A size-dependent bond failure criterion for cemented granules based on experimental studies

In order to establish a new bond failure criterion for bonded particles to be used in two-dimensional Discrete Element Modelling, the mechanical behavior of cemented granules with different cement sizes were investigated. In this paper, experimental results of five series of loading tests on cemented granules with four cement widths were presented. Then incorporated the previous experiments with different cement thicknesses, a bond failure envelope dependent on the cement size was proposed. Among a total of about 600 pairs of tested samples, three failure modes were found. Only the failure mode, in which the failure surface was regular and mechanical responses were stable and repeatable, was considered as the representative results and adopted to establish the bond failure model. The experimental results showed that: the peak normal forces in the compression and tension tests are dependent on the cement size; the peak shear forces or peak torsions in the loading tests with complex loading paths, i.e. combined compression shear test, combined compression torsion test and combined compression shear torsion test, are dependent on the normal force and cement size. The peak shear force or peak torsion increases with the normal force when the normal force is smaller than a critical value, while decreases as the normal force is larger than the critical value. The failure envelope in the nomal-shear-torsion space is in an ellipsoidal shape with a cut-off as the normal force reaches the peak compression force. It expands with the cement width and shrinks with the cement thickness. (C) 2015 Elsevier Ltd. All rights reserved.