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• The transverse laser heating effectively inhibited crack extension by introducing a maximum CRS of 32 MPa on the crack extension line. • The SEM showed that transverse heating significantly reduced the spacing between adjacent fatigue glow lines compared to the base material. • The Walker model, based on the WF, accurately predicts the crack extension life of specimens with RS under various loading conditions. • At laser heating power lower than 900 W, the local hardness decrease of the heating line on the specimen surface does not exceed 10HV 0.5. To extend the operational lifespan of the AA2524 aircraft panel, the surface of the AA2524 specimen was locally heated by laser. The specimen's microhardness distribution and surface residual stress (RS) were tested, as was its fatigue crack growth rate (FCGR). The fatigue fractography of specimen was also observed. The FCGR of specimen after laser heating was predicted by the weight function method (WFM). The consequences indicate that when the laser power is lower than 900 W, the hardness of the heating zone on the surface of the specimen decreases by no more than 10 HV 0.5. Compared to the base material (BM) specimen, transverse heating specimen creates a maximum compressive residual stress (CRS) of 32 MPa along the crack extension line. This can effectively stop the crack propagation. When laser power with the transverse heating is 900 W, the crack propagation suppression effect is optimal. The fatigue life of heated specimen is increased by 108.5 % compared to the BM specimen under a constant amplitude load with the maximum load of 2600 N and R of 0.1, and the fatigue life of heated specimen is increased by 46.4 % under a constant amplitude load with the maximum load of 3300 N and R of 0.1. The spacing among 6 adjacent striations of specimen after transverse heating is shortened from 2.79 μm to 0.88 μm compared with the BM specimen. The Walker model, which is based on the WFM, has high accuracy in predicting FCGR of specimen after laser heating under various load conditions. It is evident that local laser heating technology can extend the service life of aviation aluminum alloy panels. [ABSTRACT FROM AUTHOR]

[Display omitted] • CFRP/aluminium SLJ performance was evaluated under static and fatigue loading. • SLJs with nine different geometric combinations were studied. • Predictability of different fatigue life estimation models was analyzed. • Failure modes under static loading is assessed for each joint type. • Failure mechanism at different load level are revealed for SLJs. This study examines the effect of overlap length and adhesive thickness on the static and fatigue strength of CFRP-AA 7050-T6 single lap joints (SLJs) through both experiments and simulations. SLJs were fabricated with three overlap lengths and adhesive thicknesses, and quasi-static and high-cycle fatigue tests were performed. The experimental results show that increasing the overlap length reduces fatigue life at the same stress level, with a similar trend observed for variations in adhesive thickness. Fatigue life was estimated using a methodology, which integrates numerical simulation results with experimental data, comparing multiple strain-life fatigue criteria, including Smith-Watson-Topper (SWT), Morrow, and Manson-Hirschberg, against the experimental fatigue life. Among the criteria analyzed, the SWT criterion provided the most accurate fatigue life estimation. [ABSTRACT FROM AUTHOR]

• The damage evolution process based on modulus degradation was obtained by experimental data. DIC technique was used for surface cracks tracking, and SEM was used for fracture surface analysis. • The ductility parameters were used to correlate the lifetime of AA2024-T351 under multiaxial proportional and non-proportional loads. • The life prediction results of AA2024-T351 by the improved FS model were consistent with the experimental data. Multiaxial fatigue has been drawing much attention because it is more applicable to engineering practice. In this paper, an experimental study of aluminum alloy (AA) 2024-T351 was carried out under multiaxial loading with an aim to assess the damage evolution process and failure mechanism under in-phase and out-of-phase loadings. Firstly, fatigue life and stress response under multiaxial cyclic loads were obtained, and it found that although there is non-proportional hardening, the fatigue life subjected to proportional loading is significantly shorter than that of under a nonproportional loading, which was tried to be explained by the ductility of the material. Secondly, a detailed analysis of the damage evolution process based on the degradation of the elastic modulus and the fatigue failure process based on the digital image correlation (DIC) method was provided. Next, a micro-analysis of the specimens' fracture appearance was conducted to obtain the fracture characteristics and found that AA2024-T351 presents a dominant shear fracture mode under proportional loading and a mixed mode of tensile and shear fracture under non-proportional loading. Last but not least, The Fatemi-Socie criterion was modified by considering the material's ductility and the interaction between normal stress and shear stress acting on the critical plane. The multiaxial life prediction results of the modified FS model for AA2024-T351 in this paper were all within the scatter bands of 3 on life. [ABSTRACT FROM AUTHOR]

• The analyses includes fatigue failure mechanisms of bolted joints of carbon fibre reinforced polymers to titanium. • This work carried out the influence of precompression on fatigue properties of bolted joint structures, and the optimal design value of precompression is obtained by life prediction. Carbon fibre reinforced polymers are widely used in industry, the problem of joining them with metal materials becomes significant. This is because of the loosening of bolted joints under applied loads, leading to a rapid reduction in fatigue life and even structural failure accidents. This study focuses on fatigue failure mechanisms of bolted joints of carbon fibre reinforced polymers to titanium alloy and looking for a novel solution to improve the fatigue life of bolted joints. Firstly, fatigue life prediction of the components is conducted based on FE-SAFE. Then, experiments are conducted to verify simulation results. Finally, the thread damage and the fracture morphology are analysed after tests. It is found that the fatigue life of bolted joints can be improved by increasing the stiffness of connected parts and choosing appropriate geometric parameters. [ABSTRACT FROM AUTHOR]

• Finite element model predicts HSR concrete fatigue life. • Model assesses impact of load frequency, stress ratio, and level. • Fatigue life of environmentally damaged concrete analyzed. High-speed railways have become a critical component of modern transportation, and ensuring the stability and durability of high-speed railway concrete under environmental and train fatigue loads is essential for ensuring project safety. This paper employs a numerical simulation method to predict the performance and lifespan of high-speed railroad concrete under fatigue loading with environmental damage. The study analyzes the effects of stress level (0.5–0.8), stress ratio (0.1–0.9), and load frequency (5 Hz–40 Hz) on the fatigue performance and lifespan of railway concrete during bending fatigue loading. A four-point bending numerical model of concrete is developed in this paper, which considers elastic modulus decay and surface cracking, in order to quantify the degradation of concrete properties in response to environmental and load-induced cracks. The numerical model is well-validated with experimental results, and the study establishes a correlation between concrete degradation and environmental and load-induced cracks, as well as the fatigue resistance of high-speed railroad concrete. The bending fatigue frequency of concrete should not exceed 25 Hz at high stress levels of 0.7. This study also shows that environment-induced initial damage will greatly reduce the fatigue resistance of concrete, and fatigue life degradation and elastic modulus decay have a nearly linear relationship. This research provides a crucial foundation for the fatigue design of concrete materials for high-speed railroads. [ABSTRACT FROM AUTHOR]

