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Purpose: This paper aims to present the novel stacked machine learning approach (SMLA) to estimate low-cycle fatigue (LCF) life of SAC305 solder across structural parts. Using the finite element simulation (FEM) and continuous damage mechanics (CDM) model, a fatigue life database is built. The stacked machine learning (ML) model's iterative optimization during training enables precise fatigue predictions (2.41% root mean square error [RMSE], R2 = 0.975) for diverse structural components. Outliers are found in regression analysis, indicating potential overestimation for thickness transition specimens with extended lifetimes and underestimation for open-hole specimens. Correlations between fatigue life, stress factors, nominal stress and temperature are unveiled, enriching comprehension of LCF, thus enhancing solder behavior predictions. Design/methodology/approach: This paper introduces stacked ML as a novel approach for estimating LCF life of SAC305 solder in various structural parts. It builds a fatigue life database using FEM and CDM model. The stacked ML model iteratively optimizes its structure, yielding accurate fatigue predictions (2.41% RMSE, R2 = 0.975). Outliers are observed: overestimation for thickness transition specimens and underestimation for open-hole ones. Correlations between fatigue life, stress factors, nominal stress and temperature enhance predictions, deepening understanding of solder behavior. Findings: The findings of this paper highlight the successful application of the SMLA in accurately estimating the LCF life of SAC305 solder across diverse structural components. The stacked ML model, trained iteratively, demonstrates its effectiveness by producing precise fatigue lifetime predictions with a RMSE of 2.41% and an "R2" value of 0.975. The study also identifies distinct outlier behaviors associated with different structural parts: overestimations for thickness transition specimens with extended fatigue lifetimes and underestimations for open-hole specimens. The research further establishes correlations between fatigue life, stress concentration factors, nominal stress and temperature, enriching the understanding of solder behavior prediction. Originality/value: The authors confirm the originality of this paper. [ABSTRACT FROM AUTHOR]

This document is a compilation of various research papers and articles that discuss the use of machine learning and other techniques to predict fatigue lifetimes in different materials and structures. The papers cover topics such as the use of neural networks, XGBoost, and physics-informed machine learning models for fatigue prediction. The research focuses on different materials, including aluminum alloys and lead-free solders, and explores the effects of factors such as wear, lubrication, corrosion, and stress on fatigue life. The papers provide insights into the application of machine learning techniques in predicting fatigue lifetime and offer potential solutions for improving the accuracy of these predictions. [Extracted from the article]

As the central component in friction stir welding, the design and manufacture of welding tools for aluminum alloys have garnered substantial attention. However, the understanding of tool reliability during the welding process, especially in terms of fatigue performance, remains unclear. This paper focuses on the welding of AA2219-T4 as a case study to elucidate the predominant failure mode of the tool during the friction stir welding (FSW) of aluminum alloys. Experimental methods, including FSW welding and fracture morphology analysis of the failed tool, coupled with numerical simulation, confirm that high-cycle mechanical fatigue fracture is the primary mode of the tool failure. Failures predominantly occur at the tool pin's root and the shoulder end face with scroll concave grooves. The experimental and simulation results exhibit a noteworthy agreement, validating the reliability of the simulation model. The FSW Arbitrary Lagrangian–Eulerian (ALE) model developed in this study analyzes stress distribution and variation under the thermo-mechanical coupling effect of the tool. It reveals that stress concentration resulting from structural changes in the tool is the primary driver of fatigue crack initiation. This is attributed to exposure to alternating cyclic stresses such as bending, tension, and torsion at the tool pin's root, manifesting as multiaxial composite mechanical fatigue. Among these stresses, bending alternating cyclic stress exerts the most significant influence. The paper employs the Tool Life module in DEFORM software to predict the fatigue life of the tool. Results indicate that reducing welding speed or increasing rotation speed can enhance the tool's fatigue life to some extent. The methodology proposed in this paper serves as a valuable reference for optimizing FSW structures or processes to enhance the fatigue performance of welding tools. [ABSTRACT FROM AUTHOR]

In this paper, the thickness debit and stress concentration effects of a nickel‐based directionally solidified superalloy were investigated through strain‐controlled low cycle fatigue (LCF) and creep–fatigue interaction (CFI) experiments. Compared to the fatigue lives of solid specimens provided in the existing literature, the results of this paper indicate that when the wall thickness of the specimen is reduced from 5 to 1.125 mm, the fatigue life with different strain amplitudes decreases by about 45%. When film‐cooling holes (FCHs) are introduced into the hollow specimens, the fatigue life is further reduced by about 25%. Based on the observation of the scanning electron microscope (SEM), the formation mechanisms of the thickness debit and stress concentration effects under LCF and CFI loads were revealed. Subsequently, two parameters, the “wall‐thickness coefficient” and “hole coefficient,” were proposed to establish a new fatigue life prediction method. [ABSTRACT FROM AUTHOR]

The present review paper addresses the increasing interest in the application of machine learning (ML) algorithms in the assessment of the fatigue response of additively manufactured (AM) metal alloys. This review aims to systematically collect, categorize, and analyze relevant research papers in this domain. The most commonly used ML algorithms are presented, discussing their specific relevance to the fatigue modeling of AM metal alloys. A detailed analysis of the most relevant input features used in the literature to predict the main parameters related to the fatigue response is provided. Each work has been analyzed to highlight its strengths and peculiarities, thereby offering insights into novel methodologies and approaches for addressing critical challenges within this field. Particular attention is dedicated to the role of defects and the related size‐effect, as they strongly influence the fatigue response. In conclusion, this review not only synthesizes existing knowledge but also offers forward‐looking recommendations for future research directions, providing a valuable resource for researchers in the domain of ML‐assisted fatigue assessment for AM metal alloys. [ABSTRACT FROM AUTHOR]

Binder jetting 3D printing is an additive manufacturing technique based on the creation of a part through the selective bonding of powder with an adhesive, followed by a sintering process at high temperature to densify the material and produce parts with acceptable properties. Due to the high initial porosity in the material after sintering, which is typically around 5%, post-sintering treatments are often required to increase the material density and enhance the mechanical and fatigue properties of the final component. This paper focuses on the study of the benefits of hot isostatic pressing (HIP) after sintering on the mechanical and fatigue properties of a binder jetting Ti-6Al-4V alloy. Two different HIP processes were considered in this study: one at 920 °C/100 MPa for 4 h, and a second at a higher pressure but lower temperature (HIP-HPLT) at 850 °C/200 MPa for 2 h. The effects of the HIP on the densification, microstructure, mechanical behavior, and fatigue properties were investigated. The results show that the HIP-HPLT process produced a significant increase in the mechanical and fatigue properties of the material compared with the as-sintered parts and even with the conventional HIP process. However, the fatigue and fracture micromechanisms suggest that the oxygen content, which resulted from the decomposition of the binder during the sintering process, played a critical role in the final mechanical properties. Oxygen could reduce the ductility and fatigue life, which deviated from the behavior observed in other additive manufacturing techniques, such as powder bed fusion (PBF). [ABSTRACT FROM AUTHOR]

