High Cycle Fatigue Research Articles

Effects of electrochemical machining on high-cycle fatigue of Inconel 718 blades

Blades made from Inconel718 (IN718) are generally machined using electrochemical machining (ECM), and the high-cycle fatigue (HCF) of such blades significantly impacts the service life of aeroengines. In this study, modal analysis was performed to obtain the blade modal shape and stress distribution at first-order frequency, after which blades were machined at different current densities (9.5A/cm2, 18.2A/cm2, 34A/cm2, 46.7A/cm2, 61.2A/cm2, 70.1A/cm2) and then subjected to detailed surface-integrity analysis and fatigue tests. No surface defects (e.g., intergranular corrosion, recast layers) were observed, the microhardness was unchanged, and new residual stress was not found to be introduced to the machined surfaces. The machined surfaces were uneven and contained micro-pits, and high current density contributed to better surface quality. At a constant load of 520 MPa, the blade machined at 70.1A/cm2 had the best fatigue life of 1.4×106. The blades fractured because of micro-pits, and as the surface quality of the blades improved, so did their fatigue performance. Therefore, the fatigue failure mechanism characterized in this work provides a reference for the HCF behavior of blades machined by ECM.

Elucidating the effect of cyclic plasticity on strengthening mechanisms and fatigue property of 5xxx Al alloys

The strength of non-heat-treatable 5xxx Al alloys is derived from solid solution strengthening and strain hardening, the absence of a precipitation strengthening response results in their lower strength. In this study, significant improvements in strength can be achieved by subjecting three different Mg concentrations 5xxx Al alloys to cyclic plasticity. A quantitative analysis of the respective contributions to the yield strength has been conducted by combining transmission electron microscopy and atom probe tomography. Additionally, the fatigue performance and fatigue mechanism of the cyclic strengthened 5xxx Al alloys have been thoroughly studied due to its transformation from non-heat-treatable to precipitation strengthening. We demonstrate that the high-cycle fatigue (HCF) strength of the cyclically strengthened state only experiences a minor improvement compared to the as-received state, which is significantly disproportionate to the enhancement in tensile strength. This disparity is primarily attributed to the changes in microstructure and fatigue mechanisms, resulting in a reduction in fatigue ratio. This study provides important insights for expanding research on cyclic plasticity methods in fatigue performance, and can aid in the development of improved processes for optimal fatigue resistance.

Nondeterministic High-Cycle Fatigue Macromodel Updating and Failure Probability Analysis of Welded Joints of Long-Span Structures

Nondeterministic High-Cycle Fatigue Macromodel Updating and Failure Probability Analysis of Welded Joints of Long-Span Structures

A physics-informed deep learning approach for combined cycle fatigue life prediction

The prediction of the combined high and low cycle fatigue (CCF) life of welded components was valuable for the reliability of practical engineering structures. In this study, a physics-informed Grey-deep convolutional neural networks (DCNN) model was constructed and the model parameters was determined based on the fatigue behavior characteristics of CCF, which was proved perform well in the CCF life prediction of welded components. The predicted results indicated that the proposed model can realize reliable CCF life prediction with good accuracy (MAE = 0.49) and stability (RMSE = 0.44). Further, the proposed model also exhibited good prediction performance under different loading and geometry conditions, indicating the good universality of the proposed model. And the good universality represented that the proposed model had the potential to be applied in more engineering fields.

Mechanical and Fatigue Properties of Welded Fe-Mn-Si Shape Memory Alloys.

This paper presents the experimental results of a study evaluating the mechanical and fatigue performance of welded Fe-Mn-Si SMA. For the experimental study, welded and welded-and-heat-treated Fe-Mn-Si SMA specimens were fabricated, and fatigue tests were performed at various stress amplitudes. In addition, direct tensile tests and recovery stress tests were also performed to evaluate the material properties of Fe-Mn-Si SMAs. The elastic modulus, yield strength, and tensile strength of the welded specimens were reduced by 35.4%, 12.1%, and 8.6%, respectively, compared to the values of the non-welded specimens. On the other hand, the elastic modulus, yield strength, and tensile strength of the welded-and-heat-treated Fe-Mn-Si SMA specimens were increased by 18.6%, 4.9%, and 1.3%, respectively, compared to the values of the welded specimens. Both welded and welded-and-heat-treated Fe-Mn-Si SMAs failed at lower cycles than the conventional Fe-Mn-Si SMAs at the same stress amplitude. High-cycle fatigue failure, characterized by cycles exceeding 104, typically occurs at relatively low stress levels within the elastic region, whereas low-cycle fatigue failure, generally occurring within cycles below 104, involves high stress levels that encompass both elastic and plastic deformation. Regardless of the welding condition, the stress amplitude at which Fe-Mn-Si SMA transitions from high-cycle to low-cycle failure exceeded the yield strength.

