Fatigue Crack Initiation Lifetime Research Articles

A data‐assisted physics‐informed neural network (DA‐PINN) for fretting fatigue lifetime prediction

AbstractIn this study, we present for the first time the application of physics‐informed neural network (PINN) to fretting fatigue problems. Although PINN has recently been applied to pure fatigue lifetime prediction, it has not yet been explored in the case of fretting fatigue. We propose a data‐assisted PINN (DA‐PINN) for predicting fretting fatigue crack initiation lifetime. Unlike traditional PINN that solves partial differential equations for specific problems, DA‐PINN combines experimental or numerical data with physics equations as part of the loss function to enhance prediction accuracy. The DA‐PINN method, employed in this study, consists of two main steps. First, damage parameters are obtained from the finite element method by using critical plane method, which generates a data set used to train an artificial neural network (ANN) for predicting damage parameters in other cases. Second, the predicted damage parameters are combined with the experimental parameters to form the input data set for the DA‐PINN models, which predict fretting fatigue lifetime. The results demonstrate that DA‐PINN outperforms ANN in terms of prediction accuracy and eliminates the need for high computational costs once the damage parameter data set is constructed. Additionally, the choice of loss‐function methods in DA‐PINN models plays a crucial role in determining its performance.

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.

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

Research on the effect of micro-voids on the deformation behavior and crack initiation lifetime of titanium alloy under cyclic loading by crystal plasticity finite element method

Micro-voids defects associated with materials formed by diffusion bonding and super-plastic connection limit their usage in the aerospace industry. A crystal plasticity finite element (CPFE) model was established in the current work to investigate the relationship between local stress concentration and the micro-void defects, and predict the fatigue crack initiation lifetime. Based on the concept of the curvature of the crack tip, the shape and size of the voids are strictly separated, so that the influence of the single parameter of voids on the microplasticity deformation behavior is better obtained. It's found that the micro-voids lead to the stress concentration phenomenon in the material, the effect of the curvature of the void tip surface is greater than that of the void size. Stress concentration tends to occur in the hard grains. When L/d is greater than 2.0, stress concentration factor reaches a constant small value. The simulated results based on the Manson-Collin law and Fatemi-Socie parameter show that when the void tip curvature is greater than 0.4 μm−1 or L/d is less than 2.0, the fatigue crack initiation lifetime is less than 106 cycles, indicating that the influence of such micro-voids on fatigue crack initiation is small. This work has a good guiding significance for properties and lifetime prediction of the material with defects.

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.

In-situ investigation of the fatigue crack initiation and propagation behavior of Zircaloy-4 with different hydrogen contents at RT and 300 °C

In this paper, the effects of hydrogen content and temperature on the fatigue crack initiation and propagation behavior of Zircaloy-4 are investigated by in-situ scanning electron microscope observation. The results show that, at room temperature, with the increase of hydrogen content, the tensile strength increases and the elongation decreases, but the fatigue lifetime (fatigue crack initiation lifetime and fatigue failure lifetime) first increases and then decreases. The cut-off point is at about 200 ppm hydrogen content. The fatigue crack growth rate increases with the increase of hydrogen content. At 300 °C, with the increase of the hydrogen content, tensile strength, elongation and fatigue lifetime of Zircaloy-4 alloys exhibit the same variations as those at room temperature. However, the fatigue crack growth rate is less affected by the hydrogen content. The results also show that, with the same hydrogen content, the fatigue lifetime at 300 °C is longer than that at room temperature, and the fatigue crack growth threshold at 300 °C is lower than that at room temperature. The fatigue crack propagation path is strongly affected by the hydride and grain boundaries. The hydrogen content has a significant effect on the fatigue crack initiation mechanism. For the un-hydrided sample, the fatigue cracks initiate at the sub-surface. With the increase of hydrogen content, the fatigue cracks tend to initiate at the surface of the sample.

Fatigue crack initiation behaviour of notched 34CrNiMo6 steel bars under proportional bending-torsion loading

Fatigue crack initiation behaviour of notched 34CrNiMo6 high-strength steel bars with transverse blind holes and lateral U-shaped notches subjected to proportional bending-torsion loading is studied. Crack initiation at the geometric discontinuities is examined in situ using a high-magnification digital camera. Crack initiation mechanisms and failures modes are investigated after the fatigue testing program via scanning electron microscopy. Fatigue crack initiation lifetime is predicted using an averaged Total Strain Energy Density approach in conjunction with the Theory of Critical Distances. Crack initiation sites, crack surface angles and surface crack paths at the geometric discontinuities are successfully determined a priori from the maximum value of the first principal stress, the first principal direction, and the first principal stress field at the notch surface, respectively. Overall, fatigue lifetime predictions are very well correlated with the experimental observations.

