Fatigue Crack Growth Analysis Research Articles

Fatigue crack growth analysis of drill pipes during rotary drilling operations by the multiple reference state weight function approach

Abstract Drill-string fatigue failures are the most common and costly type of failures in Oil & Gas and Geothermal drilling operations. However, the drilling industry currently does not have a means of quantitatively evaluating drill-pipe fatigue fife. The aim of the present study is to fill this gap, providing a rapid and easy means of accurately obtaining drill-pipe fatigue life estimates. The geometry considered is the passage of a drill-pipe through a dogleg. It is characterised by a load combination of tension and bending while undergoing rotation. This load–geometry combination is taken as representative of the present-day drilling. The Stress Intensity Factors along the crack front of a semi-elliptical internal crack in a drill-pipe are obtained by means of Multiple Reference States Weight Function approach that is then implemented in a developed MATLAB code. The developed computer code is validated by comparison with data available in the literature and then applied to the geometry of interest. The Stress Intensity Factors thus obtained are then inserted in the Paris Fatigue Crack Growth Model to quantitatively evaluate the drill-pipe fatigue life. Finally, a parametric study is performed in order to identify the influence of load magnitudes, dogleg, crack shape and geometrical parameters on the fatigue life. A detailed discussion of all these effects concludes the paper. It is the contention of the authors that the method can be easily, rapidly and successfully extended to other oilfield tubulars.

Fatigue crack growth analysis of steel elements reinforced with shape memory alloy (SMA)/fiber reinforced polymer (FRP) composite patches

This paper describes a numerical framework to simulate the fatigue crack growth of single edge-notched steel elements patched with shape memory alloy (SMA)/fiber reinforced polymer (FRP) composite patches. The framework includes the small crack propagation. The small crack propagation stage was simulated using the analytical model based on the equivalent initial flaw size method. The bridging effects of the SMA/FRP composite patch were simulated by two consecutive finite element simulations considering the interfacial debonding during fatigue loading. Numerical predictions were validated by comparison with experimental results. A parametric study was conducted using the validated model. The considered parameters were the number of SMA wires used in the patch, the applied stress range, and the length of the crack in the steel substrate at the time of installing the patch. The numerical results indicated that the SMA wires increased the critical crack length at which fracture occurred and that the patch was more effective at lower stress ranges. Further, the SMA/FRP patch can substantially delay the failure of a member with very little remaining fatigue life. The results demonstrate the potential of this technique and highlight the importance of early intervention when repairing fatigue sensitive details.

Fatigue crack growth in cruciform welded joints: Influence of residual stresses and of the weld toe geometry

The aim of the present investigation is to calculate the fatigue life of cruciform welded joints by taking into account both the effect of residual stresses and the influence of the weld toe geometry. Two and three dimensional finite element models, with cracks as initial defects, will be constructed for this purpose. Fatigue crack growth analyses are performed by using the node release technique, together with the finite element program ABAQUS. The welding residual stresses, as well as the plasticity induced crack closure effects, are considered. The effective cyclic J-integral (ΔJeff) is used as crack tip parameter in a relation similar to the Paris equation for the calculation of the fatigue life. For this purpose, a specific code was written for the determination of ΔJeff at each crack length configuration. The impact of residual stresses on ΔJeff as well as on the fatigue life during short crack growth is investigated. Results reveal that the influence of residual stresses can be neglected only for large load amplitudes. The calculated fatigue lives are compared with experimental data and a good accordance between both results is achieved. The influences of the weld toe radius and of the weld flank angle are also investigated.

Oprogramowanie do numerycznej analizy wzrostu pęknięcia zmęczeniowego za pomocą modelu semi-Markowa

Oprogramowanie do numerycznej analizy wzrostu pęknięcia zmęczeniowego za pomocą modelu semi-Markowa

An Artificial Neural Network-Based Algorithm for Evaluation of Fatigue Crack Propagation Considering Nonlinear Damage Accumulation.

