Determining the Determining the Microstrain of Microstrain of

Biological Composites Biological Composites by X-Ray Diffractionby X-Ray Diffraction

Alyssa RoesslerAlyssa Roessler

Stanford Synchrotron Radiation Stanford Synchrotron Radiation LaboratoryLaboratory

August 13, 2008August 13, 2008

IntroductionIntroduction Biological composites often exhibit desirable Biological composites often exhibit desirable

properties, including properties, including emergent propertiesemergent properties that are that are present in the composite but not in the constituent present in the composite but not in the constituent materials individuallymaterials individually

In order to replicate or improve upon these In order to replicate or improve upon these biological designs, understanding the function of biological designs, understanding the function of the various components of the material is the various components of the material is necessarynecessary Mother of pearl has a Mother of pearl has a

unique unique microstructure and microstructure and exhibits exhibits surprisingly high surprisingly high strength and strength and toughnesstoughness

NacreNacre Mother of pearl, otherwise known as Mother of pearl, otherwise known as

nacre, is found in many mollusk shells nacre, is found in many mollusk shells and is also the composition of pearlsand is also the composition of pearls

Nacre is composed of two materials: Nacre is composed of two materials: the ceramic material the ceramic material aragonitearagonite (CaCO(CaCO33) and a biological ) and a biological polymerpolymer..

The aragonite (The aragonite (>95% by >95% by weightweight) is in the form of ) is in the form of hexagonal platelets about 10 hexagonal platelets about 10 μμm wide and .5 m wide and .5 μμm thick [1]m thick [1] The polymer acts as an The polymer acts as an adhesive between the adhesive between the aragonite plateletsaragonite plateletsBecause nacre is layered, Because nacre is layered, its properties are anisotropicits properties are anisotropic

Nacre DeformationNacre Deformation We wanted to determine the strain induced in nacre We wanted to determine the strain induced in nacre

more precisely than could be achieved by conventional more precisely than could be achieved by conventional teststests Full 3DFull 3D strain tensor strain tensor How much strainHow much strain each component each component was absorbingwas absorbing Stiffness Stiffness of the material in the different of the material in the different

crystallographic directionscrystallographic directions

At SSRL, we can use x-ray diffraction to directly At SSRL, we can use x-ray diffraction to directly observe the microscopic stain present in the aragonite observe the microscopic stain present in the aragonite portion of nacreportion of nacre When theWhen the crystal lattice is strained,crystal lattice is strained, the the diffraction diffraction

rings become distortedrings become distorted and the eccentricity can be and the eccentricity can be measuredmeasured

This eccentricity is a measure of the material strainThis eccentricity is a measure of the material strain

Sample PreparationSample Preparation

Sections of Red Abalone Sections of Red Abalone shell and White MOP shell and White MOP were ordered from were ordered from AustraliaAustralia

The samples were The samples were brought to the facilities at brought to the facilities at UC Berkeley and cut to UC Berkeley and cut to the desired length (~7 the desired length (~7 mm) with a low-speed mm) with a low-speed

diamond saw.diamond saw.

Sample Preparation, Sample Preparation, cont.cont.

The samples were The samples were applied to a grinding applied to a grinding disk and sanded to disk and sanded to the desired thickness, the desired thickness, about about 300 microns300 microns..

The nacre The nacre plates were plates were then cut into then cut into slices slices 480 480 microns widemicrons wide, , cleaned with cleaned with acetone and acetone and distilled distilled water, and water, and stored for stored for later use.later use.

Bracket DesignBracket Design A part was needed to attach A part was needed to attach

the specimens to the load cellthe specimens to the load cell Design parameters: Design parameters: 10 lbf load10 lbf load

cell capacity, needed a cell capacity, needed a 300 300 MPa stressMPa stress, needed to avoid , needed to avoid interference with x-ray beam, interference with x-ray beam, size constraintssize constraints

An example design An example design consideration: consideration: bucklingbuckling. We . We need the sample to be thin for need the sample to be thin for diffraction, small for the stress diffraction, small for the stress considerations, but as stable as considerations, but as stable as possible in terms of bucklingpossible in terms of buckling The notch was designed to give The notch was designed to give

the specimens maximum supportthe specimens maximum support

Experimental SetupExperimental Setup

Testing MethodologyTesting Methodology

Pictures and aragonite diffraction patterns were Pictures and aragonite diffraction patterns were collected periodically as strain was applied, collected periodically as strain was applied, typically every typically every 3 N3 N of applied force of applied force

Data was taken in both Data was taken in both tension and compressiontension and compression, , and all tests were done with the load applied in-and all tests were done with the load applied in-plane with the aragonite plateletsplane with the aragonite platelets

All in all three samples each of white mother of All in all three samples each of white mother of pearl and red abalone were testedpearl and red abalone were tested

ResultsResultsIn tension, strain was hard to control due to the rubbery In tension, strain was hard to control due to the rubbery nature of the epoxynature of the epoxyThe sample brackets held the specimens in place much better The sample brackets held the specimens in place much better under compression, and significant strain was seen in the under compression, and significant strain was seen in the aragonitearagonite

White Mother of Pearl White Mother of Pearl Red Red AbaloneAbalone

Aragonite Diffraction RingsAragonite Diffraction Rings

Discontinuous Rings show texture

Data AnalysisData Analysis The more strain present in the aragonite, the more distorted The more strain present in the aragonite, the more distorted

the diffraction rings become. The diffraction rings can be the diffraction rings become. The diffraction rings can be visually “unwrapped” to observe the eccentricity of the ring visually “unwrapped” to observe the eccentricity of the ring more clearly.more clearly.