Detection and analysis of high temperature fatigue fracture surface oxygen diffusion of GH4133B superalloy used in turbine disk of aero-engine

The chemical contents on the fatigue fracture surface of GH4133B superalloy piece suffering tension-tension fatigue and operated at high temperature 600 ºC is analyzed using an energy dispersive spectrometer, and the element content percentages at the position of carbide inclusion and that of second-phase particle in the fatigue source region are measured. It is shown that under the conditions of high temperature and air environment, the carbon element in the carbide inclusion can be easily oxidized, which results in accelerating fatigue crack nucleation and microcrack generation, reducing the fatigue crack initiation lifetime. The oxygen concentration is detected on the fatigue fracture surface along the crack propagation direction, the oxygen diffusion model is constructed, and the oxygen concentration gradient equation is derived. It is found that the oxygen content decreases gradually along the crack propagation direction, suggesting that at the crack initiation and short crack propagation stage, the alloy element reacts sufficiently with oxygen for a long time, and the oxidation accelerates the crack initiation, while at the long crack growth stage, the crack propagation rate is faster, so the alloying elements do not have adequate time for reacting with oxygen, resulting in the low oxygen content, and the oxidation has a small influence on the long crack propagation rate.

Numerical analysis of the influence of micro-voids on fretting fatigue crack initiation lifetime

Abstract In this paper, the influence of the heterogeneity in the predicted crack initiation lifetime under fretting fatigue conditions is analysed for a regular and a random distribution of micro-voids. A critical plane analysis with two multiaxial damage criteria is performed to assess the crack initiation lifetime. The predicted initiation lifetime in the heterogeneous material is compared with the results obtained in the homogeneous case. The numerical results show that the heterogeneity has a noticeable influence on the predicted initiation lifetime. Furthermore, the numerical model suggests that a crack may firstly initiate at the upper edge of the micro-voids located close to the contact edge, leading to a mean reduction of the predicted crack initiation lifetime. However, in some cases, the introduction of micro-voids reduces the stress intensity at the contact edge and thus decreasing the predicted crack initiation lifetime.

A New Approach to the Fatigue Life Prediction for Notched Components Under Multiaxial Cyclic Loading

A new fatigue life prediction approach for notched components is proposed under multiaxial cycle loading. Firstly, the pseudo equivalent strain-real equivalent stress relationship is determined by utilizing the Neuber’s rule and the material stress-strain relation under proportional loading. Secondly, the pseudo elastic strain histories at the notch need to be solved for the investigated notched components under multiaxial cyclic loading. Thirdly, for the pseudo elastic strain histories, it is proposed that the Shang–Wang multiaxial fatigue damage parameter can be used to substitute the equivalent strain under proportional loading to take account of the additional hardening due to the non-proportionality of external loadings. Meanwhile, the real equivalent stress amplitude at the notch can be solved. Fourthly, based on the real equivalent stress amplitude at the notch integrated with the Neuber’s rule, the real equivalent strain amplitude can be determined. Finally, the real equivalent strain amplitude is utilized to predict the fatigue crack initiation lifetime of notched components. The proposed method is verified by the experimental data of SAE 1045 notched shaft specimens under proportional and non-proportional cyclic loading. The results showed the prediction errors are mostly within a factor of 2.

Fatigue Lifetime of Laser-MIG Hybrid Welded Joint of 7075-T6 Aluminum Alloy by in-situ Observation

The fatigue lifetime of the laser-MIG hybrid welded joint of 7075-T6 aluminum alloy was studied by in-situ observation. The results show that there exists a strong relationship between the fatigue crack initiation lifetime and fatigue failure lifetime. For the base metal specimens the ratio of fatigue crack initiation lifetime and fatigue failure lifetime is about 64.5%, while for the welded joint specimens it is about 20.2%. The observation of fatigue fracture surface indicates that there are a large number of dimples in the base metal specimens, while lots of gas porosities appear in the welded joint specimens instead. These gas porosities are regarded to be the reason of lower fatigue crack initiation lifetime.

A methodology for probabilistic prediction of fatigue crack initiation taking into account the scale effect

An approach for probabilistic prediction of fatigue crack initiation lifetime of structural details and mechanical components is presented. The methodology applied is an extension of the generalized local model (GLM) to the fatigue case using the fatigue Weibull regression model proposed by Castillo-Canteli. First, the primary failure cumulative distribution function (PFCDF) of the generalized failure parameter is derived from experimental results for a given reference size, taking into account the non-uniform distribution of the generalized parameter (GP) the specimens are submitted to. The adequacy of the GP is presumed, ensuring uniqueness of the derived PFCDF as a material property, irrespective of the specimen shape and size, and the test chosen to this end. Next, the GP distribution is obtained by a finite element calculation and the PFCDF is applied to each finite element, considering the scale effect, to derive the probability of failure for the whole component. The suitability of the proposed approach is illustrated twice: first, assessing simulated data in a theoretical example, and second, evaluating experimental fatigue life results for riveted joints from the historical Fão Bridge. The PFCDF for the puddle iron from the bridge is calculated from standard tensile specimens, from which the initiation fatigue lifetime of the riveted connections is predicted and compared with the experimental results. In this way, the transferability from standard tests to real components is demonstrated.

