An investigation into the location of crack initiation sites in alumina, polycarbonate and mild steel

The effects of notch root radius on fracture toughness and crack initiation sites have been investigated in this paper using three different classes o f materials. Data on alumina which represent ceramics, mild steel from the metals family and polycarbonate representing plastics were obtained and ana lysed. The locations of crack initiation sites have been pinpointed by scan ning electron microscopy. These identified sites more or less are located w ithin the critical process zone or the theoretical plastic zone. The critic al process zone size (D-c) or the theoretical plastic zone size (R-YF) are independent of the notch root radius unlike the plain-strain fracture tough ness of notched specimens [K-IC(rho)]. The authors emphasize why the parame ters D-c and R-YF are useful for a quantitative evaluation of the reliabili ty of structural materials.