The paper presents phase portraits of the autonomous Duffing single-degree-of-freedom system with Coulomb dry friction in\nits ? ? ? parameter space. The considered nonlinearities of the cubic stiffness (?) and Coulomb dry friction (?) are widely used\nthroughout the literature. It has been shown that there can be more than one sticking region in the phase plane. It has also been\nshown that an equilibrium point occurs at the critical combinations of values of the parameters ? and ? which gives rise to zero\neigenvalue of the linearised system. The unstable limit cycle may appear in the case of negative viscous damping (?); ? < 0.
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