Temperature dependence of viscoelastic properties of polymers under dynamic conditions on the basis of the linear theory of thermoviscoelasticity

Abstract

Another method of taking the temperature dependence of the deformation properties of a material into account is based on the use of relationships between the coefficients of the determining equations and the temperature as a parameter [5, 6]. In this case, the temperaturedependence of the inelastic constants is usually studied by conducting long-term creep or relaxation tests [6]. Short-term tests wherein specimens are loaded with a constant strain rate [7] are occasionally employed to ascertain the temperature dependence of the modulus of instantaneous elasticity -- in this case, the initial segments of the e-e diagram or dynamic tests, conducted at various temperatures to determine the resonant vibration frequencies, are analyzed [8]. In view o f the vigorous effect of elevated temperature on the deformability of polymers, however, the inelastic properties may manifest themselves significantly even during short-term loading and in dynamic tests [4, 9, I0]. Analysis of similar experience should therefore be made, generally speaking, on the basis of equations of thermoviscoelasticity, while the temperature dependence of the effective elastic modulus, which is derived experimentally from short-term tests, reflects the effect of inelasticity to a significantly greater degree than the temperature dependence of the modulus of instantaneous elasticity. In our study, we attempted to describe quantitatively the temperature dependence of the dynamic shear modulus and the loss factor of a rigid cellular polymer from the results of quasistatic ~ tensile-creep tests conducted at room and elevated temperatures on the assumption that the modulus of instantaneous elasticity is a constant independent of temperature. We compared comlmted results with experimental data obtained at different temperatures during torsion tests under conditions of natural damping vibrations. Initial data on the viscoelastic properties of ED-6 epoxy resin were obtained from ten