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A multi-stage precipitation model is formulated to predict the microstructural evolution and explain the high performance of additive friction stir deposited aluminum alloy 7050 (AA 7050) for hole repair. The first stage is the heating process due to the high-temperature thermomechanical process of the stir. In this process, small η precipitates dissolve as they lose their stability with increasing temperature, and this causes the volume fraction of η precipitates to decrease and the concentration of Mg and Zn in the matrix to increase. The second stage is the cooling process at the end of the repair where material feeding ends and the tool is lifted away. Heterogeneous nucleation of η precipitates may occur and as the temperature cools below 250 °C, Guinier–Preston (GP) zones start to form. The final stage is the natural aging process, where the η ′ precipitate starts to grow. The volume fraction and precipitate radius are predicted for each type of precipitate. Furthermore, the fine η ′ precipitates and GP zones with a decent volume fraction improve the material strength and fatigue life. [ABSTRACT FROM AUTHOR]

ABSTRACT The time domain is the most widely chosen alternative in mechanical fatigue tests to completely represent random events. However, the main disadvantages of this approach are the long time required to complete the tests and the high cost of the complex equipment. On the other hand, fatigue test in the frequency domain is a potential alternative to overcome these disadvantages. That is, it requires less sophisticated equipment, because it uses only simple actuators instead of servo actuators. Moreover, the duration of the fatigue test is reduced, because the total length of the event is replaced by constant repetitions and constant damage. The objective of this work is to propose and develop a methodology that uses the results of structural fatigue as a starting point, and through an optimization problem solved by the genetic algorithm, it determines which loads/displacements caused them in the frequency domain. The purpose is to assist future developments in fatigue tests, supplanting tests in the time domain without losing the correlation in results. [ABSTRACT FROM AUTHOR]

Cold expansion is a mechanical method for creating residual stresses. This method is a proven technique to increase the fatigue life, and checking the residual stress on it, is of particular importance. A cold expansion process is widely used to generate beneficial residual stresses into an annular region around the hole. In the present research work, AA 6016-T6 and AA 1100 aluminum alloys which are two strain rate sensitive materials, were subjected to cold expansion process with different mandrel velocities. In fact, the effect of mandrel velocity on the created residual stresses has been investigated. The constants of the Johnson-Cook material model have been determined for them and the process has been investigated, experimentally and numerically. The obtained results revealed that the values of the residual stresses created in the sheets depend on the velocity of the process especially at the edge of the sheets holes. By increasing the mandrel velocity from 5 to 500 mm/min, depending on the distance from the hole to the edge of the sheet, it is possible to enhance the hoop residual stress by 37.3–41.2% in AA 1100 aluminum alloy and by 37.6–38.1% in AA 6016-T6 aluminum alloy. This research showed that in all cases, the radial residual stresses created around the holes are negative. Also, it was cleared that due to the existence of material constraints and the movement of the sheet material, the amount of hoop residual stress created in the mid-thickness is more than the exit face and in the exit face is also more than the entrance face, exactly unlike the size of their zones. [ABSTRACT FROM AUTHOR]

Highlights Assessing the mechanical properties of CFRP and aluminum specimens exposed to hygrothermal aging is vital. Moreover, it is important to develop strategies to improve these properties. This study examines the influence of fullerene and Single‐Walled Carbon Nanotubes (SWCNT) on the fatigue life and static strength of bonded and bonded/bolted joints. The research concentrates on composite‐to‐composite and composite‐to‐aluminum substrates under three‐point bending tests, both prior to and after hygrothermal aging. The samples were classified into four groups: (1) neat specimens, (2) specimens with added fullerene, (3) specimens containing SWCNT, and (4) specimens with a blend of 50% SWCNT and 50% fullerene.The findings indicated that the optimal nanoparticle ratio for bonded joints differs from that for bonded/bolted joints. Incorporating nanoparticles into the adhesive enhanced the fatigue life of single lap joints (SLJs), particularly in samples with mixed particles and SWCNT. In some instances, nanoparticles intensified the effects of hygrothermal conditions, further increasing fatigue life. The incorporation of nanoparticles and the use of bonded/bolted joints significantly enhanced joint strength, with the combination of both yielding the best results. This study improves the understanding of aging in adhesive and hybrid joints, particularly in dissimilar configurations, and offers insights into their performance under various environmental conditions. Study examines fullerene and SWCNT impacts on CTC/CTA joint strength and fatigue. Optimal nanoparticle ratios differ for bonded and bonded/bolted joints. Nanoparticles reduce moisture absorption, aging damage, and increase failure load. Nanoparticles enhance fatigue life, varying by type, volume, load, and joint. Incorporating nanoparticles significantly improves joint strength. [ABSTRACT FROM AUTHOR]

ABSTRACT A feature transfer learning (FTL)‐based model is proposed to address small‐sample problems in fatigue life prediction of additively manufactured (AM) metals. Transfer component analysis (TCA) is studied for data alignment before model training. Correspondingly, two TCA improvement strategies are further considered to aggregate training data from distinct AM processing conditions. An experimental database consisting of 103 fatigue data is built for model evaluation. The results demonstrate that the proposed model outperforms conventional machine learning models and other transfer learning‐based models in terms of accuracy and data demand, showing good applicability for AM fatigue life assessment. [ABSTRACT FROM AUTHOR]

