Simulation Of Fatigue Crack Propagation Research Articles

An adaptive finite element method for coupled fretting wear and fatigue crack propagation simulation

Fretting wear and fatigue crack propagation often occur at the same time in the service of mechanically connected structures. In order to analyze the effect of fretting wear on the process of fatigue crack propagation, a finite element simulation method for fatigue crack propagation considering fretting wear is proposed. In this method, the Archard model is used to predict the wear process, and the conventional Paris equation is modified based on the wear rate. In order to improve the accuracy of crack propagation prediction, a crack-tip super singular element (CSSE) is used to calculate the singular stress field and fracture control parameters of the crack tip. An adaptive meshing technique that automatically adjusts the mesh density according to the simulation process is designed to ensure the computational efficiency of the algorithm and the accuracy of the numerical results. The smoothing technique used in wear simulation can alleviate the influence of contact stress fluctuation on wear profile prediction. The usage of the new simulation method is introduced through benchmark examples. It is proved that the numerical results of crack propagation obtained by the adaptive finite element method (FEM) have high precision, good convergence and high computational efficiency. It is found that wear reduces the crack growth rate compared with the simulation results without considering wear. This method has a promising application in the coupling analysis of fretting wear and fatigue crack propagation of mechanically connected structures.

An adaptive multi-patch isogeometric phase-field model for fatigue fracture

Fatigue fracture is one of the main causes of structural failure under cyclic loading, so accurate evaluation of fatigue fracture is very important for the design of structures subjected to cyclic loading. In this work, we propose an adaptive fatigue phase-field model within the framework of multi-patch isogeometric analysis to simulate crack nucleation and propagation in brittle materials under cyclic loading. Multiple non-uniform rational B-splines (NURBS) patches are used to exactly represent complex structures, and the Nitsche’s method is adopted to enforce the compatibility of the displacements, stresses and phase-field variables between two patches. The coupled governing equations of fatigue phase-field model are established based on the Nitsche’s method, and the selection of Nitsche’s parameters are determined from numerical experiments. A refinement-correction adaptive approach based on locally refined non-uniform rational B-splines (LR NURBS) structured mesh refinement strategy is developed to alleviate the computational burden caused by the requirement of small element size around crack surface and the large number of fatigue loading. The proposed multi-patch isogeometric phase-field model can deal with the coupling between equal/unequal length interfaces, thus the fatigue crack propagation simulation in arbitrary complex structure can be implemented. Several numerical examples are investigated to verify the practicality of the multi-patch isogeometric phase-field model and the effectiveness of the adaptive scheme.

Re-Distribution of Welding Residual Stress in Fatigue Crack Propagation Considering Elastic–Plastic Behavior

The welding residual stress re-distribution behavior during fatigue crack propagation in butt-welded high-strength steel plates for ship construction is investigated based on experimental test results and numerical analyses. The specimens’ initial welding residual stresses are obtained from X-ray for middle tensile (MT) specimens cut from butt-welded high-strength steel plates. Then, fatigue crack propagation experiments on MT specimens are conducted, and a strain gauge is used to measure the residual stress re-distribution field around cracks. A practical fatigue crack propagation simulation procedure is developed with a dynamic update of in-situ welding residual stress, where the residual stress intensity factor Kres of the MT specimen is deduced. The stress ratio effect on Kres during fatigue crack propagation is analyzed and a good agreement between experimental and numerical results is achieved.

Fatigue crack propagation simulation of airfoil section blade under aerodynamic and centrifugal loads

Cracks in aero-engine blades occur frequently due to high-cycle fatigue, which may cause accidents. Most of the existing studies simulating blade crack propagation are performed based on simplified blade shapes (rectangular, etc) or single loads (tension, bending, torsion, etc). These simplified treatments lead to a large deviation between the simulated crack propagation law and the actual blade propagation process. To fill the gap, the surface crack propagations of airfoil section blades under aerodynamic load, centrifugal load and the combined action of two loads are simulated based on the combined simulation of FRANC3D and ANSYS. The proposed method is verified by comparing the results with those obtained from the literature and experiment, respectively. In addition, the surface crack propagation path and the change of stress distribution during crack propagation under different loads are simulated. The results show that the crack propagates to the trailing edge (TE) and leading edge (LE) under aerodynamic load and centrifugal load, respectively. In addition, the cracks show three-dimensional shape characteristics under a single load. However, the crack propagates approximately along the plane under the combined action of two loads. The study can provide a theoretical basis for cracked blade failure analysis.

