Download or read book Simulation of time dependent crack propagation in a quasi brittle material under relative humidity variations based on cohesive zone approach written by Ngoc Anh Phan and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cette thèse est consacrée à la simulation du comportement à la rupture de bois sous des chargements à long terme et sous des conditions d'Humidité Relatives (HR) de l'air variables. Il est connu que le bois est un matériau fortement hygroscopique, ses propriétés mécaniques et de rupture sont en effet très dépendantes de sa teneur en eau. En outre, la stabilité d'une fissure existante dans un élément structural peut être fortement influencée parles variations, en particulier brusques, d'humidité relative qui peut conduire à la rupture inattendue de l'élément.L'approche thermodynamique proposée intègre l'effet de mécanosorption dans l'expression analytique de la déformation, en découplant les déformations mécaniques et celles dues au comportement mécanosorptif du matériau. En outre, la rupture quasi-fragile du matériau boisest traduite par un modèle de zone cohésive dont les paramètres de cohésion sont fonctions de la teneur en eau afin de simuler l'effet de l'humidité sur les propriétés de rupture. Sur cette base, une formulation incrémentale permet l'intégration de l'effet des variations soudaines d'humidité relative (autrement dit, le choc hydrique) sur la zone d'élaboration(zone cohésive) en introduisant un champ de contraintes supplémentaires le long de cette zone. Fonction de la variation de HR, ce champ de contraintes supplémentaires dépend de l'état de contrainte et de l'ouverture de la fissure le long de la zone cohésive, mais également de l'humidité en pointe de fissure (matériau non endommagé). Dans l'analyse par éléments finis, un opérateur tangent algorithmique est utilisé pour résoudre le problème non linéaire en combinant le modèle de mécanosorption et le modèle de zone cohésive et en intégrant l'effet du choc hydrique.La simulation du comportement d'une éprouvette entaillée soumise à un chargement constant et à des variations cycliques de HR montre un fort couplage entre le comportement mécanosorptif et l'effet du choc hydrique HR sur la zone d'élaboration. Ce couplage entraîne une augmentation de la propagation des fissures et conduit à une fissuration plus précoce par rapport à celle obtenue à partir du modèle de mécanosorption seul ou à partir du modèle de zone cohésive en intégrant l'effet des variations soudaines de HR. En outre, le couplage entre le modèle mécanosorptif et le modèle de zone cohésive en intégrant l'effet du chochydrique montre l'intérêt d'une telle approche numérique pour décrire le comportement complexe des éléments de charpente en bois soumis à des conditions climatiques variables,comportement qui ne peut être prédit par une simple superposition des deux modélisations.
Download or read book Simulations of Dynamic Crack Propagation in Brittle Materials Using Nodal Cohesive Forces and Continuum Damage Mechanics in the Distinct Element Code LDEC written by and published by . This book was released on 2006 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental data indicates that the limiting crack speed in brittle materials is less than the Rayleigh wave speed. One reason for this is that dynamic instabilities produce surface roughness and microcracks that branch from the main crack. These processes increase dissipation near the crack tip over a range of crack speeds. When the scale of observation (or mesh resolution) becomes much larger than the typical sizes of these features, effective-medium theories are required to predict the coarse-grained fracture dynamics. Two approaches to modeling these phenomena are described and used in numerical simulations. The first approach is based on cohesive elements that utilize a rate-dependent weakening law for the nodal cohesive forces. The second approach uses a continuum damage model which has a weakening effect that lowers the effective Rayleigh wave speed in the material surrounding the crack tip. Simulations in this paper show that while both models are capable of increasing the energy dissipated during fracture when the mesh size is larger than the process zone size, only the continuum damage model is able to limit the crack speed over a range of applied loads. Numerical simulations of straight-running cracks demonstrate good agreement between the theoretical predictions of the combined models and experimental data on dynamic crack propagation in brittle materials. Simulations that model crack branching are also presented.
