The Stepped Isothermal Method for Estimating the Long-Term Creep Strain and Creep Rupture Strength of Polypropylene Resins Used in Civil Engineering Applications

摘要

The Stepped Isothermal Method (SIM) is a special form of Time-Temperature-Superposition (TTS) that has been used to predict long-term creep behavior from very short-term tests (~ 24 hours). A single test specimen undergoes a series of short-term (10,000 seconds) creep tests, each separated by a constant temperature step. At the end of the experiment, one obtains a series of creep curves, each at a different temperature. The results are shifted based on known TTS techniques and a master curve obtained. Creep modulus and creep strain are determined under lower loads, while creep rupture times can be determined under higher loads. It was originally developed in these laboratories on high strength polyester (PET) geotextiles and geogrids for soil reinforcement applications. The results on PET, Kevlar, Nylon, and PP have correlated well to conventional creep results. This paper will describe the test, how the data are analyzed to generate a master curve and show several examples of its use with polypropylene resins.