The use of hollow specimens for the mechanical testing of metals in gaseous hydrogen environments has gained significant attention over the past five years. Numerous laboratories are investigating this test rig, which offers several advantages, including low implementation and operational costs, as well as safety reduced constraints [1]. However, this test remains limited to unnotched geometrical configurations, thus excluding its use for fracture mechanics tests, especially for the characterization of toughness and crack propagation in hydrogen environment.

The objective of this paper is to explore the possibility of modifying the existing hollow specimen test design for the characterization of fatigue crack propagation in gaseous hydrogen environments. To achieve this, the modification of the specimen geometry is studied by finite element analysis using the Zset software suite and the Zcrack module, which allows the explicit simulation of fatigue crack propagation REF. A new geometry is proposed that incorporates a notch on the inner surface of the specimen. Crack propagation modeling is used to qualify the crack propagation from this notch for different crack shape assumptions, all of which converge to a homogeneous case which is favorable for fatigue crack propagation kinetic analysis. In addition, these propagation simulations are used to test the capability of conventional crack size measurement techniques: the compliance method and the direct current potential drop (DCPD) technique. The analysis demonstrates the clear superiority of the DCPD technique, which offers good sensitivity to crack growth, providing sufficient conditions for precise tracking of crack propagation

Keywords: Fatigue crack growth testing; Crack growth measurement techniques; In situ hydrogen testing 

[1] : Freitas, T., Konert, F., Nietzke, J., Krzysch, Z., Böllinghaus, T., Michler, T., … & Sobol, O. (2024). Tensile testing in high-pressure gaseous hydrogen using the hollow specimen method. MRS Bulletin, 1-9.