Study For The Viscoelastic Properties Of Solids With Transient Wave Propagation Methods

By the application of polymer and elastomer in the industry, it's applied very important to determine the mechanical characteristics of a medium. So we don't ignore the effect of inner amortisseur of these materials, these similar materials are called the viscoelastic. After describing the principle of the method, this paper present the determining the viscoelastic properties of solids .Since about ten years, the theory of determining the viscoelastic properties of solids by transient wave propagation methods is developed and perfected by scholar Mr. Blanc. This method has some advantages: no-destruct, simpleness, economy.After describing the principle of the method we propose two theoretical solutions. Expressions are first established for c(w) and a(w) in terms of the Fourier transforms of the wave shapes after two distances of travel. This is the general solution of the problem. It is expressed quite simply in terms of the transfer function of these two wave shapes. On the other hand, the behaviour of the medium is completely determined by measuring the real cr complex Poisson's ration. Secondly, the same pulses are applied to selective frequency filters, and again the required results are obtained from their response.Any homogeneous viscoelastic medium subjected to one-dimensional tension and compression can be characterized in terms of the phase velocity c(w) and the attenuation coefficient deduce the complex modulus and the other equivalent viscoelastic functions. To determine these functions, a slender bar of the medium under investigation is subjected to a single mechanical transient and the resulting wave is observed.The principle of the method is as follows. Let us consider a slender bar of the medium, with a constant cross-section area. A short axial disturbance is produced at one of the bar, resulting in the propagation of a wave. In viscoelastic media, the high frequency waves propagate and are damped more quickly than the low frequency ones, so that the shape of the wave will change continuously as it propagates. Lets us assume that we know the successive shapes of the pulse as a function of time after it has travelled two distances xl and x2 along the bar. It is proposed to deduce the corresponding functions c(w) and a(w).The bar is assumed to be thin, which means that the largest dimension of its cross-section is small in comparison with the wavelengths involved in the disturbance. The one-dimensional theory will then be valid. The result treated with the programme Labview bear out the exactness of the theory.