In the aerospace and aviation sectors, the damage tolerance concept has been applied widely so that the modeling analysis of fatigue crack growth has become more and more significant. Since the process of crack propagation is highly nonlinear and determined by many factors, such as applied stress, plastic zone in the crack tip, length of the crack, etc., it is difficult to build up a general and flexible explicit function to accurately quantify this complicated relationship. Fortunately, the artificial neural network (ANN) is considered a powerful tool for establishing the nonlinear multivariate projection which shows potential in handling the fatigue crack problem. In this paper, a novel fatigue crack calculation algorithm based on a radial basis function (RBF)-ANN is proposed to study this relationship from the experimental data. In addition, a parameter called the equivalent stress intensity factor is also employed as training data to account for loading interaction effects. The testing data is then placed under constant amplitude loading with different stress ratios or overloads used for model validation. Moreover, the Forman and Wheeler equations are also adopted to compare with our proposed algorithm. The current investigation shows that the ANN-based approach can deliver a better agreement with the experimental data than the other two models, which supports that the RBF-ANN has nontrivial advantages in handling the fatigue crack growth problem. Furthermore, it implies that the proposed algorithm is possibly a sophisticated and promising method to compute fatigue crack growth in terms of loading interaction effects.

An experimental investigation of propagation the semi-elliptical surface cracks in an austenitic steel

This paper presents the results of experimental studies of propagation of the semi-elliptical cracks in 1.4541 austenitic steel commonly used for the construction of the industrial pipelines. The work includes the results of studies of the structure and mechanical properties of 1.4541 steel used to build new pipeline sections and steel after many years of service. Fatigue crack growth analysis was performed by using the method of electrical potential drop (EPD). In order to confirm correctness of the electrical potential drop measurement method a two other experimental methods were used in comparative studies, staining of fatigue fracture and using a strain propagation gauge. Elaborated EPD measurement methodology enables a continuous recording of the dimensions of propagating semi-elliptical cracks, both under variable tension and under constant bending, which was confirmed during the tests.

Fatigue crack growth analysis in layered heterogeneous material systems using peridynamic approach

In this study, the peridynamic fatigue model for a homogeneous material is extended to the layered heterogeneous material. Thermal residual stress and the corresponding stress intensity factor are calculated, within the framework of the peridynamic theory, by considering the cooling process using a pairwise force function caused by the thermal loading effect. To avoid overlapping of the cracked surfaces due to compressive thermal residual stress, the notion of short range force (Macek and Silling, 2007) is newly introduced. In addition, an auxiliary reference configuration is used to define the cyclic bond strain in the constricted material. The proposed approach is validated by performing an illustrative case study.

Fatigue crack growth analysis of an interfacial crack in heterogeneous materials using homogenized XIGA

In this work, the fatigue life of an interfacial cracked plate is evaluated in the presence of flaws by homogenized extended isogeometric analysis (XIGA). In XIGA, the crack faces are modeled by discontinuous Heaviside jump functions, whereas the singularity in the stress field at the crack tip is modeled by crack tip enrichment functions. Holes and inclusions are modeled by Heaviside function and distance function respectively. The discontinuities are modeled in a selected region near the major crack whereas the region away from the crack is modeled by an equivalent homogeneous material. The stress intensity factors (SIFs) for the interface cracks are numerically evaluated using the domain based interaction integral approach. Paris law of fatigue crack growth is employed for computing the fatigue life of an interfacial cracked plate. The results show that the defects/ discontinuities away from the main crack barely influence the fatigue life.

Numerically efficient modified Runge–Kutta solver for fatigue crack growth analysis

We present a modified Runge–Kutta algorithm which yields a conservative estimate of the crack size for fatigue crack growth even for large integration step sizes. Conservative in this context means to overestimate the crack size. Commonly used algorithms (e.g. Euler, Runge–Kutta) usually underestimate the crack growth and only converge for small step sizes to an accurate value. As the presented algorithm overestimates the crack growth even for large and converges for small integration step sizes, it can be used for instance in Monte-Carlo based probabilistic fracture mechanics simulations, which might be otherwise computational impractical.

