Week 24/2019

Explosion force against wear

The LSP system at the ZAL TechCenter – one of only three machines worldwide.
The LSP system at the ZAL TechCenter – one of only three machines worldwide.
As elegantly as airplanes seem to float in the sky, when flying, they are exposed to extreme temperature fluctuations and a wide variety of weather conditions that can include lightning, ice and storms, as well as heavy brake loads during landing. In order for the aircraft structure to withstand these stresses for decades and to minimize fatigue, it is treated with special procedures. The Center of Applied Aeronautical Research (ZAL) in Hamburg has now installed Europe's first commercially available facility for a new process – and is thus working more precisely than with previous processes.

The new technique is called laser shock peening, LSP for short. In the process, a metal component is coated with a lightproof film which is covered with a fine film of water. The area to be treated is then subjected to a high-energy laser. The resulting plasma literally explodes on the surface of the component, and the explosion wave causes deformation in the material – unfailingly contained by the water layer. One can imagine it like a New Year's Eve firecracker over which a blanket is put before it is ignited, limiting the explosion. These locally introduced small deformations generate inherent compressive stresses in the material, which have a positive effect on the fatigue properties of the component.

High precision

The process is suitable for making surfaces more resistant to fatigue after having passed through production processes. One example is the engine blades, which often wear out at the joint: due to the high permanent load, tiny cracks develop there over time. If the surface is treated with LSP, the signs of wear are delayed or completely avoided.

LSP has considerable advantages over the process previously used, known as shot peening: Despite the martial-looking energy discharge, it is much more precise. It also scores in terms of environmental friendliness, as it mainly uses light and water. Compared to shot peening, LSP treatment can achieve up to 20 times the penetration depth.

One of only three plants worldwide at ZAL

Until now, there have only been two machines worldwide for the LSP process from LSP Technologies, neither of them in Europe. With the installation of a third machine at the ZAL TechCenter, LSP can now for the first time also be used extensively in the research environment in Europe. With a total of 2.6 million euros, it is the largest single investment in the history of ZAL to date. The machine is available to aircraft manufacturers for the treatment of ready-to-use components. It is also used as a test infrastructure for research purposes.

The process is a prime example of successful spill-over effects from military aviation. LSP has been used in the US military sector since the 1990s. For some years now, civil aviation has also been benefiting from the advantages, and now it has come to Europe. With the new facility, ZAL and thus German aeronautical research will rise to become part of the leading international group in this field.