High performance bolts, made of continuous fiber reinforced silicon carbide composites (C/SiC), are crucial to the design and preparation of the hot-end C/SiC components with large complex structures both in aerospace and aeronautical fields. In this work, in-situ grown SiC whiskers were uniformly introduced into the porous laminated 3DN C/SiC countersunk bolt, in order to improve the brittle nature of the 3DN C/SiC threads. Results showed that 7 % increase of tensile strength of the 3DN C/SiC countersunk bolts was achieved via in-situ grown SiC whiskers, and a fatigue life of 106 cycles was also passed. The stud fracture morphologies indicated that the SiC whiskers grew within the woven pores and toughened the layered SiC matrix, so that the load transfer between the layered SiC matrix and carbon fibers was improved under tension. Further high temperature tests showed that the tensile and the shear strengths of the in-situ toughened 3DN C/SiC countersunk bolts were degraded to 64.74 % and 28.83 % at 1000 °C in air respectively. During the thermal exposure, the carbon fibers were largely consumed by oxidation, while the SiC whiskers grew slender and formed a fluffy layer to partially reinforce the SiC matrix. The synergy effect of SiC whiskers and carbon fibers to hinder crack propagation and to toughen the SiC matrix contributes to the above mechanical properties of the bolts. [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]

New materials have emerged in the dental field to replace the cobalt-chrome (CoCr) alloy used for the metal frameworks in removable partial denture (RPD) such as Titanium (Ti) and PolyEtherEtherKetone (PEEK). However, few studies have demonstrated their mechanical and biological performance. The purpose of this systematic review was to compare the performance of Ti and PEEK in RPD using CoCr metal framework as a reference. This review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Three data bases were analyzed, including PubMed/MEDLINE, Embase and Web of Science before March 2024. Only studies assessing the mechanical and/or biological properties of RPD in Ti, PEEK and CoCr were included. The quality of the studies was assessed by using the software Rayyan. The risks of bias were assessed with the methodological index for nonrandomized studies (MINORS). The mechanical (retention force, fatigue life, deformation strength, machinability, rigidity, porosity and surface roughness) and biological (plaque indices, ion release and biocompatibility) aspects were assessed. Among 138 articles identified, only 18 studies were included in this review. Majority had a low to moderate risk of bias. Retention forces and fatigue were significantly lower for Ti and PEEK than for CoCr, and the same was true for Ti rigidity. PEEK showed less deformation. Both materials were suitable for machining. In terms of biological properties, both materials showed adequate biocompatibility for clinical use. Ti and PEEK seems to be promising as alternative materials to CoCr frameworks for RPD, in terms of both their mechanical and biological performance. However, additional studies are needed to better understand their clinical and long-term limitations to enable the best-informed clinical choice for the patients and the professionals. [ABSTRACT FROM AUTHOR]

The multi-parameter characteristics of the physical model pose a challenge to the fatigue life prediction of 2024-T3 aluminum (Al) alloy. In response to this issue, a parameter-solving method that integrates particle swarm optimization (PSO) with extreme gradient boosting (XGBoost) is proposed in this study. The fatigue performance and failure mechanism of the 2024-T3 Al alloy are analyzed. Furthermore, the fatigue life prediction physical model of the 2024-T3 Al alloy is established by using the energy method of fracture mechanics. The physical model incorporates critical physical parameters. Meanwhile, the PSO algorithm optimizes the hyperparameters of the XGBoost model based on fatigue data of the 2024-T3 Al alloy. Eventually, the optimized XGBoost model is used to solve the parameters of the physical model. Furthermore, the analytical equation of the fatigue life prediction model is obtained. This paper provides a new method for solving the parameters of the fatigue life prediction model, which reduces the error and cost of obtaining the model parameters in the experiment and shortens the time required. [ABSTRACT FROM AUTHOR]

This study experimentally assessed the shear performance of reinforced concrete (RC) beams strengthened with U-shaped High-Performance Fibre-Reinforced Concrete (HPFRC) under static and fatigue loading. Key parameters included HPFRC jacket thickness and beam shear span–depth (a/d) ratio. Five beams were tested under static loads to determine ultimate shear strengths, followed by fatigue tests on identical beams at 30–70% of ultimate shear strengths at 4 Hz. In static loading experiments, all the HPFRC jacketing proved effective, increasing the shear strength of RC beams by 95% to 130%. Although the strengthening system did not change the failure mode of the beams, the strengthened beams exhibited pseudo-ductile behaviour. As the a/d increased, the shear enhancement capability of the HPFRC jackets decreased. In fatigue loading experiments, all the HPFRC systems improved the fatigue life of RC beams. Specifically, in beams with an a/d ratio of 2.0, the fatigue life was extended from 75 cycles to a maximum of 951 cycles, while in beams with an a/d ratio of 3.5, it increased from 12,525 cycles to 48,786 cycles. In addition, a predictive model has been developed for the fatigue life of HPFRC/UHPFRC shear-strengthened beams, utilising the maximum fatigue load and the design's ultimate shear strength under static loading conditions. [ABSTRACT FROM AUTHOR]

