Fracture-toughness estimation from small-punch test in hydrogen exhibiting ductile and ductile-brittle fracture modes

In this study, an energy-based fracture toughness estimation method based on a small-punch test in a hydrogen environment, exhibiting either ductile or combined ductile and brittle fracture modes is proposed. For the ductile fracture mode, the energy term due to gas pressure in the small-punch test in hydrogen environment is simply added to the existing energy-based fracture toughness estimation equation. For the combined ductile and fracture mode, modified equations for the plastic energy term are proposed to correct overestimation due to brittle cracking. The estimated fracture toughness values are shown to consistent with the published API X70 and X42 test data.