Efficient Forced Response Minimization Using a Full-Viscosity Discrete Adjoint Harmonic Balance Method

A forced response induced by inlet distortion and blade row interactions can lead to high-cycle fatigue failure, especially when the unsteady excitation frequency is close to the natural vibration frequency of a blade. This paper presents the study of forced response sensitivity analysis and minimization using a full-viscosity unsteady discrete adjoint method. The goal is to improve the aeroelastic performances of turbomachinery blades and simultaneously constrain/improve aerodynamic performances. The decoupled modal reduction method is used to compute the forced response, which is considered the objective function in adjoint-based design optimization. To analyze aeroforcing and aerodamping flow and adjoint fields efficiently, the harmonic balance method and its adjoint counterpart developed by an automatic differentiation tool are applied. Two cases—the NASA Rotor 67 with inlet distortion and a three-row configuration with multiple fundamental frequencies in the second row—are used to demonstrate the effectiveness of the aerodynamic and aeroelastic coupled design optimization system developed in this work. For the latter case, the Fourier-transform-based method that first decomposes and then matches the time and space modes at two sides of an interface is used for interface coupling. The almost-periodic Fourier transform method is used to determine the time instances for cases with multiple fundamental frequencies.

Effect of coating-substrate microstructure on nucleation and growth of surface microcracks in a PtAl-coated Ni-based SX superalloy with sheet specimens during HCF at 900 °C

The fatigue crack initiation process accounts for the main portion of the high-cycle fatigue (HCF) life. Although coated superalloys are well-known to be prone to surface microcracks, the influence of the coating-substrate microstructure on the damage mechanism during HCF of the coated single crystal (SX) superalloys remains unclear. In the current study, HCF failure and interrupted tests were conducted at 900 °C under a low applied maximum stress on a PtAl-coated third-generation SX superalloy using sheet specimens. The HCF crack initiation was investigated by analyzing the evolution of surface microcracks and coating-substrate microstructure. The results show that the surface microcracks nucleation and growth are controlled by the initial microstructure of the coating-substrate region and the oxidation process during the HCF crack initiation stage. The rapid nucleation and growth of the surface microcracks are promoted by grain boundaries (GBs) in the coating and the interdiffusion zone (IDZ). Comparatively, the surface microcracks are blunted by oxidation in the SX substrate due to the loss of GBs, leading to a slower microcrack growth. However, the surface microcracks can gradually grow further into the substrate by repeating the processes as follows: oxidation at the crack tip, formation of γ′-depleted region due to oxidation, recrystallization at the γ′-depleted region and cracking along the GBs in the recrystallized γ′-depleted region. Subsequently, the surface microcracks, which reach the critical size, propagate along the slip bands during the progressive propagation stage. This study will contribute to improve the HCF durability of the PtAl-coated SX superalloy.

High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Alloy with Inherent Internal Defects: A Critical Literature Review

The inadequate fatigue performance of Laser Powder Bed Fusion (L-PBF) Ti-6Al-4V alloy, primarily due to intrinsic defects, poses a significant challenge for industrial applications. Internal defects often serve as initiation sites for fatigue cracks, significantly impacting the fatigue life of L-PBF Ti-6Al-4V components. Accurate evaluation of the role of internal defects in fatigue performance and quantitative analysis of influential parameters are crucial for guiding optimal L-PBF manufacturing design. This study aims to critically review recent notable contributions focusing on high-cycle fatigue (HCF) in these alloys, with many of the presented insights being easily transferred to other types of AM alloys. Efforts have been made to identify correlations between fatigue life at various stages and critical internal defects. Key aspects, including microstructure and post-processing treatments, and their effects on HCF have been thoroughly analyzed. The findings enhance the scientific understanding of fatigue performance of L-PBF Ti-6Al-4V alloy and open new avenues for future research.

