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To prevent overheating of the airframe, an aero-engine is often designed to play a role in shielding heat radiation heat shield. Since the thermal protection system used in this paper is active, it is subject to a cold gas pressure load on the outside and a thermal radiation load from the combustion chamber on the inside. Therefore, the working environment of the heat shield is very harsh. Taking the heat shield of an aero-engine as the research object, the finite element method (FEM) is used to analyze the thermal-mechanical coupling (TMC) of the actual working process of the heat shield, and the mechanical quantities such as the thermal stresses and mechanical stresses are comprehensively analyzed. According to the finite element simulation results, two stress concentrations are obtained near the connecting lug, and the stress concentrations are set as the initial crack insertion locations. Using the theory related to linear elastic fracture mechanics (LEFM) and the Forman-Newman-de Koning (FNK) model, the fatigue crack propagation life (FCPL) and its law of the merged double cracks of the engine heat shield are calculated. The results show that the FCPL of the heat shield decreases nonlinearly and the critical crack length decreases linearly under different working conditions. This law applies not only to single cracks but also to merged double cracks. In terms of FCPL, the merged double cracks are lower than the single crack with a maximum life reduction rate of 70.9%. [ABSTRACT FROM AUTHOR]

Our study delves into analyzing fatigue damage in notched structures, an essential field in structural mechanics. We aim to understand how geometric and dimensional variations in the notches affect fatigue damage under different modes and amplitudes of cyclic loading, focussing on the behavior of steel. Our research methodology integrates experimental and numerical approaches. Experimental validation encompasses material properties, mesh selection, and boundary conditions. The finite element method is tailored to address steel's elastoplastic behavior, employing calibrated parameters for kinematic and isotropic cyclic hardening models within the numerical realm. Specific findings elucidate the cyclic response of notched structures, tracking damage progression to critical thresholds, including the number of cycles to failure (Nf) and the critical crack length (Lc). Hysteresis curves vividly depict stress–strain relationships, offering insight into material behavior under cyclic loading. Implications span engineering domains, focussing on reliability and durability in the aerospace, automotive, and civil engineering sectors. Future directions include real-world applications and advanced techniques such as the Extended Finite Element Method (XFEM). In conclusion, this research enriches our understanding of fatigue damage analysis in notched structures, poised to impact safety and robust engineering design. [ABSTRACT FROM AUTHOR]

The article explores the in-depth residual stress evolution of a surface-rolled titanium alloy subjected to fretting fatigue. The study aims to provide data for establishing an accurate fretting fatigue life prediction model by examining the surface residual stress distribution at different stages of fretting fatigue loading. The research highlights the complex stress distribution at the fretting wear zone and the impact of fretting wear on the evolution of residual stress, emphasizing the role of contact stress and fatigue stress in this process. The study suggests practical engineering approaches to mitigate residual stress release during fretting fatigue loading, such as using lubricants and employing techniques like induction hardening for surface strengthening. [Extracted from the article]

Translation abstract Repair welding on bridges in serviceOn steel bridges, fatigue damage repeatedly occurs in weld seams as a result of increasing traffic loads as well as design and construction defects. To carry out the repair works, the bridge must be closed to bridge traffic during re‐welding in order to prevent the movement on the crack flanks. According to the current state of the art, welding works during traffic is not allowed, because until now there has been insufficient knowledge about achievable seam qualities and fatigue strengths for welding seams in service. The aim is to provide reliable methods that allow welding work on steel structures during traffic or cyclic loading. As a basis, measurements were carried out on a representative steel bridge in order to derive realistic gap opening parameters for welding tests under cyclic loading. The description of the crack behaviour and force redistribution during welding in service presents a particular challenge in the laboratory. To quantify the influence of different welding boundary conditions, the experimental investigations were carried out based on displacement and force control. In both limit cases, standard‐compliant weld seam qualities and fatigue strengths were realised, which demonstrate the technical possibility of welding in service under defined boundary conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT It remains inconclusive about the stability and optimal fixation scheme of screw internal fixation for lateral malleolus oblique fractures in clinical practice. In this study, the effects of different screw internal fixation methods on the biomechanics of lateral malleolus oblique fractures were investigated. These efforts are expected to lay a theoretical foundation for the selection of internal fixation methods and rehabilitation training regimens in the treatment of lateral malleolus fractures. A healthy ankle joint model and a lateral malleolus fracture internal fixation model were established based on CT data with the aid of some software. Besides, the effects of screw internal fixation modalities on the fracture displacement of fibula fractures, fibula Von Mises stress, and screw Von Mises stress under different physiological conditions and loading conditions were investigated using finite element methods (FEMs) and in vitro physical experiments. The double screw vertical fibular axis internal fixation approach had the lowest fracture displacement of fibula fractures and screw Von Mises stress values; while the double screw vertical fracture line internal fixation approach had the lowest fibula Von Mises stress values. Under different physiological conditions, the magnitude of the peak Von Mises stress of the fibula and screw was ranked as plantarflexion 20° > plantarflexion 10° > neutral position > dorsiflexion 10° > dorsiflexion 20°; and the magnitude of the peak displacement of the fibula fracture breaks was ranked as plantarflexion 20° > plantarflexion 10° > neutral position > dorsiflexion 20° > dorsiflexion 10°. The results of in vitro physical experiments and finite element analyses were in good agreement, which validated the validity of finite element analyses. The vertical fracture line screw implantation method displays a better load‐sharing ability; while the vertical fibular axis screw implantation method exhibits a better ability to prevent axial shortening of the fibula and also reduces the risk of screw fatigue damage. Overall, the double screw achieves better therapeutic effects than the single screw. Given that the ankle joint has high stability in the dorsiflexion position, it is recommended to prioritize dorsiflexion rehabilitation training, rather than dorsiflexion and plantarflexion rehabilitation training with too large angles, in the treatment of lateral malleolus fractures. [ABSTRACT FROM AUTHOR]

A bottom–up multi-scale performance transfer chain is developed to ascertain the gradual change in the law of vibration characteristics in spatial steel truss structures under fatigue loading. This chain derives the interrelationship between vibration characteristics and the performance of each structural component. Based on the evolution characteristics of the performance model of the member scale in the transfer chain, a new analytical model of the shape function is established. Building on these foundations, a refined model was formulated to depict the gradual change of vibration characteristics in spatial steel truss systems under fatigue loading. This model integrates the cumulative damage rule, the structural residual performance rule, the finite element method and other pertinent theories. The gradual change in vibration characteristics of a steel truss girder bridge subjected to train loads was analyzed using a self-developed three-dimensional finite element analysis framework tailored explicitly for assessing gradual change issues in spatial steel truss structures. The analysis results indicate that the effective residual cross-sectional area and the structural frequency continuously decline as the service time increases. This comprehensive study advances the understanding of fatigue-induced changes in spatial steel truss structures. It offers analytical perspectives for predicting and mitigating the long-term impacts of dynamic loads on large-scale infrastructural components. [ABSTRACT FROM AUTHOR]