The stress state of the primary circuit main pipeline is very complex mixed constant stress and periodic cyclic stress during the operation of nuclear power plants, which often affects the failure behavior of the stainless steel (SS) pipe. The fatigue behavior of 304LN SS under mixed constant stress and cyclic stress was investigated, and it was found that the coupling effect of constant stress and cyclic stress has a significant collaborative acceleration on the fatigue behavior. The research results showed that the cracks in the 304LN SS did not propagate even after 78 days under both constant load conditions of 5 KN and 7.5 KN, while the crack growth rate (CGR) of the specimen increased by about an order of magnitude when coupled with a cyclic fatigue load. The fatigue life of 304LN SS was the longest under 200 °C high-temperature water, and its life was roughly the same under 250 °C and 300 °C water. In a 300 °C high-temperature water environment, the fatigue life under the coupling of constant stress and cyclic fatigue stress is significantly lower than that under symmetric cyclic stress alone. There is a synergistic acceleration effect on the fatigue life of 304LN SS when constant stress is coupled with periodic cyclic stress, which is attributed to the combined effect of a corrosion environment and mechanical factors. [ABSTRACT FROM AUTHOR]

The operational practice of the design of the Bozena 5 demining machine has shown that its belts are the critical component that fundamentally affects the functionality of the entire machine. This article is a practical continuation and extension of the previous research results from the point of view of materials (research of the uniaxial fatigue life in bending and torsion), calculation (creation of the necessary mathematical, analytical and numerical models for the research) and construction (i.e., patented design of the belt tensioning of this machine). All these actions are aimed at a single objective—to achieve a condition that guarantees a sufficient service life without malfunctions, since repairing these machines in the field is often impossible. Therefore, this study examined the fatigue life of welded joints (uniaxial bending and torsion) of S960 QL and S500MC steels welded by MAG technology. Subsequently, the data were compared with previous results (electron and laser welds) and the influence of each type of weld on the fatigue life relative to the base material was discussed. It was found that conventional MAG technology had a more significant negative impact on the fatigue life of the base material than non-conventional technologies. This trend was particularly true for the bending stress. At the same time, the bending stress was identified by the FEM analysis as the dominant load on the belt. The maximum stress in the belt link under the considered boundary conditions was approximately 240 MPa (in bending). This stress corresponded to the continuous fatigue life (more than 107 cycles) for both base materials tested (S960QL, S500MC). In the whole studied spectrum of controlled deformation amplitudes (Manson–Coffin), the life of MAG welds was lower in comparison with the base material and with welds made by unconventional technologies. All the activities carried out so far (research on microstructure, hardness, strength, residual stresses, tribological properties and fatigue life) have shown that the original belt design (S500MC) using MAG technology has significant deficiencies in the state of optimal life. It is expected that the proposed material change (use of S960QL instead of S500MC) and work with advanced technologies will bring this state significantly closer. [ABSTRACT FROM AUTHOR]

The fatigue behavior of metal specimens is influenced by defects, material properties, and loading. This study aims to establish a multi-scale fatigue crack growth model that describes physically short crack (PSC) and long crack (LC) behavior. The model allows the calculation of crack growth rates for uniaxial loading at different stress ratios based on the material properties and specimen geometry. Furthermore, the model integrates the Gaussian distribution theory to consider material heterogeneity and the experimental measurement errors that cause fatigue scatter. The crack growth rate and fatigue life of metal specimens with different notch geometry were predicted. The curves generated by the multi-scale model were mainly consistent with the test data from the published literature at the PSC and LC stages. [ABSTRACT FROM AUTHOR]

Biodegradable implants as bone fixations may present a safe alternative to traditional permanent implants, reducing the risk of infections, promoting bone healing, and eliminating the need for removal surgeries. Structural integrity is an important consideration when choosing an implant material. As a biodegradable implant is being resorbed, until the natural bone has regrown, the implant material needs to provide mechanical stability. However, the corrosive environment of the human body may affect the fatigue life of the material. Conversely, mechanical stress can have an effect on electrochemical corrosion processes. This is known as corrosion fatigue. In the presented work, an experimental setup and methodology was established to analyze the corrosion fatigue of experimental bioresorbable materials while simultaneously monitoring the electrochemical processes. A double-walled measurement cell was constructed for a three-point bending test in Dulbecco's Phosphate-Buffered Saline (DPBS− −), which was used as simulated body fluid (SBF), at 37 ± 1 °C. The setup was combined with a three-electrode setup for corrosion measurements. Rod-shaped zinc samples were used to validate the setup's functionality. Preliminary static and dynamic bending tests were carried out as per the outlined methodology to determine the test parameters. Open-circuit as well as potentiostatic polarization measurements were performed with and without mechanical loading. For the control, fatigue tests were performed in an air environment. The tested zinc samples were inspected via scanning electron microscopy (SEM). Based on the measured mechanical and electrochemical values as well as the SEM images, the effects of the different environments were investigated, and the setup's functionality was verified. An analysis of the data showed that a comprehensive investigation of corrosion fatigue characteristics is feasible with the outlined approach. Therefore, this novel methodology shows great potential for furthering our understanding of the effects of corrosion on the fatigue of biodegradable implant materials. [ABSTRACT FROM AUTHOR]

Mechanical failure of biological nanostructures due to sustained force application has been studied in great detail. In contrast, fatigue failure arising from repeated application of subcritical stresses has received little attention despite its prominent role in engineering and potentially biology. Here, paclitaxel-stabilized microtubules are up to 256 times bent into sinusoidal shapes of varying wavelength and the frequency of breaking events are observed. These experiments allow the calculation of fatigue life parameters for microtubules. Repeated buckling due to 12.5% compression–equal to the compression level experienced by microtubules in contracting cardiomyocytes – results in failure after in average 5 million cycles, whereas at 20.0% compression failure occurs after in average one thousand cycles. The fatigue strength (Basquin) exponent B is estimated as − 0.054±0.009. [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]

