https://popups.uliege.be/2684-6500/index.php?id=349 Issues fr Wed, 19 Aug 2026 14:38:23 +0200 Wed, 19 Aug 2026 14:39:16 +0200 https://popups.uliege.be/2684-6500/index.php?id=349 0 https://popups.uliege.be/2684-6500/index.php?id=350 Previous studies have shown that one can create an efficient model for bolted structures by spidering the interface to a pair of nodes, and then connecting them with a nonlinear Iwan element. However, no method has been developed for predicting the parameters of the Iwan element from first principles; in all studies to date, experimental vibration measurements have been acquired and optimization has been used to solve for the Iwan parameters that best reproduce the measurements. This work investigates an alternative strategy that uses a local finite element model in which the bolt and surrounding area are modeled in detail with contact, Coulomb friction and the applied preload. A series of static loads are then applied to this local model and the resulting nonlinear force-displacement behavior is extracted and used to identify either a linear spring or an Iwan element that captures the predicted behavior. The identified springs and Iwan elements are then inserted into a reduced-order model of the structure, and the effective, amplitude-dependent natural frequency and damping of several modes of the structure can be computed, or dynamic transient analysis performed. This work evaluates the proposed modeling strategy using two-dimensional models of cantilever beams containing one and three bolts. In each case, the frequency and damping behavior of the reduced order models, whose Iwan elements were identified using the proposed procedure, are compared those of a truth model. The results show that, while each bolt in a structure can be loaded quite differently, the proposed procedure provides a reasonable approximation to the damping behavior of a joint, predicting the average nonlinear damping in the system within a factor of 1.5-3. Wed, 19 Aug 2026 14:46:39 +0200 https://popups.uliege.be/2684-6500/index.php?id=350 https://popups.uliege.be/2684-6500/index.php?id=367 Decoupling methods based on measured Frequency Response Functions (FRFs) are well established for linear systems, yet their extension to nonlinear systems remains in its infancy. Existing frequency-based decoupling techniques for nonlinear systems are limited to localized nonlinearities and specific configurations that require prior knowledge of the nonlinearity location; a general decoupling method for nonlinear systems does not yet exist. This paper introduces a general nonlinear decoupling framework. The proposed Nonlinear Frequency-Based Decoupling (NL-FBD) framework uses quasi-linear FRFs of the coupled system via response-controlled testing (RCT), and measured or calculated FRFs of the known substructure; and then applies a linear decoupling formulation, to calculate the quasi-linear FRFs of the unknown nonlinear structure at several response levels. Subsequent linear modal identification yields response-dependent nonlinear modal parameters, which are then used to synthesize constant-force FRFs of the unknown nonlinear substructure. The proposed approach is capable of; i) handling multiple nonlinear elements located arbitrarily within the structure, ii) addressing systems even with distributed nonlinearities, iii) accommodating nonlinearities in both substructures, and iv) achieving decoupling at multiple degrees of freedom. The applicability limits of the proposed approach are examined in detail, together with an assessment of its accuracy through numerical case studies. In particular, nonlinearities in both substructures are demonstrated for the single degree-of-freedom connection case, whereas multiple-degree-of-freedom connections are investigated for systems with a known linear substructure. Experimental validation on a nonlinear beam--linear beam assembly confirms that NL-FBD accurately decouples the unknown nonlinear beam, yields a reliable nonlinear modal model, and predicts the forced response of a new assembly incorporating the decoupled nonlinear beam, with excellent agreement to measurements even at high forcing levels. Tue, 06 Oct 2026 14:26:21 +0200 https://popups.uliege.be/2684-6500/index.php?id=367