Evaluation of the elastic-plastic fracture toughness JIc using side-grooved specimens requires introduction of the so-called effective specimen thickness Beff. At present, three different equations of Beff are known. These are Beff=√B0BN, Beff=B0-(B0-BN)2/B0 and Beff=BN, where B0 is the gross specimen thickness (thickness apart from the side-groove) and BN is the net specimen thickness (thickness at the bottom of the side-groove). In ASTM Standard Test for JIc, Beff=BN is used for calculation of J, but its validity does not seem to have been fully confirmed. Thus, this paper examined experimentally which one is appropriate among the above three equations. Experiments were carried out using side-grooved compact tension specimens of 2024-T3 Al alloy. The net specimen thickness BN was chosen so that BN>25JIc/σfs was satisfied. J was calculated using the well-known formula J=(A/Bb)f(a/W). Substituting each of the above three equations of Beff for B, JIc was estimated and compared with the value of JIc as obtained from the non-side-grooved specimen. It was found that there exists a case in which Beff=√B0BN or Beff=B0-(B0-BN)2/B0 is more appropriate than Beff=BN. This result is useful in further investigations of the effective thickness.