ABSTRACT Under vibration conditions, continuous alternating loads cause fatigue damage to structures, affecting their stability, durability, and overall safety. In this paper, the additional damping structures with entangled metallic wire material (EMWM) is proposed. Dynamic tests with different loading frequencies and loading amplitudes are carried out to evaluate the energy dissipation and stiffness characteristics of the different structures in terms of energy dissipation, loss factor, and average stiffness. Fatigue tests are conducted, and the fatigue life tests are applied with different loading amplitudes and loading frequencies using displacement control, and the fatigue properties are obtained under different numbers of cyclic loading. The test results are analyzed with respect to the energy dissipation mechanism of EMWM and the characteristics of the additional damping structure. The hysteresis curves under different loading times are identified by parameters, and the fatigue mechanical models are constructed. Comparison between the predicted data of the model and the hysteresis curve data of the test indicates that the model has high accuracy. [ABSTRACT FROM AUTHOR]

Quasi-static monotonic, fatigue pre-crack initiation, and crack propagation tests were initially conducted on composite rock–concrete beams. Experimental results showed that during the fatigue pre-crack initiation, damage accumulated around the pre-crack tip, and its rate strongly depended on the upper fatigue load level Smax and load ratio R. For the studied rock–concrete interface, the crack-mouth-opening displacement corresponding to the initial cracking load of monotonic test (CMODini,m) can be considered as a crack initiation criterion in the fatigue loading. Subsequently, a local stress-based fatigue damage evolution law involving Smax and R was derived based on the concept of energetic equivalence from linear elastic fracture mechanics and continuum damage mechanics. This was followed by the simulation of fatigue pre-crack initiation for composite rock–concrete beam. The good agreement between the experimental and numerical results suggested that the combination of the derived damage evolution law and the CMODini,m-based crack initiation criterion can successfully simulate the fatigue pre-crack initiation of rock–concrete beam. The derived damage evolution law effectively characterized the local fatigue damage featured with microcracking. The numerical analysis of the damage distribution in the damage region around the pre-crack tip showed that Smax greatly affected the rate of fatigue damage evolution, the total damage area, and damage distribution at the time of pre-crack initiation, whilst R primarily affected the rate of fatigue damage evolution and had a minor effect on the final damage results. Using the derived fatigue damage evolution law, the variation in structural stiffness during the initiation of preexisting interfacial cracks can be predicted under specific fatigue loading conditions, providing valuable guidance for load selection during design and operation. Highlights: Rate of damage development during the fatigue pre-crack initiation strongly depended on the upper fatigue load level and load ratio. Crack-mouth-opening displacement corresponding to initial cracking load of monotonic test can be considered as a fatigue crack initiation criterion. A stress-based fatigue damage evolution law was derived to characterize the local fatigue damage. An approach was proposed to predict crack initiation process of rock–concrete interface under fatigue loading below the initial cracking load. [ABSTRACT FROM AUTHOR]

The fatigue damage evolution of rocks subjected to cyclic loading and unloading has always been a hot spot that receives worldwide attention in the field of rock mechanics. Recent studies that rely on advanced nondestructive testing (NDT) techniques enable accurate monitoring and assessment of the dynamic damage in cyclically loaded rocks, and well contribute to revealing the complicated failure mechanism. These works are critical to ensure safe underground tunnelling and mining activities. As a promising NDT technique, the electromechanical impedance method (EMI) has been successfully applied to many aspects in structure health monitoring. In this paper, the EMI method was extended to measuring the rock fatigue damage. Firstly, uniaxial cyclic compression tests with increasing amplitude were performed on three types of cylindrical rock specimens, including sandstone, granite and carbonaceous shale. The varying mechanical properties and energy conversion characteristics were analyzed. In particular, the damage evolution characterized by elastic energy dissipation was determined. Concurrently with cyclic tests, conductance signatures in response to two excitation modes of the surface-bonded piezoelectric transducers were collected, and the spectral localized and overall variations were analyzed. It is discovered that the resonant frequency shift and the statistic metric MAPD within the transverse mode-dominated frequency range could accurately indicate the rock fatigue damage. This research sufficiently confirms the effectiveness and reliability of the EMI method in quantifying the accumulative damage of different rocks under uniaxial cyclic loading and unloading. Highlights: The damage evolution based on energy dissipation of rocks under uniaxial cyclic compression was studied. The localized and overall variations of conductance spectra of PZT transducers were tracked and analyzed. The resonance frequency shift is consistent with the fatigue damage evolution of cyclically loaded rocks. The metric MAPD under the d33-dominated mode serves as an excellent indicator of rock fatigue damage. [ABSTRACT FROM AUTHOR]

In order to study the fatigue failure behaviour and fatigue strength of orthotropic steel deck in an urban rail transit steel bridge, a full-scale test model of the orthotropic steel deck was established based on the main span beam of a cable-stayed bridge for urban rail transit. During the test, the stress values and the cracking condition of the structure were observed to evaluate the fatigue strength. The results show that there is no cracking during 2 million external load cycles; the main tensile stress values of each key test point before and after each cycle exhibit little difference. This shows that there is no obvious redistribution of stress, and the fatigue performance of the model under 2 million external load cycles meets requirements, and has a certain safety reserve. The load amplitude was increased and another 1.5 million cycles were carried out. When the external load cycles to 3.25 million times, cracks appear at the joint of the plate and U-rib. When the external load cycles to 3.5 million times, cracks are found at the symmetrical position of the first crack, and the test is terminated. The paper provides a theoretical and an experimental basis for the same type of bridge. [ABSTRACT FROM AUTHOR]

This paper proposes an equivalent spectrum method to predict the fatigue crack propagation (FCP) life of metallic materials subjected to random loading. To adequately account for the coupling effects between crack propagation and the random response of structures, a coupling analysis model is introduced. The stress intensity factor (SIF) can be estimated based on the power spectral density (PSD) of an equivalent displacement. Random vibration fatigue tests were conducted to evaluate the proposed model on aluminum alloy specimens. Results indicate significant variations in natural frequency with crack length. The predicted results are compared with the experimental values, demonstrating satisfactory prediction accuracy of the proposed coupling analysis model. This model enables the assessment of coupling effects between crack length and random response, facilitating more precise predictions of FCP life in metallic materials and guiding the expanded application of damage tolerance criteria in structural engineering. [ABSTRACT FROM AUTHOR]

