Analysis of near-tip crack bridging in WC/Co cermet

The remarkable toughening effect usually found in WC/Co cermets has been an alyzed by means of a fracture mechanics approach based on R-curve character ization and in situ measurements of crack opening displacement (COD). The u se of a crack stabilizer specially designed for the bending geometry enable d to detect the rising R-curve behavior of the material starting from the v ery neighborhood behind the crack tip (i.e. < 100 mu m). In situ COD measur ements were related to the rising R-curve behavior through theoretical equa tions for bridged cracks. As a result, the toughening effect in the cermet was explained using a constant (average) distribution of bridging stress wh ich shields the crack in the very neighborhood behind its tip. The magnitud e of the bridging stress was found to be close to the ultimate strength of the Co metal phase. Only a very minor effect on toughening was found to be operated by metal ligaments in regions far away from the crack tip. (C) 199 8 Elsevier Science Limited. All rights reserved.