The paper investigates the issue of post-impact fatigue damage of the 2060 aluminium–lithium alloy, a representative material of third-generation aluminium–lithium alloys extensively employed in the fuselage of C919 aircraft due to its notable attributes of high specific stiffness and strength. Initial impact damage is identified utilizing a residual stress–strain field obtained from a quasi-static simulation. Then, the continuum damage mechanics approach is applied to predict the fatigue life of the impacted 2060 aluminium–lithium alloy plates accounting for the combined effects of residual stress, plastic damage, and fatigue loading. A comparative analysis between calculated and experimental results is conducted to validate the efficacy of the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper develops a thermodynamic entropy-based life prediction model to estimate the low-cycle fatigue (LCF) life of the nickel-based superalloy GH4169 at elevated temperature (650 °C). The gauge section of the specimen was chosen as the thermodynamic system for modeling entropy generation within the framework of the Chaboche viscoplasticity constitutive theory. Furthermore, an explicitly numerical integration algorithm was compiled to calculate the cyclic stress–strain responses and thermodynamic entropy generation for establishing the framework for fatigue life assessment. A thermodynamic entropy-based life prediction model is proposed with a damage parameter based on entropy generation considering the influence of loading ratio. Fatigue lives for GH4169 at 650 °C under various loading conditions were estimated utilizing the proposed model, and the results showed good consistency with the experimental results. Finally, compared to the existing classical models, such as Manson–Coffin, Ostergren, Walker strain, and SWT, the thermodynamic entropy-based life prediction model provided significantly better life prediction results. [ABSTRACT FROM AUTHOR]

This paper presents a model to calculate the opening angle of crack initiation in notched fractures subjected to multiaxial loading. To validate the proposed model, a study was performed on polished AZ31B-F magnesium alloy specimens under multiaxial high-cycle fatigue loading. The specimens exhibited a notch in the smaller cross-sectional area, which was created with a special drilling jig to promote the formation of fatigue cracks in this localized area of the specimen. The load paths used in the experiments and numerical analyses were proportional and non-proportional, resulting in different stress states in the crack front opening, which were determined by finite element analysis to validate the proposed model. To obtain more accurate numerical results for these estimates, these finite element analyses were performed using the nonlinear Chaboche plasticity model of ABAQUS® 2021 software. A sensitivity analysis was also performed to determine which load component—axial or torsional—has a greater influence on the fatigue strength and contributes significantly to the crack opening process. The results show that the type of load path and the stress level of each load component—axial and torsional—has a strong influence on the opening angle of the notch crack and the fatigue lifetime of the specimen. This result is confirmed not only by the experimentally determined fatigue strength, but also by a fractographic analysis performed on the surface of the specimens for both load paths. Moreover, the results show an acceptable correlation between the experimental results and the estimates obtained with the proposed model and the stresses obtained with the finite element analysis. [ABSTRACT FROM AUTHOR]

Inevitable defects have an important impact on the fatigue lifetime of additive manufacturing materials. Therefore, it is critical to thoroughly characterize the characteristics of the defects, which requires effective semantic segmentation of the imaged defects. In this paper, a defect dataset for SLM Ti-6Al-4V alloy was obtained by synchrotron radiation computed tomography. Then a semantic segmentation method was developed based on the DeepLabV3 + network to automatically extract defects. Cropping and undersampling were introduced in the dataset pre-processing. A weighted scheme based on the ratio between the number of defect and matrix pixels was applied in the classification layer, and morphological operations were employed in image post-processing to improve the accuracy of identifying small-target defect. Finally, the above method was applied to segment the X-ray computed tomography data for two batches of SLM Ti-6Al-4V materials, and the defect segmentation results were used to predict the fatigue lifetime. The semantic segmentation method performs well with a pixel recognition accuracy of 98.2% for the test dataset, and the error in the predicted fatigue lifetime lies within the scatter band of ±2.2. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 2)'. [ABSTRACT FROM AUTHOR]

Abstract–The Weibull distribution is the most applied model in reliability field for lifetime analysis. The Weibull location parameter, characterizing the minimum possible life, plays a significant role in engineering applications. In this paper, we consider the interval estimation on the location parameter when the product's lifetime follows the three-parameter Weibull distribution with a known shape parameter. A novel approach based on the relationship between the minimum order statistics, the location parameter, and the sample size is developed to construct confidence intervals for the Weibull location parameter. Thereafter, we compare it with other two interval estimation approaches by the performances of the coverage probability and the average length via simulations and a real application. The results show that the proposed method outperforms the pivot quantity (PQ) method and the bias-corrected and accelerated (Bca) bootstrap method in small and medium samples in terms of coverage probability. [ABSTRACT FROM AUTHOR]

Aluminum‐lithium alloys are a class of advanced materials designed to reduce weight and improve performance in aerospace and other high‐tech applications. This paper presents a research investigation on the in‐phase and out‐of‐phase multiaxial fatigue behaviors of the third‐generation AW2099‐T83 aluminum‐lithium alloy that have not been addressed before. Additional hardening was observed under nonproportional loading condition at high strain amplitudes. Fatigue lives were estimated using von Mises equivalent strain and two critical plane models: the Fatemi‐Socie (FS) and the Smith‐Watson‐Topper (SWT). In addition, a supervised machine‐learning model (support vector machine—SVM) was employed to predict the fatigue life under the above‐mentioned loading conditions. The FS criterion was found to yield better fatigue life predictions than SWT. The estimations of FS model mostly fall within ±3× scatter bands with some data falling within the conservative and non‐conservative regions. The SVM model resulted in excellent predictions within ±2× scatter bands. [ABSTRACT FROM AUTHOR]

This paper was attempted to investigate the microstructure degradation and low cycle fatigue (LCF) performance of a serviced K465 Ni‐based superalloy turbine blade. LCF tests were carried out with small‐scale plate specimens sampled from the blades. Relationship between residual LCF life and microstructure state was estimated. The results indicate that the coarsening of γ/γ′ phases was the most significant microstructure degradation mode for the serviced blades. Both the γ matrix width and the γ′ precipitate diameter increased with the increase of service duration, while the γ′ precipitate volume fraction slightly decreased. The most severe microstructure degradation occurred at the leading edge along the chord direction, particularly at 50–70 % airfoil spans. The residual LCF life exhibited an accelerated decrease characteristic as increases of microstructure degradation degree. The coarsened microstructure diminished shear resistance of the superalloy, which resulted in additional accumulated inelastic deformation and a corresponding reduction in LCF life. Highlights: Service induced microstructure evolution and LCF life decay of a blade were investigated.Coarsening was identified as the main degradation form of γ/γ' phases in serviced blade.Accelerated decrease of residual LCF life was identified as increases of coarsening.Reduced plastic deformation resistance owing to coarsening is crucial to decay LCF life. [ABSTRACT FROM AUTHOR]

In this paper, the high-temperature constitutive behaviour of an additively manufactured ductile nickel-based superalloy is investigated and modelled, with application to thermomechanical fatigue, low-cycle fatigue and creep conditions at temperatures up to ${800^ \circ }$ 800 ∘ C. Thermomechanical fatigue tests have been performed on smooth specimens in both in-phase and out-of-phase conditions at a temperature range of $100 - {800^ \circ }$ 100 − 800 ∘ C, and creep tests at ${625^ \circ }$ 625 ∘ C, ${700^ \circ }$ 700 ∘ C, ${750^ \circ }$ 750 ∘ C and ${800^ \circ }$ 800 ∘ C. Additionally, low-cycle fatigue tests at different strain ranges and load ratios have been performed at ${700^ \circ }$ 700 ∘ C, and tensile tests have been performed at ${600^ \circ }$ 600 ∘ C, ${700^ \circ }$ 700 ∘ C and ${800^ \circ }$ 800 ∘ C. A clear anisotropic mechanical response is obtained in the experiments, where the anisotropic effects are larger at high stress levels in creep loadings. To capture this behaviour, a rate-dependent strain based on a double-Norton model has been adopted in the model, by which the creep and mid-life response of the thermomechanical fatigue tests can be simulated with good accuracy. [ABSTRACT FROM AUTHOR]

