Fracture Toughness Test Methods for Material Qualification in Gaseous Hydrogen

Abstract This paper focuses on the use of a variety of different small scale test methods to assess the fracture resistance of the material in gaseous hydrogen and study susceptibility to subcritical crack growth. The test methods include ASTM E1681 constant load and constant displacement approaches, the ASTM E1820 rising displacement approach and a modified ASTM F1624 with additional fatigue pre-conditioning in a defined manner per the DNV method (also called ‘constant K’ method). The study shows similitude in the threshold toughness results with the methods that do not involve fatigue pre-conditioning. The toughness threshold defined at Δa≈0mm from the rising displacement J-R curve is preferred and gives a similar toughness threshold to the constant load test method. However, when a defined fatigue crack growth is preceding the fracture test the local crack sharpening effect can dramatically reduce the threshold for the onset of stable subcritical crack growth in certain microstructures such as vintage textured ferritic-pearlitic microstructure.