Academic literature on the topic 'Fatigue crack front shape'
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Journal articles on the topic "Fatigue crack front shape"
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Lin, X. B., and R. A. Smith. "Fatigue Growth Prediction of Internal Surface Cracks in Pressure Vessels." Journal of Pressure Vessel Technology 120, no. 1 (February 1, 1998): 17–23. http://dx.doi.org/10.1115/1.2841878.
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Fatigue crack growth was numerically simulated for various internal surface cracks with initially either semi-elliptical or irregular crack fronts. The simulation was directly based on a series of three-dimensional finite element analyses from which the stress intensity factors along the front of growing cracks were estimated. The fatigue crack growth law obtained from small laboratory specimens was incrementally integrated at a set of points along the crack front, and a new crack front was then re-established according to the local advances at this set of points by using a cubic spline curve. This method enabled the crack shape to be predicted without having to make the usual assumption of semi-elliptical shape. Fatigue analysis results are presented and discussed for fatigue shape developments and deviations from the semi-elliptical shape, aspect ratio changes, stress intensity factor variations during crack growth, and fatigue life predictions. Some of the results were also compared with those obtained by two simplified methods based on one and two degree-of-freedom models, respectively.
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Zakavi, Behnam, Andrei Kotousov, and Ricardo Branco. "The Evaluation of Front Shapes of Through-the-Thickness Fatigue Cracks." Metals 11, no. 3 (March 1, 2021): 403. http://dx.doi.org/10.3390/met11030403.
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Fatigue failure of structural components due to cyclic loading is a major concern for engineers. Although metal fatigue is a relatively old subject, current methods for the evaluation of fatigue crack growth and fatigue lifetime have several limitations. In general, these methods largely disregard the actual shape of the crack front by introducing various simplifications, namely shape constraints. Therefore, more research is required to develop new approaches to correctly understand the underlying mechanisms associated with the fatigue crack growth. This paper presents new tools to evaluate the crack front shape of through-the-thickness cracks propagating in plates under quasi-steady-state conditions. A numerical approach incorporating simplified phenomenological models of plasticity-induced crack closure was developed and validated against experimental results. The predicted crack front shapes and crack closure values were, in general, in agreement with those found in the experimental observations.
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Fiordalisi, S., C. Gardin, C. Sarrazin-Baudoux, M. Arzaghi, and Jean Petit. "Influence of Crack Front Shape on 3D Numerical Modelling of Plasticity-Induced Closure of Short and Long Fatigue Cracks." Key Engineering Materials 577-578 (September 2013): 213–16. http://dx.doi.org/10.4028/www.scientific.net/kem.577-578.213.
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The simultaneous effect of crack length and crack front shape on plasticity-induced crack closure (PICC) for a 304L austenitic stainless steel is simulated through 3D numerical modelling using finite element software Abaqus for through-thickness cracks with different curved crack fronts in CT specimens in comparison with bidimensional through crack with a straight front. The influence of possible loading history effect is avoided by applying constant K amplitude. The local stress intensity factor range for crack opening Kopis evaluated from the simulation of the loss of the last local contact between the crack lips near the crack tip. The pertinence of the different crack front shapes is discussed in term of the effective stress intensity factor range Keffand in comparison with the experimental crack front observations.
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Hutař, Pavel, Martin Ševčík, Luboš Náhlík, and Zdeněk Knésl. "Fatigue Crack Shape Prediction Based on the Stress Singularity Exponent." Key Engineering Materials 488-489 (September 2011): 178–81. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.178.
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In many industrial applications it is necessary to predict fatigue lifetime of the structures where the stress field near the crack front have a three-dimensional nature. Due to the existence of vertex singularity in the point where the crack front touches free surface, crack propagation in 3D structures cannot be reduced to a series of plane strain or plane stress problems along the crack front. The paper describes the influence of the vertex singularity on crack shape for three-dimensional structure. The iterative process for estimation of a real crack front based on a stress singularity exponent is presented. In each node defining the crack front the stress singularity exponent has been estimated and complete crack front shape corresponding to the constant stress singularity exponent was found. The methodology presented can help to estimate crack front shape in a linear elastic fracture mechanics framework and estimate fracture parameters of fatigue cracks more accurately.
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Gardin, Catherine, Saverio Fiordalisi, Christine Sarrazin-Baudoux, and Jean Petit. "3D Numerical Study on how the Local Effective Stress Intensity Factor Range Can Explain the Fatigue Crack Front Shape." Advanced Materials Research 891-892 (March 2014): 295–300. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.295.
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The plasticity-induced crack closure of through-thickness cracks, artificially obtained from short cracks grown in CT specimens of 304L austenitic stainless steel, is numerically simulated using finite elements. Crack advance is incremented step by step, by applying constant ΔK amplitude so as to limit the loading history influence to that of crack length and crack wake. The calculation of the effective stress intensity factor range, ΔKeff, along curved shaped crack fronts simulating real crack fronts, are compared to calculation previously performed for through-thickness straight cracks. The results for the curved crack fronts support that the front curvature is associated to constant ΔKeffamplitude, thus assumed to be the propagation driving force of the crack all along its front.
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Kaplunenko, V. G., and T. I. Matchenko. "Shape of the fatigue crack front." Strength of Materials 21, no. 8 (August 1989): 986–90. http://dx.doi.org/10.1007/bf01529369.
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Lin, X. B., and R. A. Smith. "Direct simulation of fatigue crack growth for arbitrary-shaped defects in pressure vessels." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 213, no. 2 (February 1, 1998): 175–89. http://dx.doi.org/10.1243/0954406991522257.
