AUTHOR=Li Benyun , Tian Yunlei , Tian Jiao , Zuo Shuangying , Chen Shiwan 

TITLE=Bending-damaged fracture criterion and numerical implementation of limestone beam under three-point bending test

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2023.1147129

DOI=10.3389/feart.2023.1147129

ISSN=2296-6463

ABSTRACT= To study the characteristics of tensile cracking by rock bending damage, the bending stress-strain curves and the cumulative ringing counts were obtained by three-point bending test and acoustic emission (AE) monitoring of limestone beams. Based on the lemaitre strain equivalent principle and the continuous damage theory, the bending damage variable D is defined by the AE cumulative ringing counts, and the bending crack damage evolution equation is established according to the Weibull distribution of rock element strength. To realize the numerical test of bending deformation, the damage variable D was used as the intermediate variable, the specific process of damage bending stress transformation and the realization of the tensile crack criterion were secondary developed by FISH language in FLAC3D. According to the results, the central part of rock beam deforms downward under the action of bending stress, both ends tilt up. Therefore, the bending failure begins with the tensile crack at the bottom of the rock beam, and gradually extends to the compression zone. The maximum damage value is about 0.402 before the peak stress. The compressive stress in the x direction increases from the neutral layer to the top of the rock beam, the tensile stress in the x direction increases from the neutral layer to the bottom of the rock beam. The maximum tensile stress is distributed in the central of the bottom of the specimen where the bending effect is obvious. The stress-time curve can be divided into (Ⅰ) compaction stage, (Ⅱ) expansion stage and (Ⅲ) penetration stage, accordingly, the evolution of damage equation is divided into three stages: initial damage stage, slow damage stage, accelerated damage stage. The curves of experimental result, theoretical model prediction result and numerical simulation result are in good agreement with each other, which indicated that the numerical simulation based on the criterion of rock damaged fracture can better reflect the bending process of rock beams under three-point bending stress.