Utilization of Notched Ring Test for larger diameter pipes and fittings

Session 9A
11:00 am

Sunwoong Choi, Hannam University

The Notched Ring Test (NRT) has been recently developed to measure slow crack growth (SCG) in plastics pipes and fittings. The NRT specimen in the form of a notched full ring is directly obtained from the extruded pipe or injection molded fitting and has demonstrated its effectiveness in generating slow crack growth in a time frame of order of magnitude shorter than the currently available test methods. Recently, the NRT test has been utilized to include larger pipes up to 400mm diameters and the results indicated that when plotted with stress intensity factor versus – time curve NRT results from various sized specimens (110mm, 300mm, 400mm SDR 11) came together in what seem to be a single curve. From these results, testing 110mm diameter pipe is being recommended as the standard test specimen as they provide simplicity and cost effectiveness in carrying out the NRT test for the determination of slow cracking behavior of plastic pipes and fittings. A solution to the difficulty associated with the detection of on-set slow cracking will be demonstrated with the development of the modified displacement method and a generalized solution for the stress intensity factor calculation for NRT specimens will be described and examples presented.

Sooho Pyo*, Junghyun Nam*, Yoonsang Kim* and Sunwoong Choi**

** Professor (swchoi@hnu.kr), *Graduate student
Department of Polymer Science & Engineering, Hannam University, Daejeon 305-811, Korea