Simulation Of Fatigue Crack Growth Research Articles

Experiment and simulation of fatigue crack growth of SLM nickel base superalloy with different stress ratios and building directions

Building orientation and stress ratio have much affection on long fatigue crack growth for Selective Laser Melting (SLM) Inconel 625. Compact-tension (CT) specimens in different orientations were tested with stress ratios (R) of 0.1. The Fatigue Crack Growth Rate (FCGR) in Paris was influenced by the loading factor and the difference of microstructure. With the help of finite element software (Abaqus/Franc3D), the FCGR data were calculated excitedly for different directional specimens under R of 0.5. Scanning Electron Microscopy (SEM) method was also introduced to observe the fracture mechanism of FCG in Paris region.

Effect of laser beam welded reinforcement on integral skin panel fatigue life

In this paper, numerical analyses of fatigue crack growth in integral skin-stringer panel produced by means of laser beam welding (LBW) are presented along with fatigue results verified by previously conducted experiments. Skin-stringer panel is fail-safe structure widely used in aircraft industry, which requires a good estimate of fatigue life after crack initiation. In the past, experimental work was the only successful method for fatigue life estimation of complex damaged structure, but nowadays researches have powerful numerical tools, such as extended finite element method (XFEM), for three-dimensional crack growth analysis. In research presented here, XFEM was initially used for crack growth simulation in simple flat plate made of aluminium 6156 T6 and 6156 T4 for the purpose of procedure verification, since fatigue life for simple plate was known from experiment. Then, XFEM was used to simulate fatigue crack growth in the panel reinforced with four stringers. Fatigue life obtained on the basis of calculated stress intensity factors (SIFS) along the crack fronts on LBW skin-stringer panels was, as expected, significantly longer than experimentally measured life of simple flat plate. Finally, several numerical simulations were performed in order to analyse the influence of mesh size on accuracy of estimated fatigue life of damaged LBW skin panels. For that purpose, average element sizes of 1, 2 and 4 mm were used.

Numerical simulation of fatigue crack propagation in mixed-mode (I+II) using the program BemCracker2D

PurposeThe purpose of this paper is to present the application of the boundary element method (BEM) in linear elastic fracture mechanics for analysis of fatigue crack propagation problems in mixed-mode (I+II) using a robust academic software named BemCracker2D and its graphical interface BemLab2D.Design/methodology/approachThe methodology consists in calculating elastic stress by conventional BEM and to carry out an incremental analysis of the crack extension employing the dual BEM (DBEM). For each increment of the analysis, the stress intensity factors (SIFs) are computed by the J-Integral technique, the crack growth direction is evaluated by the maximum circumferential stress criterion and the crack growth rate is computed by a modified Paris equation, which takes into account an equivalent SIF to obtain the fracture Modes I and II. The numerical results are compared with the experimental and/or BEM values extracted from the open literature, aiming to demonstrate the accuracy and efficiency of the adopted methodology, as well as to validate the robustness of the programs.FindingsThe paper addresses the numerical simulation of fatigue crack growth. The main contribution of the paper is the introduction of a software for simulating two-dimensional fatigue crack growth problems in mixed-mode (I+II) via the DBEM. The software BemCracker2D coupled to the BemLab2D graphical user interface (GUI), for pre/post-processing, are very complete, efficient and versatile and its does make relevant contributions in the field of fracture mechanics.Originality/valueThe main contribution of the manuscript is the development of a GUI for pre/post-processing of 2D fracture mechanics problems, as well as the object oriented programming implementation. Finally, the main merit is of educational nature.

Fatigue crack growth simulation of two non-coplanar embedded cracks using s-version finite element method

In this paper, the fatigue crack growth simulation of two non-coplanar embedded cracks using the s-version finite element method is presented, and the validity and reliability of the alignment rule for two non-coplanar cracks are evaluated. According to the previous numerical and experimental studies on two non-coplanar surface cracks, the simulated fatigue crack growth behavior is categorized into five patterns to discuss the criteria for the application of the alignment rule. The results suggest that the strength of interaction between the non-coplanar embedded cracks is similar to that between non-coplanar surface cracks. Finally, the interaction of the cracks is evaluated by the stress intensity factor, and the categorization of the fatigue crack growth behavior is discussed by the stress intensity factor. It can be found that the boundary corresponding to the criteria of the application of the alignment rule can be determined as the ratio of the stress intensity factor is 4%. Thus, instead of making a decision of the fatigue crack growth pattern based on the visual inspection, the ratio of the stress intensity factor can be used, and should give more quantitative evaluation of the interaction of two non-coplanar embedded cracks.

