A Summary Report on the 21 st Century Needs and Challenges of Compression Science Workshop

Transcription

1 A Summary Report on the 21 st Century Needs and Challenges of Compression Science Workshop Bishop s Lodge, Santa Fe, NM September 22-25, 2009 LA-UR Organizers: Dave Funk, Rusty Gray, Tim Germann, and Rick Martineau Image by NASA/JPL-CalTech 1

2 TableofContents 1. Introduction Breakout Summaries Static Compression Science Scientific Discovery Challenges: Static Compression Science Structure and bonding at high compression New physics in cold dense matter Fundamental thermodynamics Time-dependent transformations High-pressure strength, plasticity, and rheology Synthetic chemistry frontier Optimized new materials Radiation-induced high-pressure chemistry Earth science, planetary science and astrophysics Life in extreme environments Technical Grand Challenges in Static Compression Science Reaching 1 TPa and beyond Developing multi-probe intelligent devices Stress-strain states and P-T calibration Advancing x-ray methods Real time x-ray imaging with nm resolution Neutron scattering to multi-megabar pressures Challenge of liquids and amorphous materials Filling the strain rate gap: Static to shock Transport properties Thermochemical measurements at multimegabar pressures Dynamic Compression Science Scientific Discovery Challenges: Dynamic Compression Science Kinetics and mechanisms of melting, freezing, and solid-solid phase transformations Warm dense matter (WDM): metallization, release around critical points Evolution of microstructure under dynamic loading including defect distributions Experiment/theory convergence: Developing the ability to reproduce simulations of real systems for better understanding of experimental observations Resolving the details of detonation and shock-induced chemistry Discovering new phases and forms of matter at ultra-high compression using tunable pathways and controlling reaction chemistry through pressure and temperature Discovering and understanding of the partitioning between dissipative and non-dissipative mechanisms Determine the role of shear in deformation processes Develop understanding of the role of interfacial boundaries Develop an understanding of the transition in material plasticity and damage evolution across the thermally activated to shock to drag control regimes Technical Grand Challenges in Dynamic Compression Science Characterization of melting, freezing, and solid-solid phase transformations Real-time diagnostics for dynamic mapping of the thermo-mechanical field Ability to make experimental measurements to link length scales ranging from atomic to continuum dimensions Ability to make in situ spectroscopic measurements including those of electronic structure Complex loading path control Develop first-order continuum analyses that produce better subscale models and capture defect evolution

3 3.2.7 Learn how to conduct and diagnose experiments relevant to 3D applications Design experiments that overlap different loading regimes and experimental platforms Increase experimental throughput Develop improved materials and standards for uniform comparisons Scientific Discovery Challenges for Compression Science Theory and Modeling Track dynamic microstructure evolution in situ Discover new and unexpected high-pressure and temperature solid phases Design novel experiments to isolate key physics Move beyond planar impact: Non-uniaxial strain experiments Design novel simulations to isolate key physical mechanisms and observables Develop ability to predict the kinetics of phase transitions (solid-solid, solid-liquid, and liquid-solid) Understand relationship between microstructure and constitutive properties (e.g., strength) during dynamic processes Understand material failure Resolve melting discrepancy in transition metals Understand the behavior of the full anisotropic stress state at extreme pressures and temperatures, e.g., Poisson s ratio approaching melt Technical Grand Challenges for Compression Science Theory and Modeling Multiscale modeling free of ad hoc parameters: linking subscale processes to higher length/time scales Better theoretical tools in the mesoscale (1 10 mm) regime Transferable density functionals, pseudopotentials, and classical MD potentials valid at extreme conditions Equation of state treatment of materials beyond simply pressure and volume Codes that preserve the integrity of material models Quantitative dynamic x-ray probes (diffraction, XANES, EXAFS, etc.) Develop local temperature and stress tensor gauges Local structural identification in static experiments, e.g., DAC, for amorphous materials and liquids D orientation image mapping to dislocation length scales under dynamic conditions Extracting useful information from high-resolution 3D data (e.g., from 3D tomography or large-scale simulations) Conclusions Appendix I Workshop Agenda Appendix II Participants Appendix III Cross-cutting issues identified during the workshop

4 ExecutiveSummary Theinfluencethatcompressionsciencehashadonnationalsecurityscienceandits manifestationthroughdiscoveryandapplicationcannotbeoverstated.inadditionto supportingthecertificationofournuclearstockpileintheabsenceofundergroundtesting andabroadspectrumofengineeringanddefenseapplications,compressionsciencehas alteredourviewofthematerialworldaroundus.thediscoveryofunexpectedphysicaland chemicalphenomenaandnewmaterialsthroughtheapplicationofcompressionscience techniqueshasledtoanewandrefinedunderstandingofthenatureofchemicalbondingin extremeenvironments.however,itisclearthatmanyimportantaspectsregardingthe responseofmaterialstocompressiveloadingarestillnotunderstood,letalonemodeledina predictivemode.asaresult,wehavenotderivedthemanybenefitsthatapredictive understandingwouldbring.asoneproductoftheworkshopweheld,weidentifiedfive challengesthatcapturethescientificneedsthatarerequiredtoachievefullunderstanding andthatultimatelysupportourultimategoalofmovingfrom observationtocontrol. Thesefivechallengesareasfollows: Acquiretimeandspatiallyresolvedinsitumeasurementsatalllengthscales(i.e., atomistic,micro,meso ). Discovernewphysicsandchemistryinextremeenvironments. Incorporatematerialcomplexityintomulti scalesimulationstoachievepredictive capability. Unifystaticanddynamiccompressionunderstandingacrossrelevantlengthandtime scales. Leveragescientificknowledgederivedfromtheoryandexperimenttothedesignand controlofrealmaterials(i.e.,chemistry,microstructure,defects,etc.) Makingprogressonthesechallengeswillrequireasuiteofnewexperimentaltoolsand diagnosticsaswellasasuiteofconceptualframeworksandtheoreticalconstructs.thesuite ofexperimentaltoolsmustincludethedevelopmentofdiagnosticcapabilities,suchasnext generationlightsources,forpeeringintoandachievingtime resolvedmeasurementsin compressedmaterialsatthelowestrelativelengthscaleswhilesimultaneously characterizingthemathigherlengthscales.thetheoreticalsuitemustincludenew frameworksofcomputationthatwillallowtheincorporationofthestochasticnatureof matter,aswellastheabilitytoaccuratelydescribetheessentialphysicswithoutthe invocationofphenomenologicalmodels,whilelinkingtheatomistictothecontinuum response. Progressonthesechallengeswillnotonlyallowustodevelopafullunderstandingof compressionscience,itwillcreateanenvironmentinwhichwecantrainthenext generationofscientistsandprovidethemwiththetoolsneededtomakeprogressandmove fromstudying Ideal to Real materials. 4

5 1. Introduction Forapplicationsinthefuture,thedesign,synthesis,andmanufactureofnewmaterialswith increasedperformanceandfunctionalityrequireanincreaseinourfundamental understandingofmatteroverthebroadestrangeofthermomechanicalconditions. Furthermore,accesstoextremestatesofmatterresultsinaricharrayofphysicaland chemicalchangesthatrequiresabroadrangeofscience fromquantumphysicstothe collectivecontinuumresponse tointerpret.infact,currentresearchreiteratesthisneed: Compressioninduceschangesinbondingproperties,givingrisetoaltogethernew compoundsandcausingotherwiseinertatomsormoleculestocombine.whencoupledwith changesintemperature,altogethernewformsofmattermaybeproduced.forexample,it hasrecentlybecomepossibletouselaboratorytechniquestocompressmaterialstothe pointwheretheinteratomicspacingsarereducedbyuptoafactoroftwoanddensities increasedbyoveranorderofmagnitude.atthesedensities,thechangesintheelectronic structurebegintoinfluenceourverynotionsofchemicalinteractionandatomicbonding. 1 Thus,fullyexploitingthepossibilitiesofchemicalbonding,asderivedfromtheapplication ofpressureandtunedwithtemperature,willrequirenewtoolstogeneratetheseextreme environments,butwillalsorequireanabilitytodiagnoseand calculate them.thefieldof compressionsciencehasgeneratedrichinsightandmadeusawareofthefactthatwedonot fully understand the nature of the processes that we induce with pressure. Presently, pressures reached during static compression can exceed the 300 GPa(3 Mbar) range and cantemporarilyexceedtemperaturesgreaterthanthatofthesurfaceofoursun(>6,000k), whilethosepressuresreachedduringdynamiccompressioncanexceedtheterapascal(tpa or10mbar)range.inaddition,thedynamicprocessesofshockcompressionaresofastthat the loading is usually adiabatic, the typical durations range from femtosecond to microsecondtimescales,andtemperaturesreachgreaterthan10 4 K,dependingontherate of loading and the magnitude of the peak compression. Developing new capabilities for reaching further extremes and diagnosing these equilibrium states of matter with unprecedented spatial resolution will inform and advance our understanding, assisting in ourgoalofmovingfrom observationscience to controlscience. Toquantifytheseneedsandfuturedirections,leadersinthestatic,dynamic,andtheoryof compression sciences participated in a workshop entitled, 21 st Century Needs and ChallengesinCompressionScience, heldseptember22 25,2009,inSantaFe,NewMexico. A series of plenary talks were given (see Appendix I), followed by a day of breakout discussionsintheareasofstaticcompressionscienceneeds,dynamiccompressionscience needs, and theoretical needs of compression science to define the decadal technical challengesandnecessarydevelopmentstomeetthesechallenges 1 Basic Research Needs for Materials Under Extreme Environments, a report of the Basic Energy Sciences Workshop on Materials Under Extreme Environments, June 11-13, 2007, Jeff Wadsworth, Chair, George Crabtree and Russel Hemley, co-chairs. 5

6 Atitshighestlevel,theneedsofcompressionsciencecouldbecapturedbythefollowingfive challenges: Acquiretimeandspatiallyresolvedinsitumeasurementsatalllengthscales(i.e., atomistic,meso,micro ). Discovernewphysicsandchemistryinextremeenvironments. Incorporatematerialcomplexityintomulti scalesimulationstoachievepredictive capability. Unifystaticanddynamiccompressionunderstandingacrossrelevantlengthandtime scales. Leveragescientificknowledgederivedfromtheoryandexperimenttothedesignand controlofrealmaterials(i.e.,chemistry,microstructure,defects,etc.). The ability to address these challenges will require a new set of characterization tools, temporally and spatially enhanced diagnostics, and the development of new predictive models to characterize the behavior of matter under these extreme conditions. The information gathered in static compression science experiments, when combined with informationacquireddynamically,offerstheopportunityofunderstandingthefundamental mechanisms that drive the processes occurring in the matter observed throughout the universe, ultimately leading to an ability of controlling matter to meet our energy and nationalsecurityneeds. 6