The high‐temperature fretting fatigue damage characteristics of dovetail specimens strengthened by nanosecond laser (NL) and nanosecond combined femtosecond laser (F‐NL) were investigated. The results show that the fretting fatigue life of the NL strengthened sample (NL sample) is improved by 211.2% compared to the base metal samples (BM sample). The lifetime of the nanosecond combined femtosecond strengthened sample (F‐NL sample) was increased by 319.6%. It was attributed to the strengthening introducing hardened layers, residual compressive stress field, and high density of dislocations. The combined strengthening process reduces the surface roughness of the NL strengthened surfaces, while the strengthening influence layer is further increased. The fracture morphology shows that the crack source of the strengthened specimen has changed from multi‐source sprouting to single‐source sprouting, and the crack source sprouted on the subsurface. The fatigue strip morphology similarly confirms that a reduction in the crack propagation rate occurs. Highlights: Dovetail specimens were subjected to fretting fatigue testing at 500°C.Composite laser peening reduces surface roughness and stress concentrations.Mechanism of fatigue property enhancement after combined laser peening revealed. [ABSTRACT FROM AUTHOR]

The very high‐cycle fatigue (VHCF) fractographies of high‐strength steel AISI 4340 with tensile strength ranging from 1285 to 2363 MPa fabricated by tempering were systematically observed and quantitatively analyzed. It is found that the fatigue crack initiation sites were gradually transferred from the specimen surface to the interior with increasing the tensile strength or decreasing the stress amplitude. Such phenomenon has become common rule in the high‐cycle fatigue (HCF) or VHCF regimes of high‐strength steels. Based on the fracture mechanics, a simplified transition mechanism for fatigue crack initiation sites is established in terms of the influence of applied stress amplitude and microstructure, which is beneficial to enhance our understanding on the variation of fatigue strength increasing the tensile strength. Highlights: The effects of tempering temperature on fatigue crack initiation are studied.The sites of fatigue crack initiation is counted, and influence mechanism is discussed.A model is proposed to explain the relationship between tensile and fatigue strength. [ABSTRACT FROM AUTHOR]

Purpose: This case study aimed to diagnose the cause(s) of a seasonal, and objectionable odour reported by travellers and drivers in the railway cars of Australian passenger trains. The research questions were to: (1) identify whether significant microbial colonisation was present within the air handling system of trains and causing the odours; to (2) identify other potential sources and; (3) remedial options for addressing the issue. Methods: A mixed-methods, action research design was used adopted. Sections of the heating, ventilation, and air conditioning (HVAC) systems from odour-affected trains were swabbed for bacteria and fungi and examined for evidence of wear, fatigue and damage on-site and off-site. Insulation foam material extracted from the walls of affected trains was also subjected to a chemical assessment following exposure to varying humidity and temperature conditions in a climate simulator. This was accompanied by a qualitative sensory characterisation. Results: Upon exposure to a variety of simulated temperature and humidity combinations to recreate the odour, volatile chemical compounds released from the insulation foam by water were identified as its likely cause. In addition, a range of potentially serious pathogenic and odour-causing microbes were cultured from the HVAC systems, although it is considered unlikely that bacterial colonies were the odour source. Conclusion: The research has implications for the sanitising and maintenance policies for HVAC systems on public transport, especially when operating in humid environments. The sanitary imposition, especially in the wake of COVID-19 may be required to ensure the safety of the travelling public and drivers. [ABSTRACT FROM AUTHOR]

Characterizing the fatigue behavior of cement-stabilized aggregates (CSAs) is essential to semirigid base asphalt pavement design. However, the relevant research is relatively limited and retains significant challenges. Therefore, fatigue tests subjected to multilevel loads were designed, and a mechanical damage evolution rule was proposed to describe the CSA's damage behavior better. Four-point bending fatigue tests were conducted following the designed loading steps composing different cyclic stress levels and frequency combinations. The damage evolution patterns in sequential and disorder loading cases, together with the plastic strain accumulation trends, were analyzed to uncover the factors influencing CSA's damage evolution. It was found that the general damage evolution of CSA exhibited a three-stage pattern, and it was affected by the cyclic stress level, loading sequence, and history of plastic and damage evolution. Remarkably, loading frequency appeared to have a negligible impact. Plastic strain and damage evolution demonstrated congruent evolution trends in most cases; however, they differed in disorderly loading. To address these, a new damage evolution rule was proposed based on the continuum damage mechanics and driven by the equivalent plastic strain rate. The damage dissipation rate was introduced to characterize the impact of effective stress level, and the damage variable and plastic strain path were also included in the proposed rule to reflect the effect of loading or damage history. The comparison results between the fitted and measured damage evolution curves validated the effectiveness in characterizing the fatigue damage behaviors of CSA when subjected to multilevel loads. Furthermore, the proposed damage evolution rule was also employed to model the damage curves of CSA's uniaxial and indirect tensile fatigue tests with single-level loads. The commendable agreement between the fitting and experimental results confirmed the validity of the proposed rule and showed its broad applicability under different fatigue loading forms. [ABSTRACT FROM AUTHOR]

The traditional peridynamic fatigue model is capable of simulating the fatigue behaviors in stable region because of its correlation to the Paris law, which describes the stable evolution of fatigue crack growth rate. Hence, the traditional model exhibits pronounced inaccuracies in the near-threshold and unstable growth regions due to its linear constraint. To address this problem, we proposed a whole-rate-region fatigue crack growth model (WRR model) that incorporates both linear and nonlinear regions. To integrate the effects of fatigue threshold and fracture toughness within this model, the threshold cyclic bond strain and the critical bond strain parameters are introduced. Consequently, the nonlinear evolution of crack growth rates in the near-threshold and unstable growth regions could be characterized by the WRR model. Validation of the WRR model's efficacy and precision is achieved through comparative analysis between simulated fatigue behaviors and experimental data. The fatigue crack propagation behavior under biaxial loading is further analyzed based on the proposed model. Relative to a traditional model, the WRR model provides a more accurate and realistic simulation of crack behaviors. [ABSTRACT FROM AUTHOR]

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]

The present research work assessed the influence of zinc and tin alloying elements on the wear behavior of hydroxyapatite-reinforced magnesium-based composites such as Mg/HA, Mg-Zn/HA and Mg-Sn/HA. These composites were made through the new ultrasonic-assisted squeezing rheo casting method. The SEM analysis reveals the even distribution of HA and formation of MgZn as well as Mg2Sn secondary phases. The microhardness and compression test results showed that the mechanical properties of Mg-Sn/HA composites were better. Wear tests were performed under a simulated body fluid environment with a constant load of 45 N, sliding velocity of 2 m/s and sliding distance of 1000 m. Wear test results revealed that the Mg-Sn/HA sample had a lower wear rate and COF than the other samples. The predominant form of wear was abrasion but there was also evidence of fatigue cracks, oxidation, adhesion and delamination. The improvement in mechanical properties and wear resistance shown by Mg-Sn/HA composites has been attributed to grain size reduction as well as proper dispersion of secondary phases and formation of protective tribolayers between the sliding surfaces. Thus, the 1% Sn alloyed Mg/HA composite can be adopted as a wear-resistant implant in biomedical applications. [ABSTRACT FROM AUTHOR]

