Fretting Fatigue Crack Initiation Research Articles

Modelling of microscopic crack initiation behaviour of fretting fatigue based on X-ray micro-computed tomography scan

Fretting fatigue is a particularly destructive form of fatigue failure that has drawn significant attention from researchers. This paper proposes a numerical modelling method based on tomography scan to investigate the impact of inclusions on fretting fatigue crack initiation behaviour. The results reveal that inclusions can affect the crack initiation direction and reduce the initiation lifetime. The difference between the properties of inclusions and matrix leads to local mechanical response mismatch, resulting in local stress, strain, and damage concentration. The mismatch in strain and damage follows a gradient distribution along the thickness as the distribution in these mechanical responses. These could explain why particles closer to the surface are more likely to cause damage. Additionally, the aggregation distribution of inclusions results in merging and connecting local regions with high stress, strain, and damage concentration, ultimately promoting fracture behaviour. Finally, the numerical models are validated with experimental data from fretting fatigue tests. Compared to the homogeneous model, the numerical model that considers inclusions from topography data can more accurately analyse the material damage and provide a more comprehensive understanding of fretting fatigue behaviour.

A comparative study of several life prediction models based on the critical plane approach for fretting fatigue crack initiation

AbstractTo reasonably forecast the crack initiation characteristics of fretting fatigue, this study evaluates the accuracy of several damage models. The existing experimental and simulation investigations are compared, noting the similarities and differences in the crack initiation location, crack orientation angle, and crack initiation life predicted by various damage models. It is crucial to employ a reasonable and reasonable damage prediction model of fretting crack initiation life, as fretting fatigue, a phenomenon of mechanically fastened connecting parts, can considerably reduce the fretting fatigue life of the components. This paper compares the fatigue damage prediction models of fretting fatigue specimens under partial slip conditions, and it will help researchers understand the benefits and drawbacks of various damage models and give them the knowledge and foundation to select the more reasonable fretting fatigue damage model.

Experimental and numerical study on the multi‐site fretting fatigue crack initiation of press‐fitted axles

AbstractIn this study, fretting fatigue tests were conducted to gather information on both fretting fatigue and fretting wear. Subsequently, an evaluation methodology that combined the Modified Wöhler Curve Method (MWCM) with the theory of critical distance (TCD) was established to investigate multi‐site fretting crack initiation. The results showed that the fretting fatigue damage could be reasonably evaluated using the MWCM equivalent stress σMWCM. σMWCM is greatly influenced by both bulk stress and fretting wear‐induced stress concentration. The stress field close to the wear boundary increased due to the continuous fretting wear, leading to an increase in σMWCM; meanwhile, the bulk stress near the wear boundary decreased as the crack propagated, resulting in a decrease in σMWCM. The combined effect of the fretting crack propagation and wear caused σMWCM, which was located within an annular strip of the axle, to exceed the critical value, causing the multi‐site fretting crack initiation.

An arc-tenon attachment for nickel-based single crystal turbine blade with improved high-temperature fretting fatigue performance

Nickel-based single crystal (NBSC) turbine blade tenon is prone to fretting fatigue failure. In this study, an arc-tenon attachment was proposed and its fretting fatigue life increased by up to 408.18 % at 600 ℃ compared with the plane-tenon structure under the applied peak stress of 65 MPa. The arc-tenon attachment could effectively reduce the maximum von-Mises stresses and resolved shear stresses near the contact region, regulating the stress distribution and reducing the stress gradient, which was beneficial to alleviating the activation of octahedral slip systems and delaying crack initiation, thereby improving the fretting fatigue life at high temperature. Meanwhile, high temperature promoted the formation of oxide layer on the contact surface, providing low coefficient of friction and further reducing the contact stress. The large resolved shear stress near the contact leading edge region facilitated the activation of octahedral slip systems, then the resultant multiple slip lines sheared both the γ matrix phase and γ′ precipitates. The further growth of the slip lines accelerated the fretting fatigue crack initiation and propagation. The arc-tenon attachment could provide long fretting fatigue life and showed great potential in engineering application.