Analysis of Fatigue Crack Growth in Ship Structural Details

Abstract Fatigue failure avoidance is a goal that can be achieved only if the fatigue design is an integral part of the original design program. The purpose of fatigue design is to ensure that the structure has adequate fatigue life. Calculated fatigue life can form the basis for meaningful and efficient inspection programs during fabrication and throughout the life of the ship. The main objective of this paper is to develop an add-on program for the analysis of fatigue crack growth in ship structural details. The developed program will be an add-on script in a pre-existing package. A crack propagation in a tanker side connection is analyzed by using the developed program based on linear elastic fracture mechanics (LEFM) and finite element method (FEM). The basic idea of the developed application is that a finite element model of this side connection will be first analyzed by using ABAQUS and from the results of this analysis the location of the highest stresses will be revealed. At this location, an initial crack will be introduced to the finite element model and from the results of the new crack model the direction of the crack propagation and the values of the stress intensity factors, will be known. By using the calculated direction of propagation a new segment will be added to the crack and then the model is analyzed again. The last step will be repeated until the calculated stress intensity factors reach the critical value.

A Hydrogen-Induced Decohesion Model for Treating Cold Dwell Fatigue in Titanium-Based Alloys

Cold dwell fatigue in near-alpha Ti alloys is a time-dependent fracture process at ambient temperature that involves fatigue in the presence of creep to produce cracking on low-energy fracture (e.g., cleavage) facets in hard alpha grains. In this article, cold dwell fatigue is treated as a hydrogen-induced decohesion process by using a nonlinear cohesive stress-strain relation to describe the decrease in the cohesive strength with increasing local hydrogen contents. It is postulated that during cold dwell fatigue, time-dependent deformation occurs by 〈a〉 slip that results in dislocation pileups in soft alpha grains. The stress and dilatational fields of the dislocation pileups assist the transport of internal hydrogen atoms from soft grains to neighboring hard grains. The accumulation of internal hydrogen atoms at the trap sites leads to decohesion along crystallographic planes, which can be slip or hydride habit planes. The decohesion model is applied to treat cold dwell fatigue in Ti-6Al-4V with a basal-transverse texture by modeling the effects of hydrogen-induced decohesion on the stress-fatigue life (S-N f) response, the time-dependent crack growth response (da/dt), and the fracture toughness (K c) as functions of grain orientation. A probabilistic time-dependent fatigue crack growth analysis is then performed to assess the influence of microtexture on the dwell fatigue life of a Ti-6Al-4V ring disk subjected to a long-duration hold at the peak stress of the loading cycle. The results of the probabilistic life computations indicate that dwell fatigue resistance in Ti-6Al-4V may be improved and the risk of disk fracture may be reduced significantly by controlling the microtexture or reducing the size and volume fraction of hard alpha grains in the microstructure.

A robust stress analysis method for fatigue life prediction of welded structures

In the case of structural weldments, the procedure for estimating fatigue life requires information concerning geometry of the object, loads, and material. Detailed knowledge of stress fields in the critical regions of weldments is used to determine the fatigue life. The main theme of the research discussed in this paper is to provide details of the methodology which has been developed to determine the peak stress and associated non-linear through-thickness stress distribution at the critical weld toe crack plane by using only the geometry-dependent stress concentration factors along with appropriate unique reference stress calculated in an efficient manner, e.g., without modeling geometrical weld toe details. The peak stress at the weld toe can be subsequently used for estimating the fatigue crack initiation life. The non-linear through-thickness stress distribution and the weight function method can be used for the determination of stress intensity factors and for the analysis of subsequent fatigue crack growth. Accurate peak stress estimation requires 3D fine mesh finite element (FE) models, accounting for the micro-geometrical features, such as the weld toe angle and weld toe radius. Such models are computationally expensive and therefore impractical. On the other hand, stresses at the sharp weld corners obtained from 3D coarse FE meshes are inaccurate and cannot be used directly for fatigue life estimations. This paper describes a robust, sufficiently accurate, and efficient stress analysis method for fatigue life estimation of welded structures based on 3D FE coarse mesh models. Another objective is to establish a methodology which is capable of accounting for the actual variability of stress concentration factors at welds, welding defects such as misalignment, and incomplete penetration resulting from the manufacturing process. The methodology described in the paper has been validated by analyzing several weldments of varying geometrical and load configurations. The proposed methodology not only reduces conservative fatigue design of welded structures but also leads to significant savings concerning modeling and computation efforts.

