In FREDA project within FIMECC DEMAPP Program, advanced numerical tools have been developed to tackle fretting damage. A great deal of the project has been the advanced approach for dealing with the coefficient of friction in contact surfaces and in-depth experimental and numerical analysis of fretting fatigue behaviour in complete contacts, i.e., contacts having “sharp” contact edges. Numerical models are verified by experimental testing and novel experimental data is produced employing various material combinations and surface treatments. These tools and results can be utilized in component level simulations to optimize designs against fretting. As an outcome, a novel modelling methodology has been developed and successfully applied in diesel engines in order to optimize and increase safety margin to fretting damage.
Fretting fatigue and fretting wear is considered as the plague of modern industry. Fretting can notably decrease the fatigue life of components. It often has disastrous consequences as fatigue cracks are allowed to initiate and grow unobserved within a contact. More accurate prediction of fretting damage and life-time of highly loaded assemblies increase cost-efficiency and reliability.
The methodology have been developed and applied in diesel engines. Results make it possible to more accurately predict fretting damage in real components by using modern simulation methods. This reduces the need for expensive and time-consuming component level testing and the risk of catastrophic failure. Some of the results can be used immediately at the design stage without the need of simulation. A connecting rod and counterweight for a crankshaft have been successfully optimized and increased safety margin to fretting damage. Basically, the developed methodology can be extended to be used in, for example, bolted connections and different kind of fits in mechanical highly loaded assemblies.
Arto Lehtovaara, Tampere University of Technology
Wärtsilä Finland Oy, Metso Paper Oy, Tampere University of Technology