A crystal plasticity based methodology for crack initiation lifetime prediction of fretting fatigue in AA2024-T351 alloy

AA2024-T351 alloy finds extensive use as a component material in the fields of civil engineering, machinery and aerospace, which are prone to long-term contact loading during service that may cause catastrophic failure such as fretting fatigue. In this work, a crystal plasticity finite element (CPFE) model has been established to predict the fretting fatigue crack initiation (FFCI) lifetime of AA2024-T351 alloy. Submodel methods for frictional contact parts are adopted, and crystal plasticity theory is utilized to obtain more accurate simulation results. The hotspots for fretting fatigue crack nucleation are determined by the difference of maximum value of maximum principal strain. The accumulated plastic slip and accumulated energy dissipation are utilized as fatigue indicator parameters (FIPs) to accurately predict FFCI lifetime. The results show that both FIPs predicted crack initiation lifetime are within twice the scatter band. Furthermore, the submodel is employed to generate diverse grain orientation sets while maintaining a constant total of 800 grains. The results indicate that different sets have little effect on the prediction of FFCI lifetime, but has a significant impact on the cumulative shear strain distribution between each individual grain at the mesoscale.

Prediction of the effect of shot peening residual stress on fretting fatigue behaviour

Fretting occurs at two contact bodies, which sustain oscillation loading. The fretting phenomenon decreases the fatigue lifetime dramatically. Shot peening is a commonly used surface treatment to enhance the resistance to damage because the residual stress is introduced to the surface of the material. Some studies showed that residual stress was helpful to improve fatigue lifetime. Under fretting fatigue condition, there are two main stages: crack initiation stage and the crack propagation stage. In this paper, the authors apply the Critical Plane (CP) method combined with the Theory of Critical Distance (TCD) to study the fretting fatigue crack initiation behaviour under the influence of shot peening residual stress, including the crack initiation position, orientation and the crack initiation lifetime. Meanwhile, the Linear Elastic Fracture Mechanics (LEFM) theory and the Extension Maximum Tangential Stress (EMTS) criterion are adopted to study crack propagation behaviour considering shot peening residual stress effect. The results show that the methods applied in this paper can make good predictions of fretting fatigue behaviour, including both initiation and propagation stages. Meanwhile, the influence of residual stress in these two stages are studied as well.

A deep neural network approach combined with Findley parameter to predict fretting fatigue crack initiation lifetime

In the aviation field, the crack initiation stage could be the dominant one of the whole damage failure process of components subjecting to fretting fatigue. Thus, getting an accurate prediction of the crack initiation lifetime become an important topic in research of fretting fatigue problems. In this work, a new prediction method for fretting fatigue crack initiation lifetime is proposed, which is based on Deep Neural Network (DNN), Findley Parameter (FP) and Finite Element Method (FEM). Input features are shear stress amplitude and maximum normal stress in the critical plane, and crack initiation lifetime is set as the output target. Dropout and bootstrapping are considered to improve the performance of DNN. Through comparative analysis, it is shown that this new proposed approach can effectively predict the fretting fatigue crack initiation lifetime. The prediction accuracy and stability are greatly improved compared with the theoretical formulation based on FP.

Numerical simulation of the effect of surface microgeometry and residual stress on conformal contact fretting fatigue crack initiation behavior

AbstractConformal contact is a commonly presented contact form in assemblies. Non‐proportional loading is the main characteristics of conformal contact, which leads to prominent difficulty in revealing fretting crack behavior. In this paper, a finite element prediction model for Ti‐6Al‐4V pin‐hole contact fretting fatigue crack initiation was developed, which simultaneously considered the effect of fretting wear, surface roughness, surface skewness, surface kurtosis, and residual stress. The results show that phase differences of stress component, change in direction of principal stress, and high stress gradient are the main reasons for the initiation of fretting fatigue under conformal contact condition. The model based on the Fatemi–Socie (FS) parameter successfully predicted the location, orientation, and fatigue life of crack initiation, which agrees well with the experimental results. Additionally, machining‐induced residual stress can effectively inhibit mode I crack initiation at valleys. Moreover, ignoring the surface microgeometry characteristics reduces the prediction accuracy of the crack behavior.

