Search

Wind turbines in wind farms often operate in waked or partially waked conditions, which can greatly increase the fatigue damage. Some fatigue considerations may be included, but currently a full fidelity analysis of the increased damage a turbine experiences in a wind farm is not considered in wind farm layout optimization because existing models are too computationally expensive. In this paper, we present a model to calculate fatigue damage caused by partial waking on a wind turbine that is computationally efficient and can be included in wind farm layout optimization. The model relies on analytic velocity, turbulence, and loads models commonly used in farm research and design, and captures some of the effects of turbulence on the fatigue loading. Compared to high-fidelity simulation data, our model accurately predicts the damage trends of various waking conditions. We also perform example wind farm layout optimizations with our presented model in which we maximize the annual energy production (AEP) of a wind farm while constraining the damage of the turbines in the farm. The results of our optimization show that the turbine damage can be significantly reduced, more than 10 %, with only a small sacrifice of around 0.07 % to the AEP, or the damage can be reduced by 20 % with an AEP sacrifice of 0.6 %.

Pubovisceral muscle (PVM) injury during a difficult vaginal delivery leads to pelvic organ prolapse later in life. If one could address how and why the muscle injury originates, one might be able to better prevent these injuries in the future. In a recent review we concluded that many atraumatic injuries of the muscle-tendon unit are consistent with it being weakened by an accumulation of passive tissue damage during repetitive loading. While the PVM can tear due to a single overstretch at the end of the second stage of labor we hypothesize that it can also be weakened by an accumulation of microdamage and then tear after a series of submaximal loading cycles. We conclude that there is strong indirect evidence that low cycle fatigue of PVM passive tissue is a possible mechanism of its proximal failure. This has implications for finding new ways to better prevent PVM injury in the future.

PurposeThe purpose of this paper is to contribute to the solution of the fatigue damage problem of reinforced concrete frames in bending.Design/methodology/approachThe problem of fatigue damage is formulated based on the rheological–dynamical analogy, including a scalar damage variable to address the reduction of stiffness in strain softening. The modal analysis is used by the finite element method for the determination of modal parameters and resonance stability of the selected frame cross-section. The objectivity of the presented method is verified by numerical examples, predicting the ductility in bending of the frame whose basic mechanical properties were obtained by non-destructive testing systems.FindingsThe modal analysis in the frame of the finite element method is suitable for the determination of modal parameters and resonance stability of the selected frame cross-section. It is recommended that the modulus of elasticity be determined by non-destructive methods, e.g. from the acoustic response.Originality/valueThe paper presents a novel method of solving the ductility in bending taking into account both the creep coefficient and the aging coefficient. The rheological-dynamical analogy (RDA) method uses the resonant method to find material properties. The characterization of the structural damping via the damping ratio is original and effective.

The corrosion environment of a steel truss bridge significantly shortens its service life, particularly the chemical pollution in the air. A linear corrosion prediction model is proposed based on Miner’s linear cumulative damage concept to solve the difficulty of implementing accelerated corrosion tests. Moreover, an equivalent fatigue test is designed in combination with the corrosion prediction model. The results indicate that the bridge’s fatigue resistance can meet the design requirements when the corrosion environment is not considered. When the corrosion effects are jointly considered, the fatigue durability of the bridge is insufficient. With the increase in fatigue cycles, stiffness degradation presents a three-stage trend. The intermediate stage is a gentle development stage from the fatigue test results, accounting for approximately 80% of the total life cycles. Finally, a fatigue damage prediction model considering corrosion factors is established, and the law of fatigue damage and stiffness degradation of the structure under a corrosive environment is determined.

Fatigue damage assessment is critical for the structural design of the wind turbine nacelle chassis. However, existing fatigue damage indicators and assessment method cannot be both fast and accurate. In this paper, we propose a quantitative support vector regression-based fatigue damage assessment (SVR-FDA) method. First, the equivalent stress amplitude (ESA) is defined to simplify the fatigue damage indicator. Second, we establish the pre-calculated ESA database, including the ESAs of the wind turbine nacelle chassis under many varying wind flow conditions. Finally, based on the pre-calculated ESA database, we establish the SVR-FDA model, which can calculate the ESA of any given wind flow condition. A wind turbine nacelle chassis fatigue damage dataset, released by Goldwind, was applied to validate the proposed method. The results demonstrated that the SVR-FDA yielded the highest assessment accuracy for the lifetime ESA, as compared with four popular machine learning algorithms, including the least absolute shrinkage and selection operator, random forest, extreme gradient boosting, and deep neural network.

This paper shows a technical study and analysis of the fatigue damage assessment of bus structural steel under service loading. Two bus prototypes (passenger-loaded and empty) are used in the experimental measurement for a typical city road. A deterministic analysis is performed for fatigue damage assessment and the remaining strength. These parameters are used for the construction of fatigue design curves, which can predict the designed fatigue life to failure. Results show a promising prediction that can be used for best practice in future design. To complete the investigation, this work also examined the different perspectives of system failure on the basis of the probability of fatigue life in the form of a distribution function. All results are satisfactory from the analysis perspective. However, design improvement should be addressed to achieve the target life.

