In the "Knight Rider" television show, which starred Hasselhoff, his supercar K.I.T.T. had a hydrogen turbo motor which allowed it to chase bad guys at over 300 miles an hour. It's no secret that hydrogen is regarded as the best alternative fuel for our transportation future but metals like steel, aluminum and magnesium - commonly used in automotive and energy technology – hydrogen is bad because it can make those metals brittle; the ductility of the metal becomes reduced and its durability deteriorates. This can lead to sudden failure of parts and components. Beside the fuel tank itself, or parts of the fuel cell, but ordinary components like ball bearings could also be affected. These are found not only in the car, but also in almost all industrial machinery.
Not quite K.I.T.T. yet, but it is getting closer.
This lightest of the chemical elements permeates the raw materials of which the vehicle is made not only when filling the tank, but also through various manufacturing processes. Hydrogen can infiltrate the metal lattice through corrosion, or during chromium-plating of car parts. Infiltration may likewise occur during welding, milling or pressing. The result is always the same: the material may tear or break without warning. Costly repairs are the consequence. To prevent cracks and breakage in the future, the researchers at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg are studying hydrogen-induced embrittlement.
Since the risk potential mostly emanates from the diffusible, and therefore mobile, portion of the hydrogen, it is necessary to separate this from the entire hydrogen content. Researchers can release and simultaneously measure the movable part of the hydrogen by heat treatment, where samples are continuously heated up. In addition, the experts can measure the rate that hydrogen is transported through the metal while simultaneously applying stress to the material samples mechanically.
They can determine how the hydrogen in the metal behaves when tension is increased. For this purpose, the scientists use special tensile test equipment that permit simultaneous mechanical loading and infiltration with hydrogen. Next, they determine how resistant the material is.
The researchers use the results from the laboratory tests for computer simulation, with which they calculate the hydrogen embrittlement in the metals. In doing so, they enlist atomic and FEM simulation to investigate the interaction between hydrogen and metal both on an atomic and a macroscopic scale. "Through the combination of special laboratory and simulation tools, we have found out which materials are suitable for hydrogen, and how manufacturing processes can be improved. With this knowledge, we can support companies from the industry," says Dr. Wulf Pfeiffer, head of the process and materials analysis business unit at IWM.