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ABSTRACT This paper evaluates the applicability of Neuber's and equivalent strain energy density (ESED) rules to predict the material response below the root of a sharp U‐notch under variable‐amplitude (VA) loading for crack propagation simulations. The Voce–Chaboche (V‐C) combined hardening constitutive model, coupled with the above‐mentioned approximation rules, is used to resolve the elasto‐plastic response over a range of depths below the notch root. The response at each load reversal is extracted, and the maximum and minimum stress and strain quantities are used to evaluate fatigue damage using the Smith–Watson–Topper parameter. Results from approximation rules are compared to finite element method (FEM) at and below the notch root. Prediction accuracy varied at different points below the root depending on the size of the plastic zone, with predictions made using the original Neuber's and ESED rules being less accurate below the root. Applying stress redistribution correction to the stress field improves its accuracy below the root; however, strain values are significantly amplified as a result. A modified Neuber's rule with stress redistribution and constraint corrections predicts the distribution of the material response and fatigue damage with consistent accuracy. [ABSTRACT FROM AUTHOR]

A finite element model, combined with a damage accumulation method, was developed to explore the mesoscale effects of microstructure on the evolution of low-cycle fatigue damage in AA 2024-T3 aluminum alloy. In this model, the maximum shear strain of the slip systems was computed as the damage criterion using crystal plasticity (CP) theory combined with continuum damage mechanics (CDM), the slip strength is related to the evolution of dislocation density, and the nonlinear kinematic hardening rule was used to capture the cyclic response. This constitutive model was capable of quantifying the local fatigue damage in 3D microstructural applied to the Voronoi polycrystals like the AA2024 Al alloy. The results show that grains with high Schmid factors usually suffer more severe damage than those with lower Schmid factors, while grains with lower Schmid factors mainly suffer damage at grain boundaries. The proposed constitutive model demonstrates the ability to capture the fatigue damage evolution of polycrystalline metal. [ABSTRACT FROM AUTHOR]

The fatigue performance of emulsified asphalt mastics directly affects the long-term service performance of emulsified asphalt cold recycled pavement. Fatigue properties of 24 different mastics before and after short-term aging composed by the combination of 3 different fillers and 4 filler-binder ratios (F-B) were evaluated based on the viscoelastic continuum damage (VECD) model. Atomic force microscopy (AFM) was employed to analyze the surface morphology of the mastics and determine the interaction between filler and asphalt. The results show that increasing the F-B or the aging effect reduce the stress–strain withstand capacity of emulsified asphalt mastic, increase its integrity damage rate, and further reduce the fatigue life. Comparing three mastics, limestone mastic with a low F-B exhibits a better fatigue performance. The limestone mastic is more affected by short-term aging, while cement mastic and coal gangue mastic are significantly affected by F-B. Filler types, F-B and aging can obviously change the surface morphology of mastics. The microscopic morphology change of coal gangue mastic with a low F-B is dominated by the dispersing effect of the filler, whereas the microscopic morphology of mastic with a high F-B is dominated by the adsorption effect. [ABSTRACT FROM AUTHOR]

A three-point bending fatigue experiment was conducted on a component consisting of an I-beam and a welded steel plate. The magnetic leakage signal at the position of the weld was continuously collected during the process of fatigue; the factors influencing magnetic leakage signal were analyzed to explore its change law. Moreover, the characteristic parameters based on magnetic leakage signal were proposed to analyze the fatigue process and fatigue damage of weld. The results indicate that increasing the distance between the magnetic probe and weld will weaken the distribution characteristics of the magnetic leakage signal, then reducing the accuracy of the detection results. The change characteristics of the magnetic characteristic parameter G with the load are analyzed. The change of G presents three development stages with the increase in the load. The loading conditions of the experiment specimen can be determined by observing the change in the value of G. At different fatigue stages, the magnetic leakage signals of the weld show different trends. And the variation law of magnetic eigenvalue K extracted from the magnetic leakage signal can essentially match with the fatigue process of weld, and the magnitude of the eigenvalue can approximately characterize the fatigue damage of the weld. The time node of the state deterioration for the weld can also be approximately judged by the change node of eigenvalue, and the state of weld can be warned in time. Besides, A quantitative relationship between the damage index m and the residual fatigue life R is established. [ABSTRACT FROM AUTHOR]

In this paper, the fatigue damage degree of low-alloy structural steel is evaluated by using the attenuation characteristics of laser-induced surface acoustic wave (SAW) during propagation. Taking the typical structural steel material Q345 as an example, a cracks model of fatigue damage is established, and the finite element method is used to solve the model. The results showed that the attenuation coefficient of SAW can reflect the depth and density of fatigue cracks. The surface measurement experiments of specimens with stress cycles of 0, 50000, 100000, 150000, and 200,000 showed that with the increase of stress cycles, the attenuation coefficient of SAW increases as a whole, indicating that it is feasible to evaluate the fatigue damage degree based on the attenuation of SAW. A method of applying tensile stress to the material to improve the sensitivity of fatigue damage evaluation is proposed. The tensile stress is used to offset the horizontal amplitude of the SAW, keeping the fatigue cracks in an open state and increasing the attenuation coefficient of SAW. The attenuation coefficient measurement experiment shows that this method is feasible. [ABSTRACT FROM AUTHOR]

