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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]

An enhanced nonlinear fatigue damage cumulative model proposed is based on the strength degradation characteristics of composites, aiming to investigate damage progression under fatigue loading. Building upon this foundation, given the assumption of a linear correlation between fatigue cumulative damage and stress level, a methodology is presented for extrapolating the damage curve of untested stress levels from that of tested stress levels. The model substantiates its reliability by validating against experimental data from several distinct material types. The reliability of the model has been validated using experimental data from multiple groups of materials. The experimental results indicate that the model can effectively reflect the fatigue damage development characteristics of composite materials. Simultaneously, the predicted stress levels derived from the proposed methodology show lesser deviation from the fitted data. Finally, a life prediction method founded on the proposed model is introduced, validated for its high prediction accuracy through experimentation. Highlights: An enhanced fatigue damage model of composites is established.A novel residual strength model for composites has been established.Present a methodology for calculating the stress level damage curve.The fatigue life prediction method of the proposed model is developed. [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]

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]

The largest normal stress excursion during contiguous turn time instants of the maximum torsional stress is presented as an innovative path-independent fatigue damage quantity upon the critical plane, which is further employed for characterizing fatigue damage under multiaxial loading. Via using the von Mises equivalent stress formula, an axial stress amplitude with equivalent value is proposed, incorporating the largest torsional stress range and largest normal stress excursion upon the critical plane. The influence of non-proportional cyclic hardening is considered within the presented axial equivalent stress range. Moreover, according to proposed axial equivalent stress amplitude, an energy-based damage model is presented to estimate multiaxial fatigue lifetime upon the critical plane. In order to verify the availability of the proposed approach, the empirical results of a 7050-T7451 aluminum alloy and En15R steel are used, and the predictions indicated that estimated fatigue lives correlate with the experimentally observed fatigue results well for variable amplitude multiaxial loadings. [ABSTRACT FROM AUTHOR]

Remaining useful fatigue life monitoring of wind turbine drivetrains is important. However, the implementation of real‐time monitoring often faces efficiency and accuracy challenges. In order to resolve this, this paper proposes a vibration‐based damage monitoring digital twin (VBDM‐DT) that enables the online intelligent evaluation of wind turbine gearboxes, using gear tooth surface durability as an example fatigue mode. The VBDM‐DT integrates a random wind load model, a high‐fidelity dynamics model, and a fatigue damage model. The random wind load model takes the wind speed from the supervisory control and data acquisition (SCADA) as input to estimate the input torque of the drivetrain in real time. Simultaneously, VBDM‐DT uses the vibration signals from the condition monitoring system (CMS) to intelligently calibrate the dynamics model, allowing it to be continuously adjusted and optimized in response to actual vibrations. The fatigue damage model takes the real‐time dynamic loads estimated by the high‐fidelity dynamic model as input to achieve real‐time fatigue damage monitoring of key components in the wind turbine gearbox. Applying the VBDM‐DT model to a 2 MW wind turbine gearbox, the results indicate that the model provides satisfactory accuracy in estimating input loads and good adaptability in intelligent calibration of the dynamic model. Based on this model, the fatigue life estimation for gears and bearings is more credible and reliable. [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 failure of rock in cold regions due to repeated freeze–thaw (F-T) cycles and periodic load-induced fatigue damage presents a significant challenge. This study investigates the evolution of the multi-scale structure of fractured granite under combined freeze–thaw (F-T) cycles and periodic loading and develops a constitutive damage model. The results indicate that after F-T cycles, network cracks develop around pre-existing cracks, accompanied by block-like spalling. After applying the fatigue load, the nuclear magnetic resonance (NMR) T2 spectrum shifts to the right, significantly increasing the amplitude of the third peak. The freeze–thaw process induces a "liquid–solid" phase transition, weakening the original pore structure of the rocks and leading to meso-damage accumulation. The pores in fractured granite progressively enlarge and interconnect, reducing the rock's load-bearing capacity and fatigue resistance. The combined effects of F-T cycles and periodic loading induce particle movement and alter fracture modes within the rock, subsequently affecting its macro-damage characteristics. The theoretical curves of the constitutive model align with the experimental data. The findings can serve as a theoretical reference for preventing and controlling engineering disasters in fractured rock masses in cold regions. [ABSTRACT FROM AUTHOR]

Considering the inherent characteristics of strength degradation, a residual strength model is improved reasonably through the incorporation of the two‐parameter Weibull distribution. Building upon this foundation, an enhanced nonlinear fatigue damage accumulation model that is closer to the actual situation is proposed in view of the randomness of fatigue damage. The model takes into account the effect of load action on fatigue damage. To ascertain the feasibility of the proposed model, the time‐varying reliability of the model is evaluated by applying the probability density evolution method. The model's precision in predicting residual life is corroborated through five experimental data sets under bilevel and multilevel loading conditions. The results demonstrate that the proposed model exhibits excellent applicability and remarkable precision, thereby confirming its potential value in practical applications. Highlights: Using strength degradation characteristics, new residual strength model is crafted.Combined with the Weibull distribution, a new fatigue damage model is established.The PDEM is applied to obtain the time‐varying fatigue reliability curve. [ABSTRACT FROM AUTHOR]

As a new binder, polyurethane (PU) is used to overcome the poor durability of porous pavement. This study focuses on the fatigue performance of a porous polyurethane mixture (PPM) under immersion conditions and compares it with a porous asphalt mixture (PAM). The results showed that under the immersion conditions, the initial stiffness of the PPM decreased by approximately 50%. However, the initial stiffness of the PAM was almost unaffected by the immersion conditions. In addition, the PPM exhibited a longer fatigue life under immersion conditions. In comparison, the fatigue life of the PAM decreased. The cracking propagation rate of the PPM decreased under immersion conditions, while the cracking propagation rate of the PAM increased. The fatigue termination condition for the PPM was set to S1 = 0.45S0 (S0 is the initial stiffness, and S1 is the termination stiffness), and that of the PAM was set to S1 = 0.4S0. Compared to the Weibull function, the Chaboche function provides a more accurate description of fatigue damage in the PPM and PAM. From the obtained data, it can be inferred that the fatigue performance of the PPM is far superior to that of the PAM. Therefore, polyurethane has broad application prospects in long-life permeable pavements. [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]

