| Sumario: | The dependence of mechanical properties on the excitation amplitude shows the presence of nonlinear effects. Several experimental devices, however, are not sensitive enough to detect the amplitude dependence, or measure the mechanical response on assuming ab initio a linear viscoelastic behavior. This paper gives an alternative procedure to determine the existence of nonlinear processes, based on the frequency or time dependence of the dynamic or quasistatic moduli and compliances. The methodology is applied to stress relaxation curves of (Formula presented) and poly(vinylchloride). Furthermore, some experimental problems involved in the study of nonlinear mechanical behavior of materials are discussed. © 1998 The American Physical Society.
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