In this present work, a damage-coupled cyclic plasticity model has been developed for more accurate ratcheting–fatigue life estimation under strain and stress controlled ratcheting. Ratcheting–fatigue damage behavior under uniaxial multistep strain-controlled ratcheting shows that the incremental mean ratcheting strain deteriorates the elastic slopes cycle by cycle, by means of ratcheting damage. Severe ratcheting strain accumulation rate has been observed in tertiary region under uniaxial stress controlled ratcheting. The proposed damage-coupled model has been constructed which incorporates both fatigue damage and damaging effect of the accumulated mean plastic strain. The proposed model incorporates a critical fatigue damage parameter which can predict effects of early fatigue crack nucleation due to combined ratcheting and fatigue damages. The performance of the proposed damage-coupled model has been investigated in the present study based on the critical fatigue damage parameter. The proposed model is calibrated on experimental data of SA333 Gr. 6 carbon steel and SA508 Gr. 3 steel. The proposed formulations have been applied in user material subroutine UMAT of finite element software, ABAQUS. The proposed model has been validated by comparing predicted ratcheting behavior with experiments for the two different steels. All the predicted number of cycles to failure are located within 0.5 times error band. The proposed damage-coupled model has demonstrated excellent capabilities of predicting ratcheting–fatigue life under cyclic loading with ratcheting damage. [ABSTRACT FROM AUTHOR]

Compressive cyclic loads induce a progressive failure in rock materials, and the long-term stability can not be guaranteed by the strength under monotonic load. To this end, the present study aims at establishing an elastoplastic fractional fatigue damage model for predicting the accumulative deformation of rock materials in a unified framework. A fractional-order plastic flow rule is introduced to describe volume transformation of rock sample from compression to expansion, eliminating the need for plastic potential functions. And a hardening function with an equivalent plastic shear strain is adopted. Concerning the fatigue effects, the progressive deterioration of material due to cyclic loads is intricately linked to microstructural degradation, depicted by a convolution law. In the context of creep deformation, loading cycle serves as an equivalent time measure, connecting the plastic deformation with the fatigue damage. In order to verify the accuracy, the proposed model is numerically implemented by a returning mapping procedure simulate the mechanical responses of three types of rocks in both uniaxial and triaxial cyclic tests. Comparative analysis with associated fatigue model is also provided to evaluate the accumulative deformation and damage evolution of concerned rocks. • A fractional-order fatigue damage model for predicting the accumulative deformation of rocks is established. • The continuous progression due to cyclic damage is linked to microstructure degradation by a convolution law. • The model is numerically implemented by a returning mapping procedure considering the plastic and damage effects. • The accuracy is validated by comparison with experimental data of different types of rocks in cyclic tests. [ABSTRACT FROM AUTHOR]

To ensure the safe operation of equipment, it is necessary to conduct health monitoring and life assessment for key steel structures susceptible to damage. Firstly, nonlinear ultrasonic guided waves, which offer high detection efficiency and sensitivity to micro-damage, are used for both off-line and on-line nonlinear detection methods to assess the fatigue damage of Q460 high-strength steel. The relationship between nonlinear ultrasonic parameters and fatigue life curve is established. Secondly, a fatigue life evaluation method for Q460 high-strength steel is established based on the relationship curve between nonlinear ultrasonic parameters and fatigue life. Both off-line and on-line experimental results show that the nonlinear ultrasonic parameter increase first and then decrease with the fatigue life, and the peak value appears when the fatigue life is near 60%. [ABSTRACT FROM AUTHOR]

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]

Despite ensuring the integrity of bogie frames for railway vehicles via nondestructive inspections during periodic maintenance, the possibility of fatigue cracks occurring at locations other than the predetermined inspection points cannot be dismissed. Therefore, fatigue cracks can be prevented more efficiently by assessing the overall degree of fatigue damage to the entire bogie frame and determining the results via nondestructive inspections. In this study, dynamic stresses in the bogie frame during running were estimated via finite element dynamic analysis by using the axle box acceleration as input, and the degree of fatigue damage and life were calculated from the waveform of the estimated stresses. Furthermore, we developed a bogie frame fatigue prediction system based on a high‐speed and high‐precision stress calculation method. The developed system visualized the overall relative life. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The traditional finite element method (FEM) has limitations in accurately modeling crack propagation. Peridynamics, a nonlocal extension of the classical continuum theory, provides an alternative approach to remedy the limitations of the FEM but with a higher computational cost. In this paper, a peridynamic bond-based fatigue damage model is developed and incorporated into a commercial finite-element software (ABAQUS 2017) via user subroutines. Model-predicted results including the crack path spatial position and the damage accumulation rate were validated against empirical data. The predicted crack growth as a function of loading cycle and crack trajectory showed good agreement with the experimental data over 200,000 loading cycles. Therefore, the integration of the peridynamic bond-based fatigue damage model into existing FEM software provides an economical means to simulate complex fracture behaviors, such as crack growth, in a compact tension specimen examined in this paper. [ABSTRACT FROM AUTHOR]

