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Crack Propagation (crack + propagation)
Kinds of Crack Propagation Selected AbstractsIn Situ SEM Observation and Analysis of Martensitic Transformation During Short Fatigue Crack Propagation in Metastable Austenitic Steel,ADVANCED ENGINEERING MATERIALS, Issue 4 2010Ulrich Krupp Abstract High cycle fatigue (HCF) life of metastable austenitic steels is governed by the ability of the parent austenite phase to transform into ,, martensite via metastable , martensite. The mechanism of this strain-induced transformation is closely related to the grain size, the crystallographic orientation distribution, as well as to amplitude, and cyclic accumulation of plastic strain. Aim of the present study is to identify and to quantitatively describe the basic principles of strain-induced martensite formation by means of in situ cyclic deformation experiments in a scanning electron microscope (SEM) in combination with electron back-scattered diffraction (EBSD) and numerical modeling using a boundary element approach. It was shown that during HCF loading martensite formation is inhomogeneous and not directly linked with crack initiation. Only when the fatigue crack propagates by operating multiple slip systems, the cyclic plastic zone exhibits martensitic transformation. [source] Fatigue Crack Propagation and History Effects Induced by Plasticity,ADVANCED ENGINEERING MATERIALS, Issue 9 2009Sylvie Pommier Abstract For security-relevant components, a fracture mechanics assessment has to be carried out. When complex loading conditions are encountered, various problems arise. Among them the prediction of history effects induced by plasticity remains a difficult task and is the object of this paper. After an overload, for instance, plasticity-induced crack closure is known to decelerate the crack growth. This effect is known to be related to residual stresses ahead of and behind the crack tip. Since residual stresses are related to the material stress,strain behavior, the overload effect may vary significantly from one material to another. Finite-element (FE) methods are commonly employed to model plasticity and were shown to give very satisfactory results. However, if millions of cycles need to be modeled to predict the fatigue behavior of an industrial component, the method becomes computationally too expensive. By employing a multiscale approach, very precise analyses computed by FE methods can be brought to a global scale. The data generated using the FE method enables the identification of a global cyclic elastic-plastic model for the crack tip region. Once this model is identified, it can be employed directly with no need of additional FE computations, resulting in fast computations. This method was employed so as to predict fatigue crack growth under variable amplitude fatigue in steels at room temperatures and correlates well with experimental data. It was also extended so as to model fatigue crack growth in a nickel base superalloy under non-isothermal fatigue-dwell conditions. At present, the method is being extended to mixed-mode variable-amplitude loading conditions. [source] Crack Propagation in Tool Steel X38CrMoV5 (AISI H11) in SET Specimens,ADVANCED ENGINEERING MATERIALS, Issue 9 2009Masood Shah An approach is proposed for the evaluation of surface fatigue damage of hot forming tools that undergo severe thermo mechanical loading. Fatigue crack propagation in a hot work tool steel X38CrMoV5-47HRC is investigated using single-edge cracked tension specimens with 3 different thicknesses (2.5, 1, 0.6,mm) and two R-values. [source] Thirty years on from the paper ,Gust Spectrum Fatigue Crack Propagation in Candidate Skin Materials', Fatigue of Engineering Materials and Structures, Vol.FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2009IMPACT OF THE PAPER This paper1 addressed a very specific topic and by itself would not have had much impact in the intervening years. However, most of the paper's content was subsequently included in an extensive report on the Damage Tolerance (DT) properties of aluminium alloys.2 This report enabled guidelines for flight simulation fatigue crack growth testing to be formulated.3,4 [source] The Role of Filler Networking in Fatigue Crack Propagation of Elastomers under High-Severity ConditionsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2009Manfred Klüppel Abstract Structural parameters of the filler network have been evaluated by fitting quasi-static stress/strain cycles to the dynamic flocculation model. It is found that the size of filler clusters as well as the strength of filler,filler bonds increase with filler loading and carbon black activity (specific surface). This correlates with the behavior of the tear resistance obtained for pulsed loading under high-severity conditions, implying that the characteristics of the filler network govern the fracture properties of filled elastomers. The behavior of the power law exponent of fatigue