• A dual loop circulating water thermal fatigue test method based on high-throughput testing technology was established. • The thermal corrosion fatigue crack growth rate of tubular structures was studied for the first time with a dual loop device. • The model relationship between crack growth rate and cooling rate was established. • A numerical simulation method had been established to predict the thermal fatigue crack propagation life. The influence of transient water temperature changes on the fatigue crack growth behavior of 304SS pipeline structures was studied based on high-throughput testing method through the modification of dual loop circulating water equipment. Results demonstrated that the fatigue crack growth rate gradually decreased with the decrease of cooling rate, and the crack growth rate was exponentially related to the cooling rate. Both the base material and weld of the stepped pipe showed a transgranular cracking mode, and propagated continuously by slip-oxidation mechanism. Compared with the fine equiaxed grain of the base material, the grain in the weld was coarse and the residual strain was large, and the crack growth rate of the weld was obviously higher. Then, the thermal fatigue crack growth rate model for stepped pipes was established by combining finite element thermo-mechanical coupling simulation and three-dimensional crack propagation analysis software, and the model was modified based on the experimental results. [ABSTRACT FROM AUTHOR]

• The field tests were carried out for more than two years on Chinese high-speed railway lines, it is found that the main failure cause of the BBF is the resonant vibration of 8–20 Hz which excites the first-order natural mode of the frame. • It is found that the measured data are quite different from the IEC61373 standard, it is necessary to reassess whether the limits in the standard are safe or not for Chinese high-speed railway lines. • The bolster exhibits obvious non-Gaussian characteristics, it could be inferred that the Gaussian signal maybe not always suitable for the input load spectrum. Aiming to solve the failure problem of welded frame suspended under high-speed EMU, a long-term tracking test was carried out. The modal resonance of 8–20 Hz is the main cause of structural failure. The characteristics of the in-service vibration environment and the difference with the standard load spectrum are analyzed. The measured load spectrum exceeds the IEC61373 standard load spectrum in the frequency range of 10–20 Hz and 30–120 Hz. Meanwhile, the kurtosis of measured acceleration signal does not always follow the Gaussian distribution for the carbody bolsters, and the acceleration and dynamic stress amplitude of the bolster and suspension equipment frame increase more with higher train speed. After a finite element model with welded joints was developed to evaluate the fatigue life, an optimized prototype BBF was designed. The reliability of the optimized structure is verified by rig test. The optimized structure avoids 8–20 Hz resonance and meets the test requirements. [ABSTRACT FROM AUTHOR]

• The proposed model addresses corrosion fatigue life estimations under asymmetric cyclic loadings. • The proposed model requires a material parameter and of convenience for engineering applications. • Intrinsic damage dissipation targeted at fatigue damage was employed for fabrication of the proposed model. • The proposal provides great potential for its simplicity in the evaluation of CF lifetime under asymmetric cyclic loadings. Numerous scholars have conducted theoretical research on corrosion fatigue lifetime prediction models based on continuum damage mechanics and linear fracture mechanics. However, most of the predicted models require several material parameters, making them difficult to apply in practice. For practical application, the existing models, including the Goodman, Gerber, SWT and Walker models, are empirical or statistical and have not gained wide acceptance. Hence, an urgent need exists for an equally simple, easy-to-apply, and mechanics-based model for engineering applications. Therefore, this study proposes a corrosion fatigue stress equation associated with equivalent life based on the intrinsic damage dissipation energy. The method attached to a material parameter can be used to predict corrosion fatigue lifetime and provides a novel approach for easy application. The comparisons of experimental results and the results predicted by our proposal and the existing models were carried out, indicating that our proposal provides better correlations with experimental results than others. The proposal provides great potential for its simplicity in the evaluation of corrosion fatigue lifetime under asymmetric cyclic loadings. [ABSTRACT FROM AUTHOR]

• Surface and subsurface failures are mainly induced by lack of fusion. • Defect size and melting pool boundary are related to building direction. • Transition crack size and threshold values for crack growth are evaluated. • A fatigue index parameter-dominated model with a defect size effect is proposed. The influence of the building direction (0°, 45°, and 90°) on the high cycle fatigue properties of a laser powder bed fusion (LPBF) Al-Si alloy was investigated by uniaxial loading fatigue tests under a stress ratio of 0 in combination with multi-dimensional imaging and electron backscattered diffraction (EBSD) analysis. Surface/subsurface failures were induced by single irregular lack of fusion defect that originated from unmelted powder or inhomogeneous microstructure. The fatigue properties decreased with increasing building angle, which was attributed to the size difference of the original defect dominating crack nucleation and the distribution difference of melting pool boundaries deflecting crack growth. According to the stress intensity factor evaluation, the threshold value of long crack growth and the transition size of crack growth exhibited a decreasing tendency as the building angle increased. Considering the influence of building direction on defect size distribution, a fatigue index parameter-controlled crack nucleation life prediction model was established, and the prediction result was satisfactory for safety design. [ABSTRACT FROM AUTHOR]

• Systematic material experiments are analyzed to obtain the parameters of TMF life prediction. • The predicted life based on the new parameter determining method falls within twice the error band. • Using Neu/Sehitoglu model, oxidation and fatigue dominate the total damage under OP TMF. • Oxidation parameters are more sensitive to the TMF damage. The increase in engine power has resulted in a significant rise in both thermal and mechanical loads on cylinder heads, leading to the emergence of thermomechanical fatigue (TMF) as one of the significant issues. This paper proposed a parameter identification method for the Neu/Sehitoglu model, utilizing multi-objective optimization (MOO), and applied it to predict the TMF life of compacted graphite cast iron (CGI) material used in cylinder heads. The study assessed the TMF behavior of RuT450 material through various experiments, including tensile, low cycle fatigue (LCF), creep, TMF, and oxidation experiments. Employing the MOO, the unknown model parameters are estimated and optimized to predict the TMF life of RuT450 materials. Results demonstrated that over 95% of the predicted TMF life falls within twice the error band of experimental values. Furthermore, plastic strain amplitude, temperature, and strain rate significantly influenced the damage mechanism and life prediction. The TMF life under out-of-phase (OP) loading conditions was found to be smaller than that of in-phase (IP) loading. Notably, under out-of-phase thermomechanical fatigue (OP TMF), oxidation damage and fatigue damage together contributed to over 95% of the total damage in RuT450 materials. Moreover, variations in oxidation damage parameters had a considerable impact on the predicted life. This study might offer an effective method for determining Neu/Sehitoglu model parameters and establish material boundaries for TMF life assessment of cylinder heads. [ABSTRACT FROM AUTHOR]

