Simulation Of Fatigue Crack Growth Research Articles

2D fracture mechanics analysis of HFMI treatment effects on the fatigue behaviour of structural steel welds

The purpose of this paper is to present the extension of a previously developed strain-based fracture mechanics (SBFM) model from one to two dimensions for simulating fatigue crack growth in steel arc welds. The one-dimensional (1D) SBFM model is first briefly reviewed. Steps for extending it to simulate 2D growth of a semi-elliptical surface crack in a weld are then described. An application of the new model is lastly presented, which consists of analysing the behaviour of structural steel weld specimens from a previously published fatigue test program, in which the fatigue performance of weld specimens was enhanced by high frequency mechanical impact (HFMI) treatment. In this application, the effect of the treatment-induced compressive residual stress on the crack shape is simulated, and it is shown how the extended 2D SBFM model can be used to establish probabilistic design stress-life (S-N) curves for various loading conditions.

A cohesive XFEM model for simulating fatigue crack growth under various load conditions

This study presents calibration and validation of a cohesive extended finite element model for fatigue crack propagation in ductile materials. The approach relies on a separation between plasticity around the crack tip and fatigue crack growth at the crack tip such that the influence of plasticity on fatigue driving forces is predicted. This implies that characterization of crack growth requires effective Paris parameters. It is shown that the calibrated model can capture fatigue crack growth behaviour in ductile materials for in-phase and out-of-phase biaxial fatigue loading as well as in-phase biaxial loading with an overload.

An Abaqus plug-in to simulate fatigue crack growth

Fatigue crack propagation is an important consideration in evaluating the design life of engineering components, especially in the energy and transport industries. Despite its importance, fatigue analyses are not usually supported by commercial Finite Element (FE) codes; in fact, most FE codes require the addition of costly plug-ins to perform fatigue crack growth simulations. Therefore, this paper introduces a new, freely distributed plug-in to simulate fatigue crack growth with the commercial FE code Abaqus. The plug-in includes five different fatigue crack growth models and relies on the extended FE method to simulate crack propagation. The plug-in is limited to 2D analyses, but covers all necessary steps for fatigue crack growth simulations, from creating the geometry to job submission and post-processing. The implementation of the plug-in is validated by comparing its predictions to analytical and experimental results. Finally, we hope that the simplicity of the plug-in and the fact that it is distributed freely will make it a useful simulation tool for industrial, research and educational purposes.

Characterization of Surface Fatigue Crack Nucleation and Microstructurally Small Crack Growth in High Strength Aluminum Alloys

It is well established that fatigue crack nucleation and small crack growth in high strength aluminum alloys are highly influenced by the surrounding microstructure including grain boundaries, texture, inclusion barriers, among other factors. As such, specific and targeted experimental and computational methods are necessary to accurately capture and predict the discrete behavior of microstructurally small fatigue cracks. In this study, surface fatigue crack nucleation and microstructurally small crack growth in high strength aluminum alloys, commonly used in aerospace applications, are evaluated through a holistic approach encompassing fatigue testing, crack measurement, and computational prediction of crack growth rates. During fatigue testing, crack shapes and growth are quantified using a novel surface replication technique that is applied to investigate crack nucleation, as well as to collect validation data that includes an accurate description of crack shape during crack propagation, a challenging and essential component in predicting crack growth. Computational simulation of fatigue crack growth in non-straight, complex surface crack arrays typically requires high fidelity analysis using computationally expensive methods to account for the mathematical and geometrical complexities inherent in the solution. A dislocation distribution based technique has been previously demonstrated to rapidly and accurately predict the stress intensity factors for through cracks of complex shape. This method was expanded and investigated as an approach for rapidly predicting the crack growth rate of kinked and tortuous surface crack arrays, using the crack configuration and bulk material properties as inputs. To investigate the accuracy and effectiveness of this characterization approach, surface crack growth in AA7075-T7351 was experimentally analyzed and modeled under high cycle and low cycle fatigue conditions. This comprehensive approach was determined to be an expedient and applicable method for characterizing and evaluating the nucleation and crack growth rate of non-planar microstructurally small and short crack configurations.

Deterministic fatigue crack-growth simulations for a railway axle by Dual Boundary Element Method

The maintenance of railway axles requires an optimization of their inspection intervals in order to reduce costs. Such components can endure more than 30 years of service life and are subjected to scheduled Non Destructive Testing (NDT) inspections. It is therefore important to assess the influence of the severe in-service loads on the propagation of cracks in the axles. This manuscript reports deterministic fracture calculations, for the simulation of cracks propagating through a railway axle, by the Dual Boundary Element Method. Once Stress Intensity Factors along the crack front are obtained, the residual fatigue life estimates were calculated through a user made spreadsheet, taking into account the complex loading conditions of the axles. The presented results support the application of the crack propagation simulation for the determination of axle NDT intervals under different loading conditions.

