Fatigue crack growth in compacted and spheroidal graphite cast irons

The present paper focuses on the fatigue life of a Compacted Graphite cast Iron (CGI) as compared to a Spheroidal Graphite cast Iron (SGI). Fatigue crack growth laws have been determined with digital image correlation. Main difference between the materials is that cracks propagate faster in the CGI than in the SGI. X-ray tomography was also used in order to assess graphite morphologies and crack shapes. A complex morphology was observed for the vermicular graphite with rounded edges that limit notch effects. The crack spreads easily in CGI via a quasi cleavage mechanism and by propagating through graphite mainly by breaking the vermicules.