The Manson-Halford (M-H) nonlinear cumulative damage model is widely applied for fatigue life analysis problems under multi-level loading. In this model, the influence of loading sequence on the fatigue life can be better considerer, but the loading interaction effect is ignored. An improved whale optimization algorithm (IWOA) by integrating multiple strategies is proposed. The ability of global search and local exploitation is balanced and improved through nonlinear convergence factor, adaptive weighting factors and the Cauchy reverse learning strategies. In order to fully account for loading interaction effect, loading weighting factors are introduced to modify the M-H model, and the parameters are optimized through the global search properties of IWOA. The model is evaluated on multi-level loading fatigue experimental data from five metal materials and two aluminum alloy welded joints. The results suggest that the proposed IWOA has better optimization accuracy compared to the standard whale optimization algorithm (WOA). The proposed modified M-H model has better prediction performance compared to the four traditional cumulative damage models, which can be effectively applied to multi-level loading fatigue life analysis problems under actual working conditions. The proposed model is useful for the study of fatigue life evaluation methods. [ABSTRACT FROM AUTHOR]

Purpose: The present paper aims to study the influence of the substrate system on the thermomechanical response of various lead-free die attach materials used in power electronics using nonlinear finite element simulations. Design/methodology/approach: Particularly, three ceramic substrate systems, including direct copper bonded (DCB) and aluminum nitride (AlN) – as well as silicon nitride (Si3N4) –based insulated metal substrate (IMS) configurations are examined in this study. Additionally, three die attach systems, namely, silver-tin transient liquid phase (TLP), sintered silver (Ag) and sintered copper (Cu) are included in the analysis. ANSYS software is employed to build the finite element models of the power modules and to conduct the nonlinear thermomechanical investigations. Findings: The simulation results revealed that the IMS, Si3N4 and DCB-based power modules end up with significantly lower interconnect inelastic strains and inelastic strain energies suggesting better fatigue life performance. Additionally, the bonding layer stresses and expected failure mechanism are not influenced by the substrate configuration rather than the bond material. For instance, the silver-tin TLP joints develop high stresses and hence brittle failures are expected. Nonetheless, the sintered Ag and sintered Cu have significantly lower stresses which could lead to fatigue-induced failures. Originality/value: Power electronics use various ceramic-based substrate systems because of their improved thermal conductivity, electrical insulation and heat resistance properties. The proper selection of the substrate structure could highly enhance the thermal fatigue of the power modules. Markedly, the findings of this research are useful for designing highly reliable and effective power modules continuously subjected to thermomechanical loadings. [ABSTRACT FROM AUTHOR]

The uniformity and efficiency of ultrasonic needle peen-forming (UNPF) cannot be achieved by a handheld single-needle peening device. Thus, a novel robotized UNPF system is designed in this paper with a multi-needle peening device. By taking the aluminum alloy 2024-T3 specimens as an example, the peening device's travel velocity and standoff distance are first determined to balance processing efficiency and safety. Thereafter, the resulting arc height for Almen-size specimens with respect to other manipulated variables (MVs), such as the vibration amplitude, the air pressure, and the number of peening passes, are fitted by the data-driven models. As the radius of curvature at the saturation state is identical for small and large specimens with similar shapes, its relationship with the arc height and at the saturation state is represented by a function of elliptic paraboloid for understanding the limit of UNPF capability. It is shown that specimens of different sizes but the same aspect ratio have a consistent radius of curvatures after being treated with the same MVs. Notably, by increasing the vibration amplitude from 21 to 35 μ m , the ratios of peening time required for achieving full coverage to its counterpart for achieving saturation state reduced from 76 to 8.3%, showing a significant improvement in forming productivity and capability. Furthermore, increasing the number of peening passes, from 1 to 32 significantly reduces surface roughness by up to 86.4%, approaching the as-received specimen's smoothness. Moreover, the maximum compressive residual stress after UNPF is - 500 MPa at a depth of 1.2 mm, and the hardness is drastically increased by 45.4% for specimens of thickness 1.5 mm, improving their fatigue life. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Quality & Reliability Engineering International. The issue showcases original research presented at the 2023 International Conference on Quality, Reliability, Risk, Maintenance, and Safety Engineering. The research papers cover a diverse range of topics related to reliability and safety in modern engineering systems. The papers address areas such as reliability modeling and analysis, reliability-based design and optimization, failure/safety analysis and prevention, and maintainability. The authors express their appreciation to the journal and the reviewers for their support and hope that the research presented will be valuable to researchers, engineers, scientists, and students in the field. [Extracted from the article]

Air pollution monitoring is an important issue in environmental science. The Birnbaum–Saunders (BS) distribution, originally applied to describe product failure time distribution to fatigue failures and general random wear failures, is also well to describe the pollutant concentration data due to accumulations of various pollutants in the air over time. Sulfur dioxide (SO2) is a critical factor in air pollution. Hence, it is important to monitor its concentration variation for air pollution prevention. Due to the complexity of its distribution form, there is no reliable and easy‐to‐use control chart for monitoring pollutant concentrations based on the BS distribution. We found that the SO2 concentration data follows the BS distribution. In this study, we propose a new median control chart based on the exact sampling distribution of the monitoring statistic to detect shifts in the median of BS distribution. Thus, given the false alarm rate, the control limits for such control charts can be obtained precisely satisfying a preset in‐control average run length using Monte Carlo simulations. The out‐of‐control average run lengths are calculated by simulation to evaluate the detection performance of the proposed chart when the median shifts occur. We further compare the detection performance of the proposed chart and those of the existing control charts based on asymptotic sampling distributions. In order to improve the detection ability of the proposed chart for small median shifts, an exponentially weighted moving average (EWMA) control chart is constructed. The results of numerical analyses demonstrated that the proposed EWMA chart performs much better than all existing control charts for monitoring the median of BS distribution. Finally, the proposed control charts are applied to monitor the median of SO2 concentrations for air pollution control, showing that both charts can effectively detect a shift in the median of SO2 concentrations. The proposed EWMA control chart even detects out a small shift in the median of SO2 concentrations. The results provide a continuous monitoring solution for air pollution prevention. [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]