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An advanced technique has been developed by the authors to predict fatigue crack growth for longitudinal and circumferential planar defects with arbitrary shape in pressure vessels. This is based on the step-by-step integration of an experimental fatigue crack growth law at a set of points along the crack front, enabling the crack shape developed during the fatigue process to be predicted. The stress intensity factors along the crack front are calculated by a three-dimensional finite element method. Automatic regeneration of finite element models for propagating cracks designed for this technique makes the simulation technique highly efficient. In this paper, following a description of the principle of the technique, some typical crack geometries are investigated. These include external and internal surface longitudinal cracks, an embedded longitudinal crack, a twin crack configuration and two circumferential surface cracks. The results obtained are compared with both the widely used ASME XI and BSI PD6493 guidelines, and some discussion on the safe use of the two guidelines is made.
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Jesus, Joel de, Micael Borges, Fernando Antunes, José Ferreira, Luis Reis, and Carlos Capela. "A Novel Specimen Produced by Additive Manufacturing for Pure Plane Strain Fatigue Crack Growth Studies." Metals 11, no. 3 (March 5, 2021): 433. http://dx.doi.org/10.3390/met11030433.
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Fatigue crack growth is usually studied using C(T) or M(T) specimens with through-thickness cracks. The objective of the present study is to propose a cylindrical specimen with central crack, produced by additive manufacturing. This geometry allows to have pure plane strain state along the whole crack front, avoiding the complexities associated with corner points, crack shape, and variation of crack closure along crack front. Additionally, this geometry may be used to develop studies in vacuum, avoiding expensive vacuum equipment, since the air is not in contact with the crack front. Cylindrical specimens of Ti6Al4V titanium alloy were produced by Selective Laser Melting and tested at a stress ratio R = 0. Marking with overloads was the solution adopted to measure the length of the internal cracks. The fracture surfaces presented circular crack fronts and the da/dN-ΔK curves showed a great influence of atmosphere on fatigue crack growth. An average difference of 50% was found between the results in air and vacuum. Therefore, this geometry with internal crack is an interesting alternative to through-thickness geometries.
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Ferrié, Emilie, Jean Yves Buffière, Wolfgang Ludwig, and Anthony Gravouil. "X-Ray Micro-Tomography Coupled to the Extended Finite Element Method to Investigate Microstructurally Short Fatigue Cracks." Materials Science Forum 567-568 (December 2007): 301–4. http://dx.doi.org/10.4028/www.scientific.net/msf.567-568.301.
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In this paper we will present how it is possible to couple a 3D experimental technique with a 3D numerical method in order to calculate the stress intensity factors along the crack front taking into account the real shape of the crack. This approach is used to characterize microstructurally short fatigue cracks that exhibit a rather complicated 3D shape. The values of the stress intensity factors are calculated along the crack front at different stages of crack propagation and it can be seen that the crack shape irregularities introduce rather important fluctuations of the values of KI, KII and KIII along the crack front. The values of KI obtained taking into account the real shape of the crack are significantly different from the ones calculated using an approach based on a shape assumption
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Wu, Zhi Xue. "Shape Prediction of Fatigue Crack Based on a Given Stress Intensity Factor Distribution." Key Engineering Materials 353-358 (September 2007): 19–23. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.19.
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There is an inherent relationship between the shape and the corresponding stress intensity factor (SIF) distribution of a crack. A typical inverse problem of linear elastic fracture mechanics about a crack, i.e. to predict the shape of a crack assuming that some information of SIF distribution is known, is presented. A finite-element based numerical procedure is used to determine the shape, correspondingly the SIF, of a mode-I planar crack based on a specified SIF distribution. The crack front is modeled using cubic splines, which are determined by a number of control-points. The crack front shape is achieved iteratively by moving control-points based on a gradientless algorithm. Numerical examples for planar cracks in through-cracked and surface-cracked plates with finite thickness and width are presented to show the validity and practicability of the proposed method. The SIFs obtained by present method are compared with the known solutions for cracks with same dimensions. The presented method is considered to be a promising alternative to the evaluation of SIFs and the prediction of shape evolution for fatigue cracks.
Dissertations / Theses on the topic "Fatigue crack front shape"
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Harrington, David Stuart Carleton University Dissertation Engineering Mechanical and Aerospace. "Fatigue crack coalescence and shape development; an experimental investigation." Ottawa, 1995.
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Zhang, Yahui. "Low cycle fatigue of shape memory alloys." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLY004/document.
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Dans cette thèse, nous proposons une analyse globale multi-échelles de la fatigue à faible nombre de cycles des matériaux à mémoire de forme (MMF). Dans un premier temps, une large campagne d’essais a été menée pour différents chargements thermomécaniques comprenant des tests de fatigue sous contrainte et déformation imposée et pour différentes fréquences de chargement. A partir des résultats des essais, un critère de fatigue, basé sur l’énergie de déformation, a été développé ; on montre que l’énergie de déformation est un paramètre pertinent pour prédire la fatigue des MMF en tenant compte du couplage thermomécanique et du type de chargement : contrainte ou déformation imposée. Ensuite, en prenant appui sur la répartition de l’énergie de l’hystérésis en dissipation et énergie stockée, on avance une interprétation physique du mécanisme de la fatigue des MMF. Dans la troisième partie, on propose une modélisation multi-échelles de l’initiation des fissures de fatigue dans les MMF à partir de la notion de plasticité de transformation (PlTr). Dans ce cadre, on montre que la fatigue de MMF est contrôlée par la (PlTr) et que la température maximale lors de la transformation de phase est le paramètre à retenir pour prédire la rupture par fatigue des MMF. Le modèle permet également de prédire le lieu d’initiation des premières fissures de fatigue. Enfin, un procédé – fondé sur l’«éducation» des MMF – permettant d’améliorer la résistance à la fatigue est proposéThe thesis proposes a multi-scale comprehensive analysis of low cycle fatigue of shape memory alloys (SMAs). First, low cycle fatigue of SMAs is experimentally investigated; comprehensive tensile-tensile fatigue tests under both stress and strain controlled loadings at different frequencies are carried out and results are discussed. Second, a new strain energy-based fatigue criterion is developed; it is shown that the use of total strain energy is a relevant parameter to predict fatigue lifetime of SMAs for different thermomechanical conditions and under different types (strain-control or stress-control) loadings. A physical interpretation of the mechanism related to the low-cycle fatigue of SMAs is then provided based on the conversion of hysteresis work into dissipation and stored energy. Third, fatigue crack initiation during cyclic stress-induced phase transformation is modeled based on transformation induced plasticity (TRIP); it is shown that the maximum temperature during the cyclic loading is a relevant indicator of the fatigue of SMA. Furthermore, the effect of the macroscopic mechanical load on the the fatigue lifetime is addressed as well as the spatial location of crack initiation. Finally, a mechanical training process that allows enhancing resistance to low cycle fatigue of SMAs is proposed
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Patel, Surendra Kumar. "Experimental And Numerical Studies On Fatigue Crack Growth Of Single And Interacting Multiple Surface Cracks." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/276.