In order to study the effects of wheel-rail impacts on the fatigue damage of the fastening clips at the rail joints of a high-speed railway, field tests were carried out on the wheel-rail impacts at the rail joints of a high-speed railway in China. On the basis of the track irregularities at the rail joints obtained from field measurements, a nonlinear vehicle-track coupling dynamics three-dimensional (3D) model with consideration of Timoshenko beam elements and a refined finite element model of WJ-8 fastening system were constructed. And combined with the theory of cumulative damage and the method of fatigue analysis, the effects of wheel-rail impact at the rail joints on the fatigue life of fastening clips were analyzed. The results showed that the impacts of the wheel-rail in the joint area caused high-frequency fluctuations in the stress-time curves of the clips, which significantly increased the amplitude of stress cycle and increased a lot of stress cycles, of which the amplitudes were reached at a large level; the clips in the area where a rail joint was located suffered the most serious fatigue damage and had the shortest fatigue life; in the actual operation line, besides the clips in the rail joint area, it is also necessary to be concerned about the fatigue performance of fastening clips near the rail joint area.

Adoption of heavy haul traffic on many railroads, comprising Russian railways, has highlighted the relevance of assessing the effect of increased axial loads on the contact fatigue life of rails.The article describes a set of theoretical studies carried out to create a scientifically substantiated method for predicting the contact fatigue life of rails depending on the values of axial loads. The stress-strain state of the contact area has been determined using the finite element model of wheel rolling on a rail. It has been found that the wheel-rail rolling contact area undergoes complex multiaxial loading with the simultaneous action of normal and shear strains. Based on the analysis of models describing multiaxial fatigue damage, the Brown–Miller model was chosen, which considers the simultaneous action of normal strains at the contact area and of maximum shear strains, which most fully describes the stress-strain state of the wheel-rail rolling contact area. To apply the Brown–Miller model, fatigue stress-strain curves for rail steel have been identified. Based on the analysis of methods for determining the parameters of stress-strain curves carried out by V. A. Troschenko, a modified Roessle– Fatemi hardness method has been applied. Based on the experimentally determined values of hardness on the rolling surface, the parameters of the curves of elastic and plastic fatigue have been revealed by calculation and experiment. To establish the damaging effect of the load from wheel rolling on a rail, the concept of relative damage per rolling cycle had been assumed which is the value inverse to the number of cycles preceding formation of a contact-fatigue crack at a given value of the axial load.Calculations of the relative damage rate of the rolling surface of rails caused by contact fatigue defects were carried out with the Fatigue software package considering mean values of the indicators of the degree of fatigue strength and plasticity of rail steel and the calculated stresses in the wheel-rail contact area, as well as the plasticity correction using Neuber method. The polynomial dependence of relative damageability of the rolling surface of rails is obtained. The established functional dependence of relative damageability of the rolling surface of rails on the values of vertical forces can be used as the basis for the developed methodology for predicting the contact fatigue life of rails.

This paper studies the flexural fatigue performance of damaged steel beams strengthened by carbon fiber reinforced plastic-optical fiber bragg grating (CFRP-OFBG) plates. By analyzing the test beam’s failure mechanism under cyclic loading and the strain data monitored by the CFRP-OFBG panel in real-time, a life prediction model based on cumulative fatigue damage is proposed. The test results show that CFRP-OFBG plate reinforcement effectively reduces the fatigue crack growth rate of damaged steel beams and increases the fatigue life of damaged steel beams by 22.46%. The analysis and test results show that the minimum error between the calculated value of the life prediction model and the test value is −24.13%, and the maximum error is −5.61%. This study provides some suggestions for improving the service life of existing fatigue-damaged steel beams and establishing a simple fatigue life evaluation model.

In cases of aortic stenosis, bioprosthetic heart valves (BHVs), with glutaraldehyde-fixed bovine pericardium leaflets (GLBP), are often implanted to replace the native diseased valve. Widespread use of BHVs, however, is restricted due to inadequate long-term durability, owing specifically to premature leaflet failure. Mechanical fatigue damage and calcification remain the primary leaflet failure modes, where glutaraldehyde treatment is known to accelerate calcification. The literature in this area is limited, with some studies suggesting mechanical damage increases calcification and others that they are independent degenerative mechanisms. In this study, specimens which were non-destructively pre-sorted according to collagen fibre architecture and uniaxially cyclically loaded until failure or 1 million cycles, were placed in an in vitro calcification solution. The weakest specimen group (those with fibres aligned perpendicular to the load) had statistically significantly higher volumes of calcification when compared to those with a high fatigue life. Moreover, SEM imaging revealed that ruptured and damaged fibres presented calcium binding sites; resulting in 4 times more calcification in fractured samples in comparison to those which did not fail by fatigue. To the authors’ knowledge, this study quantifies for the first time, that mechanical damage drives calcification in commercial-grade GLBP and that calcification varies spatially according to localised damage levels. These findings illustrate that not only is calcification of GLBP exacerbated by fatigue damage, but that both failure phenomena are underpinned by the collagen fibre organisation. Consequently, controlling for GLBP collagen fibre architecture in leaflets could minimise the progression of these primary failure modes in patient BHVs. Statement of significance Mechanical damage and calcification are the primary premature failure modes of glutaraldehyde-fixed bovine pericardial (GLBP) leaflets in bioprosthetic heart valves. In this study, commercial-grade GLBP specimens which were uniaxially cyclically loaded to failure or 1 million cycles, were placed in an in vitro calcification solution. MicroCT and SEM analysis showed that localised calcification levels varied spatially according to damage, where ruptured fibres offered additional calcium binding sites. Furthermore, specimens with a statistically significant lower fatigue life were associated with statistically significant higher calcification. This study revealed that mechanical damage drives calcification of GLBP. Non-destructive pre-screening of collagen fibres demonstrated that both the fatigue life and calcification potential of commercial-grade GLBP, are underpinned by the collagen fibre architecture.

