Analytical study of the J integral evaluation formula for compact test pieces.

Rice has shown a simplified method for estimating the J-integral for a deeply cracked bend bar. For a compact specimen used in the elastic-plastic fracture toughness JIC test, Merkle and Corten have shown a simplified method for estimating the J-integral which is taken into account the axial force. Now, a modified Merkle-Corten formula is generally used in the JIC test. In this study, an applicable range of these J estimation formulas for a compact specimen is analytically studied for three materials ; linear elastic, rigid perfectly-plastic and elastic perfectly-plastic. Results show that the original Merkle-Corten formula is superior to the modified one and the Rice formula in accuracy. Based on the results, use of the original Merkle-Corten formula and a recommended precrack length for the compact specimen in the JIC test are proposed.