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Design based on damage tolerance concepts has become mandatory in high technology structures. These concepts are also essential for evaluating life extension of aged structures which are in service beyond originally stipulated life. Fracture analysis of such structures in the presence of single or multiple three-dimensional flaws is essential for this approach. Surface cracks are the most commonly occurring flaws and development of accurate methods of analysis for such cracks is essential for structural integrity evaluation of newly designed or aged structures. The crack fronts of these surface flaws are usually approximated mathematically to be of either part-elliptical or part-circular in geometry. In this thesis, some of the issues related to fatigue crack growth of single and multiple surface cracks are studied in detail. Here emphasis is given to the development of simple and accurate post-processing techniques to estimate stress intensity factors for surface cracks, development and/or implementation of simple numerical methods to simulate three-dimensional single and multiple cracks in fatigue and their experimental verification.
Modified virtual crack closure integral (MVCCI) technique for estimation of strain energy release rates has been improved (chapter II) to deal with curved crack front and unequal elements across the crack front. The accuracy of this method is evaluated and presented in this chapter for certain benchmark surface flaw problems. The improved MVCCI is used in the investigation of interaction between multiple surface cracks in three-dimensional solids. The interaction effects are studied for both interacting and coalescing phases as observed to occur in the growth of multiple surface cracks. Extensive numerical work is performed to study the effects of various parameters such as aspect ratio, thickness ratio, interspacing on the interaction factors. These solutions are used in formulating empirical equations to estimate interaction factors. This facilitated the development of a simple semi-analytical method to study fatigue crack growth of multiple cracks.
The growth of surface cracks under fatigue loading in the finite width specimens of an aero-engine superalloy has been studied experimentally (presented in chapter III). Four configurations for single semi-elliptical cracks are considered. Fatigue crack growth is simulated by two models viz. two degrees of freedom and "multi degrees of freedom with ellipse fit'. These models are sometimes referred to as semi-analytical models as the crack growth is predicted by numerical integration combining Paris equation with an empirical form of stress intensity factor solution. In order to use two degrees of freedom model for fatigue crack growth prediction of semi-elliptical cracks, empirical solution for the Ml range of geometric parameters for stress intensity factor is required for the considered
configurations. The available Newman-Raju solution is useful for this purpose within a limited range of surface crack length to width (c/W) of the specimen. Based on the present finite element results, the empirical equations are developed for extended values of c/W. It is well understood that the fatigue prediction for two-dimensional crack can be improved by inclusion of crack closure effects. Usually, in semi-analytical models for growth of surface cracks under fatigue loading, the crack closure is included as a ratio of crack closure factor at surface and depth locations of semi-elliptical crack. In the present work, this ratio for the considered material of specimens is obtained by an experimental study. The difference in characteristics of preferred propagation path between semi-elliptical crack in a finite width plate and a wide plate is clearly brought out.
Current crack growth predictions for most of the structures are based on the presence of only a single crack. However, in structures several cracks may initiate simultaneously within a stress critical zone and may interact depending upon their geometry, spatial location, structure geometry and mode of loading. In this work various configurations of twin semi-elliptical cracks have been studied by experiments. The beachmarks created on the specimens during experiments are used in the investigation of crack shape progression during fatigue. A three degrees of freedom crack growth model for interacting and coalescing cracks has been proposed. The experimentally determined crack shape and lives have been compared with the corresponding values from numerical simulation.
The correlation of experimental results with numerical predictions was carried out through improved MVCCI for eight-noded brick elements. This has worked well in the configurations analysed. However, it is known in literature that there are benefits of using 20-noded singular elements. There could be special situations where the regular elements could fail, and singular elements could be essential. For this purpose, further development of MVCCI were carried out using 20-noded quarter-point elements (presented in chapter IV). Also a novel technique of decomposed crack closure integral (DCCI) was developed (presented in chapter V) for both regular and singular elements to represent the variation of MVCCI more accurately along the crack front.
It is well known that quarter-point elements at crack front produce the required singularity at the crack tip and give accurate stress distribution with fewer degrees of freedom than conventional elements. Thus to develop more efficient post-processing tools, the MVCCI expressions are formulated for 20-noded singular quarter-point element for various assumptions regarding stress and displacement distributions in the elements across the crack front. A comprehensive study is presented (chapter IV) on MVCCI for 20-noded singular brick element including various simplified expressions for three-dimensional part-through cracks in pure and mixed-mode state of deformation of fracture. The developed MVCCI expressions are also valid for 15-noded quarter-point Penta elements. The reduction in model size can further be obtained if 12-noded three-dimensional singular element is employed at the crack front and eight-noded elements are used away from the crack front. The MVCCI expressions are also developed for 12-noded singular element and their accuracy is evaluated by numerical solutions.
