THE BLUNTING LINE IN ELASTIC-PLASTIC FRACTURE

The blunting line evaluation procedure used in the ESIS standard fract ure toughness test method ''Procedure for Determining the Fracture Beh aviour of Materials'' is re-evaluated to see if a simpler format can b e developed. An equation based on the ultimate tensile strength was fo und to represent the blunting line in a simple manner. This equation i s in error at most +/-5% from the analytical representation and is as accurate as the graphical procedure used to determine the blunting lin e. It is recommended that this equation be used for fracture toughness test standards which use the ESIS blunting line. A comparison of the ESIS blunting line and the ASTM blunting line is made using some J-R c urve data generated with an elastic unloading compliance test procedur e. These data do not favor one line over the other. Microscopic evalua tion of the blunting line reported in the literature using the stretch zone width measured on the fracture surface suggests that the ESIS bl unting line better represents the physical blunting process.