Mechanical Characterization of Plastics for Hydrogen Technology

Plastics are frequently used in electrolysers and fuel cell systems, for example as seals or structural components in pipes, tanks, and housings. These materials are exposed to gases and liquids that often have acidic or alkaline properties.

Understanding the mechanical behavior of these materials under such conditions is crucial for the design and safe operation of plastic components. Therefore, it is necessary to account for the relevant influencing factors as early as the material characterization stage. This includes the wide range of possible mechanical stresses in the aforementioned systems, which can occur under varying loading rates and frequencies, such as quasi-static loads, creep loads, cyclic fatigue loads, and highly dynamic stresses in crash or impact scenarios.

Behavior under liquid media, extreme temperatures, or combined stress scenarios

The issue of media exposure does not refer solely to direct contact with hydrogen. Depending on the application, specific requirements regarding behavior under liquid media, extreme temperatures, or in combined stress scenarios may also be relevant. One example is fuel cells, in which cooling fluids act on plastic components at high temperatures.

Mechanical methods adapted to application conditions

At Fraunhofer LBF, various mechanical methods are available for investigating such stress scenarios, which can be specifically adapted to the respective application conditions. The measured values obtained and the material properties derived from them help characterize plastics, elastomers, and composites in terms of their mechanical behavior. This data also serves as input parameters for structural mechanical models and simulations, for which Fraunhofer LBF offers support in their development.

The available methods are summarized below. The specific testing options depend on the particular application.

Cyclic fatigue in liquid media

• Force range: up to 0.001 kN – 63 kN
• Load type: Axial, torsional, multi-axial, internal pressure
• Internal pressure: up to 270 bar
• Temperature range: -75 °C to 200 °C
• Liquid media:
  • e.g., coolants, oils, and non-flammable media
  • Corrosive and flammable media upon consultation
• Frequency: 1–50 Hz
• Strain measurement: Strain gauges, optical crack monitoring

Cyclic fatigue and quasi-static tensile loading in pressurized hydrogen

• Force range: up to 63 kN
• Load type: Axial
• Pressure range: up to 50 bar
• Temperature range: –40 °C to 130 °C
• Gaseous media:
  • Hydrogen (concentration up to 99.9999%)
  • Nitrogen (up to 10 bar)
• Strain measurement: Strain gauge

Creep and quasi-static tension in liquid media

• Force range: up to 5 kN (4 channels), up to 10 kN (1 channel)
• Load type: Axial tension, multi-axial (internal pressure)
• Pressure range: Atmospheric pressure (tension), 270 bar (internal pressure)
• Liquid media:
  • e.g., coolants and partially transparent media
• Temperature range: 23°C to 120°C (depending on the medium)
• Strain measurement: optical gray-level correlation

Multiaxial testing of elastomers at high and low temperatures

• Force range:
  • Uniaxial tensile, planar tensile, compression: up to 30 kN
  • Biaxial inflation test: up to 6 bar (air)
• Load type:
  • Uniaxial tensile, planar tensile, compression & biaxial tensile (inflation test)
  • Tests can be conducted statically, cyclically, or as creep tests.
• Temperature range: -40°C to 200 °C
• Strain measurement: optical gray-level correlation or strain gauges

High-dynamic characterization of preconditioned samples at high and low temperatures

• Force range: up to 50 kN
• Load type: Axial tension, puncture
• Speed: up to 20 m/s
• Specimens are preconditioned in liquid media prior to testing
• Temperature range: -35°C to 75°C
• Strain measurement: optical gray-level correlation