Damage index proposals applied to quasi-brittle materials simulated using the lattice discrete element method

119

The paper describes experimental and numerical results of concrete fracture under quasi-static uniaxial compression. Experimental uniaxial compression tests were performed on concrete cubic specimens. Fracture in concrete was detected at the aggregate level by means of three non-destructive methods: three-dimensional X-ray microcomputed tomography, two-dimensional scanning electron microscope and manual two-dimensional digital microscope. The discrete element method was used to directly simulate experiments. Concrete was modelled as a random heterogeneous four-phase material composed of aggregate particles, cement matrix, interfacial transitional zones and macrovoids based on experimental images. Two- and three-dimensional analyses were carried out. In two-dimensional analyses, the real aggregate shape was created by means of clusters of spheres. In three-dimensional calculations, spheres were solely used. A satisfactory agreement between numerical and experimental results was achieved in two-dimensional analyses. The model was capable of accurately predicting complex crack paths and the corresponding stress–strain responses observed in experiments.

Section: Introductionmentioning

confidence: 99%

Discrete element method simulations of fracture in concrete under uniaxial compression based on its real internal structure

Suchorzewski

Tejchman

Nitka

2017

119

“…The version of the DEM used in this work to simulate the size effect can be found in several applications, as in Miguel et al (2010) and Iturrioz et al (2009); Rios and Riera (2004) for concrete beam; Riera et al (2014) for rocks dowels; Kosteski et al (2011) for the analysis of crack propagation in solids; Rodrigues et al (2016) for damaging indexes applied to quasi-brittle materials. The LDEM also allows the simulation of acoustic emission (AE) events, as presented by Iturrioz et al (2013a) and(2013b).…”

Section: Introductionmentioning

confidence: 99%

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

Colpo

Kosteski

Iturrioz

2016

Self Cite

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.

“…The discrete element method (DEM) is emerging as an increasingly adopted method for investigating the damage behavior of materials (Chiu et al, 2015;Feng et al, 2015;Rodrigues et al, 2016;Shyshko and Mechtcherine, 2013;Zhu et al, 2008). It was originally developed by Cundall and Strack (1979) and provides a promising way to investigate the self-healing constitutive model of microcapsule-enabled self-healing cementitious materials.…”

Section: Introductionmentioning

confidence: 99%

Modeling microcapsule-enabled self-healing cementitious composite materials using discrete element method

Zhou

Zhu

et al. 2017

Concrete with a micro-encapsulated healing agent is appealing due to its self-healing capacity. The discrete element method (DEM) is emerging as an increasingly used approach for investigating the damage phenomenon of materials at the microscale. It provides a promising way to study the microcapsule-enabled self-healing concrete. Based on the experimental observation and DEM, a three-dimensional damage-healing numerical model of microcapsule-enabled self-healing cementitious materials under compressive loading is proposed. The local healing effect can be simulated in our model, as well as the stress concentration effect and the partial healing effect. The healing variable of the DEM model is developed to describe the healing process. We examine the dependence of the mechanical properties of the microcapsule-enabled self-healing material on (a) the stiffness of the solidified healing agent, (b) the strength of the solidified healing agent, (c) the initial damage of specimens, and (d) the partial healing effect. In particular, the proposed numerical damage-healing model demonstrates the potential capability to explain and simulate the physical behavior of microcapsule-enabled self-healing materials on the microscale.