University of Illinois at Urbana Champaign

Literature Review:

Ballistic Resistant Materials in Nature (Nacre)

“Protection of High Voltage Bushings from High Velocity Impact”

Chinweike Osubor

ME 497 (Independent Study)

Professor: Dr. Iwona Jasuik

18th December 2015

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Abstract

This paper will extensively cover the ballistic resistive properties of Nacre, a material found in

nature that may be used in the coating of wires (in order to make them more resistive to bullet

penetrations and explosive impacts. We will come to an understanding that this material displays

high tensile and compressive strength, hardness and ductility. Other material properties that are

crucial to ballistic resistance such material strength to weight ratios, density, conduction and

their behaviors to change in environment were discussed. Similarities and differences noted.

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Table of Content

Introduction 3

Structure and Composition 4

Mechanical properties 4

Bending Stress & Fracture Toughness 5

Tensile and Compressive Strength 7

Hardness of Nacre 9

Shear Stresses in Nacre 11

Summary 14

Importance of Nacre in Context 16

Works Cited 17

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Introduction

The issue of protecting power lines is one that has been fast growing in concern, as safety in

today’s world is a relevant matter. Thus it is crucial to come up with a procedure in protecting

these vulnerable power carrying wires from bullets and explosions. Consequently, it is as

significant to investigate materials which may be used in the coating of these wires to make them

resistive to impacts. These materials would have to be environmentally friendly, electrically and

thermally nonconductive, light in weight, and lastly and importantly these materials must

characterize of important ballistic mechanical properties (adequate compressive and tensile

strengths, good strength-weight ratio, high hardness, low thermal expansion, moderate ductility).

This paper investigates one natural material that meets these specifications. It gives a detailed

description of this material and its material mechanical properties, and also suggests

techniques/methods to optimize these material properties.

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Structure and Composition of Nacre

Nacre is an organic-inorganic composite material fond in the inner layer shells of Mollusks. It

composes of 95 wt% aragonite, which is a crystallographic form of CaCO3 (a form of calcium

carbonate), and also made up of 5 wt% of organic material. The hexagonal platelets of

aragonite which are arranged in a continuous parallel lamina are approximately 10-20 µm wide

and 0.5 µm in thickness. The layers are equally separated by sheets of organic matrix which are

made up of elastic biopolymers. This juxtaposition of brittle platelets and layers of elastic

biopolymers make this material specifically very strong and resilient.

Picture 1: Structure and Composition of Nacre

Mechanical Properties

Nacre Is an an-isentropic material, meaning the mechanical properties vary depending on the

orientation and mode of applied force. The strength varies when subjected to compression, shear,

tension, bending, etc.

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Bending Strength and Fracture Toughness

REFRENCE A:

Rösler, Joachim, H. Harders, and M. Bäker. <i>Mechanical Behaviour of Engineering Materials: Metals, Ceramics, Polymers, and Composites</i>. Berlin: Springer, 2007. Web. 12 Dec. 2015.

Credit of testing and results to:

A three-point bending test was evaluated according to the international standards for Young’s

Modulus, bending strength and fracture toughness which can be seen in Figure 1 below. The

tested samples were 25x2.5x2 mm for bending test and 25x2x2.5 mm for the tests of fracture

toughness. There were a total of 60 specimens tested. These specimens were tested in four

different stages of hydration (dry, distilled water, 0.9% NaCl and sea water), with five samples

each. Congruently ten dry bio ceramic samples were tested for fracture toughness. [A]

The testing results proved that the fracture toughness of nacre was higher for the specimens that

were conditioned in the 0.9% NaCl than for dry specimens (5.3±0.6 vs. 4.3±0.7 MPa m½,

p=0.061). The fracture toughness of the bio ceramic examined was noticed to be greater than dry

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nacre (5.8±0.4 vs. 4.3±0.7 MPa m½, p≤0.001). The Young’s Modulus of nacre was seen to be

approximate to published values ranging from 64-73 GPa. However, we did note higher fracture

toughness values of about 3.3-4.6 MPa m½ [1, 3].

REFERENCES:

[1] Barthelat et al., A Math Phys Eng Sci 2007, 365:2907–2919. [2] Fischer et al., Dent Mater 2008, 24:618–622. [3] Jackson at al., Proc R Soc Lond B 1988, 234:415–440. [4] CeramTec AG, Scientific Information & Performance Data, p11. [5] Roesler et al., Springer 2008, ISBN 978-3-540-73446-8. [6] Munch et al., Science 2008, 322:1516-1520.

