Abstract
Effect of plastic zone at the tip of small defect on the fracture toughness calculated with rupture strength and defect size was studied.
(1) Fracture toughness evaluated by approximating the cross section of the small fracture defect with the inscribed circle or the ellipse is smaller than that determined by the Bridge Indentation method based on linear elastic fracture mechanics. The difference between the two values increases with the decrease of defect size and the increase of Co content.
(2) Fracture toughness estimated by taking account of the yielding of the plastic zone at the tip of defect agrees with the measured value by the BI method.