This study comprehensively explores the research landscape within statistical and reliability studies, focusing on the Birnbaum-Saunders distribution, Gaussian inverse distribution, cumulative damage models, and fatigue life prediction. Using a combination of bibliometric analysis, network visualization, thematic mapping, and latent Dirichlet allocation, we analyze 465 articles from the ISI Web of Science database. These articles were selected for their relevance based on a targeted search strategy. Our analysis identifies key trends, collaboration networks, and emerging research themes. Notable growth in scholarly activity was observed from 2015 to 2021, with a peak around 2021, followed by a decline in the number of publications. Relevant contributions were noted from countries such as Brazil, Canada, Chile, China, Iran, Japan, and the United States. The thematic analysis of keywords reveals influential motor themes like the Birnbaum-Saunders distribution and expectation-maximization algorithm; specialized niche areas such as producer risk; emerging or declining themes like the generalized Birnbaum-Saunders distribution; and foundational themes including cumulative damage and fatigue life distributions. A cluster analysis states key focus areas, such as material durability and advanced statistical methods. Integrating latent Dirichlet allocation, six main topics are derived, capturing broad thematic structures. However, some niche areas do not align directly due to their specialized nature and limited cross-field impact. These findings map the current research on this thematic and suggest future research directions, including deeper exploration of niche themes, integration of advanced statistical methods in practical applications, and increased collaboration across diverse research areas to enhance the robustness and applicability of reliability models. [ABSTRACT FROM AUTHOR]

Three fatigue damage models based on entropy, originally developed for constant amplitude loading, were assessed and compared to each other aimed at stating whether its applicability can be extended towards variable amplitude loading conditions. A variable amplitude loading history, applied on a 2024‐T3 aluminum alloy reported in the literature, was processed using both rainflow cycle counting and spectral techniques to transform it into a distribution of simple processes with constant amplitudes, then the damage models were assessed under the new loading conditions. The results showed that the model by Khonsari, combined with the rainflow technique, exhibited the highest accuracy with regard to the referenced experimental results with a −0.67 standard deviation from the average data and a 16% error from the median. Therefore, it is possible to assess the fatigue damage accumulation in metallic materials under variable amplitude loading through a thermodynamic approach with models developed for constant amplitude loading. Highlights: Fatigue criteria for variable amplitude loading were coupled to damage models based on entropy, aimed at assessing and extending their applicability.Three fatigue damage models based on entropy were assessed in order to identify which of them can predict fatigue life better in variable amplitude loading scenarios.The best combination of a fatigue damage model with a signal processing technique was determined, and estimated fatigue life was compared with experimental results found in literature. [ABSTRACT FROM AUTHOR]

Fretting fatigue contributes significantly to the fatigue failure process in steel wire ropes at the wire‐to‐wire trellis contact region with partial slip conditions. In this respect, this work demonstrates a new damage‐based fretting fatigue model for the prediction of such a failure process. The model is based on Lemaitre's damage equations for quasi‐brittle material with a damageable micro‐inclusion embedded in an elastic meso‐element. It incorporates the cyclic degradation of the elastic modulus of the drawn steel wire material. The fatigue life model acknowledges the mean stress effect. The constitutive and damage equations are formulated into user material (UMAT) subroutine for integration with Abaqus finite element analysis code. The localized fretting fatigue damage mechanism is simulated with an isolated two‐wire model. The effect of the contact condition with the coefficient of friction of 0.2 and 0.8 on the contact mechanics of the drawn wires is considered. The fretting fatigue mechanism map is established for each simulation case. The simulated results of N0 (no of cycles to initiate damage) and damage variable, D, confirm the fretting fatigue condition as the damage occurs in the slip region of the contact area for both the frictional conditions. The results were found in agreement with the previously establish Ruiz fretting parameter. This study will provide a base for the onward reliability assessment of steel wire ropes. Highlights: A damage‐based Lemaitre two‐scale model has been modified for the fretting fatigue mechanism in the steel wire ropes.A unified curve of residual elastic modulus has been established through interrupted fatigue tests for different load ratios.A UMAT Subroutine is developed using ABAQUS software. The response of the damage model has been investigated using different parameters like Damage D, Residual Elastic Modulus E(N), Number of cycles to initiate damage N0, and von Mises stress at the contact region. [ABSTRACT FROM AUTHOR]

To reasonably forecast the crack initiation characteristics of fretting fatigue, this study evaluates the accuracy of several damage models. The existing experimental and simulation investigations are compared, noting the similarities and differences in the crack initiation location, crack orientation angle, and crack initiation life predicted by various damage models. It is crucial to employ a reasonable and reasonable damage prediction model of fretting crack initiation life, as fretting fatigue, a phenomenon of mechanically fastened connecting parts, can considerably reduce the fretting fatigue life of the components. This paper compares the fatigue damage prediction models of fretting fatigue specimens under partial slip conditions, and it will help researchers understand the benefits and drawbacks of various damage models and give them the knowledge and foundation to select the more reasonable fretting fatigue damage model. Highlights: A structured meshing technique and coupled constraint loading strategy are proposed.The cyclic characteristics of fretting contact parameters are analyzed.A normalized parameter for comparing the fatigue damage models is proposed.The accuracy of the different fretting fatigue damage models are compared. [ABSTRACT FROM AUTHOR]