With the rising importance of virtual engineering in an increasingly competitive marketplace, there is a growing need for simplified representations of finite element (FE) modeling for spot joints in lightweight structures without losing accuracy in structural life evaluation. For this purpose, this paper presents a spot weld element with an implicit weld representation and its numerical implementation as a user element for deployment in commercial FE code for reliably computing traction structural stress in a mesh‐insensitive manner. The spot weld element is formulated by degenerating conventional first‐order four‐nodes shell elements by imposing kinematic constraints with respect to a series of virtual nodes placed in the region around a spot weld. The simplicity and effectiveness of the spot weld element have been validated by comparing with the explicit weld representation for computing mesh‐insensitive structural stresses and fatigue life correlation of welded components. Highlights: A robust method is proposed to accurately determine structural stress around spot welds.A special shell element formulation is provided for implicitly modeling of spot welds.A user element subroutine of spot weld element is programmed for FEM solver.The spot weld element is validated for correlating fatigue test data [ABSTRACT FROM AUTHOR]

This work investigates the impact of temperature on the fatigue life All Aluminum Alloy Conductors (AAAC) made of 6201‐T81. A heating chamber was developed to simulate thermal effects induced by electric current passage. Wöhler fatigue curves were generated under isothermal conditions at 75 and 150°C and later compared with the one at 20°C. The conductor exhibited similar fatigue life at 20 and 75°C; however, a significant increase of life was observed for tests at 150°C. Hardness tests and failure analysis of wire breakages were carried out on samples extracted from the conductor coil and on artificially aged samples maintained at controlled temperatures. The analyses revealed that at a temperature of 150°C, there is formation of small precipitates of magnesium and silicon within the aluminum matrix, which impeded the propagation of discontinuities, increasing the material's hardness and fatigue resistance. Highlights: The designed heating chamber simulates thermal effects during fatigue tests on conductors.S‐N curves at 20, 75, and 150°C reveal enhanced conductor life at higher temps.Failure analysis present similar patterns across all temperature fatigue failures.Samples' hardness on conductor wires shows a temperature‐induced mechanical changes. [ABSTRACT FROM AUTHOR]

In this paper, a modified theory of critical distance (TCD) method (i.e., Gradient‐TCD method) is proposed, which combines fatigue parameter gradient and the TCD, to estimate fretting fatigue life of dovetail joints. The advantage of Gradient‐TCD method lies in utilizing the gradient parameters to effectively characterize the local effect zone caused by fretting, thereby enabling the determination of a suitable critical distance length independent of material fatigue parameters. The reliability and predictive capability of the method is validated through experimental results. Furthermore, this method demonstrates insensitivity to mesh size, resulting in an 83.6% reduction in computational time while maintaining the predictions within the two‐times scatter band. The novel Gradient‐TCD method may provide an efficient and reliable approach for fretting fatigue life prediction, which holds promise for evaluating complex full‐scale fretting problems. Highlights: A Gradient‐TCD method was proposed to determine the length of critical distance.The Gradient‐TCD method effectively predicts the dovetail joints fretting fatigue life.Its insensitivity to mesh size results in an 83.6% reduction in computation time.It provides a promising solution for full‐scale fretting fatigue evaluation. [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]

This research delved into the mechanical and fatigue attributes of hemp fiber–reinforced concrete (HFRC) using both natural crushed aggregates (NCA) and recycled concrete aggregates (RCA) for sustainable rigid pavements. The additional hemp fiber ratios were 0%, 0.5%, 0.75%, and 1.0% by volume of concrete. The accelerated setting times were found due to hemp fibers facilitating rapid cement hydration. The compressive strengths were found to typically decrease with increasing hemp content. Mixes with 0.5% hemp (NCA-0.5H-FRC and RCA-0.5H-FRC) met the local road authority's rigid pavement standards, with enhanced energy absorption and ductility. Flexural strength was optimal at 0.5% hemp, with all mixes meeting the standard 4.2 MPa. The flexural fatigue test indicated that higher hemp content significantly improved the fatigue life of HFRC under repetitive loading. Scanning electron microscopy (SEM) analysis demonstrated hemp fibers' role in enhancing bond strength and interactions with cement matrix, thereby improving the concrete performance. While NCA mixes outperformed RCA ones, hemp fiber's reinforcing effect was consistent across both types of aggregates. The study indicated hemp fiber's potential in applications like pavements, highlighting 0.5% as the optimal hemp content for balancing enhanced mechanical properties while mitigating potential drawbacks. This research paves the way for the broader adoption of hemp fiber–reinforced concretes in sustainable construction endeavors. [ABSTRACT FROM AUTHOR]