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 multia...

In this work, a new fatigue damage model considering the additive manufacturing (AM) effects is established. We first present the elastoplastic constitutive model with the newly established fatigue damage model considering AM effects. The method to calibrate the material parameters is put forward, and the numerical solution of the theoretical model is implemented. Second, the fatigue lives of two AM metal materials are predicted, and the applicability of the theoretical model is verified by the test results. Finally, the influence of the volume energy density ratio on the fatigue life of AM metal materials is analyzed, and the results show that the volume energy density ratio has a great influence on the fatigue behavior of AM metal materials. When the ratio is less than 1.0, the fatigue life increases rapidly with the increase of the ratio. The fatigue life increases with the stress ratio when the volume density ratio keeps as a constant. The research work in this paper provides a feasible method to predict the fatigue life of AM metal materials by continuum damage mechanics in engineering.

The multiaxial character of high-speed railway brake disc thermomechanical fatigue damage is studied in this work. Although the amplitudes and distributions of temperature, strain and stress are similar with uniform and rotating loading methods, the multiaxial behavior and out-of-phase failure status can only be revealed by the latter one. With the help of a multiaxial fatigue model, fatigue damage evaluation and fatigue life prediction are implemented, the contribution of a uniaxial fatigue parameter, multiaxial fatigue parameter and out-of-phase failure parameter to the total damage is discussed, and it is found that using the amplitude and distribution of temperature, stress and strain for fatigue evaluation will lead to an underestimation of brake disc thermomechanical fatigue damage. The results indicate that the brake disc thermomechanical fatigue damage belongs to a type of multiaxial fatigue. Using a uniaxial fatigue parameter causes around 14% underestimation of fatigue damage, while employing a multiaxial fatigue parameter without the consideration of out-of-phase failure will lead to an underestimation of about 5%. This work explains the importance of studying the thermomechanical fatigue damage of the brake disc from the perspective of multiaxial fatigue.

Author's accepted manuscript The rain-induced fatigue damage in the wind turbine blade coating has attracted increasing attention owing to significant repair and maintenance costs. The present paper develops an improved computational framework for analyzing the wind turbine blade coating fatigue induced by rain erosion. The paper first presents an extended stochastic rain field simulation model that considers different raindrop shapes (spherical, flat, and spindle), raindrop sizes, impact angles, and impact speeds. The influence of these raindrop characteristics on the impact stress of the blade coating is investigated by a smoothed particle hydrodynamics approach. To address the expensive computational time, a stress interpolation method is proposed to calculate the impact stress of all raindrops in a random rain event. Furthermore, coating fatigue analysis is performed by including the fatigue crack initiation in the incubation period and the fatigue crack propagation in the mass-loss-rate increasing period due to raindrop impact. Finally, the proposed computational framework is verified by comparing the estimated fatigue life with those obtained in literature. The results from the study show that by incorporating the statistics of rainfall data, the proposed framework could be used to calculate the expected fatigue life of the blade coating due to rain erosion.

The core of structural health monitoring is to provide a real-time monitoring, inspection, and damage detection of structures. As one of the most promising technology to structural health monitoring, the Lamb wave method has attracted interest because it is sensitive to small-scale damage with a long detection range. However, in many real-world structural health monitoring applications, the nature of the problem implies structures work under normal condition in most of its operating phases; therefore, classes of data collected are not equally represented. The predictive capability of damage detection algorithms may significantly be impaired by class imbalance. This article presents a damage detection method using imbalanced inspection data which is collected through Lamb wave detection. Aiming at maximizing detection accuracy, an improved synthetic minority over-sampling technique using three-point triangle (triangle synthetic minority over-sampling technique) is proposed to conduct the over-sampling procedure and increase the number of minority samples. The iterative-partitioning filter is employed to remove the noisy examples which may be introduced by triangle synthetic minority over-sampling technique. Three conventional classification methods, namely, support vector machine, decision tree, and k-nearest neighbor, are used to perform the damage detection. A fatigue crack detection test using Lamb wave is performed to demonstrate the overall procedure of the proposed method. Three damage sensitive features, namely, normalized amplitude, correlation coefficient, and normalized energy, are extracted from signals as datasets. A cross-validation is performed to verify the performance of the proposed method for crack size identification.