crack propagation versus tearing energy can be explained by flash temperature effects in the crack tip area. [source] Crack propagation in anisotropic, plane composite structuresPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Martin Steigemann No abstract is available for this article. [source] Mechanical properties of single crystalline and glassy lithium triborateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2008I. P. Shakhverdova Abstract Mechanical properties of LiB3O5 single crystal plates with different orientation as well as of glass with the same composition have been investigated. The nano- (H) and microhardness (HM), the reduced Young's modulus (Er) and the crack behaviour of the samples were studied. Both hardness and Young's modulus of glass appeared smaller in comparison to corresponding single crystal data (H , 7 , 8 GPa, HM , 6 GPa, Er , 70 , 80 GPa for glass and H , 10 , 15 GPa, HM , 6 ,11 GPa, Er , 93 , 155 GPa for single crystal). H, Er, and the plane of crack propagation proved orientation-dependent. Cracks in the glass sample were not observed up to 0.49 N microindentation load, whereas for the single crystal the cracks appeared already at 0.098N. In single crystals the observed cleavage planes {211} and/or {412} are oriented nearly parallel to planes of B-O rings. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crack Propagation in Tool Steel X38CrMoV5 (AISI H11) in SET Specimens,ADVANCED ENGINEERING MATERIALS, Issue 9 2009Masood Shah An approach is proposed for the evaluation of surface fatigue damage of hot forming tools that undergo severe thermo mechanical loading. Fatigue crack propagation in a hot work tool steel X38CrMoV5-47HRC is investigated using single-edge cracked tension specimens with 3 different thicknesses (2.5, 1, 0.6,mm) and two R-values. [source] Suppression of Premature Fracture of Silicon under Three-Point Bending: Role of Nanoscale Localized Deformation of Metallic Multilayered Coating,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Yuan-Ping Li Brittle single crystal Si with and without Au/Cu multilayer coating was investigated via three-point bending test. Load-bearing capacity of the Si coated with the Au/Cu multilayer is improved evidently compared with the bare Si. Especially the nanoscale plastic deformation of the multilayer was observed to be effective in delaying instable crack propagation within the Si. That would shed significant light in toughening methods of brittle materials. [source] Fatigue crack initiation detection by an infrared thermography methodFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2010D. WAGNER ABSTRACT In this paper, the study of the temperature variation during fatigue tests was carried out on different materials (steels and aluminium alloys). Tests were performed at ambient temperature using a piezoelectric fatigue system (20 kHz). The temperature field was measured on the surface of the specimen, by means of an infrared camera. Just at the beginning of the test, it was observed that the temperature increased, followed by a stabilization which corresponds to the balance between dissipated energy associated with microplasticity and the energy lost by convection and radiation at the specimen surface and by conduction inside the specimen. At the crack initiation, the surface temperature suddenly increases (whatever the localization of the initiation), which allows the determination of the number of cycles at the crack initiation and the number of cycles devoted to the fatigue crack propagation. In the gigacycle fatigue domain, more than 92% of the total life is devoted to the initiation of the crack. So, the study of the thermal dissipation during the test appears a promising method to improve the understanding of the damage and failure mechanism in fatigue and to determine the number of cycles at initiation. [source] On the estimation of fatigue life in notches differentiating the phases of crack initiation and propagationFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2010J. VÁZQUEZ ABSTRACT Over the last three decades, a variety of models have been developed in order to predict the life of components under fatigue. Some of the models are based on the definition of the fatigue process as a combination of the phases of crack initiation and crack propagation, considering component life as the sum of the duration of each phase. Other models consider only one of the phases; some consider only initiation while others only propagation, though in this case, from cracks with lengths in the order of the microstructural dimensions. This article will carry out a comparative analysis of the methods that consider life as the sum of the duration of both phases. In this same line, it proposes yet another method, which simulates crack growth according to damage theories. In analysing the behaviour of each model, this paper will describe various elements: the prediction that each of them produces regarding notched specimens