Numerical simulation and experimental verification of fatigue crack propagation in high-strength bolts based on fracture mechanics.

To investigate the fatigue crack propagation behavior of high-strength bolts for high-speed train brake discs, the fatigue crack propagation of high-strength bolts with initial defects under various load ratios was numerically simulated and experimentally verified based on fracture mechanics in this paper. Firstly, the fracture mechanics model of a three-dimensional hexahedral mesh with initial root defects was established using ABAQUS-FRANC3D interactive technology. Then the stress intensity factor (SIF) of the crack front was calculated by the stress superposition of the crack surface to simulate the coupling effect of preload and axial cyclic load. Based on it, fatigue crack propagation was simulated. Finally, the corresponding fatigue experiments on prefabricated crack bolts were carried out. The results show that mode I cracks dominate in the process of crack propagation. The stable crack propagation zones of the fractured high-strength bolts all show a semi-elliptical cross-section. The SIF of the crack front decreases with the increase of the load ratio, thus making the crack propagation life increase with the increase of the load ratio. The experimental outcomes are in great agreement with the simulation results, which verify that the numerical simulation method can effectively and accurately evaluate the fatigue life of high-strength bolts with initial defects and provides an effective means for predicting the fatigue crack propagation life of the same type high-strength bolts in engineering applications.

Recent progress in computational predictions on fatigue and fracture resistance of steel connection joints

AbstractSteel structures are often subjected to cyclic loads, and sometimes to monotonic overloads, during the technical lifetime, which causes their performance degradation. Incidentally, they undergo progressive collapse, especially due to local failure of connections or joints. To ensure the overall integrity of the steel structures and to make sure the efficient transfer of the load between different components, it is necessary to evaluate the ultimate capacity and fatigue resistance of steel connections. Advances in material modelling and well‐controlled experiments at various scales in recent years have increased confidence in the finite element method as an effective way to predict the ultimate resistance and fatigue life. On examples of two common steel connections: bolted connection and welded connection, the recent progress will be presented in ductile fracture and fatigue crack initiation and propagation simulation.

Fatigue crack propagation simulation of vertical centrifugal pump runner using the extended finite element method

The performance evaluation of fatigue crack propagation is essential for the safe and stable operation of power plants. In this study, the Walker equation is employed, considering the loading ratio effect. The parameters in the Walker equation for AISI 304 L are fitted by a normal probability distribution based on the experimental information . A numerical simulation of the fatigue crack growth is carried out using the extended finite element method with the Walker equation embended in, and verified on a round compact tension model with the loading ratios of R = 0.1, 0.5, and 0.85. Finally, a fatigue crack growth simulation of a vertical centrifugal pump-turbine runner under turbine conditions is conducted with two crack positions. The crack morphology can be captured together with the corresponding fatigue life by using the developed fatigue crack propagation simulation method based on the extended finite element method. The numerical results can be used as guidance for improving the maintenance plan of pump plants.

Numerical simulation of fatigue crack propagation in heterogeneous geomaterials under varied loads using displacement discontinuity method

Numerical simulation of fatigue crack propagation in heterogeneous geomaterials under varied loads using displacement discontinuity method

Mixed-mode fatigue crack propagation simulation by means of [formula omitted] and walker models of the structural steel S355

In this paper, a numerical simulation method of mixed-mode fatigue crack propagation was explored using the extended finite element method (XFEM) and the Virtual Crack Closure Technique (VCCT). Both 2D and 3D numerical models were selected to simulate the fatigue crack propagation of steel specimens. Two coefficients were proposed to calculate the equivalent energy release rate (Geq) for a better simulation of the mixed-mode fatigue crack propagation of S355 steel. The Walker equation and the calculation formula of Geq were realized by a user-defined subroutine. A set of optimal correction coefficients of mode II energy release rate (GII) and mode III energy release rate (GIII) were quantitatively comparing the simulation results and test data. The results will contribute to fatigue crack propagation prediction of steel structures in the civil engineering field.

