VALIDITY DOMAIN OF AN ENERGETIC METHOD FOR THE ESTIMATION OF MODAL DAMPING IN THE CASE OF NON LINEAR LOCALIZED DISSIPATION

Abstract eng:
Modal damping estimation errors can be introduced when using assumptions such as proportional damping or a diagonal generalized matrix of localized dissipation at interfaces [1]. Previous work has studied the estimation of modal damping in bolted joints using many methods [2, 3]. One such method, used in this work, is the iterative energetic method (EM), developed in [4]. The present study investigates the EM for calculating the modal damping associated with localized nonlinear dissipative interfaces of a global linear structure. This method has limitations in two cases: localized linear damping [5] and localized nonlinear damping. The validity domain of the EM in the linear case was studied previously in [5]. The main conclusions were that EM is not valid in the following conditions : when eigenfrequencies are closely spaced, when localized dissipation exceeds a specific damping level, and if the response is not projected on a single mode of vibration. To the best of our knowledge, the nonlinear limitations of the EM are still unknown and have yet to be identified in the literature. The main goal of this paper is to investigate the iterative EM and define its validity domain for harmonic excitations as a function of the level of external structural loads and the level of nonlinear damping. We propose to investigate these parameters and their influence for the prediction of equivalent modal damping in a simple beam structure with a bolted nonlinear interface. Through use of an academic example with exact solutions, we will be able to quantify the error of our predictions, and thus provide accurate validity domains for the method.

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