The effect of fatigue on the behavior of steel structures has long been the focus of researchers. However, with the widespread damage of steel structures after the Northridge earthquake, it is important to investigate the issue of low cycle fatigue. The bylaws attempted to address the weaknesses of the connections and introduced prequalified connections. In the present study, the behaviors of two prequalified welded unreinforced flange-welded webs and reduced beam section under low cycle fatigue were investigated. The behavior of high cyclic fatigue was the focus of many researchers, while there is only a limited scope of experimental data available for LCF. In this study, the S-N-curve was used to obtain the Nastar method and available experimental data. This curve was developed using the available experimental results for the low cycle region. Four buildings with different heights were analyzed using linear time history analysis and their behavior under low cycle fatigue was considered. Then, the cumulative fatigue damage was investigated by the Palmgren-Miner fatigue analysis method for the above two connections. Rainflow method was also used for counting cycles. By defining the cumulative fatigue index, for the critical beam of structures, the maximum value of this index was observed at the WUF-W, which was obtained for 0.059 3-storey structure and was increased by 0.24 with the increasing structural height. The index for the critical column in the WUF-W junction in the 15-storey structure was 0.042, while in the other structures, the maximum value was up to 0.197. Also, the fatigue index values for WUF-W binding were higher than those obtained for RBS, indicating that the first connection performance was weaker. Maximum rate of cumulative fatigue index in beams on WUF-W to RBS was 1.29 and for columns, this rate was 1.34. The results indicated the need for greater attention to the effect of low cycle fatigue on connections of steel moment frames, especially on the WUF-W.

Fatigue damage accumulation is a critical factor resulting in the failure of prestressed concrete (PC) bridges. The fatigue damage is usually caused by the coupled effect of cyclic vehicle loading and environmental corrosion. This study investigated probabilistic fatigue damage on aging PC bridges considering both stochastic traffic loading and corrosion. A stochastic traffic model was derived based on long-term monitoring data aiming to simulate fatigue stress spectra of critical rebar. The effect of cracks on the fatigue stress spectra was investigated in order to model the fatigue stress state more realistically. A three-stage traffic growth model was established based on traffic volume histories of three highways in China. A fatigue limit state function considering traffic growth and corrosion effect was deduced for fatigue reliability assessment of PC bridges. Numerical results show that the stress amplitude of rebar considering cracks is 1.53 times greater than the rebar with no-cracks, resulting in a decrease of fatigue life by 68 years. In addition, the three-stage traffic growth models lead to 25 years shorter fatigue life than the one considering a linear traffic growth model. Finally, the corrosion effect results in a fatigue life of 44 years. The numerical results provide a theoretical basis for fatigue life estimation and maintenance of aging PC bridges.

Regular and long-term infrastructures monitoring is fundamental for asset management, as it provides information on the actual mechanical conditions and triggers maintenance actions. Several tools ...

This paper presents an Acoustic Emission characterisation of the damage behaviour of asphalt concrete subjected to bending fatigue loading. An experimental campaign is carried out on an old asphalt...

The influence of wave force linearisation methods on fatigue damage predictions for jack-up rigs is investigated, using Sesam software as the basis for comparison. The possible risk of significantl...

Wake effect leads to the power loss and fatigue damage increase on wind turbines. Therefore, wind turbine wake is seriously considered as one of the key parameters in the micro-sitting and layout o...

Conventional tractor transmission spiral bevel gears are designed and evaluated based on the engine rated load, which is significantly higher than the load conditions in the field. In this study, the fatigue life of a spiral bevel gear is evaluated to obtain data for design optimization. The equivalent load was calculated using the field load data, and the integrated equivalent load was calculated based on the annual usage of major field operations in Korea. The fatigue life of three spiral bevel gear samples was evaluated using the accelerated life test (ALT) under an engine rated load condition of 120%. It was also evaluated under engine rated, plow equivalent, and integrated equivalent load. Fatigue life was estimated using the ALT results and the fatigue damage exponent based on the ALT equation. We observed that the fatigue life of the spiral bevel gear under the plow equivalent and integrated equivalent loads is higher than that under the rated load by 214 and 9,400 times, respectively. The results of this study can provide useful information for the design optimization of tractor transmission spiral bevel gears considering the field equivalent load.

Based on the modulus mortification rule of continuum internal variable theory of thermodynamics connected to concrete materials under frazzle loading, a simple, reliable, better and computational efficient theoretical fatigue damage model due to formation of microvoids, microcracks, microdefects and fractal is proposed. The prescribed new theory is linked with strain-based approach where “strain” is the main domain and is capable for prediction of fatigue life of concrete as well as cementitious and brittle material. Investigational data from fatigue test were employed to validate the model, and results show that the model can describe the fatigue damage progression of concrete materials under different frazzle loadings by verifying the predicted fatigue life. Mortification of elastic modulus, damage enlargement corresponding to the normalized life, degradation of stress level from elastic to plastic and its accumulation subjected to variable frazzle loading including its verifications are well discussed.