Thermomechanical fatigue (TMF) crack growth of Alloy 718 when the cycle includes long high‐temperature tensile dwells is often accelerated because sustained‐load crack growth occurs during the dwells and a temperature affected zone (TAZ) develops ahead of a crack tip that reduces fatigue crack growth resistance upon application of a cycle after the long dwell. This paper presents new TMF and sustained‐load tests that aim to study and characterize the TAZ development and growth ahead of semi‐elliptical and single‐edge cracks. The influence of constraint on crack growth is assessed. This investigation focuses on a coarse‐grained (CG) Alloy 718 at 650°C. By comparing the crack growth behavior between a fine‐grained and CG microstructure after a long tensile dwell, a modification of the TAZ growth prediction model that includes the influence of grain size is proposed. Using this improved model for TAZ growth and acceleration, the TMF crack growth prediction of surface cracks is improved. Highlights: Temperature affected zone (TAZ) develops during tensile dwells in Alloy 718.The extent of TAZ is reduced when grains are larger.The extent of TAZ is also dependent on the constraint near the crack tip.A new grain size dependent TAZ growth model improves TMF predictions. [ABSTRACT FROM AUTHOR]

High frequency fatigue behavior of near surface of turbine disk are critical for its application and operation. High frequency indentation fatigue tests of GH4169 alloy under different load amplitudes, frequencies and mean loads at small length scale were conducted, and the dependence of load amplitude, load frequency and mean load on high frequency indentation fatigue property of GH4169 alloy are discussed in this paper. Depth amplitude (ha), mean depth (hm) and depth propagation rate (dh/dN) were employed as evaluation indicators of the indentation behavior. Results show that depth amplitude is only relevant with load amplitude, while mean depth is related to all the adopted influencing factors, ranked in an ascending order as load amplitude, mean load and frequency with a ranking relation of nm1=1.4 < nm2=1.71 < nm3=2.02. Furthermore, a modified Paris law was utilized to reveal the fatigue mechanism, and found the fatigue mechanism is dominated by intrinsic mechanism under the influence of mean load and load amplitude, while for the influence of frequency, the fatigue mechanism is governed by extrinsic mechanisms. Combined with SEM results and three-dimensional morphology analysis, it can be deduced that dislocation movement mode in high frequency indentation fatigue is dislocation slip. [ABSTRACT FROM AUTHOR]

Foreign non‐metallic inclusions can significantly reduce the low‐cycle fatigue (LCF) life of powder metallurgy (PM) superalloy and greatly affect the safety and reliability of aeroengines. In this paper, LCF experiments on PM FGH96 superalloy with and without inclusions were conducted. Effects of inclusions on the fatigue life and damage mechanism of FGH96 alloy are discussed by fractography analysis. Parameters related to inclusion characteristics such as strength–inclusion coefficient are proposed. By introducing characteristic parameters of inclusions, the LCF life prediction models are established based on the Manson–Coffin relationship, which significantly improved the prediction accuracy and reduced the scattering band by a factor of 2. Highlights: By performing strain‐controlled low‐cycle fatigue tests at different strain amplitudes, statistical analyses were carried out to assess the influences of size, location, and type of inclusions on LCF life, with a quantitative relationship established between them.The change law of LCF life of powder metallurgy superalloy under different inclusion conditions is summarized. Effects of inclusions on the LCF life of FGH96 alloy were clarified and applied to the establishment of fatigue life prediction models considering characteristic parameters of non‐metal inclusions.A modified Manson–Coffin life prediction model considering inclusion characteristics is proposed to support the safety and reliability assessment of turbine disks made of PM superalloy FGH96.By introducing characteristic parameters of inclusions, the LCF life prediction models are established based on the Manson–Coffin relationship, which significantly improved the prediction accuracy and reduced the scattering band by a factor of 2. [ABSTRACT FROM AUTHOR]

The aim of the paper is to investigate experimentally the fatigue and creep-fatigue material behaviour of improved materials and welded joints for the application in flexible future power plants. These materials promise a reduction in manufacturing costs as well as an increase in flexibility by providing enhanced creep strength thorugh a wall thickness reduction. At the temperature range between 500°C −550°C, the investigation focusses on the creep and low-cycle fatigue behaviour of dissimilar welded joints from conventional materials (bainitic and martensitic materials T24 and T92) to nickel-based alloys (A617B and HR6W) fabricated as tubes. At the temperature range between 700°C and 750°C, it focusses on the creep, low-cycle fatigue and creep-fatigue behaviour of similar and dissimilar welded joints from nickel-based alloys (A740H, A617B and A263) fabricated as tubes and as pipes. Metallographic investigations after testing provide support for understanding the influence of temperature, strain amplitude and dwell time on the microstructure change and the fatigue strength. [ABSTRACT FROM AUTHOR]

• The behavior of low cycle fatigue at typical temperatures was comprehensively investigated. • The life prediction model based on entropy increase theory is in good agreement with the experimental data. • This paper offers a methodology for finite cycle prediction of overall fatigue life. Nickel-based single-crystal superalloys (Ni-SX) are prominently utilized in the fabrication of turbine blade materials for advanced aero-engines, owing to their commendable material characteristics. This paper delves into the low cycle fatigue (LCF) characteristics of a second-generation Nickel-based single-crystal superalloy across a temperature spectrum ranging from room temperature to 1000 °C. During this procedure, there is an escalation in the trend towards deformation homogenization, leading to a transition in fracture mode from shear fracture to normal fracture. A novel approach is introduced in the form of an entropy-based fatigue life prediction model, grounded in the correlation between cumulative plastic strain and entropy increase rate. Through a comparative examination with experimental data, the model demonstrates proficiency in precisely forecasting the fatigue life of Ni-SX under diverse strain amplitudes and temperature conditions. [ABSTRACT FROM AUTHOR]

Vast aging metallic structures are suffering from fatigue cracking, jeopardizing structural integrity and personnel safety. Therefore it is of great benefit to develop strengthening solutions to achieve complete fatigue crack arrest. A bonded and prestressed fatigue strengthening solution on the basis of an iron-based shape memory alloy (Fe-SMA) shows great potential in this term. An experimental campaign has been carried out in this paper to achieve complete fatigue crack arrest in metallic plates. Several activation methods greatly affecting the prestressing level have been experimentally tested, it has been found that the gas torch activation is the most effective method, extending the fatigue crack growth life by 6.9 times. The experimental campaign has demonstrated that prestressing forces required to achieve complete fatigue crack arrest capability could be realized by increasing the Fe-SMA patch width combined with the most effective activation method. In addition, the results show that the length of the Fe-SMA repair together with the activation length can be reduced without sacrificing the repair efficiency. The findings of this paper are greatly beneficial for industrial sectors suffering from fatigue cracking in metallic structures, small bonded Fe-SMA patches can be easily activated to achieve complete fatigue crack arrest capability. • The proposed fatigue strengthening solution is able to arrest fatigue cracks. • The prestressing forces continues to retard fatigue crack growth. • Instantly high activation temperature does not damage the bondline. • The prestressing forces can be tailored to retard the fatigue crack growth. • The proposed fatigue strengthening solution is versatile. [ABSTRACT FROM AUTHOR]

