Brittle failure criteria of CNRB specimen for fracture toughness test

Abstract

This paper proposes a technique to determine the dimensions of a CNRB specimen to be used for plane fracture toughness tests. First, the brittle fracture behavior satisfying the small-scale yielding condition is investigated through an elasto-plastic analysis. The analysis parameters are the shape parameters such as the notch ratio of the specimen based on the parallel part diameter and notch bottom diameter; tip radius; and notch angle. Based on the analysis results obtained, a fracture toughness test is conducted on a JIS-S45C (quenched and tempered) specimen to evaluate the small-scale yielding condition. The experimental results confirm a linear relationship between the square of the value obtained by dividing the plane-strain fracture toughness by the yield stress and specimen diameter. Further, the diameter of the CNRB specimen satisfying the small-scale yielding condition varies with the shape parameters. With these results, a function that can determine the CNRB specimen diameter at which brittle failure occurs under uniaxial tensile loading is proposed and validated.