Abstract : The vibratory instabilities, such as the brake squeal noise, are often studied by complex Eigenvalues analysis (CEA) on finite elements models (FE). The purpose of this thesis is to improve these models by taking the material viscoelasticity into account which induces damping and stiffening of materials according to the frequency.For that a tester was developed. It makes it possible to characterize the shearing behavior of materials between 100 and 3500Hz, without using time-temperature equivalences. This tester allows feeding in parameters the rheological model of generalized Maxwell by the means of a new robust identification method. The generalized Maxwell model is then introduced into FE models thanks to a state-space model on an accurate subspace.These improved models predict less instability occurrences because of damping, but they also show that viscoelasticity may induce destabilization because of stiffening.