Plain and notch fatigue strength of ductile cast iron GJS600: The role of defect sensitivity

The present work is aimed at exploring the applicability of the theory of critical distances (TCD) to the plain and notch fatigue prognosis of the ductile cast iron GJS600. Particular attention is paid to investigating how defectiveness influences material critical length. It was found that fatigue damage is triggered by microshrinkage porosity in plain samples and by graphite nodules in notched samples. This evidence makes cumbersome the applicability of TCD, which postulates the notch-crack equivalence. According to this postulate, the critical distance can be inferred from a plain and a notched or cracked specimen configuration. Since the plain variants examined in this paper exhibit a fatigue damage phenomenon different from the notched ones, the critical distance inferred in this way leads to inaccurate predictions of the fatigue strength of independent notched variants. To overcome this shortcoming, we explore here the possibility of inferring the critical distance from two notched variants with different notch severity.