Three-dimensional Fatigue Crack Research Articles

Predicting high-cycle fatigue strength and three-dimensional fatigue crack growth in simulated compressor blade by phase-field model

Predicting high-cycle fatigue strength and three-dimensional fatigue crack growth in simulated compressor blade by phase-field model

Three-dimensional fatigue crack initiation and propagation behavior of stress-corroded steel wires for bridge cables

The fatigue test was carried out to investigate the fracture morphology and fatigue life of stress-corroded steel wires. The influence of stress corrosion degree on the initial value of crack propagation and fracture toughness of steel wires was explored. The theoretical method of crack initiation and propagation life of corroded steel wires based on CM-EIFS (Corrosion Modified Equivalent Initial Flaw Size) model was proposed. Finally, the variation law of crack tip stress was studied through the numerical method considering the corrosion surface, and the general expression of shape factor of crack tip and the reduction factor of fracture toughness of corroded steel wires were given. The results showed that the fatigue life of steel wires had a good nonlinear decrease trend with the stress corrosion degree increase. The crack initiation is often located in the surface corrosion pit, and the initiation zone was related to the intermetallic compound containing Fe and Mn. It was necessary to consider the reduction of fracture toughness for steel wires with high degree of stress corrosion. When the stress corrosion degree reached 24 %, the fracture toughness of steel wire was only 50.86 MPa·m0.5, which was 52 % lower than that of the non-corrosion ones. The higher the stress corrosion degree and stress concentration factor, the lower the proportion of crack initiation life. When the stress concentration reached a certain degree, the total fatigue life was mainly composed of crack propagation life. The depth-width ratio of corrosion pit and the residual thickness of corroded steel wires were the key factors affecting the stress intensity factor at the crack tip. The three-dimensional crack propagation results obtained by XFEM (Extended Finite Element Method) based on the corrosion surface were highly consistent with the test results.

Analysis of tooth root three-dimensional fatigue crack initiation, propagation, and fatigue life for spur gear transmission

The gears in aviation gear systems are susceptible to fatigue fracture due to high-speed, heavy-load, and load alternation operating conditions. Therefore, a numerical calculation model with multiple mesh positions loading form has been proposed in this paper to analyze the fatigue crack initiation and propagation behavior, and to estimate the fatigue life of these gears. The fatigue life of the gear is determined by separately calculating the fatigue crack initiation life and the fatigue crack propagation life. The tooth root fatigue stress and the fatigue initiation life are calculated by the multi-axial fatigue life prediction method with the Smith-Watson-Topper criterion and the critical plane method. Afterwards, the tooth root stress–strain field is calculated in Finite element (FE) software and the stress intensity factors of the crack tip are calculated in three-dimensional (3D) crack analysis software. Then, the tooth root fatigue crack propagation trajectory and the fatigue crack propagation life are obtained separately. Finally, the influence mechanism of the loading conditions, the geometry parameters of gears, and the initial crack positions on the tooth root fatigue crack initiation life, propagation life, and fatigue crack propagation trajectory are analyzed, and a tooth fatigue test bench is built for verifying the crack propagation trajectory.

Three-dimensional fatigue crack quantification using densely connected convolutional network-assisted ultrasonic guided waves

Linear and nonlinear ultrasonic guided wave (UGW)-based methods are available for fatigue crack detection and quantification. However, linear methods usually fail to detect undersized cracks, while nonlinear methods struggle to assess cracks once they have extended to a certain degree. The fusion of linear and nonlinear UGW features offers a new opportunity to enhance evaluation precision and effectiveness, yet it necessitates highly complex modeling. Motivated by this, a regression model is proposed based on the famed densely connected convolutional network, DenseNet, for three-dimensional (3D) fatigue crack quantification in both crack initiation and growth stages. Via the continuous wavelet transform (CWT), the spectra of UGW signals embracing both linear and nonlinear features of UGW are obtained. Subsequently, DenseNet is adopted to extract implicit features of spectra images. Finally, the last fully connected layer of DenseNet is modified as a regression layer to estimate the length and depth of 3D fatigue cracks. A dataset comprising 500 UGW signals is created for validating the proposed model. The results demonstrate that the model can characterize the length and depth of 3D cracks in both initiation and growth stages, establishing it as a promising proof-of-concept for the deep learning-based quantification of 3D fatigue cracks.