The foundations of Fracture Impedance Spectroscopy (FIS) as a theoretical framework for analyzing and predicting fatigue and corrosion fatigue crack growth rate in real structures under complex loading waveforms from laboratory data obtained under simple, "pristine" loading conditions is presented. FIS is based upon an analogy between current flow (crack growth rate) in an electrical circuit in response to an applied, time-dependent voltage (time-dependent stress intensity factor). In this paper, the framework of the theory and its application for two different aerospace alloys are presented. • The theory of Fracture Impedance Spectroscopy (FIS) is presented. • Crack growth rate (CGR) can be calculated using stress intensity factor (SIF) for arbitrary loading waveform and frequency. • FIS is based upon an analogy between current flow (CGR) in an electrical circuit in response to a voltage (SIF). • "Fracture impedance" for crack growth in metal defined by transforming the perturbation and response into the Laplace frequency domain. • Crack growth rate calculations show the viability of the FIS concept. [ABSTRACT FROM AUTHOR]

Abstract This work presents an experimental apparatus for fatigue testing of chain links subjected to out-of-plane bending. The test consists of a pre-tensioned chain segment subjected to a cyclic transverse displacement of the middle link, resulting in out-of-plane bending of the adjacent links. Aiming to obtain new data for the evaluation of fatigue-life prediction methodologies, eight tests were designed considering different interlink angles and mean stress levels. The tests were conducted with positive interlink angles, a condition typically found in the fairlead/mooring chain system. A stress-based fatigue analysis using the Smith-Watson-Topper parameter yielded life estimates within factor-of-three boundaries. This very good correlation resulted from a combination of factors: a fatigue parameter that considers the mean stress effect, its calibration using test data from specimens with a surface condition similar to that of the chains, and a reasonable engineering estimate of the stress at the hotspot. Highlights • Experimental apparatus for fatigue testing of chain links under out-of-plane bending • New experimental data with positive interlink angle • Stress-based fatigue life estimates within factor-of-three boundaries. • Conventional design rules may produce nonconservative life estimates. [ABSTRACT FROM AUTHOR]

Abstract Estimation of remaining useful life/prognostics of an aircraft structure permits aerospace industry to timely schedule maintenance activities. Accurate planning through prognostics ensures safer flight operation and lower downtimes. The core of any prognostic algorithm is the state transition/degradation model. In the reported research work, Particle Filter (PF) based prognostic algorithm is used to predict crack growth with three different state transition/life distribution models. PF (Bayesian Sequential Monte Carlo) allows using of non-linear state-transition and non-Gaussian/multimodal noise distributions. The typical candidate life distributions for modeling crack growth are Exponential, Weibull and Lognormal distributions. A framework is proposed where effectiveness of the candidate distribution for modeling degradation phenomenon can be adjudged. The algorithm is tested on actual historical NDT data of crack growth on countersunk (CSK) rivet holes on an Airbus A310 aircraft's wing. Historical data is bifurcated into two periods i.e. training and validation periods. The most appropriate distribution based on the comparison of the above mentioned candidate distributions is proposed for prediction of the degradation/ flaw propagation. Highlights • Actual historical aircraft wing's NDT data is used in the reported research work • Sequential Monte Carlo is used to predict the future health mode of countersunk rivet holes of an aircraft wings. • A frame work is developed in which Weibull, Exponential and Lognormal distributions are used to model crack growth • Exponentials ability to predict crack growth of countersunk rivet hole is superior to other distributions. • 3D polar plots further compare the outcomes of these models [ABSTRACT FROM AUTHOR]

• The MKRC creep-fatigue life prediction model of the turbine blade material was established, which considers stress fluctuation and high-temperature effect. • The microscopic mechanism of the creep-fatigue interaction of the turbine blade material at 850℃ was investigated. • The creep-fatigue life prediction model of the aero-engine turbine blade structure is established considering the effect of shape-size- microscopic defect differences. Aiming at the creep-fatigue interaction damage failure problem of turbine blades in aeronautical engineering, firstly, based on the modified Kachanov-Rabotnov-Chaboche (MKRC) damage mechanics theory, the creep-fatigue life prediction model of turbine blade material was constructed with the experimental verification completion of nickel-based superalloy DZ125. Meanwhile, the creep-fatigue interaction behavior was investigated with the mechanism revelation. Then, considering the shape, size and microscopic defect difference effect from the material to the structure, the creep-fatigue life prediction model of turbine blade structure is proposed by introducing the comprehensive correction factor with experimental verification. Finally, the research results show that there are a large number of interwoven tear edges, micro-cracks and micro-pores in the fracture morphology, and creep and fatigue interact with each other in the form of effective stress. Simultaneously, the creep-fatigue life prediction model has a high life prediction ability with an error of 3%, which can provide a theoretical reference for the damage tolerance design of the turbine blade. [ABSTRACT FROM AUTHOR]

