Advisor(s)

Ashkan A. Vaziri

Date of Award

2011

Date Accepted

8-2011

Degree Grantor

Northeastern University

Degree Level

M.S.

Degree Name

Master of Science

Department or Academic Unit

College of Engineering, Department of Mechanical and Industrial Engineering

Keywords

mechanical engineering, mechanics, cellular structures, finite element analysis, honeycomb, impact, in-plane, two-dimensional

Disciplines

Mechanical Engineering

Abstract

This thesis presents a study of the in-plane cylindrical impact of a two-dimensional cellular structure with regular hexagonal honeycomb microstructures with various kinetic energies, radii, and relative densities. Many studies have been conducted on the in-plane full length crush of cellular structures with regular hexagonal honeycomb microstructures but the localized curvature at the impact site has not previously been considered. The effect of impacting body curvature on the in-plane response of a cellular structure was investigated using the finite element method.

A finite element model composed of a rigid cylindrical impacting body, a cellular structure, and a flat rigid body base support was developed. Throughout the simulations conducted the kinetic energy and radius of the impacting body were varied along with the relative density of the cellular structure. The effect of momentum or impulse, friction, and linear strain hardening on the system response were also investigated.

The response of the system was quantified using three critical parameters: critical strain, effective energy absorption, and the effective damaged region. The critical strain is a measure of the maximum crush of the honeycomb structure. The effective energy absorption is a measure of the energy absorbed by the cellular structure through the permanent plastic deformation of the the cells. The effective damaged region is a measure of how much the cellular structure is compromised.

From the results obtained a strong correlation was shown to exist between the maximum indentation depth of the rigid impacting body and the kinetic energy for all curvatures and densities conducted in this study. The energy dissipated in a plastic fashion showed a strong linear correlation with kinetic energy regardless of the system parameters. The damaged region was also shown to have a strong correlation with kinetic energy regardless of overall system parameters.

However, slight variations were observed between varying densities and radii runs at constant kinetic energy levels. Results show that when the curvature of the impaction body is decreased there is a decrease in the maximum indentation, energy dissipated, and the region damaged within the cellular solid. For the simulations conducted variations in the honeycomb's relative density were shown to have very little effect on the results. The effect was a slight decrease in the maximum indentation, energy dissipation. and the damaged region as the relative density was increased.

Results indicated for a quasi-static impact that the volume of permanent plastic deformation, maximum indentation depth, and damaged region can be used to estimated the relative curvature and speed of an impacting body in cases of damaged cellular structures. The damaged region is useful for assessing the portion of the honeycomb structure that is compromised to facilitate the replacement of that portion of the structure. The permanent plastic deformation and the maximum indentation depth used together can be used in tandem to identify specific curvatures with known honeycomb densities.

The response impact of the structure was also shown to be dependent on the impulse of the impacting body. Two distinct regions are shown when simulations were run using varying impulse values. At lower impulses the dynamic effects are dominate and the system response as measured by the maximum indentation depth, permanent plastic deformation, and damaged region is shown to dramatically decrease with decreased impulses. At higher impulse values where quasi-static effects dominate the system response is shown to remain constant.

Document Type

Master's Thesis

Rights Information

copyright 2011

Rights Holder

Jonathan M. Erickson Hammel


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