The influence of torsion effect on fracture behavior of Pipe Ring Notched Bend specimen (PRNB)

Through the time, researches realize the problem of inability to measure the fracture toughness of pipe material in some cases, because of inability of producing standard specimens from pipe wall. This problem is especially expressed in thin walled pipes. In that sense, a lot of alternative procedures and nonstandard specimens are proposed but with no notable success. One of the latest and the most convenient one is Pipe Ring Notched Bend specimen (PRNB) proposed by Gubeljak and Matvienko (Patent No. RU 2564696 C1, 10.10.2015.: Matvienko Y.G. and Gubeljak N., Model for Determination of Crack - Resistance of the Pipes). Lot of research are made on the PRNB specimen and this paper presents further analysis of such a specimen. Due to the specific geometry of PRNB specimen and loading which is three - point bending, torsion effect occurs in the region of crack. This paper deals with analysis of influence of this torsion effect on fracture behavior of PRNB specimen. In order to obtain more detailed analysis of torsion effect influence, J - integral versus thickness of the specimen curves are presented for the specimen with and without torsion effect and for various a/W ratios. Further, comparison of maximal J - integral values (at half of wall thickness B/2) for specimens with and without torsion effect in relation to the a/W ratio has been analyzed.