Simulation Of Fatigue Crack Growth Research Articles

Effect of KIII on Fatigue Crack Growth Behavior

In this study, mixed-mode fatigue tests are conducted using surface-cracked specimens. Slant surface-cracked specimens are prepared with crack angles of 15 deg, 30 deg, 45 deg, and 60 deg. It is shown that a “factory roof” fracture is formed at the deepest point of the surface crack due to ΔKIII and causes the crack growth rate to decrease. Additionally, fatigue crack growth is simulated using the superposition finite element method (FEM) with crack growth criteria. It is shown that conventional crack growth criteria are not applicable to factory roof fractures. Finally, a modified criterion for the prediction of crack growth rate is proposed, fatigue crack growth simulation is conducted using this criterion, and the results are compared with experimental results.

Two-stage planar approximation of non-planar crack growth

Mechanical components subject to multiaxial variable amplitude loading may experience non-planar crack growth, which usually requires three dimensional finite element analyses for high fidelity simulation of non-planar fatigue crack growth. This is computationally expensive and prohibits recurrent use of high fidelity models in further probabilistic life prediction analysis. This paper presents an efficient and accurate two-stage approach for planar approximation of non-planar crack growth that reduces the computational effort. In this method, the non-planar crack is first approximated using an equivalent planar crack. Then, using the equivalent representation, planar crack growth analyses designed to account for uncertainty in crack growth are conducted. The proposed methodology employs two surrogate models: the first surrogate model is trained using 3-D simulations of non-planar fatigue crack growth to capture the relationship between the applied load history and equivalent planar crack orientation. The second surrogate model is trained using planar crack growth simulation to calculate the stress intensity factor as a function of crack size, crack orientation, and load magnitude for use in planar crack growth analysis. Individual predictions of the two surrogate models, as well as their combined predictions are verified for accuracy using full 3-D finite element simulations. The verified two-stage approach is then demonstrated in an illustrative example of uncertainty quantification in 3-D crack growth prediction in a mechanical component similar to a rotorcraft mast.

Fretting fatigue crack growth simulation based on a combined experimental and XFEM strategy

A combined experimental and numerical study is presented in order to predict fretting crack propagation. It rests on 2D and 3D fretting tests, with carefully controlled loading conditions leading to cracking as the main material response, the extraction of 2D and 3D crack geometry from post-mortem cross-sections, a three-dimensional X-FEM model based on a three field weak formulation accounting for 3D non-planar frictional crack and the level set formalism authorising a direct use of actual reconstructed crack shape, the stress intensity factors quantification, a mixed mode Paris law identification and finally the crack growth simulation. The 2D fretting tests are numerically simulated. The mixed mode crack growth law identified is then used to simulate the fretting crack growth. A very good agreement with experimental results is obtained. Then 3D fretting tests are simulated and the crack fronts are compared with actual ones.

피로균열성장의 유한요소 시뮬레이션: Paris 법칙의 지수 m의 결정

The finite element simulations of fatigue crack growth are carried out. Using only the mechanical properties usually obtained from the tensile test as input data, we attempted to predict the fatigue crack growth behavior. The critical crack opening displacement is determined by monitoring the change in displacements at the node close to the crack tip. Crack growth is simulated by debonding the crack tip node. The exponent in the Paris law was determined and compared to the published exponent. Plotting with respect to the effective stress intensity factor range yielded more consistent results.

Fatigue Crack Growth in a Solid Circular Shaft Under Fully Reversed Rotating Bending

The axle of a load train failed after 5.37 × 106 cycles from its service. Macro-fractography showed clearly the fatigue fracture. The stress distribution in the shaft revealed that the maximum alternating stress was considerably less than the material modified fatigue limit obtained at 107 cycles from the S–N diagram. Micro-fractography reported from the metallurgical laboratory proved the existence of a surface flaw. Ultimately, fatigue crack growth simulation was performed based on the simple Paris–Erdogan model for estimating the fatigue life of the defective axle. The results showed that the actual life of the axle could be satisfactorily predicted by means of the Paris–Erdogan model.

