Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

THOMPSON, LONNY L

Committee Member

LI , GANG

Committee Member

FADEL , GEORGES M

Abstract

Composite sandwich structures have replaced homogenous dense solids in many applications due to their advantages of high stiffness to weight ratio, and higher damping characteristics. Higher damping in engineering applications is desirable to reduce structural vibrations. The application of a viscoelastic layer between two thin face sheets gives rise to the concept of constrained layer damping which is an effective technique to achieve increased damping in engineering applications.
Honeycomb cellular structures are often used for the core in sandwich construction because of their low density and high stiffness properties. Regular honeycombs are defined by conventional hexagonal geometry, which gives rise to effective transversely isotropic properties. Auxetic honeycombs have cellular geometry defined such that their effective Poisson's ratio is negative, and have potential for increased shear modulus and nonconventional design compared to their regular counterparts.
In this study, the damping nature of auxetic and regular honeycombs cores within a sandwich plate structure with equal mass density is studied using finite element analysis. A new concept of constrained layer damping is introduced within the honeycomb cell walls, making the honeycomb core, itself, a composite structure. By introducing the composite honeycomb core between two thin face sheets in the macro sandwich structure, further increases in damping can be achieved. The thickness of the constraining layers is defined such that the effective stiffness is increased for the same mass of a sandwich plate with homogeneous honeycomb core. Comparisons are made for both quasi-static cyclic loading and dynamic analysis subjected to impact loads.
The amplitude of loading is defined at a level such that the yield stress within the base materials is not exceeded. Dissipation energy at the end of the loading step in the finite element analysis is used to quantify the structural loss factor.
Results show higher damping is achieved with the novel concept of constrained layer viscoelastic damping in honeycomb cell walls. In the case of out-of-plane loading direction, sandwich plates with composite auxetic honeycomb core gives higher damping over homogeneous honeycomb core sandwich plates and its regular honeycomb counter parts. However, when loaded in the in-plane direction, a condition was found where sandwich plates with homogenous auxetic honeycomb core gave higher damping than with a composite core and its regular counter parts, suggesting that further development is needed to optimize the relative thicknesses of the constraining layer in the honeycomb cell walls.

Share

COinS