Impact Resistance of Marine Sandwich Structures Engenharia e Arquitectura Naval

119 Pages·2014·10.39 MB·English

Impact Resistance of Marine Sandwich Structures

Tiago da Silva Rodrigues Castilho

Dissertação para obtenção do Grau de Mestre em
Engenharia e Arquitectura Naval

Júri
Presidente: Doutor Carlos António Pancada Guedes Soares
Orientador: Doutor Leigh Stuart Sutherland
Vogal: Doutor Yordan Ivanov Garbatov

Junho de 2014

Acknowledgements
A great part of my gratitude goes to Dr. Leigh Sutherland, for the guidance, and shared knowledge and
interest during the development of the work. Would also like to thank for giving me the freedom to make
mistakes and learn with them.
To Dr. Carlos Guedes Soares, by the guidance through the whole course.
To Estaleiros Navais de Peniche, for the great support, providing all the materials and human resources
with immense know-how, both extremely important during the development and manufacturing of the
sandwich panels.
To Amorim Cork Composites, for gently providing the Corecork panels and sharing the interest and
knowledge to solve unexpected problems related with the use of cork on the panels.
To DeCivil laboratory staff, for the support solving all kind of problems during the preparation and test
stages, especially, cutting the specimens.
To my friends and colleagues, for the criticism, but also for the support and friendship.
Last but not least, a special thanks to my family, especially my parents, José and Belmira, for all the
support and sacrifices.

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Resumo
Este trabalho é motivado pela crescente utilização de estruturas em materiais compósitos sandwich.
É apresentada uma revisão de literatura, com foco no impacto em estruturas marinhas. A segunda parte
do trabalho consiste na produção e ensaio à flexão, indentação e impacto de uma série de compósitos
marinhos com estrutura em sandwich.
Quatro tipos de núcleo são utilizados (PVC, Balsa, Corecork NL10 e NL20) para produzir painéis em
sandwich, com faces de polyester reforçadas com fibra de vidro.
Os testes de impacto são realizados até que se obtenha a rotura da segunda camada do provete, por
perfuração ou separação da camada do núcleo. Os provetes de PVC e NL20 mostram resultados
repetíveis, enquanto os provetes de NL10 falham de maneiras diferentes, sem que haja uma relação
com a espessura da primeira camada ou com a velocidade do impacto. Os provetes de NL10
apresentam uma má cura, que leva a uma baixa rigidez mas a uma grande capacidade de plastificação
e absorção de energia.
Apesar de as forças máximas relacionadas com a rotura das primeira e segunda camada de fibra de
vidro serem 1.5 vezes superiores nos testes de impacto, o comportamento global dos provetes de PVC
e NL20 é bem aproximado pelos testes de indentação. Por outro lado, o comportamento dos provetes
de NL10 varia significativamente, aumentando 3 vezes a energia absorvida.
Este trabalho indica que as estruturas compósitas sandwich com cortiça têm potencial em aplicações
com solicitações de impacto, com a desvantagem de apresentarem menor rigidez e maior peso.

Palavras chave: Resistência ao impacto; Compósitos marinhos; Compósitos sandwich; Cortiça; Testes
de indentação; Testes de impacto

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Abstract
This work is motivated by the ever increasing range of applications of sandwich composite materials in
the marine industry. A brief literature review is presented, focused in areas with special interest for
marine impact. The second part of the work consists in the manufacture and flexure, quasi-static and
impact tests of a series of marine sandwich composites.
Four different core materials (PVC, Balsa Corecork NL10 and NL20) are used to produce a sandwich
laminate, with E-glass/polyester skins.
Drop-weight tests are performed until the failure of the second skin, either by penetration or separation
from the core. PVC and NL20 specimens show predictability and repeatability of results, while NL10
present different failure modes, without any relation with skin thickness or incident velocity. NL10
specimens present bad cure of the skin, which leads to low stiffness but high plasticization and energy
absorption capabilities.
Apart from the peak forces related with the failure of both skins, that are around 1.5 times higher in the
impact tests, the overall behaviour of the PVC, Balsa and NL20 specimens is well predicted by quasi-
static tests. On the other hand, NL10 specimens’ behaviour change dramatically from static do impact
test, increasing 3 times the absorbed energy.
This work indicates that cork sandwich composites have potential in applications with impact
requirements, with the downside of lower stiffness and higher weight.

Keywords: Impact resistance; Marine composite; Sandwich; Cork; Quasi-static test; Drop-weight test

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Contents
Acknowledgements ............................................................................................................................... iii
Resumo .................................................................................................................................................. v
Abstract ................................................................................................................................................ vii
Contents ................................................................................................................................................ ix
List of Tables ......................................................................................................................................... xi
List of Figures ...................................................................................................................................... xiii
List of abbreviations ............................................................................................................................ xix
1. Introduction ..................................................................................................................................... 1
1.1. Motivation ................................................................................................................................... 1
1.2. Aim and structure of the dissertation .......................................................................................... 1
2. State of the art ................................................................................................................................. 3
2.1. General impact ........................................................................................................................... 3
2.2. Marine impact ............................................................................................................................. 8
2.2.1. Impact modeling ..................................................................................................................... 8
2.2.2. Material selection and structural solutions ............................................................................ 12
2.2.3. Impact behaviour comparisons of Classification Society Rules ............................................ 14
2.2.4. Residual strength .................................................................................................................. 14
2.2.5. Water absorption .................................................................................................................. 16
2.3. Conclusions .............................................................................................................................. 17
3. Experimental procedures .............................................................................................................. 19
3.1. Typical marine sandwich........................................................................................................... 19
3.2. Relevant impact scenario ......................................................................................................... 20
3.3. Selection of the experimental tests ........................................................................................... 20
3.3.1. Bending test .......................................................................................................................... 20
3.3.2. Static indentation test ........................................................................................................... 20
3.3.3. Impact test ............................................................................................................................ 21
3.4. Specimen preparation............................................................................................................... 21
3.4.1. Material selection and sandwich design ............................................................................... 21
3.4.2. Panel manufacturing ............................................................................................................. 22
3.4.3. Specimen cutting and preparation ........................................................................................ 25
3.5. Specimen tests ......................................................................................................................... 29
3.5.1. Bending tests ........................................................................................................................ 29
3.5.2. Quasi-static indentation tests ................................................................................................ 34
3.5.3. Impact tests .......................................................................................................................... 37
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4. Result analysis .............................................................................................................................. 43
4.1. Bending tests ............................................................................................................................ 43
4.2. Quasi-static indentation ............................................................................................................ 48
4.3. Impact tests .............................................................................................................................. 54
4.3.1. Evolution of failure with increasing energy ............................................................................ 54
4.3.2. Quasi-static testing vs Impact testing ................................................................................... 59
5. Conclusions ................................................................................................................................... 65
5.1. Future work ............................................................................................................................... 66
6. References .................................................................................................................................... 67
Appendices ........................................................................................................................................... 70
A. List of marine impact references by place and research area .................................................. 70
B. Specimen dimensions............................................................................................................... 72
C. Impact test data: Load vs displacement and Absorbed energy vs Displacement ..................... 76
D. Post-test specimen photographs .............................................................................................. 85
D.1 Quasi-static tests .............................................................................................................. 85
D.2 Impact tests ...................................................................................................................... 87

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