PSI - Issue 33

S. Schoenborn et al. / Procedia Structural Integrity 33 (2021) 757–764 S. Schoenborn, T. Melz, J. Baumgartner, C. Bleicher / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The greatest challenge of our time is to combat climate change and the associated massive reduction of greenhouse gas emissions and the abandonment of fossil fuels. The European Union is pursuing the goal of becoming climate neutral by 2050 and massively reducing CO 2 emissions [1]. However, it should be noted that Germany itself was only able to meet its national targets for 2020 because public life and the economy were subject to severe restrictions due to the Corona pandemic. By 2030, greenhouse gas emissions are to be reduced by at least 40 % (in discussion even up to 55 %) and by as much as 80–95 % by 2050 compared to 1990. Analyses have shown that 75 % of the EU's greenhouse gas emissions are due to energy consumption. According to an analysis by the Federal Statistical Office in 2016 [2], 27 % of energy consumption was in the sector of private households and the higher share of 73 % is accounted for by the manufacturing sector. In order to achieve these set targets, an overhaul of the energy system is necessary. In this context, green hydrogen produced from renewable energy through electrolysis is becoming increasingly important and can make a significant contribution to the decarburization of industry, transport, power generation and buildings across Europe and achieving the climate targets by the year 2050. The transformation of the energy economy with the development of a hydrogen-based economy opens up the opportunity to have a sustainable positive impact on the environment and global climate protection. Nevertheless, possible bottlenecks on this way are the sufficient availability of hydrogen as well as the point of safety in its application. Due to the known embrittling influence of hydrogen in contact with metallic materials, so-called hydrogen embrittlement with a reduction of the strength, ductility and fatigue life takes place in many metallic materials. It is important to ensure that there is no risk of premature component failure with regard to the safe operation of hydrogen loaded components, especially when high loads lead to high local stresses and strains. In detail, the adsorption and absorption of atomic hydrogen in the metal lattice leads to a change in material properties – hydrogen-induced material fatigue occurs during cyclic loading. Different theories exist to describe the damage processes during hydrogen embrittlement, e.g. (pressure theory, adsorption theory, Hydrogen Enhanced Localized Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE)). An often used concept for describing the fatigue processes of metallic materials under hydrogen is the so-called HELP model (Hydrogen Enhanced Localized Plasticity) [3]. This model is based on a reduction in the Peierls stress, which states that hydrogen atoms accumulate at dislocations in the tensile stress field, lowering the energy threshold for dislocation movement [4, 5, 6, 7]. Not only is the dislocation movement possible even with lower mechanical stresses, the nucleation of kinks is also accelerated, which generally leads to a higher dislocation velocity [8]. This locally enhanced plastic deformation then leads to microstructural changes at grain boundaries and/or precipitations and subsequently to failure of the component. In the past, numerous investigations have already been carried out with electrochemically applied hydrogen. Due to the very complex experimental procedure under pressurized hydrogen, there are only a few fatigue strength results on differently notched specimens. The current results should therefore contribute to the description of the fatigue behavior under compressed hydrogen as well as the development of methods for the design of components for compressed hydrogen applications.

Nomenclature R z

average roughness

nominal stress amplitude

σ a,n

K t

notch factor

stress

σ

wt.-% weight percent

N f

number of cycles to failure

ppm

parts per million

N i

number of cycles to crack initiation