Plastic rotational factors in three point bending test of steels with various crack length to width ratio

Abstract

Since Crack tip opening displacement (CTOD) has been proposed as a fracture mechanics parameter CTOD in 1960s CTOD is widely used in steel structure industries for toughness evaluation of the materials and/or defect assessment of the welded structures based on the fitness for service standard. National standard in each country and also ISO standard have been established which is a similar procedure to the firstly standardized DD19 in British Standard Institution in 1972. The CTOD calculation is composed of plastic hinge model which assumes rotational deformation around the specific point. Standard range of crack length to width ratio (a₀/W) is limited to be from 0.45 to 0.5. In the last 15 years, the discussion of CTOD has revived at a chance of the J based CTOD proposal in ASTM. The J based CTOD is capable of CTOD calculation in the wide a₀/W range. CTOD evaluation using single edge notched tension (SENT) specimen with a sallow crack is also desired by industries at the same time. However, the capability of rotational CTOD evaluation in the wide a₀/W range has not completely been concluded, yet. In this study, aiming to propose the new calculation method of CTOD, the rotational deformation is examined in the a₀/W range from 0.05 to 0.70, and the applicability of rotational CTOD calculation for a shallow cracked specimen is discussed.