To investigate the concrete damage of prefabricated steel spring floating slab tracks (SSFST), a three-slab prefabricated SSFST system was established using the ABAQUS finite element software. Full trainload conditions and fatigue load conditions of a train passage were successively applied to the system. Plastic damage and fatigue damage of the floating slab were simulated based on concrete damage plasticity theory and model code, respectively. For comparison, a simulation of the fatigue experiment was conducted. Parametric analyses of the concrete strength and isolator stiffness were also performed. The results show that the maximum positive and negative bending moments of the floating slab throughout the loading stage are close in value. The positive bending moment causes stress concentration on the top slab surface which leads to plastic damage and low-cycle fatigue damage, while the negative bending moment causes middle-level elastic tensile stress on the bottom slab surface which leads to high-cycle fatigue damage. Under experimental conditions, damage on the bottom surface is much more severe, while the upper part is undamaged. Improving the concrete strength can reduce both kinds of damage, while increasing the isolator stiffness can only mitigate the high-cycle fatigue damage. Accordingly, recommendations are provided for improving fatigue experiments and structural design of prefabricated floating slabs.This study can inform the design and maintenance of the prefabricated SSFST system, ultimately enhancing their safety and longevity. [ABSTRACT FROM AUTHOR]

Micro-texture regions (MTR), defined as a cluster of grains with similar crystallographic orientations, have a significant detrimental effect on the fatigue life of Ti alloys. This paper proposes a novel multiscale approach, coupling the Parametrically Upscaled Constitutive Model (PUCM) for predicting component-scale deformation with the Parametrically Upscaled Crack Nucleation Model (PUCNM) for fatigue crack nucleation in polycrystalline microstructures of α / β Ti6Al4V alloy containing MTRs. The PUCMs represent higher-scale constitutive models whose coefficients are explicit functions of Representative Aggregated Microstructural Parameters (RAMPs), representing statistical functions of key morphological and crystallographic descriptors of the underlying microstructure. A novel RAMP is proposed for the quantification of the MTR intensity that incorporates a measure of the relation between the MTR crystallographic orientation and the local principal stress direction, in addition to morphological and crystallographic characteristics like MTR size, crystallographic orientation, average misorientation, and misorientation distribution within the MTR. The MTR intensity parameter is incorporated in the physics-informed PUCNM for macro-scale analysis of fatigue crack nucleation. The PUCNM is validated using experimental dwell fatigue tests with different microstructures. A WATMUS-accelerated PUCM-based FE model of a double-edged notched specimen is simulated under dwell fatigue loading to investigate the effect of notch geometry and microstructural features on dwell fatigue crack nucleation. Studies examine the interplay between the specimen geometry, macroscopic stresses, and the underlying microstructure with MTRs on the nucleation life. [ABSTRACT FROM AUTHOR]

An increasing number of arch and suspension bridges have been built in railway networks. Suspender cables serve as the critical load-transmitting component in these cable-supported bridges, which are subjected to a combination of the adverse impacts of train-induced fatigue stress and a corrosive environment. However, little research effort has been made on the corrosion fatigue performance of railway bridge suspender cables. This paper proposes an approach for the corrosion fatigue evaluation of the suspenders that integrates a sophisticated fatigue stress computational model and an enhanced corrosion fatigue model. The dynamic stresses of the suspenders are computed using a three-dimensional (3D) train–bridge interaction (TBI) model, which is established to consider the train-induced flexural vibrations on the suspender. Then, the corrosion fatigue damage of steel wires is characterized by a continuum damage mechanics-based model. The condition for the transition from pitting to fatigue crack is derived. Based on this, the corrosion fatigue assessment framework for suspenders is formulated, which can describe the time-dependent damage evolution that considers significant effects. A tied-arch railway bridge is investigated to showcase the effectiveness of the proposed approach and gain insights into the corrosion fatigue performance of the suspender cables in railway bridges. The field test data are employed to validate the stress computational model. In addition, the time-dependent corrosion fatigue evolution and service life of the suspenders are obtained. The results show that the suspender flexural vibrations cause considerable variations in the equivalent stress range and number of stress cycles. The corrosion fatigue life (CFL) of the critical suspender is reduced by 25% on average due to train-induced flexural vibrations. [ABSTRACT FROM AUTHOR]

The unique properties of aluminium alloys and their high strength-to-weight ratio make them the preferred choice for aircraft design. However, fatigue cracking in ageing fleets remains significant. This study investigates microstructural cracking of cooled and heat-treated Al 7075–0, T6, and T7 alloys used in airframes and stringers. To study the effect of heat treatment, medium voltage test pieces were used according to the guidelines of ASTM E647. Scanning Electron Microscopy (SEM) was used to observe the crack surface morphology. The results show that Al 7075-T7 exhibits higher resistance to the Fatigue crack growth (FCG) threshold than Al 7075-O and T6. In the case of the quenched Al 7075-O, the fatigue performance remains constant for samples oriented with a perpendicular and countersunk rivet hole. SEM analysis of fatigue cracking surface indicates that the microcracks leading to fracture originate from inclusion zones, secondary stage grains, and microstructural defects. In addition, as the heat treatment condition increased from O to T6 to T7, the area of the semi-subdivision planes and the width of the fatigue bands initially increased and then decreased. The final fault zones exhibit dimpled properties, with increasing size and deeper changing depth as heat treatment annealing progresses from O to T6 to T7. In summary, the study highlights the outstanding fatigue resistance of Al 7075-T7 and provides valuable insights into the microstructural aspects of fatigue cracking in aircraft alloys subjected to different heat treatments. These results contribute to the understanding and managing of ageing fleets, supporting the development of more reliable aircraft designs. [ABSTRACT FROM AUTHOR]

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]

As the demand for polar ships with long‐term service in ice environment increases, the steel materials are required to have key properties of high strength, toughness, and fatigue properties. The mechanical properties of hull structure steel with three different composition systems are investigated by tensile test, impact test, hardness test, and high‐cycle fatigue test, and the microstructure is observed and analyzed by optical microscope, scanning electron microscope–electron backscatter diffraction, and transmission electron microscope. The results show that the addition of V and V–N elements improves the mechanical properties of steel plates, especially the fatigue performance. The fatigue limits of V0, V and V–N steels are 250, 275, and 292 MPa, respectively. The microstructures of the steel plates are composed of ferrite and bainite, and the proportion of ferrite in steels increases with the addition of V and V–N elements. The fatigue cracks initiate in the soft phase nearby the soft/hard phase interface and propagate along the soft phase to form transgranular fracture. The fatigue limit of steels is elevated by doping V and V–N elements which increases the strength of ferrite. Moreover, the enhancement effect of V–N compound addition is better than that of V individual addition. [ABSTRACT FROM AUTHOR]