Concrete linings containing cold joint defects may crack or detach under the aerodynamic fatigue loading generated by high-speed train operation, which posing a serious threat to the normal operation of high-speed trains. However, there is currently no simulation method specifically for fatigue damage of concrete linings containing cold joints. Based on the Roe-Siegmund cycle cohesive force model, a cohesive force fatigue damage elements were developed. A large dataset was constructed through numerical simulation software to build a BP neural network for back-calculated parameter of cohesive force fatigue damage elements. By combining experimental data, fatigue damage parameters corresponding to different pouring interval cold joints were back-calculated. These back-calculated parameters were then incorporated into the numerical model to compare simulation results with experimental results to validate the applicability of cohesive force fatigue damage elements and back propagation neural networks (BP neural network). The research results show that the difference between the fatigue life and fracture process calculated by numerical simulation and experimental data is small, verifying the applicability of the method proposed in this paper. The pouring interval directly affects the initial strength of the cold joint interface and the starting conditions of fatigue damage. The possibility of fatigue damage and fracture of concrete components containing cold joints increases with the increase of pouring interval, while the variability of fatigue life decreases with the increase of pouring interval. Interface strength and thickness are the main factors affecting the possibility of fatigue damage occurrence and the variability of fatigue life. The research results can be used to analyze the damage and cracking status of concrete linings containing cold joints under aerodynamic fatigue loading. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effects of soil penetration resistance, tillage depth, and operating speeds on the deformation and fatigue of the subsoiling shovel based on the real-time measurement of tractor-operating conditions data. Various types of sensors, such as force, displacement, and angle, were integrated. The software and hardware architectures of the monitoring system were designed to develop a field operation condition parameter monitoring system, which can measure the tractor's traction force of the lower tie-bar, the real-time speed, the latitude and longitude, tillage depth, and the strain of the subsoiling shovel and other condition parameters in real-time. The time domain extrapolation method was used to process the measured data to obtain the load spectrum. The linear damage accumulation theory was used to calculate the load damage of the subsoiling shovel. The magnitude of the damage value was used to characterize the severity of the operation. The signal acquisition test and typical parameter test were conducted for the monitoring system, and the test results showed that the reliability and accuracy of the monitoring system met the requirements. The subsoiling operation test of the system was carried out, which mainly included two kinds of soil penetration resistances (1750 kPa and 2750 kPa), three kinds of tillage depth (250 mm, 300 mm, and 350 mm), and three kinds of operation speed (4 km/h low speed, 6 km/h medium speed, and 8 km/h high speed), totaling 18 kinds of test conditions. Eventually, the effects of changes in working condition parameters of the subsoiling operation on the overall damage of subsoiling shovels and the differences in damage occurring between the front and rear rows of subsoiling shovels under the same test conditions were analyzed. The test results show that under the same soil penetration resistance, the overall damage sustained by the subsoiling shovels increases regardless of the increase in the tillage depth or operating speed. In particular, the increase in the tillage depth increased the severity of subsoiling shovel damage by 19.73%, which was higher than the 17.48% increase due to soil penetration resistance and the 13.07% increase due to the operating speed. It should be noted that the front subsoiling shovels consistently sustained more damage than the rear, and the difference was able to reach 16.86%. This paper may provide useful information for subsoiling operations, i.e., the operational efficiency and the damage level of subsoiling shovels should be considered. [ABSTRACT FROM AUTHOR]

Aviation aircraft will be subjected to a large number of complex random vibration loads during service， and its structure is prone to vibration fatigue，which leads to damage or even failure，which can cause serious losses. The stress intensity factor（SIF）solution method for cracked beams under random vibration loading is investigated，and a time-domain method based on Hudson's theory is proposed to estimate the vibration fatigue crack growth life by combining with the Paris formula. The theoretical analysis and vibration fatigue test are conducted on a typical cantilever beam as an object. The results show that the life prediction results of the proposed time-domain method based on the Hudson's theory is better than that of the experimental estimation results，which can verify that the method can effectively describe the random vibration crack growth behavior.

