bioinspired design owoseni t. a materials science and engineering stream african university of...
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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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Background and Motivation Cont’d
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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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Background and Motivation Cont’d
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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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Literature Survey cont’d
• 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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Literature Survey cont’d
• 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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Literature Survey cont’d
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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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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