Erratum to: A procedure for the simulation of fatigue crack growth in adhesively bonded joints based on the cohesive zone model and different mixed-mode propagation criteria

Erratum to: A procedure for the simulation of fatigue crack growth in adhesively bonded joints based on the cohesive zone model and different mixed-mode propagation criteria

Study of an On-Line Crack Compliance Technique for Residual Stress Measurement Using 2D Finite Element Simulations of Fatigue Crack Growth

Abstract There are several methods available to measure residual stress fields present within a structural component. Recently a new so called on-line crack compliance technique has been proposed, which is based on linear elastic fracture mechanics. This experimental method uses incremental crack mouth opening displacements measured during fatigue crack growth testing to generate information on the existing residual stresses along the crack line. The present study employs two dimensional (2D) plane stress finite element simulations of fatigue crack growth from a cold worked hole to investigate the performance of this technique. Using the simulation results, the stress intensity factors due to the residual stress field normalized by the maximum applied stress intensity factor KIrs/KImax were obtained from the on-line crack compliance method. For validation, the J-integral approach was used to calculate KIrs/KImax values from fatigue crack growth simulations in an elastic material. The two methods generated nearly identical results. Fatigue crack growth was also simulated in an elastic-plastic material. Even though the stress intensity factor is not the appropriate crack tip characterizing technique for elastic-plastic material conditions, it is still investigated here to approximate the actual testing conditions, where plastic deformation near the crack tip is unavoidable. The KIrs/KImax solutions are presented for different cold work levels and applied loadings. Results indicate that the agreement between the elastic and elastic-plastic crack growth solutions is dependent on the maximum applied loading level, as might be expected.

Life Prediction of Aluminum Alloy Structure Subjected to Corrosion Fatigue and Corrosion Damage

The strength of the aging structure deteriorates mainly as a result of corrosion and fatigue damage. In this paper, the life prediction methods of corroded and corrosion fatigued aluminum alloy structure were proposed. The stress multiplication of aluminum alloy structure subjected to corrosion damage was simulated by ANSYS software. We proposed the AFGROW software simulation method to predicate the numerical simulation of corrosion fatigue crack growth. At last, the life cycles of structures subjected to corrosion damage and corrosion fatigue were estimated, and a very good performance of the proposed methods are achieved after validation with the experimental data.

Fatigue-life estimation of functionally graded materials using XFEM

The present work deals with the fatigue crack growth simulation of alloy/ceramic functionally graded materials (FGMs) using extended finite element method (XFEM). Various cases of FGM containing multiple inhomogeneities/discontinuities along with either a major edge or a center crack are taken for the purpose of simulation. The fatigue life of the FGM plate is calculated using Paris law of fatigue crack growth under cyclic loading. The effect of multiple inhomogeneities/discontinuities (minor cracks, holes/voids, and inclusions) on the fatigue life of cracked FGM plate is studied in detail. These simulations show that the presence of inhomogeneities/discontinuities in the domain significantly influences the fatigue life of the components.

Simulations of fatigue crack growth by blunting–re-sharpening: Plasticity induced crack closure vs. alternative controlling variables

Finite-deformation elastoplastic analysis of plane-strain crack subjected to mode I cyclic loading with constant amplitude at various load ranges and ratios, as well as with solitary over- and under-load cycles, is presented. The Laird-Smith mechanism of crack advance by cyclic blunting and re-sharpening, which transfers material from the crack tip towards its flanks, is visualised. In the present modelling, crack closure has never been detected. As well, the supposed origin of plasticity induced crack closure (PICC), which is habitually attributed to filling-in a crack with material stretched out of the crack plane behind the tip, is ruled out. Nevertheless, the rate of simulated fatigue crack growth (FCG) by blunting–re-sharpening reproduces the key experimental trends concerning the effects of ΔK and single over-/under-load peaks. Calculated compliance curves are bent in spite of the absence of PICC, which raises the doubt about their trustworthiness as the means of the crack closure detection and assessment. This way, performed modelling manifests ambiguities concerning PICC as the universal intrinsic factor able to control FCG ubiquitously. On the other hand, having PICC absent, calculated near-tip stress–strain responses, being driving forces of fatigue damage and crack advance by bond-breaking, manifest affinities with the experimental FCG trends without intervention of PICC, too. This implicates both independent parameters of crack-tip cyclic loading under small scale yielding, such as the couple Kmax and Kmin, or Kmax and ΔK, or other equivalent one, as the indispensable variables that drive FCG directly without mediation of PICC.