Reliability of SiC MOSFETs in the High Cycle Fatigue Regime under Fast Power Pulses

Device reliability is an important factor in application, especially in the field of electric mobility. In this paper high cycle fatigue power cycling results of SiC devices in baseplate free modules are presented. To minimize testing time, the devices were stressed with load pulses corresponding to a 50 Hz load. The reliability results are the first fatigue results for temperature swings below 30 K for SiC devices. The lifetime in the high cycle fatigue area is limited by solder fatigue for high virtual junction temperatures of 150 °C. In theory, the reliability should increase exponential since the elastic-plastic transition area is reached. The experiment revealed that the lifetime can still be described by the Coffin-Manson approach also in the high cycle fatigue area. It can be observed that the high junction temperatures weaken the stability of the solder layer, so no major lifetime increase can develop. The measured temperature data are additionally corrected by a three-dimensional (3D) simulation to ensure a validity of the results.

On the notch sensitivity of as‐built Laser Beam Powder Bed–Fused AlSi10Mg specimens subjected to Very High Cycle Fatigue tests at ultrasonic frequency up to 109 cycles

AbstractThe notch effect significantly influences the fatigue response of components and is particularly relevant for parts produced with additive manufacturing (AM) processes, characterized by complex geometries and possible geometric discontinuities inducing local and critical peak stresses. Moreover, the low surface quality, as well as manufacturing defects and residual stresses, interacts with the local peak stress induced by geometric discontinuities, complicating the assessment of the notch effect for AM parts and requiring extensive experimental fatigue investigations. In the present paper, the notch sensitivity of as‐built AlSi10Mg specimens produced with the laser beam powder bed fusion in the Very High Cycle Fatigue regime is investigated. Ultrasonic fatigue tests up to 109 cycles have been carried out on rectangular bars and rectangular bars with a central through‐thickness hole. The notch effect has been found to significantly affect the fatigue response of the investigated AlSi10Mg specimens, with surface defects having a main role and pointing out the influence of the surface quality on the crack formation.

Effect of welding residual stresses on the fatigue life assessment of welded connections

Welding residual stresses impose significant influences on the fatigue behavior and structural integrity of welded connections in various engineering applications. Understanding the effects of these residual stresses on fatigue life is crucial for ensuring the reliability and safety of welded structures. This paper proposes a damage-incorporated thermal–mechanical simulation method to examine the effect of welding residual stresses on the fatigue life prediction of welded plates and circular hollow section (CHS) X-joints. Compared to the experimental X-ray diffraction measurements and the fatigue tests, the predicted residual stresses and fatigue life demonstrate good agreement with experimental results for both high-cycle and low-cycle fatigue. The location of fatigue cracks resembles closely the estimation from a uniform fatigue damage indicator. The fatigue life prediction without incorporating the welding residual stresses does not affect significantly the life estimation for low-cycle fatigue but can cause substantial over-predictions for high-cycle fatigue.

Influence of Non-Metallic Inclusions on Very High-Cycle Fatigue Performance of High-Strength Steels and Interpretation via Crystal Plasticity Finite Element Method

The fatigue behaviors of high-strength bearing steel were investigated with rotating bending fatigue loading with a frequency of 52.5 Hz. It was revealed that the high-strength steel tended to initiate at interior non-metallic inclusions in a very high-cycle fatigue regime. During fractography observation, it was also seen that the inclusion acting as a failure-originating site was seldom smaller than 10 μm. Moreover, prior austenite grains could also act as the originating source of failure when inclusion was absent. The crystal plasticity finite element method (CPFEM) was adopted to simulate the residual stress distribution around non-metallic inclusions of different sizes under different loading amplitudes. The accumulated plastic strain around the inclusion suggested that the existence of inclusion may reduce material strength and lead to more fatigue damage. The value of accumulated plastic strain around different inclusion sizes also resembled the crack nucleation or propagation of the materials. The simulation results also indicated that inclusions smaller than 5 μm had little influence on fatigue lifetimes, while inclusions larger than 10 μm had a significant influence on fatigue lifetimes.

