Two important roles of porosity in the fracture pro­cess were identified. First, the interaction between the applied stress field and the pores caused loca­lized stress intensification, promoting crack initiation from favorably oriented pores at low applied stresses. Second, propagating cracks could be drawn toward pores in their vicinity, presumably under the influ­ence of the stress field around the pore. In some instances, such pore/crack encounters served to accelerate crack growth; however, occasionally, a crack was arrested by a pore and did not break free

until higher applied stresses were attained. Pores of many shapes and sizes were observed in the graphite microstructure, but larger, more slit-shaped pores were more damaging to the graphite.