Cell model simulation of void growth in nodular cast iron under cyclic loading

The failure of cast iron under high plastic cyclic strains is controlled by the mechanisms of formation, growth and coalescence of voids. A cell model approach is used to simulate nodular cast iron as a periodic array of loosely bonded spherical inclusions in the matrix material. The models are analyzed by the finite element method under cyclic loading while keeping the stress triaxiality constant. Different types of matrix hardening are used: isotropic, kinematic and combined hardening. The graphite inclusions are simulated by a rigid body. Deformation and void growth are studied in dependence on stress triaxiality and strain range. In most cases after a few cycles a non-symmetric stationary mesoscopic cyclic stress-strain curve is established. The deformation response and the development of the void volume fraction are strongly affected by the value of triaxiality. The void volume is incrementally increasing with each load cycle in a ratcheting manner. The void growth rate depends on the chosen hardening type and is smallest for kinematic hardening. The comparison with simulations in absence of graphite inclusions revealed that void evolution is favored by the inclusions.