Fatigue Crack Propagation of Corroded High-Strength Steel Wires Using the XFEM and the EIFS

A fatigue test and numerical simulation on corroded high-strength steel wires with multiple corrosion pits were conducted. A new approach combining the eXtended Finite Element Method (XFEM) and the Equivalent Initial Flaw Size (EIFS) was proposed to investigate three-dimensional fatigue crack growth and life prediction. The EIFS values for the steel wires were determined under various stress ranges and corrosion pit conditions. The fatigue crack propagation path, the fatigue life, and the stress variation under different pit types and depths were investigated. The results reveal a significant linear relationship between the maximum principal stress range and the fatigue life in logarithmic coordinates for steel wires with various pit types. Additionally, the EIFS is found to be dependent on the stress range and the pit depth. All the predicted outcomes fall within a range of twice the margin of error. The accuracy of this novel method is further verified by comparing predicted results with the test data. This research contributes to a better understanding of the fatigue performance of corroded high-strength steel wires and can assist in the design and maintenance of notched components.

Three-dimensional fatigue crack growth based method for fatigue reliability of metallic materials

Fatigue is one of the greatest threats to structural integrity. It is sensitive to the uncertainties of material quality, manufacturing quality and service load, making fatigue reliability analysis important and challenging. Here, a reliability analysis method considering these uncertainties is proposed. Firstly, the distribution of equivalent initial crack sizes in the material was obtained from the S-N data by back-extrapolation based on three-dimensional (3D) fatigue crack growth prediction. Then, the sample set for reliability analysis was obtained by randomly combining the applied stresses and crack sizes under the assumption that the crack sizes and applied stresses are independent. Further, the fatigue life of every sample is predicted with the 3D crack growth method, and the cumulative distribution of fatigue life was obtained to analyze the reliability. Based on the obtained initial crack distribution with stress ratio R ≥ 0, the predicted P-S-N diagrams of different stress ratios and stress concentrations were in accordance with the experimental data, indicating that the obtained initial crack size distribution has a certain universality. Finally, the influence of sampling numbers on the reliability analysis is analyzed with five types of commonly used metallic alloys. It is shown that the cumulative distribution of fatigue lives could be obtained with a less sampling number. Compared with Monte Carlo and importance sampling methods, this method can reduce the number of samples effectively and achieve the reliable probability of different fatigue life intervals.

Three-dimensional high-resolution crystallographic observation of the entire volume of microstructurally small fatigue cracks in Ni-Co based superalloy

The crystallographic features of microstructurally small fatigue cracks (MSFCs) in a Ni-Co-based superalloy were analyzed by using a Xe plasma focused ion beam scanning electron microscope (PFIB-SEM) system in conjunction with electron backscatter diffraction (EBSD) analysis. The crystallographic orientation of the three-dimensional (3D) fatigue crack growth path was successfully observed using a large-volume, high-resolution 3D image. The major parts of the crack surface were close to the {111} slip plane. Our results indicated that the Mode II fatigue crack growth mechanism is locally more predominant than the general blunting-resharpening Mode I fatigue crack growth mechanism, not only in the Stage I region but also in the larger part of the Stage II region of MSFC growth process.

Three-dimensional fatigue crack growth prediction method based on consistency retention

To reduce the influence of uncertain factors, a three-dimensional fatigue crack growth prediction method based on consistency maintenance is proposed. Firstly, the crack growth update under complex loads is realized based on XFEM. Subsequently, the life correction method based on the improved particle filter and the path correction method based on the improved maximum tangential stress criterion are proposed. Taking real crack data as input, the accuracy of prediction results is improved from two dimensions of life and path. Finally, five cases are used to verify the proposed framework, which proves that it can realize dynamic tracking of crack growth.

An X-FEM based framework for 3D fatigue crack growth using a B-spline crack geometry description

This paper presents an X-FEM based iterative framework for numerical simulation of three-dimensional fatigue crack propagation. To accurately describe the crack geometry, B-spline curves and surfaces are used for the crack front and faces respectively. A new crack front extension method based on the Möller–Trumbore algorithm is introduced to achieve fully automated crack growth for complex geometries. To validate the presented work, three different cases are discussed: (1) compact tension specimens with an asymmetrically located hole, (2) a beam with a slanted crack subjected to a three-point bending load and (3) a beam with a slanted crack subjected to a torsion load. Good agreement between the numerical and experimental results is observed.

Three-dimensional fatigue crack propagation by means of first order SIF approximation

In this paper we make use of a closed-form solution for mode I Stress Intensity Factors (SIF) in three-dimensional planar flaws based on homotopy transformations of a disc. The utilised equations are very accurate when the flaw is a small deviation from a circle. Under the hypothesis of an isolated crack, the SIF at each point of the crack border is calculated to assess the crack shape after propagation. The solution is proposed in terms of the Fourier series and the crack growth rate equation is taken according to Paris’ low. Many examples are proposed with the aim of predicting the final shape of different types of embedded planar flaws in butt welded joints under fatigue tensile loading.