Acknowledgements: This research was funded by the Collaborative Research Center 599 for

Biomedical Technology, a Center of the German Research Foundation (DFG).

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Tensile and Compressive Strength and Young’s Modulus

REFRENCE B:

Wang, R. Z., Z. Suo, A. G. Evans, N. Yao, and I. A. Aksay. "Deformation Mechanisms in Nacre." <i>Journal of Materials Research J. Mater. Res.</i> 16.09 (2001): 2485-493. Web. 10 Nov. 2015.

Credit of Testing and Result to:

To test for the compressive and tensile strengths lamellar samples of Nacre were used. They

were comprised of alternating layers of thickness approximately 0.2–0.9 µm separated by

nanoscale organic inter layers of approximately (20 µm diameter), in such a manner that the

cross sections mimicked brick wall orientation. [B]

Four Point bending tests were performed with 5 specimens each about 1.6 mm deep and 2.5 mm

wide, 16mm in length. The results can be observed in Figure 3 below. We see that the

compressive curves are linear with a Young’s modulus of E=70 GPa. The stress reached about

370 MPa before testing was discontinued.

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It is noticeable that the tensile curves are very nonlinear. Post yielding and following early stages

of strain hardening which happens over a strain range of 0.1%, the subsequent inelastic

deformation happens in steady state.

Results summarized that the failure strain was approximately 8% much higher than it was in

bending. We also realized that the elastic modulus was only 8GPa. The compressive strength

was approximately 160MpPa, this value significantly lower than that parallel to the lamellae

which was greater than 370MPa.

9    

The unloading and reloading measurements reveal hysteresis was can be seen in Figure 3 below.

This is indicative of internal friction, having an unloading modulus of 17GPa, slightly greater

than that upon initial loading.

Hardness of Nacre

REFRENCE C:

Kati, Kalpana. "Nano Mechanical Properties of Nacre." <i>Cambridge.org</i>. Department of Civil Engineering, North Dakota State University, 12 Aug. 2005. Web. 10 Dec. 2015.

Credits of Testing and Results to:

10    

Nano indentation tests were carried out on nacre using a triboscope Nano mechanical testing

instrument. A diamond tip was used. The test was load controlled using a 5x5x5 trapezoidal

function. The first section of pressing subjected the specimen to a loading at uniform rate in 5

seconds up to the maximum load. The second sector was maintaining this maximum load at peak

for another 5 seconds. The third sector comprised of unloading in a 5 second span. The specimen

was a 6x6x1 mm sample of nacre.

The test was performed at various load from 10 -10,000 µN. There were a total of 20

indentations carried out at each load. The orientation of indentation was in the direction

perpendicular to the face of the platelets as can be seen in the Figure 1 below: [C]

The observed hardness ranged from 0.69-18.32 GPa at loads of 10 µN. For loads of 10,000 µN

the values varied from 1.32 to 3.1 GPa. This can be seen in figure 4 below showing the hardness

vs load plot for the testing at different max loads.

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REFRENCE C

It is apparent in the plot that the average values of hardness and the variation in hardness at each

load is consistently decreasing as load indentation and indentation depth increases.

Shear Stresses in Nacre

REFRENCE D:

Albert Yu-Min Lin. "Interfacial Shear Strength in Abalone Nacre." J O U R N A L O F T H E M E C H A N I C A L B E H A V I O R O F B I O M E D I C A L M A T E R I A L S 2. Science Direct, 3 May 2009. Web. 12 Dec. 2015.

Credits of Testing and Results to:

12    

The shear strength of the interface between tiles of aragonite in the nacre of red abalone Haliotis

rufescens was investigated through mechanical tensile and shear tests. Dog-bone shaped samples

were used to determine the tensile strength of nacre when loaded parallel to the plane of growth;

This can be seen in the schematic below:

The mean strength was found to be about 65 MPa. Shear tests were conducted on a special

fixture with a shear gap of 200 µm, approximately 100 µm narrower than the spacing between

mesolayers. The shear strength is found to be 36.9 ± 15.8 MPa with an average maximum shear

strain of 0.3. Assuming the majority of failure occurs through tile pull-out and not through tile

fracture, the tensile strength can be converted into a shear strength of 50.9 MPa. Three

mechanisms of failure at the tile interfaces are discussed: fracture of mineral bridges, toughening

13    

due to friction created through nanoasperities, and toughening due to organic glue. An additional

mechanism is fracture through individual tiles

Due to the high variability commonly associated with biological materials, a Weibull statistical

(Weibull, 1951) analysis was applied to the mechanical testing results. The plot in Fig. 3 shows a

50% failure probability when a stress of approximately 65 MPa was applied. This is within

reason to the average tensile strength of the Gastropods Turbo marmoratus (116 MPa) and

Trochus niloticus (85 MPa) reported by Currey (1977).

