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The interconversion relations for viscoelastic functions are derived with the consideration of the time-dependent bulk modulus, K(t), for both traditional and fractional Prony series representations of viscoelasticity. The application of these relations is to replace the fitting parameters of Young’s relaxation modulus, E(t), by the unknown parameters of K(t) and the known parameters of the shear relaxation modulus, G(t), and to fit the E(t) to the experimental data for obtaining the parameters of K(t). The fitting results show that only two experiments for measuring the viscoelastic functions of an isotropic material are not enough to determine the other viscoelastic functions. However, if we consider the relaxation rates of K(t) and G(t), we may conclude that the constant bulk modulus is a more reasonable assumption, and the corresponding Poisson’s ratio, ν(t), is a monotonic-increasing function. [ABSTRACT FROM AUTHOR]

A new representation for viscoelastic functions, the tensor relaxation-creep duality representation, is introduced. The derivation of a tensor time-differential constitutive equation for anisotropic viscoelastic materials using this new presentation is presented. The relaxation-creep duality characteristic ingrained in the new representation enables the interconversion of viscoelastic functions, which is not possible with the conventional Prony series representation of viscoelastic functions. The new representation therefore offers a better representation of the physics of viscoelasticity leading to a reduced number of viscoelastic parameters required to describe a viscoelastic function. The new representation has been demonstrated on two anisotropic viscoelastic crystallographic systems: (i) the symmetric systems with material- and time-independent eigenvectors and (ii) the symmetric systems with material-dependent but time-independent eigenvectors. [ABSTRACT FROM AUTHOR]

The monotonicity of the linear viscoelastic functions, namely, the shear creep compliance, the Young’s relaxation modulus, the stretch creep compliance, the P-wave relaxation modulus, the Lamé’s first function, and the time-dependent Poisson’s ratio, were examined analytically and numerically. It was shown that both the Lamé’s first function and time-dependent Poisson’s ratio can be non-monotonic. Furthermore, in contrast to the reports by other researchers, the values of the time-dependent Poisson’s ratio were found to be bounded by the limits between −1 and 0.5 after the physical constraints of the bulk and shear relaxation moduli are taken into account. [ABSTRACT FROM PUBLISHER]

The interconversions between relaxation moduli and creep compliances, including stretch, shear, bulk parts, and the time-dependent Poisson’s ratio, are derived by using the relaxation-creep duality representation. The relaxation-creep duality representation for the viscoelastic functions introduced in this paper is composed of an exponential function that characterizes the relaxation behavior and a complementary one that characterizes the creep behavior. All viscoelastic functions can be represented as the same form. The new sets of coefficients, called the modulating constants, between viscoelastic functions obey the elastic-like interconversions, and do not involve the characteristic times. The relationships of characteristic times between those functions are also derived. These interconversion formulas can then be calculated easily. Three literatures are referenced to calculate the consistency of the viscoelastic functions via the new interconversions introduced in this work. The Young’s relaxation modulus in one literature is not consistent to the shear one in another literature. By assuming a constant bulk modulus, the modified Young’s relaxation modulus and time-dependent Poisson’s ratio that was derived by the new interconversions can meet the measured curves and can be consistent to the shear creep compliance in the literatures. The fitted data from experiments can then be checked via the new mathematical interconversions for the consistency. [ABSTRACT FROM PUBLISHER]