PSI - Issue 75

KADIRI Mounir et al. / Procedia Structural Integrity 75 (2025) 633–641 KADIRI Mounir/ Structural Integrity Procedia (2025)

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Keywords: self-heating under cyclic loading; martensitic steel; thermometric measurements; hydrogen

1. Introduction The study of fatigue properties is essential to ensure the reliability and durability of structures subjected to cyclic loading, especially in environments considered severe (e.g. marine environment). Characterizing fatigue performance through classical tests is time-consuming and requires a large number of specimens. For example, obtaining a fatigue curve using the traditional “staircase” method on a servo -hydraulic tension-compression testing machine can take approximately 24 days. To overcome these constraints, the self-heating method, based on thermometric measurements under cyclic loading, provides a rapid estimation of the endurance limit while also considering the energy dissipation mechanisms associated with fatigue damage. This approach requires only one specimen and can be conducted in a single day. One of the main objectives of this study is to highlight the effect of hydrogen on fatigue properties using the self heating method. As a short-term objective, we aim to demonstrate the effect of hydrogen on the self-heating curve of the material under investigation. Other long-term objectives include identifying the mechanisms leading to the initiation of fatigue cracks under cyclic loading in the presence of hydrogen and adapting a two scales probabilistic model to predict fatigue properties while considering the hydrogen effect. In the literature, various studies have addressed the effect of hydrogen on metallic materials. The results presented in (Oudriss 2025) illustrate the effect of hydrogen on the mechanical properties of Nickel. Indeed, it has been proven that the presence of hydrogen in Nickel leads to a loss of ductility. Another study detailed in (Skipper et al. 2008), highlights the effect of hydrogen on the fatigue life of austenitic steels where their fatigue life increases when they are charged with hydrogen. Regarding shape-memory alloys, article (Mostofizadeh et al. 2019) demonstrates the effect of hydrogen on the self-heating curve of a Ni-Ti alloy, showing that hydrogen charged material exhibits a different self heating curve compared to non-charged material. In our study, we focus on the effect of hydrogen on the self-heating curve of martensitic steel. To this end, we will first present the material and the hydrogen-charging procedure, which requires applying a coating to the specimen, then the configurations tested and the self-heating method. Finally, a comparison between the different self-heating curves is established. Our study focuses on a 12.9 grade steel which is a martensitic steel widely used in mechanical applications subjected to severe cyclic loading. The chemical composition of this steel is not disclosed for confidentiality reasons. Its martensitic microstructure, which is a quadratic crystal structure, provides excellent yield strength but also makes it more vulnerable to embrittlement particularly in the presence of hydrogen. This behavior makes it a pertinent candidate for studying fatigue performance and hydrogen induced damage mechanisms. 2.2. Hydrogen charging and coating protocol The hydrogen charging of the specimens was carried out by cathodic polarization (Figure 1), a method commonly used to introduce hydrogen in a controlled manner into metallic materials. The 12.9 grade steel specimens were immersed in an electrolyte (hydrochloric acid) and electrochemically polarized at a cathodic potential of -1300 mV/SCE (saturated calomel electrode) for 24 hours. This level of polarization enables intensive hydrogen uptake. 2. Experimental protocol 2.1. Studied material