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

This study investigated the flexural fatigue performance of pavement-grade geopolymer concrete (GPC) developed using low-carbon binders containing waste clay bricks (WCB), slag, and fly ash. Concrete was developed using two types of binders, one with a ternary blend of WCB, slag, and fly ash and one with only slag and fly ash as a full replacement for ordinary portland cement (OPC). Test specimens were subjected to flexural fatigue by four-point bending under three levels of stress which are equivalent to 75%, 80%, and 85% of the maximum static flexural strength. A two-parameter Weibull distribution was considered in the probabilistic analysis of fatigue life data, which corresponds to the number of cycles until failure. At all stress levels, GPC showed better fatigue performance compared to OPC concrete. At lower stress levels, the performance of GPC with WCB in the binder was better than the performance of conventional GPC with only slag and fly ash. However, GPC with WCB shows reduced performance at higher stress ratios. Survival probability of all concrete types (i.e., GPC and OPC concrete) decreased with increasing stress level. At a selected stress level, the fatigue life of all concrete types increased with the decrease of survival probability. The ultimate fatigue strength of GPC was higher than the OPC concrete. GPC with WCB binders showed an ultimate fatigue strength of more than 68% considering 107 repeated loading cycles. Practical Applications: Improving sustainability within the construction industry is a current major challenge, and all the while it is becoming an indispensable necessity. Transitioning from conventional materials with high negative environmental impacts such as OPC to more sustainable alternatives can significantly enhance sustainability in the construction industry. However, absence of data regarding the overall performance of newly identified low-carbon materials is a limiting factor to the industry uptake of these alternatives. The findings from this research characterize the fatigue behavior of low-carbon concrete that is developed using WCB-based binders and designed for pavement applications specifically. Understanding the fatigue performance is crucial for any material intended for use in pavement applications. The results from the current work provide valuable insights into the targeted application of these innovative materials, addressing a critical gap in information. [ABSTRACT FROM AUTHOR]

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In recent research on building materials, researchers have increasingly focused on replacing cement with agricultural waste. This approach offers significant advantages in terms of reducing global CO2 emissions and promoting the sustainability of building materials. In this paper, the use of the agricultural waste walnut shell ash (WSA) to partially replace cement in sustainable green mortars is explored. Specifically, equal amounts of WSA (5%, 10% and 15%) were used to replace cement. To offset the reduction in strength caused by the partial replacement of cement with WSA, basalt fibers were added to the mortar mixture. The effect of these fibers on the mechanical properties of the WSA-reinforced mortar was examined in compression tests, split tensile tests, and flexural fatigue cycle tests. In the flexural fatigue tests, the parameter and length of basalt fibers were varied and different stress levels (0.85, 0.8 and 0.75) were applied. The fatigue equations were developed using the Weibull model and p–s–n curves with a survival probability of 0.5 were derived. The results showed that the compressive strength and split tensile strength of the specimens increased with the addition of basalt fibers, with maximum values of 34.7 MPa and 3.8 MPa, respectively, and maximum increases of 8.78% and 21.95%, respectively. In addition, the average fatigue life of WSA mortar was 247,541 cycles, which increased by 139.26% when the stress level was 0.75, fiber length was 9 mm, and dosage was 0.3%. The linear regression fitting showed good correlation and provided valuable insights for practical engineering applications.Article Highlights: Walnut shell ash is an excellent supplementary cementitious material. Basalt fibers effectively increase the compressive and splitting resistance of mortars. Establishment of fatigue equations using the Weibull model, with a good linear regression fit in the test results. Maximum fatigue limit strength of 15% walnut shell ash replacement cement mortar by 1% volume parameterized 9 mm basalt fibers. [ABSTRACT FROM AUTHOR]

3D printing technology proves itself to be effective in the field of medical industry due to processing potential of titanium alloys. Nonetheless it also has its drawbacks, the most severe being high roughness of printed elements’ area as well as the need to remove support structures created following the printing. Mechanical processing is commonly used for said parameters being enhanced. The completion of that process, however, takes a lot of time and prevents hard-to-reach elements from being reached. The task of this article is to provide a new method of firming the print’s surface and removing load-bearing structures. To achieve this, selective laser melting (SLM) technology will be used along with bathing prints in HF/HNO3 solution, all of which are supported by ultrasound. This process will enhance the material fatigue processing while reducing the postprocessing time and complexity. [ABSTRACT FROM AUTHOR]

