Modification of the G-criterion for crack propagation subjected to compression

Abstract

Brittle materials subjected to compression can fail and the resulting cracks can propagate in mode I and mode II in two dimensions. The maximum strain energy release rate criterion ( G-criterion) is examined for its capacity of predicting the mixed mode crack propagation. When this criterion is applied to an inclined crack subjected to compression, it predicts the shear failure but not the tensile failure. The reason for this phenomenon is discussed and a new form of this criterion, namely the F-criterion, is proposed. The F-criterion uses the sum of normalized G I and G II (F = G I/G Ic + G II/G IIc) as the factor which represents the crack propagation and its direction. Implemented into the numerical displacement discontinuity method (DDM), the F-criterion can predict both mode I and mode II propagation of a crack system. The capacity of the F-criterion in predicting both mode I and mode II propagation is demonstrated for two models subjected to uniaxial compression for a single crack and a set of two cracks. The numerical simulations show good agreement with the results of laboratory experiments conducted on rocks and gypsum.