The progressive fatigue damage (PFD) model is a comprehensive method to simulate the fatigue damage behavior of laminated composites under multiaxial cyclic stress. The generalized material property degradation (GMD) technique is a component of the PFD model. Also, the fatigue life modeling of a UD ply under a uniaxial state of stress is a subcomponent of the GMD technique. The present article compares and evaluates the results achieved by using different fatigue life models within the GMD technique. For this purpose, three commonly used fatigue life models (the normalized fatigue life model, the Luders fatigue life model, and the unified fatigue life model) were considered. Based on the capabilities of these models in predicting the fatigue life of unidirectional plies, a combined fatigue life model is developed and integrated into the progressive fatigue damage model. The results demonstrate that using the combined fatigue life model improves the prediction accuracy of the PFD model. [ABSTRACT FROM AUTHOR]

Accelerated durability evaluation aims to quantify the fatigue damage of automotive components in a shorter time. The quality of accelerated editing directly affects the evaluation's efficiency and accuracy. In this paper, an index-controlled accelerated spectrum editing method is proposed, and the equivalent fatigue damage model of the component is derived. Taking an automotive steering knuckle as the verification object, the proposed accelerated editing method is evaluated from multiple perspectives. The evaluation results show that the proposed method has apparent advantages in compression efficiency, damage consistency, and retaining the frequency domain impact on the component. [ABSTRACT FROM AUTHOR]

This study introduces an analytical micromechanical model considering progressive damage designed to predict the elastic and strength properties of plain weave composites subjected to fatigue loading. The presented model is composed of a multi-scale micromechanical model, wherein a progressive damage mechanism has been incorporated. During the development of this multi-scale micromechanical model, a representative volume element was chosen and homogenized, utilizing assumptions pertaining to identical out-of-plane stresses and in-plane strains. These assumptions satisfy the conditions of equilibrium and displacement continuity in the representative volume element and, through a three-step process, enhance the model's accuracy in applying the damage model and predicting the elastic properties of plain weave composites under static loading. Subsequently, the damage mechanism was progressively developed by accounting for the crucial role of matrix crack growth. This was achieved by employing the kinetic theory of fracture for polymers and integrating it with the multi-scale micromechanical model. Ultimately, the elastic and strength properties of plain weave composites under fatigue loading were predicted. A comparison of the results derived from the present model with those available in the literature demonstrated a high degree of agreement. [ABSTRACT FROM AUTHOR]

A metal fatigue damage model is established in this study by employing real-time strain monitoring to evaluate the damage state of metal materials. The fatigue life simulation, based on crystal plasticity finite element analysis, establishes the constitutive relationship between strain and damage before microcrack initiation in the low-cycle fatigue state of aerospace aluminum alloy. Subsequently, a comprehensive analysis of the strain–damage relationship is conducted under various stress conditions. Electron backscattering diffraction analysis (EBSD) is used to examine the fatigue damage state of the grooved specimen before initiating fatigue cracks at various stages. This analysis validates the metal fatigue damage model proposed in this paper and is based on strain monitoring, contributing to the enhanced confirmation of the model's accuracy. [ABSTRACT FROM AUTHOR]

The heat alternation and bending during the service process of the pipeline structure are the key issues affecting its residual strength. The nonuniform plastic deformation of its cross-section causes nonlinear damage to the structure, which makes it difficult to calculate the residual strength of the overall structure. This study proposed a novel variable-strength material damage model with damage accumulation, which achieved the coupling analysis of structural damage and material fatigue residual strength, making the structural strength of nonlinear damage cross-section computable. Based on this, a theoretical ultimate load model for nonlinear damage cross-section and a finite element analysis model for dynamic material strength with damage accumulation were established. The analysis was conducted on the repeated banding damage to coiled tubing. The results showed that the residual yield strength of nonlinear damaged coiled tubing showed a trend of first rapid decrease and then slow decrease with damage accumulation, and the tensile displacement showed an increasing trend with damage accumulation. The ultimate internal pressure strength of nonlinear damaged structures showed a similar downward trend to the yield strength. The nonlinear damage coupling analysis model proposed in this study has significant practical engineering application value. [ABSTRACT FROM AUTHOR]

Interlaminar fracture or delamination is one of the major failure modes for fiber reinforced polymer (FRP) laminate. Especially, the synergistic effect of environmental exposure and fatigue loads accelerates interface degradation. The main objective in this work was to investigate the fatigue damage propagation of basalt FRP (BFRP) laminate under coupling of acidic environment and fatigue load. The fatigue cycling of 40,000 and the maximum stress of 30% fu (fu = ultimate tensile strength) were adopted. The fatigue specimens under air condition (air fatigue), immersing in water (water fatigue) and immersing in acid (acid fatigue) were introduced. The double cantilever beam (DCB) test was used to evaluate the interlaminar damage of BFRP laminate after fatigue cycling. The fatigue damage propagation mechanism was explored by means of failure modes, load displacement curves, mode I fracture toughness and crack propagation resistance model. The results show that the fatigue weakened the interlaminar properties and resulted in reduced fiber bridging. Especially for the acid fatigue, the laminate was damaged by the coupling of fatigue and acid corrosion. The linear loading stage, nonlinear slow growing stage, stable crack propagation stage and linear unloading stage for DCB after fatigue were observed in the load–displacement curve. The fatigue cycling has caused fracture toughness decrease of 15.0%, 13.8% and 24.1% on air fatigue, water fatigue and acid fatigue respectively. Compared to air fatigue, additional 9.1% interlaminar toughness decrease was evidenced for acidic corrosion fatigue due to the coupling effect of chemical corrosion and physical swelling. The fluctuating decline of crack resistance was caused by discontinuous interface damage, and the interlayer damage was randomly distributed. Thus the interface damage model was proposed to characterize the damage distribution and the damage size. Highlights: Degradation law of BFRP under the coupling effect of acid immersion and fatigue load.Interface damage model for characterization of the damage distribution and damage size.Fatigue damage propagation of BFRP under coupling effect of cyclic load and corrosion. [ABSTRACT FROM AUTHOR]

