Eccentricity correction for the evaluation of fracture toughness from cylindrical notched test small specimens

Abstract

This paper presents the latest results of an extensive research program started in 1985 on the cylindrical notched test (CNT) specimen that evaluates fracture toughness. Specimen geometry is the cheapest methodology in manufacturing, which can produce values for fracture toughness and is also smaller than the standard compact tension test (CT) specimen. The CNT specimen has many advantages and can be used in many applications that are not possible with standard CT specimens. Requirements for the minimum diameter of the CNT specimen are discussed and compared with the similar requirements for the CT specimen. As was reported earlier, however, a major problem in CNT specimen testing is that only a very small part of all samples has the pure co-circular geometry after pre-cracking which is suitable for analytical consideration. The present paper discusses an approximate analytical approach which was developed to estimate the fracture toughness from specimens with an eccentrically displaced ligament. This approach is suitable for the calculation of the stress intensity factor for many eccentrically and externally cracked bodies. It has been validated by comparison with FE results and known analytical solutions. The testing procedure and the analytical approach presented agree well with independent CT specimen testing results.