The upscaling of Wind Turbines puts tough materials challenges to ensure structures integrity and reduce the CAPEX and OPEX of offshore industry. For structural optimized design, a particular attention must be paid for dimensioning mooring chains and select the appropriate High Strength Steel (HSS). One of the main issues remains the assessment of fatigue and fatigue-corrosion properties of the selected materials in such environment. To prevent corrosion, new coatings are being developed to meet current standards. However, the coating process induces hydrogen introduction in the material which could modify its fatigue properties and presents a risk of hydrogen embrittlement given the sensitivity of these materials to this phenomenon.

A number of research has been interested in characterizing fatigue properties from self-heating tests under cyclic loadings. This method is commonly used to study the fatigue of a wide range of several materials. However, the effect of hydrogen on fatigue in the HCF domain has not yet been addressed.  This study aims to assess this effect using self-heating method which deals with the temperature monitoring during cyclic loading. A special attention has been given to highlight the role of initial hydrogen content on the self-heating behavior of R5 and R6 HSS steels by setting up and experimental protocol to enable ex situ hydrogen charging and hydrogen content control and then perform self-heating tests on hydrogen charged specimens. Regarding the results obtained in different studies, the influence of hydrogen content on the self-heating curve could indicate that the fatigue properties of these materials are affected. 

This study has enabled to contribute towards the prediction of fatigue properties from self-heating results.  Classical fatigue tests have been performed to confirm the conclusions made from self-heating results.

Keywords: self-heating under cyclic loading, HSS R5, R6 steels, hydrogen embrittlement, thermometric measurements