[Display omitted] • The S-N curves showed poorer fatigue properties in GA2/GA3 compared to GA1. • Crack initiation mechanism changes between GA1 and GA2/GA3 relative to stress. • Intergranular crack initiation is observed only in GA3. • Change in slip character as a function of stress/alloy variant influences fatigue life. • The fracture mechanism map underlines the different fatigue crack initiation mechanisms. The paper investigates the influence of different impurity/scrap elements on the high cycle fatigue (HCF) properties of 6082 Al-alloy. Accordingly, HCF tests are carried out on the different variants- GA1, GA2 and GA3 (designed as a function of varying impurity content)- of this alloy, which resulted in a lower fatigue limit in GA2/GA3 compared to GA1. To explain such behavior, detailed fractographic and microstructural investigations are conducted which bring out that although the crack initiation and propagation modes are mostly transgranular irrespective of alloy variant and stress levels, intergranular crack initiation is promoted in GA2/GA3 at 150 MPa in contrast to occurrence of run-out in GA1 at the same stress level. This phenomenon is found to be facilitated by intermetallic particles anchoring the grain boundaries. These observations point out the possibility of strong sensitivity of stress and alloy variant (varying impurity content) to fatigue life. The difference in fatigue properties as a function of alloy variant could be attributed to the variation in initial microstructure/particle size distribution as well as the slip character. In light of these, a fracture mechanism map is generated which underlines the different mechanisms responsible for fatigue crack initiation among different alloy variants. [ABSTRACT FROM AUTHOR]

• Static and cyclic response to 4 heat treatments on AM samples of AlSi10Mg evaluated. • Microstructure reveals negative effects of the printing strategy on the contour. • Self-heating tests result in a thermal response unique for every heat treatment. • Fatigue limits estimated based on thermal response while promising accuracy reached. This research delves into the analysis of various properties of additively manufactured specimens from AlSi10Mg with an as-printed surface, comparing the effects of three distinct heat treatments with an untreated variant. The study assesses both static properties and fatigue responses for each heat treatment, including a detailed examination of the microstructures. In the high-cycle fatigue region, the treatment causing the silicon network to break provides the best output, while the low-cycle fatigue response is dominated by the heat treatment by artificial ageing alone. In addition, this paper introduces a novel proposal on fatigue limit estimation inspired by Luong's and Risitano's approaches based on the self-heating phenomenon. Demonstrating efficiency in its simplicity, this approach holds promise for estimating the fatigue limit. This method provides a cost-efficient and time-saving way to determine the fatigue limit transition on the basis of fewer samples than the traditional methods require. [ABSTRACT FROM AUTHOR]

• The microstructure, fracture behavior and failure mechanism of the joints was analyzed from macro and micro perspectives. • The fatigue failure mechanism and fatigue fretting mechanism of DP590/AA5754 self-piercing riveting joint under different load levels were investigated. • Fatigue crack initiation and propagation behavior of self-piercing riveting joint are revealed. • It is revealed that there is a competitive relationship between the crack propagation of the lower sheet and the rivet during the fatigue failure of the self-piercing rivet. • The fatigue life of DP590/AA5754 self-piercing riveting joints were estimated using Paris law. This paper investigates the fatigue properties of self-piercing riveted joints made by DP590 steel and AA5754 aluminium alloy. The fatigue failure mechanism and fatigue fretting mechanism of the joint were well revealed by analysing the microstructure features of fracture surfaces of sheets and rivets as well as viewing and measuring the distribution and chemical composition of fretting debris. The fatigue life of the joint was also predicted based on the stress intensity factor of the kinked crack of the lower sheet. The results confirmed that two failure modes occurred during fatigue: lower sheet fracture and rivet fracture. During the fatigue failure, cracks appeared in both the lower sheet and the rivets, indicating a competitive relationship between the propagation of cracks in the lower sheet and the rivets. In the range of 40 % and 50 % load level, fatigue crack propagation of the lower sheet is dominant and fracture failure of the lower sheet occurs. Rivet fatigue crack propagation has a significant advantage in the 60 % load range and rivet fracture failure often occurs. It was found that the fatigue failure of the lower sheet is mainly influenced by the main crack, which produces two different morphological sections. Fretting wear of the contact surface was the source of crack initiation, and the fretting debris promoted crack initiation and propagation. Cracks propagate along the width and thickness of the plate, as well as the thickness of the rivet neck. The stress intensity factor range can properly predict the fatigue life of joints. [ABSTRACT FROM AUTHOR]

The spherical pressure hull of deep-sea manned submersible is subjected to the alternating load with high dwell pressure during the cyclic working state of diving, operating and rising. Therefore, the compressive dwell fatigue behavior is a key factor to be considered in the structural safety evaluation of the pressure hull for manned submersibles. In this paper, a structure-grade dwell fatigue test of the pressure hull and a variety of specimen-grade compressive dwell fatigue tests were performed for Ti–6Al–4V ELI and Ti–6Al–2Sn–2Zr–3Mo-X alloys. Results show that no obvious structural deformation occurs in the spherical hull after the dwell fatigue test and no detectable out-of-standard defect is found in the welds when the dwell pressure value is the maximum operating pressure. The cumulative compressive strains of dwell fatigue specimens show that the base metal and welding joint have undergone plastic deformation when the maximum compressive stress value is 0.9 R p0.2. No microcracks or changes in the microstructure characteristics are observed in the specimens. The present results support the structural design and safety assessment of deep-sea manned submersibles for long-term service. • Experimental investigations explore the compressive dwell fatigue behavior of pressure hull. • Strains of measurement points mainly remained unchanged after a small initial increase under maximum operating pressure. • No obvious structural deformation occurs in the spherical hull after the dwell fatigue test. • Base metal and welding joint have undergone plastic deformation when the maximum compressive stress value is 0.9 R p0.2 • No microcracks or changes in the microstructure characteristics are observed in the specimens. [ABSTRACT FROM AUTHOR]

Iron-based shape memory alloy (Fe-SMA) is an emerging class of material having a great potential for civil engineering, especially seismic engineering applications. However, the behavior of Fe-SMA strongly depends on temperature-sensitive martensitic transformation, and thus the influence of temperature on the behavior of Fe-SMA should receive particular attention. The current study experimentally investigates how temperature variation affects the mechanical properties, including monotonic tensile strength, low cycle fatigue (LCF), and impact toughness, of Fe-SMA (Fe-17Mn-5Si-10Cr-5Ni in wt%), with a particular focus on its low-temperature behavior. Specifically, the considered temperatures used for conducting monotonic tensile and LCF tests were −40°C , −10°C , and 20°C, whereas the range of temperature for impact toughness tests was from −100°C to 20°C. Additional tests were performed on S30408 stainless steel and conventional Q355 structural steel for comparison purposes. The experimental results suggest that low temperature leads to increased strength and reduced ductility of Fe-SMA. The impact toughness of Fe-SMA is comparable with that of S30408 steel, exhibiting ductile fracture characteristic observed even at −100°C. Fe-SMA outperforms conventional steels with an evidently greater LCF life given the considered temperature variation; although, its LCF life decreases at lower temperatures due to the inhibited reversible martensite transformation. This study also provides a set of practical parameters that facilitate constitutive modeling and strain-based fatigue life prediction of Fe-SMA under various temperatures. [ABSTRACT FROM AUTHOR]