The high-speed trains designed and constructed in Indonesia will use Aluminum alloy Al 6061-T6 as a structural material. Aluminum alloys are prone to fatigue failure due to the absence of endurance limit of the material, hence fatigue life prediction has to be carried out. Fatigue cracks could initiate at the defects of welded joints. Analyzing the fatigue load spectrum of critical locations in the train structures is crucial to predicting fatigue life. These critical locations are selected from areas with high static stress and stress concentration. The loads are analyzed using the multibody dynamic with rigid body assumptions and track roughness following UIC Standard Code 518. The finite element method is used to calculate the stresses from the loads generated by the multibody dynamic. The load sequence is further analyzed with rainflow counting method, and the load exceedance curve can be constructed. Finally, the Miner Linear Cumulative Damage Model is used to predict fatigue life. [ABSTRACT FROM AUTHOR]

In the fatigue design and analysis of concrete structures, an understanding of the dissipated energy characteristics of the material under cyclic loading is important. However, due to the heterogeneity of concrete, the quantitative analysis of dissipated energy is extremely challenging. To investigate the evolution characteristics and influencing factors of dissipated energy, a series of fatigue tests were conducted. Four variable-amplitude cyclic loading schemes were designed to study the relationship between dissipated energy and stress levels, loading frequency, and loading history. The results show a three-phase characteristic of falling-stable-rising in the evolution of single-cycle dissipated energy. The steady value in the second phase is related to the fatigue damage accumulation rate and presents an exponential function with the maximum and minimum stress level. A stress level of 0.75 is considered as the threshold for evaluating the effect of loading history on fatigue damage. The total energy dissipated in the fatigue test has a lower limit close to the energy absorbed in the static test. The relationship between the total dissipated energy and the fatigue life can be described by a linear function in logarithmic coordinates. Based on the evolution characteristics of dissipated energy, a nonlinear fatigue life prediction formula was proposed from the linear damage accumulation model. This study is of great significance for the development and application of the energy-based concrete fatigue damage models. [ABSTRACT FROM AUTHOR]

Fatigue delamination damage is one of the most important fatigue failure modes for laminated composite structures. However, there are still many challenging problems in the development of the theoretical framework, mathematical/physical models, and numerical simulation of fatigue delamination. What is more, it is essential to establish a systematic classification of these methods and models. This article reviews the experimental phenomena of delamination onset and propagation under fatigue loading. The authors reviewed the commonly used phenomenological models for laminated composite structures. The research methods, general modeling formulas, and development prospects of phenomenological models were presented in detail. Based on the analysis of finite element models (FEMs) for laminated composite structures, several simulation methods for fatigue delamination damage models (FDDMs) were carefully classified. Then, the whole procedure, range of applications, capability assessment, and advantages and limitations of the models, which were based on four types of theoretical frameworks, were also discussed in detail. The theoretical frameworks include the strength theory model (SM), fracture mechanics model (FM), damage mechanics model (DM), and hybrid model (HM). To the best of the authors' knowledge, the FDDM based on the modified Paris law within the framework of hybrid fracture and damage mechanics is the most effective method so far. However, it is difficult for the traditional FDDM to solve the problem of the spatial delamination of complex structures. In addition, the balance between the cost of acquiring the model and the computational efficiency of the model is also critical. Therefore, several potential research directions, such as the extended finite element method (XFEM), isogeometric analysis (IGA), phase-field model (PFM), artificial intelligence algorithm, and higher-order deformation theory (HODT), have been presented in the conclusions. Through validation by investigators, these research directions have the ability to overcome the challenging technical issues in the fatigue delamination prediction of laminated composite structures. [ABSTRACT FROM AUTHOR]

To investigate the fatigue crack propagation (FCP) behaviors of high‐strength 7075 and 2024 Al alloys, FCP experiments are conducted for the two alloys at different aging states (underaged [UA], peak aging, and overaged). It is found that strength and plasticity are the main factors influencing the FCP. For 7075 Al alloy, the FCP curves almost coincide for the three aging states that have similar tensile properties. However, 2024 Al alloy shows the lowest FCP rate at the UA state which has the strongest strength–plasticity match among the three aging stages. Based on the low‐cycle‐fatigue damage model, the effect of strength–plasticity balance on FCP rate of the two Al alloys at different aging states is quantitatively analyzed. It is found that the larger the strength–plasticity balance of the alloy, the smaller the FCP rate under the same stress intensity factor. This study indicates that the FCP rate of high‐strength Al alloys is mainly influenced by the strength–plasticity balance due to the difference in the aging states. [ABSTRACT FROM AUTHOR]

Superload (SL) vehicles have unique axle configurations and high axle weights, indicating the potential for a low number of SL applications to cause significant fatigue damage to a jointed plain concrete pavement (JPCP). The current JPCP fatigue model in the AASHTO Pavement Mechanistic-Empirical (ME) Design Guide is unable to account for damage caused by SLs because the stress prediction models within it do not consider these unique axle configurations. As a result, it is not possible to account for the potential fatigue damage accumulation caused by SL applications or identify critical conditions that contribute to damage accumulation using Pavement ME. To address this, a critical, SL stress-prediction model was developed that can be used along with the current fatigue damage model. Typical SL configurations in Pennsylvania were identified based on available permit data, and a database of critical tensile stresses generated by these SLs for various JPCP structures was developed using finite element analysis. This database was used to train a series of artificial neural networks (ANNs), which predict critical tensile stress as a function of SL axle configuration, temperature gradient, and pavement structure. The method for determining fatigue damage accumulation using the ANNs to predict stresses is then presented. [ABSTRACT FROM AUTHOR]