submitted to testing, the advantages and inconveniences of each, and lastly, the possibilities of applying each of the models to more realistic geometries. [source] Experimental and numerical studies on dynamic crack growth in layered slate rock under wedge impact loads: part II , non-plane strain problemFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2007M. R. ALAM ABSTRACT Dynamic crack propagation in non-plane strain (or 3D) slate blocks under wedge impact loads was investigated numerically in this part of the paper. A parabolic-shaped crack trajectory was taken into consideration to model the crack propagation in slate blocks for analyzing the impact splitting of layered slate rock. Major and minor axes of the parabola were determined from the condition of equal mode I stress intensity factors (SIFs) along the crack front. Mode I SIFs were determined for experimental breaking loads for each increment of crack growth in a manner similar to that mentioned in part I of this paper. These values were compared with the plane strain material fracture toughness value obtained from experimental studies and very good agreement was obtained between them, for the case of actual load applied on the specimen. Numerical analysis of a field problem, i.e., separation of a large-sized slate slab from the rock strata in a slate quarry using wedge impacting, was also carried out in this paper. It can be observed that a large magnitude of load is required to break large-sized slate blocks; but this load is applied through a number of smaller load-capacity actuators-in-parallel, requiring large power capacity for the hydraulic pumps. However, this required power could be reduced considerably if the load applied on the line of hydraulic actuators is cascaded across the (line of) actuators (starting from centrally placed actuators) with a small time delay (equal to the initial crushing time in slate rock). [source] The effect of gentamicin sulphate on the fracture properties of a manually mixed bone cementFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2007M. BALEANI ABSTRACT This work investigates the effect of adding gentamicin, an antibiotic, on the fracture properties of bone cement. Endurance limit, fatigue crack propagation and fracture toughness were determined for a polymethylmethacrylate-based cement, containing 10% w/w of barium sulphate as radiopacifying agent, and the same formulation modified by the addition of 4.22% w/w of gentamicin sulphate. The antibiotic does not affect the endurance limit nor the fracture toughness of the material. There are significant differences in the parameters of the Paris' law fitting the crack growth data: once the main crack is nucleated, it initially propagates at a lower rate but thereafter accelerates faster in gentamicin loaded bone cement. Despite this difference, the growth rate for the same stress intensity factor remains of the same order of magnitude in both formulations. The addition of 4.22% w/w of gentamicin sulphate to radiopaque bone cement has a negligible total effect on the fracture properties of the material. [source] Effects of non-proportional loading paths on the orientation of fatigue crack pathFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2005L. REIS ABSTRACT Fatigue crack path prediction and crack arrest are very important for structural safety. In real engineering structures, there are many factors influencing the fatigue crack paths, such as the material type (microstructure), structural geometry and loading path, etc. In this paper, both experimental and numerical methods are applied to study the effects of loading path on crack orientations. Experiments were conducted on a biaxial testing machine, using specimens made of two steels: 42CrMo4 and CK45 (equivalent to AISI 1045), with six different biaxial loading paths. Fractographical analyses of the plane of the stage I crack propagation were carried out and the crack orientations were measured using optical microscopy. The multiaxial fatigue models, such as the critical plane models and also the energy-based critical plane models, were applied for predicting the orientation of the critical plane. Comparisons of the predicted orientation of the damage plane with the experimental observations show that the shear-based multiaxial fatigue models provide good predictions for stage I crack growth for the ductile materials studied in this paper. [source] Computational prediction of fatigue crack paths in ship structural detailsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005Y. SUMI ABSTRACT The characteristics of fatigue crack propagation and the remaining life assessment of ship structures are investigated focusing attention on a curved crack path due to the effects of welds, complicated stress distributions at three-dimensional structural joints and structural redundancy. An advanced numerical simulation method is demonstrated for the remaining life assessment for curved crack propagation. The