Numerical study of microstructural fatigue crack growth using damage mechanics

Abstract Generally the external load applied to engineering components is significantly below the yield strength. Yet, the materials fail without showing any visible indication. Furthermore, the fatigue crack growth behavior should be observed microscopically. Thus, the microstructural study of fatigue crack growth becomes important. The microstructural study of fatigue crack growth in metals does not only demonstrate the effect of microstructural properties (grain size, grain boundary thickness, etc.) on the mechanical response of the system but also informs about a microstructural modification to resist fatigue crack growth so that fatigue life of the component can be enhanced. In the present work, fatigue crack growth simulations are performed on compact tension (CT) specimen. The microstructure region is generated near the crack tip using the Voronoi tessellation approach. Further, an in-house MATLAB code based on the finite element method and continuum damage mechanics (CDM) is implemented to perform the numerical analysis. Damage based analysis is done on the microstructure meshing system to visualize the effect of microstructural quantities (average grain size, grain boundary thickness) and material constant on the fatigue crack growth in this work. Here, the obtained result shows good agreement with the experimental result and the effect of microstructural quantities on the crack initiation life is observed.

Elasto-plastic fatigue crack growth simulation considering the shape of the crack front of SGV410 steel

Elasto-plastic fatigue crack growth simulation considering the shape of the crack front of SGV410 steel

Phase field modeling of fatigue crack initiation and growth under various loading situations

AbstractIn this work we illustrate the ability of a phase field model for fatigue crack growth in terms of extension capability to various amplitude loading and mean stress effects. The additional energy density contribution accounting for the energy associated with fatigue is modified in order to provide a more general model. Results obtained from numerical fatigue crack growth simulations are briefly presented and discussed.

A Strain-based continuum damage model for low cycle fatigue under different strain ratios

In this paper, a strain-based damage model is developed to account the effect of different strain ratios on the fatigue failure. Thereafter, continuum damage mechanics and extended finite element method based framework is proposed to simulate the low cycle fatigue crack growth simulations. The proposed damage model is imposed in the developed framework to evaluate the fatigue life of cracked specimen. Chaboche mixed hardening model is implemented to determine the stress–strain accurately in the cracked domain. The acquired stress-strains are incorporated in the proposed damage model to estimate the remaining fatigue life. The computed strain life curves at different strain ratios as well as crack growth curves are compared with the experimental results available in literature. The simulated results are found in good agreement with the experimental observations. This work ensures that the continuum damage mechanics based damage law is an excellent and readily applicable method to acquire the effect of strain ratios on the strain life. This work also provides comprehensive and significant modeling insights for computing the low cycle fatigue crack growth efficiently.

Initiation and Propagation Characteristics of Multi-Source Fatigue Crack in Superalloy Disk

The multi-source fatigue crack growth characteristics of a turbine disk were studied via high-speed rotating low cycle fatigue test, fracture analysis and crack growth simulation analysis. The results show that the fatigue initiation life N0 of Superalloy disk and its simulation parts is less dispersive and similar, and the S-N0 curve of the material is not conservative to predict the N0 of the disk. The fracture of eccentric hole of disk is multi-source fatigue fracture, and the surface characteristic of the crack L/D decreases rapidly from 7.5 to 2, which is obviously different from the single source fatigue crack growth. Because of the long and thin stress distribution at the eccentric hole and the small dispersivity of GH698 crack initiation life, it's relatively easy to crack on the plane A of the eccentric hole, which is prone to multi-source fatigue. At the stage of a ≥ 1.23 mm, the reverse life of crack propagation fracture of 2# and 5# eccentric holes is consistent, and the error between the simulation value of single source fatigue crack propagation life and the reverse life is below 5%. In the stage of 0.61 mm ≤ a < 1.23 mm, the simulation crack growth rate of 5# eccentric hole of multi-source is close to that of fracture inversion. Accurate simulation analysis of multi-source crack growth needs to define the initial crack accurately, at the same time, consider the influence of existing fatigue damage on crack growth.

