  We report on the existence of stable, completely delocalized response regimes
in a nonlinear defective periodic structure. In this state of complete
delocalization, despite the presence of the defect, the system exhibits
in-phase oscillation of all units with the same amplitude. This elimination of
defect-borne localization may occur in both the free and forced responses of
the system. In the absence of external driving, the localized defect mode
becomes completely delocalized at a certain energy level. In the case of a
damped-driven system, complete delocalization may be realized if the driving
amplitude is beyond a certain threshold. We demonstrate this phenomenon
numerically in a linear periodic structure with one and two defective units
possessing a nonlinear restoring force. We derive closed-form analytical
expressions for the onset of complete delocalization and discuss the necessary
conditions for its occurrence.