Purpose: During the forming process, aluminum alloy sheets develop various types of textures and are subjected to cyclic loading as structural components, resulting in fatigue damage. This study aims to develop polycrystalline models with different orientation distributions and incorporate suitable fatigue indicator parameters to investigate the effect of orientation distribution on the mechanical properties of Al-7.02Mg-1.78Zn alloys under cyclic loading. Design/methodology/approach: In this study, a two-dimensional polycrystalline model with 150 equiaxed grains was constructed based on optical microscope images. Subsequently, six different orientation distributions were assigned to this model. The fatigue indicator parameter of strain energy dissipation is utilized to analyze the stress response and fatigue crack driving force in polycrystalline models with different orientation distributions subjected to cyclic loading. Findings: The study found that orientation distribution significantly influences fatigue crack initiation. Orientation distributions with a larger average Schmid factor exhibit reduced stress response and lower fatigue indicator parameters. Locations with a larger average Schmid factor experience greater plastic deformation and present a higher risk for fatigue crack initiation. RVE with a single orientation undergoes more rotation to reach cyclic steady state under cyclic loading due to the ease of deformation transfer. Originality/value: Currently, there are no reports in the literature on the calculation of fatigue crack initiation for Al-Mg-Zn alloys using the crystal plasticity finite element method. This study presents a novel strategy for simulating the response of Al-7.02Mg-1.78Zn materials with different orientation distributions under symmetric strain cyclic loading, providing valuable references for future research. [ABSTRACT FROM AUTHOR]

This paper deals with the effect of defect size and shape under high cycle fatigue for metallic alloys. A large simulation campaign based on a multiaxial fatigue criterion and a non-local approach is presented. A relative defect size based on a ratio between the defect size and a characteristic length introduced by the non-local approach is defined. A normalized Kitagawa–Takahashi diagram is then obtained. A competition between the highly stressed volume size and the local maxima due to the defect is observed and seem dependent on the relative defect size. The effect of the loading mode (uniaxial and pure shear) and of the plasticity are discussed. Finally, a comparison of the simulation results with experimental data on a 316L L-PBF demonstrates the robustness of the proposed approach and explains the negligible effect of the defect morphology compared to its size. • The effect of defect size and shape under high cycle fatigue is investigated. • A multiaxial fatigue criteria with a non-local approach is applied. • A competition between the highly stressed volume and the local maxima is underlined. • A simulated normalized Kitagawa–Takahashi diagram is proposed. • The effect of the loading mode and the plasticity is discussed. [ABSTRACT FROM AUTHOR]

• Ratchetting–fatigue interaction is found prevalent at higher temperature. • Ratchetting damage arises from the cavitation in the interior of specimens. • Mesomechanical energy-based damage variable is adopted in our theory. • Imperfect interface theory is used to consider the ratchetting damage. • The theory shows a good agreement with our experimental measurements. Fatigue failure is a significant concern for magnesium (Mg) alloy components. However, fatigue damage mechanisms of Mg alloys, particularly in the case of ratchetting–fatigue interaction at elevated temperatures, are still not well understood. In this paper, we combine experiments and theoretical analysis to investigate the high-temperature damage mechanisms of the extruded AZ31 Mg alloy, specifically focusing on the effects of ratchetting–fatigue interaction. We reveal a distinct demonstration of damage, namely the formation of microvoids in the alloy due to significant ratchetting deformation, defined as ratchetting damage. Notably, this ratchetting damage is more prevalent at higher temperatures. Considering the mesomechanics-based energy mechanisms associated with grain boundaries (or twin boundaries), a mesomechanical damage model is established to capture the ratchetting damage under elevated temperatures and large ratchetting deformations. This model can reasonably simulate the intricate process of damage evolution and predict the critical condition of microvoid or microcrack formation. This work has the potential to serve as a theoretical tool for the safety design of structures made from Mg alloys under complex mechanical and thermal conditions. [ABSTRACT FROM AUTHOR]

• Unveiling VHCF behavior of laser powder bed fused A20X, a novel Al-Cu-Mg-Ag-TiB 2 alloy. • Experimental revelation of asymptotic trend at 109 cycles. • Insights into defect/microstructure influence on enhanced fatigue performance. • Fisheye morphology observed, revealing internal crack-initiating site. This study presents a comprehensive exploration of the fatigue response in the very high cycle fatigue (VHCF) regime for an additively manufactured (i.e., laser powder bed fused) A20X aluminum alloy. Although the need for high-performance materials with exceptional fatigue qualities has increased dramatically, the VHCF behavior of Al-Cu-Mg-Ag-TiB 2 (A20X) structures remains largely unknown. A series of ultrasonic fatigue tests were performed to assess the prolonged fatigue life of the A20X alloy (in the VHCF domain where the number of cycles to failure is beyond 10 million cycles). The VHCF response, assessed through ultrasonic fatigue testing, was investigated by examining the stress-life (S-N) curves in a statistical framework, the fatigue crack initiation and propagation behavior, and the fracture surfaces. An asymptotic trend was experimentally found at 109 cycles, with a stress amplitude of 110 MPa for stress-relieved (SR) and 125 MPa for artificially aged (T7) materials, indicating the presence of an endurance limit. Furthermore, fracture surfaces showed the typical fisheye morphology, with a fine granular area (FGA) containing an internal crack-initiating site. The findings of this paper can assist in optimizing fatigue and durability design allowable for applications for extended fatigue life in the VHCF domains. [ABSTRACT FROM AUTHOR]

• AMed Ti-6Al-4V with different sizes via ultrasonic cycling up to very-high-cycle regime. • S - N data showing size effect: large sized specimens with small fatigue life or strength. • A new probabilistic control volume scheme to predict fatigue property of large specimens. • A size sensitivity exponent to quantify size effect on fatigue property of AMed alloys. • A general form of probabilistic control volume model to unify original and new models. The effect of specimen size on the fatigue performance of additively manufactured (AMed) Ti-6Al-4V is investigated in this paper. The fatigue tests of Ti-6Al-4V specimens made by laser powder bed fusion were conducted via ultrasonic axial cycling up to very-high-cycle regime with stress ratio R = –1. The S - N data of five group specimens show an evident size effect, that is, with the increase of specimen size, the fatigue life or fatigue strength decreasing gradually. A new probabilistic control volume scheme is developed to evaluate the fatigue life of large sized specimens by the tested data of small sized specimens. The applicability of the proposed model is validated by the present data and those of our previous investigation. Moreover, a general form of probabilistic control volume model is derived to show the original and present models are the special cases for conventional cast and AMed alloys. [ABSTRACT FROM AUTHOR]

