Bioinspired Design Owoseni T. A Materials Science and Engineering Stream African University of Science and Technology, Abuja, Nigeria. M. Sc. Thesis Presentation.

Bioinspired Design

Owoseni T. A

Materials Science and Engineering Stream African University of Science and Technology, Abuja, Nigeria.

M. Sc. Thesis Presentation

Advisor: Prof. Soboyejo W. O

April 2012

Sponsor: AUST/ADB & NMI

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Outline

Background and Introduction

Literature Survey

Characterization of the Multi-Scale Structure of Kinixys

erosa Shell

Analytical and Computational Model of Shell Structure

Concluding Remarks and Suggested Future Work

Acknowledgements

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• Bioinspired design involves the use of concepts observed

in natural biological materials in engineering design. The

hope is that the leveraging of biological materials in the

engineering domain can lead to many technological

innovations and novel products

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Background and Motivation

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Background and Motivation Cont’d

• Unlike the design of conventional engineering materials

that often involve the use of multiple materials chemistries

in the design of engineering components and systems,

natural biological materials are made from relatively few

chemical constituents. For example, bone, cartilage, skin,

and the cornea in the eye is built from type I collagen.

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• Usually hard biological materials exist as composite. These

high-performance natural composites are made up of

relatively weak components (brittle minerals and soft

proteins) arranged in intricate ways to achieve specific

combinations of stiffness, strength and toughness.

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• Determining which features control the performance of

these materials is the first step in Biomimetics. These ‘key

features’ can then be implemented into artificial bio-

inspired synthetic materials, using innovative techniques

such as layer-by-layer assembly or icetemplated

crystallization.

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• The microstructure and mechanical property of different

species of turtle have been studied, but there have not been

detailed studies of the effects of shell structure on their

mechanical properties.

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Unresolved Issues

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Unresolved Issues cont’d

• Shell theory has been sparsely applied in the bioinspired

design of materials and structures. These will be explored

in this study using a combination of experiments and

analytical/computational models.

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Objectives of Research

• The objective of this thesis is to develop a fundamental

understanding of the deformation and stress responses of a

Kinixys erosa tortoise shell structure as a potential source

of inspiration for the design of a failure resistant

shell/layered structure.

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Scope of the Work

• This work presents a combination of experimental,

theoretical and computational studies of the structure and

mechanical properties of kinixys erosa tortoise shell

structures as potential sources of bioinspiration for the

design of shell structures that are resistant to bending.

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Literature Survey

• Meyers et al (2008) studied several biological materials

(e.g. nacre, ligaments, hoof, blood vessels, beak interior,

chameleon, etc.) using diverse approaches, like SEM,

TEM, AFM, Nano-Indentation, and Molecular Simulations

and Modelling, among others, identifying their unique

features.

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Literature Survey cont’d

• Rhee et al (2009) studied the mutilscale structure of

Terrapene carolina carapace (Tc) using a combination

microscopic technique, EDX, and mechanical

characterization.

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Figure 1: Mutilscale hierarchy and structure of Terrapene carolina carapace

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Figure 2: Elemental Composition of Terrapene carolina carapace

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Figure 3: Indentation test results obtained from (a) nano-indentation and (b) Vickers hardness tests on the side surface of the turtle shell carapace.

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Figure 4: Stress/strain curves from the quasi-static compression test results on the turtle shell carapace coupon specimens under various strain rates and specimen geometries.

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Figure 5: Comparison of three-point bending test results obtained from actual data and ABAQUS finite element simulations; (a) without considering foam material effect, and (b) considering foam material effect.

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• Chenzhao et al (2012) carried out mechanical and

structural characterization of both the shell and shell

material of Trachemys scripta (Ts).

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Figure 6: Microstructure of the turtle shell of Trachemys scripta.

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Figure 7: Load-displacement curve of Compression failure tests of Ts shell.

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Table 1: The tensile modulus and strength of Ts shell materials.

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Table 2: The elastic modulus and ultimate strength of Ts strenghen rib.