Download or read book Static and Dynamic Crack Propagation in Brittle Materials with XFEM written by Fleming Petri, Wagner Carlos and published by kassel university press GmbH. This book was released on 2013-01-01 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this thesis is the simulation of progressive damage in brittle materials due to cracking. With this aim, the mathematical crack model will be solved using the eXtended Finite Element Method for the spatial discretization and time integration schemes for the numerical integration in the time domain. The time integration schemes considered are the Generalized-? method, the continuous GALERKIN method and the discontinuous GALERKIN method.
Download or read book Multi Scale Simulation of Crack Propagation in the Ductile Brittle Transtions Region written by Geralf Hütter and published by . This book was released on 2013 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Three Dimensional Gear Crack Propagation Studies written by and published by . This book was released on 1998 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three-dimensional crack growth simulation was performed on a split-tooth gear design using boundary element modeling and linear elastic fracture mechanics. Initial cracks in the fillet of the teeth produced stress intensity factors of greater magnitude (and thus, greater crack growth rates) than those in the root or groove areas of the teeth. Crack growth simulation was performed on a case study to evaluate crack propagation paths. Tooth fracture was predicted from the crack growth simulation for an initial crack in the tooth fillet region. Tooth loads on the uncracked mesh of the split-tooth design were up to five times greater than those on the cracked mesh if equal deflections of the cracked and uncracked teeth were considered. Predicted crack shapes as well as crack propagation life are presented based on calculated stress intensity factors, mixed-mode crack propagation trajectory theories, and fatigue crack growth theories.
Download or read book Numerical Modelling of Crack Propagation in Quasi brittle Heterogeneous Materials written by Elia Gironacci and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dynamic Crack Propagation in Brittle Materials written by Jozef Cornelis Walterus van Vroonhoven and published by . This book was released on 1996 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Improved Cohesive Zone Model for Ductile Dynamic Crack Propagation written by Marc Sagimon Buch and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ductile dynamic crack propagation is a current field of research in aerospace industry. The damage created by an explosion in a flying airplane depends on the fracture behaviour of the fuselage materials. Thus the rate of fracture for aluminium 2024 T3 is being studied. Analytical and empirical calculation methods do not predict correctly the experimental fracture velocity. Numerical simulations using cohesive elements with standard material models do not estimate it correctly either. Then a new numerical approach is being carried out which is focussed on a rate dependent (Perzyna) cohesive zone model. Basically, in this model the energy dissipated during the fracture depends on the fracture loading rate. To improve the accuracy of the time integration of the constitutive equations, an implicit scheme has been implemented and it has been checked the situations where a previous explicit implementation may be less accurate. New fracture experiments on aluminium pressurized barrels have been modeled using the Perzyna model. The results show a good agreement in terms crack behaviour and crack velocity. In addition it has been observed a big influence of the loads in fracture speed during the crack propagation.
Download or read book Mixed mode Crack Behavior written by Keith John Miller and published by ASTM International. This book was released on 1999 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crack Propagation Theories written by Fazil Erdogan and published by . This book was released on 1967 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: This article consists of two parts. In the first part, the crack propagation theories for brittle and quasi-brittle solids fracturing under a single application of the external loads are considered. The emphasis has been on the dynamic aspects of the fracture phenomenon and the related quantitative theories. Thus, the problem is discussed only from the viewpoint of continuum mechanics and classical thermodynamics. Two theoretical approaches are presented in detail. These are the dynamic crack propagation theory based on the concept of modulus of cohesion proposed by Barenblatt and various forms of the energy balance theory based essentially on the ideas proposed by Griffith. A detailed analysis of the energy balance around the periphery of the crack is given and it is shown that the energy available at the crack periphery to create new fracture surfaces is equivalent to the crack closure energy, which is different from the released strain energy if the inertia effects are not negligible. The results are applied to plane extensional and anti-plane shear problems. The techniques used in and the results obtained from the available experimental studies are then discussed.
