Mechanical properties and strain fatigue lives of insulation polymers
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Insulation polymers are not well characterized for their mechanical properties particularly in terms of fatigue strains. This article aims to examine the durability and strain fatigue lives of three commonly used cable insulation polymers, viz., (1) polyvinyl chloride (PVC), (2) crosslinked polyethylene (XLPE), and (3) polyphenylene ether (PPE) under selected strain and temperature ranges. The tensile properties of these materials were measured using an Instron testing machine at constant and controlled loading rates. Fatigue tests were performed at three selected temperatures, −40, 25, and 65 °C, to characterize the temperature effects on fatigue life. From the tensile test results, it was observed that PVC and XLPE are ductile and exhibit significantly more elongation prior to breaking, while PPE exhibits brittle behavior. When the loading rate is increased, there is an improvement in the tensile strength of PPE and elastic modulus of PPE and PVC. The durability of XLPE under strain fatigue testing was the largest, followed by PVC and PPE. The strain fatigue lives of PVC and XLPE decreased drastically at −40 °C and demonstrated a noted increase at 65 °C compared to fatigue lives at room temperature. This trend was not observed in PPE where the strain fatigue life showed improvement at both lower and higher temperatures.
KeywordsFatigue Fatigue Life Dynamic Mechanical Analysis True Strain Volumetric Strain
SCW thanks the ASEE Summer Faculty Program and R. Andrew McGill at the U.S. Naval Research Laboratory.
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