SUMMARYAiming at 3SPS+1PS parallel hip joint simulator, the maximum stress of branched chains under the suggested trajectory is obtained by elastodynamic analysis. Based on Corten-Dolan fatigue damage theory and Rain-flow counting method, the dynamic stress of each branched chain is statistically analyzed. The fatigue life prediction shows that branched-chain A2P2C2 is the weakest component for the simulator. Finally, the fatigue reliability is analyzed and the fatigue life and reliability under different structural parameters are discussed. The study shows that the fatigue life of each branched chain can be increased or balanced by increasing structural parameters or exchanging initial motion parameters.

While the present structural integrity evaluation method is based on the philosophy of assumed similitude, Fatigue and Damage Tolerance (F&DT) evaluations for next generation of air-vehicles require high-fidelity physical models within cyberspace. To serve the needs of F&DT evaluation in digital twin paradigm, a fatigue damage-cumulative model within peridynamic framework is proposed in this paper. Based on the concept of fatigue element block and damage accumulation law in form of Coffin-Manson relationship, the proposed model applies to both fatigue crack initiation and fatigue crack growth; fatigue crack growth rates under constant-amplitude and simple variable-amplitude block loading cases can be well predicted for three common structural materials without inputs of Paris law parameters. Additionally, the proposed model can also be easily extended to a probabilistic version; for verification, multiple-site-damage problems are simulated and the statistic nature of fatigue process in experiments can be well captured. In the end, main features of the proposed model are summarized, and distinctions from the other models are discussed. There may be a potential for the peridynamic damage-cumulative model proposed in this work to numerically predict fatigue problems in digital twin paradigm for future generations of aerospace vehicles.

In the last five years, towing to increasing demand for liquefied natural gas (LNG), researchers have actively analyzed and conducted studies on the sloshing phenomenon. However, there are limitations in the 1:1 model experimental method for LNG tanks installed in actual vessels. This study verified the validity of the average pressure prediction according to the scale ratio of a prismatic LNG tank that was developed through a correlation analysis between the sloshing analysis and model test. We then presented an average pressure prediction for the tank of a full-scale vessel. In addition, to ensure the safety of the tank, this study investigated the degree of cumulative fatigue damage that could be caused by cyclic loading through a fatigue analysis.

Vortex-Induced Vibration (VIV) is a major contributor to the fatigue damage of marine risers which are often arranged in an array configuration. In addition to helical strakes and fairings, studies have been strived in searching for possible VIV suppression techniques. Inspired by giant Saguaro Cacti, flexible cylinders of different cactus-shaped cross sections were tested in a water tunnel facility, and test results showed that cactus-like body shapes reduced VIV responses of a cylinder at no cost of significant increase of drag. A series of experiments were conducted on a pair of two tandem-arranged flexible cylinders and an array of four cylinders in a square configuration to investigate the effects of wake on the dynamic responses of cylinders and the VIV mitigation effectiveness of the cactus-like body shape. Results showed that the cylinders in a square configuration, either at the upstream or downstream positions, might have larger dynamic responses than those of a single cylinder. The cactus-like body shape could mitigate VIV responses of cylinders at upstream positions in an array configuration; however, similar to helical strakes, the mitigation efficiency was reduced on downstream cylinders. Note that the cactus-like cross-sectional shape investigated was not optimized for VIV suppression. The present study indicates that the modification of the cross-sectional shape of a cylinder to a well-designed cactus-like shape may be used as an alternative technique to mitigate the VIV of marine risers.

To study the influence and selection of rational elastic-dissipative parameters for under wing pylon-mounted engine suspension, a mathematical model of aeroelasticity of a large-sized transport aircraft has been developed by taking into account the kinetic moment of the engine rotors and specially designed engine attachment points to the pylons. It is shown that the elastic-dissipative parameters of the attachment points, which implement the concept of a released engine, have a significant effect on the integral aeroelastic and strength characteristics of the aircraft. Schematic diagrams of the engine mounts to the pylon are proposed. The usefulness of the concept of a released engine for increasing aeroelastic stability and reduce the level of fatigue damage of the aircraft structural elements has been proved.

Failure of the cables can cause a bridge to collapse. Fatigue damage of steel wire is one of the causes of cable failure. In this paper, we study the relationship between the fatigue damage and the group speed of guided waves in the steel wire. The relationship between cyclic loading times and group speed of steel wire is obtained by applying tension to steel wire. The results show that the group speed of guided waves increases linearly before the 6.02 million cyclic-loading times, increases exponentially from 6.02 to 6.97 million times. The curve of the relationship between the group speed of the guided waves and the number of cyclic loading times can be fitted to an exponential function, and this curve can be used as a calibration curve to evaluate the fatigue damage of steel wire.

Fatigue damage accumulation model plays a critical role in life prediction and anti-fatigue design of material. It is still a challenging issue to accurately quantify its development process and probabilistic characteristics. In this study, a probabilistic model of fatigue damage accumulation is presented based on Weibull distribution and reliability analysis theory. Firstly, the general rule of fatigue damage accumulation is analyzed, and three basic assumptions about fatigue life and fatigue damage are drawn. Subsequently, two typical fatigue reliability analysis models are elaborated, and a probabilistic model of fatigue damage accumulation is proposed based on the principle of failure probability equivalence. Finally, three sets of experimental data of aluminum alloy are utilized to verify the proposed model. The results show that the proposed model is capable of quantifying the dynamic probability characteristics of fatigue damage accumulation. Moreover, the proposed model has high calculation accuracy, and it can be easily established based on fatigue life data of material.