• The fatigue life increases as a power function with the increase of alternating times. • The damage morphology of the specimen surface presents three different stages and the primary form of damage due to corrosion is pitting. • The concept of fatigue impact factor has been introduced, which exhibits an exponential increase with the increase in the number of corrosion-fatigue alternating times. • Under the alternating effects of corrosion fatigue, fatigue initially inhibits corrosion, and then promotes corrosion. This paper investigates the fatigue performance of ZL114A cast aluminum alloy through laboratory corrosion-fatigue alternating test conducted under simulated tropical marine humid-hot atmosphere. The study examines the impact of different alternating frequency on the fatigue properties of the aluminum alloy. At the same time, the micro morphology of the specimen surface and fatigue fracture were observed, and the damage mechanism under the alternating action of corrosion-fatigue was analyzed. The concept of 'fatigue impact factor' in alternating test was proposed to reflect the effect of fatigue on corrosion in alternating process. The results show that the increase of alternating frequency leads to an extended fatigue life for the alloy, following a power function relationship. Pitting is identified as the primary form of corrosion damage on specimen surfaces, with multi-crack initiation observed in fatigue fractures. It is found that the fatigue impact factor exponentially increases with each alternating cycle during testing. In early alternating cycles of test, the presence of fatigue inhibits corrosion by promoting passivation of corrosion pits; however, in later alternating cycles, propagation of fatigue cracks accelerates growth in size for these corrosion pits which subsequently promotes further corrosion. [ABSTRACT FROM AUTHOR]

• Load shedding is stronger when the soft-hard grain pair is embedded inside. • The grain directly attached to the hard grain has the most significant effect on load shedding. • The load shedding is higher for stronger textured materials. • Reverse load shedding can be observed due to the creep in the neighboring grains. Load shedding under cold dwell fatigue in titanium alloys has been a threat to the safety of the aero-engine since it is responsible for crack formation. The strain incompatibility between the soft-hard grain pair arises from the significant creep in the soft grain during the dwell period, which is fundamentally related to the load shedding. Such deformational heterogeneity is not only affected by the soft-hard grain itself but also by its neighboring grains, but the effect of the latter is rarely reported. In this paper, the effect of neighboring grains, including location, crystal orientation, texture, etc., on load shedding is quantitatively investigated using a three-dimensional rate-dependent crystal plasticity model by controlling the microstructural morphology of the grains. In particular, the mechanism that the dwell fatigue cracks tend to nucleate from the sample's interior rather than the free surface is revealed. Restriction of rigid body rotation from neighboring grains can further enhance load shedding. The crystal orientation of individual and group neighboring grains sitting at different locations with respect to the soft-hard grain pair is evaluated. The grain directly attached to the hard grain has the strongest influence. The statistics of load shedding are analyzed by conducting hundreds of simulations with different textures. Stronger textures are found to be able to enhance load shedding and thus deteriorate the service lifetime. The change of locations showing the highest stress during the dwell period arising from plastic deformation in neighboring grain may lead to the phenomenon of reverse load shedding. Understanding the neighboring grain effects from both the mechanistic basis and the statistical point of view is important in integrity evaluations and service life assessments of titanium components in aero-engines. [Display omitted] [ABSTRACT FROM AUTHOR]

• Low cycle fatigue behavior of core–shell heterogeneous grain structured CoCrFeMnNi high entropy alloys is investigated. • The effects of core–shell network structure on cyclic response and LCF failure are revealed. • The LCF induced inhomogeneous plastic deformation in the core–shell network structure is revealed. • The LCF resistance remains when the strain amplitude is below 0.5%. Heterogeneous grain structured high-entropy alloys (HEAs) exhibit excellent strength-ductility synergy due to the peculiar grain structure topology. However, the understanding of cyclic response and deformation mechanism under low cycle fatigue (LCF) loading is still inadequate. Therefore, the LCF behavior and deformation mechanism of CoCrFeMnNi HEAs with a three-dimensional core–shell grain structure were investigated in this paper. The effects of core–shell network structure on cyclic response and fatigue life are revealed. The dislocations activity dominantly appears in the soft core regions prior to the hard shell region. The LCF resistance remains when the strain amplitude is below 0.5%. [ABSTRACT FROM AUTHOR]

• SQS's structures of β-TiX alloys were established through open-source software ICET and utilized formation energy to estimate their thermal abilities better. • The elastic constants of the disordered structures are determined, and the impact of varying Nb or Zr contents on the bulk modulus, Young's modulus, and shear modulus of β-TiX alloys is assessed. • Elastic anisotropies of Young's modulus and an analysis of the types of alloys prone to fatigue cracking were finished. This paper employs first principles to calculate the elastic modulus and anisotropies of β-TiX (X =Nb/Zr) disordered models. Based on the special quasi-random structures (SQS) theory and utilizing the open-source software ICET, disordered structures of β-TiX (X =Nb/Zr) are established, and their formation energies and the stability of the β phase are determined. Subsequently, the elastic constants of these structures are computed, followed by calculations of the elastic anisotropies of Young's modulus and an analysis of alloys prone to fatigue cracking. The insights provided contribute to a deeper understanding of the mechanical properties of β-TiX alloys, facilitating their design and optimization for various applications. [ABSTRACT FROM AUTHOR]

• A prior progressive fatigue life prediction framework of L-DED Ti-6Al-4V was established based on machine learning. • Stress, pore types, size, position, shape, and the existence of FGA are the main factors influencing fatigue life of L-DED Ti-6Al-4V. • The proposed fatigue life framework exhibited strong generalization capability, robustness and efficiency. Pores are major cause of fatigue failure in laser-directed energy deposition (L-DED) titanium alloy. For the safe application of L-DED titanium alloys, it is essential to establish a fatigue life prediction method based on pore-induced fatigue. This paper proposes a prior progressive fatigue life prediction framework based on ridge classification and kernel ridge regression algorithms. The fatigue life prediction was carried out on L-DED Ti-6Al-4V alloy in three steps: critical pore identification, fine granular area existence prediction and final fatigue life prediction. The fatigue life prediction method adopted in the current study outperform the others with a correlation coefficient as high as 0.951, followed by a comparison with the results derived from different machine learning algorithms. The results show that the proposed fatigue life prediction framework can predict the fatigue life of L-DED Ti-6Al-4V alloy based on computed tomography tests and microstructure features. Due to its strong generalization ability and effectiveness, the proposed prediction method is expected to be valuable for fatigue-resistant design of L-DED Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

In the process of material removal, the metallurgical and mechanical properties of the surface layer of GH4169 superalloy have changed significantly, which has an adverse effect on the fatigue life. Therefore, surface strengthening process is indispensable as the last process of part manufacturing. In the paper, once and four times of ultrasonic surface rolling process (USRP) are carried out on GH4169 superalloy. The results show that USRP treatment improves the degree of grain refinement, the proportion of low angle grain boundaries (LAGBs) and dislocation density of the surface layer. The USRP treatment with four times forms a preferred orientation (〈101〉//TD) on the surface layer, and, the grain refinement mechanism is revealed. Moreover, USRP treatment changes the crack propagation mode from transgranular to intergranular. The fatigue tests indicate that the fatigue life of samples treated with USRP with once and USRP with four times increase by 55.6% and 138.6%, respectively. It can be inferred that the surface topography, residual stress, microstructure and degree of working hardening are the main factors affecting the low cycle fatigue properties of USRP treated samples. • The grain refinement mechanism of USRP treated samples was revealed. • The effect of USRP treatment on grain texture orientation was researched. • The effect of USRP treatment on crack propagation mode was analyzed. [ABSTRACT FROM AUTHOR]

As the reliability and lifespan requirements of modern equipment continues to escalate, the problems with very high cycle fatigue (VHCF) has obtained increasingly widespread attention, becoming a hot topic in fatigue research. Titanium alloys, which are the most extensively used metal materials in the modern aerospace industry, are particularly prone to VHCF issues. The present study systematically reviewed and summarized the latest (since 2010) developments in VHCF research on titanium alloy, with special focus on the (i) experimental methods, (ii) macroscopic and microscopic characteristics of the fatigue fractures, and (iii) construction of fatigue fracture models. More specifically, the review addresses the technological approaches that were used, mechanisms of fatigue crack initiation, features of the S–N curves and Goodman diagrams, and impact of various factors (such as processing, temperature, and corrosion). In addition, it elucidates the damage mechanisms, evolution, and modeling of VHCF in titanium alloys, thereby improving the understanding of VHCF patterns in titanium alloys and highlighting the current challenges in VHCF research. [ABSTRACT FROM AUTHOR]