Download or read book Advances in Crack Growth Modeling written by M.H. Aliabadi and published by Trans Tech Publications Ltd. This book was released on 2013-07-15 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume is indexed by Thomson Reuters BCI (WoS). Crack growth is a complex phenomenon and difficult to model without assumed simplifications. In recent years, there has been an increasing realization that advanced computational methods such as the Finite Element Method, the Boundary Element Method and Mesh Free Methods can be used to simulate crack growth in complex structural parts. This special issue contains original papers written by active researchers in the field of computational fracture mechanics. The aim is to inform those in the fracture mechanics community who might not be at the forefront of computational research of the recent developments and techniques available and the wide range of applications for which solutions are now possible.
Download or read book Crack Propagation Under Creep and Fatigue written by K. Sadananda and published by . This book was released on 1984 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crack growth under cyclic, static and combined loads in several high temperature alloys is presented from both material and fracture mechanics aspects. Parametric representation of high temperature crack growth in terms of linear and non-linear fracture mechanics is discussed along with the experimental determination of these parameters for several specimen geometries. Crack growth is characterized as cycle-dependent, time-dependent or combined cycle- and time-dependent processes depending on material, temperature, load frequency and environment. While the cycle dependent process is due to fatigue damage, the time-dependent process could be due to creep or environmental effects or both. It is shown that the applicability of a particular fracture mechanics parameter to characterize high temperature crack growth depends on micromechanics of the growth.
Download or read book Computer Simulation of Linear and Nonlinear Crack Propagation in Cementitious Materials written by Túlio Nogueir Bittencourt and published by . This book was released on 1993 with total page 668 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of computer graphics is stressed not only to control the crack propagation process, but also to allow fast and comprehensive interpretation of results.
Download or read book Problems of Mixed Mode Crack Propagation written by E.E. Gdoutos and published by Springer. This book was released on 1984-05-31 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Peridynamic Models for Crack Nucleation in Brittle and Quasi Brittle Materials written by Sina Niazi and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Failure in materials initiates from the microscale (defects, pores, etc.) and can affect, sometimes catastrophically, the structure scale. In this thesis, peridynamics (PD) is adopted to study crack nucleation in brittle and quasi-brittle materials.PD models of bodies without pre-cracks, based on a single fracture parameter (associated with the critical fracture energy), produce different strengths when different horizon sizes are used to simulate crack nucleation under quasi-static conditions. To maintain the same strength and fracture energy under different horizon sizes, extra parameters have to be introduced in the failure model, leading to, e.g. bilinear and trilinear models. We study crack nucleation in a plate with a hole under quasi-static loading using these models. We provide analytical formulas to calibrate the models to measurable material properties. We show convergence for both strength and fracture toughness, for both brittle and quasi-brittle systems. We then introduce similar PD models to study crack nucleation and rupture in soft materials, by which one can capture crack nucleation sites and final rupture similar to those seen in the experiment.In this work, we also introduce a PD model for simulating brittle damage and fracture in elastic porous materials based on an Intermediate Homogenization (IH) approach. In this approach, instead of explicitly representing the detailed pore geometry, we use homogenization but maintain some information about the microstructure (porosity) in the model. Porosity is introduced as initial peridynamic damage, implemented by stochastically pre-breaking bonds to match the desired porosity. We use the IH-PD model to study the fracture behavior of notched sandstone-type samples under three-point bending tests. Results by the IHPD model, in contrast with those with a fully-homogenized model, agree very well with experiments: we obtain different failure modes depending on the length of the off-center pre-notch. The results show the importance of inserting some information about heterogeneities (like pores) into the models aimed to study brittle damage initiation and growth in porous materials.
Download or read book Crack Propagation Associated with Stress assisted Diffusion of Impurities Under Creep Conditions written by Yan Xu and published by . This book was released on 1999 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Continuous discontinusous Model to Simulate Crack Branching in Quasi brittle Failure written by Jordi Feliu Fabà and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the material failure of quasi-brittle materials, such as concrete, is of vital importance in civil engineering. A continuous-discontinuous model using X-FEM enrichment can be useful when an explicit representation of cracks is required. Besides crack propagation, crack branching can also be modelled by the appropriate X-FEM enrichment. Multiple applications of crack branching simulation can be found, including fracking and dynamic crack propagation.