• Developing an innovative model, addressing existing limitations, by incorporating critical plane and phase difference angle in multiaxial fatigue life prediction. • Increased accuracy and reliability in predicting the fatigue life of engineering materials under complex multiaxial loading conditions. • Comprehensive investigations ensure the validity and applicability of the proposed model for multiaxial fatigue prediction. • Rigorous statistical analyses and comparisons demonstrate superior performance of the proposed model over existing models. Multiaxial loads are the main cause of fatigue failure in engineering applications, where this failure affects the components and structure of these applications directly. The probability of failures can be decreased by using multiaxial fatigue analysis to assess the service life of components. This study proposes a simple and effective approach for measuring fatigue life in the presence of multiaxial loading. The proposed damage parameter includes terms such as the critical plane and phase difference angles. Calculating fatigue life using this model under proportional and nonproportional loading conditions is possible. The accuracy and validity of the model were tested by comparing the experimental results of four experimental datasets with the life estimation results. The analysis results of four metal materials show that the predicted life correlated well with the experimental observations. In addition to the proposed model, five famous fatigue prediction models were used, and the results of the proposed model were compared with these models. The suggested damage parameter is better for predicting fatigue life under different loads. This was shown through model comparison and prediction error analysis. The findings show good agreement between the suggested model's life estimation results and the experimental findings. Predicting fatigue life becomes more realistic with the suggested approach for any angle between 0 and 90°. The proposed model showed the highest accuracy among the tested models. Afterwards, the Fatemi and Socie FS, Kandil Brown and Miller (KBM), Smith Watson and Topper (SWT), maximum share stress (MSS), and ES models demonstrated lower levels of prediction error, respectively. [ABSTRACT FROM AUTHOR]

The present paper investigates the low cycle fatigue of fillet welds made of high strength weldable steel, Weldox S1100. The investigation was inspired by lifting equipment used in the wind turbine industry, where mobility calls for light weight, making high strength steels the preferred material candidate. Quite often the number of operations for this type of equipment is within a few thousand operations or less before the equipment is obsolete. 4 point bending tests were carried out at stress amplitudes between 500 MPa - 1500 MPa and at a stress ratio of R  = −1. The results showed that at N  ≈ 1000–3000 cycles there is a distinct drop in fatigue strength, indicating a change of slope of the Δ S  −  N curve. It is also shown that the ultimate tensile strength may be used as the basis for constructing Δ S  −  N curves from static material data. [ABSTRACT FROM AUTHOR]

For engine components under complex loadings, multiaxial fatigue life prediction is critical for ensuring their structural integrity and reliability. Combining the critical plane method with the virtual strain energy concept, a new multiaxial fatigue damage parameter is proposed to characterize the influence of both shear/normal mean stress and non-proportional hardening on fatigue life. Particularly, no extra material constants are needed for model application. Experimental data of TC4 and GH4169 alloys under various loading paths are utilized to evaluate and validate the proposed damage parameter as well as four other models. Results show that the proposed damage parameter yields a higher accuracy on multiaxial fatigue life prediction than others. [ABSTRACT FROM AUTHOR]

The small punch creep deformation behavior estimation of Incoloy800H was performed theoretically and experimentally in this study. The results indicate that three creep stages of the small punch test are similar to that of the conventional creep tests. Considering the deformation characteristics and geometry form, an obvious initial elastic-plastic deformation is presented and the primary creep stage is proven to be nonnegligible in the small punch test. Both the three-point bending model and the modified geometric model were proposed. It indicates that creep strain is proportional to small punch deflection in the primary and steady creep stages. Meanwhile, membrane stretching model was modified and a constant stress phase during deformation was found. The results indicate that small punch character parameters are capable to replace traditional creep data in the creep curve analysis of Incoloy800H. Thus, the creep curves with three deformation phases were analyzed and predicted by both of the modified Norton-Bailey model and modified theat model. Finally, the primary, steady and tertiary creep stages were described, and the creep life prediction of Incoloy800H was realized. [ABSTRACT FROM AUTHOR]

The corrosion fatigue behavior of FV520B steel in water and salt-spray environments at different temperatures is the focus of this study. Temperature has a significant effect on the fatigue behavior of FV520B steel in water and salt-spray environments, but has only a negligible effect in an air environment. Fatigue life decreases as temperature increases in water and salt-spray environments, and this trend is much more remarkable at a low stress amplitude level. As compared to air and water-spray, it was found that the chloride ion in salt-spray accelerated the fatigue damage of FV520B steel. Micro observation revealed that the fatigue cracks were initiated on the surfaces of the specimens in all experimental environments, and significant evidence of corrosion pits and micro cracks was found on the surfaces of the specimens in the salt-spray environment. Based on the pitting corrosion mechanism, a modified fatigue life prediction model that considered the combined effects of stress, temperature and corrosion was proposed. The study results show that the model predictions are in good agreement with the test data. [ABSTRACT FROM AUTHOR]

Electrical vehicles (EVs) have a significant role in reducing transportation emissions and dependence on fossil fuels. This research has developed a high energy density in-wheel switch reluctance motor (SRM) drivetrain for a small car. The SRM drivetrains overcome the cost and availability issues associated with the permanent magnet motor (PMM), mostly used in EVs. However, the in-wheel SRM developed has an increased mass on suspensions when compared with an equivalent power output PMM drivetrain. Hence, the main aim of this paper is to assess the durability and life cycles for a small car suspension due to an increased mass. This fatigue study used a rain flow counting cycle method to generate damage and life matrix for the suspension. Using Plamgren-miner rule, the fatigue life cycles are predicted based on identified cumulative damages to the suspension. [ABSTRACT FROM AUTHOR]

To predict the residual life of structure under repeated impacts, the crack behavior of standard specimens with and without notch were studied experimentally and numerically. The history of crack propagation and energy absorption was recorded, and the fracture surface appearance was observed experimentally. A energy-based life prediction method for repeated impacts was proposed and validated by experiments, which includes the effects of strain rate and cumulative damage. It is found that structures under repeated impacts are extremely sensitive to notch or crack. With the increasing number of impacts, both the ratio of plastic energy to elastic energy raises and finally approaches to infinite at fracture. [ABSTRACT FROM AUTHOR]

This paper describes the fatigue failure of a rotary dryer in a chemical plant. The process conditions required the dryer to be rotated continuously at a speed of about two and half revolutions per minute. The shell structure of this large drum is formed by combining segmented shell parts using bolted ring flange joints. Because of the gross weight of the dryer in operation time, each joint was subjected to bending moment. In the first two years in service, micro cracks were occurred by fatigue. The failure was analyzed using the fatigue curves given in ASME Boiler and Pressure Vessel Code Section VIII Division 2 and EN 13445 Unfired Pressure Vessels Part 3 Codes. Finally, flange joints were removed from the drum and new cylindrical parts adapted to the drum using butt welding after reaching better results in FEM and fatigue calculation. [ABSTRACT FROM AUTHOR]

