In this paper, the cracks situated along a straight line were investigated, and using complex stress functions, the stress intensity factors were formulated.For the two cases of only two collinear cracks and a single crack inside an infinite plate, the exact solutions of stress intensity factors were presented. Finally, by using the two collinear crack model and a single crack model, a new fracture criterion for brittle materials under compression was developed based on the traditional fracture criterion. In some special cases, this new crack propagation criterion can be simplified, and the results were very interesting, especially, for the case of materials without pre existing macrocracks, the new crack propagation criterion was identical with the well known Coulomb Mohr criterion.