The diffraction peaks were found and the full three-dimensional The diffraction peaks were found and the full three-dimensional strain tensor was calculatedstrain tensor was calculated

Unstrained In Compression

Stress vs. Strain in Aragonite

0

50

100

150

200

250

0 0.05 0.1 0.15 0.2 0.25

Strain

Str

ess

[111] [031] [041] [141]

[231] [222] [232] [241]

Stress vs. Strain in Aragonite

Slope = E,Young’s Modulus

Each diffraction ring represents a different crystallographic direction

Material StiffnessMaterial Stiffness

Since our experimentally determined Young’s modulus in Since our experimentally determined Young’s modulus in each crystal direction was higher than the theoretical value, each crystal direction was higher than the theoretical value, we can conclude that the aragonite portion of the material we can conclude that the aragonite portion of the material is in fact taking less than its weight percent in loadis in fact taking less than its weight percent in load

Literature cites a Literature cites a 92 GPa92 GPa bulk Young’s modulus for bulk Young’s modulus for aragonite [2] and a aragonite [2] and a 70 GPa70 GPa Young’s modulus for nacre as a Young’s modulus for nacre as a whole [3]whole [3]

Lattice Direction

Apparent Young’s Modulus (GPa)

Theoretical Young’s Modulus (GPa)

% Load Carried by Aragonite

[041] 86.7 78.1 89.0%

[031] 88.3 79.6 89.1%

[111] 91.2 82.6 89.6%

[222] 91.5 82.6 89.3%

[232] 92.3 86.7 93.5%

[141] 93.8 80.5 83.5%

[231] 99.0 91.3 91.6%

[241] 99.4 86.9 85.6%

ConclusionConclusion

X-Ray diffraction allowed us to observe more X-Ray diffraction allowed us to observe more detailed strain data than conventional detailed strain data than conventional methods, and the full strain tensor was methods, and the full strain tensor was computed for a variety of strain levelscomputed for a variety of strain levels

The percent of strain on each component of The percent of strain on each component of the material was found. While the polymer the material was found. While the polymer portion of nacre constitutes less than portion of nacre constitutes less than 5% of 5% of the material by weightthe material by weight, it carries between , it carries between 6.5 6.5 and 16.5 percent of the loadand 16.5 percent of the load..

This could explain the high toughness This could explain the high toughness exhibited by nacreexhibited by nacre

Still to ComeStill to Come The relative loads carried by the aragonite and polymer The relative loads carried by the aragonite and polymer

sections of nacre sections of nacre in tensionin tension has yet to be explored has yet to be explored Testing should also be done Testing should also be done perpendicularperpendicular to the to the

platelets as well as in the in-plane directionplatelets as well as in the in-plane direction Diffraction data should be collected from Diffraction data should be collected from polymerpolymer

portion of nacre to confirm the results suggested by the portion of nacre to confirm the results suggested by the aragonite diffractionaragonite diffraction

There are several species of nacre, so testing should be There are several species of nacre, so testing should be done on the done on the other varietiesother varieties for comparison for comparison

Better methods of determining macroscopic strain on Better methods of determining macroscopic strain on the material should be used. Digital Image Correlation the material should be used. Digital Image Correlation (DIC) methods work well for this.(DIC) methods work well for this.

AcknowledgmentsAcknowledgments Thanks to my mentor Apurva Mehta, Matt Bibee, Thanks to my mentor Apurva Mehta, Matt Bibee,

David Bronfenbrenner, and all the scientists and David Bronfenbrenner, and all the scientists and machinists at SSRL that provided help with this machinists at SSRL that provided help with this project.project.

Also thanks to the DOE Office of Science for funding Also thanks to the DOE Office of Science for funding this exciting research experience and to the SULI this exciting research experience and to the SULI program directors for making sure this experience program directors for making sure this experience was so rewarding.was so rewarding.

References:References:[1] Chen, P.Y., A.Y. M. Lin, A.G. Stokes, Y. Seki, S.G. Bodde, J. McKittrick, [1] Chen, P.Y., A.Y. M. Lin, A.G. Stokes, Y. Seki, S.G. Bodde, J. McKittrick,

and M.A. Meyers. "Structural Biological Materials: Overview of Current and M.A. Meyers. "Structural Biological Materials: Overview of Current Research." Research." JOMJOM os June (2008): 23-32. os June (2008): 23-32.

[2] Bruet, B. J. F., Panas, R., Tai, K., Frick, L., Ortiz, C., Qi, H. J., and [2] Bruet, B. J. F., Panas, R., Tai, K., Frick, L., Ortiz, C., Qi, H. J., and Boyce, M.C. “Nanoscale morphology and indentation of individual nacre Boyce, M.C. “Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusk trochus niloticus.” tablets from the gastropod mollusk trochus niloticus.” Journal of Journal of Materials ResearchMaterials Research (2005). (2005).

[3] Evans, A.G., Z. Suo, R.Z. Wang, I.A. Aksay, M.Y. He, and J.W. [3] Evans, A.G., Z. Suo, R.Z. Wang, I.A. Aksay, M.Y. He, and J.W. Hutchinson. "Model for the Robust Behavior of Nacre." Hutchinson. "Model for the Robust Behavior of Nacre." Journal of Journal of Materials ResearchMaterials Research 16 (2001): 2475-2484. 16 (2001): 2475-2484.