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

This paper presents the latest results of an extensive research program sta rted in 1985 on the cylindrical notched test (CNT) specimen that evaluates fracture toughness. Specimen geometry is the cheapest methodology in manufa cturing, which can produce values for fracture toughness and is also smalle r than the standard compact tension test (CT) specimen. The CNT specimen ha s many advantages and can be used in many applications that are not possibl e with standard CT specimens. Requirements for the minimum diameter of the CNT specimen are discussed and compared with the similar requirements for t he CT specimen. As was reported earlier, however, a major problem in CNT sp ecimen testing is that only a very small part of all samples has the pure c o-circular geometry after pre-cracking which is suitable for analytical con sideration. 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 calc ulation of the stress intensity factor for many eccentrically and externall y cracked bodies. It has been validated by comparison with FE results and k nown analytical solutions. The testing procedure and the analytical approac h presented agree well with independent CT specimen testing results. (C) 19 99 Elsevier Science Ltd. All rights reserved.