Experimental Identification of GHM and ADF Parameters for Viscoelastic Damping Modeling

Abstract

Viscoelastic materials can be used as an effective means of controlling the dynamics of structures, reducing and controlling the structural vibrations and noise radiation. They can be used as surface mounted or embedded damping treatments, utilizing passive viscoelastic materials alone, the so-called passive treatments, or in an unified way with active materials such as piezoelectrics, the so-called hybrid treatments. The use of these materials in damping treatments provides high damping capability over wide temperature and frequency ranges. The extensive use of passive or hybrid treatments using viscoelastic materials has motivated the development of damping models to be used and integrated into commercial or home-made finite element (FE) codes. The implementation of the Golla-Hughes- McTavish (GHM) and anelastic displacement fields (ADF) models in a general FE model with viscoelastic damping is presented and discussed in this paper. Additionally, a direct frequency analysis (DFA) is also described and employed.A methodology to identify the complex shear modulus of viscoelastic materials is described. Thus, the identified complex shear modulus of the viscoelastic material 3M ISD112 is curve-fitted in order to obtain the modeling parameters of the GHM and ADF models. A sandwich plate with a viscoelastic core and elastic skins is analyzed. Measured and FE-based predicted FRFs based on a DFA, GHM and ADF models, were compared in order to assess the damping models and validate the experimental procedure for the material properties identification and the curve fitting process.It was found that the application of a discrete dynamic system, describing a SDoF analytical model, provides a reliable identification methodology, since it is based on the direct (in opposition to indirect measuring approaches based on vibrating beams) characterization of the complex stiffness of a viscoelastic material sample in shear deformation, providing results similar to those published by the material manufacturer. Regarding the internal variables models under analysis here, which were implemented at the FE model level, the ADF model leads to an augmented model of the damped structural system with a lower size than the GHM model. To the opinion of the authors, the ADF model represents the best alternative to accurately model the damping behavior since it yields good trade-off between accuracy and complexity. One major disadvantage in using internal variables models such as the GHM or ADF is the creation of additional dissipation (or anelastic) variables increasing the size of the coupled damped FE model. However, an alternative based on the DFA using the FE spatial model and re-calculating the complex viscoelastic stiffness matrix for each discrete frequency value might be used with the outcome of being simpler to implement and the drawback of being time-consuming and not providing directly the modal parameters of the damped structural system. All the models showed similar accuracy and yielded representative results of viscoelastically damped structural systems.