ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

Scale bridging modeling of hydrogen enhanced crack propagation in steels

Hydrogen embrittlement (HE) affects the loading capacity and toughness of almost all metals, in particular of high-strength steels. To understand the huge amounts of experimental findings, many mechanisms and models have been proposed to explain hydrogen-induced failure. Figure 1 demonstrates three appealing mechanisms which have been frequently discussed in the literature. Hydrogen Enhanced Local Plasticity (HELP) studies show that the formation of hydrogen atmosphere around dislocations effectively reduces the interaction energy between dislocations and thus yields an enhanced glide mobility of dislocations. A non-uniform distribution of hydrogen leads to a strongly localized plastic deformation and formation of micro cracks.

Hydrogen Enhanced DEcohesion (HEDE) advocates that hydrogen atoms reduce the cohesive strength of interatomic bonds at crack tips or in areas with localized tensile strength and thereby promotes decohesion. The hydride formation and embrittlement mechanism suggests that cracking could proceed by the formation and cracking of a hydride at the sites of stress centers (e.g. crack tips) and at grain boundaries. The significance of these mechanisms depends on the materials and their service condition.


Left:Schematics of hydrogen embrittlement mechanism. HELP: Hydrogen Enhanced Local Deformation, HEDE: Hydrogen Enhanced DEcohesion; and Hydride formation and embrittlement. Right: Stress concentration at the triple junctions of grain boundaries under tensile loading. The grain boundaries are described by cohesive zone models.

This project focuses on studying the HELP and HEDE (non-hydride formation) mechanisms. It takes the findings of other ICAMS projects and combines them into a single continuum model. Density Function Theory (DFT) studies reveal that the elastic constants and the cohesive energy decrease with increasing hydrogen concentration (see AMS-03-01 and AMS-01-04). Atomistic modeling on the HELP mechanism (see CMD-09-01) provides a possibility to derive hydrogen influenced kinetics of dislocation glide. Another crucial problem on continuum level is to quantify the diffusion of hydrogen atoms under external mechanical loading. This leads to a coupled deformation-diffusion problem.

Project Files:

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Schematics of hydrogen embrittlement mechanism. HELP: Hydrogen Enhanced Local Deformation, HEDE: Hydrogen Enhanced DEcohesion; and Hydride formation and embrittlement.
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Stress concentration at the triple junctions of grain boundaries under tensile loading. The grain boundaries are described by cohesive zone models.

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