Document Type

Thesis - Open Access

Award Date

2016

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Todd Letcher

Keywords

additive manufacturing, cellular metamaterials, finite element analysis, hierarchical honeycomb

Abstract

Cellular metamaterials are of immense interest for many current engineering applications. Tailoring the structural organization of cellular structures leads to new metamaterials with superior properties providing lightweight and very strong/stiff structures. The incorporation of hierarchy to regular cellular structures enhances the properties and introduces novel tailorable metamaterials. For many complex cellular metamaterials, the only realistic manufacturing process is additive manufacturing (AM). The use of AM to manufacture large structures may lead to several types of defects during the manufacturing process, such as imperfect cell walls, irregular thickness, flawed joints, partially missing layers, and irregular elastic plastic behavior due to toolpath. It is important to understand the effect of defects on the overall performance of the structures to determine if the manufacturing defect(s) are significant enough to abort and restart the manufacturing process or whether the material can still be used in its defective state. Honeycomb structures are often used for the high strength to weight ratio applications. These metamaterials have been studied and several models have been developed based on idealized cell structures to explain their elastic plastic behavior. However, these models do not capture real-world manufacturing defects resulting from AM. The variation of elastic plastic behavior of regular honeycomb structures with defects has been studied, but the performance of hierarchical honeycomb structures with defects is still unknown. In this study, cell wall defects are modeled as the worst case scenario, which is entirely missing cell walls. The effects of missing cell walls are investigated to understand the elastic behavior of hierarchical honeycomb structures using finite element analysis. Hierarchical honeycombs demonstrated more sensitivity to missing cell walls than regular honeycombs. On average, the axial elastic modulus decreased by 45% with 5.5% missing cell walls for regular honeycombs, 60% with 4% missing cell walls for first order hierarchical honeycomb and 95% with 4% missing cell walls for second order hierarchical honeycomb. The transverse elastic modulus decreased by about 45% with more than 5.5% missing cell walls for regular honeycomb, about 75% with 4% missing cell walls for first order and more than 95% with 4% missing cell walls for second order hierarchical honeycomb.

Library of Congress Subject Headings

Metamaterials.
Honeycomb structures.
Three-dimensional printing.
Manufactures -- Defects.
Finite element method.

Description

Includes bibliographical references (page 59-62)

Format

application/pdf

Number of Pages

102

Publisher

South Dakota State University

Rights

Copyright © Kazi Moshiur Rahman

Included in

Manufacturing Commons

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