A peridynamic approach to simulating fatigue crack propagation in composite materials.

In this article, a numerical tool is proposed in the framework of bond-based peridynamics to simulate fatigue crack propagation in composite materials and structures. The cycle-dependent damage-cumulative model derived from Peerlings' law and applied to a bilinear constitutive law is used to evaluate the fatigue degradation of the bond stiffness. Several benchmark cases are studied to validate the proposed approach. Finally, static and fatigue crack propagations in composite systems with single or multi-inclusions are simulated to illustrate the capabilities and characteristics of the developed approach. This article is part of the theme issue 'Ageing and durability of composite materials'.

Residual stress influence on fatigue crack propagation of CFRP strengthened welded joints

In order to take into account the influence of welding residual stresses on fatigue crack growth, thermo-elastic-plastic finite element models of steel cruciform welded joints were developed by the ABAQUS software. The distribution and magnitude of longitudinal and transverse residual stresses were obtained in consideration of different welding currents and speeds. Uniaxial tensile fatigue tests on cracked cruciform joints strengthened with carbon fiber reinforced polymer were conducted. The coupling actions of residual stresses and fatigue loads were applied to subsequently simulate fatigue crack propagation via using the Extended Finite Element Method. Good agreement between the simulated and theoretical transverse residual stresses at the weld toe along the plate thickness direction verifies the accuracy of numerical results. The welding speed has a greater impact on residual stresses than the welding current. The stiffness ratio of carbon fiber reinforced polymer and steel plate is larger, and a better reinforcement effect will be achieved. Whether specimens repaired or not, it significantly decreases the fatigue life of cracked welded joints in the presence of residual stresses, but the fatigue crack growth trajectory is almost unchanged.

Fatigue crack propagation analysis in offshore mooring chains and the influence of manufacturing residual stresses

The main objective of this work has been the validation of a methodology to assess fatigue crack propagation in offshore mooring chains under service conditions. For this purpose, analytical Stress Intensity Factor (SIF) solutions with step-by-step application of the Paris law and the Extended Finite Element Method (XFEM) implemented in the Abaqus® 2018 software have been studied. The fatigue crack propagation analysis is divided in two stages. First, a static analysis -pre-stretch and subsequent unloading-representative of the manufacturing process is performed. Next, the fatigue crack propagation simulation is performed under simplified loading conditions and taking into account the residual stresses induced in the previous analysis. Finally, analytical solutions, numerical simulations and experimental results have been compared. Results justify the use of the Extended Finite Element Method (XFEM) for fatigue crack propagation analysis in mooring chains.

Fatigue crack propagation simulation method using XFEM with variable-node element

The extended finite element method (XFEM) with the local refinement technique using the variable-node element (VNE) is proposed to simulate the fatigue crack propagation under the cyclic loadings, in which the initially generated coarse mesh around the crack tip is refined after the crack propagation and the VNE is used to connect the refined elements and the adjacent elements. The local refine elements are used to improve the accuracy of stress near the crack tip and it is unnecessary to conform the discretization to the crack surfaces. The maximum tangential stress criterion is used to determine the crack propagation angle θc and the fatigue life is estimated by the Paris law. With this method, the condition number of the global stiffness matrix is alleviated by using the only discontinuous branch enrichment function and the crack increment size can be set flexibly and small enough to reproduce true crack path. Because only the refined mesh around crack tip is updated at each increment step during crack propagation, the simulation cost is much less than that of the method in which global fine mesh is required. Numerical examples of the crack propagation under the monotonic and cyclic loadings are given out and it is demonstrated that the proposed method can calculate the stress intensity factors (SIFs) and predict the crack paths more accurately with the local refine elements near the each crack tip. The proposed method is also suitable to simulate the crack propagation of the functional graded materials under the thermal loadings in the future works, in which the material non-homogeneity near the crack tip requires accurate modeling.

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.