Stochastic fatigue crack growth analysis of metallic structures under multiple thermal–mechanical stress levels

This paper proposes an analytical–empirical framework for stochastic assessment of fatigue crack growth. The study offers solutions for drastic problems in studying fatigue field including dispersion and scarcity of fatigue data, and impact of several factors on fatigue crack growth. The research composes of two complementary phases. The first phase analyses the behavior of fatigue models under probabilistic conditions. The propagation of uncertainty is studied in fatigue models in this phase under cyclic loads. The research is based on two fundamental deterministic fatigue models: Walker and Forman correlations. The second phase employs probabilistic distributions for stochastic assessment of fatigue crack growth. A new approach is introduced to simulate fatigue crack growth stochastically under the effects of different variables through combining lognormal distribution and stress life models. Bayesian approach is applied for parameter estimation. The final presented models offer the ability of predicting fatigue crack length with desirable probability under multiple stress levels. Although the method is examined on an automotive application, the presented approach is universal and applicable for other industries dealing fatigue damage with multiple impacting factors.

Fatigue crack growth analysis of T junction under biaxial compressive–compressive loads

The objective of the present research is to analyze systematically the effect of biaxial compressive–compressive stresses on crack growth behavior of T junctions. Pressure structures have many components which are designed to be compressively stressed. This paper describes and summarizes biaxial compressive fatigue crack initiation and propagation characteristics through several T junctions under biaxial fatigue tests. Unlike uniaxial compressive fatigue, multiaxial compressive–compressive fatigue has the intricate characteristics of multi-point crack initiating, short crack group growth behavior and long crack propagating behavior. Moreover, the effective stress intensity factor range Keff and the crack opening threshold Kop,max are used to explain the crack growth under biaxial loads instead of the Paris law. Predictions of fatigue crack growth behavior based on the extended McEvily formula agree well with experimental observations.

Evaluation of magnetic flux leakage signals on fatigue crack growth of mild steel

In engineering applications, analysis of crack growth life is useful in situations where an unexpected crack has been found in a component of a machine, vehicle, or structure. The objective of this research is to investigate the correlation curve of magnetic flux leakage, Hp(y) signals by evaluating their critical value point with respect to step size. Moreover, the relation of fatigue crack growth rate, da/dN toward the stress intensity range, ΔK and Hp(y) in metal components is also discussed in this paper. The tension-tension fatigue test was conducted with the metal magnetic memory scanning device and crack opening displacement (COD) gauges in 10 Hz (testing frequency) by applying a load for 3.0-5.0 kN respectively. As a result, the correlation curve of Hp(y) was built with the R-Squared values in the range of 0.99 and one mathematical model has been developed for estimation analysis. The sigmoidal shape curve was plotted on the graph of da/dN versus ΔK and also with Hp(y). Thus, for validation, the linear relation is represented between ΔK and Hp(y) that present a good approach for magnetic parameter to be developed in the fatigue crack growth analysis. Therefore, the magnetic method has greater capability to analyze the fatigue crack propagation life in a real application.

Dual boundary element analysis of fatigue crack growth, interaction and linkup

Multiple-site and widespread fatigue damage have been an issue to the aircraft and construction industry for a long period. Structural components develop cracks at several locations which grow with crack paths that are difficult to predict. When two cracks approach one another, their stress fields influence each other leading to an enhancing or shielding effect which depends on the position and orientation of the cracks. Since there are no generalized analytical methods for predicting crack stress fields, simulation of multiple-crack growth is an important and challenging task which is still an evolving area of research.This paper describes a two-dimensional application of the dual boundary element method (DBEM) to the analysis of mixed-mode multiple-crack growth in linear elastic fracture mechanics, under fatigue loading. The crack-growth process is simulated with an incremental multiple-crack extension analysis based on the maximum principal stress criterion. For each increment of the analysis, in which crack extensions are modelled with new straight boundary elements, the DBEM is applied to perform a single-region stress analysis of the cracked structure and the J-integral is used to compute the stress intensity factors. The incremental analysis is based on a prediction–correction technique that defines, in each increment of the analysis, the direction and the extension of the multiple interacting cracks, thus taking into account the discreteness of the analysis and ensuring that the requirement of the path uniqueness is satisfied. Based on the ligament yield criterion which assumes that when the plastic zones of two adjacent cracks touch each other, the ligament between the cracks fails and the cracks coalesce, plates with multiple-site damage can be analysed. The fatigue life and residual strength of the structure are introduced as a post-processing procedure on the results of the multiple-crack growth. Results of this incremental analysis are presented for several geometries with multiple-site damage, demonstrating the accuracy and efficiency of the strategies adopted in the analysis.