To ensure the safe operation of injection‐production pipelines in underground gas storage, this study establishes fatigue simulation models for both straight and elbow sections of the pipeline to address the issue of fatigue failure under cyclic loading. The analysis includes differences in fatigue life and stress distribution between straight pipes and elbows and the effects of internal average pressure, alternating load amplitude, and frequency on their fatigue life. The results indicate that the elbow of the injection‐injection pipeline bears a greater maximum equivalent stress than the straight pipe, has a smaller number of fatigue cycles, and the maximum fatigue damage occurs on the inner wall inside the center of the elbow. As the average pressure, alternating load amplitude and frequency increase, the fatigue life of the injection‐injection pipeline decreases. For example, when the average pressure on the elbow increases from 20 to 45 MPa, the minimum fatigue cycle number decreases from 7.694 × 1011 to 9.039 × 103 cycles. The research results provide a theoretical basis for optimizing the gas storage injection‐production process and preventing fatigue failure of injection‐production pipelines. [ABSTRACT FROM AUTHOR]

The complexity of product functionality and composition often involves at least two or more interrelated performance characteristics jointly reflecting the degradation. At the same time, the intricacy of the underlying failure mechanisms often results in degradation processes exhibiting intricate nonlinear patterns, where the mean and variance can display different nonlinear behaviors. Additionally, the random effect of the degradation process should not be overlooked. Therefore, an accurate depiction of degradation regulation is a crucial prerequisite for reasonable model construction and effective reliability analysis. To settle the challenges posed by complex nonlinear scenarios, this paper proposes a bivariate degradation model based on generalized nonlinear Wiener processes, incorporating a shared frailty factor to characterize the correlation between performance features. An approximate analytical expression for the cumulative distribution function of the first hitting time is derived for reliability analysis. Furthermore, unknown parameter estimation is carried out through a combination of the expectation–maximization algorithm and the genetic algorithm. Finally, the effectiveness of the proposed model and reliability analysis method is validated through a comprehensive simulation investigation and a practical case study involving fatigue crack propagation. [ABSTRACT FROM AUTHOR]

X-ray computed tomography (CT) was used to investigate the fatigue crack growth behavior of continuous SiC fiber reinforced Ti alloy (SiCf/Ti). Based on the three-dimensional morphology of the fatigue crack and the tortuosity of the SiC fibers, we investigated the fatigue crack growth behavior and their dependence on the tortuosity of the fibers. The results revealed that the fatigue crack tends to intersect fibers with higher tortuosity compared to their straighter counterparts, which could explain the crack initiation position and its propagation behavior in continuous fiber reinforced composites. [ABSTRACT FROM AUTHOR]

AbstractThis study presents an innovative numerical approach for predicting pressurized welded pipelines’ cyclic behavior and failure mechanisms under complex loading conditions. Focusing on X52 steel pipelines subjected to internal pressure and three-point bending, we investigate the interplay between structural integrity, weld joint positioning, and boundary conditions. Our methodology integrates advanced finite element analysis with a sophisticated material model capturing isotropic and kinematic hardening. The constitutive behavior is calibrated using the Voce model, accurately representing the material’s cyclic response. We employ the von Mises yield criterion to characterize the multiaxial stress state within the pipeline. A key innovation is our application of the eXtended Finite Element Method (XFEM) coupled with the calibrated hardening model, enabling high-fidelity simulation of crack initiation and propagation. Our model’s predictive capabilities are rigorously validated against experimental data, demonstrating excellent agreement across various loading scenarios. Through comprehensive parametric studies, we elucidate the critical influences of internal pressure, end-fixation conditions, and weld joint locations on the pipeline’s structural response. Force-displacement hysteresis curves reveal complex, nonlinear behaviors significantly impacting fatigue life and failure modes. This research advances the understanding of cyclic plasticity and fatigue in welded pressurized pipelines, providing a robust computational framework for predicting long-term performance. The insights gained have far-reaching implications for enhancing critical energy-transportation infrastructure’s safety, reliability, and longevity, potentially informing future design criteria and regulatory guidelines. [ABSTRACT FROM AUTHOR]

ABSTRACT The TC4 titanium (Ti) alloy has been widely utilized in various industries such as aerospace and shipbuilding, owing to its numerous advantages. Its exceptional properties have made it a material of choice for applications requiring high performance and reliability. The total weld thickness was 140 mm, and microstructures and high‐cycle fatigue properties were investigated at three different layers within the 140‐mm section. Experimental results show that the overlap area at two weld roots has the highest microhardness and largest nonuniformity of the overall joints, so the area is found to have the poorest high‐cycle fatigue properties. The microstructures in every layer of the weld metal of the joints were analyzed to determine the causes of the poor fatigue properties in the overlapping area at the weld roots. Significant amounts of α′ acicular microstructure are present in the weld metal of joints, while the overlap area at weld roots contains more α′ acicular microstructure with a finer size. Compared with other layers, the weld metal and base metal in Layer 2 (overlap area) have the largest microhardness gradient, where the stress concentration is more serious in the fatigue experimental process. Heat dissipation conditions was a critical factor for the inhomogeneity of microstructure and mechanical properties along the thickness direction of 140‐mm double‐sided electron beam welding joint. Fatigue damage (micropore) is formed at β phases in priority, and fatigue cracks propagate via series connection of micropores, indicative of transgranular ductile cracks. [ABSTRACT FROM AUTHOR]

The mechanical properties of Mn- and Fe-doped Na0.5Bi0.5TiO3 ceramics in unpoled and poled states were examined and analyzed for the first time through measurements of Young's modulus, the elastic modulus, Poisson's number, compressibility modulus K, hardness, fracture toughness and bending strength on one hand and by stress–strain measurements on the other hand. It was found that both the introduction of Fe and Mn ions into Na0.5Bi0.5TiO3 and E-poling lead to improvements in their mechanical properties. The additives also cause improvement of the piezoelectric properties. The stress–strain curves revealed a changing mechanical response with the Mn and Fe doping of the NBT. With the doping, there was a decrease in coercive stress, which enhanced the remnant strain. In contrast, the E-poling led to an increase in the coercive stress, which reduced the remnant strain. Induced internal stresses associated with non-180° domain switching were determined. It was found that the investigated materials displayed significant ferroelastic deformation and large remnant polarization even under external stress of 180–250 MPa. Modification of NBT by Mn and Fe ions and E-poling were found to be effective ways of improving actuator performance and controlling operating stresses in order to minimize irreversible fatigue damage. The results suggest that the investigated materials could replace PZT ceramics in actuator applications where high blocking stress is required. [ABSTRACT FROM AUTHOR]

