Fatigue crack growth analysis in porous ductile cast iron microstructure.

The aim of this work is to propose an engineering procedure to simulate the fatigue strength of ferritic ductile iron castings, developing a case study. Starting from detected defect features, the fatigue behavior is studied numerically looking separately at the two fundamental phases, i.e. crack initiation and crack growth. The fatigue crack growth is simulated by finite element analysis using the Virtual Crack Closure Technique, starting from experimentally detected initiation sites and cast defect dimension on a set of specimens extracted from heavy-duty tile press frames and fatigue tested with a classical staircase methodology. Results show that crack takes longer time to initiate rather than to propagate, and that the local defect morphology plays a crucial role in it. As a deeper understanding of the fatigue crack initiation phase becomes necessary, a 3D reconstruction methodology of casting defects has been setup and the definition of a defect equivalent size in terms of local stress has been attempted.