Failure Analysis of a Working Roll Under the Influence of the Stress Field Due to Hot Rolling Process

Crack growth leads to roller failure and damages other parts. The three-dimensional modeling of crack growth, the effect of different factors on the fatigue life of roller, and the effect of stress distribution are important factors that should be considered. The purpose of this paper is to investigate the failure and modeling of three-dimensional fatigue crack growth and fatigue life prediction of high chromium steel (HCS) rollers in hot rolling to minimize the failure of rollers by practical solutions. This article uses boundary element method for fatigue crack growth under the influence of stress field. The proposed method allows modeling each of the components involved separately in the contact area. As a result, this method is faster than finite element models with contact components. In this regard, the types and causes of cracks in the roller are analyzed with the effect of residual stresses on the roller. By selecting the HCS roller and sheet, modeling and stress analysis are performed by finite element method. This study includes the effect of crack growth factors such as load ratio, length, and initial crack angle. The results of the numerical model showed a good agreement with the results obtained in the field observations.

Three-dimensional fatigue crack propagation analysis of welded steel beam based on global-local numerical model

The existing fatigue assessment approaches were mainly conducted on the component level. The interaction of local component damage and the global response cannot be well addressed. In this study, three-dimensional (3D) fatigue crack propagation analysis approach based on global-local numerical model was implemented, and examined to be accurate and effective through a series of systematic experimental data obtained by Fisher. Afterwards, the approach was introduced into a typical steel truss bridge for realizing more refined fatigue assessment from the global structural level. The fatigue performance of the longitudinal steel welded beam in the steel truss bridge was investigated based on global-local model and local model respectively. It was found that there is no difference in terms of the fatigue crack growth mechanism between the simulation between global-local model and local model due to that the stress level of the whole structure is relatively low. At last, the effect of heavy haul train operation on the fatigue performance of the steel truss bridge was analyzed. It was observed that the residual life of the longitudinal steel welded beam would have an obvious reduction when the axle load was increasing. The research work in this study presents a technical solution for the fatigue assessment of the global structure and can provide beneficial reference for relevant practical engineering projects.

Three-dimensional fatigue crack propagation simulation using extended finite element methods for steel grades S355 and S690 considering mean stress effects

The assessment of fatigue crack propagation of steel structures is essential and important especially to improve the application of high strength steel in construction. The load ratio R, reflecting mean stress effects, will be changed with crack extension in the steel structures with complicated geometry. In this paper, the Walker equation is employed to fit the fatigue crack propagation rate of steel grades S355 and S690 based on experimental data in the literature to incorporate the mean stress effects. The material fatigue crack propagation parameters with 95%, 97.7%, and 99% guarantee of Walker equation were obtained by a stochastic analysis using the Monte Carlo method. The fatigue life was firstly predicted by the analytical method and was used as a baseline for numerical fatigue crack propagation simulation. A user-defined fatigue crack propagation subroutine based on the Walker equation was developed using phantom nodes-based extended finite element method (PN-XFEM) and Virtual Crack Closure Technique (VCCT) to consider the mean stress effects. The proposed three-dimensional fatigue crack propagation simulation subroutine is successfully validated of both steel grades, S355 and S690.

The effects of periodic overloads on fatigue crack growth in a pearlitic Grade 900A steel used in railway applications

The objective of this paper is to predict a three-dimensional fatigue crack growth (FCG) in a pearlitic Grade 900A steel used in railway applications in the presence of periodic overloads. Numerical and experimental methods are used to investigate the behavior of FCG in the rail specimens. A 3-D boundary element model, using the BES tool is used to estimate the stress intensity factor (SIF) using the crack opening displacement (COD) approach in rail specimens. Also, the crack growth rate is predicted utilizing the Forman–Newman–de Koning (FNK) model. Linear elastic fracture mechanics (LEFM) is used to predict the fatigue life developed from a two-stage fatigue loading cycle where both mechanical loads and periodic overloads are present. The maximum tangential stress (MTS) crack extension criterion is used to obtain the FCG paths. The results revealed that fatigue life is highly sensitive to periodic overloads. Therefore, this factor significantly affects the fatigue life of railway rails during service conditions. In the present investigation, the periodic overloads have remained constant and the effect of load ratio and the number of overloads on the fatigue life has been investigated.