Recent studies have proposed a simple formula, which is based on Elber's original approach to account for R-ratio effects, for determining the crack closure-free ΔKeff versus da/dN curve from the measured R-ratio-dependent ΔK versus da/dN curves. This approach, which is termed "Simple Scaling," has been shown to collapse the various R-ratio-dependent curves onto a single curve. Indeed, this approach has been verified for a number of tests on metals, polymers, and a medium-entropy alloy. However, it has not yet been used to help assess/determine the closure-free ΔKeff versus da/dN curve. The current paper addresses this shortcoming and illustrates how to use this methodology to assess the ΔKeff versus da/dN curves given in the open literature for tests on a number of steels, aluminum alloys, STOA Ti-6Al-4V, a magnesium alloy, and Rene 95. As such, it would appear to be a useful tool for assessing fatigue crack growth. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper investigates the ability of the self‐heating method to characterize the fatigue behavior of 316L stainless steel produced by Laser Powder Bed Fusion. Nearly dense cylinders are built vertically using various process parameters corresponding to various volumetric energy densities. Fatigue specimens are then machined from these cylinders and polished. Fully reversed tension–compression fatigue tests (R = −1) are conducted. The self‐heating method is used for the estimation of the fatigue limits. These fatigue limits are compared to results obtained from S‐N curves in the high cycle regime. Whatever the set of process parameters, the self‐heating curves show three distinct domains of heat dissipation. Thanks to microstructure analysis, fractographic observations, and correlations with S–N curves, these domains can be closely linked to damage mechanisms associated or not with defects. [ABSTRACT FROM AUTHOR]

Structural components with curved edges are common in many engineering designs. Fatigue cracks, corrosion and other types of defects and mechanical damage often initiate from (or are located close to) edges. Damage and defect detection in the presence of complex geometry represents a significant challenge for non-destructive testing (NDT). To address this challenge, this paper investigates the fundamental mode of the quasi-symmetric edge-guided wave ( Q E S 0 ) propagating along a curved edge, as well as its scattering characteristics in the presence of different types of edge defects. The finite element (FE) approach is used to investigate the propagation and mode shapes of the Q E S 0 . It was found that the wave attenuation dramatically increases when the radius-to-thickness ratio is less than 20. Moreover, the mode shapes are significantly affected by the waveguide curvature as well as the excitation frequency. Additionally, to evaluate the sensitivity of Q E S 0 to edge defects, different sizes of edge defects were investigated with the FE model, which validated against experimental results. The validated FE model was further employed to quantify the dependence of the amplitude of scattered waves for different types of edge defects. These studies indicate that the amplitude of scattered wave is very sensitive to the presence of edge defects. The main outcome of this work is the demonstrated ability of the Q E S 0 wave mode to propagate over long distances and a high sensitivity of this mode to different types of edge defects, which manifest its great potential for detecting and characterising damage near the curved edges of structural components. [ABSTRACT FROM AUTHOR]

This study presents a method for determining the optimal gear ratio in electric trains by examining the effects of motor efficiency, wheel wear, and relative damage to the input and output shafts of the reduction gear. In electric trains, reduction gears and wheels are critical for converting the driving motor's torque and determining the motor's operational point, which in turn affects efficiency and durability. Over time, wheel wear from regular use and periodic profiling reduces the wheel radius, causing an effective increase in the gear ratio, which impacts the motor efficiency and load distribution across drivetrain components. This study models the dynamic behavior of the vehicle's drivetrain system using MATLAB/Simulink and incorporates real-world data on wheel wear to address the problem. Through simulations with varying gear ratios, it analyzes changes in motor efficiency and uses Miner's rule to assess the relative damage on the reduction gear's input and output shafts. The results enable the identification of a gear ratio that balances motor efficiency and reduces cumulative fatigue damage, which is especially important for maintaining long-term drivetrain durability. This approach provides a systematic way to enhance the overall performance and lifespan of electric train systems by selecting a gear ratio that optimally aligns efficiency and durability. [ABSTRACT FROM AUTHOR]

Existing anchor solutions are limited in their applicability to the floating offshore wind industry, which demands prolonged load endurance in extreme weather conditions and varied seabed soils. This limitation restricts project feasibility and increases costs. In order to address these challenges, the Deeply Embedded Ring Anchor (DERA) is proposed to achieve substantial reductions in anchor costs through efficiency enhancements. Ensuring the long-term safety and reliability of the DERA, especially considering a minimum operational period of 25 years, necessitates a comprehensive understanding of fatigue damage. Induced by repetitive loading below material yield strength, fatigue poses a significant threat to structures exposed to waves and currents. Anchors, vital for station keeping, are susceptible to fatigue damage, particularly in the padeye area. This paper conducts a fatigue analysis, focusing on factors such as the wall thickness of the ring anchor, inner stiffeners, and stiffener thickness, to evaluate the performance of DERA in this context. The results showed that the stiffener significantly affects the elongation of the total life of the anchor. In conclusion, this paper focuses on advancing innovations like DERA, enabling the efficient utilization of offshore wind resources, and addressing safety concerns through meticulous fatigue analysis. [ABSTRACT FROM AUTHOR]

With the advancement of high-speed and lightweight vehicles, the occurrence of wheel tread wear, including wheel flats, has escalated. The resulting impact loads on axle-end components and the dynamic response of the axle cannot be overlooked. On-track tests were conducted on wheel flats to obtain wheel-rail forces, axle box vibration accelerations, and axle stresses during service. Time–frequency analysis was employed to uncover patterns of variation with speed. Additionally, a dynamic model of the high-speed train–track system was developed to replicate test conditions, investigating the characteristics of wheel–rail loads and structural elastic vibrations under high-frequency excitation for various flat sizes and higher operating speeds. The findings reveal that under wheel flats, the time-domain response of the wheel–rail system exhibits periodic impacts, while the frequency-domain shows high-frequency energy comprising multiple harmonics of the wheel rotation frequency. Wheel–rail forces, axle box vibration accelerations, and axle stresses exhibit inflection points with increasing speed, particularly within the 120–160 km/h range. In the high-frequency domain, axle stresses display characteristic frequencies that remain unchanged with speed, attributed to the coupled vertical bending vibration modes of the wheel–rail system. These research results offer foundational support for predicting fatigue damage to axle-end components, assessing axle stress, and establishing tolerances for tread defect limits. [ABSTRACT FROM AUTHOR]

Recently, understanding the complex relationship between the mechanical properties and material characteristics of desulfurized rubber asphalt has received significant research attention. In this study, the rheological properties of rubber asphalt prepared by three kinds of desulfurized rubber powder are analyzed, and the mechanical response of rubber asphalt mixture is predicted using various mathematical models. Firstly, the rheological properties of desulfurized rubber asphalt are assessed through multiple stress creep recovery test, linear amplitude scanning test, and low-temperature creep test. The results indicate that the high-temperature performance index of desulfurized rubber asphalt is highly sensitive to the degree of desulfurization. As the degree of desulfurization of the rubber powder increases, the fatigue damage rate of asphalt gradually decreases, leading to an increase in the fatigue life. Notably, the difference between the m-critical temperature and stiffness-critical temperature (ΔTc) for only ML40MA does not exceed the threshold value, indicating that it has the best low-temperature cracking resistance. Additionally, the swelling capacity of desulfurized rubber powder in asphalt is better than that of ordinary rubber powder. Finally, the comprehensive performance of desulfurized rubber asphalt is characterized based on the gray correlation method. The gray correlation coefficient of ML60MA is 0.78, which is higher than that of ML40MA and ML80MA, indicating its best overall performance. [ABSTRACT FROM AUTHOR]

