Experimental J and COD analysis of crack initiation in through-thickness cracked pipes

The paper relates on results of a research, carried out at Laboratories of the Istituto di Impianti Nucleari of the University of Pisa in cooperation with CNEN-Casaccia Laboratories, on experimental J and COD analysis of crack initiation in through-thickness cracked pipes. General aim of the research is to utilize EPFM parameters in order to forecast the fracture behaviour of pipes, considered as simple structures. Testing is carried out at room temperature on low carbon steel pipes, that are 100 mm in outer diameter and 4 mm thick, in two basic conditions: - burst tests under internal pressure on longitudinally cracked pipes; - four point bending tests on circumferentially cracked pipes. During the tests, both the clip gauge opening displacement and the load Application point displacement are recorded seperately in terms of the load. Heat tinting technique is also used for measuring crack growth. J and COD crack initiation related values are also compared with the results of tensile tests obtained on no-standard cracked specimens made with the self-same material of the tested pipes. (orig.)