Thermal-aging constitutive model for a silicone rubber foam under compression

Abstract

Silicone rubber foam is a key function component in engineered systems. The long-term effect of temperature and compressive strain can degrade the mechanical properties of the foam. In this work, the temperature and aging time dependence of the mechanical behavior of the silicone rubber foam under long-term compressive strain was investigated by accelerated aging tests and uniaxial compression tests. The Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and crosslinking density were used to evaluate the chemical changes of the foam samples under different conditions. The ATR-FTIR and crosslinking density results indicate that crosslinking reaction and chain scission reaction occurred simultaneously. The crosslinking reaction dominated during the aging process resulting in the increase of the crosslinking density. The mechanical properties results show that the increase in the temperature and/or aging time can lead to the hardening of mechanical behaviors due to thermal aging-induced oxidative reactions. A thermal-aging constitutive model for the compressed foam was established by incorporating the dependence of the model parameters on temperature and aging time into the Hyperfoam model. Two types of exponential models were proposed to describe the dependence of model parameters on temperature and aging time. The performance of the thermal-aging constitutive model was verified by comparing the model predictions with independent testing data. Results show that the model can accurately describe the compressive stress-strain responses of the unaged and the aged foams under long-term compressive strain.