As infrastructure ages, their stability and durability of bridge structures will face new challenges caused by the coupling of multiple physical fields, among which the thermal stress has a particularly profound impact on the structural integrity and safety of bridges. Centered on this coupling effect, this study aims to give a comprehensive investigation on the thermal stress of bridge structures under the influence of multi-field coupling and assess their fatigue life. At first, this study explores in detail the calculation methods for homogeneous material properties, such as the coefficient of linear expansion, elastic modulus, and Poisson's ratio under the influence of various physical fields, and gains accurate calculation results of the linear expansion coefficient and thermal stress of bridge concrete. Then, models are built for analyzing the bridge fatigue performance based on stiffness degradation, including a bridge structure fatigue damage model and a fatigue damage model based on load-bearing capacity degradation, also, a model for the degradation of load-bearing capacity of bridges with stiffness degradation and its residual load-bearing capacity are computed. Existing studies mostly focus on the effects of a single physical field or simplified fatigue damage accumulation models, neglecting the influence of the complex coupling of physical fields and the nonlinearity nature of material properties. By introducing considerations about the structural stiffness degradation under multi-field coupling, this study provides a new perspective and method for assessing the fatigue life of bridges. The findings of this paper not only increase the accuracy of structural thermal stress analysis but also provide theoretical basis and practical guidance for the prediction and maintenance of long-term bridge performance in bridge engineering through establishment of fatigue damage models. [ABSTRACT FROM AUTHOR]

This paper presents a progressive fatigue damage model to predict the damage progress and the fatigue life of composite laminates under cyclic loading. First, the maximum stress criterion was applied in the fiber direction for fiber failure (FF), and Puck's failure criteria were employed in the matrix direction in which the fracture plane is defined to determine the inter-fiber fracture (IFF). Next, material degradation rules consisting of strength and stiffness degradation were derived, and different degradation rules according to the presence of failure and failure mode were utilized for each material. The proposed model was implemented into the UMAT subroutine of ABAQUS for the finite element (FE) analysis with tension–tension cyclic loading. Finally, the progressive fatigue damage model was validated with flat-bar specimens with various lay-ups ([0]8, [90]8, [30]16, [02/902]s, [0/902]s, [0/904]s) and compared with the experimental data of static and fatigue tests. The fatigue life prediction was also conducted on the pin-loaded quasi-isotropic (QI) laminates. The simulation results showed a good agreement with the experimental data and the ability to capture the damage progress of composite laminates during their lifetime. [ABSTRACT FROM AUTHOR]

The failure of composite laminates under cyclic fatigue loads is complex, as multiple failure mechanisms are in play at different scales and interact with each other. Predicting the remaining fatigue life as well as the residual capacities of a composite laminate or component is crucial, particularly for safety-critical applications. A progressive fatigue model is proposed to describe the catastrophic failure of open-hole laminates under tensile cyclic fatigue. To represent both intra-laminar and inter-laminar damage, a combination of a continuum damage mechanics model (CDM) and a discrete cohesive zone model (CZM) is implemented in the finite element (FE) software Abaqus. The CDM combines fibre- and matrix-dominated S-N curves with the Palmgren–Miner accumulation rule and Hashin's residual strength to form a fatigue failure criterion differentiating between fibre failure (FF) and matrix failure (MF). The CZM implemented in this work is the CF20 model proposed by NASA. Fatigue cycling is simulated using an external cycle-jump scheme, where the stiffness degradation is conducted between the FE simulations outside of the implicit solver [90/0] s. Glass fibre reinforced polymer (GFRP) open-hole specimens were tested in tensile cyclic fatigue at a load ratio of 0.1. The experiments were reproduced numerically and the results compared. After calibration of a set of parameters based on one load level, the model was able to reproduce the experimental S-N curve very well, predicting a slope of −0.10, while the experimental value was −0.11. The failure sequence of the laminate was also successfully reproduced. The growth of the split from the hole, and its interaction with inter-laminar delamination, was successfully captured. The proposed approach was able to describe the fatigue failure of an open-hole laminate with a minimal set of material inputs using a simplified fatigue damage model while avoiding convergence issues. [ABSTRACT FROM AUTHOR]

Bistable composite laminates have large-scale applications in morphing and energy-harvesting structures, but their fatigue performance remains largely unexplored. This study investigates the stiffness and damage progression and evaluates bistable performance to develop protocols for long-term applications. We analyze the effects of displacement-controlled fully reversible high cycle fatigue-loading on stiffness, damage, curvature, and snap-through load in the out-of-plane loading direction at eight different combinations of parameters with frequency from 1 to 10 Hz, two boundary conditions, and temperature from 22°C to 150°C up to 3 to 10 million cycles. Stiffness and damage evolution analysis demonstrate the first two stages in out-of-plane fatigue loading. The study proposes a damage definition in terms of load adapting with two fatigue damage models: (1) Shiri Model and (2) Wu Model, while both models exhibit reasonable accuracy in predicting damage for the first two stages despite deviating at the final cycle due to assuming this cycle as the final failure cycle. Of the two models, the Shiri model provided a smaller range of model parameter values, 0.22 and 0.43, for parameters p and q, respectively, which reflects adjustability to different test conditions by maintaining a moderate range. Specimens encountered no final failure by fiber breakage and did not lose bistability for any combination. Curvature and snap-through load measurements have not substantially changed due to fatigue loading. These findings confirm application protocols with a broad range of parameters for which the laminates can operate without significant fatigue damage and maintain their bistable performance for an infinite lifetime. [ABSTRACT FROM AUTHOR]

The strengthening effect of low‐amplitude loading at elevated temperatures was investigated experimentally. A powder metallurgy nickel‐based superalloy FGH96 was preloaded with different cycle numbers and stress levels, and the residual fatigue life was tested under subsequent high‐amplitude loads. The results show that when the number of preloading cycles is in a specific range, the residual fatigue life is higher than that of the virgin specimen under the same load. A novel damage accumulation model was proposed to incorporate the strengthening effect into the life prediction framework. The proposed model was validated using experimental results for various materials in the literature. The mechanism of the strengthening effect of FGH96 was discussed based on electron backscatter diffraction (EBSD) analysis. Highlights: The strengthening effect was found in FGH96 under low‐high sequence loading.The effect of pre‐applied load on the strengthening effect was investigated.A new fatigue damage model considering the strengthening effect was proposed.The microscopic mechanism of the strengthening effect was discussed [ABSTRACT FROM AUTHOR]

