decreased stress concentration factors, which are typically the source of fatigue damage. AM has advantages over conventional manufacturing processes, allowing for creation of complex and optimized geometries. Based on a real case study, this paper evaluates the possibility of bio-inspired optimization of a connection between a tubular profile and a steel plate through AM technology. The results reveal a significant decrease in the stress concentration factor for the optimized bio-inspired AM solution compared to traditional construction solutions. [ABSTRACT FROM AUTHOR]

Due to the uncertainty sources in fiber-reinforced plastic, deterministic analysis of damage of laminates under specific loadings, such as fatigue modes is not given much attention. This study's purpose is to define a fuzzy fatigue damage model (FFDM) for the prediction of composite laminate under cyclic conditions based on the continuum damage mechanics (CDM) model. At first, a damaged material's evolution and constitutive equations are formulated. Therefore, to estimate the unknown parameters of the CDM‐based damage model the experimental data of damage behavior in fiber, matrix, and shear direction at ply scale are expressed by fuzzy sets and are fitted utilizing a fuzzy linear regression. Data scattering and uncertainty in the empirical failure model are reflected in the definition of membership functions. After estimating unknown parameters of the FFDM according to obtained experimental data of damage mechanisms associated with the composite laminate under cyclic loading, a finite element model was executed to estimate the fatigue life of multidirectional fiber-reinforced plastic laminates. The prediction results have been compared with the experimental data in the literature and shown that by considering the uncertainty sources in stiffness reduction, the proposed model will be able to estimate the lower and upper bounds of a fatigue life of composite laminate under cyclic loading conditions. Overall, the results show that the use of fuzzy theory allows us to consider many more parameters than deterministic or classical statistical methods. [ABSTRACT FROM AUTHOR]

The constant/variable amplitude loading fatigue test with interior inclusionfine granular area-fisheye induced failure under R=0 were carried out on carburized Cr-Ni steel. The results showed that the fatigue life under variable amplitude loading is longer than that under constant amplitude loading in very-high-cycle fatigue regime under same maximum stress level, and the surface morphology of fine granular area under variable amplitude loading is coarser than that under constant amplitude loading under same order of magnitude of fatigue life. Simultaneously, it can be determined that the formation micro-mechanism of fine granular area is caused by the continuous deboning due to stress concentration around interior micro-defects. Furthermore, the life prediction model based on double nonlinear fatigue damage, which considers the coupling effect of local equivalent stress (surface residual stress and local stress concentration effect), loading sequence, failure mechanism and nonlinear characteristics of fatigue damage under constant/variable amplitude loading is established, and predicted life has good accuracy within the factor-of-three lines. [ABSTRACT FROM AUTHOR]

The repeated oscillatory shearing is widely used to characterize the fatigue damage of the bituminous binder in the laboratory scale. Acquisition of full stress waveform data in a strain-controlled test can help in the precise damage quantification. When the full stress waveform data in a strain-controlled test is subjected to harmonic analysis, the magnitude of the third harmonic of the stress ( I 3 ) can be used to identify the onset of damage. The evolution of I 3 , when subjected to time-sweep tests at given strain magnitude is hypothesized to represent the damage evolution in the binder. Two types of bitumen in the long-term aged condition are subjected to repeated oscillatory shear under constant strain amplitude, temperature, and frequency for 10000 cycles. From the experimental investigations, three types of evolution of I 3 were observed for the binder. In the first type, the magnitude of I 3 was negligibly small and it remains constant with a number of cycles. In the second type, the I 3 remains constant during initial cycles and increased on further loading. In the third type, I 3 started to increase from the initial cycles of shearing indicating the initiation of damage from the first cycle of loading. The type of evolution of I 3 with number of cycles varied with the temperature, frequency and the type of binder. Further, the ratio of I 3 / I 1 , where I 1 is the first-order harmonic stress, is used to identify the damage initiation point. The point of damage initiation obtained from the ratio of I 3 / I 1 is related to conventional method of fatigue damage estimation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Wind turbine (WT) foundations with an embedded steel ring (ESR) are widely used in onshore WTs due to construction convenience. The research group found that WT foundations with damage were often accompanied by blade issues. To investigate the potential correlation between aerodynamic imbalance and fatigue damage of the WT foundation with an ESR, this study focuses on a 2 MW WT with an ESR. It investigates the influence of an error in pitch angle (PAE) on the WT’s foundation load and stress, utilizing one year of SCADA data to analyze the fatigue damage caused by PAE. The main conclusions are as follows: Firstly, the effect of PAE on the amplitude value of load and stress is significantly greater than on the average value of load and stress. Secondly, when the PAE is within the range of −3° to 3°, the foundation fatigue damage incurred over one year is minimal, but once this limit is exceeded, the foundation fatigue damage increases dramatically. Thirdly, the peak value of fatigue damage to the foundation caused by PAE does not necessarily occur in the main wind direction, but in the direction with the highest probability of the occurrence of high wind speeds, and the larger the PAE, the more significant the trend.

