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Variable amplitude fatigue of high-strength cast iron alloys for automotive applications

 
: Schoenborn, S.; Kaufmann, H.; Sonsino, C.M.; Heim, R.

:

International journal of fatigue 91 (2016), Pt.2, S.445-458
ISSN: 0142-1123
Englisch
Zeitschriftenaufsatz
Fraunhofer LBF ()

Abstract
In the automotive sector, the cumulative damage calculation method generally applied is the Palmgren–Miner-Hypothesis with its modification according to Haibach (steeper slope of the SN-line after the knee-point) as a means of also including the damage by stress amplitudes below the knee-point. This approach results in the total damage sum of the spectrum Dspec. However, the resulting question is the value of the allowable damage sum Dal for the evaluation of Dspec ⩽ Dal. The only design code that considers the assessment of cast iron components under spectrum loading is the FKM-Guideline of the Cooperative Research Association for Mechanical Engineering (FKM, Frankfurt/Germany) for designing machine components. Here, the theoretical Palmgren–Miner-damage sum Dth = 1.0 is still suggested as the allowable damage sum Dal despite the fact that this damage sum renders unsafe calculated fatigue lives in about 90% of all published results.
The results obtained with component-like notched specimens of modern high-strength cast iron alloys (Rm = 650–800 MPa) such as EN-GJS-500-7, SiboDur 700-10 and MADI (Machinable Austempered Ductile Iron), which were investigated under a standard Gaussian spectrum for chassis applications and also for a fuller injection pump spectrum, suggest the allowable damage sum Dal = 0.3 for fatigue life estimations of components manufactured with these materials can be proposed; i.e. the allowable fatigue life is about one third compared to calculations with the theoretical damage sum Dth = 1.0 that is still used.

: http://publica.fraunhofer.de/dokumente/N-417848.html