A more exact determination of the JIc-integral fracture toughness values obtained by compact tests

Fracture toughness K_JIc values, determined on standard compact specimens by the use of modified equations of Rice, Paris and Merkle, and Merkle and Corten, are presented. The equations permit elimination of errors caused by inaccuracies in the loadline displacement measurements, and they can be applied not only for deeply cracked specimens but also for a wider range of ratios a/W. Experimental results, obtained on two low strength steels using 75 and 40mm thick specimens, showed a very good agreement between the K_JIc values calculated by both equations. These values do not differ by more than 2%.