Presently, MVCCI, estimates the average stress intensity factor at the center of each element along the crack front. In this thesis, a Decomposed Crack Closure Integral (DCCI) is formulated to represent an assumed variation of stress intensity factor along the crack front in each element. The DCCI is formulated for 8-noded brick, 20-noded conventional brick and 20-noded singular brick elements. The numerical examples presented here deal with three-dimensional problems of patch repair technology and part-through cracks. The technique showed a major advantage for the patch repair problems where SIF variations along the crack front are of significance and large mesh sizes are computationally expensive. This along with MVCCI for 12-noded and 20-noded singular elements formed a part of the work on development of accurate and effective post-processing tools.
It is expected that the present work will be helpful in damage tolerance design and assessment of aerospace structures and the experimental work performed as a part of this thesis will enhance confidence in the damage tolerance analysis.
The thesis is concluded in chapter VI presenting the contributions of this thesis and projecting future lines of work possible in this area.
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Ventura, Antunes Fernando Jorge. "Influence of frequency, stress ratio and stress state on fatigue crack growth in nickel base superalloys at elevated temperature." Thesis, University of Portsmouth, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285929.
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Fessler, Emmanuel. "Etude des interactions fatigue-fluage-environnement lors de la propagation de fissure dans l'Inconel 718 DA." Thesis, Toulouse, INPT, 2017. http://www.theses.fr/2017INPT0141.
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L’Inconel 718 est un superalliage base nickel largement utilisé par les motoristes tels Safran Aircraft Engines pour l’élaboration des disques de turbine. Après forgeage des disques, un traitement de vieillissement appelé « Direct Aged » est appliqué. En service, le régime de croisière représente un temps de maintien sous chargement constant pour les disques. Bien que pas complètement compris, il est largement admis qu’un temps de maintien dans un cycle de fatigue a un effet néfaste sur le comportement en fissuration de l’Inconel 718 ainsi que d’autres superalliages. Cette étude porte donc sur la fissuration en fatigue-fluage dans l’Inconel 718 DA à 550°C et 650°C. Des essais sont menés pour des temps de maintien allant jusqu’à 1h. Des développements de la méthode de suivi de fissure par mesure de potentiel (DCPD) ont permis d’identifier la décharge-recharge (contribution de fatigue) d’un cycle de fatigue-fluage comme la partie la plus néfaste du cycle. L’application d’un temps de maintien amplifie cette contribution. Le temps de maintien induit également des fronts de fissure extrêmement courbes et tortueux, contrairement à de la fatigue pure. Une stratégie numérique a été développée, couplant la simulation 3D de la propagation et la méthode dite DCPD, permettant de réaliser des « essais numériques ». La propagation de fronts courbes et tortueux est simulée. Il a été démontré que le comportement en propagation est directement lié à la forme du front de fissure et son évolution. Des essais complexes ont été menés, sous vide, ou impliquant des surcharges. Lorsque l’effet du temps de maintien est annihilé, les morphologies complexes des fronts disparaissent. Elles sont alors associées à une inhibition locale de l’effet endommageant de l’environnement due à la plasticité et aux vitesses de déformation locales. Tous les essais présentés sont analysés en considérant l’effet de la vitesse de déformation locale qui influe largement le comportement en fissuration de l’Inconel 718Inconel 718 is a nickel-based superalloy widely used by aeroengines manufacturers like Safran Aircraft Engine to manufacture turbine disks. After forging, disks are given an ageing treatment called “Direct Aged”. In service, during cruise, these critical components handle hold-time periods at constant loading. It is well known, although not fully understood, that hold-time increases crack growth rates (CGR) in Inconel 718 as well as others superalloys. Therefore, this study focuses on crack propagation under hold-time conditions in DA Inconel 718, at 550°C and 650°C. Experiments were carried out for different hold-times, up to 1h. Developments on the crack monitoring technique (DCPD) led to the conclusion that the most damaging part of the cycle is load-reversal (fatigue contribution). This contribution is enhanced by the hold-time period. Holdtime leads to dramatically curved and tortuous crack front, contrary to pure fatigue cycles. A numerical framework was developed, combining crack growth and DCPD simulations, so that “numerical tests” can be carried out. Using this method, crack growth simulations were performed from curved and tortuous, experimentally reproduced, crack front. It was concluded that increased crack CGR under hold-time conditions are closely related to the crack front morphology and its evolution during propagation. More complex tests, with overloads or under vacuum, were carried out. When the hold-time effect is inhibited, complex morphologies vanish. Such morphologies were associated to local inhibition of the environmental damaging effect due to local high plastic strain and strain rates. The large variety of experiments, presented in this study, was then successfully analyzed considering the effect of local strain rates which greatly influence the crack growth behavior of Inconel 718
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Neely, Jared A. "Correlation of Stress Intensity Range with Deviation of the Crack Front from the Primary Crack Plane in both Hand and Die Forged Aluminum 7085-T7452." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1557162451907811.
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Zouhar, Petr. "Predikce tvaru čela šířící se únavové trhliny." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241674.
