La conception analytique des propriétés viscoélastiques optimales des materiaux pour les sandwichs et les composites = Analytical Formulation of Optimal Viscoelastic Designer Material Properties for Sandwich / Composites

Harry H. Hilton (1)

1 AE - Aerospace Engineering Department [Urbana]

Viscoelastic materials are known for their ability to dissipate energy. This property has been successfully used by the author and his colleagues to produce effective passive structural control for column and plate creep buckling, various vibratory modes, and aero-viscoelastic phenomena, such as torsional divergence, lifting surface and panel flutter, and attenuation of aerodynamic noise in panels. In self-excited systems the application of increased dissipation may stabilize or destabilize such systems depending on the influence of damping and all other forces on phase relations. Conventional design and analysis formulations call for use of the best available “off the shelf” materials. On the other hand, the optimum designer material protocols based on calculus of variation principles developed in [1] are formulated to determine the global best elastic or viscoelastic properties for specified service conditions. It has been previously established in [2] that in isotropic and anisotropic viscoelastic materials the shape of the relaxation curve is a major contributor to the material ;s response performance. In particular, it has been shown that Region C and the ratio E0 / E1 of the relaxation modulus, as seen in Fig.1, are the most influential in dictating material dissipation rates. Consequently, such relaxation modulus functions are tailored through prescriptions of appropriate functionally graded viscoelastic materials to produce the desired designer material performance. Relaxation moduli are, of course, highly temperature sensitive and performances must be evaluated relative to operational demands. In this paper, an analytical study presents optimal sandwich combinations of high shear modulus auxetic [3] webs with composite faceplates of proper number of stacking sequences and fibers as well as their orientations, and their viscoelastic material properties. The constraints that can be imposed consist of one or more selected from weight, dimensions, cost, deformations, failure probabilities, survival / life-times, etc. Some preliminary results are presented. The delamination failure analyses are based on uniaxial viscoelastic experimental data found in [4] and the theoretical stochastic failure criteria developed in [5]. For the same structural weight, the optimized designer viscoelastic sandwich composite plate clearly shows substantial longer survival times and orders of magnitude smaller probabilities of delamination. Extensions of these analyses to multi-element structures, i. e. entire structures, are also presented.

Mots clés: aero-servo-viscoelasticity; designer viscoelastic materials; functionally graded materials; failure probability; servo controls; structural control; survival times; torsional creep divergence; viscoelasticity

Domaines: Matériaux; Mécanique [physics.med-ph]

Harry H. Hilton. La conception analytique des propriétés viscoélastiques optimales des materiaux pour les sandwichs et les composites = Analytical Formulation of Optimal Viscoelastic Designer Material Properties for Sandwich / Composites. JNC 16, Jun 2009, Toulouse, France. 10 p. ⟨hal-00392800⟩