Floating ice loading is a severe natural hazard for offshore wind turbines (OWTs) operating in cold sea regions. The long-term ice-induced vibration resulting from winter drift ice presents a significant threat to the fatigue reliability of OWTs. Machine learning not only exhibits robust data-driven capabilities but also efficiently handles complex relationships among multiple factors. Through effective learning and utilization of diverse features, a comprehensive assessment of the fatigue reliability of structures becomes achievable, consequently resulting in increased efficiency, accuracy, and adaptability of the assessment. This study conducts ice-induced vibration simulations on a 5-MW monopile OWT. Employing orthogonal experimental methods, the study investigates the influence of three critical ice parameters, i.e., ice thickness, ice velocity, and ice crushing strength, on the fatigue damage caused by ice loading on OWTs. Additionally, it explores the effects of ice loading exceedance probability on extreme fatigue damage values of OWTs under combined ice and wind loadings. Furthermore, a surrogate model based on support vector machine (SVM) is developed to effectively capture the intricate mapping relationship between fatigue damage and various random environmental parameters. By conducting a comprehensive evaluation that considers the probabilistic characteristics of ice loading, wind loading, and the S-N curve, this study assesses the fatigue reliability under combined ice and wind. Moreover, this study analyzes the impact of operational duration during winter drift ice on the fatigue reliability index of OWTs. The findings of this study can provide a theoretical basis for devising operational strategies for OWTs operating in icy sea regions. [ABSTRACT FROM AUTHOR]

Abstract Recycled aggregate (RA), as a backfill subgrade material, has strong reproducibility and environmental protection, which cannot only effectively reduce resource consumption and environmental pollution but also achieve recycling of resources. Therefore, a study on the bending fatigue performance of RA backfill subgrade is proposed. Based on linear elastic state, softening state, and damage accumulation state, the variation law of bending fatigue damage variables is analyzed, and the stiffness of RA under cyclic load is calculated. According to the correlation between fatigue damage corresponding to two different load links and the constitutive relationship of RA, the identification results of bending fatigue damage state based on RA backfilling subgrade is obtained. The advantages of the fatigue damage model of RA are analyzed, and the fatigue life equation is established based on the damage evolution equation. Strain, stiffness modulus, asphalt saturation, and asphalt mixture adjustment coefficient are selected as model parameters to establish the fatigue damage model of RA. The flexural bearing capacity of the double-reinforced rectangular section is calculated, and the flexural fatigue performance of RA backfill subgrade is analyzed. The test results show that the high stress level in this method leads to a sharp decline in the fatigue life of the specimen, and the influence of fatigue damage gradually appears, which is helpful to improve the durability and safety of the subgrade structure. The range of change shows a small range, which is close to the reduction coefficient result, indicating that this method has high reliability in analyzing the bending fatigue performance of RA backfill subgrade.

The influence of post-weld heat treatment (PWHT) and fatigue damage on the hydrogen embrittlement sensitivity of X80 steel welded joints, obtained using flux-cored arc welding method, was investigated in the study. Compared to the as-welded specimens, the sensitivity of hydrogen embrittlement after PWHT was decreased. However, the coupling effect of PWHT and fatigue damage improved significantly the HE sensitivity. Furthermore, the fracture site of the PWHT + pre-fatigue specimens with hydrogen-charged was transferred to the weld metal, and the fracture was characterized by intergranular fracture, quasi-cleavage (QC) and shallow dimples ductile fracture. The increase of the hydrogen content might be attributed to the evolutions of dislocation and the proportion of high-angle grain boundary caused by fatigue damage. Meanwhile, the size of QC for the hydrogen-charged welded joints was related to the degree of fatigue damage, hydrogen content and microstructure strength.

The results of experimental research involving nine one-way slabs are detailed in this report. The objective was to investigate the impact of different parameters on the structural performance of these slabs in their absence and with strengthening. Externally bonded CFRP sheets strengthened six of the nine slabs; the three remaining slabs served as control specimens. Before subjecting the specimens to monotonic loading, pre-fatigue damage of 50% and 70% repeated loading was induced. An exhaustive assessment was conducted on each slab, in which it was compared to its control slab. Several crucial elements were incorporated into the evaluation, including the ultimate load capacity, the reason for failure, crack patterns, and load-deflection curves. Examining these metrics was intended to provide insight into the efficacy and structural performance of the employed fortification technology. Compared to unenhanced reinforced concrete slabs (control slab), the highest stresses on slabs supported with bonded CFRP sheets are between 20 and 44% better. Compared to the control slab, an almost 70% reduction in deflection was observed. The flexural performance of compromised reinforced concrete slabs repaired with this technology can be brought up to date and enhanced.

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

In the serviced components of a 7075 aluminum alloy, the propagation of fatigue crack can be retarded because of the overload effect; however, the corresponding retardation mechanisms are complex. To provide further insights into the retardation mechanisms of 7075 aluminum alloys, this study addresses the crack tip damage response of a cracked 7075 aluminum alloy under an overload effect. Based on the dual-scale modeling approach and the damage-coupled crystal plasticity model, the effect of the microstructure of a 7075 aluminum alloy on the damage behavior ahead of the crack tip under an overload was studied. The factors affecting fatigue damage accumulation ahead of the crack tip, such as dislocation density, the variation in the activities of slip systems, and the orientation effect of the nearest neighbor grains, are described. The results show that for the 7075 aluminum alloy, the compressive residual stress induced by the overload effect not only decreases the number of activated slip systems, but also lowers the rate of increase in dislocation density. This causes a decrease in fatigue damage accumulation during deformation. Moreover, the overload effect decreases the slip system activity as well as the resultant plastic slip; however, the decrease in plastic slip varies with the grain orientation, indicating that the overload effect depends on the grain orientation. It can also be found that both the damage strain energy release rate and lattice strain are influenced by the orientation of the nearest neighbor grains, which can eventually affect the overload effect. These findings contribute to understanding the retardation mechanisms from a microscopic perspective and provide guidance on improving the material design of a 7075 aluminum alloy to some extent. [ABSTRACT FROM AUTHOR]

