Abstract
Sharply notched specimens of porous silicon carbide with porosity 37% were fatigued undercyclic four-point bending. The crack propagation curve was divided into stages I, II and III. The crack propagation rate first decreased with crack extension in stage I and became constant in stage II. In stage III, the crack propagation rate increased. The transitions from stage I to II and from II to III took place at constant values of crack extension. The anomalous variation of the crack propagation rate as a function of the crack length or the stress intensity factor was caused by crack-tip shielding due to crack face contact. The amount of crack-tip shielding was estimated from in-situ SEM observation of crack opening behavior of cracks.