simulation method is based on a step-by-step finite-element analysis. The crack path is predicted by the perturbation method with the local symmetry criterion, which gives a higher order approximation of the crack path, while the finite-element re-zoning is carried out by an improved paving method. Fatigue crack paths in the welded structural details of the transverse girder of a ship structure are investigated by experiments and simulation. The present method may offer an efficient simulation-based tool for the design of critical details, which prevents the failure of the plates forming a compartment boundary. [source] Effects of solidification structure on tear resistance of Al,7% Si,0.4% Mg cast alloysFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2004S.-W. HAN ABSTRACT The tear resistance behaviour of Al,7% Si,0.4% Mg cast alloys was examined using Kahn-type tear test specimens. Tests were performed for two permanent mould casts with an ordinary dendrite structure and a semi-liquid die cast with a globular cell and fine grain structure. The microstructure of the two permanent mould casts was controlled by the cooling rates and the addition of Ti elements. Tear resistance was evaluated by the ,pop-in' stress, the energies required for crack initiation, UEi and the crack propagation, UEp. Special attention was paid to an effective microstructural parameter for tear resistance improvement. Pop-in, indicating sudden crack extension and arrest, was observed in all specimens. Homogeneous deformation occurs near the notch tip of the semi-liquid die cast, characterized by a refined grain structure. Refinement of the grain size is more effective than that of the dendrite cell size or eutectic Si particle size to increase the energy for crack initiation. Unit propagation energy, UEp, can be converted into a critical stress intensity factor, Kc, which in the semi-liquid die cast was improved due to an increased amount of slant or shear fracture surface. [source] Image analysis to reveal crack development using a computer simulation of wear and rolling contact fatigueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2003D. I. FLETCHER ABSTRACT Plastic flow of near-surface rail material under contact loading is a feature of rail,wheel contact, and severe flow typically leads to both wear, and the initiation and development of small surface-breaking cracks. This paper presents results from a ratcheting based computer simulation, which has been developed to allow the simultaneous investigation of wear, crack initiation and early crack propagation. To identify repeatably small crack-like flaws, image analysis is applied to the visual representation of the wearing surface generated by the model. This representation shows a good similarity to traditional micrographs taken from sections of worn surfaces. The model clearly reveals the interaction of wear with crack development, processes which are linked because wear truncates surface-breaking cracks, and can completely remove small surface-breaking cracks. [source] Variable amplitude loading in the very high-cycle fatigue regimeFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8-9 2002S. E. STANZL-TSCHEGG ABSTRACT Ultrasonic fatigue testing is appropriate to perform random loading tests in the regime of very high numbers of cycles. It has been shown that neither an endurance limit nor a threshold stress intensity exists under loading with randomly varying amplitudes even for materials that do show these limits under constant amplitude loading conditions. The technical features of the ultrasonic testing technique in order to perform random fatigue tests are shortly described. Endurance tests were performed on smooth specimens of AlSi7Mg (A356.0) aluminium alloy and on notched AISI 4142 and C45 steel specimens. The previous studies of crack propagation and threshold behaviour on AISI 420 ferritic chromium steel and GGG 100-B cast iron are included. Experimental results on lifetime and fatigue crack growth measurements under randomly varying amplitudes, as well as lifetime predictions, based on constant amplitude measurements and damage accumulation calculations are reported. [source] Mechanical and microstructural investigations into the crack arrest behaviour of a modern 2¼Cr-1 Mo pressure vessel steelFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2001E. Bouyne Tests were performed on a 2¼ Cr,1 Mo steel to measure the fracture toughness at initiation, KIc and at arrest, KIa,. The results were compared with those obtained on another pressure vessel steel (A508) of similar strength. Two techniques were used to measure KIa,: (i) isothermal compact crack arrest (CCA) tests, and (ii) specially designed thermal shock experiments using an externally notched ring. These specimens were cooled to ,196 °C and then heated by induction in the centre of the ring to produce very steep thermal gradients. This caused crack initiation from the notch. The crack propagates very rapidly (,500 