14    

Summary of the Mechanical Properties of Nacre in Comparison to Other Materials:

Overall REFRENCES D:

1. Bar-Cohen, Yoseph. Biomimetics: Nature-based Innovation. Boca Raton: CRC, 2012. Print.

2. Proulx, Tom. "Mechanics of Biological Systems and Materials, Volume 2."Bokus.com. Society for Experimental Mechanics, Inc, Spring 2011. Web. 27 Aug. 2015.

3. "Proceedings of the Royal Society of London Series B Biological Sciences."(eJournal / EMagazine, 1905) [WorldCat.org]. The Royal Society, June 1990. Web. 27 Aug. 2015.

4. Katti, Kalpana S. "Nanomechanical Properties of Nacre." (2006): 1237-242.Department of Civil Engineering. Web. Aug. 2015.

15    

What is the importance of Nacre in Context?

The toughness of Nacre in abalone shells is more than 3000 times greater than that of the

individual shell components. It has the highest impact resistance of any biological material. It is

also non-conductive and is highly resistant to degradation. These properties below make it a high

potential target for our aim in using this material as a coating mechanism for wires, in an aim of

making the wires impact resistive. The properties of nacre are outlined below:

Properties of Nacre

• Non Conducting (Significant due to electrical application)

• Highly Impact Resistance

• High Strength to Weight Ratio

• Eco-Friendly

• UV Resistant

• Weather Proof

• Relatively Cheap

16    

Noting these general properties, we see hat Nacre is an important fit for use as a coating

mechanism for bulletproof and explosive proof wires. For example being non-conducting is quite

significant in context, as we are applying this to electrical systems thus being non-conductive

helps in making a safer system. High strength to weight ratio means it is relatively light, thus

meaning it would not put significant weight stress on the wires or the system. Simulated as a

coating mechanism, we see nacre is almost massless. Other qualities like weather proof is also as

important as it means the material would not degrade under exposure to sunlight, rain or other

extreme weather conditions. In summary these material properties displayed by nacre makes it a

very competitive material.

17    

Works Cited:

1. Bar-Cohen, Yoseph. Biomimetics: Nature-based Innovation. Boca Raton: CRC, 2012.

Print.

2. Proulx, Tom. "Mechanics of Biological Systems and Materials, Volume 2."Bokus.com.

Society for Experimental Mechanics, Inc, Spring 2011. Web. 27 Aug. 2015.

3. "Proceedings of the Royal Society of London Series B Biological Sciences."(eJournal /

EMagazine, 1905) [WorldCat.org]. The Royal Society, June 1990. Web. 27 Aug. 2015.

4. Katti, Kalpana S. "Nanomechanical Properties of Nacre." (2006): 1237-242.Department

of Civil Engineering. Web. Aug. 2015.

5. Albert Yu-Min Lin. "Interfacial Shear Strength in Abalone Nacre." J O U R N A L O F T

H E M E C H A N I C A L B E H A V I O R O F B I O M E D I C A L M A T E R I A L S 2.

Science Direct, 3 May 2009. Web. 12 Dec. 2015.

6. Kati, Kalpana. "Nano Mechanical Properties of Nacre." <i>Cambridge.org</i>.

Department of Civil Engineering, North Dakota State University, 12 Aug. 2005. Web. 10

Dec. 2015.

7. Wang, R. Z., Z. Suo, A. G. Evans, N. Yao, and I. A. Aksay. "Deformation Mechanisms in

Nacre." <i>Journal of Materials Research J. Mater. Res.</i> 16.09 (2001): 2485-493.

Web. 10 Nov. 2015.

8. Rösler, Joachim, H. Harders, and M. Bäker. <i>Mechanical Behaviour of Engineering

Materials: Metals, Ceramics, Polymers, and Composites</i>. Berlin: Springer, 2007.

Web. 12 Dec. 2015.