To quickly obtain the fatigue life of cranes in service, the metal structure that determines the crane life is anchored. Meanwhile, the fast prediction method of fatigue life of crane metal structures based on the Stacking ensemble learning model is proposed. Firstly, in line with the structural stress method, the global rough model of the metal structure is established by the co-simulation technology to obtain the fatigue damage regions of the structure. The local fine model is constructed by local cutting and boundary condition transplantation to determine the critical weld at the failure regions. Secondly, through weld definition, equivalent structural stress acquisition, and fatigue life calculation, the sample data set with lifting load and trolley running position as input and fatigue life cycle times as output is constructed. Then, the Stacking integrated learning model combining gradient boosting, ridge regression, Extra Trees, and linear is built. On this basis, combined with the Miner theory, the rapid prediction of crane fatigue life is realized. Finally, the proposed method is applied to the QD40t × 22.5 m × 9 m general bridge crane. The results show that the life sample set constructed by the structural stress method is more accurate and reasonable than the nominal, hot spot, and fracture mechanics methods. The life prediction results of the Stacking integration model were improved by 6.3 to 49.2% compared to the single model. The method has theoretical and practical significance in reducing accidents and ensuring the safe operation of cranes. [ABSTRACT FROM AUTHOR]

This study investigates the impact of tightening torque (preload) and the friction coefficient on stress generation and fatigue resistance of a Ti-6Al-4V abutment screw with an internal hexagonal connection under dynamic multi-axial masticatory loads in high-cycle fatigue (HCF) conditions. A three-dimensional model of the implant–abutment assembly was simulated using ANSYS Workbench 16.2 computer aided engineering software with chewing forces ranging from 300 N to 1000 N, evaluated over 1.35 × 107 cycles, simulating 15 years of service. Results indicate that the healthy range of normal to maximal mastication forces (300–550 N) preserved the screw's structural integrity, while higher loads (≥800 N) exceeded the Ti-6Al-4V alloy's yield strength, indicating a risk of plastic deformation under extreme conditions. Stress peaked near the end of the occluding phase (206.5 ms), marking a critical temporal point for fatigue accumulation. Optimizing the friction coefficient (0.5 µ) and preload management improved stress distribution, minimized fatigue damage, and ensured joint stability. Masticatory forces up to 550 N were well within the abutment screw's capacity to sustain extended service life and maintain its elastic behavior. [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 large cutout structure is a key component in the bottom skin of an airplane wing, and is susceptible to developing fatigue cracks under service loads. Early fatigue crack detection is crucial to ensure structural safety and reduce maintenance costs. Nonlinear Lamb wave techniques show significant potential in microcrack monitoring. However, nonlinear components are often relatively weak. In addition, a large cutout structure introduces complex boundary conditions for Lamb wave propagation, making nonlinear Lamb wave monitoring more challenging. This article proposes an integrated data processing method, combining phase inversion with continuous wavelet transform (CWT) to enhance crack detection in complex structures, with phase-velocity desynchronization adopted to suppress the material nonlinearity. Experiments on a large cutout aluminum alloy plate with thickness variations were conducted to validate the proposed method, and the results demonstrated its effectiveness in detecting fatigue cracks. Furthermore, this study found that nonlinear components are more effective than linear components in monitoring closed cracks. [ABSTRACT FROM AUTHOR]

In traditional short-term hydropower scheduling problems, which usually determine the optimal power generation schedules within one week, the off-design zone of a hydraulic turbine is modeled as a forbidden zone due to the significantly increased risk of turbine damage when operating within this zone. However, it is still plausible to occasionally operate within this zone for short durations under real-world circumstances. With the integration of Variable Renewable Energy (VRE) into the power system, hydropower, as a dispatchable energy resource, operates complementarily with VRE to smooth overall power generation and enhance system performance. The rapid and frequent adjustments in output power make it inevitable for the hydraulic turbine to operate in the off-design zone. This paper introduces the operating zones associated with various production costs derived from fatigue analysis of the hydraulic turbine and calculated based on the turbine replacement cost. These costs are incorporated into a short-term hybrid scheduling tool based on Mixed Integer Linear Programming (MILP). Including production costs in the optimization problem shifts the turbine's working point from a high-cost zone to a low-cost zone. The resulting production schedule for a Hydro-Solar hybrid power system considers not only short-term economic factors such as day-ahead market prices and water value but also lifetime hydraulic turbine cost, leading to a more comprehensive calculation of the production plan. This research provides valuable insights into the sustainable operation of hydropower plants, balancing short-term profits with lifetime hydraulic turbine costs. [ABSTRACT FROM AUTHOR]

Cemented pavement materials (CPMs) are essential components in pavement structures, yet accurately predicting their service life due to fatigue damage remains challenging. Laboratory fatigue test results are commonly employed to predict the service life of CPMs by applying a lab-to-field shift factor (SF). However, traditional approaches rely heavily on experimental data, posing challenges in ensuring the certainty of lab-to-field results. Additionally, inconsistencies in lab-to-field fatigue failure criteria further complicate SF development. To address these challenges, this study proposes a mechanism-based methodology for developing SF. This methodology comprises a rigorous two-scale fatigue model developed by the authors to characterise the fatigue performance of CPMs at the lab scale and predict their performance at the field scale, thereby facilitating the development of SFs. These SFs are established based on a consistent lab-to-field fatigue failure criterion (i.e. the modulus reduction of CPMs). By accounting for strain differences between laboratory and field scales, SFs are derived in the strain-fatigue life space. Application of this approach to typical Australian CPMs, namely siltstone and hornfels, yields mechanism-based SFs of 1.19 and 1.21, respectively. [ABSTRACT FROM AUTHOR]

The life of compressor impeller is very short under extreme working conditions, so it is necessary to explore the life extension method and mechanism. Since the crack initiation location cannot be accurately predicted in advance, the hole drilling strategy of prefabricated hole will determine the remaining life of impeller after cracks appear. This article presents a strategy of prefabricated hole to extend the fatigue crack propagation life (FCPL) of compressor impeller. The stress distribution of impeller during operation is simulated by finite element method, and the crack initiation location is determined. The Forman-Newman-de Koning model is used to investigate the effects of hole drilling strategy and rotational speed on FCPL, and the three-dimensional crack propagation process is simulated. In addition, this paper investigates the main phenomena and influencing mechanism for the extension of FCPL due to prefabricated hole. It is found that the prefabricated hole can attract the crack propagation path, and make the crack pass through the hole more easily. At this time, the crack propagation driving force will decrease sharply, and the crack propagation rate will decrease accordingly, thus extends the FCPL. Even if it cannot pass through the hole, the optimal hole drilling strategy can extend life by 104.23%. The life extension effect of prefabricated hole increases with the increase of speed. The design in this paper can reduce the economic cost to a great extent, and provides a new idea for the life extension problem of complex models. [ABSTRACT FROM AUTHOR]