In order to reveal the deformation behavior similarity between creep and fatigue, a series of creep and cyclic load tests were performed on siltstone under various load levels. First, the mechanical characteristics of creep and fatigue were compared, by analyzing the strength, ultimate strain, and steady deformation rate of siltstone. Then, a modified fatigue damage creep model was established by connecting a viscoplastic damage element in series with Burgers mode. Finally, the applicability of the model was verified, and the model parameters were analyzed. The results show that the fatigue failure of siltstone is controlled by fatigue strength and limit strain. The modified fatigue damage creep model can accurately describe the whole deformation process of siltstone under cyclic load test. Compared with creep test, the cyclic load hardly affects the elastic modulus of this model. However, the viscosity coefficient of this model is greatly weakened by the cyclic load. Highlights: The deformation behavior between creep and fatigue of siltstone was compared.The modified fatigue damage creep model of siltstone was established.The effect of cyclic load on the creep model parameters of siltstone was analyzed. [ABSTRACT FROM AUTHOR]

Global approaches have been the main procedure to design structural details and components under fatigue loading. This procedure is easy to apply but it disregards not only the effect of the material type but also the influence of the geometry in complex components. On the other hand, local approaches rely on the specific local damage parameters that can be assessed for each type of material and detail geometry. The parameters derived from low cycle fatigue (LCF) tests are the most common damage parameters used to predict the fatigue life and establish reliable fatigue design approaches. Recently, Huffman proposed a fatigue damage model based on strain energy density and on the dislocation density of the material. In this regard, S235 was selected to perform a metallographic and mechanical assessment aiming to define the dislocation density of the material and to describe the fatigue behavior using the Huffman damage model. Additionally, fatigue tests on structural details (plate with hole) were conducted and results were compared with fatigue life predictions based on Huffman local approach. It was found that Huffman model based on dislocation density is a reliable approach to predict the fatigue life of structural steel details. [ABSTRACT FROM AUTHOR]

The present study evaluates the effects of tensile residual stresses on fatigue behaviour of ASTM A516 pressure vessel steel specimens. In this regard, fatigue specimens containing a smooth notch region are studied. A damage coupled elastic-plastic constitutive material model is developed to investigate effects of residual stresses on fatigue life. Isotropic and kinematic hardening parameters of the material are experimentally determined. Additionally, the damage model parameters are specified from fatigue experiments conducted on standard specimens in different stress ratios. Tensile residual stresses are introduced into the smooth notched specimens through employing four-point-bending method. The hole drilling technique is utilized to measure the residual stress magnitudes. The results indicate that about two third of fatigue life of the specimens is decreased due to the existed tensile residual stresses. Furthermore, fatigue crack initiation and propagation behaviour in the specimens containing residual stress are studied based on the developed continuum damage model. [ABSTRACT FROM AUTHOR]

In this paper, comprehensive progressive damage analyses are performed to evaluate the effects of patch sizes and layups on restarting crack growth of single‐side repaired aluminum panels with central inclined cracks under high cycle fatigue loading. Complicated nonlinear damage behavior of adhesive bonding, composite patch, mixed‐mode cracks, and fatigue loadings require precise numerical tools to consider and analyze the coupling effects of various damages on fatigue life of such complex component. In progressive damage analysis, high cycle fatigue cohesive zone modeling is used for debonding of patch, and high cycle fatigue continuum damage model used for composite patches. Practical composite patch layups and sizes are selected in huge number of models, and the restarting crack growth life is predicted. The obtained results show the possibility of increasing the restarting crack growth life using an appropriate composite patch layup and geometry dimensions. Highlights: Restarting crack growth of single‐side repaired panels fatigue loadingComprehensive progressive damage analysesEffects of composite patch size and layup on restarting crack growthCrack growth retardation using appropriate composite patch [ABSTRACT FROM AUTHOR]

Fatigue damage accumulation will not only cause the degradation of material performance but also lead to the growth of effective stress and critical stiffness. However, the existing fatigue reliability models usually ignore the effective stress growth and its influence on the critical stiffness of a composite material. This study considers the combined effects of performance degradation and effective stress growth, and a pair of fatigue reliability models for a composite material are presented. Firstly, the fatigue damage in a composite material is quantified by its performance degradation, and the fitting accuracy of several typical fatigue damage models is compared. Subsequently, the uncertainties of initial strength and initial stiffness are considered, and a pair of probabilistic models of residual strength and residual stiffness are proposed. The performance degradation data of Gr/PEEK [0/45/90/−45]2S laminates are utilized to verify the proposed probabilistic models. Finally, the effective stress growth mechanism and its influence on the failure threshold are elaborated, and a pair of fatigue reliability models for composite materials are developed. Moreover, the differences between the strength-based and stiffness-based reliability analysis results of composite materials are compared and discussed. [ABSTRACT FROM AUTHOR]

To investigate the fatigue reliability of reinforced concrete (RC) bridges under stochastic traffic loading and the effectiveness of limiting the truck load, this study presented an analysis method for evaluating the bridge fatigue reliability under the action of random traffic flows based on truck weight limits. Firstly, a simply RC T-beam bridge was selected as an example to illustrate the presented approach, and the traffic-induced stress spectrum of the tensile rebars in the critical girder of the bridge was obtained. Secondly, based on the collected traffic data from two specific areas, the corresponding random traffic flow was simulated respectively, and then calibrated using the weight limit referring to the current regulation and overload violation rates (VR) to exclude overweight trucks. Finally, based on the S–N curve from Eurocode 3 and Miner's cumulative damage model, the effects of violation rate, average daily truck traffic (ADTT) and truck weight limit (TWL) on the fatigue reliability index of the bridge were studied. The results show that heavy duty trucks will induce serious cumulative fatigue damage, and degrade the durability of RC bridges, while limiting the truck weight can obviously slow down the reduction of the fatigue reliability index. Both the ADTT and the VR can significantly affect the fatigue reliability of the bridge. More specifically, the bridge fatigue reliability index shows a clear downward trend with the increase in the ADTT and the VR. Furthermore, the performance to satisfy the target fatigue reliability of the bridge was compared between TWL for each type of trucks and unified TWL for all the trucks, and then the unified TWL for all the trucks are determined to ensure the target reliability index of the RC bridge after 100 years' service life. [ABSTRACT FROM AUTHOR]