7 2. Breakout Summaries 2.1 Static Compression Science Staticcompressionscienceisaburgeoningfieldthatisundergoingunprecedentedgrowthin addressingabroadrangeofmaterialsproblemsthatspanthephysical,engineering,and biologicalsciences.methodsthatrelyonstaticcompressionexperimentshavemany advantages,includingtheavailabilityofmultiplesimultaneousdiagnostics.these diagnosticshavethepotentialforfullmaterialscharacterizationwithanaccuracy,precision, andsensitivitythatapproachesmeasurementsonmaterialsatnearambientconditions.the fieldisturningitsattentiontoaddressingmajorgrandchallengesinmaterialsscience, includingthedoegrandchallengesofmovingfromobservationtocontrolscienceand harnessingmaterialsfarfromequilibrium.thereisastrongsynergybetweenconventional staticcompression,dynamiccompressionmethod,andtheory;indeed,manyproblems cannotbeaddressedwithoutthecombinationofallthreeoftheseapproaches.withthe prospectsforthecreationofnewfacilities,includingmajorradiationsources,many breakthroughsareonthehorizon. 2.2 Scientific Discovery Challenges: Static Compression Science Structure and bonding at high compression Basedonrecentwork,wecurrentlyhavealimitedunderstandingofstructureandbonding incondensedmatteratveryhighcompressions.makingmeasurementswithanaccuracy andresolutionequaltothoseattainableatambientconditionsoverabroaderrangeofp T conditions,particularlyathigherpressures,willallowthedevelopmentoftrulypredictive theory:anewparadigmforunderstandingcondensedmatter.wewillextendthis knowledgeacrosstheperiodictableoverthefullrangeofpressureandtemperature,and extendchemistryfromvalencetocoreelectrons,effectivelytoexploreanddevelop kilovolt chemistry. Ourknowledgeofmaterialsislargelybasedonunderstandingobtainedfromsystemsat near ambientconditions.becauseofthis,therearenumerousexamplesofintriguingand poorlyunderstoodphenomena,nearlyallofwhichwerenotpredictedtheoreticallyorwere simplyunexpected.amongthemanyexamplesaretherecentobservationsofthenovel (O2)4cluster basedstructureofdenseoxygen;theunprecedentedpolymorphismofna whichexhibitssome11differentphasesandmeltingbelowroomtemperatureatmegabar pressures;andtheremarkablepressure inducedtransformationofbothliandnafrom metaltoinsulator.theoriginofthebehaviorinallthreepreviousexamplesatthelevelof trulypredictive,generaltheoryislacking.currentstaticcompressiondataobservationsare basedonphenomenaobservedtopressuresof GPa.Whathappensathigher pressures,e.g.,at1tpaandbeyond?therearenumerouspossibleotherapplications/fields forstatichigher pressurecompression,includingmaterialsscience,andplanetaryscience, astrophysics. 7

8 2.2.2 New physics in cold dense matter Theorysuggeststheexistenceofnewphysicsinmaterialsatveryhighpressures(e.g.,0.5 1TPa)andlowtemperatures.Therearecurrentlynoexperimentaldatainthisregime; indeed,itislikelythatexperimentswillrevealaltogethernewphenomenanotpredictedby theory.achievinghigherpressurestogetherwithvariabletemperaturesandotherextreme fieldsincombinationwithnewdiagnosticswillleadtoadeeperunderstandingofthenature ofmatter.thenewphysicsthatwillberevealed,forexample,willdrivenewtheoryintothe mechanismsofmagneticandelectronicorder. Anexcellentexampleisthepredictedmetallicsuperfluid;itisaproposedmagnetic techniquethatwouldbeasignatureofthepredictednewstateofmatter:asuperfluid superconductor.thefirstchallengeisreachingthecombinedpressures,temperatures,and fieldsneededandcontaininghydrogentoexplorethis.thediagnosticswouldinvolve imagingthevortexmatterthatwouldbecreated,aspredictedbytheory.beyond fundamentalphysics,therearenumerouspotentialimplicationsforenergy,planetary science,andastrophysics Fundamental thermodynamics Wecurrentlyhavealimitedunderstandingofthebasicthermodynamicpropertiesofmany materials,includingrelativelysimpleelementalsubstances,inthecurrentlyaccessible megabarpressurerange.thesepropertiesincludephasediagramsofmanysystems,where insomecasesextremelylargediscrepanciesinmeltingtemperaturesexistbetweenstatic studies,shockcompression,andtheory.sinceeachoftheseapproacheshasitsown limitations,andmoreimportant,mayexploredifferentphenomenaorstatesofmaterials (e.g.,stableversusmetastable,relaxedversusunrelaxed),theexistingputative discrepanciesmayprovideevidencefornewbehaviorinmaterials.excellentexamples includethemeltingcurvesofbcctransitionmetals,suchasta.bybridgingthecurrentgaps thatexistbetweenthesemethods,wewillfindsolutionstoapparentdiscrepanciesinphase stability,structures,transitionsmechanisms,anddynamics,andtherebydevelopan understandingofthegeneralphasebehaviorofmaterialsatextremep Tconditions.For this,accurateinsituprobesofstructures,dynamics,andequationsofstateareneededupto multimegabarpressures(e.g.,0.5tpa)andtemperaturesfrommillikelvinsto~1ev. AnotherexampleoffundamentalthermodynamicsatextremeP Tconditionsisthenatureof equilibriumdefectsandgrainboundariesundertheseextremeconditionsinpuresystems aswellasinterfacialphenomenoninalloys,composites,andcomplexmaterials.sofar,there hasbeenverylittleworkonstudyinginterfacesdirectlyunderanydegreeofcompression. Aninterfaceathighpressureisaburiedinterface,sothemostprevalenttoolsofsurface scienceareuseless.interfacescurrentlymaybestudiedusingamonolayerofamaterial withauniquesignatureorusingasurface sensitivespectroscopicmethodsuchassumfrequencygeneration.newinterfacesensitivestructuralprobesareneeded.thescientific challengesincludeunderstandinghowinterfacesandinterfacialinteractionsbetween similarordissimilarmaterialsareaffectedbyhighpressure,howinterfacialstructure(e.g., interfaceswithhighsurfacefreeenergyversusinterfaceswithlowersurfacefreeenergies) changeswithpressure,andhowinterfacialreactivity(e.g.,thereactivityatthesurfaceofa heterogeneouscatalyst)respondstopressure.theapplicationsinclude(1)lubrication resultingfromthebehaviorofthinlayersoflubricantsbetweensurfaces;(2)adhesion, 8

9 adhesionfailure,andmaterialaging,e.g.,theinteractionsofadhesiveswiththesurfacesof materials;(3)catalysisandelectrocatalysiswherethestructuresand,therefore,reactivities ofthecatalyticentitiescanbecontinuouslyvariedbytheapplicationofhighpressure;(4) controlofthestrengthofmaterialsbycontrollingthegrainboundarystructure;and(5) geoscienceandplanetaryscienceinwhichthisinformationiscrucialforunderstandingthe large scalestructureandphysicalpropertiesofplanets,includingtheirevolutionand dynamicsoftheirdeepinteriors Time-dependent transformations Equilibriumphasediagramsandstabilityrelationsareonlyafirststep.Ingeneral, equilibriumpropertiesdonotadequatelydescribematerialbehaviorindynamicprocesses. Compression ratedependenceofphasenucleation,growth,melt,andmicrostructureare vitaltounderstandingandmodelingdynamicevents.bypioneeringabroadrangeoftimeresolveddiagnosticprobes(e.g.,withx rays,neutrons,orlasers),weneedtoselectively interrogatematerialsduringpressure inducedtransitionswiththeprecisioncharacteristic ofstaticcompressiontechniques.suchmeasurementswillproviderate dependentkinetic phasediagramsandestablishanexperimentalbasisforimplementingpredictivecapability. Developmentofafundamentalunderstandingoftheinfluenceofkineticsandcompressionratedependenciesofphasetransitionwillhaveaprofoundimpactonhigh pressurescience andtechnology.measurementandstudyofkineticphasediagramsarecrucialto understanding,modeling,andsimulatingdynamicprocesses.asamaterialisdynamically drivenacrossaphaseline,thenucleationandgrowthkineticsarethecriticalparameters determiningthedevelopmentofthenewphase.indeed,atexceedinglyhigh compression rates,thematerialmaytransformtoaltogethernew(e.g.,amorphous)phasesratherthan thethermodynamicequilibriumphase.experimentaldataregardingkineticsathigh pressuresisverylimitedandcrediblepredictivetheoreticalapproachesdonotexist. Pressure driveswithprecisecontrolandtunabilityacrossabroadrangeofpressures, temperatures,andcompressionsrateswillprovidecrucialdataforestablishinginsightsinto thischallengingareaofresearch. Thisworkwilladdressthelargelyunexploredareaofphasetransitionkineticsand dynamicsandwillbevaluableindevelopingmodelsofmeteoriticimpacts(geophysics)and otherimpactphenomena(doe/nnsaanddod).controlofphasetransformationkinetics directlyimpactsthemicrostructureandassociatedconstitutivepropertiesofmaterialsfor technologicalapplications.inaddition,athigh compressionrates,thepossibilityexiststhat thesynthesisofmaterialswithuniqueidentificationofnovelmetastablematerialsalong reactionpathscouldhaveimportanttechnologicalandgeoscienceimplications High-pressure strength, plasticity, and rheology Materialresponseundercompressionisafunctionofchemistry,phasecontent, microstructure,defects,impurities,aswellaspressureandloadingrate.bydeveloping novelx raydiffractionandnano imagingtechniquesandpressuredeviceswiththeabilityto applycontrolledandcharacterizeduniaxialorshearstraininwellcharacterized environments,wewillquantifythecompletestressstateinmaterialsexposedtohigh pressureandthedeformationmechanismsandflowstressasafunctionofstrainrateand acrossgrainboundaries. 9

10 Thelimitedstatic(orquasi static)high pressurestrengthmeasurementsperformedtodate relyonassumptions(e.g.,magicangleanalysis,peakbroadening),anddonottake advantageofnewdevelopments(e.g.,emergingnanobeamprobesandimagingmethods). Requiredarenewimagingtechniquesasafunctionoftime,whichwillrequireinturn advancesinanvilcelldesigns.thesedesignswillpermitpre definedandcontrolledloading paths,directnanoimagingofthestressstatewithnanometerresolutionatnanosecondtime scales,3dtomographicmappingofstrainofgrainsincompositematerials,andfull definitionofthestressstateasafunctionofmaterial,pressure,andloadingrate. Determinationofstresstensorsacrossmaterialmicrostructuresasafunctionofhydrostatic anddeviatoricstressesprovidescriticalinputtotheory,modeling,andsimulation.the resultswouldpotentialprovidethebasisfornewphysicallybasedmodelsforhighp T strength,includingstrainratedependence.thisinformationisofcrucialimportancefor weaponsphysics,buttherearealsoprofoundimplicationsforgeoscience,astrophysics,and planetaryphysics Synthetic chemistry frontier Pressurecanbeusedasanovelreactivevariableinchemicalsynthesis.Byinterrogating intra andintermolecularbondcharacteristicsusingnovelx rayandopticalspectroscopies, byutilizingtime resolvedprobesfollowingcompression,andbyusingtheorytodevelop recoverystrategiesandelucidatingthermodynamicpathdependencies,wewillpredictand controlchemicalreactionofnovelmaterialsandtherebydevelopabetterunderstandingof thedeeperintramolecularandintermolecularinteractionsunderextremeconditions. Asonethelargestrangesofanyexternalvariable,pressurecanbeusedasatoolor catalyst foraffectingnewchemicalreactionsandbondingconstructsnotobservedunder atmosphericconditions,openingupintriguingpossibilitiesforthediscoveryofnewmatter andnovelmethodsofsynthesis.pressureincreaseslocalreactantconcentrations,producing molecular(steric)configurationsthathavebeenshowntoinfluencetransitionstatesor intermediates,andresultantproductspeciesalongthereactioncoordinate.the combinationofcontrollableandwell definedhigh pressure/temperatureconditionsoffered bymodernhigh pressurecellsdevices,combinedwithadvancedtoolsforprobingthese molecularstatesalongthereactioncoordinate,suchasopticalandvibrational spectroscopies,x rayspectroscopies,andx rayandneutronscatteringmethodsoffers excitingpossibilitiesforcontrollingchemicalreactionsanddiscoveringordesigningnew materialsundertheseconditions. Thechallengestoprobingchemicalreactionsunderhigh pressure/high temperature conditionsincludesmallsamplevolumes,thepotentiallylowthresholdsformaterial damagesubjectedtoionizingradiation,alackofmethodsfortemporally controlled pressurizationcombinedwithtransientprobesofbond breaking/makingsteps,anddearth ofin situtechniquestypicallyusedinthechemicalsynthesislaboratorywithinhighpressuredevicesintheabsenceofrecoveryandpost mortemanalysis.structural relationshipsforawidervarietyofchemicalfunctionalitiesunderarangeofhighpressure/temperatureconditionsandpathwaysareneeded.thisfundamentalknowledge, combinedwiththeoreticalcalculationsofhigh pressurereactantsurfaces,couldeventually leadtorationaldesignofsynthetictargets,muchlikethecurrentstatusofthefieldof 10

