Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Thompson, Lonny L

Committee Member

Joseph , Paul F

Committee Member

Ju , Jaehyung

Abstract

Composite sandwich structures with a viscoelastic core material constrained between thin stiff face sheets are an effective means of damping in engineering applications. Damping introduces energy dissipation which helps control vibration amplitudes. Conventional Hexagonal honeycombs are often referred to as regular honeycombs and are defined by cellular geometry with effective positive Poisson's ratio. Regular honeycombs are commonly used for the cores of sandwich plates because of their low density and high stiffness properties. Honeycombs with negative in-plane Poisson's ratio are known as Auxetic honeycombs and offer enhancement of mechanical properties such as impact absorption, damage resistance, when compared to regular honeycombs.
In this study the modal vibration and damping capabilities of honeycomb sandwich plates with viscoelastic core are analyzed using a finite element model developed in ABAQUS. The viscoelastic material used for the base material of the honeycomb core is defined using a Prony series corresponding to the generalized Maxwell model. Damping loss factors are calculated from the ratio of energy dissipation over elastic strain energy for both a quasi-static analysis with a sinusoidal pressure load, and an implicit dynamic analysis with instantaneous pressure load. Additionally loss factors are calculated using a direct steady-state frequency response analysis, using half-power bandwidth method.
Comparisons are made between regular and two configurations of auxetic honeycomb. The first auxetic honeycomb (Auxetic-I) considered has the same extensional in-plane effective moduli as regular honeycomb. In the other auxetic honeycomb, (Auxetic-II), the mass is the same as that of regular honeycombs. In addition, comparisons are made between in-plane and out-of-plane loading.
Results showed that in the frequency domain, for both in-plane and out-of-plane loading honeycomb sandwich plates with both the Auxetic configurations show higher damping than the regular counterpart, and also shifts the natural frequencies to lower values. Results also show that for both regular and auxetic with in-plane loading display higher loss factors compared to out-of -plane loading. In the time domain, when a stiffer viscoelastic material is assigned to the core, Auxetic honeycomb showed higher loss factors compared to Regular. Whereas when softer viscoelastic moduli is defined, regular showed higher loss factors.

Share

COinS