Energy absorption characteristics of sandwich structures subjected to low-velocity impact

This dissertation presents experimental, numerical and analytical investigations of sandwich plates subjected to quasi-static loading and low-velocity impact. The objectives of this research are to predict the low-velocity impact response and damage in a sandwich structure, and to characterise the e...

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Main Author: Foo, Choon Chiang
Other Authors: Chai Gin Boay
Format: Theses and Dissertations
Language:English
Published: 2009
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Online Access:https://hdl.handle.net/10356/15558
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-155582023-03-11T17:37:49Z Energy absorption characteristics of sandwich structures subjected to low-velocity impact Foo, Choon Chiang Chai Gin Boay Seah Leong Keey School of Mechanical and Aerospace Engineering Centre for Advanced Numerical Engineering Simulations DRNTU::Engineering::Materials::Composite materials This dissertation presents experimental, numerical and analytical investigations of sandwich plates subjected to quasi-static loading and low-velocity impact. The objectives of this research are to predict the low-velocity impact response and damage in a sandwich structure, and to characterise the energy absorbed by the structure. Aluminium sandwich plates and composite sandwich plates made of Nomex honeycombs and carbon/epoxy skins were investigated under both static indentation and low-velocity impact loadings using a hemispherical indentor/impactor. Emphasis was placed on the damage characteristics and the energy absorption capabilities of these structures. Based on the least-squares method, a single equation that links absorbed energy with the impact energy and the damage initiation threshold energy was derived for composite sandwich plates. It was found that the proportion of impact energy absorbed by the composite plate was inversely related to the damage initiation energy, but directly related to the relative loss of the plate’s transverse stiffness after damage. This energy equation is useful for further studies on damage resistance and tolerance. A three-dimensional FE model was also developed to simulate the indentation and impact tests. In contrast to the equivalent continuum core normally used by other investigators, the cellular honeycomb core was discretely modelled with shell elements so that it was geometrically more accurate. A progressive damage model was also included to predict damage initiation and progression in the laminated skins. Comparison of numerical results with test results demonstrated the ability of the model to capture the impact characteristics. Core damage was identified to be one of the damage mechanisms at initial damage. Parametric studies also showed that denser cores resulted in greater peak loads and smaller damage profiles in the impacted structure. However, the energy absorbed during impact was independent of the core density. Finally, an analytical model was proposed to predict the impact response of a sandwich structure beyond the onset of damage. Closed-form solutions were derived for three parameters that described the plate’s structural behaviour, namely, the plate’s elastic structural stiffness, the critical load at the onset of damage, and the reduced stiffness after damage. The critical load was found to be theoretically predictable by accounting for the elastic energies absorbed by the sandwich plate up to core failure. These parameters were then included in a modified energy-balance model coupled with the law of conservation of momentum to predict transient load and deflection histories for the plate subjected to impact. This impact model is an efficient design tool which can complement detailed FE simulations. DOCTOR OF PHILOSOPHY (MAE) 2009-05-13T03:54:55Z 2009-05-13T03:54:55Z 2009 2009 Thesis Foo, C. C. (2009). Energy absorption characteristics of sandwich structures subjected to low-velocity impact. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/15558 10.32657/10356/15558 en 214 p. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic DRNTU::Engineering::Materials::Composite materials
spellingShingle DRNTU::Engineering::Materials::Composite materials
Foo, Choon Chiang
Energy absorption characteristics of sandwich structures subjected to low-velocity impact
description This dissertation presents experimental, numerical and analytical investigations of sandwich plates subjected to quasi-static loading and low-velocity impact. The objectives of this research are to predict the low-velocity impact response and damage in a sandwich structure, and to characterise the energy absorbed by the structure. Aluminium sandwich plates and composite sandwich plates made of Nomex honeycombs and carbon/epoxy skins were investigated under both static indentation and low-velocity impact loadings using a hemispherical indentor/impactor. Emphasis was placed on the damage characteristics and the energy absorption capabilities of these structures. Based on the least-squares method, a single equation that links absorbed energy with the impact energy and the damage initiation threshold energy was derived for composite sandwich plates. It was found that the proportion of impact energy absorbed by the composite plate was inversely related to the damage initiation energy, but directly related to the relative loss of the plate’s transverse stiffness after damage. This energy equation is useful for further studies on damage resistance and tolerance. A three-dimensional FE model was also developed to simulate the indentation and impact tests. In contrast to the equivalent continuum core normally used by other investigators, the cellular honeycomb core was discretely modelled with shell elements so that it was geometrically more accurate. A progressive damage model was also included to predict damage initiation and progression in the laminated skins. Comparison of numerical results with test results demonstrated the ability of the model to capture the impact characteristics. Core damage was identified to be one of the damage mechanisms at initial damage. Parametric studies also showed that denser cores resulted in greater peak loads and smaller damage profiles in the impacted structure. However, the energy absorbed during impact was independent of the core density. Finally, an analytical model was proposed to predict the impact response of a sandwich structure beyond the onset of damage. Closed-form solutions were derived for three parameters that described the plate’s structural behaviour, namely, the plate’s elastic structural stiffness, the critical load at the onset of damage, and the reduced stiffness after damage. The critical load was found to be theoretically predictable by accounting for the elastic energies absorbed by the sandwich plate up to core failure. These parameters were then included in a modified energy-balance model coupled with the law of conservation of momentum to predict transient load and deflection histories for the plate subjected to impact. This impact model is an efficient design tool which can complement detailed FE simulations.
author2 Chai Gin Boay
author_facet Chai Gin Boay
Foo, Choon Chiang
format Theses and Dissertations
author Foo, Choon Chiang
author_sort Foo, Choon Chiang
title Energy absorption characteristics of sandwich structures subjected to low-velocity impact
title_short Energy absorption characteristics of sandwich structures subjected to low-velocity impact
title_full Energy absorption characteristics of sandwich structures subjected to low-velocity impact
title_fullStr Energy absorption characteristics of sandwich structures subjected to low-velocity impact
title_full_unstemmed Energy absorption characteristics of sandwich structures subjected to low-velocity impact
title_sort energy absorption characteristics of sandwich structures subjected to low-velocity impact
publishDate 2009
url https://hdl.handle.net/10356/15558
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