Bill R. Vanhoose, Jarrett A. Nelson, Christa K. McNish, Richard W. Thomas
Papers # 2014 Chicago
The Stepped Isothermal Method (SIM) is a form of Time-Temperature Superpositioning (TTS) that involves measuring the creep rate of a sample while it is subjected to a series of isothermal temperature steps. The accelerated temperature results can then be shifted back to room temperature to produce a master-curve. Performing multiple temperature steps on a single specimen reduces the noise associated with sample-tosample variability. This test has been used for over 15 years to characterize the creep behavior of a variety of products made with different polymers. The products include high-strength geotextiles, geogrids, mooring lines, underground storage tanks, and pipe. The polymers evaluated include polyester, polypropylene, polyamides, polyethylene naphthanate (PEN), and polyethylene. The purpose of this study was to validate results obtained by SIM on polypropylene by comparing the SIM results to conventional room temperature creep tests. The results demonstrate that the SIM results correlate well to conventional tests for up to 10,000 hours. Additionally, the SIM results can be considered superior to conventional tests because one can control variables much better over a 24 hour period than a 10,000 hour period.