Simulations of Crack Extensions in Small Arc-Shaped Tension Specimens of Uncharged and Hydrogen-Charged 21-6-9 Austenitic Stainless Steels Using Nodal Release Method

Abstract Crack extensions in small side-grooved arc-shaped tension specimens of uncharged and hydrogen-charged conventionally forged 21-6-9 stainless steels are simulated using two-dimensional plane strain finite element analyses with the nodal release method. The finite element analyses are conducted with the input crack extension-displacement curves from the experiments. The crack extensions are simulated by releasing the nodal points ahead of the initial crack tips. The crack extensions follow the experimental results based on the electric potential drop method. The maximum opening stresses and the separation work rates as functions of the crack extension are then determined for determination of the cohesive strength and cohesive energy for a two-dimensional cohesive zone modeling approach. With the nodal release method for crack extensions, the experimental J-R curves are shown to be significantly higher than the separation work rates and therefore the use of the experimental J-integral values as guides for the selections of the cohesive energies should be careful for small fracture specimens. The computational results are useful for identification of the varying cohesive strengths and cohesive energies for the two-dimensional cohesive zone modeling of crack extensions in small fracture specimens.