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QUANTITATIVEFRACTUREANALYSISOFA BIOLOGICALCERAMICCOMPOSITE By THOMASJERALDHILL ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 2001 ACKNOWLEDGMENTS First,I wouldliketothankmywife, Aidines. She ismyreason. Herlove, encoiiragement,andfriendshipthroughthetoughtimeshavealwaysbeenstrongandfor thatIcannevertrulyrepay. Iwouldalsoliketothankmymotherforherunending support. Shetaughtmethevalueofperseveranceandhardworkamongotherthings,and thevaluessheinstilledhavebeeninstrumentalinwhereIamtoday. Secondly, I would like to thank my professors and mentors, especially Dr. KennethAnusaviceandDr. JackMecholsky,whoprovided guidanceandmuch- neededadvicewheneveraskedfor. Icanneverrepaythecountlesshourstheyspent assistingme,teachingme,andhelpingtomakemeabetterscientisteachday. Next,IwouldliketothankJasonGriggsandAlvaroDeliaBona. Icouldnotask forbetterresearchpartnersandfriends. AndIwouldalsoliketothankalltheotherswho havecrossedmypathalongthisjourneyandhavebeenmorethanfriendsbutverymuch likefamily:AUyson,Ben,Zhang,Nicola,Kallaya,andCliff. TABLEOFCONTENTS Eage ACKNOWLEDGMENTS ii LISTOFTABLES v LISTOFFIGURES vi ABSTRACT x CHAPTERS 1PURPOSE 1 1.1ResearchRationale 1 1.2MaterialSelection 2 1.3ResearchObjectives 2 1.3.1SpecificAim1 2 1.3.2SpecificAim2 2 1.3.3SpecificAim3 3 1.3.4SpecificAim4 3 2BACKGROUND 4 2.1BiologicalCeramics 4 2.1.1Introduction 4 2.1.2MolluscShells 5 2.1.3Strombusgigas 6 2.2FractureofBiologicalComposites 8 2.2.1CompositeAnalysis 8 2.2.2StrainRate 13 2.2.3Water 14 2.3FractalAnalysis 16 2.3.1FractalDimension 16 2.3.2MeasurementMethods 18 2.3.3FractalAnalysisofBrittleComposites 20 iii 3MATERIALSANDMETHODS 22 3.1SpecimenFabrication 22 3.1.1Forming 22 3.1.2WaterStorage 23 3.1.3ProteinRemoval 24 3.2MaterialProperties 24 3.2.1Density 24 3.2.2Hardness 27 3.2.3ElasticModulusandPoisson'sRatio 27 3.2.4CrystalPhaseIdentification 28 3.3MechanicalPropertyDetermination 29 3.3.1FlexureStrength 29 3.3.2WorkofFracture 32 3.3.3FractureToughness 33 3.4FractalAnalysis 35 3.4.1ModifiedSlitIslandMethod 35 3.4.2BoxCountingTechniqueUsingthe AtomicForceMicroscope 38 4RESULTSANDDISCUSSION 40 4.1PhysicalPropertiesAnalysis 40 4.1.1Density 40 4.1.2Hardness 41 4.1.3ElasticModulusandPoisson'sRatio 42 4.1.4CrystalStructure 46 4.2MechanicalPropertiesAnalysis 50 4.2.1Strength 50 4.2.2FractureToughness 54 4.2.3WorkofFracture 56 4.2.4Fracture 58 4.2.5Water 64 4.3FractalAnalysis 75 4.3.1ModifiedSlitIslandAnalysis 75 4.3.2BoxCountingTechniqueUsingthe AtomicForceMicroscope 78 5CONCLUSIONS 79 APPENDIXTABULATEDDATA 82 LISTOFREFERENCES 96 BIOGRAPHICALSKETCH 101 iv LISTOFTABLES Table Page 1. Four-pointflexuralstrengthdatafromStrombusgigasspecimensstoredinair 82 2. Four-pointflexuralstrengthdatafromStrombusgigasspecimensstoredinartificial seawater 83 3. Four-pointflexuralstrengthdatafromStrombusgigasspecimensheattreatedat200°C for24h 84 4. Four-pointflexuralstrengthdatafromStrombusgigasspecimensstoredindeionized water 85 5. Four-pointflexuralstrengthdatafromStrombusgigasspecimensstoredinpH4buffer solution 86 6. Four-pointflexuralstrengthdatafromStrombusgigasspecimensstoredinpHl0 buffersolution 87 7. Four-point flexural strengthdatafromStrombusgigas specimens stored innatural seawater 88 8. Four-pointflexuralstrengthdatafromStrombusgigasstressingratespecimensin water 89 9. Four-pointflexuralstrengthdatafromStrombusgigasstressingratespecimensinair..91 