Down to the Last Nanometer

Friction and wear play an ever increasing role in automotive engineering. The trend to virtual development methods in particular makes it all the more important to have models that give early predictions of contact friction and wear at various operating points. Online wear measurements with radioactive nuclides are ideal for checking and improving simulation quality. IAV and its partner DSI offer such measurements.

Friction occurs wherever there is relative movement between bodies. It makes reciprocal movement more difficult, causing an increase in fuel consumption and thus also in CO2 emissions. Wear also reduces component service life. Vehicle components particularly affected by friction and wear include the piston rings, the main and conrod bearings, as well as camshaft bearings and frequently also the timing drive.

One aim in developing new components is to minimize friction and wear as far as possible. “Given the current virtualization trend, we need models that give an exact description of friction and wear”, says Dr. Michael Berg, Senior Vice President for NVH, Development Methods and Prototyping at IAV. “Precise wear measurements are needed to develop and improve these models.”

Geometric measurement of abrasion during an endurance run on the test bench is one option for measuring wear. But this method is not suitable for comparison with simulation models. “It only produces integral statements, i.e. total wear after a certain period of time”, explains Klaus Herrmann, Team Manager for Base Engine Testing at IAV. “But what we are really interested in is the wear at certain operating states and how it changes with the transition to other states. We want to observe transient processes with live monitoring of the wear rate as this is the only way of finding the real relationship between cause and effect.”

This is where the radionuclide method for wear measurement comes in. First of all, the component under review, such as a piston ring, is placed in a particle accelerator and exposed to protons, deuterons (proton plus neutron) or alpha particles (two protons plus two neutrons). The particles react with the nuclei in the piston ring which becomes radioactive in a thin layer (approx. 20 to 100 micrometers), thus creating the prerequisites for live wear measurement.

When the engines then run after being fitted with the radioactive components, increasing numbers of radioactive particles enter the oil circuit due to the effects of wear. The radioactivity is measured by a gamma radiation detector to produce a time curve for the progression of wear. It is thus possible, for example, to make the effects of oil additives visible. “We have a very short reaction period of a few seconds for transient processes”, Berg reports, “together with high sensitivity levels of less than one nanometer per hour”. The radionuclide method can even be used for real-time measurements of very hard layers with minimum wear rates, across the whole map and without affecting the characteristic engine values.

IAV holds all the permits necessary for handling radioactive materials and can perform its own measurements with this established method. “In this field we work together with the Belgian company Delta Services Industriels (DSI), who have been using the radionuclide method for precise real-time measurements of engine wear for more than 15 years”, says Herrmann. “DSI has established a global reputation for using radioactive marker techniques with a customer base spread across the automotive, lubricant and aviation industry.”

One special aspect of IAV’s method is its highly sensitive high-purity germanium (HPGE) detector for gamma radiation, which is thirty times superior to sodium iodide (NaI) detectors. Wear can thus be monitored live in up to five components at the same time, compared to maximum two components with NaI detectors. However, this depends on being able to activate each of the five parts radioactively in a different way so that they emit gamma radiation with different energy levels.

IAV is currently using the radionuclide method for wear measurements in combustion engines; in future it is also to be used on test benches for components, transmissions or e-axles.