Keywords: structural damping, finite element method, damping characterization, parameter identification, mixed numerical-experimental procedures, composite laminates, material properties, modal analysis.

Due to their inherent advantages over traditional materials like metals, composite materials are over the last decade increasingly used in the design of many engineering components such as aerospace elements, automotive parts, marine structures and sports goods like badminton rackets or snowboards. For the designer, a precise prediction of the damping characteristics in a single structural component is of prime importance in noise and vibration control or in impact resistance and fatigue analysis of composite structures, since these physical properties play a crucial role in the amplitude of the free or forced vibration response of the structure. This issue is particularly challenging in single- or multi-layered fibre-reinforced polymer composites because the damping properties can be tailored in a wide range by modifying the constituent materials, lamina thickness, ply orientation, stacking sequence or fibre fraction.

Modal mixed numerical-experimental identification techniques constitute powerful tools for estimating the elastic properties of composite materials. Based on the minimization of the discrepancies between the natural frequencies and mode shapes of structures modelled using a finite element formulation with adjustable constitutive properties and the corresponding experimental modal quantities, these characterization methods seem to be promising candidates for the identification of the damping properties in composite materials. This paper describes an original mixed numerical-experimental identification method for estimating the storage and loss factors of structurally damped thick laminated shells. The technique is founded on the minimization of the discrepancies between the complex mode shapes, natural frequencies and modal damping factors computed with a finite element formulation with adjustable elastic and structural damping properties (complex stiffness modulus approach) and the equivalent measured data. On the computational level, a highly accurate composite shell finite element model derived from a higher-order shear deformation theory and taking structural damping effects into account has been formulated. On the experimental level, a precise measurement setup formed by a scanning laser vibrometer and an acoustic- or shaker-based excitation has been developed.

The proposed procedure has first been applied to an isotropic PMMA plate in order to check the validity of the damping mechanism adopted. Although viscoelastic materials exhibit in general frequency-dependent properties whereas structural damping induces little frequency dependence of the material constants, identification results have shown excellent agreement of the storage and loss factors with values measured independently with a dynamic mechanical analyzer. In a second example devoted to a unidirectional carbon-epoxy plate, the method has been able to characterize precisely the storage parameters and the main loss factors of the specimen. However, investigations have highlighted that the minimization function on the modal damping properties is not sufficiently sensitive to some dissipative parameters and that further improvements of the identification method are required.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £145 +P&P)