The cyclic loading generated by injection and production operations in underground gas storage facilities can lead to fatigue damage to cement sheaths and compromise the integrity of wellbores. To investigate the influence of cyclic loading on the fatigue damage of well cement, uniaxial and triaxial loading tests were conducted at different temperatures, with maximum cyclic loading intensity ranging from 60% to 90% of the ultimate strength. Test results indicate that the compressive strength and elastic modulus of well cement subjected to monotonic loading under high-temperature and high-pressure (HTHP) testing conditions were 14–21% lower than those obtained under ambient testing conditions. The stress–strain curve exhibits stress–strain hysteresis loops during cyclic loading tests, and the plastic deformation capacity is enhanced at HTHP conditions. Notably, a higher intensity of cyclic loading results in more significant plastic strain in oil-well cement, leading to the conversion of more input energy into dissipative energy. Furthermore, the secant modulus of well cement decreased with cycle number, which is especially significant under ambient test conditions with high loading intensity. Within 20 cycles of cyclic loading tests, only the sample tested at a loading intensity of 90% ultimate strength under an ambient environment failed. For samples that remained intact after 20 cycles of cyclic loading, the compressive strength and stress–strain behavior were similar to those obtained before cyclic loading. Only a slight decrease in the elastic modulus is observed in samples cycled with high loading intensity. Overall, oil-well cement has a longer fatigue life when subjected to HTHP testing conditions compared to that tested under ambient conditions. The fatigue life of well cement increases significantly with a decrease in loading intensity and can be predicted based on the plastic strain evolution rate. [ABSTRACT FROM AUTHOR]

Integrated gate commutated thyristors (IGCTs) are critical components in high-voltage, high-current, and high-power conversion systems, particularly in offshore wind energy systems. However, the working environment of offshore wind energy conversion systems is extremely harsh. In this article, we propose an active damage control approach aiming at enhancing the reliability of the conversion system. By employing electro-thermal modeling for the equipment of the offshore wind energy conversion system, the junction temperature and fatigue damage of IGCT are simulated during the operation process. Using the improved model predictive current control (MPCC) method, active damage control effectively regulates the switching frequency of IGCT. IGCTs are symmetrically distributed on each leg of the converter, so the lifespan of the two IGCTs on each leg is also considered to be similar. This method balances the life of the IGCTs on the three legs of the converter and optimizes their utilization to the maximum extent. These measures effectively enhance the reliability of the conversion system and lower the operation and maintenance cost of high-power IGCT converters. The effectiveness of the proposed method is validated by co-simulation results by ANSYS and MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

Since a multiaxial loading environment may lead to the fatigue failure of structures, establishing a reliable fatigue model to predict the multiaxial fatigue lives of structures has always been a concern of engineers. This study proposes a new multiaxial fatigue theoretical model (WYT model) based on the critical plane theory, which takes the plane of the maximum shear strain amplitude as the critical plane and considers the effects of shear stress and normal stress on fatigue damage. Moreover, a backpropagation neural network (BPNN) model for multiaxial fatigue life prediction with the shear strain amplitude, normal strain amplitude, mean shear stress, and mean normal stress on the same critical plane as input parameters and fatigue life as the output variable is established. Finally, the WYT model and the BPNN model are compared with two existing multiaxial fatigue models to evaluate the life prediction effects of different models for S45C and 7075-T651 under constant-amplitude and variable-amplitude multiaxial loadings. The calculation results show that the WYT model is feasible, and the BPNN model is more accurate in predicting the fatigue lives of specimens than other multiaxial fatigue theoretical models. [ABSTRACT FROM AUTHOR]