This research investigates the coupling effect of microstructure and temperature on the fatigue performance of an equiaxed Ni-base superalloy, EA, at design-significant temperatures (750–930°C) for different strain amplitudes (Δϵ/2). It is observed that distinguishing damage features (specific to the temperature and Δϵ/2) remarkably affect the extent and distribution of strain localisation, leading to the divergence in associated fatigue behaviour. The strain is uniformly distributed at lower Δϵ/2 for all temperatures. Compared to the 850 and 930°C, the strain localisations at 750°C are more effectively alleviated, accounting for the highest fatigue life. Moreover, this alloy exhibited a bilinear Coffin-Manson (C–M) relationship. It is ascertained that the strain localisation resulting from the dislocation and precipitates (γ′, Cr6C23, and γ-γ′ eutectic) interactions are mainly responsible for the dual-slope C–M behaviour. [ABSTRACT FROM AUTHOR]

In this study, the welding performance of three filler wires, ER4043, ER5356, and the newly developed FMg0.6, were systematically investigated in the gas metal arc welding of high-strength AA6011-T6 plates. An extensive analysis of the microstructural evolution, mechanical properties, fatigue resistance, and corrosion behavior of different weldments was conducted. The ER4043 and FMg0.6 joints exhibited finer grain sizes in the fusion zone (FZ) than the ER5356 joint. The as-welded ER5356 and FMg0.6 joints exhibited higher hardness and tensile strength values than the ER4043 joint. The FMg0.6 joint demonstrated the highest mechanical strength among all of the joints with superior fatigue resistance under both the as-welded and post-weld heat treatment (PWHT) conditions. In the as-welded state, the ER5356 joint exhibited the lowest corrosion resistance, attributed to the precipitation of β-Al2Mg3 at the grain boundaries. The FMg0.6 joint, characterized by a high-volume fraction of eutectic Mg2Si in the as-welded state, exhibited a higher corrosion rate than that of the ER4043 joint. However, the PWHT effectively improved the corrosion resistance of the FMg0.6 joint. Given its excellent tensile properties, superior fatigue properties, and satisfactory corrosion resistance, particularly with PWHT, the newly developed FMg0.6 filler has emerged as a promising candidate for welding high-strength 6xxx alloys. [ABSTRACT FROM AUTHOR]

Small-hole structures, such as the millions of fastener holes found on aircraft, are typical stress-concentration structures prone to fatigue failure. To further improve the strengthening process of this small-hole structure, we make up for the limitations of laser shock processing (LSP) of small holes by combining it with the ultrasonic extrusion strengthening (UES) process to form a new strengthening method—laser shock and ultrasonic extrusion strengthening (LUE). The influence of the LUE process sequence and process parameters on residual stress distribution was studied through FEM, and the gain of fatigue life of specimens after LUE strengthening was also explored through tests. The results show that when using LUE technology, the friction force decreases with the increase in amplitude and decreases by 3.2% when the amplitude is maximum. The LUE process eliminates the thickness effect generated by LSP, which can achieve good stress distribution of small-hole components under smaller laser shock peak pressure, and reduces equipment power. LUE can significantly improve the fatigue life of small-hole components, and the maximum fatigue life gain can be up to 310.66%. [ABSTRACT FROM AUTHOR]

Strain-controlled low cycle fatigue (LCF) tests were conducted on conventionally grained (CG) and ultrafine-grained (UFG) Al-Mg-Si alloys treated under various aging conditions. In the cyclic stress response (CSR) curves, CG peak-aged (PA) alloys showed initial cyclic hardening and subsequent saturation, whereas CG over-aged (OA) alloys displayed cyclic softening behavior close to saturation. The UFG materials exhibited continuous cyclic softening except for UFG 3; it originates from the microstructural stability of the UFG materials processed by severe plastic deformation (SPD). Using a strain-based criterion, the LCF behavior and life of the CG and UFG materials were analyzed and evaluated; the results are discussed in terms of strengthening mechanisms and microstructural evolution. In the CG materials, the LCF life changed markedly owing to differences in deformation inhomogeneity depending on the precipitate state. However, the UFG materials displayed a decreasing LCF life as cyclic softening induced by dynamic recovery became more severe; additionally, a relationship between the microstructural stability of the UFG materials and the cyclic strain hardening exponent n′ was suggested. [ABSTRACT FROM AUTHOR]

This study investigates the potential of the plate-shaped Zn-22 wt.% Al (Zn-22Al) alloy as an innovative energy dissipation material for seismic damping devices, since plate-shaped material is more suitable to fabricate large-scale devices for building structures. The research begins with the synthesis of Zn-22Al alloy, given its unavailability in the commercial market. Monotonic tensile tests and low-cycle fatigue tests are performed to analyze material properties and fatigue performance of plate-shaped specimens. Monotonic tensile curves and cyclic stress–strain curves, along with SEM micrographs for microstructure and fracture surface analysis, are acquired. The combined cyclic hardening material model is calibrated to facilitate finite element analysis. Experimental results reveal exceptional ductility in Zn-22Al alloy, achieving a fracture strain of 200.37% (1.11 fracture strain). Fatigue life ranges from 1126 to 189 cycles with increasing strain amplitude (±0.8% to ±2.5%), surpassing mild steel by at least 6 times. The cyclic strain–life relationships align well with the Basquin–Coffin–Manson relationship. The combined kinematic/isotropic hardening model in ABAQUS accurately predicts the hysteretic behavior of the material, showcasing the promising potential of Zn-22Al alloy for seismic damping applications. [ABSTRACT FROM AUTHOR]

This study introduces a new type of shear panel damper that utilizes iron-based shape memory alloy (Fe-SMA) with enhanced low-cycle fatigue (LCF) resistance for structural damage control, with a particular focus on the effect of solution treatment on the properties of interest of Fe-SMA. Material-level investigation was conducted first, aimed at establishing a clear connection between microscopic structure and macroscopic properties, and to determine the most suitable solution treatment method for Fe-SMAs for structural damping purposes. This was followed by laboratory tests on a Fe-SMA based shear panel damper receiving an appropriate solution treatment, along with conventional metal shear panel dampers made of low yield point steel LYP225 and mild steel Q235. Results reveal that among the considered solution treatments, 1,100°C for 1 h leads to the most desired mechanical properties, such as lower yield stress, increased ductility, and longer LCF life, of Fe-SMA for seismic damping applications. The Fe-SMA shear panel damper demonstrates a significant improvement in LCF life and total energy dissipation capacity compared to traditional steel dampers. Finally, detailed numerical investigations were carried out to analyze the seismic response. A calibrated micromechanics-based model, i.e., cyclic void growth model, was employed to predict the fracture initiation of the Fe-SMA shear panel damper under seismic loading. This approach achieved reasonable accuracy, assisting in understanding the distinctive behavior of Fe-SMA shear panel dampers. [ABSTRACT FROM AUTHOR]