11 organicchemistry.hereagain,wemustmovefromobservationtocontrol,anapproachthat sofarisessentiallylackinginhigh pressurechemicalsynthesisatpressuresabove1gpa Optimized new materials Asindicatedabove,highcompressionhasthepossibilityofcreatingnew,quenchable materialswithenhancedpropertiesandfunctionality.byusingthealteredbondedstates undersuchconditions,wewillcreatenew,usefulmaterialsthatarerecoverableto,and stableat,ambientconditions.combinedwithdevelopmentsintheorytopredictmaterial properties,suitablecatalysts,andrecoverypathways,wewilldevelopnewmaterialswith enhancedsuperconducting,magnetic,thermoelectric,hydrogenstorage,solar,andphysical properties. Thehighesttemperaturesuperconductingtemperaturesarefoundunderpressure.For example,thehg Ba CacupratehastheTcof164Kmeasuredin30GPa;however,thehigh Tcdoesnotpersistwhenrecoveredtoambientpressure.Cantheseactivemechanismsbe understoodandharnessedunderambientormoderatelycoolenvironments?other possibilities,suchas green hydrogenstoragebasedonh2oices,andthepredictionand creationofvariousultra hardmaterials,somewithpropertiessuperiortodiamondare expectedtobepossibleinthefuture.itisknownthatdoubleandtriplebonds,forexample, areparticularlyactiveunderhigh pressureconditions.polymerizationreactions,drivenby electronicinteractions,occuras reactants andarebroughtintoclosercontactwithapplied pressure.smallmolecules,suchasn2,anditsisoelectronicrelativeco,havebeenpredicted andshowntopolymerizeundermoderatepressures.apolymericformofcohasbeen recoveredtoambientconditionsandshowntobehighlyenergetic,decomposing exothermicallytogaseousco,andofferingtheexcitingpossibilityofnewclassesof explosivematerials,preparedintheabsenceofcatalystsandsolvents.stillotherexamples includetherecentcreationofbulkmetallicglassesunderpressureandtheprospectof makingothertypesofglassesbasedontheobservationofpressure induced polyamorphism. Forthese,thechallengeistherecoveryofthesematerialsinlarge quantitiesforusefulapplications.thereareobviouslysignificantimplicationsformaterials science,energyscience,andnationalsecurityscience Radiation-induced high-pressure chemistry Ionizingradiation(e.g.,x rays,visiblelight,neutrons,andprotons)canbeusedasanovel sourceofelectronicrearrangementinchemicalsynthesisaswellasanunwelcome mechanismofdamage.bypredictingbondionizationforthesynthesisofdesiredproducts withagivenfunctionality,andbyinvestigatingmolecularbondbreakingviatime resolved x rayandopticalspectroscopies,wewillbeabletodesignchemicalreactionstotargetnovel materialsaswellascalibrateandevencontroldamage. Understandingthebehaviorofmaterialsunderextremeconditionsofhighpressureand highradiationfluxisvitalforunderstandingandimprovingtheperformanceandreliability ofnuclearweaponsandnuclearreactorcomponents.inaddition,assomanystudiesof materialsareconductedusinglasers,neutrons,andx raybeamsaspartofcurrentandnext generationsources,itisvitaltoquantitativelycalibrateandassessthedamagecausedby ionizingradiation.wehavediscoveredthattherateofdamagefromx raybeamshasa strongandreproducibledependenceuponthepressure(atleastinthecaseoftatb, 11

12 slowingwithpressure),whichsuggeststhatmaterialscanbestudied,despiteradiation damage,bysubjectingthemtosufficientpressuresorusingtime resolvedprobes. Techniquesusedtostudyradiation inducedchemistrytodateincludewhitebeamenergydispersivex raydiffraction,x rayramanspectroscopy,andmonochromaticangular dispersivex raydiffraction.samplesareinterrogatedbothbeforeandafterradiation bombardmenttoassessmechanismsandratesofdamage.thechallengewillbetodevelop additionalprobesandtousediagnosticinrealtimetodetermineatomicandelectronlevel mechanismswithvaryingsources(light,neutrons,varyingenergy,varyingx rayflux).the benefitsofthisworkwouldbetwofold:(1)developingquantitativebenchmarksfor radiation induceddamageinmaterialsand(2)usingvariouskindsofradiationin combinationwithpressure,temperature,andotherfieldsfortherationaldesignofnew materialswithnewpropertiesandfunctionalities Earth science, planetary science and astrophysics Staticcompressionscienceiscreatinganever expandingpicturewindowofincreasing clarityandresolutionontheinteriorsofourplanet.despitethisadvancingvision,many regionsoftheearthremainpoorlyunderstoodintermsofmaterialproperties.anexcellent exampleistheearth score.thisregionoftheplanetismainlycomposedofiron,butina statethatisfardifferentfromtheelementfoundnearthesurfaceoftheplanet.ironhas interesting,ifnotunusualpolymorphism,elasticity,andstrength;therearedramatic changesinchemicalandmagneticproperties,andironisevenasuperconductorunder pressure.weneedtounderstandnotonlythehigh densitysolidphases,butalsothefluid statestopressuresabove350gpa.thisinformationiscrucialformodelingtheearth s magneticfieldanddeterminingthetemperaturedistributionandheatflowfromthe interior. Anotherrichareaofstudyisthecore mantleboundaryregion,whereoxideandsilicate phasesexistthatareneverseenontheearth ssurfaceandhavecompletelydifferent physicalandchemicalpropertiesfromnear surfacerocksandminerals.moreover,advances inobservationalplanetaryscienceandastronomyhaveledtomaterialsquestionsabout bodiesthroughoutthecosmos.byreachinghigherpressuresandtemperatures,andby makingaccuratedeterminationsofthephysicalandchemicalpropertiesofplanetary materialsatsuchconditions,wewilldeterminethestructure,composition,dynamics,and evolutionofthefullrangeofplanetarybodiesandotherastrophysicalobjects.thiswillhave profoundimplicationsforourcurrentunderstandingoftheevolutionofsolarsystemsand thepossibilityoflifeelsewhereintheuniverse.planets,stars,andotherastrophysical bodiesarenaturalhigh pressurechambers,sointerpretingthewealthofnewgeophysical andastronomicaldataintermsoftheircomponentmaterialswillalsoaddnew understandingofinformationthatisimportantforfundamentalphysics,chemistry,and materialsscience Life in extreme environments Wedonotcurrentlyknowthelimitsoflifeinextremeenvironments.Bydevelopingnew methodsformakinginsitumeasurementsofstructure functionofbiologicalsystems,from wholecommunitiesoforganismstocomponentmolecules,wewillbeabletodefinethe habitablezoneinthecosmos,thelimitsoflifeonearth,thepossibleoriginoflife,new 12

13 methodsfordirectedevolution,andtherebydevelopthenewfieldofhigh pressure genomics/proteomics. 2.2 Technical Grand Challenges in Static Compression Science Reaching 1 TPa and beyond Therecentdramaticimprovementsinhigh pressuregenerationandextremecondition diagnosticcapabilitiesareclearlyleadingtoimportantscientificadvances,butthisisonly thetipoftheiceberg.achievingpressuresexceeding1tpa,farbeyondthecurrentcapability of~400gpa,willenablestudiesinentirelynewregimesofphysics.novelhigh pressure apparatusdesignandmaterialsareneededtoextendcurrentpressureslimits.newanvil materials,forexample,couldbebasedoncvdsinglecrystal,nanocrystallinediamond,and newtypesofcomposites.usinganano focusedx raybeamtomeasureanvilnanostrains togetherwithlargesyntheticdiamondwithenhancedphysicalproperties,forexample,we willoptimizepressurecelldesign.suchbreakthroughswillenableopenextreme compressionlaboratoryenvironmentstomyriadofdiagnostictoolsavailableinstatic compressionstudiesandheraldnewunderstandingofmatterunderextremeconditions Developing multi-probe intelligent devices Thenextgenerationhigh pressuredesignsthatwillextendpressureslimitsto1tpaand beyondwillrequiretailoredanvilsthatenablethemeasurementofabroadrangeof physicalpropertieswithhighspatialresolution.extensionoftailoreddesigneranvilscan measurenewphysicalproperties,includingelectricalconductivity,thermalconductivity, andnmr.nano scalemanipulationandsub micronpatterningandmodificationonanvils willresultinadramaticextensionofmeasurementsthatwillbeenabledinextreme environments.theresultscouldalsoleadtonovelnanosensorswithapplicationsbeyond extremeenvironments Stress-strain states and P-T calibration Accuratecharacterizationofthestress strainstateofmaterialsiscentraltoallaspectsof high pressurescience;italsounderliesthechallengeofcalibratingpressureasonereaches evermoreextremeconditions.withthedevelopmentofmulti diagnosticprobes, abinitio calibrationsofpressurecanbedeveloped(i.e.,bymeasuringbulkmodulusanddensityon thesameloadingstate).however,wecannowgomuchfurtherandproducedetailedmaps ofthemicro strainsinsamplesfromwhichthe3dstressdistributionscanbedetermined. Thedevelopmentofmicro focusingcapabilitiesiscrucial.nano focusedx raybeamwill allowmeasurementsofnanostrainsinnotonlytheanvilsandgasketsbutalsothesamples andpressure(stress)calibrants.suchhigh spatialresolutionprobescanmakedetailed mappingofmaterialproperties.newtheoryandmodelingofcompositematerialsisneeded toproviderobustandreliablestress straininversions.accuratecalibrationoftemperature atveryhighpressureisalsoneeded;thiscalibrationneedstobecarriedoutbycombining staticanddynamiccompressionandtheory.addressingthesetechnicalchallengesis requiredinordertoopenextremecompressionenvironmentstothemyriadofdiagnostic toolsavailableinstaticcompressionstudies. 13

14 2.2.4 Advancing x-ray methods Inelasticx rayspectroscopiessuchasx rayramanspectroscopy(xrs),x rayabsorption spectroscopy(xas),x rayemissionspectroscopy(xes),extendedx rayabsorptionfine structure(exafs),nuclearforwardscattering(nfs),andnuclearresonantinelasticx ray scattering(nrixs)willbeharnessedtointerrogatedeepcore levelbondingchangesand phonondensityofstates(dos)determinationsunderextremeconditions.usingtechniques rootedinthephononmodulationofmossbauernuclearenergies,thephonondensityof statescanbedetermined.inthexas,xes,andexafstechniques,valenceelectronicstates areprobedbyphotoelectronabsorptionandemission.temperaturecanbedeterminedby appropriatefitsofthephonondos,whichcanallowpotentialnovelmethodstoascertain sampletemperatureunderextremeconditions.forexperimentsperformedtodate,be gasketsareusedtoallowx raysintoandoutofsampleregion.thereisalsolikelytobe sampledecompositionwithbombardment.xesisusuallyachievableforprimarilyheavier atoms.xrsrevealsbondingchanges(e.g.,hybridizationalteration)underextreme conditions.xasandxesprovideameasureofchangesinvalenceanddeeperelectronic changes(cf., kilovolt chemistry).thoughthesearenowestablishedtechniques,the measurementsare,ingeneral,photonlimited. NRIXSandNFSmeasurementsareonlypossiblewithhighfluxsourcesduetotheirinherent lowsignalsforconventionalhigh pressure sizedsamples(nanoliters,cubicmicrons)and therequirementforhighlyfilteredx raylightusingdoublemonochromatorstoachievemev energyresolution.thus,longdetectiontimesarerequiredduetolowsignaltonoise; moreover,measurementsatthehighestpressuresareimpossiblewithcurrenttechnology becausethesignaloverwhelmsthebackground.onlymossbauer sensitivenucleicanbe used(nrixsandnfs).mostmeasurementscannotbeperformedoverthewiderangeof pressuresneeded(e.g.,multi megabarpressures)orwithsufficientspatialresolutionto addresstheabovesciencechallenges.hence,higherbrightnessx raysourcesarerequired Real time x-ray imaging with nm resolution Theabovedualadvancesinx rayspectroscopiesandtime resolvedmethodsneedtobe combinedultimatelyforinsitutime resolvedimaging.suchimagingmethodsareessential forunderstandingthetimeevolutionofdefectsinmaterials,startingatthesubpicosecond scale.anotherexampleisthetechnologicalchallengesforstudyinginterfacesathigh pressure,whichstemsfromissuesofsensitivity,i.e.,detectingasmallnumberofinterfacial species,andselectivityandsuppressingthebackgroundoftheassociatedbulkmedia.for planarinterfacesburiedwithinopaquemedia,suchasbimetallicinterfacesinmetal,grazing x rayscatteringcouldbeuseful.butforburiedopaquecomplexinterfaces,suchasthegrain boundariesinsideapolycrystallinemetal,goodtechniquesdonotyetexist.onesuggested possibility,basedontheparadigmofnonlinearoptics,mightbetheuseofnonlinearx ray opticsusingintenseshort durationcoherentx raypulses,forexample,imaginggrain boundarystructuresusing2 photonx raymicroscopy Neutron scattering to multi-megabar pressures Neutronsarecomplementarytox rays,astheyprobenuclei(notelectrondistributions), magneticstructure,aresensitivetohydrogen,andhavehighpenetratingpower.however, neutronscatteringstudiesarecurrentlylimitedto~30gpabytheneedtouselargesample volumestoovercometheinherentweaknessofneutronsources.byusingmicro focused 14

