Constitutive modeling and experimental calibration of pressure effect for polyurea based on free volume concept

Abstract

The combined effect of pressure and temperature on the mechanical behavior of polyurea is characterized and integrated into a constitutive model based on Williams-Landel-Ferry (WLF) equation. An increase in pressure is related to a decrease in temperature, both pressure and temperature affecting the polymer's molecular free volume and thereby introducing a pressure-dependent term into the WLF equation. The model is derived based on Fillers and Tschoegl's original work, regarding the free volume as a state variable. The model provides a closed-form expression for the time scale shift factor for equivalent temperature in terms of temperature and pressure and its threedimensional surface representation. The prediction of the present model agrees well with pressure shift factor data obtained from confined compression tests of polyurea, reported elsewhere, confirming our constitutive model and its experimental calibration procedure. A simplified model of the pressure effect is also developed which yields good approximate results.

A nonlinear viscoelastic constitutive model with damage and experimental validation for composite solid propellant

“…Nantasetphong et al 54 pointed out that an increase in pressure is related to a decrease in temperature, which means the effect of temperature drop on viscoelastic materials is approximately equal to the increase of confining pressure. The TTSP is widely used to construct the master curves of viscoelastic mechanical parameters of various viscoelastic materials.…”