The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears. Meanwhile, the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures. To address this issue, a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method. The tooth profile surface roughness was considered, and its evolution during repeated meshing was simulated using the Archard wear formula. The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion. The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable. Variations in the wear depth and fatigue damage around the pitch point are described, and the effect of surface roughness on the fatigue life is addressed. The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness. Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.

A multimode kinetic model for the development of damage under cyclic loading is proposed to describe the development of fatigue failure process. To determine the coefficients of the kinetic damage equation, the well-known Smith–Watson–Topper (SWT) criterion of multiaxial fatigue fracture is used. On this basis, a procedure for calculating the kinetic equation coefficients for various modes of fatigue failure from low-cycle to very-high-cycle fatigue is proposed. A uniform numerical method is developed and examples of calculating the development of crack-like zones of damage and fatigue fracture of samples containing various defects for different cyclic loading modes are presented.

The thickness effect has a significant influence on the fatigue life of micro–nanometer thin films. Due to the increasing application of micro–nanometer thin films in the field of microelectronics, a suitable fatigue prediction model is urgently needed. To reveal the impact of the thickness effect on the fatigue life of a copper wire film, cyclic tension fatigue test of four groups of copper wire films were carried out. Based on the theory of continuous damage mechanics and damage homogenization method, a fatigue damage accumulation model that considered the film thickness was proposed. Based on the proposed fatigue damage prediction model, the damage evolution law and fatigue life of copper wire films with different thickness and strain range were predicted. Furthermore, the size effect of the copper films was analyzed. The results showed that the fatigue life of copper wire films will decrease with the increase of thickness and strain amplitude; the thinner the film, the more significant the thickness effect on the fatigue life is; with the increase of the film thickness, the film thickness effect will gradually decrease.

Purpose The purpose of this paper is to propose a method with capability of short-time implementation. Design/methodology/approach This paper was directed using both experimental tests and simulations to propose a comprehensive method for lifetime estimation of the solder joints. Findings A new method with good agreement with experimental tests has been proposed. Originality/value It is confirmed that paper is original.

In order to predict the fatigue life of frame, a new bench test method of the frame torsion fatigue is proposed, which can approximately reflect the results of enhanced road test. The frame finite element model was established and the simulation was carried out to determine the dangerous position of fatigue life failure. The load spectrum of the fatigue dangerous position was collected, and the fatigue damage value was analyzed by the rain-flow counting method and Miner criterion. The equivalent conversion relationship of the fatigue life between bench test and road test was established. The mean error between theoretical calculation result and bench test result is 5.2 %; The mean error between theoretical calculation result and road test result is 3.85 %. The results showed that the bench test method of frame torsion fatigue can improve the precision and reliability of the frame fatigue life prediction.

The fatigue analysis on orthotropic steel bridge decks is a hot topic in bridge engineering field. This study provides one method for fatigue analysis under the combined actions of vehicle loads and pavement temperature. To be specific, taking the steel bridge deck of one cable-stayed bridge as a research object, this study proposes a method of calculating life-cycle fatigue damage of orthotropic steel deck under the combined actions of vehicle loads and pavement temperature. First, a finite element model of steel bridge deck with asphalt pavement is built to analyze the influence of pavement temperature on the fatigue stress of steel bridge deck. Second, a simulation method of fatigue stress caused by random vehicle loads is proposed. Finally, a method of calculating the life-cycle fatigue damage of welded joints under the combined actions of vehicle loads and temperature is proposed. The results show that temperature has a significant effect on fatigue damage, and the cumulative fatigue damage in the rib-to-rib welded joint is significantly greater than that in the deck-to-rib welded joint. The results can provide meaningful references for bridge engineers to carry out fatigue analysis on orthotropic steel bridge decks.

For characterizing polymer modified binders, different state Departments of Transportation (DOTs) use a variety of laborious and empirical Performance Grade (PG) “Plus” test methods such as elastic recovery (ER) and tenacity. However, the effects of elasto meric and/or plastomeric polymers are not been accurately identified through these conventional tests. The main research goal of this study is to recommend alternative test method(s), which can be pursued by using a, commonly available, dynamic shear rheometer (DSR). To this end, efficacies of test methods such as multiple stress creep recovery (MSCR), elastic recovery using a DSR (ER-DSR), linear amplitude sweep (LAS), and binder yield energy test (BYET) were explored in this study. Also, a viscoelastic continuum damage (VECD) model was developed to characterize the fatigue cracking of asphalt binders. Two types of polymer modi fied binders from ten sources approved by the Arkansas Department of Transportation (ARDOT) and Texas Department of Transportation (TXDOT) were evaluated in the laboratory. Test results and analyses suggest that without risking the suppliers or users, either the ER-DSR or MSCR test can be a good replacement of the ER test method. A new ER-DSR binder grading system has been proposed. Among the selected fatigue tests, the BYET results were found to be highly related to fatigue damage.

