Fracture toughness evaluation of hardmetals: influence of testing procedure

This paper describes an examination of the dependence of fracture toughness measurement on test technique for WC-Co hardmetals. Four different testing procedures have been assessed: the single edge notched beam (SENB) method, the single edge V-notched beam (SEVNB) technique, the surface crack in flexure (SCF) procedure and the conventional indentation microfracture (IM) method. The obtained fracture toughness values are compared and discussed on the basis of the particular theoretical and experimental features underlying each test technique investigated. As a result, the measurements obtained applying the SENB and SCF methods, as related to samples where residual tensile stresses induced during the corresponding precracking procedures were first relieved, are suggested to be the most reliable of all the values determined from the test methods evaluated. This assertion is further sustained through fracture mechanics analysis combining fracture toughness evaluation, flexural strength measurement and fractographic examination. (C) 2001 Elsevier Science Ltd. All rights reserved.