Fatigue behaviour and lifetime calculation of the cast irons EN-GJL-250, EN-GJS-600 and EN-GJV-400

Abstract

The current paper focuses on the cast irons EN-GJL-250 (ASTM A48 35B), EN-GJS-600 (ASTM 80-55-06) and EN-GJV-400, which are often used as structural materials for internal combustion engines and components of the wheel suspension and in the wind energy industry, e.g. for rotor hubs. Light and scanning electron microscopic investigations were done to characterise the individual microstructure, e.g. different graphite precipitates, in particular lamellar graphite (EN-GJL-250), nodular graphite (EN-GJS-600) and compacted graphite (EN-GJV-400). In stress-controlled load increase and constant amplitude tests at ambient temperature, mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed to characterise the fatigue behaviour of the investigated materials. All measured data depend on microstructural changes due to plastic deformation processes in the bulk of the specimens and the interfaces between matrix and graphite. This data represent the actual fatigue state. The cyclic deformation behaviour is dominated by cyclic hardening processes and graphite-matrix debonding.The physically based fatigue life calculation method “PHYBAL” was modified to the specific requirements of more inhomogeneous materials like cast irons. On the basis of fatigue data determined in only nine fatigue tests, the enhanced method “PHYBALSB” allows the calculation of Woehler (S-N) curves for different probabilities of failure (Scatter-Bands). This shorttime procedure results in a reduction in experimental time up to 90% and leads to enormous scientific and economic advantages.