FRACTURE-TOUGHNESS TRANSITION CURVE ESTIMATION FROM A NOTCHED ROUND BAR SPECIMEN USING THE LOCAL APPROACH METHOD

The local approach method for the brittle or transition region describ es the fracture probability of specimens or structures using Weibull s tatistics. Many papers have discussed the characteristics of the Weibu ll parameter using notched tensile specimens and the applicability to fracture toughness scatter evaluation using CT specimens. However few papers have made clear whether the Weibull parameter of the Weibull st ress is a material property or not. In this paper the distribution of Weibull stress in the brittle fracture region using notched round bar specimens and CT specimens were investigated and it was confirmed that both distributions agreed well. Furthermore the estimation method for the fracture toughness transition curve including its scatter from no tched round bar tensile tests was proposed based on the relation betwe en the Weibull stress and the Wallin's fracture toughness transition c urve. As a result, the estimated fracture toughness curve in the britt le and lower transition region from the notched round bar specimens co incided with the measured fracture toughness curve from CT specimens. This method will be applicable to fracture toughness curve estimation under plane strain conditions even if there is no possibility of obtai ning thick enough CT specimens from a structure because of geometry or some other restrictions. (C) 1997 Elsevier Science S.A.