Mechanisms of fatigue degradation process in axially loaded grouted connections under submerged conditions

Grouted connections in offshore support structures bond overlapping steel tubes using ultra-high strength grout. These connections, used in jacket structures, face dynamic pulsating loads and submerged conditions. Current design guidelines offer simplified S-N curves that do not reflect realistic conditions for offshore wind turbines. This study introduces a new S-N curve for axially loaded grouted connections under submerged conditions, based on large-scale high-cycle fatigue experiments. It also analyses the degradation behaviour of cyclic axially loaded grouted connections to identify critical phase changes: stable, incremental, and progressive. The study examines the impact of different load levels on degradation, focusing on displacement between the pile and sleeve. Lower load levels result in longer stable and progressive phases. As load levels increase, the stable phase shortens and eventually disappears at the highest load levels. Damage within the grout material is categorised into crack-driven and crushing-driven patterns, with the latter linked to longer lifetimes. Even at the lowest load levels, minor damage occurs, precluding an endurance limit. This understanding of degradation mechanisms supports the assessment of grouted connections using monitoring systems.

Stress, Strain, or Energy? which one is superior predictor of fatigue life in notched Components? a novel Machine Learning-Based framework

This paper introduces an efficient framework for accurately predicting the fatigue lifetime of notched components under uniaxial loading within the high-cycle fatigue regime. For this purpose, various machine learning algorithms are applied to a wide range of materials, loading conditions, notch geometries, and fatigue lives. Traditional approaches for this task have mostly relied on one of the mechanical response parameters, such as stress, strain, or energy. This study also concludes which of these parameters serves as a better measure. The key idea of the framework is to use the profile (field distribution represented by some points) of the mechanical response parameters (stress, strain, and energy release rate) to distinguish between different notch geometries. To demonstrate the accuracy and broad applicability of the framework, it is initially validated using metal materials, subsequently applied to specimens produced through additive manufacturing techniques, and ultimately tested on carbon fiber laminated composites. This research demonstrates the effective use of all three parameters in estimating fatigue lifetime, while stress-based predictions exhibit the highest accuracy. Among the machine learning algorithms investigated, Gradient Boosting and Random Forest yield the most successful results. A noteworthy finding is the significant improvement in prediction accuracy achieved by incorporating new data generated based on the Basquin equation.

A study of fatigue property enhancement of 1045 steel processed by surface mechanical rolling treatment with an emphasis on residual stress influence

Several factors contribute to the observed bulk mechanical properties enhanced by surface mechanical rolling treatment (SMRT), and it is important to distinguish the influences of each major factor. A commonly used engineering carbon steel, 1045 steel, was chosen for the current study because the material does not have stress-induced phase transformation. A fully reversed strain-controlled gradual decreasing amplitude loading spectrum (ENV) was employed to release the residual stresses induced by SMRT. Fatigue experiments were conducted on the 1045 steel specimens with and without ENV to assess the influences of grain refinement and the residual stress on fatigue. It was found that SMRT refined and recombined the microstructures in the surface layer through deformation and fragmentation of brittle cementite, and extrusion of ductile ferrite between adjacent cementite layers. In the high cycle fatigue regime, both the SMRT induced residual stresses and the refined/recombined microstructures contributed to the enhancement of fatigue strength and fatigue ductility but the gradient microstructure contributed significantly more than do the residual stresses. Unlike stainless steels processed by SMRT, the carbon steel does not display a kink point in the strain-life fatigue curve, and all the crack initiations were found to occur on the specimen surface.

