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

Abstract

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.

Simulations of fracture tests of uncharged and hydrogen-charged additively manufactured 304 stainless steel specimens using cohesive zone modeling

“…However, the initial rising part of the load-crack extension curve will become smaller so the displacement at the maximum load will be at a smaller crack extension. When the cohesive energy is selected to be large and corresponding to the J-integral at the maximum load, the rising part of the loadcrack extension curve disappears, as presented in Wu et al [16] for CF stainless steels. In Table 2, the crack extensions and the J-integrals at the maximum loads are also listed.…”

“…In Wu et al [16], the values of the cohesive energy were selected as those of max J corresponding to the maximum loads for the arc-shaped specimens of uncharged and hydrogencharged conventionally forged (CF) steels in their simulations of the crack extensions in the specimens. The computational results in Wu et al [16] indicated that the load-displacement and crack extension-displacement curves from the simulations are compared reasonably well with the experimental data. However, the selection of the cohesive energy corresponding to max J will not…”

Simulations of Crack Extensions in Arc-Shaped Tension Specimens of Uncharged and Tritium-Charged-and-Decayed Austenitic Stainless Steels Using Cohesive Zone Modeling

“…The stress-strain relation for the arc-shaped tension specimens of uncharged CF 21-6-9 stainless steels was obtained from a tensile test with a round bar specimen in [3]. The Young's modulus E is determined to be 177.33 GPa and the Poisson's ratio ν is 0.3 for the uncharged CF 21-6-9 stainless steels.…”

“…where is the true stress, is the plastic strain, and K and n are material constants selected to extend the experimental data to large plastic strains. The details of the tensile test modeling and the procedures to obtain the true stress-true plastic strain curve were presented in Wu et al [3]. The material constants K of 1,770 MPa and n of 0.225 were selected in [3] to match the stress-strain relation from the experiment.…”

“…In this paper, the material constitutive relation for the uncharged CF steel reported in [3] is adopted. The material constitutive relation for the tritium-charged-and-decayed CF steel is estimated based on the experimental tensile stress-strain data of the uncharged CF steel and the tritium-charged-anddecayed HERF 21-6-9 stainless steel.…”