Papers by Keyword: Cohesive Crack Model

Abstract: A major difficulty in simulating load response of a concrete structure in mixed-mode fracture lies in the fact that crack path is not known a priori. Predicting both the crack path and the associated load response involves advanced simulation techniques and novel numerical methodologies. Here, an intrinsic cohesive crack model is employed to study mixed-mode fracture in a concrete beam. The present approach requires neither preliminary results from linear elastic fracture mechanics simulations nor a re-meshing procedure or special implementation to prevent crack locking. Simulations with regular meshes illustrate that this concise approach can provide a reasonable estimation of peak load of the pre-cracked concrete beams in mixed-mode fracture. This study shows that the energy ratio in the bilinear softening law has larger effects than the stress ratio.

Abstract: This paper presents a numerical study of failure behavior of cementitious composite materials differing in their composition (aggregate size). A set of four different materials was tested in atypical splitting test geometry. During these tests, apart from the typical outputs such as the load–displacement curves, signals from failure events causing acoustic emission (AE) were recorded. However, reliability of the procedures of the failure events localization might seem questionable in some cases – therefore, the test evaluation procedures were accompanied by analyses using 3D numerical simulation tools based on nonlinear fracture-mechanics approach and propagation of fracture events in the specimens are performed using two computational codes. One is a commercial non-linear FEM code with implementation of cohesive crack model (in the smeared cracks formulation). The second one is an own developed discrete lattice-type model. The comparison of AE records from the tests with the results of the performed numerical simulations can answer questions on the distribution and magnitude (and possibly the energy dissipation amount) of the recorded failure events and generally help in the interpretation and exploitation of AE in the research of failure of non-electric building materials.

Abstract: This article presents a new material model developed with the aim of analyzing failure of blunt notched components made of nonlinear brittle materials. The model, which combines the cohesive crack model with Hencky's theory of total deformations, is used to simulate an experimental benchmark carried out previously by the authors. Such combination is achieved through the embedded crack approach concept. In spite of the unavailability of precise material data, the numerical predictions obtained show good agreement with the experimental results.

Abstract: The cohesive crack model and the crack band model are two convenient approaches in concrete fracture analysis. They can describe in full the fracture process by the different manner: The entire fracture process zone is lumped into the crack line and is characterized in the form of a stress-displacement law which exhibits softening; or the inelastic deformations in the fracture process zone are smeared over a band of a certain width, imagined to exist in front of the main crack. The correlation of the two models is developed based on a characteristic width of crack band. The analysis shows that they can yield about the same results if the crack opening displacement in the cohesive crack model is taken as the fracturing strain that is accumulated over the width of the crack band model. Some basic problems are also discussed in finite element analysis.

Abstract: The cohesive crack model is widely employed to the fracture analysis of concrete for mode I crack. The tension softening relationship is a very important constitutive law in the cohesive crack model. The determination methods of tension softening relationship of concrete are introduced in this paper which are direct tension methods, J-integral method and inverse analysis method. Meanwhile, those simplified softening curves including linear form and nonlinear form are summarized.

Abstract: In this paper, the Symmetric Galerkin Boundary Element Method for Linear Elastic Fracture Mechanics is extended to non-linear cohesive cracks propagating through homogeneous linear elastic isotropic media. The cohesive model adopted is based on the concept of free energy density per unit undeformed area. The corresponding constitutive cohesive equations present a softening branch which induces a potential instability. Thus, a suitable solution algorithm capable of following the growth of the cohesive zone is needed, and in the present work the numerical simulation is controlled by an arc-length method combined with a Newton-Raphson algorithm for the iterative solution of nonlinear equations. The Boundary ElementMethod is very attractive for modeling cohesive crack problems as all nonlinearities are located on the boundaries of linear elastic domains. Moreover a Galerkin approximation scheme, applied to a suitable symmetric boundary integral equation formulation, ensures an easy and efficient treatment of cracks in homogeneous media and an excellent convergence behavior of the numerical solution. The cohesive zone model is applied to simulate a pure mode I crack propagation in concrete. Numerical results for three-point bending test are used to check the numerical results for mode I and are compared with some numerical results obtained by FEM analysis found in the literature.