Corrosion fatigue in biogenic fuels in the very high cycle fatigue regime

• Applicants: Professor Dr.-Ing. Tobias Melz; Professor Dr.-Ing. Matthias Oechsner; Professor Dr.-Ing. Hans-Werner Zoch
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 244527137

Due to the increased application of biogenic fuels questions concerning the compatibility of metallic alloys are raised which are not existent in those terms for fossile fuels. Aforementioned issues mainly focus on the risk of corrosion of fuel-carrying components and systems. If components are subjected to superimposed cyclic mechanical loading corrosion supported crack formation has also to be taken into account. Besides the question concerning the political and ecological benefits, which are not subject of this project, the controversial debate about the introduction of the biogenic fuel E10 in Germany reveals major concerns regarding an inadequate reliability of the materials used in service. In the medium term, the introduction of biogenic fuels with higher ethanol contents, which has already been put into effect in other parts of the world, such as Brazil (inhibition of fuels, introduction of vehicles with compatibility with E85 fuel) is a matter of controversy (USA: E15). Instead of selective tackling of corrosion problems, the growing variety of fuels with biogenic origin requires a basic investigation of the underlying damaging mechanisms and a deduction of measures for damage prevention.For fatigue loaded vehicle components, the compatibility with fuels of biogenic origin is of major interest as the simultaneous impact of mechanical and corrosive loading leads to complex interactions and damage forms. Those system specific conditions complicate a reliable dimensioning of fuel carrying components. Moreover, components are operated in the very high cycle fatigue regime but dimensioned against a maximum number of 10^7 cycles according to the current design practice. Empirically based recommendations for a calculative extrapolation of the decrease of fatigue strength within the very high cycle fatigue regime (10^9 cycles) is not considered in current rules or standards. But due to the assumable time and load dependency of the corrosion damage, a massive underestimation (inefficient material and energy input) or overestimation (risk of failure) of the structural durability cannot be prevented without a fundamental review of the underlying damage mechanisms.For this reason, the present research project focuses on a mechanism based description of the damaging processes of fuel corrosion on the basis of steel alloys used for injection system components. The determination of the underlying damaging processes is a fundamental precondition for the deduction of an analytical damage model for the corrosion fatigue behaviour in biogenic fuels which conveys basic knowledge for a later transfer to other fuel-alloy combinations.

• DFG Programme: Research Grants