An inverse method to reconstruct crack-tip cohesive zone laws for fatigue by numerical field projection

Cohesive zone failure models are widely used to simulate fatigue crack propagation under cyclic loadings, but the functional form of such phenomenological models does not have a strong micromechanical basis. While numerical techniques have been developed to extract the crack-tip cohesive zone law for monotonic fracture from experimental strain information, elucidating the unloading-reloading hysteresis representing accumulated and irreversible damage under fatigue cycling is still challenging. Here, we introduce a novel field projection method (FPM) to reconstruct the cohesive zone laws for steady-state fatigue crack growth from elastic strain field information at various loading and unloading stages within a single steady-state fatigue cycle. The method is based on the Maxwell-Betti’s reciprocal theorem, which considers the material response to be linear elastic during loading and unloading, albeit with a reciprocity gap to account for the inhomogeneous residual elastic strain accumulated at the end of each fatigue cycle. Through numerical experiments, we demonstrate that this FPM is capable of accurately extracting the crack-tip cohesive tractions and separations, along with the elusive unloading-reloading hysteresis, which constitute the cohesive zone law for fatigue crack growth. We discuss the errors and uncertainties associated with this inverse approach.

Analyses of 3D non‐planar fatigue crack propagation with smoothed particle hydrodynamics

AbstractThe present study discusses fatigue crack propagation simulation using smoothed particle hydrodynamics for nonplanar crack propagation problems in a three‐dimensional body. The algorithm for the nonplanar crack to propagate in the solid and C0 continuous crack front model, called the “chained crack front line” for the nonplanar crack, is proposed. The model is used to simulate some of the conducted experimental fatigue tests of nonplanar crack propagation. The model results matched experimental results. We conclude that the proposed method is a valuable tool in estimating the nonplanar fatigue crack propagation phenomena in actual mechanical structures.

Enhancements for technique of stable low cycle fatigue crack propagation simulation for gas turbine engine

Enhancements for technique of stable low cycle fatigue crack propagation simulation for gas turbine engine

Finite Element Simulation Technique for Evaluation of Opening Stresses Under High Plasticity

Abstract The crack closure phenomenon is important to study as it estimates the fatigue life of the components. It becomes even more complex under low-cycle fatigue (LCF) since under LCF high amount of plasticity is induced within the material near notches or defects. As a result, the assumptions used by the linear elastic fracture mechanics (LEFM) approach become invalid. However, several experimental techniques are reported on the topic, the utilization of numerical tools can provide substantial cost and time-saving. In this study, the authors present a finite element simulation technique to evaluate the opening stress levels for two structural steels (25CrMo4 and 30NiCrMoV12) under low-cycle fatigue conditions. The LCF experimental results were used to obtain kinematic hardening parameters through the Chaboche model. The finite element analysis (FEA) model was designed and validated, following the fatigue crack propagation simulation under high plasticity conditions using abaqus. Crack opening displacement versus stress data were exported from abaqus, and 1.5% offset method was employed to define opening stress levels. Numerical simulation results were compared with the experimental results obtained earlier through the digital image correlation (DIC) technique. To conclude, FEA could be a valuable tool to predict crack closure phenomena and, ultimately, the fatigue life of components. However, analysis of opening stresses using crystal plasticity models or extended finite element method (XFEM) tools should be explored for a better approximation in future studies.

Phase field simulation of fatigue crack propagation under complex load situations

Within this work, we utilize the framework of phase field modeling for fracture in order to handle a very crucial issue in terms of designing technical structures, namely the phenomenon of fatigue crack growth. So far, phase field fracture models were applied to a number of problems in the field of fracture mechanics and were proven to yield reliable results even for complex crack problems. For crack growth due to cyclic fatigue, our basic approach considers an additional energy contribution entering the regularized energy density function accounting for crack driving forces associated with fatigue damage. With other words, the crack surface energy is not solely in competition with the time-dependent elastic strain energy but also with a contribution consisting of accumulated energies, which enables crack extension even for small maximum loads. The load time function applied to a certain structure has an essential effect on its fatigue life. Besides the pure magnitude of a certain load cycle, it is highly decisive at which point of the fatigue life a certain load cycle is applied. Furthermore, the level of the mean load has a significant effect. We show that the model developed within this study is able to predict realistic fatigue crack growth behavior in terms of accurate growth rates and also to account for mean stress effects and different stress ratios. These are important properties that must be treated accurately in order to yield an accurate model for arbitrary load sequences, where various amplitude loading occurs.

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.