Upon careful examination, numerous wind turbine collapses can be attributed to the failure of the tower bolts. Nowadays, the Schmidt–Neuper algorithm is extensively accepted in wind turbine tower bolt design. It is not advisable to utilize the finite-element method, notwithstanding the effect of the flange gap. To quantitatively investigate the influence of flange gaps on bolt fatigue, a nonlinear finite-element model of a flange segment incorporating bolt pretension and contact elements is herein proposed. Three distinct types of flange gaps are defined intentionally. It is possible to determine the nonlinear relationship between the wall load and bolt internal force. The fatigue damage of bolts was thus computed using the obtained nonlinear curve. Comparing with the results with those of Schmidt–Neuper method revealed the bolt fatigue damage is susceptible to a specified flange gap.

Computer-aided engineering (CAE) is an essential tool in a digital twin not only to verify and validate a virtual twin before it is transformed into a physical twin, but also to monitor the use of the physical twin for enhanced sustainability. This paper aims to develop a CAE model for a digital twin to predict the fatigue life of materials. Fatigue damage is represented by the size of a macro-crack that grows with a cluster of micro-cracks subjected to three different loads. The growth angle is related to the maximum circumferential tensile stress, and the growth rate is determined by the stress intensity factor (SIF) at the crack tip. The prediction model takes into consideration the main factors, including micro-cracks, crack closures, and initial configurations. Simulations are developed for the growth of macro-cracks with radially distributed micro-cracks and randomly distributed micro-cracks, and we find that (1) the macro-crack in the second case grows faster than that in the first case; (2) a pure shear load affects the macro-crack propagation more than a combined shear and tensile load or a tensional load; (3) the external stresses required to propagate are reduced when the inclination angle of the micro-crack is small and within (−25° < β < 25°); (4) micro-cracks affect the propagating path of the macro-crack and generally guide the direction of propagation. The developed model has been verified and validated experimentally for its effectiveness in predicting the fracture or fatigue damage of a structure.

Nondestructive evaluation on fatigue damage of metallic materials with ultrasound is important to ensure the load-bearing capability and in-service reliability of high-performance components.The fatigue damage of industrial pure iron was studied, and a nondestructive testing method which combined the critically refracted longitudinal (LCR) wave and recurrence quantification analysis (RQA) was proposed. Results show that with the increasing loading cycles and hardening during the tensile-compressive cyclic loading until 1000 cycles, the amplitude of LCR wave and the corresponding normalized amplitude difference Adifboth evolve monotonically. The sensitivity of 5 MHz testing frequency is significantly higher than that of 2.25 MHz. A further analysis of LCR wave with RQA presents that the resulting recurrence plot possesses higher sensitivity. The normalized recurrence rate difference RRdif is extracted. The sensitivity indicates an obvious increase up to 44% compared with the maximum amplitude indexes in time domain, frequency domain, and time-frequency domain. It proves that the proposed method would be a new solution to the nondestructive evaluation on early-stage fatigue damage of metallic materials.