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• Balani et al (2011) worked on freshwater snapping turtle,

Chelydra serpentine (Cs). The microstructural-,

compositional, nanomechanical characterization of Cs was

carried out making samples from Cs carapace.

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Figure 8: Cross-sectional of Cs carapace eliciting (a) a composite sandwich structure, (b) top three layers showing the top two waxy and the rigid 3rd layer, (c) carbonaceous lamellae 4th and 5th layers, and (d) inner structure eliciting 50%–60% porous matrix (fractured and ∼polished cross-section without epoxy infiltration).

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Fig. 9: (a) X-ray diffraction pattern eliciting diffused hydroxyapatite (HA) peak and (b) Raman spectrum showing presence of amorphous top surface and calcium-phosphate in the bottom surface of the turtle’s carapace.

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Figure 10: Cross-sectional SEM image of (a) Turtle’s carapace, and elemental mapping of (b) carbon, (c) phosphorous, and (d) calcium eliciting the presence of carbon fibers in the calcium phosphate matrix.

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Figure 11: Load indentation-depth profile of the various layers, with the main image showing the structural rigid dense 3rd layer and matrix, and the inset showing a zoomed image of the dotted box for the top layer, waxy 2nd layer, and the two carbonaceous lamellae/fibrous 4th and 5th layers of the turtle’s carapace.

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Table 3: Construct of the layered structure in a turtle shell with consequent mechanical properties of each layer.

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Tan et al. (2011) studied the mechanical properties of

moso culm functionally graded bamboo structures using a

combinaton of nanoindentation, micro-tensile testing, and

resistance curve experiments.

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Figure 12: An optical image of the functionally graded mesostructure of bamboo.



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Figure 13: The Young’s moduli distribution along the radial direction of the bamboo cross-section.

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Figure 14: (a) A representative stress–strain curve for the bamboo microtensile experiment. (b) Tensile strength of the outside, side and inside specimens.

Characterization of the Multi-Scale Structure of Kinixys erosa (Ke) Shell

• Determining which features control the performance of

biological materials is the first step in Biomimetics.

Characterization is therefore necessary to decipher the key

feature underlying the multi-functionality of hard

biological materials using techniques like Microscopy,

nanoindentation, mechanical testing, and X-ray diffraction.

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Structure of a Tortoise Shell

• A tortoise shell has two parts the upper portion-carapace

and the bottom half-plastron both of which are actually

made of many fused bones numbering up to 50. A bony

bridge joins the carapace and the plastron along the side of

the turtle.

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Carapace

Plastron

Figure15: Carapace and Plastron of kinixys erosa

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1 2 3 4 51 2 3 4

1

23 4 5 6 7 8 9

1011

12

Vertebral

Cervical

Pleural

Marginal

Figure 16: Scutes on the Carapace Kinixys erosa

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Bone Structure

• Bone structure has two parts: cortical region and trabecular

or cancellous type. The cortical region is dense and

comprises the outer structure or cortex of the bone, while

the interior consists of the trabecular tissue, made of thin

plates or trabeculae loosely meshed and porous.

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Microstructure of Kinixys erosa (Ke) carapace materials

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Figure 17: (a) Cross section of kinixys erosa bone structure (b) Schematic of kinixys erosa bone structure

a b

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a

Compositional Characterization of Kinixys erosa (Ke) Carapace Materials

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Figure 18: X-ray Spectrum of kinixys erosa scute

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Diffused 9/17-Amide nylon 6 olygomer

Compositional Characterization of Kinixys erosa (Ke) Carapace Materials

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Figure 19: X-ray Spectrum of kinixys erosa bone structure

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Diffused HA peaks

Lower intensity HA peaks

Micromechanical characterization of Kinixys erosa Bone Structure

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Figure 20: Stress-strain plot of compression test on kinixys erosa carapace bone structure

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Micromechanical characterization of Kinixys erosa Bone Structure

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Figure 21: Load/deformation plot three point flexural test on kinixys erosa carapace bone structure

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Summary

• The carapace is a sandwich composite structure having

denser exterior lamellar bone layers (cortical bone) and an

interior bony network of closed-cell fibrous foam layer

(cancellous bone).