The fatigue damage evolution in glass-fiber-reinforced (GRP) mortar pipes under cyclic loading were investigated. Based on the results of fatigue tests, a two-stage linear law of stiffness degradation of a glass-fiber-reinforced plastic mortar pipe culvert is proposed, and a model for calculating its stiffness degradation is established. By proposing a reasonable residual stiffness calculating equation, this study intends to provide a useful method for an accurate prediction of the fatigue life and a valid long-term safety evaluation of GRP mortar pipes.

Reinforced concrete bridge piers are extremely vulnerable to damage during long-duration ground excitations or main shock-aftershock type earthquakes due to accumulated damage caused by a great number of reversed excursions in elastic-plastic range. However, few studies on fatigue damage of piers can be found in literature. Low-cyclic loading tests of four identical RC bridge piers with high-strength rebar HRB600E (yield strength about 600 MPa) were carried out in this study. One of specimens was taken as the benchmark and was subjected to a conventional load protocol, and the rest was subjected to one, two and three times yield displacement, respectively. The research results showed that the fatigue strength of RC bridge piers tended to drop drastically at about ten cycles and then slowed down gently. It was found that strength degradation rate increased significantly with the displacement amplitude for fatigue tests while the fatigue life decreased dramatically with the displacement amplitude. In particular, when the cyclic loading displacement exceeded 2 times the yield displacement, the fatigue life dropped dramatically. Based on the experimental data, an exponential-type damage model was proposed with the peak lateral force at the first cycle as the coefficient, the cycle count as the base and factor of the loading displacement amplitude as the exponent, which could accurately predict the degraded lateral force of the bridge piers at different constant drifts. An accumulative fatigue damage index was established to evaluate the damage level of bridge piers.

Taking Liangxiang Pagoda built in Liao Dynasty in Beijing as the research object, the vibration responses of the pagoda in the east-west direction and south-north direction under the action of trains on the Beijing–Guangzhou Railway Line and microseism were tested. On this basis, a numerical model was established by using ANSYS to further calculate the dynamic response of the pagoda, and the safety and integrity of the pagoda were evaluated based on existing standards. Cumulative fatigue damage theory was introduced to predict the remaining fatigue life of Liangxiang Pagoda. The following conclusions have been drawn: in the two directions mentioned above, the natural vibration frequencies of the pagoda of the first three orders are similar; the 1st-order vibration modes in the plane are bending, and the vibration modes of the 2nd and 3rd orders are shear-bending; under the action of trains, the peak vibration value of Liangxiang Pagoda at the position that bears the maximum load is 0.053 mm/s, which has a little impact on the safety and integrity of the pagoda; under the combined action of gravity and trains, the remaining fatigue life of Liangxiang Pagoda is 5.26 × 10 7 times. The research method used in this paper can provide data and scientific support for the protection of historical buildings, as well as the basis for the follow-up research of the studied ancient pagoda.

The presented work aims at evaluating the results of uniaxial and multiaxial fatigue failure tests using velocity and acceleration measurements. A specimen containing damaging modes at different eigenfrequencies is introduced. The tests are conducted on an electrodynamic 3D-shaker system using a random vibration environment. Different fatigue times are observed between uniaxial and multiaxial excitation. Based on the velocity and acceleration measurements, fatigue damage values are calculated for each test. While the fatigue damage values of velocities are similar between uniaxial and multiaxial tests, large deviations can be detected when using accelerations as base for the calculation. Thus, experimental verification for recently proposed multiaxial fatigue damage calculations based on different vibrational quantities is made possible.

A reliable novel monitoring approach is developed to assess the structural condition of reinforced-concrete bridge elements. The approach is based on combining acoustic emission technique and strain gauge measurements, and it is illustrated by a case study of a composite steel–concrete viaduct in service since 1957. Monitoring was performed on its reinforced-concrete deck slab under traffic and environmental loading for one year. The monitoring setup and procedure are presented. The variation of acoustic emission signals is evaluated regarding strain and temperature measurements. Parametric study, pencil-break test, statistical analysis, crack classification and b-value analysis are performed to assess the structural condition. The acoustic emission activity of the reinforced-concrete slab is evaluated for 1 year under operational conditions. From the monitoring approach, it was possible to identify the nature of the cracking activity in the concrete slab as a function of traffic loading and temperature and to assess in time the condition of the slab-girder connection.