In order to study the fatigue damage of joints in a parallel-type combined highway and railway steel truss bridge, the bridge finite element model containing refined joints as well as the multi-body models of the train and the vehicle is established. The equation of motion for the vehicle-bridge coupled system is solved using Craig-Bampton method. The dynamic weighting system is used to collect annual highway traffic flow data, and the distribution characteristics of parameters, such as vehicle type, speed, vehicle weight and vehicle spacing, are statistically analyzed. Combining the train load model, the fatigue damage of steel truss joints due to the train and vehicle loads is calculated using S-N curve and Miner linear cumulative damage theory, and the fatigue life is predicted using the rain flow counting method. The effects of train speed, load and unevenness on the fatigue damage of steel truss joints are discussed and the development of cumulative fatigue damage and life of the steel truss joints under environmental corrosion is analyzed. The results indicate that the variation of fatigue damage does not show a monotonous trend with increasing train speed. The fatigue damage increases rapidly, and the fatigue life decreases significantly with load increasing or flatness deteriorating. Considering the reduction in the joint stiffness caused by environmental corrosion, the development of cumulative fatigue damage curve is nonlinear, and the fatigue life decreases significantly. [ABSTRACT FROM AUTHOR]

In marine environment, floating photovoltaic (FPV) plants are subjected to wind, wave and current loadings. Waves are the primary source of fatigue damage for FPVs. The climate change may accumulatively affect the wave conditions, which may result in the overestimation or underestimation of fatigue damage. This paper aims to present a projection method to evaluate the climate change impact on fatigue damage of offshore FPVs in the future. Firstly, climate scenarios are selected to project the global radiative forcing level over decadal or century time scales. Secondly, global climate models are coupled to wind driven wave models to project the long-term sea states in the future. At last, fatigue assessment is conducted to evaluate the impact of climate change on fatigue damage of FPVs. A case study is demonstrated in the North Sea. A global-local method of fatigue calculation is utilized to calculate the annual fatigue damage on the FPVs’ joints. The conclusions indicate that there are decreasing trends of significant wave height and annual fatigue damage in the North Sea with the high emission of greenhouse gases. The fatigue design of FPVs based on the current wave scatter diagrams may be conservative in the future. The manufacture cost of FPVs can be reduced to some extent, which is beneficial to the FPV manufacturers.

In this research, the fatigue damage behavior under three-point bending of a composite joint incorporating a single countersunk fastener is investigated. Firstly, a self-developed fatigue test system was set up to test the fatigue characteristics of CFRP-countersunk bolted assembly under the displacement amplitude cycles of 103 to 106 to study the formation and expansion rule of damage and cracks. It found two typical damage processes, both of which involve some formal interface damage between fiber and matrix. Based on the experiment, a finite element fatigue damage analysis on this assembly was carried out according to the Hashin failure criterion. The simulation result shows an identical fatigue damage location and fatigue life with the experimental phenomenon. Moreover, it predicted the final fatigue life of the specimen under 10 hz cyclic loading with 1 mm displacement and 10 Nm bolt preloading. This research provides guidance for the engineering fatigue issues of single-bolted joint composite connection structures and provides a reference for the corresponding technical specifications formulation. [ABSTRACT FROM AUTHOR]

Producing complex fracture networks in a safe way plays a critical role in the hot dry rock (HDR) geothermal energy exploitation. However, conventional hydraulic fracturing (HF) generally produces high breakdown pressure and results only in single main fracture morphology. Furthermore, HF has also other problems such as the increased risk of seismic events and consuption of large amount of water. In this work, a new stimulation method based on cyclic soft stimulation (CSS) and liquid nitrogen (LN2) fracturing, known as cyclic LN2 fracturing is explored, which we believe has the potential to solve the above issues related to HF. The fracturing performances including breakdown pressure and fracture morphology on granites under true-triaxial stresses are investigated and compared with cyclic water fracturing. Cryo-scanning electron microscopy (Cryo-SEM) tests and X-ray computed tomography (CT) scanning tests were used for quantitative characterization of fracture parameters and to evaluate the cyclic LN2 fracturing performances. The results demonstrate that the cyclic LN2 fracturing results in reduced breakdown pressure, with between 21% and 67% lower pressure compared with using cyclic water fracturing. Cyclic LN2 fracturing tends to produce more complex and branched fractures, whereas cyclic water fracturing usually produces a single main fracture under a low number of cycles and pressure levels. Thermally-induced fractures mostly occur around the interfaces of different particles. This study shows the potential benefits of cyclic LN2 fracturing on HDR. It is expected to provide theoretical guidance for the cyclic LN2 fracturing application in HDR reservoirs. [ABSTRACT FROM AUTHOR]