Algorithm for automatic fatigue crack growth simulation on welded high strength steels

Nowadays the demand for high strength steels is increasing. In order to design and develop high performance products, it is essential to understand the fatigue behavior of these materials. When considering welded components, the fatigue behavior is even more complex. The material parameters may change along the crack growth and mixed mode crack propagation may also occur. To assess welded high strength steel fatigue behavior, different welded CT specimens were tested. The Paris law material constants were obtained for the heat affected zone material. Fatigue crack growth life predictions were made using the obtained parameters and different automatic techniques. Previous work showed that the ABAQUS extended finite element method can predict fatigue crack growth, but as the implementation of the Paris law is not straight forward, to many conversions must be made and the results are too computer intensive. A simpler and more intuitive Python algorithm was developed, to enable the use of the experimental material parameters, to predict the crack propagation path. The obtain results show a good agreement with both the experimental Paris curves, and the analytical solution.

A cohesive XFEM model for simulating fatigue crack growth under mixed‐mode loading and overloading

SummaryStructures are subjected to cyclic loads that can vary in direction and magnitude, causing constant amplitude mode I simulations to be too simplistic. This study presents a new approach for fatigue crack propagation in ductile materials that can capture mixed‐mode loading and overloading. The extended finite element method is used to deal with arbitrary crack paths. Furthermore, adaptive meshing is applied to minimize computation time. A fracture process zone ahead of the physical crack tip is represented by means of cohesive tractions from which the energy release rate, and thus the stress intensity factor can be extracted for an elastic‐plastic material. The approach is therefore compatible with the Paris equation, which is an empirical relation to compute the fatigue crack growth rate. Two different models to compute the cohesive tractions are compared. First, a cohesive zone model with a static cohesive law is used. The second model is based on the interfacial thick level set method in which tractions follow from a given damage profile. Both models show good agreement with a mode I analytical relation and a mixed‐mode experiment. Furthermore, it is shown that the presented models can capture crack growth retardation as a result of an overload.

Numerical evaluation of crack stopping mechanisms in composite bonded joints due to corrugation and bolts

In this paper, the crack stopping mechanisms in corrugated composite bonded joints and hybrid bonded/bolted joints were evaluated numerically using the cohesive zone modeling approach. For the study, the DCB (double-cantilever beam) and the CLS (crack-lap shear) specimens were modelled. The first two specimens were subjected to static loads and the latter both to static and fatigue loads. The analysis was performed using the LS-DYNA explicit FE code. Fatigue crack growth simulation was performed using an in-house developed user-defined subroutine (UMAT). The numerical results reveal a crack stopping in the corrugated DCB, no crack stopping in the corrugated CLS and a reduction of crack growth rate in the bonded/bolted CLS for both static and fatigue loads. The methods and the findings of the present study can be used for the design of crack stopping features in adhesively bonded primary composite aircraft structures.

Surface crack growth prediction under fatigue load using the S-version Finite Element Model (S-FEM)

Prediction of fatigue crack growth is one of the vital issues to prevent catastrophic failure from damage tolerance perspective. The surface of crack shape usually in semi-elliptical that maintained during the whole propagation. The investigation of this paper is to illustrate the surface crack growth that subjected to fatigue loading. The four-point bending and three-point bending have been simulated by using the S-version Finite Element Model (S-FEM). The simulation is conducted for aluminium alloys A7075-T6 and A2017-T3 with all of the parameters based on the previous experiment. The semi-elliptical crack shape is applied during the simulation process to represent with the reality of crack growth phenomena. Paris’ Law model approach is presented in fatigue crack growth simulation. The S-FEM produced the surface crack growth and fatigue life prediction. The results of the S-FEM prediction then compared with the previous experiments. The results presented in a graph for comparison between S-FEM prediction with the experimental results. The S-FEM results obtained is good agreement with the experiment results.

A Paris Law-Based Cohesive Zone Model for Fatigue Crack Growth Simulations

This paper presents a Paris law-based cohesive zone model (CZM) for fatigue crack growth simulations to enable the consideration of the plasticity induced crack closure effect, which is known to be a source of substantial cra... | Find, read and cite all the research you need on Tech Science Press

Prediction of atherosclerotic plaque life – Perceptions from fatigue analysis

Cardiovascular diseases are the leading causes of morbidity and mortality globally. Heart disease and stroke contribute to most fatalities in which atherosclerotic plaque disruption is the underlying pathology. The pulsatile blood flow in the arteries generates mechanical stresses that affect the rupture of the atherosclerotic plaque. Fatigue failure being the accumulation of the damage due to repeated loading that occurs when the stresses are much lower than those needed to rupture the plaque with normal loading. Therefore, fracture mechanics concepts were used to investigate the impact of morphology and blood pressure on the plaque life. Incremental fatigue crack propagation simulations were performed on idealized geometries based on the maximum circumferential stress criteria by using a finite element solver. XFEM, which extends the standard finite element formulation by introducing additional enrichment functions was used to model the fatigue crack growth simulations. Paris’ Law was used to determine the fatigue crack growth rate. Cracks extended radially and fatigue crack growth rate increased with increase in pulse pressure. Further validation studies on the 3D printed arteries are necessary for better understanding the factors contributing to plaque rupture. The results could help in assessing the atherosclerotic plaque life under the fatigue environment of the cardiovascular system.