Prediction of fretting fatigue crack initiation in double lap bolted joint using Continuum Damage Mechanics

In fretting fatigue, the combination of small oscillatory motion, normal pressure and cyclic axial loading develops a noticeable stress concentration at the contact zone leading to accumulation of damage in fretted region, which produces micro cracks, and consequently forms a leading crack that can lead to failure. In fretting fatigue experiments, it is very difficult to detect the crack initiation phase. Damages and cracks are always hidden between the counterpart surfaces. Therefore, numerical modeling techniques for analyzing fretting fatigue crack initiation provide a precious tool to study this phenomenon. This article gives an insight in fretting fatigue crack initiation. This is done by means of an experimental set up and numerical models developed with the Finite Element Analysis (FEA) software package ABAQUS. Using Continuum Damage Mechanics (CDM) approach in conjunction with FEA, an uncoupled damage evolution law is used to model fretting fatigue crack initiation lifetime of Double Bolted Lap Joint (DBLJ). The predicted fatigue lifetimes are in good agreement with the experimentally measured ones. This comparison provides insight to the contribution of damage initiation and crack propagation in the total fatigue lifetime of DBLJ test specimens.

In situ observation of fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy at 750°C

In this paper, the fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy with nearly lamellar microstructure was studied by in situ scanning electron microscope observation at 750 °C. Dog-bone shaped specimens with a single-edge notch were used in the test. The results showed that the fatigue crack initiated first at the central portion of the notch, and then shifted to the edge portion. As the cycle numbers went on increasing, these cracks joined together and formed a main fatigue crack, which could propagate along the surface of the specimen. During the fatigue crack propagation two or three propagation stages were found depending on the microstructure of the crack tip. When the fatigue crack was parallel to the lamellar laths, it exhibited the rapid, steady and accelerated propagation stages successively, while when the fatigue crack was perpendicular to the lamellar laths, it exhibited only the steady and accelerated propagation stages, with no rapid propagation stage being found. In these different propagation stages the fatigue crack propagation rates were different and depended intensively on the lamellar laths orientation, lamellar colony size, equiaxed gamma grains and peak stress intensity factor K max . Based on the experimental data it was concluded that the fatigue crack initiation lifetime was much longer than the propagation lifetime for the single-edge notched specimens at 750 °C.

Finite element simulation of phase difference effects on fretting fatigue crack nucleation behaviour

Fretting fatigue is a mechanical failure process, which consists of two complex failure mechanisms. Fretting is caused by small relative movement between connected parts and fatigue is due to alternating bulk load. Fretting fatigue is highly non-linear and subjected to non-proportional loading condition. The multiaxial nature of stress at contact interface can be highly influenced by different phase difference between axial, tangential and contact load. In this study, the effect of different phase difference between axial and tangential load on fretting fatigue behaviour is investigated. Moreover, by applying cyclic contact load instead of constant contact load, its effect on fretting fatigue response and crack initiation lifetime is investigated. It was found that the phase difference affects the maximum location of dissipated energy along with fretting fatigue crack initiation lifetime.

J0310205 高剛性ラップジョイントせん断試験によるはんだ接合部の疲労き裂発生寿命評価([J031-02]電子情報機器・半導体デバイス・電子部品の冷却技術(2),材料力学部門)

Shear fatigue tests of Sn-3.0Ag-0.5Cu solder joints were carried out by the combination of an advanced lap-joint specimen with high stiffness fixtures. This paper presents an evaluation of fatigue crack initiation lifetime of the joints under the condition of low strain rate followed by creep deformation. Consequently, an experimental relation between the inelastic strain range and the number of cycles corresponding to 20% load decrease were obtained.

Fretting fatigue crack initiation lifetime predictor tool: Using damage mechanics approach

Fretting fatigue is a combination of two complex mechanical phenomena. Fretting appears between components that are subjected to small relative oscillatory motions. Once these connected components undergo cyclic fatigue load, fretting fatigue occurs. In general, fretting fatigue failure process can be divided into two main portions, namely crack initiation and crack propagation. Fretting fatigue crack initiation characteristics are very difficult to detect because damages such as micro-cracks are always hidden between two contact surfaces.In this paper Continuum Damage Mechanics (CDM) approach in conjunction with Finite Element Analyses (FEA) is used to find a predictor tool for fretting fatigue crack initiation lifetime. For this purpose an uncoupled damage evolution law is developed to model fretting fatigue crack initiation lifetime at various fretting condition such as contact geometry, axial stress, normal load and tangential load. The predicted results are validated with published experimental data from literature.

1108 Sn-3.0Ag-0.5Cuはんだ接合部の熱疲労き裂発生寿命予測精度(J08-1 電子情報機器,電子デバイスの強度・信頼性評価と熱制御(1) はんだ接合部信頼性,ジョイントセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

In Sn-3.0Ag-0.5Cu lead-free solder joints of chip type resisters, a prediction of thermal fatigue crack initiation lifetime was carried out and its accuracy was also discussed. The authors have been focused on the phase growth phenomena in solder joints due to thermal cyclic loading. The prediction was based on the experimental relation between the increase in the phase growth parameter S and the crack initiation lifetime N_1. The predicted lifetime was compared with experimentally determined lifetime by SEM observations. Consequently, the accuracy is that the measured lifetime exists in the range of 90% confidence limits of the predicted lifetime.