Ratio Of Viscoelastic Materials Research Articles

Determination of the Poisson’s ratio of viscoelastic materials based on the linear rheological model using instrumented indentation

ABSTRACTBased on the linear rheological constitutive model that is used to describe viscoelastic-plastic behavior of viscoelastic materials, a formula of the Poisson’s ratio was deduced according to the relationship between the shear creep compliance and tensile compliance. Instrumented indentation under various loading conditions and universal creep tests were performed on polyamide 12 samples to obtain the relevant rheological parameters. Results show that the Poisson’s ratio for a step load indentation can obtain a constant but overrated value. However, the Poisson’s ratio approaches an asymptotic value and an accurate value can be gained at a certain loading rate.

Experimental determination of the complex Poisson’s ratio of viscoelastic materials.

An empirical procedure to determine the dynamic, complex Poisson’s ratio of viscoelastic materials as a function of temperature and hydrostatic pressure is presented. In this procedure, the Young’s modulus and the bulk modulus of the material are measured, and the complex values of these moduli are combined to compute Poisson’s ratio. The two independent measurement systems used to obtain these data are described. The Young’s modulus system requires a sample cut in the shape of a bar and relies on traditional resonance measurements for low-frequency data as well as on wave speed measurements for higher-frequency data; measurements are performed in air. The bulk modulus system measures the dynamic compressibility of a sample of arbitrary shape immersed in Castor oil. Data can be obtained at frequencies typically ranging from 50 Hz to 5 kHz, at temperatures comprised between -2 and 50° C and under hydrostatic pressures ranging from 0 to 2 MPa (Young’s) or 6.5 MPa (bulk). The two moduli can also be combined to compute any other modulus, and the two systems therefore allow the complete elastic characterization of a homogeneous and isotropic material. Data obtained on a nearly incompressible rubber are presented.

Determination of Shear and Bulk Moduli of Viscoelastic Solids from the Indirect Tension Creep Test

Because of its efficiency in analyzing complex viscoelastic problems, the finite-element (FE) analysis has been widely used to identify the time- and rate-dependent effects of viscoelastic materials on various structural conditions. When performing the FE analysis on a viscoelastic structure, most FE programs require fundamental material properties, shear and bulk moduli, of the given viscoelastic material as their input. However, the shear and bulk modulus tests are difficult to perform, so they have been commonly estimated from a single material test on the basis of the assumption that the Poisson’s ratio of viscoelastic materials is a time-independent constant. Such an assumption, however, might not be suitable because the Poisson’s ratio of the viscoelastic materials is also a function of time. Therefore, this study developed computation algorithms for determining the time-dependent Poisson’s ratio and shear and bulk moduli of asphalt mixtures, which have been well recognized as a viscoelastic materia...

Measurement methods of complex Poisson's ratio of viscoelastic materials

The methods of measuring the complex Poisson's ratio of viscoelastic materials as a function of frequency are investigated in this paper with special respect to the accuracy of determining the relevant loss factor. The measurement methods are reviewed, evaluated and compared from the point of view accuracy and frequency range. It is shown that some contradictory beliefs on the frequency dependence of dynamic Poisson's ratio and the value of loss factor are due to experimental difficulties. It is pointed out that the measurement of two complex moduli, especially the shear and bulk moduli, may be the most effective method to determine the dynamic Poisson's ratio and loss factor over a wide frequency range. An example for determining the complex Poisson's ratio of a rubber in a wide frequency range is presented.