Damage accumulation of coal caused by cyclic loading and creep impacts may ultimately lead to rock failure and dynamic disasters. Quantifying this behavior is crucial for evaluating the mechanical response under creep and cyclic loading processes. Here, creep tests were conducted after cyclic loading and unloading at 10 MPa confining pressure. The elastic modulus and Poisson's ratio indicated fatigue damage during the entire loading process. The elastic moduli in the unloading stage were slightly higher than those in the loading stage. The gap in Poisson's ratio decreased in the cyclic loading procedure. The axial and volumetric strains exhibited a slightly negative exponent trend. The stress–strain response indicated hardening and softening effects under constant axial stress. The hardening effect dominated the peak strength at lower axial stresses. The creep-hardening deformation was 0.17 and 0.21 under 88 and 100 MPa, respectively. However, the softening effect played a more significant role at higher applied stresses. Additionally, the peak strength decreased by approximately 2.7 MPa when the axial stress increased from 100 to 102 MPa. The coal near the mining-induced stress boundary experienced cyclic damage, and the creep stress gradually decreased. Thus, the mining-induced stress boundary evolution rate initially increased and was mitigated as the mining-induced stress reduced. Next, the boundary expanded outward and gradually stabilized until the applied loading did not lead to obvious rock failure. Finally, the mining-induced stress boundary in the entire gob may be flat during the long-term evolution. Considering the creep failure time and choosing a suitable time to determine the boundary are essential for preventing dynamic disasters. [ABSTRACT FROM AUTHOR]

In recent years, the use of digital image correlation (DIC) in fatigue experiments has become widespread. It is estimated that ~1000 published works exist that outline fatigue experiments in which DIC is employed for displacement and strain measurement. Of these, ~900 were published in the last 10 years. DIC is a noncontact method that uses a series of digital images to calculate full‐field strains on the surface of an object, planer or curved. Typical commercial DIC systems compute strains at resolutions high enough to trace hysteresis loops in metals. Properly operated open‐source systems can do the same. The DIC method is applied not only on optically based digital images but also on digital images from ultra‐high resolution (ultra‐HR) microscopes like a scanning electron microscope (SEM) or on volumetric images from computed tomography (CT) scans. In fatigue analysis, DIC provides much more information than that of an extensometer. Full‐field strains from DIC can be acquired at different scales (i.e., microscale, macroscale, and nanoscale) and can be related to items such as microstructural features, interacting surfaces (e.g., fretting), fatigue crack growth phenomenon, and distinct forms of energy. Because fatigue is a highly complex, strain‐induced process, the DIC method is and will be an important tool for current and future research in fatigue. This review begins with an overview of the history and fundamentals of DIC including an evaluation of the overall performance and accuracy of the method. Publications selected for review are then presented and discussed. Remarks about the present state‐of‐the‐art and an outlook for future work to be done are then provided. Highlights: Survey of digital image correlation (DIC) methods covering configurations, algorithms, performance, and accuracy is presented.Overview of how DIC is applied in dynamic applications is presented.Detailed discussion of DIC relevant to fatigue is presented. [ABSTRACT FROM AUTHOR]

The fatigue reliability assessment of deepwater risers plays an important role in the safety of oil and gas development. Physical-based models are widely used in riser fatigue reliability analyses. However, these models present some disadvantages in riser fatigue reliability analyses, such as low computational efficiency and the inability to introduce inspection data. An improved fatigue reliability analysis method was proposed to conduct the fatigue reliability assessment of deepwater risers. The data-driven models were established based on response surface methods to replace the original physical-based models. They are more efficient than the physics-based model, because a large number of complex numerical and iterative solutions are avoided in fatigue reliability analysis. The annual crack growth model of the riser based on fracture mechanics was established by considering the crack inspection data as a factor, and the crack growth dynamic Bayesian network was established to evaluate and update the fatigue reliability of the riser. The performance of the proposed method was demonstrated by applying the method to a case. Results showed that the data-driven models could be used to analyze riser fatigue accurately, and the crack growth model could be performed to analyze riser fatigue reliability efficiently. The crack inspection results update the random parameters distribution and the fatigue reliability of deepwater risers by Bayesian inference. The accuracy and efficiency of fatigue analysis of deepwater risers can be improved using the proposed method. [ABSTRACT FROM AUTHOR]