15 neutronbeams,higher intensityneutronsources,andlargersamplevolumesavailable usingnovelpressurecelltechnologies,neutronscatteringmeasurementscanbeperformed toabove100gpa.thegoalisaccuratemeasurementstoatleast300gpatoaddressthe scientificchallengesdescribedabove.thesemeasurementsincludebothelasticscattering (e.g.,diffraction)aswellasthemoredifficultinelasticscattering(e.g.,spectroscopy) measurements.meetingthesechallengesrequiresadvancesinbothhigh pressureapparatus (e.g.,largersamplevolumes)andsignificantincreasesinneutronflux notincrementally butbothbyordersofmagnitude.suchadvanceswillenablethenumerousstrengthsof neutrontechniquestobeextendedtoextremecompressions Challenge of liquids and amorphous materials Theinherentweaknessofscatteringfromliquidsandamorphousmaterialshaslonglimited theirstudy.yetawiderangeofnovelextreme conditionsphenomenaexistsinsuch materials,includingbothpolyamorphismandliquid liquidphasetransitions.wecurrently havealimitedunderstandingofthenatureofamorphousmaterialsunderhighstaticand dynamicpressures.howaretheatomsormoleculesdistributedspatially,andwhatisthe rangeoflocaldensityvariations?whatnewprobescanbringinsightsintoliquid liquid transitionsandmeltingphenomenaathigh pressureconditions?howcanmeltingbe definedordetermined(formetals,smallmolecules,etc.)?likewise,second order transitionsbetweenamorphousphases,suchasglasstransitionsinpolymers,aredifficultto discernwithcurrenttechniques.methodssuchasneutronandx rayscattering(sans,saxs, pairdistributionfunction)currentlygiveinformationaboutthedistributionofatomicpairs inamorphousorliquiddomains,butthescatteringcross sectionsarelow,signalsareoften difficulttodistinguishfromdiamondcomptonscatterorotherbackgrounds,andanalysisis difficult.acousticmeasurementsusedtoderivebulkvolumetricinformationarefrequency dependentanddonotofferatomic levelinsightsintocompressiveresponses. Thisareaofstudywillrequiredevelopingnoveldetectortechnologiestoenableinelastic Comptonscatteringtoberemoved,extendingneutronscatteringtechniquestohigher pressures,andusingnano imagingtechniques.forexample,newmethodsareneededwith enhancedsignals(orenhanceddetection)forinterrogationofamorphoussamplesathigh pressuresinsmallsamplevolumes,coupledwithhighaccuracyknowledgeoflocal temperatureandstressstates.potentialimprovementscanbegainedfromback drillingthe diamondanvilsalongtheincidentx rayaxis,useofslits,orincreasedflux.likewise,neutron scatteringmeasurementswithsmallerfocusedbeamsinlargevolumesatevenhigher pressures,asdiscussedabove,willopenupalargenumberofpotentialmeasurementson amorphousphases.themeasurementsmustbecoupledwithmodelingeffortsaimedat capturingandinterpretingthestochasticnatureoftheseformsofmatter.finally,extending thesenewtoolstothetimedomainandcombiningthemwithtransientmeasurementsof transportproperties,viscoelasticproperties,andkineticsofliquid liquidandliquid solid phasetransformationswillbenecessaryforinterpretingthedynamicaspectsofphase diagrams,improvingequationsofstateforamorphousormultiphasematerials(including melt),andevaluatingbondinginnewformsofmatter Filling the strain rate gap: Static to shock Interestingandlargelyunexploredphysicsliesbetweenthestaticanddynamictime scales athighpressure.modetransitions,aswellasphasetransformationkinetics,areknownto 15

16 bestrongfunctionsofloadingrate.bydevelopinghigh pressurecellswithprecisely controlledandcalibratedloadingratescapableofcompressionratesto10 5,cyclesatkHz, andsingle shotrapiddecompression,andbydevelopingdetectorsandprobesconsistent withthesenewexperimentalcapabilities(sub micronspatially,subnano second temporally),wewillelucidatetherate dependentpropertiesforthefirsttime. Systematicstudiesofphasetransitionscanbeachievedusingtunableprecisepressuredrivesinconjunctionwithtime resolveddiagnosticprobes(e.g.,x ray,neutron,andlaser). Thetime resolvedprobecanbesynchronizedandtimedtoselectivelyinterrogatethe sampleasitisdrivenacrossthephasetransition.thedynamicdiamondanvilcell(ddac)is oneexampleofatunablepressure drivesuitableforthesetypesofstudies.pulse selection hardwareandhigh speeddetectorsathigh performancesourcesarenecessarytechnical componentstoperformtheseproposedstudies Transport properties Therearefewmeasurementsofthermalandtransportpropertiesathigh pressures/temperatures.examplesofdesiredmeasurementsincludethermalconductivity, diffusivity,andviscosityinsmallvolumesathigh pressure/temperatureconditions.the presentstate of the artconcernstheuseofdesigneranvilsforresistivitymeasurements, NMRandrolling ballviscositymeasurementsatlowpressures,andlaser basedfoilheating methodstoestimatethermalconductivities.thesechallengescouldbemetwithadvancesin pulse probenmrmethods,developmentofnon magneticdiamondcellscapableofhigh pressures,exploitationofconfocal,ultrafastopticalmethodsforbothheatinganddetecting temperaturechangesspatiallyinhigh pressuresamplevolumes,anddesignofnew embedded probeanvilsformeasuringheatflow Thermochemical measurements at multimegabar pressures Inadditiontoconstituitive,transport,anddynamicalmeasurements,thereremaingreat challengesinmeasuringfundamentalthermochemicaldataneededtoaddressthescience challengesdiscussedabove.newtechniquesareneeded,forexample,todeterminefree energies,enthalpies,entropies,andheatcapacitiesofpure,complex,andnanophase materialsstartingatevenmodestpressures.acombinationoftime resolvedoptical methodscombinedwithhighlysensitivenanolithographictechniquesneedtobedeveloped formeasurementstobeperformedinconcertwiththeinsitustudiesdescribedabove. 16

17 3. Dynamic Compression Science Dynamic compression science has historically been a field in which measurements have been made (primarily) at the bulk or continuum level. Details of the effects of phase transformations,defectgeneration,chemicalcomposition,shock inducedchemistry,andthe effect of grain boundaries and grain orientation on dynamic material response have only beeninferredthroughwaveprofileanalysisand/orpost experimentexamination.thatsaid, thelevelofdetailgatheredinthefirstdecadesofcompressionsciencewasadequateforthe simulationandmodelingcapabilitiesavailableatthetime,andtheweaponscommunitywas abletodesignmodernweaponsystemsthroughacombinationof simple simulationand experiment.thisisnolongerthecase. Today, we are on the verge of transforming dynamic compression science from science focused on developing understanding at the continuum level to a scientific discipline focused on developing understanding at the atomistic and mesoscopic scales, ultimately leading to the linking of scales and the ability to predict and control performance under dynamic loading conditions. Our current modeling and simulation capabilities have unprecedented temporal and spatial resolution: a result of modern platform development andbetterunderstandingofmaterialresponse(thoughwehavenotyetreachedsimulation linking all scales), but we have not reached our goal of fully predicting and controlling material response. Reaching this goal will require a suite of new diagnostic tools and capabilities that can help answer the scientific challenges, described below, and provide validationdatafornextgenerationsimulationcapabilities.wewillnotsucceedifwedonot meetthesechallengingopportunities. 3.1 Scientific Discovery Challenges: Dynamic Compression Science Kinetics and mechanisms of melting, freezing, and solid-solid phase transformations Along standingproblemincompressionscienceistheidentificationofthelocation(in Pressure Volume Temperature[P V T]space)andcharacterizationofphase transformations,includingmelting,freezing,solid solidtransformations,andtheir associatedkineticrates.ofconcernisthefactthestaticanddynamicmeasurementsdonot alwaysyieldthesamelocationinphasespace.thiscouldbearesultofdifferences associatedwiththetransformationpathdependenceinp V Tspace,and/ortheeffectof strainrate(whichcanincludebothloadingandreleasepaths)onthetransformation dynamics,orsimplythatthesamplemustbesuperheatedduringshockexperimentsto observethetransformationonthetimescaleoftheexperiment.moreover,wehaveveryfew techniquesforcharacterizingphasetransformations,particularlydynamically.inprinciple, pyrometrictechniquesshouldyieldcharacteristicsignalsassociatedwiththetemperature arrestthatisindicativeofaphasetransformation,andtransientx raytechniquesshould providestructureinformationthatultimatelycouldbequantifiedtoyieldfractionalphases asafunctionoftime.neithertechniquehasreachedamaturitylevelthatunambiguously meetsourneeds,andthedatawillbeunimportantifourtheoreticalconstructsregarding transformationareinadequateoratbestphenomenological.thus,inadditiontoadvanced 17

18 diagnostictools,werequirethedevelopmentoftheoriesthataccuratelyrepresentthe physicsoftransformationsandcapturethepathandratedependenceeffects Warm dense matter (WDM): metallization, release around critical points Themetallizationofmatterwhensubjectedtoextremesoftemperatureandpressurehas beenconsideredandpursuedsincethedevelopmentofbandstructuretheoryandthe recognitionthatextremepressurecouldcauseaclosureofsuchbands.thatsaid,metalscan alsobehavecounter intuitively.forexample,lithiumandsodiumcanbecomeinsulators undertheextremesofpressure.perhapsmoreimportantly,theclassofmatterknownas warmdensematter(wdm)liesin no man sland. Itisnothotenoughfordirectapplication ofthomas Fermi,yettoohottoaccuratelycalculatethepropertiesusingclassiccold curve techniques.moreimportant,wehaveveryfewmethodsforcreatingandcharacterizingsuch matter,bothoninitialcompressionandsubsequentrelease.asanexample,ifonecould reliablymeasuretheconductivityundertheseuniqueconditions,whilesimultaneously measuringthetemperature,pressure,andvolume,thedatasetobtainedwouldchallenge andexpandourcurrentthinkingregardingtheequationofstate(eos)ofmatterinthis regime.furthermore,ifwecouldcreatecomparableconditionsinastaticsetting,wecould makeaconnectiontobetweenstaticanddynamicregimesthatwillimproveouroverall understanding.thus,thereisasignificantneedtodevelopcapabilitiesforcreatingand diagnosingthisstateofmatter,bothtodevelopafundamentalunderstandingofsuchthings asthenatureofmatteratthecoreofplanets,butalsotogainanunderstandingthatcan impactapplicationssuchasfusion,first wallmaterialstudiesfortheinternational ThermonuclearExperimentalReactor(ITER),andenhanceourunderstandingofnuclear weaponperformance,includingboost Evolution of microstructure under dynamic loading including defect distributions Mostmetallicmaterialsarepolycrystallineinnature,suchthattheyareanaggregate compositeofmetallicsinglecrystals.asthepolycrystalisdeformed,thesinglecrystals interactwitheachothersothattheinternalstresswithinthepolycrystalishighlynonuniform.simulationspredictafactoroftwoorsodifferencebetweentheminimumand maximumstresswithintheaggregate.ifthesematerialsaredeformedagreatdeal,the temperaturewillcertainlyincrease,andtheybegintodevelopdamagedregionsandfailure zones.thelocationofthesedamagedandfailedregionsishighlydependentupon microstructuralcharacteristics(e.g.,grainsizedistribution,impuritycontent,grain boundarystrength)andthenatureoftheloading(e.g.,timerateofloading,totalstrain, maximumstress).figure1showsanimageoftantalumdeformedbyplateimpactloading. Thisimagedisplaysasnapshotofamaterialthathasfailedbytheprocessofpore nucleation,growth,andcoalescence(aductileprocess).notethatthefailedregionsare spreadoutandindicatethatthephysicalprocessesinvolvedarestochasticinnature. Predictingwhenandwherematerialfailurewilloccurwithcurrenttheoreticaland computationaltoolsisstilloneofthebiggestchallengesfacingthematerialmodeling community.failureisthefinalstepinacomplexphysicalprocessofmicrostructural evolution.theabilitytounderstandandpredictwhenandwherefailurewilloccurforany typeofaggregatematerial(e.g.,polycrystallinemetals,highexplosives,concrete,fibrous composites,etc.)requiresthatwenotonlyunderstandthestatisticsofmaterialinitial 18