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The presented master’s thesis deals with fatigue crack front shape estimation. The aim of this thesis is to create an iterative process leading to the real fatigue crack front shape. Thesis is solved using finite element method. The work is divided into two logical parts. The first part of the thesis describes the basic concepts of linear elastic fracture mechanic (LEFM), methods used for estimation of stress intensity factor and stress singularity exponent. The first part further describes some phenomenon’s accompanying the mechanism of fatigue crack growth as for example crack tip curving and crack closure. In the second part of the thesis there is studied an affect of the free surface on the fracture parameters, especially the affected distance from the free surface is determined. Based on the assumption of a constant stress intensity factor and stress singularity exponent along the crack front, an iterative process leading to fatigue crack front shape is presented. The accuracy of the result is discussed by comparing of obtained crack front shapes with experimental data at the end of the thesis.
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He, Zhuang. "Effect of 3D stress states at crack front on deformation, fracture and fatigue phenomena." Thesis, 2016. http://hdl.handle.net/2440/105077.
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Theoretical, numerical and experimental studies involving elastic plate components, weakened by through-the-thickness cracks and subjected to loading parallel to the plane of the plate, are often based on plane stress or plane strain simplifications. These simplifications essentially reduce the dimensionality of the physical three-dimensional problem and enable the achievement of effective analytical and numerical solutions for many important practical problems. The influence of various three-dimensional effects, such as the variation of stresses across the plate thickness, effects of the three-dimensional corner (vertex) singularities and coupling of fracture modes II and III, on the deformation and stresses near the crack front are at present largely ignored or viewed as negligible for all practical purposes. As a result of this view, the outcomes of experimental studies and fracture tests are also commonly analysed within the framework of the plane theories of elasticity. Nevertheless, a number of theoretical and experimental studies over the past two decades have demonstrated that the predictions made within these theories can be unsatisfactory and the effect of three-dimensional stress states at the crack front on deformation, fatigue and fracture of plate components can be significant. This thesis aims to elucidate the role of three-dimensional stress states in the deformation, fracture and fatigue phenomena further. The main outcomes of this thesis are: (1) the development and validation of a simplified method for the evaluation of the fatigue crack front shapes and their effect on the steady-state fatigue crack growth rates in plate components; (2) investigation of the effect of three-dimensional corner (vertex) singularities on the stress intensities and displacement field near the crack front; and (3) development and validation of a new experimental approach for the evaluation of mode I and mode II stress intensity factors from the measurement of the out-of-plane displacements in the near crack tip region, which are affected by three-dimensional effects, and, in particular, by the 3D corner (vertex) singularity. This new research is important in many engineering contexts. For example, the new theoretical model, which takes into account the actual shape of the crack front, can be utilised in advanced fatigue life calculations, as well as in failure investigations. The latter is possible as the shape of the fatigue crack front can now be related to the parameters of fatigue loading. The new experimental approach developed in this thesis can be useful in fracture characterisation of thick plate components with through-cracks. This approach specifically addresses the situation when the Kdominance zone, or William’s solution convergence domain, are relatively small. In this case, the data extraction region can be affected by the three-dimensional stress states leading to significant errors in the evaluation of the stress intensity factors when using traditional approaches. This thesis is presented in the form of a compendium of published papers that are the summation of the research undertaken by the author. The five articles which form the main body of the thesis are united by a common theme, which is the investigation of three-dimensional effects near the crack front on stresses and displacements, fracture and fatigue phenomena. Two appendices are also included; they represent a compilation of the candidate’s publications related to the main topic of the thesis.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Mechanical Engineering, 2016.
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Chang, Yang-Hui, and 張揚揮. "Crack Shape Evolution of Three-Dimensional Fatigue Cracks." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/21726238203286417130.
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碩士國立暨南國際大學
土木工程學系
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Fatigue is the main reason that causing heavy casualties in steel structures. In many cases of steel structure which have been fatigue failure, most of the fatigue crack initiate at the toe of weld. Because the irregular geometry of weld toe, small cracks will start from weld toe after the force loading of the members. The rate of crack growth will be faster after various cracks combined, also the crack shape will change drastically. This study use finite element method with the previous theory and establish a set of automated computer program to simulate the foregoing growth process. The result showed that whether the initial crack shape is semicircular or very shallow, the value of aspect ratio is between 0.6 and 0.8 in the last stage of growth. And the maximum length of crack growth, , model width, b and height, h, are insignificant on crack shape growth simulation. This study also discuss the crack shape evolution of two symmetrical coplanar semi-elliptical after crack combined. The simulation results show that the greater distance between the center of the semi-elliptical and plane of symmetry, the required distance of the leading edge of two cracks grows into a single smooth curve is also larger.
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Дивдик, О. В., and O. V. Dyvdyk. "Підвищення залишкової довговічності елементів авіаційних конструкцій пластичним деформуванням матеріалу в околі отворів." Diss., 2020. http://elartu.tntu.edu.ua/handle/lib/33012.
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Дана робота стосується актуальної науково-технічної проблеми
підвищення залишкової довговічності елементів авіаційних конструкцій з
концентраторами напружень. Високі вимоги до надійності конструкцій і їх
безпечної експлуатації мають особливе значення в умовах циклічного
навантаження і високих напружень. Важливою є наукова задача оцінки
залишкової довговічності конструктивних елементів з експлуатаційними
пошкодженнями (втомними тріщинами) в околі функціональних і кріпильних
отворів з підвищеними вимогами до безпечної експлуатації.This work concerns the topical scientific and technical problem of increasing the residual lifetime of elements of aircraft structures with stress concentrators. High requirements for the reliability of structures and their safe operation are of particular importance in conditions of cyclic loading and high stresses. An important scientific task is to assess the residual lifetime of structural elements with operational damage (fatigue cracks) in the vicinity of functional and mounting holes with high requirements for safe operation
Books on the topic "Fatigue crack front shape"
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Center, Langley Research, and United States. National Aeronautics and Space Administration., eds. Use of marker bands for determination of fatigue crack growth rates and crack front shapes in the pre-corroded coupons. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1997.
