Date of Award

12-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Thompson, Lonny

Committee Member

Li , Gang

Committee Member

Daqaq , Mohammed

Abstract

Composite sandwich structures constructed with honeycomb core can be an effective means of absorbing impact in many engineer applications. Conventional hexagonal honeycomb exhibit an effective positive Poisson's ratio, are commonly employed due to their lightweight and high axial stiffness properties. In contrast, auxetic honeycombs offer high in-plane shear stiffness, and exhibit negative Poisson's ratios with lateral extension, instead of contraction, when stretched axially.
In this study, the dynamic response of an aluminum composite panel with a honeycomb core constrained within two thin face sheets is investigated undergoing impact with a rigid ball. The finite element models used to simulate impact of the rigid ball with the honeycomb composite panel are solved using a nonlinear explicit dynamic analysis procedure including large deformation in ABAQUS, a commercial software package. This approach enables the cost-effective analysis, accurate estimation of the impact, and further understanding of the parameters that influence the complex response.
The rebound velocity and kinetic energy time history of the rigid ball, together with the kinetic and strain energies, and displacement and velocity for the elastic structure during impact and after separation of the impacting bodies are presented to show the effect of different velocity magnitudes of the impacting ball and comparisons with regular and auxetic honeycomb cell geometries. Additionally, the effects of various impacting velocities and honeycomb geometries are compared for impact in two perpendicular in-plane directions, and from out-of-plane impact.
Using the results of the incoming and rebound velocity of the ball, as well as the velocity of the point of contact on the structure at separation, and effective coefficient of restitution (COR) for the honeycomb sandwich structure is calculated and compared. Other measures include the ratio of incoming to outgoing fall velocities and ratio of incoming to outgoing kinetic energies.
Results show that the increase of the impacting velocity increases both the kinetic energy and strain energy absorbed in the structure. Results also showed that for both in-plane and out-of-plane impacts, the regular honeycomb structure absorbed more energy compared to the auxetic structure. In addition, according to the results of the COR, impact with the auxetic model shows higher elastic rebound than the regular model.

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