A deep learning approach to predict fretting fatigue crack initiation location

Fretting fatigue is a destructive failure that usually occurs in the parts or components in the aviation field. One of the important research topics in fretting fatigue is the prediction of crack initiation location. This paper proposed a new prediction methodology of crack initiation location, which is a deep learning model based on the statistical bootstrapping technique and finite element method (FEM). In this work, two kinds of deep learning models, namely Model-I and Model-II, are established based on different input features, and with the crack initiation location as output feature. The input features of Model-I are the contact load, the tangential load, the cyclic axial stress, and the radius of the fretting pad. In Model-II, one additional feature, namely the half contact-width, is considered. Firstly, three different normalization methods (Max-min, Zero-mean, and Nonlinear) are compared. It is found that the prediction of deep learning models based on the Zero-mean is the most accurate and stable. Then, through the study of sample size reliability, it is found that the prediction accuracy gradually increases initially then becomes stable with the increase of the sampling number. The estimated intervals also gradually become narrowed and then stable. Further, another highlight from the comparison between the performance of Model-I and Model-II is that with the physical-mechanical reasoning factor as additional input features, a more stable and accurate estimated crack initiation location can be obtained from deep learning models. The range of estimated intervals is also effectively narrowed. As an alternative to FEM, the computational efficiency of deep learning is at least 30% higher. The range of estimated intervals for crack initiation location are limited to 250 μm and the errors between predictions and target values are lower than 5%. Therefore, the deep learning method proposed in this paper can effectively and efficiently predict fretting fatigue crack initiation location.

Experimental study and fretting fatigue life prediction in dovetail assembly considering stress–temperature nonlinear coupling effect

AbstractAs a paramount failure form of dovetail assembly, high‐temperature fretting fatigue seriously restricts the actual service life. Aiming at the problem of fretting fatigue life prediction of dovetail assembly of the aero‐engine compressor under the coexistence of stress and high temperature, based on D‐M contact theory and continuum damage mechanics theory, a fretting fatigue life prediction model considering stress–temperature nonlinear coupling effect is proposed in this paper by, respectively, introducing the fretting fatigue stress σfretting and the high‐temperature influence factor λ. Meanwhile, the judgment criterion of fretting fatigue crack initiation and failure is raised based on the strain–displacement method, and the fretting fatigue test is designed and carried out for experimental verification. The results show that the proposed fretting fatigue life prediction model has high life prediction ability, whose life prediction results are within ±1.7 times the error band, which can provide a theoretical reference for the structural design optimization and damage tolerance design of dovetail assembly.

Two-Scale analysis of fretting fatigue crack initiation in heterogeneous materials using Continuum Damage Mechanics

The phenomenon of fretting fatigue damage is related to tribological behaviour and commonly occurs at the contact interface between two bodies that sustain oscillation loads. Based on the complicated mechanical situation, several methods have been developed to predict the crack initiation location and life. The Continuum Damage Mechanics (CDM) approach in conjunction with Finite Element Method (FEM) is used in this paper. The fretting fatigue lifetime includes two parts, crack initiation lifetime and crack propagation lifetime, and this paper focuses on the crack initiation phase. Homogeneous materials are usually studied in fretting fatigue problems, and the influence of defects is necessary to be considered. In this study, the authors proposed several models to consider the effect of heterogeneity on crack initiation location and lifetime. The numerical model is a 2D one with plane strain assumption. To get more accurate numerical results with low computational cost, a Two-Scale Analysis approach is developed in this paper. Two macroscopic models and three microscopic models are proposed, including a Macroscopic homogeneous model (Macro-HOMO), a Multiscale Homogenization model with Direct Numerical Simulation (MH-DNS), a Microscopic homogeneous model (Micro-HOMO), a Microscopic Model with equivalent material properties by using Mean Field Homogenization method (Micro-MFH), and a microscopic model with Direct Numerical Simulation (Micro-DNS). The results obtained by using the CDM approach with different microscopic models are compared, and show that the prediction accuracy of the Micro-DNS is the best. In addition, in terms of computational cost, the Micro-DNS model shows great advantages as well comparing to the Macro-DNS model.