19 conditions such as grain size and morphology (for the case of polycrystalline metals), inclusion content and location, grain boundary shape, misorientation across grain boundaries, etc., but also how these quantities combine and evolve under service environments leading to failure. Deformation events that add to the initial heterogeneity are such things as inhomogeneous temperature change, dislocation cell formation, slip band formation, twinning, and phase transformation. Further microstructural evolution leads to discrete damage/failure processes, such as pore (ductile materials) or crack (brittle materials) nucleation, growth and coalescence, shear band formation and growth. These events also occur in three dimensions, of course, so we need to push our experimental and theoretical/computational capabilities to deliver this type of information in 3D. A two dimensional characterization will never allow us to achieve success. Fig. 1. Orientation Image Map of a deformed tantalum plate impact sample. Thus, we have the need for a new experimental capability to track, in situ, the 3D microstructural (including defect distributions) and temperature field and their evolution. The information is needed to characterize and develop associated theories that incorporate the details of defect distributions leading to pore nucleation, pore growth and coalescence, dislocation cells, slip bands and twins, as well as shear bands Experiment/theory convergence: Developing the ability to reproduce simulations of real systems for better understanding of experimental observations. One of our greatest challenges is to be able to conduct experiments and perform associated simulations that are so precise in their initial conditions (such as the defect distribution and/or polycrystalline orientations and sizes) that we are modeling the real and not the ideal system. One approach would be develop experiments that directly evaluate the results of molecular dynamics (MD) simulations, such as an LINAC Coherent Light Source (LCLS) experiment with exactly the same number of atoms as an MD simulation, and validating at the appropriate length scale. Moreover, experiments might be designed to probe a particular physical regime to isolate and provide a means for better comparison with the simulations. Too often, we end up compromising on both the experiment and the simulation, with results that need interpretation or speculation to make the connection between the experiment and the simulation. Thus, the development of a series of experiments that are standards and/or the choice of simulations that we can properly diagnose in an experiment is critical to develop real understanding and to move from observation to control. 19

20 3.1.5 Resolving the details of detonation and shock-induced chemistry It has been the firm belief of many in the Energetic Materials (EM) community that the key to predicting explosives behavior for both performance and safety lies in the intimate understanding of the molecular-level processes. Energetics are complex systems that involve inter- and intramolecular bonding, numerous morphologies, different polymorphs, crystal defects, impurities, and component inhomogenities. EM can be made stable under ambient conditions, can be stimulated to energetic decomposition, will crystallize into a knowable structure with a given density, and can be fabricated into incredibly elegant shapes and strong mechanical structures. The crystal structure and intermolecular bonding strongly affect the density of the material and, thus, the energy delivered per unit volume of explosive. The molecular structure and the intermolecular bond energies will also affect the rate at which energy put into a molecule might escape to the bulk material, which in turn strongly affects the sensitivity and safety of the compound. Unfortunately, these molecular-level processes are not known even for systems that lack many of the complicating factors listed above. Without this detailed data, we cannot develop molecular-level predictive capabilities. Present theories can only lump most of the chemistry into overall reaction rates or energy release rates. The overall goal is to develop a complete timedependent description of detonation and the evolution of the product s equation of state for military purposes as well as to facilitate the introduction of new energetic materials for military, counter-terrorism, surety, and industrial applications. These new energetic materials include explosives, rocket and gun propellants, and pyrotechnic devices. Various driving forces (which can be different for the wide variety of applications) include increased performance, increased safety margins, decreased cost, and decreased environmental impact. It is important to have optimal screening measures so that confident decisions can be made more rapidly on whether to proceed or not with a particular formulation. We need to develop the ability to screen, measure, and predict the performance of new or proposed materials for optimal use and/or unique applications Discovering new phases and forms of matter at ultra-high compression using tunable pathways and controlling reaction chemistry through pressure and temperature Asstatedintheintroduction,oneofthekeycontributionsofcompressionsciencehasbeen throughdiscovery,asgeneratedbynovelextremesofpressureandtemperature.for example,thenatureofthephaseboundaryinsodiumandlithiumwascompletely understoodwhentheexperimentelucidateditsconcavedownwardnature(inp Tspace) and,ingeneral,thatthenatureofbondingcansignificantlychangewithcompression (imaginecoreelectronparticipationintheextremes).furthermore,chemicalreactionsthat areforbiddenonthegroundstatepotentialsurface(e.g.,woodward Hoffmanforbidden) maybeaccessibleundertheextremesofpressureandtemperature.thus,theexplorationof potentialenergysurfacesasafunctionofpressuremayoffernewroutesforthesynthesis and/ormanufactureofmaterialsthatwouldotherwisebeunachievable.theclassicexample ofthisistheconversionofgraphitetodiamondusingpressure/temperature,butother examplessuchastheformationofpolymericnitrogenhavedemonstratedtheutilityofthese concepts.thus,usingabinitiocalculationsasguides,andthroughthedevelopmentofa robustexperimentalprogram(includingtheabilitytotunepressureandtemperature throughtheproperchoiceofwaveprofile,e.g.,ramp,shock,etc.),wewillbeinapositionto predictand/ordiscovernewmaterialsthatmayhavefunctionalbehaviorthatmeetour needsunderextremeserviceconditions(e.g.,armor,highneutronfluxesofreactors,etc.). 20

21 3.1.7 Discovering and understanding of the partitioning between dissipative and non-dissipative mechanisms Theconceptofashockiswelldefined.However,theunderlyingprocesseswithintheshock waveandthepartitioningbetweendissipativeandnon dissipativemechanismsarenotwell characterizednorwellpredicted.predictingandmeasuringthehugoniotelasticlimit (HEL)andstrengthunderloadingisamust.Wecurrentlyhavelittlemeansformeasuring andcalculatingtransportproperties,andtherefore,ourdescriptionoftheloadingprocessis incompleteandwecannotconnectwiththeory.wemustdevelopdiagnosticsatthe appropriatescale(e.g.,diffractionforatomic levelinformation)thatallowtheelucidationof mechanismsimportantinallrateprocesses,includingtransitionfromshocklessloadingto shockcompression,andprovidephysicaldetailsthatresolvephenomenologicalmodelsof deformationsuchastheswegle Gradyfourthpowerlaw.Inadditiontobetterexperimental characterization,wehaveaneedfortheabilitytopredicttransportproperties,damage evolution,andlocalizationphenomena Determine the role of shear in deformation processes Shearcanplayamajorroleininitiatingandcontrollingthephysicalandchemicalprocesses thattakeplaceunderdynamicloading,butneedstobequantifiedandbetterunderstood. Wecurrentlyhavelittleexperimentanddiagnosticcapabilitiesforresolvingshearsoasto ascertainitsroleindynamicmaterialprocesses,includingchemicalreactions.forexample, wewouldliketoknowthemechanismsthatcauseinelasticdeformation,damageevolution, andfailureandtheextenttowhichshearcontributestotheseprocesses.experiments designedtoexamineshearcontributionswouldprovidedatathat,inturn,wouldguidethe developmentofapredictivecapabilitybyprovidingamechanisticunderstandingof structural,chemical,inelasticdeformation,fracture,andsecond orderphasetransitionsthat canbedrivenbyshear Develop understanding of the role of interfacial boundaries Thereisalackofunderstandingoftheinteractionofwaveswithboundaries(including spallation)andthestabilityofmaterials(orlackthereof)thatresultinthedynamicmixing ofmaterialswithinlocalenvironments.thus,wemustconductcontrolledexperimentswith high resolutiondynamicimagingtomeasurethevelocityfieldevolutionanddynamic mixingasafunctionoftime,whichwouldimplytheneedformeasuringflowwithinopaque materials.furthermore,thisinformationisoflittlevaluewithoutbasictheoriesfor predictionofthelocalgeometriesaswellasthermodynamicstatesinthemixedphase regions.themixedphaseregionsincludeheterogeneousinterfacesofgrainstructureand theirevolution.inaddition,weneedtounderstandthemorphology,sizeofparticulates,and theirrelationtoglobalvariablessuchasdensityevolution.finally,weneedtheabilityto determinematerialpropertiesfromobservationsofinterfacialevolutionundergeneral loadingconditions,whichwillallowustopredictandoptimizematerialbehaviortomeet ourfunctionalrequirements Develop an understanding of the transition in material plasticity and damage evolution across the thermally activated to shock to drag control regimes Thereisalackofunderstandingoftheoperativemechanismsofdefectgenerationand storageacrossthetransitionsfromthermallyactivatedplasticityunderuniaxialstressto 21

22 uniaxialstrainshockloading.furthermore,asweincreasestrainrate,thetransitiontodrag controloccursasrelativisticeffectsbecomeoperative.todate,onlysurfacediagnostictools havebeenappliedtostudyingthesefascinatingtransitionalregimesinplasticitywithlittle insight.accordingly,theoryhasnotachievedphysicallybasedmodelstoaddressthese transitionsowingtoalackofmechanisticunderstandingofthechangesindefectgeneration, motion,andthereafterstorageprocessesasafunctionoftheappliedstrainrate. 3.2 Technical Grand Challenges in Dynamic Compression Science Characterization of melting, freezing, and solid-solid phase transformations Weneedtodevelopacomprehensivedefinitionofmelt.Weknowthatlossofshear modulus,lossoflong rangestructure,andlossofautocorrelationareindicators,andwe needdiagnosticsthatconnecttothisdefinition.(wealsorecognizethatthereisadistinction fromamorphoussolids.)toolsshouldincludethefollowing: Phonondispersionmeasurement LCLSdiffractioncorrelationinstrument? Measurementofshearmodulus Fullyutilizeadvancedlightsources Coherentimaginganddiffraction Tomography(grainscalemicrostructure) Timeresolution(kinetics) Diffusescattering(statisticalrepresentationofdefects) Smallanglescattering(nucleationandgrowthkinetics) Real-time diagnostics for dynamic mapping of the thermo-mechanical field Wehaveaneedtodeveloppredictivecapabilitythatdescribesthegenerationandevolution ofdefectsthatcontrolcontinuummaterialproperties.wemustdevelopandfieldmultiple diagnosticsforsuchexperimentstoachievethermodynamicfieldmeasurements,in particulartemperaturemeasurementsandspecificationofthefullstresstensor.these diagnosticsmustincludeinsitutemperatureandstressdiagnosticsapplicabletodifferent compressionregimesandtimescales.thiswillallowthespecificationoftime resolved thermo mechanicalvariablesatdifferentspatiallocations.thus,weneedthefollowing: Accuratetemperatureandstrain/stressfieldmeasurements o Localenvironmenttemperatureprobes o Multi axialstressprobes,e.g.,singlemoleculespectroscopy o Multi axialstrainprobes,diffraction Pre andpost experimentcharacterization 22