Tensile-compression fatigue deformation tests were conducted on AZ31 magnesium alloy at room temperature. Electron backscatter diffraction (EBSD) scanning electron microscopy was used to scan the microstructure near the fatigue fracture surface. It was found that lamellar {10-11}-{10-12} secondary twins (STs) appeared inside primary {10-11} contraction twins (CTs), with a morphology similar to the previously discovered {10-12}-{10-12} STs. However, through detailed misorientation calibration, it was determined that this type of secondary twin is {10-11}-{10-12} ST. Through calculation and analysis, it was found that the matrix was under compressive stress in the normal direction (ND) during fatigue deformation, which was beneficial for the activation of primary {10-11} CTs. The local strain accommodation was evaluated based on the geometric compatibility parameter (m') combined with the Schmid factor (SF) of the slip system, leading us to propose and discuss the possible formation mechanism of this secondary twin. The analysis results indicate that when the local strain caused by basal slip at the twin boundaries cannot be well transmitted, {10-11}-{10-12} STs are activated to coordinate the strain, and different loading directions lead to different formation mechanisms. Moreover, from the microstructure characterization near the entire fracture surface, we surmise that the presence of such secondary twins is not common. [ABSTRACT FROM AUTHOR]

Nickel-rich NiTiHf high-temperature shape memory alloys continue to garner significant interest for actuator applications. One issue impeding their widespread use is the question of actuation fatigue lifetime under high loads. This paper describes how these fatigue challenges can be overcome by partial thermomechanical cycling. By limiting actuation strain to less than the maximum value that is attainable with full transformation, actuation life cycles can be significantly extended. Strain-controlled cycling is achieved by limiting the upper cycle temperature during heating and stopping each cycle short of the austenite finish temperature. Four compositions of NiTiHf were tested to three levels of transformation. Strain-controlled cycling increased the actuation fatigue lifetimes of all compositions. However, specimens resistant to dislocation plasticity attained longer lives during full transformation cycling, but during partial cycling, they failed earlier than samples with higher resistance to plasticity. This highlights the importance of the competition between functional and structural fatigue. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Hot corrosion fatigue tests of the Nickel-based superalloy are conducted. • Lifetimes greatly reduce because of hot corrosion, with Chromium loss in the material. • A peridynamic model to describe hot corrosion fatigue behaviors is built. • The hot corrosion fatigue lifetimes are accurately predicted by simulations. Superalloys suffer from attack of the hot corrosion, leading to degradation of their fatigue durability. Previous numerical studies, mostly by the finite element method (FEM), are rare in hot-corrosion-intervened fatigue problems. In this paper, the fatigue behaviors after pre-hot-corrosion of a Nickel-based superalloy are experimentally studied. The tests capture the specimen's fatigue lifetime reduction due to hot corrosion. Besides, a peridynamic-based model is built to analyze fatigue behaviors of specimens pre-subjected to hot corrosion. The fatigue failure process of the corroded specimen is numerically described, and the simulated fatigue lifetimes agree well with testing results, validating the effectiveness of the model. [ABSTRACT FROM AUTHOR]

In this paper, the initiation and propagation behaviour of short fatigue cracks in nickel-base alloy Inconel 718 is studied extensively in the fatigue loading regime by ex-situ scanning electron microscopy on component-near notched specimens in the temperature range between 400 °C and 600 °C. To investigate the influence of different surface treatments, both specimens with polished and shot-peened surfaces were tested. For polished specimens, most fatigue cracks initiated at oxidised non-metallic inclusions, whereas for shot-peened specimens, the process-induced surface roughness also served as crack starters. It was found, that the observed scatter in lifetime for repetitive tests is mainly caused within the short crack fatigue regime below 50 μm, while cracks larger than 100 μm showed similar growth characteristics. • Ex-situ SEM crack initiation and crack propagation behaviour investigation of Inconel 718 at elevated temperatures. • Investigation of polished and shot-peened specimens. • Detailed information about crack initiation and growth behaviour. • Statistical evaluation of crack initiation sites (e.g. non-metallic inclusions or overlapping due to shot peening). • Evaluation and assessment of non-metallic inclusion distribution on fracture surface. [ABSTRACT FROM AUTHOR]

• The relative location of the pores to the surface, size, shape, and stress are main factors affecting fatigue failure of L-DED Ti-6Al-4V alloy. • Critical pore criterion based on stress state sensitive parameter of L-DED Ti-6Al-4V alloy was established. • The critical pore criterion established in this article has a low relative mean deviation and good applicability. Pores are the major factor inducing fatigue failure in laser-directed energy deposition (L-DED) Ti-6Al-4V alloy, posing obstacle to the application of the alloy in primary load-carrying components. Hence, it is essential to formulate criteria to identify critical pores that induce failure, an important step in evaluating the fatigue performance and predicting the fatigue life of L-DED Ti-6Al-4V alloy. In this paper, computed tomography was performed on tangentially blending fillets specimens to examine the distribution characteristics of pore geometric parameters, and location in the gauge section of the specimens. Then, fatigue experiments and fracture analysis were conducted. The results show that the location relative to the surface, size, and shape of the pores are the primary factors affecting fatigue failure. A stress state sensitive parameter was formulated by using location factors, projected area along the load direction, circularity of pores, and peak stress to establish a criterion for recognizing critical pores, the number of which can be reduced to two. The critical pore criterion based on stress state sensitive parameter was compared with those obtained via the other methods, proving its good applicability and effectiveness on identifying critical pores. [ABSTRACT FROM AUTHOR]

This work presents a test rig developed for testing the lifetime of electrically and cyclically activated shape memory alloy wires. This test rig is developed to provide information on the functional and structural fatigue of the wires. Therefore, electrical activation on the test rig can be carried out using different activation profiles, because it is of great research interest to determine whether those profiles have a significant influence on the wire's lifetime and functional behavior. The test rig monitors the process parameters such as stroke, current, voltage, and force. After presenting the electrical and mechanical design of the test rig, this publication evaluates an initial series of tests to demonstrate its functionality. Three different activation profiles are run in parallel on four identical test rig setups and are then evaluated. The functionality of the test rig is verified by a detailed evaluation of the process data on the one hand, and by comparing the results with existing literature on the other. The functionality of the test rig can thus be verified. At the same time, the strong influence of the different activation profiles on both the lifetime and the functional properties of the shape memory alloy wires becomes clear. [ABSTRACT FROM AUTHOR]

Based on the electromagnetic shaker table, the resonant fatigue testing system and the corresponding conventional fatigue testing system were designed respectively. The fatigue life (S-N) curves of smooth and notched 7050-T7451 aluminum alloy specimens were measured in the range of 105 - 107 cycles, and the notch fatigue property of 7050-T7451 aluminum alloy under bending resonance environment was studied. The results indicate that the fracture mechanism under bending resonant fatigue environment is roughly the same as that under bending conventional fatigue loading. All the S-N curves obtained through resonant and conventional fatigue tests show a continuously downward trend, and there are no obvious fatigue limits. Notch fatigue property under bending resonance environment presents "stage characteristics", which increases first and then decreases with the increase of cycles. There is a critical cycle number Nc at 8×105 cycles, corresponding to the maximum fatigue notch factor Kf-max (or the maximum notch sensitivity factor qmax). There are two critical cycles N1 and N2. When N¹ < N < N2, the notch fatigue property of the material and the corresponding structures under resonance environment requires more consideration than conventional fatigue loading. [ABSTRACT FROM AUTHOR]