• In random load conditions, the real service life of parts and components was verified by road simulation durability test, the prediction risk of fatigue life based on ε-N curve is evaluated through the quantitative analysis approach. • A double-parameter Coffin-Manson model is proposed. Its advantages are that the damage related to mechanical strength or machining process of parts and components can be corrected by the part ε-N curve. • The double-parameter model can be were calibrated further by random load factor β, thus the fatigue damage of random loads can be conveniently and precisely calculated by using one parameter. • The model has strong openness and expansibility in aspects of ε-N curve parameter, it can also be applied to quantify the material dispersion. The fatigue life prediction methods of constant-amplitude load have been widely studied. However, a simple and mature random loads fatigue model is more worth exploring. In this paper, the battery box brackets were taken as the study case, the road simulation technology and statistical method are adopted to analyze the prediction accuracy of random loads which is based on ε-N curve and damage accumulation law, a fatigue damage calculation procedure of random loads was established. Firstly, both the road simulation and constant-amplitude experiments of bracket were conducted respectively on the hydraulic servo rig. Simultaneously, the strain loads were collected and the part ε-N curve was constructed. In accordance with the material and part ε-N curve, an improved double-parameter (u and v) Coffin-Manson model was proposed and a fatigue ε-N curve was plotted. Then the damage originated from machining process and geometrical uncertainty was corrected by u and v. Under random load conditions, u and v were calibrated furtherly by random load factor β. Finally, the damage of the brackets was recalculated and the result has a high precision. The double-parameter model coupled with β has strong adaptability to most fatigue uncertainties. A leaf spring experiment was also performed to verify the generality and validity of the model. [ABSTRACT FROM AUTHOR]

• A machine learning method of double-layer features based on image recognition technology is proposed for multiaxial fatigue life prediction. • The proposed method can accurately predict the multiaxial fatigue life. • The proposed method has good extrapolation abilities. • Proportional and non-proportional loading paths with different phase angles, different loading frequencies can be well identified and converted by IRT. The loading path of multiaxial fatigue has an important and direct impact on the life prediction, and machine learning can predict the multiaxial fatigue life. However, machine learning cannot directly accept input from the loading path because it is graphic data. To solve this problem, the image recognition method is used to extract the loading path features and transform them into numerical data. These data are placed in the first layer and together with the second layer of identifiable strain amplitude data to construct a machine learning method based on the bilayer features. This method can predict multiaxial fatigue life of different loading paths. Experimental data of PA38-T6 and E355 under multiaxial fatigue loadings are used to verify the feasibility and applicability of the proposed method. The results show that the proposed method can accurately predict the multiaxial fatigue life and has good extrapolation abilities, and image recognition technology is suitable for the feature extraction of loading paths. [ABSTRACT FROM AUTHOR]

• Under the same strain rate, the phase difference between stress and strain was approximately considered unchanged. The loss of elastic modulus is caused by inelastic and plastic strain, which increased with the increasing of loading strain amplitude. • Due to cyclic hardening/softening and loss of elastic modulus, the plastic strain energy evolves linearly approximately with the cyclic numbers, which should be considered in the fatigue life prediction model. • A modified fatigue life prediction model according to the evolution law of plastic strain energy is proposed. The prediction error of proposed model decreased significantly from 13.73% to 7.68% after parameters correction compared with the prediction error of the strain-based life model. Accurately predicting the fatigue life of materials and components is of great significance for ensuring the safety of mechanical equipment. In most strain-controlled fatigue experiments, before fatigue fracture occurs, plastic strain accumulation and microstructure changes have a great impact on the cyclic stress–strain response of the material, which manifests as a hysteretic loop evolution. In this paper, the cyclic hardening/softening tendency under different strain amplitudes, the loss mechanism of the loading modulus and unloading modulus, as well as the evolution law of plastic strain energy of 45CrNiMoVA steel were investigated. A life prediction model based on the modified plastic strain energy was proposed according to the evolution law of plastic strain energy. The results showed that the prediction error of the modified plastic strain energy model was within the 2 times error band, which decreased significantly from 13.73% to 7.68% after parameters correction compared with the prediction error of the strain-based prediction model. [ABSTRACT FROM AUTHOR]

The objective of this study is to estimate fatigue life of irradiated austenitic stainless steels types 304, 304L, and 316, which are extensively used as structural alloys in the internal elements of nuclear reactors. These reactor components are typically subjected to a long-term exposure to irradiation at elevated temperature along with repeated loadings during operation. Additionally, it is known that neutron irradiation can cause the formation and growth of microscopic defects or swellings in the materials, which may have a potential to deteriorate the mechanical properties of the materials. In this study, uniaxial fatigue models were used to predict fatigue properties based only on simple monotonic properties including ultimate tensile strength and Brinell hardness. Two existing models, the Bäumel–Seeger uniform material law and the Roessle–Fatemi hardness method, were employed and extended to include the effects of test temperature, neutron irradiation fluence, irradiation-induced helium and irradiation-induced swellings on fatigue life of austenitic stainless steels. The proposed models provided reasonable fatigue life predictions compared with the experimental data for all selected materials. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the fatigue life of railway hollow axles with tapered bore surfaces (hereinafter indicated as RATB) that have a different inner shape than the shape of existing hollow axles. The fatigue strength evaluation method is identified in accordance with European Standards EN13103 and EN13261; the fatigue strength is also evaluated by finite element analysis of a full-scale axle test piece by way of applying an S–N curve that was identified through fatigue tests of high strength axle materials. Furthermore, a fatigue life analysis of the wheel–rail contact force was conducted using dynamic simulation results of a Korean Electric Multiple Unit (K-EMU) multi-body dynamics model. As a result of the fatigue life evaluation, the RATB for metro vehicles satisfied the fatigue strength requirements of EN, and the fatigue life by wheel–rail contact force was predicted to be safe within a standard axle replacement cycle. [ABSTRACT FROM AUTHOR]

Gas pipelines are exposed to a fatigue load related to both the ground and cars because of being buried at a depth of 1.5 m. Gas pipeline integrity is of considerable importance because earthquake-induced damage of gas pipelines can lead to gas leaks and fire, resulting in property damage and endangering lives. For these reasons, evaluation of the mechanical properties of gas pipelines must be performed. Therefore, in this study, the fatigue behavior of an API 5L X42 gas pipeline was estimated. ASTM standard specimens, curved plate specimens, and wall-thinning curved plate specimens were collected from the API 5L X42 gas pipeline, and fatigue testing was subsequently performed. Also, the S–N curves of each specimen were estimated, and then predicted by theoretical methods according to the depth of wall-thinning. Finally, it was verified that the predicted models were in good agreement with actual test data. [ABSTRACT FROM AUTHOR]

