Polymers

Tests can be executed with concurrent gaseous hydrogen exposure at pressure up to 140 MPa and at controlled temperature in the range of 220K to 450K.

– Subcritical cracking thresholds can be measured in constant displacement fracture tests.

– Instrumented test specimens enable the measurement of crack initiation, crack velocities, and crack arrest.

Exposure of polymers to gases such as nitrogen, argon, helium, and hydrogen is one of the primary challenges associated with large-pressure gradients during fuel consumption and refueling operations. Therefore, investigating the performance of polymers under the influence of a dynamic environment, such as high-pressure cycling of different gases with and without temperature cycling, is considered high value.

Measurement of frictional force and vertical wear depth profiles of polymers in 34 MPa hydrogen.

The developed in-situ Dynamic Mechanical Analysis system measures mechanical properties of targeted materials in situ at extreme conditions, such as high pressure. This system provides an understanding of the effects of extreme conditions on materials performance as well as the relationships among microstructure and materials performance in these conditions. The knowledge generated is of particular importance for developing new materials with improved performance.

Test specimens are exposed to high-pressure gaseous hydrogen or deuterium (up to 140 MPa) at elevated temperatures (up to 300ºC) for weeks to months to produce controlled hydrogen content within specimens prior to evaluation.

Environmental electron microscopy, high-resolution scanning transmission electron microscopy, scanning nanobeam diffraction, and crystallographic orientation mapping are just a few of the techniques available throughout the national labs to indirectly observe hydrogen interactions with surfaces, defect sites, and other microstructural features.

Thermal analysis of materials involves several different methods, including but not limited to differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis.

The gas permeation system consists of a hydrogen-compatible vacuum pump, a PNNL-certified environmental chamber, a stainless-steel permeation cell in which the sample is mounted, and hydrogen and nitrogen supply lines in accordance with PNNL flammable, compressed gas regulations. The system is primarily used for measuring the hydrogen permeability coefficient of polymer materials.

Thermal desorption provides an understanding of the compatibility of rubber composites under the high pressure of hydrogen. The rubber composites that are exposed to high-pressure hydrogen are tested to investigate maximum hydrogen capacity and their diffusion coefficients in a gas chromatography-mass spectroscopy environment.

Chemical and elemental analyses of rubber composites include Raman spectroscopy, GC-mass spectroscopy, solid-state NMR, small-angle and wide-angle neutron scattering, small-angle and wide-angle X-ray diffraction, and annihilation proton spectroscopy.

Use of advanced characterization techniques to measure hydrogen interactions with material microstructures at the nanometer length scale. Examples of capabilities available include the following.

– Low Energy Ion Spectroscopy (LEIS) can be used to probe hydrogen-surface interactions and hydrogen uptake, in some cases providing crystallographic information about the interactions.

– Methods that utilize scanning probe microscopy to probe hydrogen on metal surfaces in relationship to the underlying microstructures are being developed.

– A variety of additional surface sensitive imaging techniques and expertise are available at the national laboratories to investigate hydrogen interactions.

High-performance computing and computational materials science expertise is available across the national labs for the study of hydrogen effects in materials across multiple length scales from atoms to engineering. Computational tools are available for studying materials at all relevant length scales, including Density functional theory.

High-performance computing and computational materials science expertise is available across the national labs for the study of hydrogen effects in materials across multiple length scales from atoms to engineering. Computational tools are available for studying materials at all relevant length scales, including Molecular dynamics and Dislocation dynamics.

Cavitation occurs during decompression after rubbers are exposed to high-pressure diffusive gas. Existing free volume in rubbers affects the cavity evolution as well as materials performance. A phase-field model has been developed to describe the thermodynamic and kinetic processed of cavity evolution as well as predict the effect of structural defects and decompression rate on cavity nucleation, growth, and coalesce kinetics.

A continuum mechanics-based deformation model was developed to predict stress distribution and damage propagation when a polymer undergoes depressurization of high-pressure hydrogen exposure. The polymer was modeled assuming hyper-elastic material behavior and that the diffusion of hydrogen through the polymer is coupled with deformation analysis by varying pressure boundary conditions.

This model can also be used to study stress and damage evolution in the presence of multiple cavities as the damage and stress fields will be altered due to interactions among different cavities. The model can be also used to study the effect of filler materials such as silica or carbon black on the stress distribution and damage evolution in the material. These filler materials possess contrasting mechanical properties and are generally much stiffer compared to the polymer material.