Simulation of uniaxial tensile behavior of quasi-brittle materials using softening contact models in DEM

Abstract

This study proposes new contact models to be incorporated into discrete element method (DEM) to more accurately simulate the tensile softening in quasi-brittle materials, such as plain concrete and masonry with emphasis on fracture mechanism and post-peak response. For this purpose, a plain concrete specimen (double notched) and stack bonded masonry prism under direct tensile test are modeled. Furthermore, mixed mode crack propagation is investigated in concrete and brickwork assemblages. Two modeling approaches are proposed, the simplified and detailed meso modeling, both based on DEM. In the simplified meso-model, a smooth contact surface is considered between two separate blocks, whereas the internal structure of the material is explicitly represented as a tessellation into random polyhedral blocks in the detailed meso-model. Furthermore, recently developed tensile softening contact constitutive models implemented into a commercial discrete element code (3DEC) are used to simulate the softening behavior of concrete and masonry. As an important novel contribution, it is indicated that the proposed computational models successfully capture the complete (pre-and post-peak) material behavior and realistically replicate the cracking mechanism. Additionally, a sensitivity analysis demonstrates the influence of the various micro-contact parameters on the overall response of the examined materials.

Numerical modeling of the tension stiffening in reinforced concrete members via discontinuum models

“…Similar behavior can be observed in the computational model, in which the crack occurs at the contact point that has reached the capacity and presents an irregular cracking pattern under incremental tensile forces (see Figure 5). For further details on the discontinuum analysis of plain concrete subjected to direct tension, the readers are referred to [29]. Hence, the results show that the tension-softening response of concrete can be captured through semi-rigid discrete polyhedral blocks with tensile softening contact models based on the dynamic stress update scheme of DEM.…”

“…Recently, quasi-brittle construction materials (e.g., concrete and masonry) were analyzed with the same strategy, where the Laguerre tessellation was generated by the weighted points optimized to obtain specified morphological properties of the polyhedral bocks [28][29][30]. The objective was, therefore, to obtain a phenomenological approach in which the observed mechanisms are represented in such a fashion that simulations are in reasonable agreement with experiments.…”

“…The cohesion strength is assumed two times of the tensile strength, which does not have drastic influence when it is larger than as previously presented by Pulatsu et. al [29]. The results of the analyses are presented in Figure 5, revealing the stress-displacement curves of discrete element-models with different numbers of blocks.…”

Simulation of the in-plane structural behavior of unreinforced masonry walls and buildings using DEM

“…Rigid blocks may be preferable for dynamic analysis compared to deformable blocks since the rigid block model has less computational demand [14]. In DEM, discrete bodies can be represented as circular particles or polyhedral blocks considering different scales, which depend on the type of problem [15][16][17][18][19].…”

“…In this study, instead of using the standard built-in contact model in 3DEC, a new contactconstitutive model is implemented to be utilized in the explicit solution scheme of DEM ( Figure 3). It is worth noting that the proposed contact stress-displacement behavior captures all possible failure modes in masonry given in [15,16], including softening regimes in tension and shear by considering fracture energy concept at the contact stress-displacement functions. The Coulomb-…”