The relationship between heat energy and initial fatigue life of different metals under multi‐level loading stress and elevated temperature is introduced. The fatigue damage evolution model was established from the microscopic and mesoscopic perspectives to explore the fatigue damage and the crack initiation location at elevated temperature. Based on the method of continuous damage mechanics, the influence of multi‐level loads on fatigue cracking life and heat energy on strain energy of distribution were investigated. The mathematical model is verified by the experimental data. The model has important engineering significance for predicting the service life of parts at elevated temperature. Highlights: Fatigue damage model is established by the coupling of microcosmic and microcosmic.The relationship between heat energy and fatigue life is discussed.The influence of heat energy on sub‐surface damage of parts was investigated.Considering the influence of heat energy to improve the accuracy of fatigue model. [ABSTRACT FROM AUTHOR]

The fatigue damage of gear is caused by the coexistence and mutual influence of residual strength degradation and cumulative damage. The residual strength decreases continuously with the change of the loads and the increase of stress cycles. Most of the traditional cumulative damage models ignore the effect of residual strength degradation on cumulative damage. The exponential parameter in the traditional Corten‐Dolan model was defined as exponentials function related to the strength degradation coefficient, and the strength degradation coefficient was deduced by analyzing the residual strength degradation model, and the modified Corten‐Dolan model considering the residual strength degradation was established. Based on the stress‐strength interference model, a gear reliability model considering residual strength degradation was established. The effectiveness of the strength degradation model and the accuracy of the modified Corten‐Dolan model are verified by the analysis of the test data, which provides a new idea for the reliability analysis of gear. The accuracy of the gear reliability model proposed in this paper was verified by Monte‐Carlo (M‐C) simulation, which has practical significance for engineering application. [ABSTRACT FROM AUTHOR]

A large number of experiments were performed to systematically investigate the evolution of the acoustic emission characteristics, dynamic elastic modulus, and axial residual strain of rock under different cyclic loading paths. These results provide experimental support for the damage accumulation and fatigue/failure characteristics of rock structures, and for the construction of a new nonlinear fatigue cumulative damage model suitable for rock materials. More active acoustic emissions are associated with greater acoustic emission intensity, which reflects the association between the dynamic elastic modulus and greater damage. Under increasing cyclic loading, the axial residual strain increases stepwise with increasing load level, following a nonlinear function. Under decreasing cyclic loading, the axial residual strain decreased stepwise and nonlinearly with decreasing load level. [ABSTRACT FROM AUTHOR]

Fatigue damage accumulation under variable amplitude loadings is vital for the life prediction of welded structures. An approach based on damage distribution mapping is presented. S-N curves of welded joints are utilized to construct fatigue damage zones, and a corresponding polynomial fitting function is derived from the heat transfer FEA solution. Experimental results for cruciform and T joints under tensile and three-point bending are employed for validation. Compared with four existing damage models, the proposed approach shows greater accuracy and provides a better description for the early stage of fatigue. [ABSTRACT FROM AUTHOR]

As a popular technique, additive manufacturing (AM) has garnered extensive utilization in various engineering domains. Given that numerous AM metal components are exposed to fatigue loads, it is of significant importance to investigate the life prediction methodology. This study aims to investigate the high-cycle fatigue (HCF) behavior of AM AlSi10Mg, taking into account the influences of powder size and fatigue damage, and a novel ML-based approach for life prediction is presented. First, the damage-coupled constitutive model and fatigue damage model are derived, and the Particle Swarm Optimization method is employed for the material parameters' calibration of M AlSi10Mg. Second, the numerical implementation of theoretical models is carried out via the development of a user-defined material subroutine. The predicted fatigue lives of AM AlSi10Mg with varying powder sizes fall within the triple error band, which verifies the numerical method and the calibrated material parameters. After that, the machine learning approach for HCF life prediction is presented, and the Random Forest (RF) and K-Nearest Neighbor (KNN) models are employed to predict the fatigue lives of AM AlSi10Mg. The RF model achieves a smaller MSE and a larger R2 value compared to the KNN model, signifying its superior performance in predicting the overall behavior of AM AlSi10Mg. Under the same maximum stress, a decrease in the stress ratio from 0.5 to −1 leads to a reduction in fatigue life for both powder sizes. As the powder size decreases, the rate of damage evolution accelerates, leading to shorter fatigue life. [ABSTRACT FROM AUTHOR]

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

Single shear or single lap joints are the most prevalent type of adhesive joints used in advanced engineering applications, where they are exposed to fatigue loadings in their services. Although their mechanical performances under static loading have been investigated extensively, the studies related to the fatigue performances were limited. For that purpose, single lap joints' (SLJs) reaction to fatigue tensile loading was studied by varying the adherend thickness (3 mm to 6 mm) and fatigue load (3250 N to 1500 N). ABAQUS/Standard was used to create its advanced FE model. To represent the progressive damage in the adhesive layer, the fatigue damage model via the Paris Law, which links the rate of the crack expansion to the strain energy release rate (SERR), was integrated into the cohesive zone model with bi-linear traction–separation characteristics. The model was written in a UMAT subroutine. The developed model was validated using experimental data from the literature. The crack initiation cycle (Ni), the failure cycle (Nf), the fatigue load limit, the strain energy release rate, the crack propagation rate, and variation of stress components with their dependency to design parameters were investigated in depth. It was found that the service life of the SLJs with thicker adherends was more responsive to the amount of stress applied. When exposed to lesser loads, the SLJs' life span changed more noticeably. [ABSTRACT FROM AUTHOR]