The paper presents a fatigue damage accumulation model, which allows us to predict fatigue life under low cycle uniaxial loadings at elevated temperatures. The structure of the model has been based on the stress–strain curves obtained during the experimental study. The model has been verified experimentally by applying experimental studies carried out on ENAW-2024T3 aluminum alloy and 2Cr–2WVTa steel. Moreover, a comparison between the results of fatigue life prediction using the proposed damage accumulation model was done with the results obtained on the basis of various generally applied models, based on the Manson–Coffin dependency. Furthermore this paper presents the results of experimental studies carried out on the aluminum alloy ENAW 2024 T3 under uniaxial low cycle fatigue loadings in the conditions of elevated temperatures. In the course of the study, material constants and the parameters of the stress–strain curve in the range of low cycle fatigue for four levels of temperatures (20, 100, 200 and 300 °C) were set. [ABSTRACT FROM AUTHOR]

The quantitative influence of casting micro porosity on fatigue life still remains unclear. In the study, by combining the representative volume element method and theory of critical distances, a numerical analysis approach for investigating micro porosity’s effect on fatigue life of casting materials has been established. Taking as an example, the fatigue life of an A319 alloy with varying porosity volume fractions were predicted. The results indicated that the proposed life prediction approach was capable of accurately reflecting the decrease of fatigue resistance due to the increasing micro porosity volume fraction. [ABSTRACT FROM AUTHOR]

• A computational procure to quantify the stress field intensity is developed. • A new modified non-proportional hardening factor is established. • The notch effect and the stress concentration can be well characterized by the absolute value of the relative stress gradient. • A multiaxial life prediction model for notched specimens is established. Engineering components with geometric discontinuous structures generally appear notch effect, which might eventually induce fatigue failure. In this study, a novel multiaxial fatigue prediction model is established for notched components by incorporating the notch effect and non-proportional hardening. Firstly, according to the notch effect, a computational procure of damage parameters is presented by combining the notion of stress intensity with finite element simulations based on the critical plane method. Secondly, considering the non-proportional hardening effect of path modes and material properties, a new modified non-proportional hardening factor is proposed. Particularly, the relationship between the relative stress gradient and the fatigue life is investigated under different stress concentration factors. Finally, with the help of the Manson-Coffin equation, a multiaxial fatigue life prediction model is developed subjected to multiaxial proportional/non-proportional loadings. Experimental data of medium steel En8 and GH4169 alloys are utilized to evaluate and validate the proposed model as well as four other classical models (FS model, MSWT model, Yu model and CXH model). The result indicates that the proposed model yields a higher accuracy on multiaxial fatigue life than other four models, and the majority of prediction results are within the ±2 life factor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Erosion wear is analyzed based on different hydraulic and mission conditions. [•] Degradation trend of system performance is modeled under different erosive stages. [•] Hydraulic oil with particles erodes sharp edges of valve bushing and spool. [•] Worn sharp edges of spool valve degrade pressure gain, null leakage flow and lap. [•] With failure definition for the EHSV, we predict service life by mission profile. [Copyright &y& Elsevier]

Abstract: The creep rupture life of 9–12% chromium ferritic steel is predicted as a function of alloy composition, creep stress, and creep temperature. A database is made up from data in previous publications. A novel abductive network is constructed to predict creep rupture life. With a four-layer architecture, the network shows a precise prediction of creep rupture life of 9–12% chromium ferritic steel. Performance is examined and compared with backpropagation algorithm (BP) neural network. Results indicate that the proposed approach is more accurate than Larson–Miller parametric method and more efficient than that of BP neural network. Automatic relevance determination reveals that the influence of Cr and W on creep rupture life of 9–12% chromium ferritic steel are the greatest amongst the alloying elements. [Copyright &y& Elsevier]

Abstract: Thermal performance of a chip-scale packaged power device can be improved by attaching a heat spreader to the backside of the heat generating silicon die via solder thermal interface materials [STIMs]/solder die-attach. Driven by government legislation, electronics industry has advanced to lead (Pb)-free solders due to environmental and health concerns emanating from the use of Pb-based solders. Though solder compositions in the form of Sn–Ag–Cu (SAC) ternary system have been widely accepted and preferred by the electronic industry as replacements for the traditional Pb-based solder alloys, debate continues over the optimal silver content in the Sn–Ag–Cu (SAC) solder alloys. Apparently, the effect of silver (Ag) content on thermo-mechanical reliability of SAC alloy compositions as small area solder joints (flip chip solder bump or ball grid array (BGA)) has been extensively studied but not enough information exist on the effect of Ag percentage in SAC solder alloys when employed as large area solder joint (die-attach application). In this study, non-linear finite element method (FEM) is used for a comparative analysis of the effect of Ag content on the thermal fatigue performance of Sn–3Ag–0.5Cu (SAC305) and Sn–4Ag–0.5Cu (SAC405) when used in die-attach applications under three different thermal cyclic loading cases. The results show that Von-Mises stresses and strain energy in each of the two different SAC solder joints were strong function of the thermal cycle profiles, increasing in the order −55–80°C<−55–125°C<−65–150°C. In addition, this study suggests that the range of stress was relatively greater for the SAC alloy with higher Ag content (SAC405) while the lower Ag content SAC solder (SAC305) experiences a comparatively larger accumulated plastic work under the same thermal cycling condition. Further failure analysis via visual inspection reveals that for all cases of thermal cyclic loading employed in this study, maximum values of strain energy were all located in the corner regions (critical regions) of the solder joints at the side next to the silicon die independent of the Ag content of the solder joints. This paper also highlights the concerns as regards the implementation of conventional thermal fatigue models for accurate life time prediction of large area solder joint. [Copyright &y& Elsevier]

Abstract: Fretting wear and subsequent fatigue are the damage processes caused by micro slip under high cycle fatigue (HCF) loading between contacting structural members. Fretting fatigue has become recognized as a major failure mode in aircraft, which can reduce the life of a structure by as much as 40–60% under certain conditions. There are two keys to evaluating the fretting fatigue life of dovetail assemblies: one is determining the high stress gradients at the edge of the contact zone under complex loading by means of numerical methods, especially the finite element method (FEM); the other is finding suitable parameters to correlate with fretting fatigue life to improve predictive accuracy. [Copyright &y& Elsevier]