The effect of six processes including M (milling), G (grinding), MMP (milling and manual polishing), GMP (grinding and manual polishing), MCP (milling and CNC polishing), GCP (grinding and CNC polishing) on surface integrity and fatigue life of GH4169 are studied in this paper. The results show that grinding produce a larger degree of hardening compared to milling, and residual stress of grinding surface and milling surface are respectively compressive and tensile. Polishing can significantly reduce the surface roughness formed by the previous process. Surface tensile residual stress of milling is converted into compressive stress after polishing, while the degree of hardening and residual stress of grinding surface has no significant change after polishing. The roughness, residual stress, and hardening degree of the manual polishing and CNC polishing are similar, but there are many micro surface defects in the manual polishing surface. The fatigue life of GCP, MCP, GMP, and MMP gradually decreases. Therefore, the integration process of GCP can produce better surface integrity including surface roughness, hardening degree, and residual stress distribution. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) has revolutionized the production industry by offering design freedom with shorter lead times and reduced material wastage. However, the damage tolerance (DT) of AM parts is a significant concern due to their microstructural and geometric complexities, which affect their mechanical performance. This article aims to provide a comprehensive overview of the manufacturing parameters affecting the components produced by AM specifically selective laser melting (SLM). Detailed discussions are presented on the effects of manufacturing attributes on the microstructure, defects, and mechanical characteristics of AM parts. Depending on these aspects, basic concepts are studied and critically explained specifically for AM materials. The basic criterion for damage‐tolerant component design, the criterion for fatigue and fracture properties, and the effect of the defects on fatigue life are critically presented. In addition, the effect of different types of gradation on the crack growth behavior of samples processed by SLM is also investigated in depth. There is currently a lack of a specific review study in the literature that establishes a connection between process attributes and metallographic properties, and their impact on the damage behavior of additively manufactured parts. This gap in research highlights the need for a comprehensive review to bridge this knowledge deficit and provide valuable insights for understanding the relationships between manufacturing processes, material characteristics, and the structural integrity of additively manufactured components. This review concludes by addressing the challenges and opportunities in designing and qualifying AM parts for damage tolerance. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive state-of-the-art review of research on bridge deck fatigue under moving wheel loads and compares it to conventional fixed-point pulsating load fatigue. An overview and a brief history of the evolution of this test method from around the world are provided. The effect of key parameters on fatigue life and performance under moving loads are discussed, including loading magnitude and stress ratio, loading footprint, boundary conditions, loading eccentricity, loading frequency, dynamic effect and impact, reinforcement layout, slab thickness, crack control, concrete strength, and environmental exposure conditions. The fatigue accumulation rule and the incremental step (staircase) rolling load method are discussed. Cracking and failure mechanisms in slabs under rolling loads are presented and compared. It is clearly demonstrated that fixed-point pulsating fatigue loads inadequately simulate fatigue damage, stiffness degradation, and cracking patterns induced by rolling loads. For example, one rolling load cycle is shown to be equivalent to 80–1,800 pulsating load cycles. Varying the magnitude of the rolling load (dynamic effect) further reduces the fatigue life. Decreasing the spacing of the transverse rebar and compression reinforcement both can increase susceptibility to crack initiation, potentially reducing fatigue life. Environmental factors, particularly moisture intrusion, drastically reduced fatigue life. A conversion factor of stiffness degradation from pulsating to equivalent rolling load fatigue is proposed. Finally, recommendations for future work in this field are proposed. [ABSTRACT FROM AUTHOR]

ABSTRACT Aiming at the issue of fatigue test data for large‐scale mechanical components of building steel are very limited, a method for fitting P‐S‐N curves under small sample data of notched specimens is proposed to predict fatigue life. First, a fatigue life subsample augmented and its reliability assessment method are established, based on Bayesian hierarchical modeling and modified Monte Carlo method. Second, a clustering combination weighting method is proposed, to define weights of hidden variables of the binomial mixture Weibull distribution, and the expectation–maximization algorithm is used to determine probability density function of the distribution. Finally, the P‐S‐N curves under various failure probabilities are fitted with Weibull distributed life models, and the convergence and prediction accuracy of the different models are compared. The results show that the fatigue data of small samples can be predicted better by using mixed Weibull distribution, and the fitting P‐S‐N curve is more reliable and accurate. [ABSTRACT FROM AUTHOR]

AbstractStructural health monitoring and repair have become increasingly crucial in confirming the safety and longevity of damaged structures. This study presents a novel approach to enhancing the structural integrity and extending the fatigue life of a bottom-edge cracked I-beam by applying piezoelectric actuators strategically placed along the crack location by actively suppressing crack propagation. An innovative actuation system induces controlled deformations in the I-beam, effectively reducing the Stress Intensity Factor (SIF) and preventing crack propagation. The efficacy of the proposed approach is validated through a series of numerical results on the ABAQUS platform, including static loading, fatigue loading, and crack growth monitoring. Various parameters, like maximum loading capacity under static loading, interpretation of crack growth rate, and service life, are monitored and analyzed throughout the cyclic loading process. The results demonstrate that the application of 500 V to the piezoelectric actuators significantly reduces the SIF by 16.62% under a 2 kN total load, a 2.86% enhanced maximum load-carrying capacity is obtained, delayed crack propagation is found after repair, and a 72.67% extended service life is achieved under a load range of 0.2 kN to 2 kN. Overall, the outcomes of this research lead to the development of innovative and efficient techniques for delaying the propagation of cracks, thereby preventing the premature onset of catastrophic failure of cracked I-beams. [ABSTRACT FROM AUTHOR]

ABSTRACT This study presents a procedure based on constant amplitude (CA) fatigue data to predict the statistical fatigue lifetime of glass/orthopolyester composites subjected to repeated ordered and random two, three, and six sequences of block loadings. A numerical routine was developed to detect cycle‐by‐cycle the statistical strength degradation progression until failure, assuming that the strength at the end of a block cycle equals the strength at the start of the successive one and that the individual samples' static strength, the amount of degraded strength, and fatigue life share the same rank in their respective cumulative distribution function. Predictions conform to the statistically undetectable loading sequence effects and lightly overestimate the lifetimes of random and ordered high‐to‐low (1/100 cycles) repeated two‐block loadings. The vanishing effect of the loading sequence when the block extents remain fixed, the block extent effects for a given three‐block sequence, and the lifetimes of three‐block loadings were fully predicted. The six‐block sequence's experimental lifetimes with different block loading orders and block extent fell within the predicted lifetimes' cumulative distribution function. A reliable damage rule based on residual strength was proposed and compared to the Miner's rule. [ABSTRACT FROM AUTHOR]