Fatigue crack growth in real structures

Components and structures are usually constructed according to strength principles. Fatigue crack growth in components and fracture of structures consistently occur due to, e.g. high local stresses, material and manufacturing defects. The following article deals with different examples of crack growth in real structures. These examples shall exemplify learning from damages and consequently preventing failure of components and structures in the future. Furthermore a simulation method is presented to simulate fatigue crack growth in any three-dimensional structures.

Finite element based simulation of fatigue crack growth with a focus on elastic–plastic material behavior

The numerical crack growth simulation has become more and more attractive today for reasons of time and economy. The presentation of a procedure for such a simulation of fatigue crack growth in elastic–plastic materials is the aim of this paper. The remeshing of the structure and the subsequent mapping of the status variables from the old mesh to the new one after each step of crack advance are thereby the core characteristics of the proposed procedure. The crack growth life is determined by integration of a crack growth law which is based on the effective range of the stress intensity factor. The results obtained by the procedure for autofrettaged Diesel-engine injection tubes are compared with experimental results and finite element results based on a nodal release scheme. A good agreement between the two numerical analyses and between the results with the proposed procedure and the experimental results concerning the endurance limit can be stated. By looking at the fatigue lives the experimental results are underestimated by the numerical ones.

ケミカルタンカーに使用されるオーステナイト系ステンレス鋼板の疲労強度に関する一考察

Authors investigate the fatigue crack propagation behavior of solid austenitic stainless steels SUS304L, SUS316L and SUS316LN in order to conduct the characteristics of fatigue behavior of each stainless steel. Not only the constant stress amplitude tests, but also the load decreasing tests called by ΔKth test regulated by ASTM E647 are performed to identify the material constants of fatigue crack propagation. Comparison of the fatigue crack growth behavior of SUS304L, SUS316L and SUS316LN with mild steels is also performed. Authors also investigate the fatigue life of load-carrying type cruciform joints of austenitic stainless steels,which are modeled upon the lower end of vertically corrugated bulkhead of chemical tankers. Besides, the possibility of quantitative numerical simulation of the fatigue crack propagation for the stainless steels is also investigated. This simulation procedure applies for the advanced effective stress intensity factor range based on a Re-tensile Plastic zone Generation (RPG) load and the fatigue crack closure phenomenon is quantitatively considered. The experimental results are compared with the numerical simulation results in this study and the validity of fatigue crack growth simulation procedure applied in this study is confirmed.

Development of stress intensities for cracks in FGMs with orientation perpendicular and parallel to the gradation

Within this paper the development of stress intensities for cracks in functionally graded materials is addressed. Thereby crack orientations perpendicular as well as parallel to the gradation are under consideration. Those gradations basically produce two different types of changes with respect to a homogeneous and isotropic case, namely changes in the magnitude of the stress intensity (which impacts the lifetime of a structure) and changes in the mode mixity (which impacts the crack path). It will be quantified, in which way both changes depend on the mismatch ratio between the involved materials or on the slope of the gradient, respectively. Additionally the paper will focus on the issue of approximating a continuous gradient by means of sections with piecewise constant material behavior. It will be shown, that even a relatively small number of sections will be able to reasonably model a gradient region during a fatigue crack growth simulation.