An improved Artificial Neural Network for the direct prediction of fretting fatigue crack initiation lifetime

Fretting fatigue is a common type of problem in the aviation and other engineering fields. Due to its multiaxial characteristics, it leads to a shorter overall fatigue life compared to plain fatigue conditions. Fretting fatigue crack initiation lifetime is a crucial part of the total lifetime, and the currently dominant method for research on fatigue behavior is the combination of the theoretical and numerical models. With the advent of the era of data science, machine learning has been widely used to predict fatigue behavior, but there are no many applications in the field of fretting fatigue. This paper proposed an improved Artificial Neural Network (ANN) using Balancing Composite Motion Optimization (BCMO) for quick prediction of fretting fatigue crack initiation lifetime. Physical-mechanical reasoning parameters, axial stress amplitude, shear stress amplitude, half contact width, and half stick zone width are considered as input parameters, and fretting fatigue crack initiation lifetime is set as the output feature. The main aim of BCMO is to improve the robustness of the ANN based on the influential parameters, namely bias and weight. The provided results using ANN-BCMO are robust compared to ANN and traditional techniques from the literature. The Matlab code of improved ANN using BCMO can be found at https://github.com/Samir-Khatir/BCMO-ANN.git

Refined Critical Plane Methodology for Predicting Fretting Fatigue Crack Initiation Based on Shear Strain Dynamics

Refined Critical Plane Methodology for Predicting Fretting Fatigue Crack Initiation Based on Shear Strain Dynamics

A New Model for Predicting Fretting Fatigue Crack Initiation Life Based on Effective Slip Amplitude

In this study, a new model has been developed for fretting fatigue crack initiation life prediction based on the slip amplitude as a macroscopic feature of the contact interfaces. The main difference between the presented model and many other fretting fatigue life prediction models is the focus on the fretting specific characteristics. In this model, a damage parameter is combined with a damage severity factor to obtain a new fretting fatigue crack initiation life prediction parameter. To investigate the accuracy of this new parameter, a series of fretting fatigue tests have been conducted. Also, crack initiation life data from the literature were added to enhance parameter accuracy investigation. It is shown that the effective slip amplitude is an unbiased geometric-independent parameter in fretting fatigue crack initiation life prediction. Also, comparing prediction results from the effective slip amplitude with those of Smith-Watson-Topper and Ruiz parameters showed that the new parameter can outperform available fretting fatigue life prediction parameters.

Study on fretting fatigue crack initiation of scaled railway axles in consideration of fretting wear

The objective of this study is to investigate the fretting fatigue crack initiation of press-fitted railway axles. Fretting fatigue tests were conducted on scaled railway axles, and the fretting wear and crack at the fretted zone were analyzed. Based on the test results, FE models which take the fretting wear profiles into account were established. And then, three multi-axial fatigue criteria combined with the theory of critical distance were used to evaluate the fretting fatigue crack initiation. The analysis results show that the contact pressure and slip amplitude within the fretted zone are increased with the evolution of fretting wear, and thus produce a gradual increment of frictional shear stress at the inner side of the fretted zone. This finally leads to the fretting fatigue crack initiation of press-fitted axles. The fretting wear would play a more significant role in fretting fatigue initiation of press-fitted axles in the condition of lower applied stresses and higher loading cycles. As compared with the SWT criterion based on the maximum normal stress and elastic strain amplitude, the criteria considering the shear stress as the main controlling parameter (modified Dang Van criterion and McDiarmid criterion) can give a better-predicted result of the fretting fatigue crack initiation for press-fitted axles.