Fatigue crack growth simulation in adhesively bonded composite joints

AbstractA numerical model has been developed for simulating fatigue crack growth (debonding) in adhesively bonded composite joints subjected to mode‐I, mode‐II, and mixed‐mode I + II loading conditions. The model employs a cohesive zone model described by a modified bilinear traction‐separation law. Fatigue damage in the composite adherends is not considered in the model. To account for crack divergence and reduce sensitivity of numerical results on mesh density, a crack front detection algorithm based on the effective element's length was employed. The model is implemented as a user‐defined subroutine (UMAT) in the commercial FE code LS‐DYNA. The model's input parameters, in the form of a modified Paris law, and the validation data were obtained from experimental tests conducted by the authors. It was found that the model is able to successfully simulate crack growth in the regime of the experimental data.

Tension failure assessment at lug hole edges

The lug is the critical component of lug joints, and one of its failure mode is the tension failure at hole edges. In the present paper, the fatigue crack growth simulation of a semi-elliptical crack located in the lug net cross-section, at one of the two hole edges, is carried out by employing a theoretical model based on the Paris law. The lug sizes, loading conditions and crack configurations are assumed in accordance with those related to some experimental tests available in the literature, performed on lugs of PolyMethylMethAcrylate under pulsating tension.

XFEM simulation of fatigue crack growth in a welded joint of a pressure vessel with a reinforcement ring

The numerical analysis of the behaviour of a pressure vessel with a reinforcement ring subjected to both static and dynamic load is presented in this paper. This research was based on a previous analysis which involved different reinforcement ring dimensions, and their influence on the stress distribution within the pressure vessel, assuming the presence of a crack (Sedmak et al., in: International Conference on Structural Integrity and Durability, 2017). The aim was to compare the numerical results for two models, one of which was a 2D model simulated with classic FEM, whereas the other included a 3D fatigue crack, and was simulated with extended finite element method, using Morfeo software. The numerical simulation was based on a pressure vessel which is typically used as a part of hydropower plants, containing a manhole which is supported by the reinforcement ring. The analysis focused on a crack that was located in the welded joint between the reinforcement ring and the pressure vessel mantle. The results obtained by the simulations have shown the differences in the stress magnitudes and in the consequences resulting from the crack growth in both cases, depending on the type of the load, wherein the second (fatigue) load case was noticeably more extreme.

Three-dimensional mode-I/III fatigue crack propagation: Computational modeling and experiments

Three dimensional mixed mode-I/III fatigue crack growth simulations and experiments are performed on Al 7075-T651 aluminum under different mode mixity ratios. The crack growth surfaces obtained from numerical models are compared to experimental results. Good agreement is achieved with experimental results on prediction of crack growth surfaces for up to upper intermediate levels of mixed mode loadings. Based on the computed mixed mode stress intensity factors from the numerical analyses, fatigue crack propagation lives are also predicted using different criteria. The results show that all of the mixed mode criteria evaluated in this study underestimate fatigue crack growth lives.

Linear smoothed extended finite element method for fatigue crack growth simulations

In this paper, the recently proposed linear smoothed extended finite element method (LSmXFEM) is employed to simulate the fatigue crack growth. Unlike the conventional extended finite element method, the LSmXFEM does not require special numerical integration technique to integrate the terms in the stiffness matrix. The stress intensity factors (SIFs) are evaluated by using the domain form of the interaction integral technique. The fatigue crack growth rate is evaluated using the generalized Paris’ law in conjunction with the maximum hoop stress criterion. The robustness of the method is demonstrated with a few examples for which the results are available in the literature. Then, the fatigue crack growth from the numerical simulation is compared with the experimental investigations performed on CR5 grade cold formed steel. It is seen that the fatigue life and the crack path obtained from the proposed method is in close agreement with the experimental observation.

Fatigue crack growth simulation in particulate-reinforced composites by the equivalent inclusion method and distributed dislocation method

This paper presents an automatic fatigue crack propagation solution for particulate-reinforced composites. In this solution, the Eshelby’s equivalent inclusion method is used to solve the elastic fields of a two-dimensional plane containing multiple elliptical inclusions. Then the continuous distributed dislocations in an infinite plane are adopted to model the multiple cracks in the plane containing multiple elliptical inclusions. By combining the two methods, a system of singular integral equations can be formulated based on the stress condition of the cracks. The stress intensity factor of each crack can be obtained by solving the singular integral equations. The propagation of the cracks is studied based on the maximum circumferential stress criterion. Numerical examples are presented to show the complicated changes in the stress intensity factors and crack growth behaviors of the cracks affected by the inclusions.

