Characterization of hydrogen interaction with metals on meso and microscale samples

Hydrogen significantly affects the deformation, damage evolution, and failure of metallic materials used in pipelines, storage vessels, valves, compressors, and other hydrogen-exposed components. Fraunhofer IWM investigates these interactions on the meso and microscale, where local microstructural features decisively influence material performance.

Testing at these length scales makes it possible to identify hydrogen-assisted damage mechanisms at their origin and correlate them with macroscopic component behavior -a sound basis for material qualification, component assessment, and application-oriented testing strategies. Typical microspecimens have cross sections of approximately 400 µm × 200 µm, enabling targeted investigation of critical microstructural regions. Testing directly in gaseous hydrogen provides conditions far closer to service than indirect or surrogate approaches, while the reduced specimen dimensions shorten diffusion distances and increase the surface-area-to-volume ratio, accelerating hydrogen uptake and enabling shorter test or precharging times.

The approach enables targeted investigation of critical microstructural features, including:

• Grain boundaries
• Pores and internal defects
• Second phases and precipitates
• Crystallographic orientation
• Weld heterogeneities (fusion zone, HAZ, base material transitions)

Local assessment of critical regions

Component failure in hydrogen service rarely originates uniformly across a material; it begins at localized regions where microstructure, geometry, or processing history concentrate susceptibility. Meso- and microscale sampling isolates the response of these critical regions

Representative critical regions include:

• Thin-walled sections
• Geometric stress concentrators - threads, notches, fillets, and radii in valves, fittings, and fasteners, where triaxial stress states drive hydrogen accumulation
• Formed and deformed regions - cold-bent sections, flanges, and formed sheet where prior plastic strain and texture concentrate susceptibility.
• Surface treatment – Case hardened surfaces (carburizing, nitriding, induction hardening) create steep gradients in hardness, microstructure, and residual stress between case and core, driving a depth-dependent hydrogen response.

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Site specific materials assessment with minimal structural impact

A particular advantage of meso-scale testing is that specimens can often be produced from in-service materials or existing components with only minimal impact on structural integrity. 

• Minimal structural impact- specimens taken from real components or in-service infrastructure without compromising integrity, avoiding costly large-scale destructive sampling.
• One coordinated framework - Hydrogen charging (ex-situ and in-situ), mechanical testing, 2D strain mapping, gas quality monitoring, and thermal desorption spectroscopy are integrated within a single workflow, so the hydrogen environment and the resulting mechanical response are captured in one consistent, correlated dataset.
• Application-tailored setups - loading mode, pressure, geometry, and clamping adapted to the specific component and qualification task.
• Modular reconfiguration - load cells, sensors, specimen geometries, and control software can be adapted with minimal lead time, allowing test setups to be tailored quickly to new projects, materials, and loading conditions
• Comparative material insight - Different material states, manufacturing routes, and heat treatments can be benchmarked under identical conditions.

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Slow Strain Tensile testing in gaseous hydrogen

Fraunhofer IWM offers in-house tensile testing of micro specimens in gaseous hydrogen using dedicated high-pressure test chambers. The current infrastructure includes a prototype chamber for tensile testing up to 50 bar hydrogen at ambient temperature and a second prototype chamber for tensile testing up to 100 bar hydrogen at ambient temperature.

Slow strain rate testing down to 10⁻⁵ s⁻¹. This enables the investigation of hydrogen-sensitive degradation processes under loading conditions that are particularly relevant for embrittlement-sensitive materials.

Determinable materials properties

• Modulus of elasticity
• Poisson's ratio
• Yield strength
• Tensile strength
• Strain at Faliure and Reduction in Area

K factor-based strain correction in accordance with ISO 6892

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Non-contact strain measurement using digital image correlation (DIC) 

Fraunhofer IWM also offers 2D strain mapping for meso-scale specimens. This enables the determination and visualization of localized strain fields during mechanical testing and provides valuable insight into the onset and development of strain localization. The method is particularly useful for identifying locally increased deformation in geometrically or microstructurally critical regions and for visualizing localized plasticity in meso samples.  Two different variants of image correlation are used for quasistatic and fatigue tests. In-house developed software for digital image correlation and with GOM corelate professional is also possible.

