Duarte, Fernando B.Machado, J. A. Tenreiro2014-06-252014-06-2520090924-090X1573-269Xhttp://hdl.handle.net/10400.22/4578This paper studies the describing function (DF) of systems constituted by a mass subjected to nonlinear friction. The friction force is decomposed into two components, namely, the viscous and the Coulomb friction. The system dynamics is analyzed in the DF perspective revealing a fractional-order behavior. The reliability of the DF method is evaluated through the signal harmonic contents.engDescribing functionFrictionControlModelingjournal article10.1007/s11071-008-9405-8