A new framework based on continuum damage mechanics and XFEM for high cycle fatigue crack growth simulations

In this paper, we have developed a continuum damage mechanics (CDM) based methodology for high cycle fatigue crack growth simulations. A fatigue damage law is proposed and implemented in the framework of extended finite element method (XFEM). A new criterion is proposed based on damage evolution to identify the appropriate definition of stress triaxiality for acquiring the constraint effect on the stress state correctly. Few mesh regularization schemes are also employed for reducing the mesh sensitivity in the results. Simulations are performed on fracture specimens of different materials subjected to constant amplitude fatigue loading. The fatigue life of a turbine disc is also predicted under constant amplitude loading. The results obtained from present methodology (CDM and XFEM) are found in good agreement with the published experimental results. These simulations highlight that the continuum damage mechanics is a simple and effective tool to perform crack growth simulations under high cycle fatigue conditions.

Machine Learning Based Prognostics of Fatigue Crack Growth in Notch Pre-cracked Aluminum 7075-T6 Rivet Hole

Constant stress amplitude fatigue tests were conducted on the notch pre-cracked Aluminum 7075-T6 rivet hole dog-bone coupons. Monitoring of visible surface crack length by special surface engraving using digital microscope images and by ultrasonic sensors signals was carried out to yield fatigue crack length measurements in relation to number of fatigue cycles applied. The experimental results provide ultrasonic sensor validation for fatigue crack length measurements. Fracto-graphic examination of failed fatigue surfaces has provided further confirmation of notch pre-crack length, crack initiation process, and crack growth marker bands. These experimental inputs were used in NASGRO and AFGROW software fatigue crack growth simulations. The simulation results did not match the crack initiation fatigue life measured by experiments. However, there was good agreement with crack growth simulations of larger cracks. Hence, we plan to develop a machine learning application that will learn the fatigue crack initiation and crack growth processes from data obtained from our own experiments and other fatigue data available from AFGROW databases. Nonlinear AutoRegressive models with eXogenous input (NARX) artificial neural network were used to predict crack growth longer than 5.0-mm. Particle filtering modeling with Bayesian updating was applied to these experimental data for prognostics of fatigue crack growth. A concept design and preliminary implementation results will be presented.

Computational fracture mechanics: An overview from early efforts to recent achievements

AbstractAn overview of the state of the art of computational fracture mechanics is presented, starting from early efforts and going all the way up to recent achievements. Some specific aspects of linear elastic and elastic plastic fracture mechanics problems have been discussed, including the fact that even for a static loading, numerical simulation is not a simple task because of complex geometries, material nonlinearity, and heterogeneity, and especially if crack growth is considered. Therefore, micromechanical modelling of elastic‐plastic crack growth is presented as new and promising approach to overcome some of the shortages of traditional approach. Besides static loading, couple of other important practical problems are tackled, like fatigue crack growth, with remaining life in the focus of investigation, using the empirical laws for crack growth rates. Numerical simulation of fatigue crack growth is inherently complex both because of complex material damage processes and lack of sound theoretical basis to define them. Therefore, combination of theoretical, experimental, and numerical approach is presented here to get reliable and efficient estimation of life under fatigue loading.

Fatigue crack growth characterization in adhesive CFRP joints

Adhesive joints find an increasing use in lightweight structures, which is proportional to the evolution of carbon fiber-reinforced plastics (CFRPs). Understanding of fatigue crack growth behavior in adhesive CFRP joints is essential for the efficient maintenance and repair of existing joints and the design of new joints. Here, the fatigue crack growth behavior of adhesive CFRP joints under Mode-I, Mode-II and Mixed-Mode I + II loading conditions is characterized experimentally by means of Mode-I fatigue fracture toughness tests, Mode-II fatigue fracture toughness tests and the Mixed-Mode fatigue lap shear test. For the three different tests, the Double Cantilever Beam (DCB), the End-Notch Flexure (ENF) and the Cracked Lap Shear (CLS) specimens are used, respectively. Crack growth versus number of cycles is reported and modified Paris-laws are derived. The DCB specimens failed in cohesive failure mode while the ENF and CLS specimens in adhesive. The crack growth in the DCB specimens was more stable and showed a smaller scatter among the different specimens than the ENF specimens. Crack propagation with number of cycles in CLS specimen was almost linear. The results reported herein suggest a full experimental characterization of fatigue crack growth behavior of the considered aerospace CFRP/adhesive material system and can be proved very useful in the development and validation of fatigue crack growth simulation models.