How materials age and what sometimes fatal consequences this has

Can matter get tired? In any case, material fatigue is suspected to be the cause of the bursting of a giant aquarium in Berlin. But what exactly happens to a material when it “fatigues”? From the outside it is usually not obvious that a material has lost its original strength and stability and that it can suddenly break as soon as there is a peak load.

This is due to weak points in the microstructure of the construction materials. Such weak points can be broken bonds between atoms, defects in the structure of the solid or even microscopically small cracks.

Now, unfortunately, the nature of these defects is that they tend to get bigger and bigger over time. A tiny vulnerability – however it may have arisen or may have existed from the beginning – then becomes an ever larger problem. This progressive process is called material fatigue. It can occur in practically all materials - from steel to concrete to glass.

The speed of fatigue depends on the mechanical and thermal loads that a component experiences during use. If the intensity of the load changes frequently, this promotes fatigue. A piece of steel that you simply lock away in a cupboard will lie there for many years without showing any sign of fatigue.

Depending on the area of ​​application of a material, undetected material fatigue can pose a major risk to life and limb. Fortunately, the bursting of the Berlin Aquarium did not claim any lives. Things were different in 1998, when there was a serious case of material fatigue in Germany. A wheel tire that suddenly broke led to the ICE accident in Eschede, in which 101 people died and 70 were seriously injured.

More than 100 years earlier, it was also a broken tire that led to the derailment of the Amstetten locomotive on the railway line between Linz and Salzburg in 1875. This event is considered the birth of modern material testing, which has developed into an important branch of science. It was the Scottish physicist Sir James Alfred Ewing who recognized in 1903 that microscopic cracks can be the origin of subsequent fatigue failure of materials.

Today, engineers and researchers have dozens of measuring methods at their disposal to identify signs of material fatigue in components in good time and, for example, to detect tiny hairline cracks. The spectrum ranges from magnetic and electrical measurements to the use of ultrasound and X-rays.

The possible material fatigue of reactor pressure vessels has received particular public attention. After all, these play a central role in the safety of nuclear power plants. Here, a bursting would not just release a million liters of water, but radioactive substances into the environment.

The steel of a reactor pressure vessel is exposed to particular stress. It is hit by high-energy neutrons released in the reactor during the fission reaction of uranium. These neutrons knock iron atoms out of their lattice positions in the crystal lattice, causing more and more defects over time. This makes the steel more brittle. Regular checks ensure that the reactor pressure vessel is still sufficiently strong.

Neutron radiation is also one of the greatest challenges in the construction of future fusion power plants. The energy released when the hydrogen isotopes deuterium and tritium fuse consists primarily of high-energy neutrons. These fly out of the reaction chamber in all directions and will also hit the steel structural elements and embrittle them.

Either materials that withstand the neutron radiation must be used here; or other “fuels” must be used in the realization of fusion power plants that do not release neutrons when they are fused. Research is already being done on this as well.

"Aha! Ten minutes of everyday knowledge" is WELT's knowledge podcast. Every Tuesday and Thursday we answer everyday questions from the field of science. Subscribe to the podcast on Spotify, Apple Podcasts, Deezer, Amazon Music, among others, or directly via RSS feed.