V 8 LISTOFFIGURES Figure Page 2.1. Threeordersoflamellaofthehierarchicalstructureofthecross-lamellar Strombusgigasconchshell 7 2.2. Mechanicalbehaviorofnon-transformationtoughenedlaminates basedonthelaminatestructure 12 2.3. Stress-straindiagramsfordryStrombusgigasconchincompressiveloadingatquasi static(a)anddynamic(b)stressingrates 15 2.4. Fracturetoughnessversussquarerootoffractaldimensionalincrementforthree groupsofmaterials 1 2.5. Relationoffractaldimensionandsteplengthasafunctionofworkoffracture (Curreyetal.) 21 3.1. Specimencutindirectionparalleltotheaxisofshell 23 3.2.Thermogravimetric/differentialthermalanalysis(TG/DTA)graphs(a)priortoheat treatmentand(b)postheattreatment 25 3.3.Differentialscanningcalorimetry(DSC)graphs(a)priortoheattreatmentand(b) postheattreatment 26 3.4. Four-pointloadingconfiguration 31 3.5. SEMmicrographfracturesurfaceshowingmicrostructurallayers 31 3.6 Singleedgenotchedbeamconfigurationtodeterminefracturetoughnessof Strombusgigasfor(a)theweakerinnerlayerand(b)thestrongermiddlelayer 34 3.7. Opticalmicrograph(400x)showingthecoastlineofapolishedreplica 37 3.8. Plotoflogtotallengthversuslogsteplength. Theslopeisthenegativevalueofthe fractaldimensionalincrement 38 vi 3.9 Representativeimageofthefractaldimensionobtainedusingtheatomicforce microscope 39 4.1. DensityofStrombusgigasasafunctionofenvironmentinmonolithicand powderform 41 4.2. Vickershardnessasafunctionofindentationloadforfiveenvironment/temperature conditions 42 4.3 Opticalmicrographofindentationwithrespecttpa)shellmicrostructure(1OOx)and b)crushzone(400x)aroundtheindentation 43 4.4. ElasticmoduliandPoisson'sratiovaluesforfullthicknessStrombusgigasspecimen obtainedbyultrasonicmeasurements 44 4.5 ElasticmoduliandPoisson'sratiovaluesforsinglelayerStrombusgigasspecimen obtainedbyultrasonicmeasurements 45 4.6. X-raydiffractionspectraforStrombusgigas powderstoredinair. Aragonitecrystal structureistheonlyphasepresent 47 4.7. X-raydiffractionspectraforStrombusgigaspowderheattreatedat200°Cfor24h. Aragonitecrystalstructureistheonlyphasepresent 48 4.8. X-raydiffractionspectraforStrombusgigaspowderheattreatedat300°Cfor24h. Aragonitecrystalstructureistheonlyphasepresent 49 4.9. MeanstrengthforStrombusgigasspecimenstoredinair,storedindeionizedwater, andheattreatedat200°Cfor24hcalculatedusinglinearbeamanalysis,linearbeam analysisusingmiddlelayerthickness,andcompositeanalysis 52 4.10 Meanstrengthcalculatedusinglinearbeamanalysis,middlelayerlinearbeam analysis,andcompositeanalysis. Specimenswerestoredinsixenvironments: air (Air),deionizedwater(DI),naturalseawater(SW),pH4buffersolution(pH4),pHlO buffersolution(pHlO),andartificialseawatersolution(ASW) 53 4.11.Meanstrengthcalculatedbylinearbeamandmiddlelayerlinearbeamasafunction ofincreasingstressingrate 54 4.12 Meantoughnessdeterminedusingsingle-edgenotchedbeamforthreeconditions: storedinair,storedindeionizedwater,andheattreatedat200°Cfor24h 55 4.13.Workoffractureforspecimenstoredinair,storedindeionizedwater,andheat treatedat200°Cfor24h 56 vii 4.14 Workoffractureforspecimensstoredinsixenvironments: air(Air),deionized water(DI),naturalseawater(SW),pH4buffersolution(pH4),pHlObuffersolution (pHlO),andartificialseawatersolution(ASW) 57 4.15.Workoffractureasafunctionofstressingrateforgroupsstoredinairandin deionizedwater 58 4.16 SEMmicrographofthefracturesurfaceofaStrombusgigasatamagnificationof 