Micromechanical simulation of fatigue in nodular cast iron under stress-controlled loading

Nodular cast iron contains about 10 vol% of graphite particles, which debond easily and thus act as nucleation sites of voids. When an elastic–plastic porous material is subjected to cyclic loading, voids grow with each load cycle due to so-called void ratchetting until the micro-ligaments between the graphite particles begin to neck. The cyclic necking leads to void coalescence and finally to the formation of a macroscopic crack. This mechanism is modeled in this study to explain fatigue failure under stress-controlled loading. For this purpose, an axisymmetric cell model is developed and cycle by cycle simulations are performed until final failure. From the simulation results, stress-life curves are extracted and compared with experimental data collected from literature. The effects of the shape of graphite particle, type of matrix material hardening, and mean stress on the fatigue life of nodular cast iron are studied.