ABSTRACT The milled surface of TC4 titanium alloy was treated by laser shock peening (LSP) and laser shock wave planishing (LSWP) to investigate the effect of compressive residual stress (CRS) and surface roughness (SR) on the vibration fatigue performance. The results demonstrate that although the amplitude of CRS induced by LSWP is lower than that of LSPed specimens, the vibration fatigue life of LSWPed specimens increased by 63.78% due to a significant reduction in SR from Sa 14.1 μm to Sa 4.21 μm. When the SR is low, increasing the amplitude of CRS is more advantageous to enhance fatigue life. The fractographic analysis further confirmed that compared with LSPed and T0.2‐LSWPed specimens, T0.1‐LSWPed specimens have considerably less initial fatigue crack initiation, and the crack initiation location is deeper. The fatigue striation spacing of T0.1‐LSWPed specimens is the smallest (0.25 μm), greatly lowering the fatigue crack growth rate. [ABSTRACT FROM AUTHOR]

ABSTRACT Accurately and efficiently predicting the fatigue life of rubber materials has been a long‐standing challenge due to limited understanding of the fatigue mechanism. In this study, a variational assimilation‐based machine learning method assisted with incremental crack propagation model is proposed to predict the fatigue life of rubber materials. Firstly, according to the fracture mechanics theory, a new rubber fatigue life prediction model based on incremental crack propagation and sparse experimental data is established, which owns higher accuracy than the classical crack energy density model. Further, a rubber fatigue life solver coupled incremental crack propagation model and nonlinear finite element method is introduced to generate a dense fatigue life dataset of rubber materials with high accuracy. Finally, the artificial neural network model is trained, cross‐validated, and tested using the dense dataset, and the three‐dimensional variational assimilation model is employed to merge the predicted values of artificial neural network with experimental data. By comparing against the experimental data, the effectiveness of the proposed method was verified; thereby, we offer an accurate and efficient approach to predict the rubber fatigue life. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper assesses the impact of utilizing statistically defined residual stress fields from cold expansion (Cx) in linear elastic, multi‐point fracture mechanics analyses using the spatial analysis of residual stress (SpARS) methodology. There is significant value and interest in leveraging the increased fatigue life afforded by Cx, but it is imperative to quantify the variability of the residual stress to understand the expected variability in benefit due to Cx. Comparisons of the predicted fatigue lives from SpARS‐produced statistical residual stress fields are made to fatigue test data. Results demonstrated that the less compressive 95% upper bound from the mean residual stress would be a reasonable strategy as it supplies a compromise between safety and inherent material and process variability while still producing a sizable improvement in predicted fatigue life. In this study, using SpARS to incorporate statistically representative residual stress fields in fatigue crack growth analyses demonstrates a methodology to aircraft structural engineers for improved fleet management and allow increased aircraft availability through fewer inspections. [ABSTRACT FROM AUTHOR]

The damage process of composite materials, such as short fiber-reinforced plastics (SFRP), is complex. Therefore, it is necessary to accurately represent the damage process in fatigue life prediction. Herein, fatigue life prediction was conducted by combining the digital image correlation method, which is a non-destructive testing technique, with a convolutional neural network (CNN), using Xception as the network architecture. High prediction accuracy was obtained when training and testing were performed on the same SFRP specimens. In contrast, using different specimens for training and testing resulted in lower accuracy. This issue may be improved by increasing the number of specimens. The regions of interest in the model were visualized by Gradient-weighted Class Activation Mapping. Notably, the model indicated the breaking point as the region of interest from the early stages of the test. The breaking point was identified at an earlier stage by the CNN than by visual inspection, demonstrating the potential for a new method of damage observation. [ABSTRACT FROM AUTHOR]

ABSTRACT X‐ray computed tomography (XCT) is extremely useful for the non‐destructive analysis of additively manufactured (AM) components. AM components often show manufacturing defects such as lack‐of‐fusion (LoF), which are detrimental to the fatigue life of components. To better understand how cracks initiate and propagate from internal defects, we fabricated Ti‐6Al‐4V samples with an internal cavity using electron beam powder bed fusion. The samples were tested in high‐cycle and very high‐cycle fatigue regimes. XCT was used to locate crack initiation sites and to determine characteristic properties of cracks and defects with the aid of deep learning segmentation. LoF defects exposed to the outer surface of the samples after machining were found to be as detrimental to fatigue life as the internal artificial defects. This work can benefit industries that utilize the AM of high‐strength, lightweight alloys, in the design and manufacturing of components to improve part reliability and fatigue life. [ABSTRACT FROM AUTHOR]

AbstractA mechanical property degradation model of material fatigue life varying with stress level and corrosion time was developed in this study. An acidified NaCl solution was used to accelerate the corrosion of stainless-steel samples, and the relationship between laboratory-accelerated corrosion and atmospheric corrosion was established using corrosion thickness loss parameters. Based on the results of a pre-corroded fatigue test, lgN–S–T surface models and a modified version of Miner’s rule for calculating nonlinear mechanical damage accumulation were proposed. Taking a real part of a high-speed train as an example, critical operating mileages considering material fatigue performance degradation under corrosion conditions were calculated, which were consistent with failure mileages of the census results. [ABSTRACT FROM AUTHOR]