Abstract: The cause of a passenger car’s damper spring tower early failure is investigated in this paper. Inspection of the road surface, tire inflation pressure, suspension, and service load are firstly done in order to determine the further test procedures and analysis methods. The static stress of the spring tower caused by the body weight is calculated by finite element model. Public road tests with an equipped car are carried out to simulate the real usage by the customers. With the measured strain signals of different test conditions and local strain–life method, fatigue life prediction is made. The calculated fatigue life coincides with the actual failure mileage, and it turns out that the broken spring damper causes the early failure of the spring tower. It is suggested that more emphasis should be taken on the durability design and test of the spring damper. [Copyright &y& Elsevier]

Abstract: A comparison between laboratory test data on fatigue crack nucleation in a rear tow hook pin assembly of passenger vehicle and a computational methodology using commercial package software is presented. Fatigue damage is determined using local material response, measured during experimental tests. Experiments were performed simulating the actual conditions in the customer environment. Stress and strain were experimentally measured by using strain gages, bonded on the hook assembly. These experimental lives are compared with those obtained through numerical analysis using a commercial fatigue software. Fatigue analysis methods (S–N curves, rainflow counting and Miner rule) were used to determine the fatigue damage imposed on the component. Interpretation and evaluation of the measured strain and stresses, simulation tests and fatigue life assessments, on the basis of S–N curve, are described in this paper. [Copyright &y& Elsevier]

Abstract: The computational and experimental determination of the fatigue and fracture behaviour of high strength steel S1100Q is presented. Fatigue tests (low-cycle fatigue parameters , b and c) are carried out in a low cycle regime according to ASTM E 606 standard, where standardised uniform-gage test specimens are used. The fracture mechanics parameters (the coefficient of Paris equation C and m) are determined according to ASTM E 647 standard, where three-point bending specimens are use. Based on low-cycle fatigue parameters the computational analysis is performed to determine the number of stress cycles required for fatigue crack initiation. The remain service life up to the final failure can than be determined using the known parameters C and m and calculated stress intensity factor for treated machine part or structure. The computational model has been used to determine the service life of counterweight bar, which is also experimentally tested. Comparison of computational and experimental results shows a reasonable agreement. [Copyright &y& Elsevier]

Abstract: Fatigue failure investigation on anti-vibration springs, involving both metal and rubber materials, is presented. Rubber-to-metal bonded springs are widely used in industry as anti-vibration components giving many years of service. Recently a need to improve time and cost efficiencies has caused an unexpected early fatigue failure of the component with no immediate explanation. The required total fatigue life was 1.25million cycles but only 0.7million cycles achieved. There was an urgent need to investigate the causes of the fatigue failure and to modify the component design accordingly to meet the customer requirement and the supply schedule. The investigation, based on the actual fatigue loads, is carried out on these failed and modified products using a method of continuum mechanics. To simplify the simulation, a non-linear quasi-static analysis is carried out and then the residual stresses are superimposed to obtain the effective stress range to predict the metal crack initiation. For the rubber parts a three-dimensional effective stress criterion is employed to predict the fatigue crack initiation. The fatigue failure is taken as visual crack observation (normally 1–2mm). The fatigue crack initiation for the metal parts of the failed component is predicted at 225K cycles under specified fatigue load against total metal broken at 700K cycles from the test. For the modified part the minimum total fatigue life for the metal parts of the component, estimated conservatively, is 2.1million cycles against 1.75million cycles from the test without any crack observed. The rubber fatigue crack initiation is predicted at 90K cycles against crack onset around 79K cycles and crack length 40mm at 145K cycles from the test. From design point of view it is important to optimize the rubber profile under this very tight allowable space to provide the maximum support of the metal interleaves and at the same time to meet the minimum requirements of the manufacture process. It is shown that this approach can be employed at a design stage for both metal and rubber fatigue evaluations on anti-vibration springs. [Copyright &y& Elsevier]

Abstract: A common requirement of airframe fatigue analysis is to know the relative fatigue severity of two variable amplitude load spectra when they are applied to the same components or structures. For example, when the predicted service spectrum used in a full-scale airframe fatigue test is later found to be unrepresentative of the average fleet usage, it is necessary to determine the extent to which the service spectrum is more or less severe than the test spectrum. In such cases, methods are required to allow the spectra to be compared so that the results of the test may be used to represent in-service usage. Whilst conventional fatigue prediction tools/models are available for this task, these methods usually contain uncertainties which are difficult to assess without resorting to extensive coupon test programs. In this paper, a very small coupon test program is used to asses the relative severity of two spectra for crack growth from small natural cracks to failure. The two spectra were applied sequentially to fatigue coupons and the crack growth data was assessed using quantitative fractography. This allowed direct comparison of the crack growth rate from the two spectra at different times in the crack growth life. [Copyright &y& Elsevier]

Abstract: Spectrum crack growth testing of 7050-T7451 plate was performed for T-L and L-S specimen orientations to determine the influence of spectrum truncation on fatigue crack growth rates and overall life. This testing was performed on center-hole (double crack), flat, rectangular tensile specimens machined from material blanks cut from 10.16cm plate. Additional comparison T-L tests were also accomplished using blanks from available 7050-T7451 1.27cm plate. Behavior of through-thickness long (>5mm) cracks is examined. Spectrum loading used for the testing was based on a nominal fighter load spectra and truncation levels of testing were comprised of baseline (5%), plus 20% and 30% ranges. The target, ordered tensile-compressive, stress levels were based on a combination of legacy and predicted use of US fighter aircraft. Results produced representative trends in life-to-failure increases for truncation levels relative to 5% truncated levels for the L-S and T-L orientation specimens. Crack growth rate data was recorded and comparisons are exhibited for varied orientation and crack length. Findings show that although relatively small changes in life are experienced due to orientation, L-S oriented plate material life is affected by the greatest extension of up to 17%. Crack growth rates for shorter cracks in the L-S material exceed growth rates in the T-L oriented material by more than two times the rate. Characteristics of splitting, crack wandering, branching, and shielding were observed in the L-S specimen tests. These potentially undesirable characteristics resulted in temporary crack arrest or retardation in the direction perpendicular to loading and resulted in overall specimen rupture well beyond the life predicted critical crack lengths. [Copyright &y& Elsevier]

