Assessment of Very High Cycle Fatigue (VHCF) Effects in Practical Applications

Fatigue designing of high-stressed engine components is a key factor for reliable power train systems in automotive industry. In this context load assumptions are very important since this is attended with a pre-designing of important machine elements. Load analyses are done usually by experimental methods since the accuracy of load simulations are often not precise enough. For example concerning VHCF problems, modern high pressure pumps for gasoline direct injection systems have load spectra with a large amount of cycles up to 109 including a very powerful shape of the load spectra.At the same time it is necessary to consider the properties of fuels in service since they might affect the fatigue strength significantly. For example ethanol-based gasoline fuels are used in a lot of countries worldwide and may lead to significant corrosion fatigue effects. In addition it is well known that material inclusions play an important role for the VHCF behaviour especially for high-strength steels. Both effects are superimposing at the surface of high loaded components.This paper deals with possibilities to avoid VHCF problems of components in service to maintain reliable systems.