23 o Tomography o DiffractionContrastTomography Ability to make experimental measurements to link length scales ranging from atomic to continuum dimensions Continuumresponsedependsonmaterialbehavioratlowerlengthscales.Asuiteofinsitu time resolvedmeasurementsatdifferentlengthscalesisrequiredtovalidatetheoretical modelsastheytransitionfromonelengthscaletothenext.toreachthisgoal(need),we mustdevelopnewexperimentalcapabilitiesthatprovidetheselinkages.thelinkageof measurementsatdifferentlengthscaleswillleadtothefirstrealisticmodelsrequiredfor predictivecapability Ability to make in situ spectroscopic measurements including those of electronic structure Spectroscopicprobesprovideacharacterizationtoolformeasuringboththeaverageand localizedenvironmentaleffectsofcompression,dependingontheprobeanditspractical implementation.dataregardingtheeffectofcompressiononmolecularstructureand/or chemicalchangescanbeobtainedthroughvibrationalspectroscopies(e.g.,ramanandir absorption),whileelectronicspectroscopiesprovideameasureofthechangesin conductivity(asmanifestedthroughchangesinfresnelcoefficients)andchangesinthe potentialsurface.nuclearspectroscopies(e.g.,xanes/exafs)canalsoprovideinformation regardingbondingandnearestneighbors.thus,modernfacilitiesmusthavecapabilitiesfor implementingthefollowingspectroscopiesinordertomakestrongerconnectionwith theoreticalmodels: Reflectivity Raman X rayspectroscopy XANESandEXAFS XEL Complex loading path control Asdiscussedpreviously,theapplicationofcompressioncanprovideroutestootherformsof matterthatwouldnormallybesymmetrydisallowedorinaccessibleonthenoncompressed potentialsurface.thus,thepropercombinationoframpandshockcanprovidethe mechanismfortuningthepathandcreatinganenvironmentconducivetogeneratingnew formsofmatterorfor allowing normallydisallowedchemicalreactions.inaddition,the abilitytoquantifythepartitioningofenergybetweendissipativeandnon dissipative mechanismsrequirestechniquesthatallowforchangingtherelativecontributionsofthese processes.thus,ultimatelyachievingdynamicalcontroloftheseprocesseswillrequirethe abilitytocarefullytunetheloadingprofile,fromisentropictoshockloadingandanywhere inbetween,inordertovarythethermalcontentaswellasaccessportionsofthepotential energysurfacethatcanonlybeaccessedundercompression. 23

24 3.2.6 Develop first-order continuum analyses that produce better subscale models and capture defect evolution Manyofthecurrentdescriptionsofdynamicloadingarephenomenologicalinnatureand cannotbeconnectedina real sensetothematerialworld.asanexample,todesign optimalexperimentsfordirectcomparison,wehaveaneedforrealisticdescriptionsof inelasticdeformationthatincorporatesmaterialphenomenaatlowerlengthscales (microstructure,defects,texture,etc.).often,experimentalistsandtheoristsdefine experimentsthatare ideal inthesensethattheyarecapableofbeingperformed,even thoughtheexperimentortheorymaynotbemodeledortested.thus,weneedstronger experimentalandtheoreticalcollaborationtodefineoptimalconditionsanddiagnostics fromwhichtodrawmoreaccuratecomparisonsand,asaresult,abetteranalysisand interpretationofexperiments Learn how to conduct and diagnose experiments relevant to 3D applications Real worldapplicationsareinherentlythree dimensionalandwillofteninvolvephenomena thatmaynotoccurinone dimensionalexperiments.thus,wehaveaneedtodevelop experimentalmethodsanddiagnosticsthatachieveandquantifycontrolled3dloading conditionsinsuchamannerastoallowinterpretation.thisworkinherentlyincludesthe developmentofmaterialmodelsthatarepertinentto3dloadinganddevoidofknobs,ifat allpossible Design experiments that overlap different loading regimes and experimental platforms Wecurrentlyhaveatourdisposalalargenumberofplatformsforconductingdynamic experiments,withthezmachineandnationalignitionfacility(nif)asexamples.however, wehavenotdevelopedmethodsthatguidethebestuseofthesedifferentexperimental platformsandloadingregimes.toachievemaximumeffectiveness,wemustlearnhowto coordinateandintegrateexperimentsondifferentplatformsanddifferenttimeregimes. Whencoupledwithavarietyofvolume andtime scaleprobes(flexibilitytospanscaleson facility),thesetypesofexperimentswillaidindevelopingtheunderstandingoftheload pathandstrainratedependenceofmaterialpropertiesneededtoachieverealisticand completemodels Increase experimental throughput Weareoftenlimitedindynamiccompressionsciencebytherateatwhichwecanconduct experiments.wemustworktowardthedevelopmentofnewexperimentalmethodsthat alloweasierandfastermeasurementsofdynamicpropertieswhilesimultaneously developingnewexperimentalparadigmsforcombiningmultiplediagnosticsthatyield increasedefficiencies,decreasedcost,andfasterturnaround.thesenewexperimental methodswillallowforamorecompletesetofobservations,whichinturn,willincrease developmentofrealisticmodels,therebyadvancingthefield Develop improved materials and standards for uniform comparisons Lastly, we have a need for the development of a set of standard materials that will allow us to connect measurements on a variety of platforms and using a diverse set of diagnostics. For example, loading a 50-micron thick tantalum sample on NIF may require the development and 24

25 production of an extremely fined-grained material to ensure that the data is not dominated by grain boundaries. To make a direct comparison of this data with that obtained on guns may not be an easy task. To start, we should make gun measurements with the fine-grained material, but our results may still be confused with loading rates that may influence the shock wave rise time. They may be further confounded by time-dependent changes in the wave profile. One example is the change in amplitude of the elastic precursor simply as a function of sample thickness. Thus, connecting these disparate temporal and spatial regimes will require careful thought and analysis. Furthermore, if we could develop better impedance matching materials that are transparent, we could begin to imagine (nearly) looking in at the processes that are taking place in bulk. These observations will be required if we truly expect to achieve control. 3.3 Theory Needs and Challenges in Compression Science Anaccuratematerialdescriptioninvolvesthecharacterizationofmanyvariablesthatcan onlybecapturedinastatisticalsense,e.g.,chemicalcomposition,defectdensityand distribution,texture,grainsize,etc.ourpremiseisthattheseintrinsicpropertiesandtheir linkingacrossscalesdetermineamaterial sproperties(orfunctionality)andits performance.todevelopcontrol,weneedtoestablishthecorrespondencebetweena3d descriptionofamaterialanditsproperties,fromwhichwemaydevelopasetofprinciples thatprovideanintelligentsystemfortailoringmaterialsfunctionality.tomakeprogressin linkingbehaviorofmaterialstotheirprocessedcharacteristics,wemustdevelopand maintaintheintimatecouplingofexperimentwiththeoryandsimulation. Inotherwords,todevelop process aware modelslinkingmaterialsbehaviorwithits3d characteristics,werequiretoolsthatseektocoupleandlinkthespectrumofmaterials lengthscales fromtheelectronicthroughthecontinuumandtotheapplicationor integratedsystemlevel.infact,alonghistoryofsuccessfulmodelspunctuatesthelineageof materialsscienceinthisquest.somemodels,suchasopticaldevicetheory,relyon fundamentalphysics;others,suchastime temperatureheat treatingcurves,arisefrom phenomenology;andmost,suchasphasediagrams,combinetheoryandempirical observation.withinthepastthreedecades,thesubspecialtyofcomputationalmaterials sciencehasstrivedtoprovideadditionalmodelingtoolstothematerialsscientist,ranging from(i)fundamental(abinitioelectronicstructureandmoleculardynamics)calculationsat theatomic(usuallysinglecrystal)scale,to(ii)dislocationdynamicsandphasefield modelingatmesoscopiclengthscales,atwhichmicrostructuralaspectssuchastextureand interfacialeffectsbecomeimportant,to(iii)singlecrystalandpolycrystalplasticitymodels thatdescribe bulk materialsbehaviorthatcanbeencapsulatedin(iv)equationofstate (EoS)anddynamicmaterialstrengthmodelssuitableforengineering levelsimulations.our computationalmaterialssciencegoalsaretoenableanintegralandpredictivecapability, notpostdictive,andtoprovidealinkbetweenmaterials,design,manufacturing,and functionalitythatwillultimatelyenable control ofmaterialfunctionality. Thispanelattemptedtoenvisionthisfutureresearchpathandelucidatetheadvancesin multi scalemodelingtechniquesandalsotheexperimentalcapabilitiesneededtomeasure therequiredvalidationdatathatwillberequiredtomeetthisgoal.theheterogeneityofreal materialsandthenon equilibriumprocessesunderlyingdynamiccompressionphenomena aretwokeyaspectsabsentfromcurrentmodelsbaseduponadescriptionofaverage homogeneous,equilibriumbehavior.apropertreatmentofsuchaspectswillenable 25

26 predictionsofaprobabilisticbulkperformanceratherthanjusttheidealmacroscopic behavior.theultimategoalistodevelopthescientificunderstandingthatwillenablea tailored control ofthechemicalandspatialstructureofmaterialstobetoleranttoextreme environments,replacingtheconventionaltrial and errorapproach. 3.4 Scientific Discovery Challenges for Compression Science Theory and Modeling Track dynamic microstructure evolution in situ Theresponseofmaterialstodynamiccompressioninvolvesawiderangeoflengthscales, rangingfromindividualpoint,line(i.e.,dislocation),orsurfacedefectsatthenanometer lengthscale,tothenucleationandgrowthofvoids,twins,orproductphasesattensto hundredsofnm,collectivedislocationmicrostructureatmicronlengthscales,andfinallythe µmgrainscale.Currentcomputationalmaterialssciencetechniqueshavebeen developedforeachoftheselength(andcorrespondingtime)scales,butacorrespondingset ofdirectinsituexperimentalprobeshasnotyetbeendeveloped.thisleadstotwochoices fordesignandparameterizationofthehigherlength scalemodels:eitherpostdictivefitting oftheendstateofhighlyintegratedexperiments(e.g.,taylorcylinderimpactsorrecovered incipientspallsamples)oran upscaling ofdynamicmaterialpropertiesfromonemethod tothenext.thelatterremainsanextremelychallengingtaskandintroducesatypicallyunquantified(butpotentiallyquantifiable)errorfromonesteptothenext(abinitioelectronic structure,tosemi empiricalpotentialsformdsimulations,tomesoscaleandfinally continuum scalemodels).thus,thereisanenormousbenefittodirectinsitumeasurements ofthedynamicmicrostructureevolutionatthemesoscale,whichliesinthegapbetweenthe microscalewheretheoryismostreliableandthemacroscalewhereexperimental measurementsaremostreadilymade.twoofthemostpromisingcandidatesinthisregard arethefollowing: X rayscattering,whichissensitivetomicroscopicdefectssuchasvoidsand dislocations.anoutstandingchallengeisthe inverseproblem ofinferringsuch defectcontentfromexperiment. Microprobesonsynchrotronlightsourceshavereachedalevelofmaturitywherethe 3Dmicrostructureofavolumecontainingtensofgrainscanbemappedwithinan hourofbeamtime.thegrandchallengeistodosuchmeasurementsinsituduring staticcompressionandultimatelyduringdynamiccompression Discover new and unexpected high-pressure and temperature solid phases Thehigh (P,T)equilibriumphasediagramsofelementalmaterialsareinmanycasesstill poorlymappedout,andthesituationisevenworseforalloysandcompounds.the discoveryofthehcpεphaseofironbydynamicshockexperiments,onlysubsequently confirmedbystaticexperimentsandtheory,isalandmarkachievementthatgreatly enhancedthestatureofthatcommunity.theaccuracyandpredictivecapabilityofabinitio andmoleculardynamicshasreachedastatewherethatcommunityshouldstrivetoseek suchadiscovery,byexploringthevastregionsofphasespacewhichliebetweenthe principalhugoniot,isentrope,andisothermsthatdynamicandstaticexperimentshave alreadyaccessed.thequestionofthestructureofironatearth scoreandrelatedplanetary 26