• The bone structure was found to contain hydroxyapatite

while The scute contains 9/17-Amide nylon 6 olygomer. It

was also found to be resistant to concentrated acid and

base; however this requires further investigation.

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Summary cont’d

• Flexural strength of the bone structure was found to be as

against its compressive strength which was, while the

stiffness was -22.4 KN/m. The Young’s modulus in

bending (EB) was 6.4 GPa with the flexural strain and

maximum ultimate bending strain being 0.35 and 0.025

respectively.

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Analytical and Computational Model of Shell Structure

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Analytical Model Based on Theory of Shell

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Analytical Model Based on Theory of Shell cont’d

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Table 4: Analytical solutions based on theory of shell

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Figure 22: Stress distribution along the surface of the shell

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Figure 23: Strain distribution along the surface of the shell

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Figure 24: Tangential strain distribution along the surface of the shell

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Figure 25: Radial strain distribution along the surface of the shell

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Figure 26: Deformation distribution along the surface of the shell

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Figure 27: Tangential deformation distribution along the surface of the shell

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Figure 28: Radial deformation distribution along the surface of the shell

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Computational Finite Element Model

• The finite element analyses of the shell structure were

performed using a commercial code, ABAQUS, based on

the material properties (EB = 6.4 GPa and ) obtained from

the bending tests presented in Chapter 3. A 2-D model with

element type CPS4R was established and the detailed

simulation conditions are as presented in Table 5 below.

The applied pressure load (Figure 29) is the same with that

used in the analytical model.

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Single layer shell

Element type CPS4R

Number of elements 715

Number of nodes 955

Number of degrees of freedom (DOF)

1,910

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Table 5: Finite element simulation conditions



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Figure 29: Loaded 2-D finite element model of the shell structure



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Figure 30: 2-D finite element model showing stress distribution along the surface of the shell



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Figure 31: 3-D finite element model showing stress distribution along the surface of the shell

Concluding Remarks

• The carapace of Kinixys erosa (Ke) is a sandwich

composite structure with a denser exterior lamellar bone

layers (cortical bone) and an interior bony network of

closed-cell fibrous foam layer (cancellous bone).

• The scute of Kinixys erosa (Ke) was found to be resistant

to concentrated acid and base.

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Concluding Remarks cont’d

• The analytical and computational models showed that the

geometry of a shell structure has significant effects on its

deformation and stress responses.

• This work introduces the use of shell theory in studying the

deformation and stress responses of tortoise shell.

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Suggestions for future work

• In addition to the optical microscopy and XRD, SEM and

EDX study of Ke carapace materials will provide more

insight into the microstructure and composition of Ke

tortoise shell.

• Nanoindentation technique should be used to measure the

modulus of the individual layer of Ke tortoise shell

carapace, which can then be used in:

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• Object oriented finite element (OOF2) analysis to estimate

the effective modulus of the carapace. The modulus (EB)

obtained from the bending test and the OOF2 can then be

compared.

• Modeling of a multilayered-shell and layered structures to

understand their deformation and stress responses.

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Acknowledgements

• AUST/ADB

• NMI

• A-MRS AUST Chapter

• SHESTCO/NAEC

• Prof. Soboyejo W. O. (AUST/Princeton)

• Dr. Olukole S. G. (University of Ibadan)

• Mr. Gadu A. I. (Nuclear Technology Center-SHESTCO)

• Prof. Kana Z. (KWASU/SHESTCO)

• Dr. Odusanya O. S. (SHESTCO)

• Mr. Eniayehun (SHESTCO)

• Other well wishers

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Than

k yo

u

Bioinspired Design Owoseni T. A Materials Science and Engineering Stream African University of Science and Technology, Abuja, Nigeria. M. Sc. Thesis Presentation.

Documents

materials science

natural biological materials

engineering design

synthetic materials

hard biological materials

design of shell structures

effects of shell structure

engineering domain