NIMS fatigue data sheet on low- and high-cycle fatigue properties of boron steel

NIMS fatigue data sheet on low- and high-cycle fatigue properties of boron steel

Phase field modeling of underloads induced fatigue crack acceleration

This study proposes a novel methodology to model the fatigue crack growth acceleration under underloads using a phase field fracture framework. In this model, fatigue crack growth is characterized by the degradation of fracture toughness, with an emphasis on employing a representative loading strategy instead of explicit cyclic loading, thus accelerating simulations of high-cycle fatigue. The model integrates a zone-based crack acceleration approach that responds to single-cycle underload. Notably, the model adeptly captures the dynamics described by the Paris-Erdogan law. Post-underload crack growth acceleration is simulated by identifying an acceleration zone near the crack tip, inspired by existing models based on the plastic zone. This zone is defined by a strain energy density threshold, and the underload ratio governs the rate of fatigue damage accumulation attenuation within this area. The implementation leverages the UMAT user subroutine in Abaqus, utilizing coupled temperature-displacement elements where temperature analogously represents the phase field parameter. Experimental validation of the model confirms its ability to accurately reflect the loss of fatigue life and the acceleration of crack growth rates in compact tension and middle tension specimens. Additionally, the model shows promise for extension to periodic underloads, highlighting its potential for simulating real-world fatigue scenarios effectively.

Very high cycle fatigue characteristics of laser beam powder bed fused AlSi10Mg: A systematic evaluation of part geometry

This study explores the influence of geometry and part size on defect distribution, melt pool size, and mechanical characteristics in laser beam powder bed fused (LB-PBF) AlSi10Mg. Five distinct geometries—hourglass, small rod, small block, large block, and large rod—were fabricated under identical process parameters. Fully reversed ultrasonic fatigue testing, operating at a frequency of 20 kHz, was conducted to assess the very high cycle fatigue properties. The findings indicated that part geometry had a major impact on the fatigue properties of the material in the very high cycle fatigue regime. Specimens machined from large rods and large blocks had the lowest porosity and highest fatigue resistance. Microstructural analysis indicated that hourglass, small rod, and small block specimens had shallower melt pools and overlap depths compared to other geometries. This observation suggests a higher cooling rate in specimens with smaller cross-sectional areas, leading to the increased presence of entrapped gas pores and a lack of fusion defects. Understanding the relationship between part geometry and fatigue properties in LB-PBF components offers insights for optimizing design and manufacturing processes in additive manufacturing applications.

Effects of yttrium on microstructure and low cycle fatigue properties of superalloy IN713C at high temperature

In order to improve the high temperature and low cycle fatigue performance of the IN713C alloy, trace amounts of yttrium (Y) element were added to such an alloy. The effect of Y on the microstructure and fatigue performance under push-pull loading condition of the IN713C alloy at 650 °C was investigated, and the fracture mechanisms of the IN713C alloy with different Y additions at strain amplitudes of 0.3%, 0.4% and 0.5% were also investigated. The results showed that addition of Y significantly increased the fatigue life of the IN713C alloy under different strain amplitude values. Compared with the traditional IN713C, the fatigue life of the alloy with 300 ppm Y was increased by 44.4%, 213.3%, and 61.4%, and that of the alloy with 500 ppm Y was increased by 184.6%, 66.1%, and 172.1%, respectively, at the strain amplitudes of 0.3%, 0.4%, and 0.5%. Shrinkage pores were found to be the main crack source at low strain amplitude (0.3%), while carbides and other interdendritic precipitates were the source of cracks at high strain amplitude (0.4% and 0.5%). The addition of Y increased the fatigue life of the IN713C alloy by reducing shrinkage and refining carbides and grain size.

Shear and interface shear fatigue of semi‐precast slabs with lattice girders under cyclic loading

AbstractMore and more often, semi‐precast reinforced concrete slabs with lattice girders are employed for industrial buildings or bridges, where they are exposed to high cycle fatigue loading. Despite research in recent years that has led to the formulation of an S–N curve for lattice girders, the effects of cyclic loading on semi‐precast slabs have not yet been sufficiently clarified. Moreover, research has so far been limited to single‐span slabs. The effects of continuous slab systems, which are mainly realized in buildings and bridges, cannot be considered in the calculation of fatigue resistance yet. To improve the fatigue design concept for shear and interface shear, theoretical and experimental investigations were conducted at the Institute of Structural Concrete, RWTH Aachen University. In addition to the fatigue behavior of 16 tests under cyclic loading, particular attention is paid to the increase in shear and interface shear resistance at the inner support of continuous slabs. Furthermore, the influences of the support detailing were investigated. The findings illustrate further potential for optimization of the design under cyclic loading.