By utilizing fractographic approach, an applicability of a chevron notched specimen as well as a conventional compact specimen to plain strain fracture toughness, KIC, tests was examined for brittle materials; a ceramics (Si3N4), a high strength graphite (IG-11), an alumina particulate filled epoxide composite, and a low alloy steel (A533B-1) at lower shelf and transition temperature regions. The KIC test method using chevron notched specimens was found useful for these materials except A533B-1. The cleavage fracture toughness values for A533B-1 were overestimated due to difficulty of introducing a precrack by cleavage from the chevron notch tip.
Further fractographic examination showed that in both IG-11 and the epoxide composite, micro scopic appearances of a fracture toughness, a fatigue, and a stress corrosion cracking specimens were almost the same, suggesting the similar crack growing mechanism in these cases.