On fractography of shallow and deep HY-100 cracked bend specimens

The influence of shallow cracks on the fracture behavior of structural components has been studied extensively in recent years. Finite element analyses have indicated dramatic differences in the crack-tip stress states between shallow and deep cracked bend specimens. In this study, an experimental program was carried out to investigate the fracture behavior of HY-100 steel containing various initial flow depths. Four a/w ratios ranging from 0.05 to 0.5 were chosen for the notched three-point bend tests. Test results showed that higher fracture toughness values are associated with specimens having shorter surface cracks. Also, fractographic studies indicated that two sets of dimples are present for a/w = 0.5 specimen, one set of equiaxed dimple for a/w = 0.05 specimen near the crack initiation zone. As the crack grows, increases in the volume fraction of the small dimple were observed. Finally, it showed that the characteristic features of surfaces can be correlated with the previous numerical predictions.