m s,1,) and stopped when it reached the warmer region of the specimen. The specimens were analysed using an elastic,plastic finite element method to determine KIa values. These tests reveal a greater temperature shift (,100 °C) between KIc and KIa in 2¼ Cr,1 Mo steel than in A508 steel. Detailed metallographical examinations of the micromechanisms of crack propagation and arrest in the 2¼ Cr,1 Mo steel showed that this involves the nucleation of a three-dimensional network of cleavage microcracks which change their direction at bainitic packet boundaries. The remaining uncracked ligaments between the cleavage microcracks break by ductile rupture mechanism [source] Void growth and damage models for predicting ductile fracture in weldsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2000Wilsius This study reports on a numerical and experimental investigation of ductile tearing using a local approach to fracture. Two models have been analysed: (i) the Rice,Tracey (RT) void growth model; and (ii) the Rousselier continuum damage theory. The effects of the model parameters, including the mesh size, on the crack growth behaviour have been analysed, and a significant influence on both the J -values and the slopes dJ/da has been noted. The crack propagation in an overmatched welded joint has also been investigated. For the RT model, crack propagation has been simulated using the release node technique. Because this method requires one to previously assign the crack propagation path, using such a model is somewhat restrictive. This problem vanishes when dealing with Rousselier's model (and more generally with coupled models) because the elements which are damaged automatically give the crack path. [source] Action of Force on Rock Mass by Crack Water PressureGEOMECHANICS AND TUNNELLING, Issue 6 2008Guntram Innerhofer Dipl.-Ing. The formula of effective stress used in soil mechanics is adapted to the properties of rock mass by implementation of the wetting factor and the Saint-Venant factor. The wetting factor defines the area over which a hydrostatic force can actually be developed, the Saint Venant factor defines the component of this force which is balanced by reduction of the effective stress in the crack zone. Here, the consequences of this concept are discussed with respect to uniaxial, plain stress and a continuum mechanical model. The effect of the concept is considered in relation to the state of stress in crack zones, and in the adjacent rock mass, and on the action of forces on the system. The development of crack propagation and of shear failure is discussed. The intention is to contribute towards a basic understanding of the complex effects of water pressure in rock masses, applicable to engineering practice. Kraftwirkung des Kluftwasserdrucks auf Fels Die Formel für Effektivspannungen der Bodenmechanik wird, den Eigenschaften von Fels entsprechend, durch Einführen des Benetzungsgrads und des Saint-Venant-Faktors erweitert. Der Benetzungsgrad definiert die Fläche, auf die eine hydrostatische Kraft wirken kann, der Saint-Venant-Faktor die Komponente dieser Kraft, die in der Kluftfläche durch Reduktion der Effektivspannungen ausgeglichen wird. Die andere Komponente belastet das System. Anhand eines einachsigen, eines ebenen und eines Kontinuum-Mechanischen Modells werden die aus diesem Ansatz abgeleiteten Spannungszustände in der Kluftfläche beziehungsweise im klüftigen Fels diskutiert. Die Entwicklung von Kluftsprengung und Scherbruch und das Verhalten hoch- und tiefliegender Druckstollen werden beschrieben. Beabsichtigt ist, mit einer möglichst geschlossenen, auf das Wesentliche beschränkten Darstellung das Verständnis der komplexen Zusammenhänge zu fördern. [source] Cracking risk of partially saturated porous media,Part I: Microporoelasticity modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2010Bernhard Pichler Abstract Drying of deformable porous media results in their shrinkage, and it may cause cracking provided that shrinkage deformations are hindered by kinematic constraints. This is the motivation to develop a thermodynamics-based microporoelasticity model for the assessment of cracking risk in partially saturated porous geomaterials. The study refers to 3D representative volume elements of porous media, including a two-scale double-porosity material with a pore network comprising (at the mesoscale) 3D mesocracks in the form of oblate spheroids, and (at the microscale) spherical micropores of different sizes. Surface tensions prevailing in all interfaces between solid, liquid, and gaseous matters are taken into account. To establish a thermodynamics-based crack propagation criterion for a two-scale double-porosity material, the potential energy of the solid is derived, accounting,in particular,for mesocrack geometry changes (main original contribution) and for effective micropore pressures, which depend (due to surface tensions) on the pore radius. Differentiating the potential energy with respect to