Applicability of Jc-δc, Criterion to Unstable Brittle Fracture with Particular Reference to Fracture Toughness Testing

Abstract

Study has been carried out to clarify the applicable range of COD and Jc-criteria which have been proposed as useful criteria in the fracture of non-linear charactristic materials. At first, evaluation methods of COD and J- integral and the applicable range of these methods were made clear in particular, simplified formulas for estimating J-integral of a shallow notched specimen were newly established. Both COD- and J- values estimated by a proper procedure dominate the distribution of the equivalent plastic strain in the vicinity of the blunting tip of a notch ; however, they can no longer control the nominal stress σ⊥ which is related to the initiation of cleavage crack. Therefore, the critical δc- and Jc- values depend essentially upon the plastic constraint in the vicinity of notch tip. Jc-δc criterion has been newly proposed as a useful criterion for unstable brittle fracture. Using Jc-δc criterion, it could be expected that fracture toughness testing for estimating plane strain fracture toughness becomes more easy.