Recycled aggregate (RA), as a backfill subgrade material, has strong reproducibility and environmental protection, which cannot only effectively reduce resource consumption and environmental pollution but also achieve recycling of resources. Therefore, a study on the bending fatigue performance of RA backfill subgrade is proposed. Based on linear elastic state, softening state, and damage accumulation state, the variation law of bending fatigue damage variables is analyzed, and the stiffness of RA under cyclic load is calculated. According to the correlation between fatigue damage corresponding to two different load links and the constitutive relationship of RA, the identification results of bending fatigue damage state based on RA backfilling subgrade is obtained. The advantages of the fatigue damage model of RA are analyzed, and the fatigue life equation is established based on the damage evolution equation. Strain, stiffness modulus, asphalt saturation, and asphalt mixture adjustment coefficient are selected as model parameters to establish the fatigue damage model of RA. The flexural bearing capacity of the double-reinforced rectangular section is calculated, and the flexural fatigue performance of RA backfill subgrade is analyzed. The test results show that the high stress level in this method leads to a sharp decline in the fatigue life of the specimen, and the influence of fatigue damage gradually appears, which is helpful to improve the durability and safety of the subgrade structure. The range of change shows a small range, which is close to the reduction coefficient result, indicating that this method has high reliability in analyzing the bending fatigue performance of RA backfill subgrade. [ABSTRACT FROM AUTHOR]

The 16MnCr5 alloy steel samples are evaluated in a normalized condition and put through low cycle fatigue (LCF) under constant amplitude strains of εa = 0.2%, 0.25%, 0.4%, and 0.6%. Mechanical properties are reported based on the LCF results. Fatigue damage is checked in specimens that have reached 80% of their nominal fatigue life by two methods that are different from traditional electronic microscopy: measuring the roughness of the surface and looking at it through full‐field optical microscopy. In addition, the electric resistivity is determined for the test specimens. It presents an increment from the blank value of 6.5 × 10−8 Ωm (free of fatigue damage) to 1.25 × 10−7 Ωm for the fatigue test specimen (εa = 0.6%). Finally, X‐ray diffraction patterns are determined for analyzing the residual equivalent strain at the microscale for the fatigued samples. The residual equivalent strain exhibits a trend toward increasing. For instance, it increases from 18.5 (blank value) to 34.0 με for the fatigue test specimen with εa = 0.6%. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Superload vehicles (SLs) are typically defined as vehicles having a gross vehicle weight (GVW) greater than 890 kN. SLs often consist of unique axle configurations that may cause significant damage to pavements. Research has been mainly limited to SLs on asphalt pavements, therefore the effect of SLs on concrete pavements is not well established. In this study, fatigue stresses in concrete pavements were quantified for a database of pavement structures and SLs to identify critical conditions that contribute to fatigue damage. A series of load pulses were constructed from a database of finite element results to identify conditions and locations within the slab for peak stress development. Tensile stress greatest in thin pavements with a stiff base layer and large positive temperature gradients subjected to tandem axle SLs. Fatigue damage was calculated for the critical cases using several damage models, and significant variation was found between models based on inputs used. [ABSTRACT FROM AUTHOR]

In asphalt pavement structure design, traffic axle loads and pavement layer temperatures are crucial factors affecting fatigue damage calculations. To investigate the differences in fatigue damage calculations caused by different characterizations of traffic axle loads and temperature, fatigue damage calculations were conducted under equivalent standard axle loads (ESALs), axle load spectra (ALS), constant temperatures, and seasonal temperature variations using the field data from an expressway in Shandong Province, China under seven calculation plans. The results indicated: (1) the annual traffic composition is dominated by vehicle Type 9, with a proportion of about 43% in all the vehicle types, and its load level is also high, with a proportion about of 80% in the heavy load interval at all axle types; (2) The ESALs method underestimates the actual fatigue damage incurred in asphalt pavement by 6.04 times, with an accumulated damage of 2.34 × 10−9 (ESALs), 1.69 × 10−8 (ALS), respectively; (3) The fatigue damage results from a single month with consistent temperature showed similar trends, with an accumulated damage of 1.50 × 10−5, 9.07 × 10−5, respectively; (4) The cumulative fatigue damage calculated using the ALS method across the four seasons, respectively, is 6.51, 5.88, 6.42, and 4.60 times that of the fatigue damage calculated using the ESALs method. Although the ratio of fatigue damage between the two characterizations of traffic axle loads remains consistent, which is 6.04, the fatigue damage calculation that accounts for temperature variations can reveal seasonal trends in fatigue damage development. Based on the axle load spectra and considering temperature variations, fatigue damage calculation will be more closely related to the actual service state of asphalt pavement. These research findings provide insights for estimating asphalt pavement fatigue damage to some extent. [ABSTRACT FROM AUTHOR]

As a step toward revolutionizing and optimizing freight transport, autonomous truck platooning technology (i.e., a set of connected heavy-duty trucks traveling closely at specific headway intervals) has been the center of research over last few years. Connected autonomous vehicles (CAV), in the form of truck platooning, can be implemented as a novel contribution to sustainable freight transport with the potential of offering the following synergistic benefits, among others: road safety improvements, enhanced economic prospects, and environmental preservation. In this study, the impacts of fixed-path truck platooning on pavement performance were modeled and numerically quantified using elastic and dynamic-viscoelastic finite-element (FE) methods. Factors including pavement layers' geometrical and mechanical characteristics, traffic characteristics and counts, axle configuration, and seasonal temperature are analyzed to address the platooning effect in this study. Yet, other possible wandering patterns between the fixed-path and normally distributed wandering patterns, as well as the effects of speed variations, driving behaviors, and tire pressure (i.e., variation in dynamic loading), can be further studied. The mechanical responses (namely displacements, strains, and stresses) obtained from the FE modeling were used to predict the effects of truck platooning on the pavement performance due to limited wandering (lateral movement of truck tires). The FE modeling results indicated that the channeling effects (i.e., limited tire wandering) of truck platooning have negative effects on the pavement performance with respect to decay in fatigue life and increase in permanent deformation. With fixed-path platooning, the fatigue life is reduced in the range of 13.9% to 34.5% in terms of the number of load cycles over the 20-year design life. The permanent deformation (rutting) value over a fixed period is increased by a factor of 1.2 to 2.9. [ABSTRACT FROM AUTHOR]