20xdisplayingtwodistinctfracturesurfaces 59 4.17 SEMmicrographoftheinnerlayerofafracturesurfaceofaStrombusgigasata magnificationof5Ox 59 4.18 SEMmicrographofthetoughmiddlelayerofafracturesurfaceofaStrombusgigas atamagnificationof50x 61 4.19 SEMmicrographofasecondorderlamellaofStrombusgigasatamagnificationof 2500x 61 4.20 Representativestress-straindiagramsforStrombusgigasforthreeconditions 63 4.21.SEMmicrographatamagnificationof20xshowingbothfirstorderlamellaof Strombusgigas storedindeionizedwaterpriortofracture. Thepresenceofthe proteinaceousmatrixispervasive 65 4.22 SEMmicrographatamagnificationof50xofasecondorderlamellaofStrombus gigasshowingtheinterconnectingprotein 66 4.23.SEMmicrographatamagnificationof2000xshowingthestrongbondingofthe proteinwiththearagonitecrystalsofStrombusgigas 66 4.24.SEMmicrographatamagnificationof20xshowingthepresenceoftheproteinon theinterfacebetweentheinnerandmiddlelayersoftheStrombusgigas 67 4.25 SEMmicrographatamagnificationof200xshowingthehighorganizationof proteinmatrixwiththearagonitecrystalsofStrombusgigas 68 4.26 SEMmicrographatamagnificationof800xshowingthestrongbondingofthe proteinwiththearagonitecrystalsofStrombusgigas 69 4.27.Representativestress-strainplotsforgroupsstoredinair: (a)stressingrateof0.02MPa/s 71 (b)stressingrateof0.5MPa/s 71 (c)stressingrateof20MPa/s 72 (d)stressingrateof500MPa/s 72 viii 4.28.Representativestress-strainplotsforgroupsstoredindeionizedwater: (a)stressingrateof0.02MPa/s 73 (b)stressingrateof0.5MPa/s 73 (c)stressingrateof20MPa/s 74 (d)stressingrateof500MPa/s 74 4.29.Fractaldimensionalincrementasafunctionofenvironmentasmeasuredbythe modifiedslitislandanalysis 75 4.30 Fractaldimensionalincrementasafunctionofstressingrateasmeasuredbythe modifiedslitislandanalysis 76 4.31.Fracturetoughnessversussquarerootofthefractaldimensionalincrementforboth theinnerandmiddlelayersforthreeconditions: storedindeionizedwater,storedin airandheattreated. Opensymbolsareinnerlayerandfilledsymbolsaremiddle layervalues. Diamond-heattreated,Cross-air,andSquare-water 77 4.32 Fractaldimensionalincrementobtainedforinnerandmiddlelayersusingbotha macroscopictechnique(modifiedslitisland)andamicroscopictechnique(atomic forcemicroscopy) 78 ix AbstractofDissertationPresentedtotheGraduateSchoolofthe UniversityofFloridainPartialFulfillmentoftheRequirementsforthe DegreeofDoctorofPhilosophy QUANTITATIVEFRACTUREANALYSISOFA BIOLOGICALCERAMICCOMPOSITE By ThomasJeraldHill August,2001 Chairman: JohnJ.Mecholsky,Jr. Cochair: KennethJ.Anusavice MajorDepartment: MaterialsScienceandEngineering Thepurposeofthisstudywastoanalyzetheimprovedmechanicalpropertiesof theStrombusgigasovernon-biogenicaragonite(CaCOs)bycontrollingandanalyzing thepresenceoftheproteinaceousmatrixandwater. Thespecificobjectivesofthisstudywereto1)estimatetherelativeincreaseof mechanicalpropertiesfromstructureandproteinaceousinterfaceoftheStrombusgigas, 2)determineifionsinaqueous solutionofstressredistributionfromthepresenceof waterwastheprimarymechanisminincreasingworkoffracture,3)identifyifwater activatesanyviscoelasticeffectsfromtheproteinaceousmatrix,and4)identifyifthe fractal dimension can discern iftoughening mechanisms are present in the complex composite. TheStrombusgigassystemwaschosenforthisstudybecauseithasdemonstrated a10000-foldincreaseintheamountofenergytocausefailureovermonolithscomposed X