Determination of Fracture Toughness of a Material That Exhibits Pop-In Behavior

Fracture toughness of a material that undergoes pop-in crack extension was measured in two different heat treated conditions by a new procedure proposed in a recent publication. It is shown in this publication that the new procedure gives a size independent plane strain fracture toughness KIc value in thin and wide specimens prepared from relatively tough material. The present investigation examines the effect of width and the applicability of various approaches to fracture toughness measurement procedures, such as the new procedure, ASTM Test Method for Plane-Strain Fracture Toughness of Metallic Material (E 399), KIc, the ductile fracture toughness value JIc, and the crack growth resistance R curve, to a material that undergoes pop-in crack extension. The results show that whereas the new procedure can give a meaningful, reliable, and size independent fracture toughness even for a material that undergoes pop-in crack extension, the other methods, such as R curve, JIc, Kpop, or ASTM E 399 are inapplicable. The new procedure also shows that the K-KIc approach can be used in specimens whose thickness is 4.5 times less than that required by ASTM E 399.