Simulation of fatigue crack growth under consideration of cyclic plasticity

AbstractIn this paper a procedure to simulate the crack growth under consideration of elastic‐plastic material behavior by means of the finite element method is described. Within this procedure, after each increment of crack advance, the structure is remeshed and the status variables, such as the components of the backstress‐tensor and the plastic strains, are transferred from the old mesh to the new one. Due to mapping of the variables, improper conditions are possibly prevailing at the beginning of the new analysis, which has to be captured by the used material routine. The main focus of this paper is to describe these necessary numerical adjustments.

Integration of structural health monitoring and fatigue damage prognosis

This paper presents a Bayesian probabilistic methodology to integrate model-based fatigue damage prognosis (FDP) with online and offline structural health monitoring (SHM) data. The prognosis uses fracture mechanics-based fatigue crack growth modeling, along with quantification of various sources of uncertainty, including natural variability, data uncertainty and model errors. These uncertainty sources are connected using a Bayesian network and a probabilistic sensitivity analysis is performed to assess the uncertainty contributions from these sources. The cycle-by-cycle simulation of fatigue crack growth is expedited via the use of a surrogate modeling technique (Gaussian process model) to replace computationally expensive finite element analysis. Real-time monitoring data of external variable amplitude loading history is used to construct a Bayesian autoregressive integrated moving average (ARIMA) model to predict and update the loading. On-ground crack inspection data is used to quantify the uncertainty in the initial and current size of an existing crack, using the Bayesian approach. Three possible cases of inspection results are considered: (1) crack is not detected; (2) crack is detected but not measured; (3) crack is detected and measured. Different scenarios of data availability (load monitoring data and inspection data) are considered for the prognosis of an individual component in a fleet. A numerical example, surface cracking in a rotorcraft mast under service loading, is implemented to illustrate the proposed methodology. The results of prognosis are validated using Bayesian hypothesis testing.

Numeric Simulation of Fatigue Crack Growth in a Material Graded Structure

This article deals with the development of functional graded materials which is pursued by the collaborative research centre Transregio 30. The functional gradation is produced by a thermo-mechanical production process and is characterized by different fracture mechanical specific values. Because cracks are by all means responsible for failure of structural elements crack growth has to be considered during the development of these materials. In this contribution simulations of crack growth which were carried out with the system ADAPCRACK3D are presented to illustrate the influence of a material gradation on crack growth.

Fatigue Crack Growth Simulation in Railway Axles

In order to carry out the railway axle design according to the “Damage Tolerance” philosophy, reliable crack-growth models for these kind of components are necessary. Indeed, damage tolerance principles have received more and more attention from railway technical community, thanks to its ambitious task concerning the inspection intervals prevision of railway components subjected to non-stationary loading conditions. In this paper, a simple routine is exposed that is able to calculate the characteristic parameters of the Linear Elastic Fracture Mechanics (LEFM) for a generic cracked mechanical component. Such parameters are then used in a two parameters propagation law to estimate the necessary time for a crack to become critical.

Numerical Simulation of Multiple Fatigue Crack Growth with Additional Crack Initiation

In this paper, advanced numerical simulations of curved crack growth in the case of mul­tiple crack systems in combination with the analysis of the plastic limit load by the lower bound theorem of plasticity are presented. In order to take additionally initiated cracks during the crack growth process into account, the numerical simulation algorithm has been extended by using the Smith-Watson-Topper (SWT) parameter in combination with a linear fatigue damage accumula­tion.

Application of the dissipated energy criterion to predict fatigue crack growth of Type 304 stainless steel following a tensile overload

This paper presents the results of numerical simulations of fatigue crack growth performed using three-dimensional elastic–plastic finite element analysis. A simple node release scheme is used to simulate crack advancement. The crack front is assumed to be straight. Crack growth following a tensile overload is simulated. The total energy dissipated per cycle is calculated directly from the finite element analysis and used to predict fatigue crack growth. For comparison, fatigue crack growth rate experiments were performed on Type 304 stainless steel C( T) specimens to determine the effect of a single tensile overload. The dissipated energy per cycle is found to correlate well with the measured fatigue crack growth rate following an overload.