Luis Kosteski

Crack propagation in elastic solids using the truss-like discrete element method

The crack propagation simulation is still an open problem in the mechanical simulation field. In the present work this problem is analyzed using a version of truss-like Discrete Element Method, that here we called DEM. This method has been used with success in several applications in solid mechanical problems where the simulation of fracture and fragmentation is relevant. The formulation of DEM explaining the way the process of rupture could be simulated in consistent form is showed. Also are described details about how the dynamical fracto-mechanical stress intensity factors are computed. The main aim of this paper is to show the ability of this method in simulating fracture and crack propagation in solids, for this, three examples with different levels of complexity are analyzed. The obtained results are presented in terms of the variation of dynamic stress intensity factor in the fracture process, the stress map and geometric configuration on different steps in the simulation of the fracture process, the crack speed and the energetic balance during all the process. These results are compared with experimental and numerical results obtained by other researchers and published in recognized scientific papers. Final commentaries about the performance of the version of lattice model considered are carried out.

The truss‐like discrete element method in fracture and damage mechanics

Purpose – The purpose of this paper is to further develop the truss‐like discrete element method (DEM) in order to make it suitable to deal with damage and fracture problems.Design/methodology/approach – Finite and boundary elements are the best developed methods in the field of numerical fracture and damage mechanics. However, these methods are based on a continuum approach, and thus, the modelling of crack nucleation and propagation could be sometimes a cumbersome task. Besides, discrete methods possess the natural ability to introduce discontinuities in a very direct and intuitive way by simply breaking the link between their discrete components. Within this context, the present work extends the capabilities of a truss‐like DEM via the introduction of three novel features: a tri‐linear elasto‐plastic constitutive law; a methodology for crack discretization and the computation of stress intensity factors; and a methodology for the computation of the stress field components from the unixial discrete‐elem...

The size effect in quasi-brittle materials: Experimental and numerical analysis

The size effect in structures is responsible for the materials apparent properties variations as function of size. Different methodologies are proposed in the literature to address this phenomenon; however, there is still no consensus on how to specifically deal with this. For instance, if the material investigated were a quasi-brittle material, it would present a fissures development in different scales during the damaging process. In the present work, an experimental study applying uniaxial tension over expanded polystyrene specimens of different sizes is proposed. The acoustic emission events occurring during the tests were also recorded. A tailored version of a lattice discrete element method was used to simulate the tests. This numerical approach take into account several phenomena related with the damage process in quasi-brittle materials, such as the localization effect, the fractal dimension nature of the region over which the damage evolves; the collaborative effect between cluster of fissures and the avalanche effect during the damage process. It is important to mention that these characteristics are associated with the correct simulation of the acoustic emission registry. The obtained experimental and simulated results were in great agreement and clearly showed a size effect, despite the narrow range of dimension explored. The size effect evaluated during the simulations, in terms of the dissipated energy, is shown to be in agreement to the known fractal theory proposed by Alberto Carpinteri and coworkers. Moreover, results in terms of acoustic emission are preliminarily explored to determine the correlation between the acoustic emission events and the fracture mode that governs the source of these events. Finally, some conclusions related to the size effect captured during the tests and the possibilities for simulations of the fracturing process in quasi-brittle materials provided by the numerical method are point out.