Find full textBook chapters on the topic "Fatigue crack front shape"
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Masuda, Kenichi, Sotomi Ishihara, Arthur J. McEvily, and Masaki Okane. "Specimen Thickness Effects on Front Edge Shape of Fatigue Crack in Al7075-T6 Alloy." In Proceedings of the 7th International Conference on Fracture Fatigue and Wear, 336–44. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-0411-8_30.
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Smith, R. A. "Condition Monitoring for Fatigue — Implications of Fatigue Crack Shape." In COMADEM 89 International, 483–87. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4684-8905-7_77.
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Gonzáles, G. L. G., J. A. O. González, V. E. L. Paiva, and J. L. F. Freire. "Crack-Tip Plastic Zone Size and Shape via DIC." In Fracture, Fatigue, Failure and Damage Evolution, Volume 6, 5–10. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-95879-8_2.
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Wu, Zhi Xue. "Shape Prediction of Fatigue Crack Based on a Given Stress Intensity Factor Distribution." In Key Engineering Materials, 19–23. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-456-1.19.
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Shimamoto, Akira, Yasubumi Furuya, and Hiroyuki Abe. "Effect of Fatigue Crack Propagation in the Shape Memory Alloy Fiber Reinforced Smart Composite." In Advances in Composite Materials and Structures, 1093–96. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-427-8.1093.
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Denk, Tomáš, Vladislav Oliva, and Aleš Materna. "Critical Strain Energy Density along the Curved Front of the Growing Fatigue Crack." In Materials Science Forum, 307–10. Stafa: Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-964-4.307.
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Verma, Rajesh P., and Shivani Pant. "Fatigue Life Prediction of Front Axle of Truck at Different Crack Directions Using ANSYS." In Lecture Notes in Mechanical Engineering, 243–50. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-33-4684-0_25.
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Shimizu, Kenichi, Tashiyuki Torii, J. Nyuya, and Y. Ma. "Effect of Residual Stress Field in Front of the Slant Precrack Tip on Bent Fatigue Crack Propagation." In Key Engineering Materials, 1207–10. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-456-1.1207.
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"Effect of Crack Shape on Fatigue Crack Growth." In Fatigue and Fracture, 159–67. ASM International, 1996. http://dx.doi.org/10.31399/asm.hb.v19.a0002359.
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Mura, T. "A theory of fracture with a polygonal shape crack." In Small Fatigue Cracks, 3–15. Elsevier, 1999. http://dx.doi.org/10.1016/b978-008043011-9/50002-8.
Full textConference papers on the topic "Fatigue crack front shape"
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Dong, Yan, Jingxia Yue, Qian Yi, Heng Zhou, and Hao Huang. "Investigation on the Abnormal Crack Front in Fatigue Crack Growth Rate Test for Thick High Tensile Steel Plate." In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-10688.
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Complex environmental loads unavoidably lead to fatigue damage in marine structures, and it becomes worse in high tensile steel thick-welded structure which has typical tri-axial stress state and the feature of brittleness. In this paper, a standard fatigue crack growth rate test for high-tensile steel Q370QE with thickness of 36 mm was carried out, and some material parameters and the threshold of stress intensity factor were obtained. Then, the abnormal behavior of a crack front during crack growth was analyzed by finite element method. Accordingly, the varying tendency of crack front shape could be qualitatively defined, and the plastic zoon at both flat and slope crack fronts for different crack depth was demonstrated based on plasticity analysis. Finally, local constraint factor was introduced to quantitatively describe the stress state along the crack front with the growth of fatigue crack, which provided proper explanation to why the crack front changes from slope to straight with the crack growing.
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Mellings, S. C., and J. M. W. Baynham. "Automatic Fatigue Crack Growth." In ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77252.
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One of the critical requirements of fatigue crack growth simulation is calculation of the remaining life of a structure under cyclic loading. This paper presents a method which predicts the remaining fatigue life of a part, and gives information on the eventual mode of failure. The path of a growing crack needs to be understood so that informed assessment can be made of the structural consequences of eventual fast growth, and the likelihood of leakage and determination of leakage rates. For these reasons the use of standard handbook solutions for crack growth is generally not adequate, and it is essential to use the real geometry and loading. The reasons for performing such simulation work include preventive investigations performed at the design stage, forensic investigations performed after failure, and sometimes forensic investigations performed during failure-when the results provide input to the planning of remedial work. This paper focuses on the 3D simulation of cracks growing in metal structures exposed to cyclic loading, and explains the techniques which are used. The loading might arise from transients of pressure or other mechanical forces, or might be caused by thermal-stress variations. The simulation starts from an initial crack which can be of any size and orientation. The relevant geometry of the cracked component is modelled, and the loading is identified using one or more load cases together with a load spectrum which shows how the loading cycles. The effects of the crack are determined by calculating stress intensity factors at all positions along the crack front (it would be called the crack tip if the modelling was performed in 2D). The rate and direction of crack growth at each part of the crack front are calculated using one of the available crack growth laws, together with appropriate material properties. The effects of such growth are accumulated over a number of load cycles, and a new crack shape is determined. The process is repeated as required. The use of multi-axial and mixed mode techniques allows the crack to turn as a result of the applied loading, and the resulting crack path is therefore a consequence of both the detail of the geometry and the loading to which the structure is subjected. Gas or other fluid pressures acting on the crack faces can have significant impact, as can the contact between opposing crack faces when a load case causes part of the crack to close.
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Bourga, Renaud, Bin Wang, Philippa Moore, and Yin Jin Janin. "The Effect of Crack Shape Idealisation on Leak-Before-Break Assessment." In ASME 2016 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/pvp2016-63877.