Stochastic approach to fatigue crack-growth simulation for a railway axle under input data variability

Fatigue crack-growth of mechanical components is stochastic in nature and deterministic approaches do not allow for its complete study. Primary sources of this stochasticity can be: the inherent variability of material properties, the nature of service load fluctuations, the approximations assumed by the algorithms to calculate the main fracture parameters.This work reports a stochastic approach to the fatigue crack-growth in a railway axle under variability of different input parameters. The approach is used to predict the probability distribution of the residual fatigue life of a railway axle in presence of defects taking into account multiple sources of uncertainty.

An incremental elastic–plastic triaxiality dependent fatigue model

A stress-state dependent cyclic cohesive model, which accounts for accumulation of plasticity, during both tensile as well as compressive deformations, and incorporates accumulation of irreversible damage due to macroscopic plasticity as well as microstructural mechanisms, is formulated. The model is implemented in mode-I plane strain fatigue crack growth simulations. The model is validated by reproducing the effect of retardation in crack growth rates after different combinations of tensile and compressive overloads. We show accurate description of the elastic–plastic behaviour of the process zone is vital, in particular for negative stress ratios subsequent to a tensile over-load, as considerable plasticity occurs in compression at the crack-tip, significantly reducing retardation effects.

Fatigue crack growth simulation of interacting multiple cracks in perforated plates with multiple holes using boundary cracklet method

AbstractIn this study, the recently developed boundary cracklet method (BCM) is used to model the fatigue crack propagation (FCP) in complex geometries in two‐dimensional domain. Several benchmark examples of FCP are analysed to show the effectiveness of BCM. Calculated stress intensity factors and crack paths show good agreement with reference studies. BCM is further used to simulate the multiple cracks interaction in a perforated plate with multiple holes having different cases of precracks emanating from edges of the plate and outer periphery of holes under fatigue loading. FCP is assumed to follow Paris–Erdogan law, and the maximum tangential stress criteria are used to predict the direction of propagation in each step. Moreover, to describe the computational efficiency of a numerical method in fatigue problems, a new parameter is introduced: Yavuz's fatigue computational efficiency factor (YCF), which is the number of computed million cycles per hour (CPU time).

Fatigue surface crack growth behavior in flat plate and out-of-plane gusset-welded joints under biaxial cyclic loads with different phases

Although many in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading, their structural integrities are evaluated according to design codes based on theoretical and experimental investigations under uniaxial loading conditions. Additionally, most of these codes implement the S–N curves approach. This study highlights the biaxial cyclic loading with different phases. The fracture mechanics approach toward fatigue life evaluation can obtain the fatigue crack growth history. This paper confirms the applicability of the previously proposed numerical simulation method for obtaining the fatigue crack propagation histories of a cracked plate subjected to biaxial loads with a phase difference for each loading component. A fracture mechanic approach was used to establish the proposed method. The fatigue surface crack growth behavior of a flat plate and an out-of-plane gusset-welded joint under biaxial cyclic loadings with different phases was investigated by extending the applicability of the proposed method to a through-thickness crack. Comparisons between the measured crack evolution and the numerical simulation results were carried out to validate our fatigue crack growth simulation for flat plane and welded joints.

Fatigue crack growth material parameters- based on prototype pipe bend test and comparison with conventional parameters

An experimental study has been performed on a representative prototype-sized pipe bend made of SS 316 LN material to generate the relevant material parameters required for fatigue crack growth (FCG) simulation. Traditionally, FCG numerical simulation material parameters are generated based on specimen level test. In the literature there are many prototype pipe bend test results can be found. However, this paper takes a new look for generating FCG material parameters based on prototype-sized pipe bend test results.A semi-elliptical shaped pre-cracked pipe bend is used for the crack growth studies. Advancement of the crack profile has been measured in a periodic interval of cyclic testing, and the essential crack dimensions are derived to extract the FCG material parameters. FCG response curve derived, based on the prototype sized pipe bend test result, is well below the similar response curve obtained from the conventional material properties. The major reason behind this difference in FCG response is attributed to the influence of the residual stress locked during pipe bend fabrication. Based on these findings, it is recommended to adopt the material parameters derived based on the component-level test for more accurate prediction. Further studies are required to generalise the role of fabrication assisted effects in the material parameters in the case of prototype sized components.