Artificial neural network combined with damage parameters to predict fretting fatigue crack initiation lifetime

The fretting problem occurs at two contact surfaces sustaining small relative displacement, and it reduces the fatigue lifetime dramatically. Estimating accurate fretting fatigue lifetime plays an important role in engineering applications. Due to the complicated stress state, and high-stress gradient in the contact surface, the average methods are necessary to obtain the precise lifetime, but the critical distance for the average zone is difficult to estimate. In this work, Artificial Neural Network (ANN) tool combined with damage parameters is proposed to determine the optimal critical distance for different fretting conditions. This tool can also be used to accurately predict the crack initiation lifetime. The fretting fatigue lifetimes calculated by using this approach have shown good agreement with experimental results from literatures. In addition, rough estimates of critical distance for different cases are made based on the numerical results.

Fretting fatigue experiment and simulation of WC-12Co coating taking into account the wear effects

WC-12Co coating can be used to improve the wear resistance of mechanical connectors, but due to the fretting behavior between the contact interfaces during service, the problem of fretting fatigue cannot be ignored. Through the fretting fatigue experiment and simulation study of the WC-12Co coating, the fretting fatigue mechanism of the coating was investigated under the premise of considering the competitive or coupling relationship between fretting wear and fretting fatigue. Based on Smith-Watson-Topper (SWT) fatigue damage parameter and Miner-Palmgren (M-P) linear cumulative fatigue damage theory, a prediction model for fretting fatigue crack initiation life of WC-12Co coating was established, and the stress redistribution caused by fretting wear was analyzed by Archard wear theory. The analysis results show that the fretting fatigue cracks of the WC-12Co coating mainly initiate at the edge of the wear pits and gradually extend to the substrate; the increase of external load and friction coefficient will accelerate the fretting fatigue process of WC-12Co coating and reduce its fretting fatigue crack initiation life; the change of fretting fatigue crack initiation life and position of WC-12Co coatings caused by fretting wear depends on the change of contact state between contact interfaces.

In-situ SEM and EBSD study on fretting fatigue crack initiation of a directionally solidified Ni-based superalloy

Fretting fatigue is an important cause of the failure of the turbine blade-disc dovetail joint in aero-engines. In this work in-situ scanning electron microscope (SEM) fretting fatigue experiments using dovetail shape specimens were conducted. The fretting fatigue damage process of Ni-based directionally solidified superalloys including slip trace evolution and crack initiation was captured. The misorientation and geometrically necessary dislocation (GND) density induced by fretting fatigue were quantified by electron back-scattered diffraction (EBSD). The significant correlation between crack path, slip trace, grain boundary microstructure and GND density was revealed. The EBSD analysis achieved good agreement with the in-situ SEM observation.

Prediction of initiation and total life in fretting fatigue considering kinked cracks

This work proposes a methodology to compute fretting fatigue crack initiation and total life by iterative models calibrated with fatigue stress–strain-life curves. One of the main novelty of such models is the assumption that the crack initiation length is determined by the size of the critical distance. To separate initiation and propagation lives, a numerical approach with finite elements is used. The methodology incorporates not only the multiaxial non-proportional characteristic of the stress field in fretting problems, but also the stress gradient effect. Crack initiation path is obtained by means of the SWT parameter, and to validate it, the analysed results are compared with tests considering a cylindrical-flat configuration (Aluminium 7075-T651 alloy). Most of the life initiation estimates, as well as the total life ones, are within a scatter band of 3.

Fretting fatigue crack initiation behaviour in heterogeneous materials under out-of-phase loading

Fretting fatigue commonly exists at the junction of contacting bodies that are subjected to oscillating force. Meanwhile, the presence of fretting will affect the fatigue lifetime dramatically, especially when the material is heterogeneous as cracks initiate at defects such as inclusions, micro-voids and micro-cracks. Fretting fatigue is a multi-axial non-proportional loading problem, in which most components and assemblies undergo asynchronous loads. Thus, investigating the influence of phase angle (Φ) in heterogeneous materials is quite meaningful. In this study, different locations of micro-voids in three different loading phase angles are taken into consideration. The critical plane approach and quadrant method are adopted to predict the crack initiation lifetime and crack orientation. It is found that the existence of micro-voids significantly affects the damage parameter, when Φ equals 180°, and plays a relatively small effect when Φ equals 90°. In addition, the crack initiation lifetime varies with the location of micro-voids since the location of micro-voids has different effects on the damage parameters.