Numerical simulation of crack propagation under fatigue loading in piezoelectric material using extended finite element method

Piezoelectric materials due to their electromechanical coupling characteristics are being widely used in actuators, sensor, transducers, etc. Considering wide application it is essential to accurately predict their fatigue and fracture under applied loading conditions. The present study deals with analysis of fatigue crack growth in piezoelectric material using the extended finite element method (XFEM). A pre-cracked rectangular plate with crack at its edge and center impermeable crack-face boundary conditions is considered for simulation. Fatigue crack growth is simulated using extended finite element method under plane strain condition and mechanical, combined (mechanical and electrical) cyclic loading. Stress intensity factors for mechanical and combined (mechanical and electrical cyclic loadings) have been evaluated by interaction integral approach using the asymptotic crack tip fields. Crack propagation criteria have been applied to predict propagation and finally the failure.

Elasto-plastic fatigue crack growth analysis of plane problems in the presence of flaws using XFEM

In this paper, elasto-plastic XFEM simulations have been performed to evaluate the fatigue life of plane crack problems in the presence of various defects. The stress-strain response of the material is modeled by Ramberg-Osgood equation. The von-Mises failure criterion has been used with isotropic hardening. The J-integral for two fracture modes (mode-I and mode-II) is obtained by decomposing the displacement and stress fields into their symmetric and antisymmetric parts, then individual stress intensity factors are extracted from J-integral. The fatigue life obtained by EPFM is found quite close to that obtained by LEFM.

Fracture and fatigue crack growth analyses on a weld-repaired railway rail

Although repair by arc welding is a well-known method for damaged rail surface recovery due to its ease of application, the method is vulnerable to the creation of cracks. In this study, a series of failure analyses and crack growth analyses were carried out on a fractured weld-repaired rail to determine the cause of the rail failure and the effect of residual stress on the crack growth rate. For this purpose, the residual stress profiles of rails under various conditions were obtained by both sectioning the physical rail and simulating the weld-repair process of the rail using the finite element method. Subsequently, the fatigue crack growth in the weld-repaired rail was simulated by assuming that a semi-elliptical crack was initiated at the boundary between the weld pool and heat-affected zone. From these analyses, it was found that weld defects, such as porosity, lamella line cracks, and quick transitions in material hardness and microstructure, especially at the boundaries, could be the causes of the crack initiation. The crack growth rate was strongly influenced by the magnitude of the residual stress, while it was significantly increased in the presence of high tensile residual stress at the rail head due to the weld repair. Therefore, reducing the tensile stress magnitude and increasing the compressive stress magnitude in the rail head is crucial to solving this problem in railway rail weld repair.

Surface crack analysis under cyclic loads using probabilistic S-version finite element model

The failure in engineering structures has always become a norm for the engineers to encounter. Thus, it is very important to improve the quantification of uncertainty in fatigue analysis. The main objective of this paper is to examine the effect to the uncertainties parameter in numerical calculations for multiple surface crack problems. A finite thickness plate with surface cracks subjected to random loads with constant-amplitude loading is considered in the fatigue crack growth analysis using a newly developed probabilistic S-version finite element model (ProbS-FEM). The virtual crack closure method was used to calculate the stress intensity factor, whilst the Latin hypercube sampling was employed in ProbS-FEM to determine the probabilistic distribution. Specimens with a multiple notch were prepared and analysed in the fatigue tests. The crack grown both in experimental and numerical simulations were verified. The results from the newly developed ProbS-FEM agreed with the experimental findings. The newly developed approach is demonstrated on a complex cracked structure.