A phase field modeling approach of cyclic fatigue crack growth

Phase field modeling of fracture has been in the focus of research for over a decade now. The field has gained attention properly due to its benefiting features for the numerical simulations even for complex crack problems. The framework was so far applied to quasi static and dynamic fracture for brittle as well as for ductile materials with isotropic and also with anisotropic fracture resistance. However, fracture due to cyclic mechanical fatigue, which is a very important phenomenon regarding a safe, durable and also economical design of structures, is considered only recently in terms of phase field modeling. While in first phase field models the material’s fracture toughness becomes degraded to simulate fatigue crack growth, we present an alternative method within this work, where the driving force for the fatigue mechanism increases due to cyclic loading. This new contribution is governed by the evolution of fatigue damage, which can be approximated by a linear law, namely the Miner’s rule, for damage accumulation. The proposed model is able to predict nucleation as well as growth of a fatigue crack. Furthermore, by an assessment of crack growth rates obtained from several numerical simulations by a conventional approach for the description of fatigue crack growth, it is shown that the presented model is able to predict realistic behavior.

A modified three-dimensional virtual crack closure technique for calculating stress intensity factors with arbitrarily shaped finite element mesh arrangements across the crack front

To obtain accurate stress intensity factors (SIFs) with arbitrarily shaped finite element mesh arrangements across the crack front, a modified three-dimensional virtual crack closure technique (modified 3D-VCCT) is proposed in this paper. This method is based on three-dimensional virtual crack closure technique (3D-VCCT) and finite element method. To increase the SIFs calculation accuracy for the crack with arbitrary shape, the length and shape of finite element meshes across the crack front are considered in this method. Then the SIFs with arbitrarily shaped finite element mesh arrangements across the crack front are calculated by three different methods, the modified 3D-VCCT in this paper, the extension of virtual crack closure-integral method proposed by Okada and the 3D-VCCT. The solutions of SIFs obtained by three methods are compared and the comparison results show the modified 3D-VCCT has better accuracy with arbitrarily shaped finite element mesh arrangements across the crack front. In addition, the simulations of fatigue crack growth are carried out by using the modified 3D-VCCT. Then the simulation results are compared with the test results, which shows good agreement.

Effect of residual stress redistribution and weld reinforcement geometry on fatigue crack growth of butt welded joints

Redistribution of residual stress during crack growth in butt welded joint of Al5083-H111 was studied. Furthermore, the effect of post weld heat treatment and removing the weld reinforcements on fatigue crack growth rate was investigated. Three dimensional simulations of welding process and fatigue crack growth were conducted. It was shown that removing the weld reinforcements causes an increase in the residual stress. A correlation between the fatigue crack growth rate data of welded joints can be obtained with that of the parent metal by considering the weld geometry and redistribution of residual stresses in calculation of stress intensity factor.

Numerical simulation of fatigue crack growth based on accumulated plastic strain

Fatigue crack growth (FCG) is simulated here by node release, which is made when the accumulated plastic strain reaches a critical value. The numerical procedure is very robust, showing a very fast stabilization and independence relatively to the load considered for node release. A critical accumulated plastic strain of 110% was obtained for the 2024-T351 aluminium alloy, comparing the experimental value of da/dN for a crack length of 26.5 mm and a stress ratio of 0.1, with plane strain numerical predictions. This critical value was used to predict da/dN for different crack lengths. The da/dN-ΔK curve was found to be linear in log-log plot with a slope m = 2.4, which is lower than the slope m = 3.6 presented by the experimental results. The difference is attributed to crack tip mechanisms activated at relatively high loads. The variation of stress ratio and stress state did not affect the da/dN-ΔK curves, which indicates that the effect of these parameters is not linked to crack tip plastic deformation. FCG rate was also predicted for the 7050-T6 aluminium alloy and the 18Ni300 maraging steel, and slopes m = 3.09 and 2.70, respectively, were obtained for da/dN-ΔK curves. The predictions obtained for the steel agreed well with experimental results.

Structural integrity assessment of floating offshore wind turbine support structures

Floating offshore wind turbines are becoming more attractive to the wind industry due to their capability to operate larger turbines in deeper waters. The floating support structures are anchored to the seabed via mooring chains to impede the structure's unwanted movements. The combination of cyclic stresses and the corrosive marine environment makes the floating support structures vulnerable to corrosion pitting and subsequently fatigue crack initiation and propagation. In this study a framework is proposed to simulate fatigue crack growth from multiple corrosion pits at critical spots of the Spar-type floating support structures to examine the status of the crack during several years of operation. The proposed advanced fracture mechanics based approach provides a methodology to assess the integrity of the structure and subsequently plan for preventive or curative maintenance. The crack growth rate is examined for both singular and multiple cracks at different R ratios and for different stress levels using ABAQUS XFEM. Following numerical simulations, a sensitivity analysis is carried out using Crackwise software for different values of plate thickness, R ratio and initial crack size. The numerical results are discussed in terms of the corrosion pitting effects on fatigue life assessment of floating offshore wind turbines.