27 scienceissuesarebeingactivelyexploredbytheseapproaches,butotherwisethisisa largelyuntappedareaprimefordiscovery Design novel experiments to isolate key physics Todate,thevastmajorityofsimulationshasbynecessitysimplifiedthematerialdescription but,asaresult,hasneglectedthematerialcomplexitythatoftendominatesbehaviorunder extremeconditions.thephysicsthatarerelevantforunderstandingthestateofmatterat extremeconditionsincludecomposition,phase,crystalstructureandstability,elastic moduli,andlocalstressoftheperfectcrystal.inaddition,realmaterialsarecomposedofa collectionofcrystallinegrainswithvariousorientations,shapes,andinternaldefectsthat playadominantroleindeterminingthematerialbehavior.suchmaterialcomplexity includesinternalvacancies,impurities,alloyelements,dislocations,inclusions,second phaseparticles,andgrainboundaryorotherinterfaces.assimulationandexperimental scalesareapproachingeachother,itiscrucialthatsuchcomplexitybeincorporatedin simulations. Tobridgethisgapbetweentheoftenidealizedtheoryandsimulationsandtheexperiments usingofteninsufficientlycharacterizedengineeringmaterials,thereisaneedfornovel experimentsinvolvingsampleswithcontrolled(oratleastadequatelycharacterized)grain anddefectstructures.simulationscanthusbeperformedonidenticalsamples(statistically ifnotexactly),andexperimentscanbeperformedwithinternalmeasurementsofstrain rate,temperature,andstressstatethatdirectlycorrelatetosimulationobservables Move beyond planar impact: Non-uniaxial strain experiments Uniaxialandhydrostaticloadingconditionshavebeenmoststudiedprimarilybecausethey arethemosteasilyachievedinexperiments,andmodeled,butrepresentonlyaverylimited subsetofstressandstraintensorstatesthatareaccessedincomplexintegrated experiments.experimentsinvolvingobliqueimpact,sweepingwaves,bulgetests,etc.,have beenperformedandmodeled,butfurtherworkisneededtounderstandthedynamic materialresponsetothesemorecomplexloadingconditionsandtoenhanceourconfidence indynamicmaterialmodelsandcodesundertheentirerangeofstressandstrainstatesat whichtheyareutilized Design novel simulations to isolate key physical mechanisms and observables Thebehaviorofmaterialfollowingachangeinexternalconditionsisdeterminedbythe defectsinsidethematerials.bydesigningsimulationsthatdirectlymodelthesekeyunit processes,simulationswillmakeabetterconnectiontotheexperimentalobservables. Today shigh performancecomputingplatformsenablethedirectmodeling,atanatomistic level,ofmaterialsstartingfromanexperimentallycharacterizeddislocationmicrostructure. Adirectnumericalsimulationoftheshockcompressionofmaterialattheatomisticlevel revealsthedeformationbydislocationmechanisms,whichmaybedirectlyobservedwith experimentviadiffusex rayscattering. 27

28 3.4.6 Develop ability to predict the kinetics of phase transitions (solid-solid, solidliquid, and liquid-solid) Materialsexistinmanystates,andthekineticsoftransformationbetweensuchstatesis poorlyunderstood.todate,heuristicmodelshavebeenfittomacroscopicexperimental measurements,suchasvelocityinterferometersystemfromanyreflector(visar)wave profilerecords,butprovidenoinsightintothetransitionmechanisms.directnumerical simulationoftransformationsprovidesinsightintothenucleationandgrowthofthe productphaseandcaninformphysicallybasedmodels.forinstance,thekolmogorov continuummodelrequiresnucleationrates,lagtimes,interfacevelocities,andother fundamentalparametersthatcanbedirectlydeterminedfromsimulationsatlowerlength scales,includingmoleculardynamicsandphasefieldsimulations.however,theselower lengthscalemodelshaveneverbeenvalidatedatextremeconditionsbyexperiment.insitu small anglescatteringexperimentsrevealthedistributionofnucleiatagivenpointintime; suchdistributionsatmultipletimescanprovideinformationonthekinetics Understand relationship between microstructure and constitutive properties (e.g., strength) during dynamic processes Thedynamicbehaviorofamaterialdependsuponitsconstitution,whichincludesphase, microstructure,andloadingpathandrate.thedevelopmentofapredictivematerialmodel forthatresponserequirestheknowledgeofthemicrostructureevolutionalongtheloading pathatthegivenloadingrate.inparticular,strengthisprimarilydeterminedbydislocation unitmechanisms.thedislocationcontentchangesduringdeformation,andtherateof changeislargelyunknown.phenomenologicalstrainhardeningmodelsaccountforthis effectinamacroscopicwaybutdonotrepresenttheunderlyingmicroscopicphysics. Mesoscaledislocationdynamicsmodelscanaccountforthismicroscopicphysics;however thesemodelsneedtobeextendedtoincludedeformation,polycrystals,crystalrotation,and experimentalinformationondislocationmobilitiesunderextremeconditions.atomistic moleculardynamicssimulationscanalsoprovideinformationonthemobilityof dislocationsatextremeconditions,includingconditionsinthepresenceofotherdefects suchasvacancies,impurities,otherdislocations,inclusions,orgrainboundaries.this microscopicevolutionofthedislocationmicrostructuremustbecapturedinacontinuum ratemodel.thevalidationofthismicrostructureevolutionisessentialandcanonlycome fromemerginginsitu,realtime,x ray,neutron,and/orprotonprobeswithhighspatialand temporalresolution. Nothingisknownaboutthemicroscopicstateofthematerialfollowingaphasetransition, forinstancethedislocationdensityorgrain(andsubgrain)structure.thehistory dependenceofamaterialelement,followingitsevolutionthroughphasetransitions,can stronglyaffectitsresultingstrengthandotherdynamicpropertiesinanas yetpoorly knownmanner,whichneedsfurtherinvestigation Understand material failure Materialfailureundershockcompressionmayresultfromthelocalizationofdeformation andduringreleasethenucleation,growth,andcoalescenceofmicroscopicvoidsorfractures mayleadtoductileorbrittlefailure,respectively.heuristicmodelsomitsuchphysics,for instance,byassumingthatmaterialfailureoccursataspecifiedmaximumcompression(or 28

29 tensilestress)ηmin(orpmin).nucleationandgrowthmodelshavebeendevelopedfora numberofotherphysicalsituationsbuthavenotbeenwidelyappliedtomaterialfailureto date.directnumericalsimulationsofmaterialfailureundershockcompressioncanreveal theevolvingporousstateofthematerialunderloadandtheunderlyingphysicalprocesses. Forexample,mesoscalecrystalplasticitymodelswithanexplicitrepresentationof nucleationsites,informedbyatomisticsimulationsofthenucleationandgrowthprocesses, canbedeveloped.dynamicinsituradiographicimaging,andeventually3dtomography,can providedetailsofthevoidgrowthprocessneededtovalidatethemodels,overcomingthe limitationsofexistingpost recoveryanalysisofincipientlyspalledsamples Resolve melting discrepancy in transition metals Despiteseveralrecentattemptsinvolvingnewtheoreticalcalculationsandstatichighpressureexperiments,thecompressionsciencecommunityhasfailedtoresolveaglaring discrepancybetweenthehigh pressuremeltcurvesinseveralbodycenteredcubic(bcc) transitionmetals,mostnotablymoandta.whereasstatichigh pressurediamondanvilcell (DAC)experimentsusinglaserheatingrevealaverygradualriseinmeltingtemperature(a fewhundreddegreesk)athighpressures,dynamicshockexperimentsandquantum moleculardynamics(qmd)simulationsbothpredictamuchsteepermeltcurve,rising thousandsofdegreeswithremarkablygoodagreementbetweenthedynamicexperiments andtheory.thefactthatseveralgroupsinboththeunitedstatesandeuropehave demonstratedthereproducibilityofmanyofthesecalculationsandexperimentsmakesthis discrepancyevenmoreintriguingandsuggestsanoverlookedexplanationthatmay potentiallyraisequestionsaboutawiderrangeofexperimentsorcalculations.forinstance, ontheonehand,theassumptionofahydrostaticstressstateandthermalequilibriumin DACexperiments,andneglectofelectrontemperatureinvirtuallyallQMDandMD calculations,evenastemperaturesapproach1ev,couldintroducesignificanterrors.onthe otherhand,staticanddynamicexperimentsareinexcellentagreementwitheachother(and withtheory)fornon transitionmetals,includingal,fe,mg,andni,whichcouldsuggestthat anintermediatesemi orderedphaseakintoaliquidcrystalmaybeaprecursortomelting forbcctransitionmetals,confoundingtheinterpretationofwhatmeltingactuallyis Understand the behavior of the full anisotropic stress state at extreme pressures and temperatures, e.g., Poisson s ratio approaching melt Relatedtothepreviouschallenge,materialpropertiessuchasPoisson sratioandstrength approachingmeltarestillpoorlyunderstood.theexistenceofnewphases,ordrastic changesinbehaviorofexistingphasesnearmelting,couldaffecttheinterpretationof experimentsandprovideinsightintovarioustheoriesofmelting,fromborn sproposed elasticinstabilitytomoremoderntheoriesofdislocation mediatedmelting. 3.5 Technical Grand Challenges for Compression Science Theory and Modeling Multiscale modeling free of ad hoc parameters: linking subscale processes to higher length/time scales Thefieldofmulti scalemodelingtodaycontainsseveraltheoreticalandcomputationaltools, whichtogetherspanthetimeandlengthscalerangesofinteresttostaticanddynamic 29

30 compressionscience.eachmodelingtool,ingeneral,containsbothphysicallybasedand non physicalquantities(parameters)thatallowtherepresentationofmaterialresponse. Thenon physicalquantitiesexistduetoourlackofunderstandingabouteitherthephysical processesthatoccurinrealmaterialsorhowtorepresentknownphysicsintoatheoryor computationaltooladequately.ourlackofexperimentalinformationaboutdynamic responsesandstructuralevolutionofmaterialsatlengthscalesofimportancetothe physicalprocessespreventsusfromdevelopingthetheoreticalandcomputationaltoolsto adequatelyachievepredictivemodelsattherelevantlengthscalesforourproblemsof interest. Theinformationdeficitcanbeaddressedthroughhigh fidelitydiagnosticsappliedtocritical experiments.eliminatingnon physicalparametersfromtoday smodelsisthegoalatall lengthscales Better theoretical tools in the mesoscale (1 10 mm) regime Themechanicsandphysicscommunityhasovermanyyearscollectivelyproduced theoreticaltoolsthathavestartedatthecontinuumlevelandworkeddowninlengthscale orattheatomicscaleandworkedupinlengthscale.althoughthesecontinuingeffortsare critical,wedonothaveadequatetheoreticaltoolsthatdescribethecomplexwaysinwhich dislocationsinteractandformsubstructuresorhowtheyinteractwithmicrostructural featuressuchasinclusions,grainboundaries,pointdefects,precipitates,dislocationsources, etc.presentpolycrystalplasticitymodelshavedemonstratedourdeficiencyindescribing thedevelopmentandevolutionofsubgrainheterogeneitiesandstructure. Thesetheoriesmustalsorepresentrealmateriallengthscalesintheirformulationinorder toeliminatemanyofthesedeficienciesandprovidemicrostructuralsizedependence,which isknowntoexistinallmaterials.atpresent,crudetheoriesattempttorepresentreal materiallengthscales,butthesetheoriesareverycomplex,lessthanphysicallybased,and computationallyexpensive.wemustdriveourunderstandingtothepointatwhichwecan representtheselengthscaledependentbehaviorswithphysicallybasedmodelsthatareas simpleaspracticallypossibleandincludesufficientinformationtolinkacrossthelength scales,whichthatparticularmodeldivides Transferable density functionals, pseudopotentials, and classical MD potentials valid at extreme conditions Presentdayinteratomicpotentialsarelimitedtotheregimesofresponsewithinwhichthey werecalibrated.thislimitationpreventstranslationtoawidersetofphysicalregimes, whichthuslimitspredictivecapability.wemustdevelopnewcomputationalframeworks thatenableawiderrangeofknowninteratomicinteractionstoallowrepresentationofthe detailedcomplexitiesofrealmaterials,whichinherentlycontaindefectsandareexposedto extremeenvironmentalconditionsofloading.particularlyfordynamiccompression experimentsthataccessextremepressureandtemperaturestates,thereisaneedfor furtherresearchintotwotechniquesthatpromisetocorrectpotentiallyfatalweaknessesin currentdensityfunctionaltheory(dft)andmdcalculations:temperature dependent densityfunctionalsandclassicalpotentialsformdsimulationsthatareelectron temperature dependent. 30