This paper presents a multiscale progressive fatigue damage model to predict the fatigue life of composite laminates. The multi-level damage model was employed considering the interfacial debonding effect, and effective material properties were calculated through homogenization. Damage variables and damage slopes were defined at the constituent level, and fatigue damage parameters were obtained using the residual stiffness data with the chaotic firefly algorithm. The model was implemented into ABAQUS, then validated with flat-bar and pin-loaded specimens of AS4/3501-6 composite. The numerical results corresponded well with the experimental data and showed the ability to capture the failure propagation of composite laminates. [ABSTRACT FROM AUTHOR]

The wear phenomenon that occurs on the blades during operation has a significant impact on the fatigue life of the blades. To address the issue of fatigue life assessment for turbine runner blades subjected to increased dynamic stress due to sediment wear, taking a specific high-head hydropower unit's mixed-flow turbine as the research subject, a hydraulic model of the turbine was established. The wear zones of the runner blades are determined based on the distribution of the flow field's velocity and the sediment volume fraction. According to the wear rate formula for runner blade material, the amount of wear on the blades is determined, and the dynamic stress data for the dangerous areas of the blades under different degrees of wear are calculated using a unidirectional fluid–structure coupling method. The load spectrum of the time–stress history data for the dangerous area at different levels of wear was compiled using the rain-flow counting statistical method. The operating time ratios for the flood season and the non-flood season are combined. Based on the fatigue cumulative damage theory, the total fatigue damage at the maximum stress part of the runner blade was calculated for different stages of wear, providing a reference for the life calculation of mixed-flow hydraulic turbines. [ABSTRACT FROM AUTHOR]

Vibration protection is a reliable mean for safe operation of rotating machinery. In recent years, vibration protection of pumped storage unit gets more and more complicated, resulting in an increasing risk of vibration protection system failure. Focusing on vibration characteristics of pumped-storage units, the inverse-time vibration protection method for of pumped-storage unit vibration was proposed based on material fatigue damage curve and linear damage accumulation theory. Difficulties of determining damage level were provided on applying damage accumulation method to vibration protection. Simplified inverse-time protection method for vibration of pumped-storage unit was proposed, and research showed that the inverse-time vibration protection threshold should be set according to vibration accumulation that avoids all unit transient processes, the reliability coefficient can be determined from 1.5 to 2.0, the refresh periods of unit vibration characteristic values do not affect the cumulative calculation results, and the inverse-time vibration protection has characteristic of self-returning. The vibration protection method based on inverse-time has the advantages of reliable principle, simple logic, and easy implementation. It has the characteristics of reliability, selectivity, sensitivity, and rapidity as relay protection in electric engineering. It solves the problem of dual parameter coordination in the traditional protection strategy with fixed threshold and fixed time delay. The method can be extended to the vibration protection of other types of rotating machinery.

Objective It is aimed to investigate the fatigue damage of an antenna bracket structure installed at urban rail transit vehicle bogie frame end under random vibration excitation, and improvement measures are proposed. Method Finite element modeling of the antenna bracket system is conducted using finite element analysis software. Modal analysis of the structure is performed, and the on-site measured vibration ASD (acceleration spectral density) from the track is used as the load excitation instead of the standard spectrum. A random vibration simulation of the antenna bracket is conducted using fatigue analysis software nCode to obtain the bracket fatigue damage result. Improvement measures are proposed for the fatigue weak points of the bracket, and the effectiveness of the improvement measures is verified. Result & Conclusion Simulation results reveal that the fatigue weak points of this structure are at the roots of the reinforcement plates on bracket both sides, with a maximum total damage of 15.58, failing to meet application requirements. The improvement measures involve locally thickened plate roots on bracket both sides and adding support ribs on the sides. After implementing these measures, the fatigue damage value of the bracket significantly decreased, with a maximum total damage of 0.02, meeting application requirements, thereby verifying the effectiveness of the improvement scheme.

