Parametric Study on Fracture Toughness Requirement Based on the Equivalent CTOD Concept

Application of the Local Approach to Fracture Control Design (Part 4)

Abstract

This paper develops a new procedure for the fracture toughness requirement of structural steels based on the Local Approach. The new procedure is characterized by the equivalent CTOD concept. The equivalent CTOD is defined as a CTOD of the fracture toughness specimen, at which the toughness specimen presents the same Weibull stress as the structural component of concern. The validity of the equivalent CTOD concept is verified through the transferability analysis of toughness results to the fracture performance evaluation of welded joints. It is figured out that the equivalent CTOD concept relaxes the toughness requirement of materials, compared to the conventional toughness determination procedure. The CTOD ratio β=δ_{3p, Equiv.}/δ_WP (≤1) is introduced, where δ_WP is the CTOD of a wide plate component and δ_{3P, Equiv.} is the CTOD of the fracture toughness specimen which is equivalent to a δ_WP in terms of the Weibull stress. The CTOD ratio β decreases with increasing the yield-to-tensile ratio of the material. The size and type of a crack postulated in the component also exert an influence on the CTOD ratio β. A deep and short crack gives a low β. The CTOD ratio β for the surface crack is larger than those for the through-thick double-edge and center cracks.