Modeling of Crack Extensions in Arc-Shaped Specimens of Hydrogen-Charged Austenitic Stainless Steels Using Cohesive Zone Model

Crack extensions in arc-shaped specimens of hydrogen-charged and as-received conventionally forged (CF) 21-6-9 austenitic stainless steels are investigated by two-dimensional finite element analyses with the cohesive zone model. The material constitutive relation is first obtained from fitting the experimental tensile stress-strain data by conducting an axisymmetric finite element analysis of a round bar tensile specimen of the as-received CF steel. The material constitutive relation for the hydrogen-charged CF steel is estimated based on the experimental tensile stress-strain data of the as-received CF steel and the hydrogen-charged high-energy-rate-forged (HERF) 21-6-9 stainless steel. The cohesive zone model with the exponential traction-separation law is then adopted to simulate crack extensions in arc-shaped specimens of the hydrogen-charged and as-received CF steels. The cohesive strength of the cohesive zone model is calibrated to match the experimental load-displacement curve with the cohesive energy determined by the J-integral at the maximum load of the arc-shaped specimen. The computational results showed that the numerical predictions of the load-displacement and crack extension-displacement curves for the hydrogen-charged and as-received CF steel specimens are compared reasonably well with the experimental data.