Type I Fracture Toughness Test of Rock-like Materials Based on the Particle Flow Method

Bangyong Yu,Ling Yue,Chengxi Zhao,Fei Huang,Fei Guo

doi:10.1155/2020/8812205

Abstract

In order to investigate the feasibility and reliability of the three-dimensional particle flow method in simulating the type I fracture toughness test, four types of numerical samples were established by particle flow code PFC3D: straight crack three-point bending (SC3PB), edge cracked flattened semicircular disc (ECFSD), cracked chevron notched Brazilian disc (CCNBD), and edge cracked flattened ring (ECFR). Three models with different strength parameters (group A, group B, and group C) were established for each type, in which group A parameters are obtained from the concrete model, group B parameters are applied for simulating marble, and group C parameters are for granite. The type I fracture toughness and the failure form of each model are obtained by conducting the numerical test, and the curves of load versus displacement of loading point are recorded. The numerical test results show that, with the same strength parameter, the maximum difference in test results of each specimen type is 0.39 MPa·m1/2. The KIC of ECFR specimen is 0.13–0.28 MPa·m1/2 smaller than that of CCNBD specimen, and the KIC of ECFSD specimen is slightly higher than that of CCNBD sample. The KIC of SC3PB specimen is 0.06–0.21 MPa·m1/2 smaller than that of the CCNBD sample. When the loading rate is less than 0.01 m/s, the effect of loading rate on fracture toughness can be reduced to less than 0.1 MPa·m1/2.

Highlights

Huang et al [8, 9] study the influence of different particle sizes on load-displacement curves and failure modes by PFC2D. e results show that the generation of secondary cracks is mainly affected by particle sizes. e size effect in particle flow software simulation has been studied by Wong et al [10]
In order to select an optimal loading rate, the SC3PB and cracked chevron notched Brazilian disc (CCNBD) sample models are established with parameters in group A, and the test is executed under three loading rates of 0.05 m/s [9], 0.01 m/s, and 0.002 m/s [26]
First of all, the rationality and validity of the test results should be preliminarily judged. rough monitoring the generation and distribution of microcracks in the model, the failure form of the sample can be observed

Summary

Research Article

Type I Fracture Toughness Test of Rock-like Materials Based on the Particle Flow Method. E real material parameters without size effect of different rock types are constructed, and the results are used to predict the fracture trend. In order to study the applicability of numerical simulation in rock materials with different strength, three groups of micro parameters (group A, B, and C) are selected for calculation and analysis (see Tables 1–3), among which the strength parameters are lowest in group A and highest in group C. e parameters in group A are calibrated according to the results of direct shear test in the laboratory. E test results show that the cohesion c of the sample is 4.93 MPa and the internal friction angle φ is 46.7° (as shown in Figure 3); take the micro parameters as group A. e calibration and modification of parameters in group C are as follows:. According to the procedures, during the Brazil tests, the loading rate is controlled as 0.1 MPa/ s. e uniaxial compress strength of granite samples is 142.3 MPa

Multiplier of radius

Results of laboratory test Results of numerical test

Results of the Numerical Test

ECFR sample