A method has been developed for the identification of structural systems which exhibit influences of weak nonlinear stiffness and damping terms. It is based on a linear method for direct identification of incomplete system matrices from vibration test data. The basic identification equations are extended by additional stiffness and damping terms. Their contribution to the overall response is governed by higher powers of the individual response amplitudes. Hence, the method is a linearisation approach to the full nonlinear solution and basically derived from the well known ‘Harmonic Balance’ method which is applied to multi-degree of freedom systems.

The paper presents the basic theory of the method and illustrates its application to several test examples. First simulated test cases with nonlinear stiffness and damping terms are discussed. Then, as a practical application, the results of an automobile motor/gearbox assembly are given.

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