Public defence in Mechanical Engineering, M.Sc. Eric A. Fangnon

The effect of hydrogen on the performance of modern high-strength steels

In the pursuit of sustainable energy solutions to address the imminent challenges of climate change and environmental degradation, the usage of hydrogen has come to light as a viable remedy in the shift to a more efficient and cleaner energy ecosystem. As we embark on the hydrogen energy transition, a critical aspect that demands attention is the development of suitable materials for hydrogen transport and storage infrastructure. Among various contenders, steels have proven to be particularly advantageous due to their optimal balance of cost and strength. However, the interaction between hydrogen and steel poses a unique challenge known as hydrogen embrittlement (HE).
 

To better understand HE and its impact on the mechanical performance of newly developed martensitic steels, this dissertation focuses on the following three key issues: (i) enhancement of experimental conditions for the accurate measurement of hydrogen concentration (CH), (ii) assessment of the mechanical strength under different hydrogenation and mechanical loading conditions, and (iii) Development of  ANN-based tools to investigate and predict the relationship between CH and mechanical strength at failure.

A specimen cooling system was developed and integrated with the air-lock in the TDS apparatus to enhance the accuracy of CH measurements in the studied steels. The application of the new specimen cooling system, enabling temperatures down to 213˚K, proved to provide a significant improvement in CH measurement, allowing more accurate analysis of obtained thermal desorption spectra valuable for H-trapping analysis.

The H-uptake and mechanical performance of four martensitic steel grades with varying prior austenite grain morphology were studied by monotonic uniaxial tensile testing and TDS in different H-charging conditions. The results show that the H-uptake under the same H-charging conditions, under no external mechanical loading, does not vary between the steels. However, a variation in H-uptake was evident with external mechanical loading.
The developed dense ANN tools, encompassing three different models, were evaluated for the prediction of steel susceptibility to HE and CH responsible for the H-induced failure with an accuracy of up to 98°%. Enhancing the ANN models, with training data, may yield a powerful tool in the HE characterization of steels with a reduced dependency on time-consuming experimental testing.

Doctoral Student: Eric Fangnon

Opponent: Prof. Milos Djukic, Faculty of Mechanical Engineering, University of Belgrade, Serbia

Custos: Prof. Pedro Vilaça, Aalto University School of Engineering, Department of Mechanical Engineering

The public defense will be organized in Lecture Hall 213a, Otakaari 4

The thesis is publicly displayed 10 days prior to the defense in the publication archive Aaltodoc of Aalto University. 

Contact information of doctoral student:

Doctoral theses in the School of Engineering: https://aaltodoc.aalto.fi/handle/123456789/49