Researchers have been widely attracted by the lining block falling accident of Fukuoka tunnel in Japan, with the main reason that the cold joints have cause the lining blocks falling. This article constructs a numerical calculation model of the Fukuoka tunnel lining, which is based on cohesive fatigue damage units. It analyzes the damage and deformation of lining blocks with cold joints under aerodynamic fatigue loads. The study also explores the extents of aerodynamic load amplitude, pouring intervals, and block positioning on the damage to cold joint units. The study shows that this method is suitable for analyzing the damage process of lining blocks with cold joints under aerodynamic fatigue loads. The discrepancy between the predicted detachment time (40 years) and the actual time (25 years) is attributed to unclear design parameters, the exclusion of train vibration loads, and the deterioration of concrete performance. The timing of cohesive unit damage is accelerated with increasing aerodynamic load amplitude and pouring intervals, while it is delayed when the block position is lower. The greater the normal force on the lining block with cold joints, the more likely the cold joint interface elements are to be damaged.

The backfill area of tunnel projects may deform or collapse due to the cyclic disturbance of groundwater and train loads. Hence, the anti-deformation and crack resistance performance of backfill materials under cyclic disturbance is critical to engineering safety. In this paper, concrete was produced by mixing 0.85 mm, 1–3 mm and 3–6 mm rubber particles instead of 10% sand, and tested to discuss the effect of rubber particle size on the deterioration of concrete material properties (compressive characteristics and energy dissipation) after bearing cyclic loading. The stress–strain curve and various parameters obtained through the uniaxial compression test and cyclic load test were used to explore the optimal grain size that can be applied to the tunnel engineering backfill area, and numerical simulation was adopted to calculate the deformation of the surrounding rock and the structural stress of different backfill materials. Research shows that the increase in particle size lessens the compressive strength, deformation resistance and cracking resistance of specimens, but after the cyclic loading test, the concrete material deterioration analysis indicates that rubber concrete has lesser and more stable losses compared to ordinary concrete, so the optimum rubber particle size is 0.85 mm. Numerical calculations show that RC-1 reduces the arch top displacement by 0.4 mm, increases the arch bottom displacement by 0.6 mm and increases the maximum principal stress by 11.5% compared to OC. Therefore, rubber concrete can ensure the strength and stability requirements of tunnel structures, which can provide a reference for similar projects. [ABSTRACT FROM AUTHOR]

In this study, a series of impact-induced rockburst experiments were carried out by applying multilevel cyclic stresses on a cubic sandstone with a circular opening. Information on rockburst evolution was monitored using video and AE techniques together. Experimental results show that the opening in the sandstone sample was observed to undergo rock grain ejection, rock spalling and buckling in sequence. AE activity under the lower cyclic stress level followed the Kaiser's effect, while the Felicity's effect of AE was also involved at the higher cyclic stress level. Multi-axial cyclic loading can shorten the fatigue life and fatigue strength of the sandstone sample. However, the multi-axial cyclic loading can obviously reduce the AE hits and its energy rate, in which case the proportion of the AE single with low frequency is less than those under the uni-axial cyclic compression. It is also found that the failure zone in the sandstone is characterized by V-shaped notch. The depth of the failure zone is reduced sequentially under uni-axial, bi-axial, and tri-axial cyclic compression, respectively. In contrast, the extent angle of the failure zone will increase. According to the observed profiles of the failure zone, the changes of friction angle of the sandstone are interpreted by the Mohr–Coulomb strength criterion, as well as movement of the failure line due to the fatigue damage. These findings can provide insights into the study of rock failure mechanisms under various dynamic disturbances. Highlights: Impact-induced rockburst in laboratory was simulated by applying uniaxial, bi-axial, and tri-axial cyclic loadings, respectively to cubic sandstone samples with an opening. The opening in the sandstone sample was observed to undergo rock grain ejection, rock spalling and buckling in sequence. AE activity under the lower cyclic stress level can be explained by the Kaiser's effect, while the Felicity's effect of AE was also involved at the higher cyclic stress level. Failure zone around the opening in the sandstone was characterized by V-shaped notch, whose depth of the failure zone was reduced sequentially under uni-axial, bi-axial, and tri-axial cyclic compression. [ABSTRACT FROM AUTHOR]

The current renewable energy market forces hydraulic turbines to operate for longer periods of time at off-design and transient conditions. Their life expectancy is then decreased due to the wear provoked by flow instabilities and stochastic flow excitations. This study presents an experimental investigation into the fatigue damage induced on the runner blades of a Kaplan turbine model when working at speed-no-load (SNL), part load (PL) and during ramps of load. The unit was equipped with on-board sensors on the blades and the shaft as well as with off-board sensors installed on the supporting structure and the draft tube cone. The results reveal that operation at SNL induces more fatigue damage on the runner blades than at PL. The damage is then mainly induced by stochastic flow excitations at SNL and by the rotating mode of the rotating vortex rope (RVR) at PL. The ramps of load, when crossing each operating condition, cause levels of damage similar to those found in stationary operation. Finally, it was proved that the blade fatigue damage can be estimated from on-board shaft measurements at any condition. However, the blade fatigue damage can only be estimated using off-board measurements when the RVR is fully developed at PL. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]