Creep and Hysteresis Testing of Unfilled Natural Rubber Using Scanner-based Digital Image Correlation

Abstract

The conventional digital image correlation (DIC) method is not readily applicable for testing creep and hysteresis in high strain polymeric materials at temperatures above room conditions due to the limited field-of-view of the camera and the difficulty associated with heating the specimen during loading. In this work, the previously developed scanner-based digital correlation (SB-DIC) method for in-plane displacement and strain measurement was extended to investigate creep and hysteresis in unfilled natural rubber at temperatures up to 65 °C. An enclosed loading rig was designed to load the rubber specimens both mechanically and thermally. Two cylindrical quartz heaters were used to apply constant heat to the rubber specimen at controlled temperatures during loading. Speckle patterns on the specimens were created artificially and images were acquired by scanning using a flatbed scanner at regular time intervals. The zero-normalized cross correlation criterion in the DIC algorithm was used to map strains up to 400\u2009% due to creep and hysteresis. A series of creep experiments from 25 to 65 °C and hysteresis experiments from 25 to 55 °C were carried out to investigate the effect of temperature on creep and hysteresis in rubber. The full-field displacement vectors showed a rapid increase in creep strain above 35 °C. The hysteresis loops were also found to increase with temperature.