Tatsuro Nishiyama

Numerical modelling of spontaneous crack generation in brittle materials using the particle simulation method

Purpose – The main purpose of this paper is to present and use the particle simulation method to explicitly simulate the spontaneous crack initiation phenomenon in brittle materials, and to compare the particle simulation results with experimental ones on the laboratory scale.Design/methodology/approach – Using the particle simulation method, the brittle material is simulated as an assembly of particles so that the microscopic mechanism of inter‐ and intra‐particle crack initiation can be straightforwardly considered on the microscopic scale. A laboratory test has been conducted using a gypsum sample model to validate the particle simulation method for explicitly simulating the spontaneous crack initiation phenomenon.Findings – The paper finds that in terms of simulating the macroscopic sliding surface along or around the contact plane between a block and its foundation, both the laboratory test and the particle simulation have produced consistent results. This indicated that the particle simulation metho...

NUMERICAL EXPERIMENT FOR VIRTUAL PLASTER MODEL TESTS SIMULATING BLOCK SHEAR TESTS

The strength of in-situ rock masses has been estimated by in-situ rock shear tests for a long time. However, the mechanisms for the appearance of strength in such tests have not been clarified sufficiently. This paper presents the results of a numerical analysis of virtual plaster model tests used to simulate block shear tests, which are of a kind of in-situ test. In the authors’ former study, results were obtained for rock shear tests, another kind of in-situ test, along with real plaster model tests and finite element analyses. In the present study, some cases simulating block shear tests were analyzed. The appearance and propagation of cracks in the testing process were simulated with enhanced elements, which represented the displacement discontinuity in each element, as in the former analysis. The results were compared with the former results to investigate the differences between the two conditions. The shear strength in the two sets of results was found to be generally similar; however, there were some small differences. The patterns for the appearance and propagation of cracks differed from each other, while some common features also appeared. The concentration of stress in the two testing processes occurred in different parts of the materials under the two conditions, and this led to differences in both the failure mechanism and the shear strength.

Finite element analysis for the shear strength appearing in in situ rock shear tests

The mechanisms of the strength which appeared in in situ rock shear tests were examined with a finite element analysis in this paper. A set of plaster model laboratory tests simulating the in situ rock shear tests was analyzed. The plaster models were expressed initially with constant strain triangles (CSTs). Then, the displacement was imposed gradually, and each CST was replaced with a triangular element containing an embedded interface at the point when the stress in each CST reached the failure criterion of the material. The cracking patterns and the deformation obtained from the computation resembled those in the laboratory tests. The cracking pattern under each normal stress deviated from that under different conditions; and therefore, the stress path and the shear strength appeared differently under the various normal stress conditions. The relationship between the apparent shear strength and the failure criterion of the material also changed depending on the normal stress. The shear strength measured in the model tests appeared to be lower than the material strength in the lower and in the higher normal stress ranges. Such differences were thought to occur due to the influence of the stress distributions, which were not assumed, but were caused by several different cracking patterns.