crack density parameter yields the thermodynamical driving force for crack propagation, which is shown to be governed by an effective macrostrain. It is found that drying-related stresses in partially saturated mesocracks reduce the cracking risk. The drying-related effective underpressures in spherical micropores, in turn, result in a tensile eigenstress of the matrix in which the mesocracks are embedded. This way, micropores increase the mesocracking risk. Model application to the assessment of cracking risk during drying of argillite is the topic of the companion paper (Part II). Copyright © 2009 John Wiley & Sons, Ltd. [source] Cracking risk of partially saturated porous media,Part II: Application to drying shrinkageINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2010Bernhard Pichler Abstract Drying of deformable porous media results in their shrinkage, and it may cause cracking provided that shrinkage deformations are hindered by kinematic constraints. Herein, we focus on slow drying of an initially water-saturated sample of a microheterogeneous poroelastic material damaged by parallel mesocracks. The cracking risk is analyzed by means of the thermodynamics-based microporoelasticity model described in the companion paper (Part I), which is extended toward consideration of the hierarchical organization of cracked argillite. Drying of a material sample is studied in a framework where macrodisplacements in direction of the crack normal are blocked, while elsewise macrostress-free boundary conditions prevail. The model implies that the opening/closure behavior of the cracks is governed by an effective pressure, in which the average crack (under)pressure, making the crack opening smaller, competes with the average micropore (under)pressure that makes the crack opening larger. The driving force for crack propagation is a quadratic function of this effective pressure. The model proposes that if drying shrinkage deformations are hindered by kinematic constraints, onset of cracking becomes possible once air entry into the cracks is observed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Mode I crack propagation in concrete under fatigue: microscopic observations and modellingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2002A. Toumi Abstract In this study, three-point bending tests were carried out on notched beams to investigate mode I crack propagation in plain concrete under fatigue. The first part of the study focused on microscopic observations of the crack growth features. Microscopic observations were made using the replica method associated with scanning electron microscopy (SEM). Observations of fatigue crack growth both on the surface and inside the specimens are presented as a comparison between the observed crack lengths and those estimated by the compliance calibration method. In the second part, a finite element model of mode I crack propagation under fatigue is presented. According to the cohesive crack concept, a cohesive force distribution on the crack at various loading stages is assumed, according to both the stress-crack opening relation worked out by Hordijk (1991; Thesis, Technische Universiteit) and a new proposed relation with hysteresis loop. Finite element computation is used to evaluate the crack extension in the bending beams. Numerical predictions are discussed in comparison with experimental results. Copyright © 2002 John Wiley & Sons, Ltd. [source] Self-similar solution of a plane-strain fracture driven by a power-law fluidINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2002J. I. Adachi Abstract This paper analyses the problem of a hydraulically driven fracture, propagating in an impermeable, linear elastic medium. The fracture is driven by injection of an incompressible, viscous fluid with power-law rheology and behaviour index n,0. The opening of the fracture and the internal fluid pressure are related through the elastic singular integral equation, and the flow of fluid inside the crack is modelled using the lubrication theory. Under the additional assumptions of negligible toughness and no lag between the fluid front and the crack tip, the problem is reduced to self-similar form. A solution that describes the crack length evolution, the fracture opening, the net fluid pressure and the fluid flow rate inside the crack is presented. This self-similar solution is obtained by expanding the fracture opening in a series of Gegenbauer polynomials, with the series coefficients calculated using a numerical minimization procedure. The influence of the fluid index n in the crack propagation is also analysed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Computation of the J -integral for large strainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008Ágnes Horváth Abstract The phenomenon of failure by catastrophic crack propagation in structural materials poses problems of design and analysis in many fields of engineering. Cracks are present to some degree in all