In this study, the characteristics of the fracture evolution of argillaceous shale under increasing-amplitude loading were investigated. The GCTS RTR-2000 test system and in-situ acoustic emission (AE) monitoring were employed to execute the tests. The following results were observed. (1) The strength, deformation, and fatigue life increased with the frequency, and the morphology of the hysteresis curve changed regularly with time. (2) The cumulative damage of the rock at the location in which the stress amplitude suddenly increased exceeded that at the fatigue loading stage. The AE count and AE energy were affected by the loading frequency. (3) The secant modulus exhibited different values for different loading frequencies; the smaller the loading frequency, the fewer loading stages the samples experienced, and the faster the secant modulus decreased. The change in Poisson's ratio over the entire process was composed of a steady growth stage and a rapid growth stage. (4) The rock exhibited two stages of damage evolution, with rapid damage accumulation occurring at the beginning of the loading and relatively smooth damage occurring thereafter. This study developed a cumulative fatigue damage model that can adequately fit the accumulated damage during the fracturing process. The experiments revealed that variable amplitude fatigue loading at different frequencies significantly influences the damage deterioration and the failure law of the rock. The results are expected to improve the understanding of the frequency effect on the fracture behavior and help predict the lifespan of rock structures. This is of great significance to the promotion of slope management, landslide disaster prevention, and mine reuse at the West Open-pit Mine. [ABSTRACT FROM AUTHOR]

The aim of this paper is to characterize the fatigue under various random strain loads that consider the effects of cycle sequence conditions. Due to the frequent exposure of fatigue damage to a leaf spring, the fatigue life calculation needs to consider a load cycle sequence effect. A finite element analysis is performed to determine the critical region on the leaf spring. In addition, the strain loads were experimentally captured under three different road load conditions, i.e., rural, campus, and highway, in order to obtain the strain load behavior under random data. The fatigue life predicted using an established strain-life model was 3.63 × 103 to 4.19 × 107 cycles/block, and the effective strain damage model was 1.04 × 105 to 1.75 × 106 cycles/block. The correlation fatigue life data show the data are within the 1:2 and 2:1 boundary condition with a high R2 value in a range of 0.9994–0.9998. It shows fatigue life data are highly correlated because they reflect the effects of cycle sequence. Hence, the effective strain damage model that considers the cycle sequence effect can provide an accurate fatigue life prediction compared to the traditional strain-life model under various road loads. [ABSTRACT FROM AUTHOR]

Based on the continuum damage mechanics theory, a frequency‐dependent high‐cycle fatigue damage evolution model was established. According to the fatigue results of API X80 steel, the frequency‐dependent damage evolution parameters were regressed. Using the available riser mechanical model, the user subroutine of high‐cycle fatigue damage evolution was compiled, and the accelerating effect of corrosion pits on fatigue crack initiation of the marine riser was analyzed. The results show that a single corrosion pit at the surface can reduce crack nucleation life by more than 80%. In a double corrosion pits' case, the stress interference between pits significantly affects the crack nucleation. Circumferential double pits can produce a fatigue crack earlier than the single pit, but the effect of axial double pits is just the opposite. When the spacing reaches a certain distance, the stress interference disappears, and the crack nucleation life approaches that of a single pit case. Highlights: A special frequency‐dependent high‐cycle fatigue damage model was established.Frequency‐dependent damage parameters were determined from fatigue tests of X80 steel.The acceleration effect of corrosion pits on fatigue crack nucleation was evaluated. [ABSTRACT FROM AUTHOR]

This paper proposed a high‐cycle fatigue life prediction method for Al–Zn–Mg alloy welded joints considering the thermal process of welding and the effect of welding pores. First, the welding process was simulated by a numerical thermal–mechanical analysis. The residual stresses were then obtained and applied as the initial stress field of the subsequent fatigue life calculation. Second, a fatigue damage model was constructed by introducing a dimensionless quantity to equivalently describe the effect of interior pores. Further, a corresponding damage mechanics–finite element numerical method was numerically implemented by the ABAQUS platform to calculate the high‐cycle fatigue life for Al–Zn–Mg alloy welded joints. The calculated lives have good consistency with test data, which validates the feasibility and applicability of the proposed model and the calculation method. Finally, the curves of the cyclic stress versus fatigue life of Al–Zn–Mg alloy welded joints with different interior pore sizes were calculated to explore the influence law of the welding pore. Highlights: An HCF damage model considering the effect of inner pores is developed and validated.Fatigue lives of welded joints are predicted under various cyclic stresses and pore sizes.The influences of interior pores on fatigue damage and fatigue life are studied in detail. [ABSTRACT FROM AUTHOR]

A phenomenological 3D anisotropic nonlinear fatigue damage model has been developed for a short glass fiber-reinforced polyamide. The model is formulated within the framework of continuum damage mechanics and is based on a proposed anisotropic hyperelastic strain energy function. The proposed model accounts for the effects of fiber content and nonlinear material behavior. The mechanical behavior of polyamide reinforced with 20% and 30% wt short glass fiber has been experimentally investigated under quasi-static and fatigue loading. Fatigue tests under bending loading are carried out on rectangular specimens cut in the parallel and perpendicular direction to the mold flow direction. The proposed fatigue damage model allows predicting the fatigue damage of composite materials reinforced with short fiberglass, considering fiber orientation and fiber content. The model is used to predict the damage evolution and the number of cycles to failure, and good agreement between predicted values and experimental data is observed. [ABSTRACT FROM AUTHOR]

Mechanical clinching is used to create lightweight hybrid structures. In order to estimate the service life of clinched components, its fatigue properties need to be known under different mechanical loading conditions. In addition to fatigue, corrosion is another factor that affects the fatigue life of clinched joints. In the literature, many corrosion and high-cycle fatigue damage models exist. However, little is known about how both phenomena interact in clinched joints. In this article, the influence of galvanic corrosion on clinched EN AW-6014/HCT590X + Z sheets on the fatigue life is investigated by means of numerical simulations and experimental results. An accurate prediction of the Wöhler lines of non-corroded and pre-corroded clinched specimens is shown. [ABSTRACT FROM AUTHOR]