Three-dimensional fatigue crack closure numerical modelling: Crack growth scheme

Numerical models based on finite element method have been employed to analyse the plasticity induced crack closure phenomenon for a long time. These numerical analyses require the development of a plastic wake. During the development of the plastic wake a transient behaviour can be observed on the numerical results. Most of these previous analyses have been performed considering bi-dimensional models. The use of three-dimensional models has been extended during last years. Nevertheless, the methodology considered has been inherited from the bi-dimensional ones.Optimising the numerical parameters involved on the development of the plastic wake is a key issue to keep the computational cost under control, particularly when a three-dimensional analysis is considered. This study presents a three-dimensional analysis of the influence of the crack growth scheme on fatigue crack closure results. This three-dimensional analysis allows to study the influence of the number of loading cycles not just on plane stress or plane strain conditions but all along the thickness.In the present work, a CT aluminium specimen has been modelled three-dimensionally and several calculations have been made in order to evaluate the influence of the number of loading cycles between node releases and after releasing the last set of nodes on fatigue crack closure results. The numerical accuracy is analysed in terms of crack closure and opening values and in terms of strain and stress fields.

Application of Response Surface Method in Probabilistic Fatigue Crack Propagation Life Assessment using 3D FEA

Fatigue crack growth life assessment is an important task in damage tolerant design practices. Being able to assess variability of crack propagation path and remaining useful life requires both deterministic and probabilistic modeling capabilities. Three-dimensional fatigue crack growth finite element modeling and Radial Basis Function based Response Surface modeling is shown to be an accurate and efficient route to predict crack propagation path in uncertainty quantification studies. A mixed-mode fatigue crack growth experimental measurement from literature is used for validation purposes and for quantifying crack path sensitivity due to off-nominal specimen geometry. Two sets of deterministic 3D crack propagation simulations are performed to relate geometric deviations to crack path predictions: first set is used to calibrate the response surface model while the second for verification purposes. Once verification requirements are satisfied, the response surface model can be employed in Monte Carlo type probabilistic simulations.

Three-dimensional fatigue crack growth simulation of embedded cracks using s-version FEM

PurposeSince the most of structures and structural components suffers from cyclic loadings, the study on the fatigue failure due to the crack growth has a great importance. The purpose of this paper is to present a three-dimensional fatigue crack growth simulation of embedded cracks using s-version finite element method (SFEM). Using the numerical results, the validity of the fitness-for-service (FFS) code evaluation method is verified.Design/methodology/approachIn this paper, three-dimensional fatigue crack propagation analysis of embedded cracks is performed using the SFEM. SFEM is a numerical analysis method in which the shape of the structure is represented by a global mesh, and cracks are modeled by local meshes independently. The independent global and local meshes are superimposed to obtain the displacement solution of the problem simultaneously.FindingsThe fatigue crack growth of arbitrary shape of cracks is slow compared to that of the simplified circular crack and the crack approximated based on the FFS code of the Japan Society of Mechanical Engineers (JSME). The results tell us that the FFS code of JSME can provide a conservative evaluation of the fatigue crack growth and the residual life time.Originality/valueThis paper presents a three-dimensional fatigue crack growth simulation of embedded cracks using SFEM. Using this method, it is possible to apply mixed mode loads to complex shaped cracks that are closer to realistic conditions.

Numerical modelling of three-dimensional fatigue crack closure: Plastic wake simulation

Finite element method has been broadly used to study fatigue crack closure. The simulated plastic wake length is one of the key modelling parameters involved. This paper presents a complete analysis in fatigue crack closure 3-D models.It is aimed at two aspects: the influence on the calculation of opening and closure values, and the effect on other main results. Conclusion indicates a 0.6 times Dugdale’s plastic size length to stabilise results as plastic zone or contact area, but a reduced length could be acceptable in terms of crack closure results. This suggests some independence among this parameter and fatigue crack closure.

An Analysis of Three-dimensional Non-planar Fatigue Crack Propagation with Smoothed Particle Hydrodynamics Method and Its Experimental Verification

An Analysis of Three-dimensional Non-planar Fatigue Crack Propagation with Smoothed Particle Hydrodynamics Method and Its Experimental Verification

Applications on Three-Dimensional Mixed Mode Fatigue Crack Propagation Using Fracture and Crack Propagation Analysis System (FCPAS)

In this study, results from two applications on three-dimensional fatigue crack propagation using the in-house developed “Fracture and Crack Propagation Analysis System (FCPAS)” are presented. FCPAS uses finite element models to calculate three-dimensional mixed mode stress intensity factors and other sub-modules to predict shapes of the incrementally growing crack fronts and the resulting fatigue crack propagation lives. The evolving crack surfaces are generated by successively adding the incremental growth surfaces and re-meshing and re-solving the finite element model using the standalone program FRAC3D, a finite element-based standalone program employing three-dimensional enriched finite elements. The results show that the fracture surfaces evolve into a mode-I type three-dimensional crack as expected. Very good agreements are obtained between the results of the current studies and those of numerical applications in terms of both evolving crack surfaces and crack propagation lives. Therefore, it is concluded that the applied method is capable of accurately predicting linear elastic three-dimensional mixed mode fatigue crack propagation problems.