Crack propagation and coalescence in brittle materials under compression

Two particular cases concerning crack propagation and coalescence in brittl e materials have been modeled by using the rock failure process analysis co de, RFPA(2D), and the results have been validated by reported experimental observations. Firstly, axial compression of numerical samples containing a number of large, pre-existing flaws and a row of suitably oriented smaller flaws are simulated. It has been confirmed that under axial compression, wi ng-cracks nucleate at the tips of the pre-existing flaws, grow with increas ing compression, and become parallel to the direction of the maximum far-fi eld compression. However, coalescence of the wing-cracks may be in either t ensile mode or shear mode, or a combination of both modes. The numerical re sults show qualitatively a reasonably good agreement with reported experime ntal observations for samples with similar flaw arrangements. The numerical results demonstrate that, with a confining pressure, the crack growth is s table and stops at some finite crack length; whereas a lateral tensile stre ss even with a small value will result in an unstable crack growth after a certain crack length is attained. Secondly, failure mode in a sample contai ning inhomogeneities on grain scale has also been simulated. The results sh ow that the failure mode strongly depends on the mechanical and geometric p roperties of the grains and inclusions. (C) 1998 Elsevier Science Ltd. All rights reserved.