Mechanical characteristics, instability precursors, and fatigue life prediction of rocks under fatigue loading are significant for the prediction and prevention of mining disasters. Taking the porous siltstone widely distributed in the mining area of western China as the research object, a characteristic stress determination method based on the evolution characteristics of the multiphase volumetric strain of porous rocks was established. Referring to the characteristic stress interval, bivariate fatigue damage-controlled tests with different upper limit loads and different numbers of cycles were conducted. The results indicate that the strengthening and the weakening of the macroscopic strength of siltstone under fatigue loading are caused by the competition of two mesostructure effects, namely the "weak structure failure effect" and the "compaction embedment effect". The dominant effect varies with different upper limit loads and different numbers of cycles. Importantly, the transition of the bulk compliance from positive to negative is an early precursor of fatigue failure, while the simultaneous sudden increase in cumulative acoustic emission count, acoustic emission bk value, and energy dissipation ratio is an imminent precursor of fatigue failure. The evolution characteristics of the strain, acoustic emission, and energy dissipation indicate that the crack damage stress of siltstone is a reliable indicator of its fatigue strength. Furthermore, a nonlinear viscoplastic damage element was introduced to construct a nonlinear fatigue rheological damage model, and model validation and quantitative analysis of parameter effects were conducted. Finally, by determining the accelerated rheological start threshold and the accelerated rheological failure threshold, a rapid prediction method for the fatigue life was established. Highlights: A characteristic stress determination method suitable for porous rock. Mesoscopic mechanism of strength strengthening and weakening. Early and imminent precursors of fatigue rheological failure. A nonlinear fatigue rheological damage model. [ABSTRACT FROM AUTHOR]

Public transport via trams has become increasingly important in daily life to meet the growing demand for economic and environmental considerations. In order to ensure the safety of the railway system and reduce service costs, it is necessary to understand the tribological behavior of the system. There are various types of damage such as fatigue, wear, and cracking that can harm the wheels and rails. To determine the wear mechanisms and identify the situations in which wear movements occur, it is crucial to monitor factors such as temperature, surface roughness, and contact micro-hardness between the wheel and the rail. The objective of this study is to analyze the tribological behavior and the impact of climatic conditions on the wheel–rail contact system in the desert area of the Ouargla tramway in Algeria. To achieve this, an intelligent sensor programmed by a microcontroller was utilized to measure the temperature of the wheel–rail contact. Additionally, a hardness tester was used to measure the micro-hardness of the rail, and a roughness tester was utilized to monitor the surface condition of the rail. The measured temperature values during the passage of the tramway varied between ambient temperature and a temperature of 450∘C. The micro-hardness values ranged from 270 Hv to 440 Hv, and the roughness values varied between 0.4 μ m and 2.7 μ m. [ABSTRACT FROM AUTHOR]

In this paper, a reasonable explanation is given to unify notch effect and geometric size effect into notch geometric feature effect (NGFE), and energy gradient is utilized to depict the influence of the NGFE on the critical distance. The correlation of energy gradient with critical distance and fatigue life is discussed respectively. The weight index of the high energy region is used to quantify the contribution of the high energy region to the fatigue damage. Finally, a model of the reconstructed critical distance theory considering the geometric notch characteristic effect is established. The fatigue test of Q355 (D) alloy steel notched components was carried out, and the evaluation precision of the presented method is compared with Yang' model and Shen' model combining with the existing fatigue test data of En8. The results indicate that prediction results of the proposed method are consistent with the test results. Highlights: Based on the energy gradient to characterize notch geometric feature effect, the critical distance theory is reconstructed.The association degree of the energy gradient with fatigue life and critical distance is discussed.The high energy region weight index is defined to quantify the contribution of high energy region to fatigue damage. [ABSTRACT FROM AUTHOR]

Corrosion fatigue behavior and mechanism of the weld joint of Q690qE high‐strength bridge steel was investigated in a simulated marine environment. It reveals the sub‐critical heat‐affected zone (SCHAZ) and coarse‐grained heat‐affected zone (CGHAZ) are the most vulnerable sites to corrosion fatigue cracking. The CGHAZ of the Q690qE steel weld joint was prone to corrosion fatigue initiation mainly because of micro‐galvanic corrosion between CGHAZ and weld metal (WM). The corrosion fatigue failure in SCHAZ mainly resulted from local stress/strain concentration due to weld softening. The final fracture location was determined by the competition between these two effects. Highlights: Corrosion fatigue mechanism of the weld joint of high‐strength bridge steel was proposed.The final corrosion fatigue fracture of the Q690qE steel weld joint mostly occurred in SCHAZ.SCHAZ was vulnerable to corrosion fatigue cracking mainly due to local softening. [ABSTRACT FROM AUTHOR]

For welded structures, the concept of damage is highly abstract and difficult to describe, leading to a lack of physical foundation and universality for existing fatigue damage accumulation models. A new fatigue damage parameter definition based on remaining bearing capacity is proposed in this paper, which is constructed by the equivalent stress on the remaining bearing surface and the equivalent stress intensity factors along the crack front curve. Tension and three‐point bending fatigue tests under two‐level loading block sequences were conducted, and the real fatigue damage evolution processes were obtained by combining measured crack front information and FEA simulation. Five damage accumulation models were utilized to estimate the fatigue damage evolution processes of the two specimens. Results show that there are differences in describing the damage evolution processes and predicting the early fatigue lives. The Rege model is most consistent with the measured data, demonstrating its applicability and effectiveness. Highlights: The physical essence and description of the welded joint fatigue damage are investigated.A damage definition based on remaining bearing capacity for welded joints is proposed.Real damage evolution processes of two welded joints are obtained.Validation of four nonlinear damage accumulation models is carried out and discussed. [ABSTRACT FROM AUTHOR]

In this paper, the deformation behavior of plastic zone at crack tip during crack propagation of 304 stainless steel was studied. Firstly, the fatigue crack propagation tests of 304 stainless steel material were carried out. Combined with digital image correlation (DIC) technology, the strain field data of plastic zone at crack tip, the size of plastic zone, and the strain evolution law of crack tip region at different positions were obtained. Then, combined with the theoretical model and the numerical model, the theoretical, numerical, and experimental results were compared to verify the accuracy of the model. Finally, the effects of cyclic loading, specimen thickness, and weld position on plastic zone at crack tip were analyzed. The research results provide a reference for accurately predicting the fatigue crack growth of 304 stainless steel. Highlights: Digital image correlation was used to measure the deformation fields of plastic zone at crack tip in the fatigue crack propagation tests.Plastic zone size was investigated by experiment, theory, and numerical analysis.The effect of plastic zone on crack growth rate was investigated.The effects of cyclic loading, specimen thickness and weld position on plastic zone at crack tip were explored. [ABSTRACT FROM AUTHOR]