  The concept of nonlinear modes is useful for the dynamical characterization
of nonlinear mechanical systems. While efficient and broadly applicable methods
are now available for the computation of nonlinear modes, nonlinear modal
testing is still in its infancy. The purpose of this work is to overcome its
present limitation to conservative nonlinearities. Our approach relies on the
recently extended periodic motion concept, according to which nonlinear modes
of damped systems are defined as family of periodic motions induced by an
appropriate artificial excitation that compensates the natural dissipation. The
particularly simple experimental implementation with only a single-point,
single-frequency, phase resonant forcing is analyzed in detail. The method
permits the experimental extraction of natural frequencies, modal damping
ratios and deflection shapes (including harmonics), for each mode of interest,
as function of the vibration level. The accuracy, robustness and current
limitations of the method are first demonstrated numerically. The method is
then verified experimentally for a friction-damped system. Moreover, a
self-contained measure for estimating the quality of the extracted modal
properties is investigated. The primary advantages over alternative vibration
testing methods are noise robustness, broad applicability and short measurement
duration. The central limitation of the identified modal quantities is that
they only characterize the system in the regime near isolated resonances.
