A comparison of several analytical techniques for calculating [formula omitted] Curves from load-displacement data and their relation to specimen geometry

Abstract

Various methods to determine crack growth resistance curves have been compared. Ferritic ductile cast iron (grade 60-40-18) was machined into three different specimen geometries (compact tension, bend bar and Charpy V-notched) which were fatigue precracked and then tested under displacement control at room temperature. Crack resistance curves were generated using the current standard, ASTM E813-81, and a new J-R curve standard, ASTM E1152-87. It was found that R- curves calculated with these two approaches were similar up to approximately 1 to 3 mm of crack extension, at which point the R- curve calculated with ASTM E1152-87 began to drop off. A geometry dependence of the R- curves was observed between the different specimen geometries for both ASTM E813-81 and ASTM E1152-87. The modified J formulation of Ernst was also found to give a geometry dependent R- curve for the ferritic ductile iron.