• Full-field strain measurement via two dedicated digital image correlation (DIC) configurations, optimised for quasistatic and cyclic fatigue loading
• Proprietary in-house DIC software enabling tailored strain field analysis and post-processing
• Integration with GOM Correlate Professional for industry-standard full-field deformation and strain evaluation

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Fatigue testing in gaseous hydrogen

Fraunhofer IWM offers fatigue testing of micro specimens in gaseous hydrogen up to 100 bar at ambient temperature. This allows the assessment of hydrogen-related damage evolution under cyclic loading and supports the investigation of crack initiation, crack propagation, and fatigue degradation at the microstructural level. We can offer both force-controlled and displacement-controlled tensile tests. Fatigue tensile tests with load cycles high cycle fatigue, HCF, (up to approx. two million load cycles) are standardly carried out. The simultaneous regulation of the sample frequency and vibration amplitude creates controlled load conditions. These can be maintained in a frequency range between 0.1 - 120 Hz and at positive medium voltages (depending on geometry).

Determinable materials properties

• S-N curves in gaseous hydrogen environment
• Fatigue life (number of cycles to failure)
• Fatigue strength and endurance limit
• Crack initiation site and mechanism identification
• Fatigue crack growth rate (da/dN) as a function of stress intensity factor range (ΔK)
• Hydrogen-induced fatigue degradation relative to inert reference conditions
• Fracture surface analysis for microstructural damage characterisation

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Ex-situ hydrogen charging

For materials with low hydrogen diffusivity, ex-situ hydrogen charging can be carried out prior to mechanical testing using an in-house developed mobile charging tube. This setup enables the charging of micro specimens at elevated temperature and pressure and is particularly suitable for materials such as nickel, copper, and austenitic stainless steels. The current documented setup allows charging at temperatures up to 300 °C and pressures up to 150 bar. Meso-scale specimens can be stored in a liquid nitrogen bath to maintain their condition prior to testing.

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Gas quality monitoring

In addition to mechanical testing, the moisture and oxygen content of the test gas can be measured. After testing, the gas can either be sent directly to the corresponding sensors for immediate analysis or transferred to a small pressure vessel for subsequent purity assessment. For hydrogen testing, Purity 5 hydrogen is used. This contributes to reliable and reproducible test conditions and supports technically meaningful evaluation of hydrogen-related materials behavior.

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Publications

DelRio, F. W.; Schmitz-Elbers, M.; Strohmeier, U.; Straub, T., Local Failure Strain and Reduction of Area Provide Early Metrics for Hydrogen Embrittlement in Microscale Austenitic Stainless Steel Tensile Specimens, Experimental Mechanics, Online First (2025) 9 S. Link

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Reference Projects

HyLife

A physics-based tool for predicting the service life of structural materials in contact with hydrogen

The HyLife project aims to develop a physics-based service life prediction tool for materials in contact with hydrogen. Innovative test methods and materials models will be used to reliably predict the service life of components under the influence of hydrogen, thereby making a decisive contribution to the safety and efficiency of hydrogen infrastructures.

Project profile: HyLife

H2Mare

Offshore Technologies

The sea offers ideal conditions for generating renewable electricity. The direct production of green hydrogen in offshore plants from wind energy without a grid connection can significantly reduce costs compared to onshore production. The H2Mare flagship project researched the offshore production of green hydrogen and other power-to-X products.

Project profile: H2Mare

H2Leichtbaurohr

Development and validation of high-strength lightweight tubes for the production, transport, and application of pressurized hydrogen

There is a great need for cost-effective material solutions for small-sized pipes with thin walls for distributing hydrogen in plants or vehicles. The project developed a lightweight construction concept and demonstrated its industrial feasibility.

Project profile: H2Leichtbaurohr

TransHyDE

Hydrogen transportation

As part of the TransHyDE project “Safe Infrastructure”, six industrial companies were working with three Fraunhofer Institutes to develop new concepts for safe components for hydrogen technology as well as sensor technology for monitoring hydrogen storage facilities, pipelines, and connection points.

Project profile: TransHyDE

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