Abstract: This paper summarises recent developments in the formulation and application of the generalised Frost–Dugdale crack growth law. We first reveal the relationship between the generalised Frost–Dugdale crack growth law, dislocation based crack growth laws, the two parameter crack growth model, and fractal fatigue concepts. We then show that a range of aircraft materials characterisation test data are consistent with this law and how it can be used to predict crack growth in a range of full-scale aircraft fatigue tests, and coupon tests including crack growth in aircraft fuselage lap joints. [Copyright &y& Elsevier]

Abstract: This paper gives a case study about the failure of steam pipe fitting equipment in a chemical factory. The observation and analysis are done by way of SEM, EDS, tensile tests, and fracture mechanics. The reasons for failure, the fracture mechanisms, and the failure modes are revealed and discussed. A prediction of the fatigue life of a bolt of the fitting flange is made. [Copyright &y& Elsevier]

The objective of the present work is to carry out a performance analysis of roller bearings used in railway ore transportation wagons. Data from 47,000 failed bearings divided in seven groups, were used to determine the failure distribution. Six groups corresponded to operation in the years 1985–1988, 1990, 1991 and one group included all the others. The failure distribution in bearings was described by the three parameter Weibull distribution. To conduct the statistical analysis it was necessary to estimate these parameters by the nonlinear regression method, because it does not require the whole group of failed bearings, and direct inference on the sample. A Monte Carlo technique was used to validate the procedure. Analytically two estimate methodologies were considered. Methodology I is a well established technique while Methodology II is an alternative approach proposed by the authors, which was inspired by a procedure used to design rail shafts. Studying the bearing failure behavior led to the following observations: based on sample inference techniques, an excessive variation was observed in the parameters that characterize the failure distribution. A dispersion of the order of 40 or 25% was found in the minimum and nominal lives when evaluated by the direct inference method or by the nonlinear regression method, respectively, and a dispersion of 17% calculated by nonlinear regression was observed for the shape parameter, βˆ. In spite of this dispersion, it was found that the minimum lives estimated by direct inference were conservative by a factor of four, when compared to analytical methods, while estimates of the nominal life were shown to be similar to its smallest value observed in the sample groups. [Copyright &y& Elsevier]

In the present study, the effect of welding process and procedure on fatigue crack initiation from notches and fatigue crack propagation in AISI 304L stainless steel welds was experimentally investigated. Full penetration, double-vee butt welds have been fabricated and CCT type specimens were used. Lawrence''s local-stress approach (a two-stage model) is used to predict the fatigue life. The notch-root stress method was applied to calculate the fatigue crack initiation life, while the fatigue crack propagation life was estimated using fracture mechanics concepts. The fatigue notch factor is calculated using Lawrence''s approach. Constant amplitude fatigue tests with stress ratio, R=0 were carried out using 100 kN servo-hydraulic DARTEC universal testing machine with a frequency of 30 Hz. The predicted lives were compared with the experimental values. A good agreement has been reached. It is found that the weld procedure has a stronger effect on lives to initiation than on propagation lives. [Copyright &y& Elsevier]

• A unified S-N curve for bolts under axial loading was proposed based on experiments and simulation. • A total of 133 fatigue tests were conducted under 46 different fatigue conditions. • Simulation was conducted to calculate the critical multiaxial stress components. • Unified S-N curve predicted high-cycle fatigue life with a mean absolute error of 15 %. Bolts tend to show different fatigue behavior with respect to the size or shape of a bolt and the level of preload though it is the same material. This makes it difficult to predict the fatigue life of bolts. In this study, a novel method to construct a unified stress-life (S-N) curve was proposed for the three different bolts with different sizes and lengths subjected to various external axial loading conditions and preloads, ranging from 44 % to 88% of the ultimate tensile stress. A total of 133 experiments for 46 different fatigue conditions were conducted and finite element analysis was also performed to calculate multiaxial stress components at the root of the thread. The fatigue characteristics of the bolts were investigated depending on various loading conditions, and the life prediction performance with fitted S-N curves was compared with respect to four mean stress correction models. The unified S-N curve showed high accuracy in life prediction; 15 % mean absolute error without exceeding ± 50 % for finite life loading conditions. [ABSTRACT FROM AUTHOR]

• A predictive fatigue damage modeling technique is developed to estimate the fatigue life of composite craft under slamming loads. • This model can predict the fatigue damage sequences under arbitrary loading conditions. • This model can be used in the design stage of composite crafts. • By minimizing the number of required experiments, this model can be very cost-effective. A reliable predictive method is developed based on the progressive fatigue damage modeling technique to estimate the fatigue life of high-speed composite craft. In this method, at each loading cycle, the occurrence of different failure types would be inspected and based on the failure type, either gradual or sudden degradation rules would be followed to update the material properties. This procedure continues until the final failure of the structure. To implement this method, a MATLAB code is developed based on material degradation rules which integrating with the Abaqus it can be used for complex geometries. This method enables us to predict the fatigue life of composite structures with different layup configurations under arbitrary loading conditions only by knowing the static and fatigue behavior of unidirectional laminates. To even more reduce the number of required tests, the energy-based unified fatigue life model is employed. Owing to the low number of required tests, this method can be very cost-effective in the design stage of composite structures that are intended to endure cyclic loads. [ABSTRACT FROM AUTHOR]

• The types of bolt competitive failure were characterized as loosening, critical state, and fatigue. • The transverse load always accelerated bolt failure, while the effects of the axial load varied according to the magnitude. • The load-life prediction curves of the bolt under combined loading were obtained. • The competitive failure life prediction model of the bolt was obtained. Bolt joints are often subjected to combined loading conditions, and there exists a competitive failure relationship between bolt loosening and fatigue under combined loading. To study the competitive failure characteristics of bolt loosening and fatigue and predict the competitive failure life, a competitive bolt failure test was conducted. According to the test data, the clamping force recession, load-life prediction, and critical-value prediction curves of the axial load to restrain bolt failure under combined loading were obtained. The bolt failures were categorized as loosening, critical state of loosening and fatigue, and fatigue, and the failure types were determined by the load ratio. The transverse load always accelerated the bolt failure, while the effects of axial load varied according to the magnitude. Additionally, a reasonable form of load combination in the bolt connection design and a competitive failure-life prediction model were proposed, thus providing a reference for the failure-life prediction of bolts under combined loading. [ABSTRACT FROM AUTHOR]