Distinct Element Approach on Mesoscopic Fracture Mechanism in Quasi-brittle Rock

• Main Authors: Chia-Chuan Chang, 張家銓
• Other Authors: 陳立憲
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/k2sejr

碩士 === 國立臺北科技大學 === 土木與防災研究所 === 95 === Due to the growth of microcracks leading to localization within quasi-brittle materials, the engineering structure subjected to different stress paths would be caused an unexpected damage prior to peak load. Therefore, it is more important to understand the evolution of microcracks for the stability of structural materials. This study presents a numerical simulation of displacement discontinuity behavior by using Particle Flow Code in three dimensions（PFC3D）which bases on the principle of distinct element method（DEM）. First of all, we proceed the sensitivity of parametric studies to calibrate the consistency of micro-to-macro material properties during both triaxial including unconfinement case and Brazilian test, and discuss mesoscopic behavior of quasi-brittle rock under different stress paths. Secondly, the numerical results in terms of the development of micro crack as well as the failure type of cracks between particles were compared with experimental data of acoustic emission qualitatively. It evolves the failure characteristic of quasi-brittle materials by viewing mesoscopic fracture behavior and conventional global failure criterion, and provides an option to identify the location of damage zone under certain stress level. This numerical simulation shows that, by setting proper micro-geometrical parameters, a significant influence of particle radius on some macroscopic material parameters such as E, υ, qu. In this study, 7000 balls of particle numbers were used to conduct a series of parametric studies. Furthermore, the relation between micro- and macro- material properties: micro elastic modulus versus macroscopic elastic modulus, and bond strength versus confinement strength are found the existence of linear relation. In addition, there is a fair correlation between the normal/ shear stiffness and Poisson’s ratio. Macroscopic friction angle is also controlled by micro friction coefficient in spite of the upper bound of friction angle may not be controlled well with respect to different material and stress path. According to analysis of sensitivity parametric, numerical model fitting is able to match through triaxial test including unconfing case. It shows that the micro-properties of PFC3D indeed response a good agreement with laboratory results in terms of both elastic and plastic parameters. By monitoring shear/ tensile cracks increment ratio and localization of particle cracks corresponding different load level, local shear cracking somehow dominated the damage around peak in uniaxial compression test. On the other hand, by simulating Brazilian test with same micro-properties, relatively tensile crack in element which dominates damage was found. However the estimation of tensile strength is higher than laboratory experiment value about 3 times. Finally, appearance of localization are obtained about 61% and 51% for numerical simulation and experimental AE data under uniaxial test respectively, and about 65% and 61% under Brazilian test. It shows that PFC3D could be used to verify the growth of micro cracks as well as its localization qualitively.