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Based on detailed 3D finite element (FE) analyses, idealized and non-idealized axial through-wall flaws were evaluated in a cylinder under internal pressure. The key parameters (Stress Intensity Factor, Reference stress, and Crack Opening Area) from widely accepted structural integrity assessment procedures (BS 7910 and API 579-1/ASME FFS-1) were explored and compared between idealized (perpendicular straight-sided flaw) and non-idealized geometry. The effect of crack shape on the evolution of stress intensity factors and crack opening areas along the crack front were also investigated. Non-idealized crack shapes have been modelled assuming a straight crack front with different internal and external crack lengths. The influence of crack shape has been evaluated by varying the crack front location and lengths ratios. The current findings highlight the significance of assessing a more realistic crack shape and should be considered in a leak-before-break (LBB) analysis. A non-idealized crack has a significantly smaller crack opening area than the equivalent idealized through-wall crack. Therefore the leakage rate at this stage of crack growth will be lower than predicted by standard solutions. Stress intensity factor solutions should also take the crack shape variation into account with regards to fatigue crack growth as a surface flaw propagates through-thickness.
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Price, A. J., P. Tsakiropoulos, M. R. Wenman, and P. R. Chard-Tuckey. "Modelling Fatigue Crack Growth in a Residual Stress Field." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93174.
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Tensile residual stresses can have a detrimental affect on the safe operating limits of components. In most cases, these residual stress fields can be relieved through various treatments but in many cases it is not realistic to expect the complete elimination of these stresses. When considering the Reactor Pressure Vessel (RPV) located within a Nuclear Reactor Plant (NRP), knowledge of fatigue and fracture within a residual stress field is essential in support of safety cases. This research has investigated the behaviour of flaws that lie within a residual stress field with emphasis on fracture toughness through a series of fracture toughness tests. Alongside this experimental series, a finite element model has been created to predict the stress distributions prior to fracture. To enable an accurate simulation of the residual stress field distribution before loading to fracture it is important that the introduction of a fatigue crack is accurately modelled. This paper details several methods of introducing a fatigue crack into a simulation. During this research it has been shown that the introduction of a crack in progressive stages will lead to a better representation of the residual stress distribution prior to fracture. It has been shown that it is essential to use experimentally determined crack front shapes for the final stage of crack growth as this shape can significantly alter the residual stress distribution.
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Dominguez, Garivalde, Mohammed Uddin, Minh Tran, and Do Jun Shim. "Natural Crack Growth of Nozzle Corner Crack Using Extended Finite Element Method (XFEM)." In ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-84876.
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Abstract The nozzle corner region in a pressure vessel experiences stress concentration under various loading such as internal pressure and thermal transients. There are many situations in which a postulated or detected flaw at the nozzle corner needs to be addressed for life assessment and fitness-for-service determinations which require stress intensity factor (KI) solutions. To assess the remaining life, the crack growth calculation of nozzle corner crack is typically performed with KI assuming a semi-circular or semi-elliptical crack shape which are limited to KI values at the deepest and surface points of the crack. However, due to the complex geometry of the nozzle corner crack, it is desired to compute KI along the entire crack front. To that end, the extended finite element method (XFEM) which can simulate cracks without the need for modeling the crack-tip can be used to calculate KI along the entire crack front for arbitrary crack shapes. Using the KI values calculated from XFEM, ‘natural’ crack growth can be simulated. The objective of this paper is to perform a feasibility study in evaluating the fatigue crack growth behavior of a nozzle corner crack using XFEM. For this purpose, an initial circular nozzle corner crack was used for benchmarking the KI values from XFEM against those from a traditional 3-D finite element model. In the next step, the XFEM model was subjected to cyclic internal pressure to grow the crack where the ‘natural’ crack behavior was studied. Using the fatigue crack growth equation (i.e., Paris Law), the succeeding crack profile was calculated for a given number of cycles using the K values from the previous step and the updated crack profile was then used as an initial crack in the next step. This iterative procedure is automated using Python Script in ABAQUS® and the final crack shape is determined for total number of cycles. Finally, the XFEM based fatigue crack growth results were validated using existing experimental data and were also compared against the crack growth results using an existing KI solution.
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Kannusamy, Ragupathy, and K. Ramesh. "Analytical Prediction of Fatigue Crack Growth Behavior Under Biaxial Loadings." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69480.
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Aircraft and pressure vessel components experience stresses that are negative biaxial or multiaxial in nature. Biaxiality is defined as the ratio of stress applied parallel and normal to the crack front. In recent years many experimental studies have been conducted on fatigue crack growth under various biaxial loading conditions. Biaxial loadings affect crack front stresses and strains, fatigue crack growth rate and direction, and crack tip plastic zone size and shape. Many of these studies have focused on positive biaxial loading cases. No conclusive study has been reported out yet that accurately quantifies the influence of negative biaxiality on fatigue crack growth behavior. Lacking validation, implementation on real life problems remains questionable. To ensure safe and optimum designs, it is necessary to better understand and quantify the effect of negative biaxial loading on fatigue crack behavior. In this paper, attempts were made to quantify the effect of biaxial load cases ranging from B = −0.5 to 1.0 on fatigue crack growth behavior. Also an attempt has been made to establish a simplified approach to incorporate the effect of biaxiality into da/dN curves generated from uniaxial loading using an analytical approach without conducting expensive biaxial crack growth testing. Sensitivity studies were performed with existing test data available for AA2014-T6 aluminum alloy. Detailed elastic–plastic finite element analyses were performed with different stress ranges and stress ratios with various crack sizes and shapes on notched and un-notched geometries. Constant amplitude loads were applied for the current work and comparison studies were made between uniaxial and different biaxial loading cases. It was observed from the study that negative biaxiality has a very pronounced effect on the crack growth rate and direction for AA2014-T6 if the externally applied load exceeds 20% of the yield strength as compared with 40% of externally applied load for alloy of steel quoted in the literature.