structures. They may exist as basic defects in the constituent materials or they may be induced in construction or during service life. Using the finite element method, a lot of papers deal with the calculation of stress intensity factors for two- and three-dimensional geometries containing cracks of different shapes under various loadings to elastic bodies. In order to increase the accuracy of the results, special elements have been used. They are described together with methods for calculating the stress intensity factors from the computed results. At the vicinity of a crack tip, the strains are not always small, but they may also be large. In this case, the J -integral can also be applied to characterize the cracks in elastic or elastic,plastic bodies. This paper describes the computation of the two-dimensional J -integral for large strains to elastic and elastic,plastic bodies and represents some numerical examples. Copyright © 2007 John Wiley & Sons, Ltd. [source] Towards the algorithmic treatment of 3D strong discontinuitiesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2007J. Mergheim Abstract A geometrically non-linear finite element framework for the modelling of propagating discontinuities in three-dimensional continua is presented. By doubling the degrees of freedom in the discontinuous elements, the algorithm allows for arbitrary discontinuities which are not restricted to inter-element boundaries. The deformation field is interpolated independently on both sides of the discontinuity. In contrast to the X-FEM, the suggested approach thus relies exclusively on displacement degrees of freedom. On the discontinuity surface, the jump in the deformation is related to the cohesive tractions to account for smooth crack opening. Computational difficulties characteristic of three-dimensional crack propagation are addressed. The performance of the method is elaborated by means of a homogeneous three-dimensional tension problem and by means of the classical peel test. Copyright © 2006 John Wiley & Sons, Ltd. [source] Efficient finite element simulation of crack propagation using adaptive iterative solversINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2006A. Meyer Abstract This paper delivers an efficient solution technique for the numerical simulation of crack propagation of 2D linear elastic formulations based on finite elements together with the conjugate gradient method in order to solve the corresponding linear equation systems. The developed iterative numerical approach using hierarchical preconditioners has the interesting feature that the hierarchical data structure will not be destroyed during crack propagation. Thus, it is possible to simulate crack advance in a very effective numerical manner, including adaptive mesh refinement and mesh coarsening. Test examples are presented to illustrate the efficiency of the given approach. Numerical simulations of crack propagation are compared with experimental data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Computational modelling of the surface fatigue crack growth on gear teeth flanksINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 8 2001S. Glode Abstract The paper describes a 2-dimensional computational model for simulation of the surface initiated fatigue crack growth in the contact area of gear teeth flanks that leads to surface pitting. The discretized model of a gear tooth with the assumed initial crack is subjected to normal contact pressure, which takes into account the EHD-lubrication conditions and tangential loading due to friction between gear teeth flanks. The model accounts also for the influence of a fluid driven into the crack by hydraulic mechanism on crack propagation. The J -integral method in the framework of the finite element analysis is used for simulation of the fatigue crack propagation from the initial to the critical crack length, when the surface material layer breaks away and pit appears on the surface. The model is applied to a real pitting problem of a gear and corresponding computational results in terms of pit sizes correlate well to the development of micropits observed in experimental testing. Copyright © 2001 John Wiley & Sons, Ltd. [source] Smoothed nodal forces for improved dynamic crack propagation modeling in XFEMINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010Thomas Menouillard Abstract Improvements in numerical aspects of dynamic crack propagation procedures by the extended finite element method are described and studied. Using only the discontinuous enrichment function in XFEM gives a binary description of the crack tip element: it is either cut or not. We describe a correction force to modify the forces to smoothly release the tip element while the crack tip travels through the element. This avoids creating spurious stress waves and improves the accuracy of the stress intensity factors during propagation by decreasing the oscillations. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||||||||