ABSTRACT
The transient experiments to which we referred in the preceding chapter provide information on the linear viscoelastic behavior of materials in the
time domain for values of t larger than 0.1 s. However, it is often necessary to obtain the responses of viscoelastic materials to perturbation force fields at very short times. For example, when materials are used as acoustic iso lators in buildings, or to eliminate noise in vibrating metallic sheets by depositing layers of viscoelastic materials on them, etc., it is important to know how the storage and loss viscoelastic functions change with the fre quency of the perturbation. Information of this kind can be obtained by studying the responses of materials to dynamic perturbation fields (1-6). Moreover, by taking into account that an experiment carried out at a fre quency co is qualitatively equivalent to others performed in the time domain t = co-1, the combination of transient and dynamic experiments provides informations on the viscoelastic behavior of materials in a wide time scale covering several decades. The information thus obtained is important not only on practical grounds but also from a basic point of view. Actually, the knowledge of viscoelastic responses over a wide time scale is important to the study of the molecular motions responsible for the viscoelastic behavior of materials.