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Sugawara, Kota, Hirohito Koya, Hiroshi Okada, Yinsheng Li, Kazuya Osakabe, and Hiroshi Kawai. "Fully Automated SCC and Fatigue Crack Propagation Analyses on Deep Semi-Elliptical Flaws." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97678.
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In this paper, some results of crack propagation analyses of deep initially semi-elliptical flaws under assumed residual stress fields are presented. The crack propagation analyses were performed by using a software system that has been developed by Okada and his colleagues. It is based on a conventional finite element program but uses the quadratic tetrahedral finite elements to model the structure with the crack. The finite element model with the crack can be generated in an automated manner. The stress-intensity factor computations are performed by using the virtual crack closure-integral method (VCCM) for the quadratic tetrahedral finite element which was also proposed by Okada and his colleagues. The automatic meshing scheme for the crack propagation analyses has also been developed by the authors. By the authors’ previous publication, it was shown that the stress intensity factor of deep semi-elliptical surface flaw under assumed residual stress field reached its maximum value at the mid-depth of the crack. Hence, in present study, in order to investigate the feature of the crack propagation of deep surface cracks, we are conducting crack propagation analyses that can predict the crack extension from each point along the crack front for an arbitrary shaped surface flaw. It can also account for material anisotropy in the crack propagation behavior. Then, the SCC crack propagation analyses for a deep semi-elliptical surface flaw in a plate under assumed residual stress fields are being conducted. The results of the crack propagation analyses suggest that the shapes of the crack after the SCC crack propagation may not be exact semi-elliptic in its shape. In this paper, the analytical procedures and some results are presented. The same analytical procedures can be adopted to perform fatigue crack propagation analyses.
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Farhangdoost, Khalil, and Payman Hamrahan. "Analysis of ASME Codes for Fatigue of Pressure Vessels." In ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/pvp2010-25320.
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In industries, pressure vessels or in general thick-wall cylinders under internal pressure are important parts and analysis of their applications in various conditions is essential. Therefore, for design of pressure vessels usage of standard codes like ASME is necessary. Most of cracked or damaged pressure vessels are exposed to cyclic loading. This failure process is fatigue. ASME codes have some codes for analyzing this process. These codes show the conditions and formulas for fatigue analysis. In this paper, a thick wall pressure vessel is analyzed with three cyclic loading regimes. The maximum stress intensity, fatigue life and damage factor are calculated by ASME codes. Then by usage of finite element method, ASME results are compared for fatigue life analysis. Previous investigations show that nozzle connection area of pressure vessels have high stress concentration, and usually crack is propagated from this zone. Thus fatigue analysis is accomplished for nozzle connection of pressure vessel by ASME codes and finite element method. Then nine shape of crack with same crack front size are modeled on the maximum stress zone of the nozzle connection. Then stresses of crack fronts and stress intensity factors of cracks are computed by finite element method with ABAQUS software which is powerful for fracture mechanic analysis. The critical crack which is elliptical prismatic crack virtually is grown step by step and for each step, stress intensity factor is computed by ABAQUS software. With relation between stress intensity factor and crack size also using Paris formula, fatigue life is computed. This operation is done for two type of crack growth. In first type length and depth of crack are grown and in second type only crack length is grown. Finally, the fatigue life obtained from Paris formula and ASME codes are compared.
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Okuda, Yukihiko, Yuuji Saito, Masayuki Asano, Masakazu Jimbo, Hiroshi Hirayama, and Masaaki Kikuchi. "Crack Propagation Analysis Procedure Using FEM Applied to the Three-Dimensional Stress Field." In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71060.
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Recently, several cracks have been found on the weld joints of Boiling Water Reactor (BWR) core shrouds during inspection. In order to ensure the continuous operation of nuclear power plants, it is necessary to assess the structural integrity of core shrouds with cracks on the weld joints. In general, a crack propagates in a complicated manner according to three-dimensional stress field and it is difficult to predict crack propagation direction and crack shape change. Usually, half ellipsoid crack shape is assumed and the propagation of the crack is calculated in the constant direction for assessment. In this study, crack propagation analysis procedure using the Finite Element Method (FEM) is developed for general shaped crack, and the procedure is verified by experiments. In this procedure, it is assumed that the crack propagates according to the maximum J-integral under three-dimensional stress fields and the re-mesh technique is used in the FEM analysis in order to calculate crack shape variation during propagation. The fatigue crack propagation tests under cyclic tensile load were performed to verify the analysis procedure. The specimens are made of a plate from 316SS and designed to generate non-uniform stress distribution on the crack front in order to observe continuous crack propagation direction change.
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Kikuchi, Masanori, Yoshitaka Wada, Kazuhiro Suga, and Chikako Ohdama. "Numerical Simulation of Coalescence Behavior of Multiple Surface Cracks." In ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57155.
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Study on the interaction of multiple cracks during fatigue crack growth processes is important for the integrity evaluation of nuclear structure. By using S-version FEM, this problem has been simulated by authors. In this study, coalescence behavior of 2 surface cracks is simulated using the method. It is assumed that 2 surface cracks exist on the same plane, and grow towards each other by fatigue. As the inner crack tips overlap, coalescence of 2 cracks occurs, and shape of cracks change significantly over very short cycles. This process is simulated in detail, and changes of stress intensity factor distributions along crack front are studied precisely. Three cases of changing crack sizes are simulated and coalescence behaviors are studied. Experimental studies are also conducted and results are compared with those of numerical simulations. Results are compared with conventional evaluation code and discussed.