The evolution of materials characterization methods and of the amount of materials tested nationwide in the past decades made it possible to organize a road pavements database. These are essential information for pavement design with transfer functions that allow performance prediction from computational modeling. The main objective of this work is to develop a transfer function associating laboratory fatigue damage characterization data to surface cracked area observed in field. The tools used were the asphalt stiffness, characterized by the complex modulus, and the fatigue life, characterized by the integrity curve (C vs S) and the failure envelope (GR vs Nf), and associated with multilayer elastic analysis and a reduced damage variable. Calculated damage evolution results were used to predict field observations of percent cracked areas. In a calibration phase using 27 test sections, it was possible to obtain a unique transfer function between laboratory predictions (in terms of calculated damage) and field observations (in Terms of percent cracked area). The validation of the transfer function was performed with 17 other sections. Through 2 pavement design examples, it was observed an important aspect of the conventional definition of the average reduced damage variable, especially in the prediction of pavements with surface course greater then 15cm. A evolução dos métodos de caracterização e da quantidade de materiais testados em âmbito nacional nas últimas décadas possibilitou a organização de um banco de dados de pavimentos rodoviários. São informações essenciais para métodos de dimensionamento, cujas funções de transferência possibilitam a previsão do desempenho a partir de modelagem computacional. O principal objetivo do presente trabalho é desenvolver uma função de transferência que associa dados de caracterização de dano por fadiga em laboratório à área trincada observada em campo. As ferramentas usadas foram a rigidez da mistura, caracterizada pelo módulo complexo, e a vida de fadiga, pelas curvas de integridade (C vs S) e de envoltória de falha (GR vs Nf), associados à análise elástica multicamadas e a uma variável de dano “reduzida”. Os resultados de evolução de dano calculada foram usados para prever observações da evolução do percentual de área trincada em campo. Numa etapa de calibração envolvendo 27 trechos experimentais, foi possível se obter uma função de transferência única entre as previsões de laboratório e as observações de campo. A validação da função foi realizada com dados de 17 outros trechos. Através de 2 exemplos de dimensionamento, observou-se uma questão importante relativa à definição convencional da variável de dano médio reduzido, sobretudo na previsão de comportamento de pavimentos com espessura de revestimento maior que 15cm.

Weld of mining dump truck (MDT) frame is prone to fatigue damage due to the unreasonable local structure of cavity with stiffeners. However, there are considerable limitations in the engineering im...

A modern large-sized aircraft dynamic properties analysis, determined by the specificity of its layout scheme, demonstrates that the engines on under the wing elastic pylons lightly damped oscillations cause a number of undesirable phenomena, including intense accumulation of fatigue damage of the pylon-to-the-wing attachment, in fact in the area of engine installation in the pylon and the wing. The results of theoretical and experimental research show that with some engine attachment to the pylon structural modification it becomes possible to use the engines inertial and gyroscopic properties to absorb these oscillations. In this case, the motor tones damping coefficients increase by an order of magnitude or even more, so the gyroscopic coupling of elastic vibration tones is realized. With the rational choice of the additional parameters of elastic and dissipative bonds in the engine attachments it is possible to affect the aircraft wing and engines aero elastic vibrations effectively, which has a significant effect on the aircraft elements structural capabilities. A mathematical model of aero elasticity (MMAE) with respect to the kinetic moment of the engine rotors and specially designed units for attaching the engines to the pylons was developed in order to study the influence and the selection of rational elastic-dissipative parameters of the pylons-under-the-wing aircraft engine mounts. The method of predetermined basic forms is used for the aircraft with running engines on the pylons MMAE synthesis. The given forms are considered as the aircraft basic structure forms natural vibrations in the void. This work treats the engine nacelle and the rotor as absolutely rigid bodies, the elasticity of the rotor to the nacelle attachment is neglected. The pylon is modeled by an elastic beam, and the elastic and dissipative properties of the pylon-to-the-wing and the engine-to-the-pylon attachments are correspondingly by elastic-dissipative bonds. Schematic diagrams of the engine to the pylon attachments are proposed. The results of the study devoted to the influence of the proposed attachment points modifications on the load and integral strength characteristics of the main structural elements of the engine – pylon – wing dynamic system on the example of an An-124 aircraft are presented. The practical implementation of the proposed solutions aimed to reduce the level of fatigue damage to structural elements of the aircraft feasibility is proved.

The present paper studies fatigue damage and life of single-lap bolted joints tightened with different torque magnitudes subjected to uniaxial load cycles. The adherends were constructed from E-glass/epoxy layers using a hand layup technique and assembled by 1.5, 3, and 8 N m of applied torques. Increasing the torque magnitude benefitted the final fatigue life of the joints so that the high-cycle fatigue life of the joint sample tightened with 8 N m was as high as 10 times that of the joint tightened with 1.5 N m. In the numerical section of this study, a three-dimensional finite element analysis was employed, and the impacts of applied torques were included in the progressive damage model to assess damage and failure in the bolted joints. For the joints tightened with higher torque levels, numerical results revealed higher fatigue lives but at the cost of more delamination at the vicinity of the hole. Laminate fracture surface was investigated through scanning electron microscopy and more cracking/damage progress was evidenced in matrix, fiber, and matrix–fiber interface as composite joints experienced fatigue cycles. Experimental life data of tested joints agreed with those anticipated through the use of finite element analyses indicating the developed model as an appropriate tool in evaluating the effects of applied torques on the fatigue fracture behavior of bolted laminates.

The Smith–Watson–Topper (SWT) fatigue damage parameter has been discussed based on the critical-plane concept. It was found that the fatigue life prediction obtained by the SWT model tended to be unconservative during the non-proportional loading as only the tensile components on the plane of maximum principal strain range has been considered. To overcome this shortcoming, a virtual strain energy density model has been proposed using the von-Mises criterion, where the shear component on the plane of maximum principal strain range can be included during the non-proportional loading conditions. However, on the other hand, this model will be equivalent to the SWT model under the uniaxial and/or proportional loading conditions.