31 3.5.4 Equation of state treatment of materials beyond simply pressure and volume Avoidrelianceonsimpleseparationintohydrostaticanddeviatoricstresses Two temperature(electronandion)eos s Presentdaytheoriesarebuiltuponthesimplificationofdecouplingtheeffectsonmaterials ofthehydrostatic(pressure)anddeviatoric(shear)partitionsofstress.inreality,the equationofstateforanycrystalstructure(exceptacubicatreferenceconfiguration) compressesthroughapplicationofhydrostaticpressurebychangingbothvolumeand shape.theoriesusedtodaydonotaccountfortheeffectoftheshearresponseduring hydrostaticcompression.theoriesaccountingforthiscouplingatpresentlacksufficient experimentalinformationtoenabletheircompletedevelopmentanduse.thelackof couplingbetweenpressureandshearpreventsanadequatetreatmentofpressure dependentplasticityandcalculationofthermodynamics.additionaldatafromboth experimentsandsimulationscanbeusedtocalibratemorecompleteeosformulations. CurrentEoSframeworksassumetheBorn Oppenheimerapproximationthatelectron contributiontothethermodynamicsstatevariablesisnegligible.thisforcestheassumption oflocalthermodynamicequilibrium(lte)atallconditions.itiscurrentlybelievedthatlte doesnotexistunderstrongshockconditionsandinwarmdensematter.extending formulationstotwotemperatures(electronandion)isafirststeptowardprovidingabetter treatmentfornon LTEconditions Codes that preserve the integrity of material models Currentnumericalframeworksdonothandlesteepgradientsinloadingandmaterialstate adequately.thisdiffusesfields,preventingtheadequatetreatmentofsurfaces(either materialvariablesorinterfaces).manyofthesesteepgradientsarebelowtheresolutionof thecomputationalgrid.numericalschemesarerequiredtomoreadequatelyrepresent steepgradientsand/ortrackmaterialstatewithoutdiffusion Quantitative dynamic x-ray probes (diffraction, XANES, EXAFS, etc.) Insitudeterminationofphase Measurevolumefractionofgrowingproductphase Toacquirenecessaryexperimentalinformationatlengthscalesthatarenotpresently achievable,newdiagnosticprobeswillberequired.ingeneral,diffractiontechniquesare usedtodistinguishmaterialphaseinformationinavolumeaveragedfashion.diffuse scatteringisimpactedbytheexistenceandevolutionofdisorderinwhichthematerialscan beboththermalandstructural.ofparticularinterestisthespatialdistributionof dislocationsandtheevolutionofdislocationdensitywithdeformation,whichiscrucialin understandingtheevolutionofstrength.small anglex rayscatteringissensitivetothe presenceofdensityheterogeneityinthematerials,andthesematerialsincludeprecipitates, voids,secondphaseparticles,andphasenuclei.bothdiffractionandsmallanglescattering canbeusedtodeterminethegrowingvolumefractionofphase. 31

32 TheXANESandEXAFStechniquesprobetheelectronicstateoftheatomandaresensitiveto thelocalenvironmentsurroundingtheatom,includingnearestneighborspacing,stress,and temperature.thesetechniquesornewtechniquesmustbedevelopedtoenablethe measurementofthenucleationofthesephasechangeseventsatverysmalltimeandlength scales.inaddition,newvisualizationanddataprocessingtoolswillbenecessarytodeal withthelargedatasetsproducedfromthethree dimensionalmeasurements Develop local temperature and stress tensor gauges Presenttemperatureprobesarelimitedtothesurfaceofthesampleorareinvasiveand havethepotentialtoinfluencetheresultsbytheirexistence(e.g.,thermocouples).surface probesarebasedupontheemissivityofthesample,andtheoriesdescribingemissivityasa functionoftemperatureareinadequateforthebasingmeasurementuponemissivity. Temperatureisafundamentalquantityindeterminingthethermodynamicstateofthe materialandintheinfluencethatthethermalstatehasontheconstitutiveresponseofthe material.wemustdevelopthetoolstoenablethemeasurementofinsitutemperatureina deformingbodyatlengthandtimescalesthatareconsistentwithpresentmodelingtools (e.g.,1micronand1ns).advancementsofphotoniccrystalsthatcouldbeembeddedintoa materialsandimagesproducedwitharadiationsourcecouldholdpotentialforattaininga realthree dimensionaltemperaturefield. Aswehavediscussedearlier,wemustbegintoaccountforthecomplexthree dimensional stressstateinboththetreatmentofeosandstrengththeories.todothis,wemustdevelop techniquestomakeinsitumeasurementsofthefullstresstensorfieldinmaterialsasa functionofposition.thiswillallowustomorecompletelyevaluatethelocalconstitutive behaviorofmaterials.measurementofonlythedeformationfieldwillstillrequireusto estimatethroughmodelingthekineticresponseofthematerial.manganingaugesare presentlyusedandarelimitedtofinitevolumesandareusedfortractiononly noshear. Thepaneldidnotoffergoodsuggestionsfortechnologiesthatmightshowpromisein makingthesemeasurementsinsituandatasmalllengthscale Local structural identification in static experiments, e.g., DAC, for amorphous materials and liquids Statichigh compressionexperimentaltechniquesdowellforcrystallinesolidmaterials particularlydiffractiontechniques.thesamediagnosticcapabilitiesdonotexistforother classesofmaterialssuchasamorphoussolidsandliquids,yettheirbehaviorisnotwell characterized.wemustdevelopthediagnostictechniquestoenablethemeasurementof localscalestrain,stress,structureformaterialsthatlackcrystallinityorareatleastonly partlycrystalline D orientation image mapping to dislocation length scales under dynamic conditions Theresponseofmetallicmaterialstoexternallyimposedloadingisnotsimplyafunctionof thetypesofelementalmaterialsexistinginthematerials.theirresponseisalsoafunctionof thespatialpositioneachofthoseelementalmaterialshasinthebulkmaterial.imperfections anddefects(e.g.,grainboundaries,dislocations,impurityinclusions)alsoplayamajorrole indeterminingthedeformationbehaviorofmetallicmaterials.thespatialarrangementof atomsanddefectsinthematerialcomprisewhatiscommonlytermedasthematerial 32

33 microstructure.themicrostructurealsoevolvessubstantiallywithdeformation(distortion, dislocationmovement/evolution/arrangement,heterogeneityevolution)andwhen conditionsareextreme,thisevolutionleadstomaterialdamageandfailure.theseare unsolvedproblemsfromatheoreticalperspective.wesimplyarenotyetabletomodel thesecomplexprocessesinapredictivemanner.weneedtobeabletomeasurethe evolutionofthemicrostructureduringdynamicloadingconditionstoenableustomakein situobservationsofhowmicrostructuralheterogeneitiesevolveandleadtodamageand failure.orientationimagemapping(oim)isawell known2dtechnique,whichispresently usedtocharacterizethecrystallographicorientationofpolycrystallinemetallicmaterials. Coupledwithlaboriousmechanicalserialsectioning,itcanpresentlybeusedasawayto characterizethe3dmicrostructureofamaterialforasamplerecoveredfromamechanical deformationhistory.this2dtechniqueteachesusagreatdealaboutthebehaviorofa materialbutonlyin2dandafterthefact.togettothenextlevelofunderstanding,weneed haveatoolwhichwilltellusinformationlikeoimisabletonowbutin3dandduring dynamicloadingresponses Extracting useful information from high-resolution 3D data (e.g., from 3D tomography or large-scale simulations) Asourabilitytoproduceverylargeexperimentalorcomputationaldatasetsbecomes greater,sotooistheneedtobeabletoextractusefulphysicsinformationfromthoselarge datasets.aswebegintothinkabouthowmaterialmicrostructuresevolvetoproducean observedbehaviororaswebegintobeabletousenewphysicsunderstandingtoenableus toproducematerialmicrostructuresthattakeadvantageofinherentheterogeneitiestoour advantage,itwillbeincreasinglyimportanttomakethelinkingbetweendifferentphysics events.forexample,wemaywishtoderiveanevolving3dvelocity,strain,orstrainrate field,byperformingimagecorrelationsfor100time sequenced3dmicrostructuralimages tothelevelofresolutionoftheimages.thiswillrequirecharacterizingeachimage(oim typeinformation)butalsolinkingeachimagetothenextimageornextfewimagestobe abletoproposeanevolvingfield.thesamecanbesaidfortheanalysisoflarge scalemd calculations.muchinformationisproducedduringthosesimulationsandthecorrelationsof eachatomwithitsnearestneighborswilldefinealatticestrainfieldbutalsomayhelpto defineanewsolidphasedependinguponthelocalstructure.theanalysesperformedwill generallyhaveabasisinaparticularphysicsquestion,whichwemaywishtoaddress.many oftheprocesseswehavediscussedherehavebeenaroundtheconceptofevolvingstatistics. Wewillalsoneedhigherorderstatisticalmodelstobeabletotractablycapturethestatistics ofmaterialbehaviorintosomethingwhichwecanusetohelpuslinktheevolutionof heterogeneitiestoobservedordesignedproperties.wecanalsousethesestatisticalmodels tohelpdefineinitialconditionmicrostructuresformd,phasefield,andpolycrystalmodels thatrepresentrealmaterialsofinterest,whichwillalwaysbeginataninitialstateof heterogeneity(defectstructure). 33

34 4.0 Conclusions Theworkshopofferedanopportunityforopendiscussionoftheproblemsandchallengesin thefieldofcompressionscience.theseproblemsandchallengespresentopportunitiesfor advancingourfieldandmovingthefieldfromthatofdiscoveryandobservationtothatof predictionandcontrol.thistransitionrequiresthatwediagnoseanddevelopan understandingofmaterials,notinanidealsenseoftheoryalone,butalsoinareal world senseofexperimentandmeasurement.tomakeprogressonthesehigh levelgoalsrequires thecommunitytomeetasetofchallengesthatincludethefollowing: Acquiretimeandspatiallyresolvedinsitumeasurementsatalllengthscales(i.e., atomistic,micro,meso). Discovernewphysicsandchemistryinextremeenvironments. Incorporatematerialcomplexityintomulti scalesimulationstoachievepredictive capability. Unifystaticanddynamiccompressionunderstandingacrossrelevantlengthandtime scales. Leveragescientificknowledgederivedfromtheoryandexperimenttothedesignand controlofrealmaterials(i.e.,chemistry,microstructure,defects,etc.) Furthermore,wehaveidentifieddetailedchallengesandopportunitieswithinthe frameworkofstatic,dynamic,andtheoreticalcompressionsciencethatworktoward attainingourendgoalofcontrol.resolvingallofthesechallengesisnecessaryfortrue predictiveunderstanding,whilepartialresolutionwillleadtonewparadigmsregardingour thoughtprocessesonthematerialworldaroundus.compressionscienceoffers opportunitiesfordiscovery,yetchallengesourabilitytofullycomprehendthecontrolling chemistryandphysics.asscientists,werecognizethecomplexityandacknowledgethe underlyingbeautyinthefieldofcompressionscience,andwelookforwardtothesurprises tocomeandtheexpectedsuccessofourpredictivecapability. 34

35 Appendix I Workshop Agenda 21 st CenturyNeedsandChallengesinCompressionScienceWorkshop Bishop slodge,santafenm Tuesday,September22,2009 7:00PMDinner TesuqueA,B Ifyouareavailable,weareexpectingaspeakeronTuesday,September22,2009 (unfortunately,notconfirmed):8:00pm Wednesday,September23,2009 TesuqueA,B 8:00 8:30AMContinentalBreakfast TesuquePavilion 8:30AMWelcome,IntroductionandWorkshopKickoff DavidFunkandRustyGray LosAlamosNationalLaboratory 9:00AMTheFutureofStaticCompressionScience... MalcolmMcMahon UniversityofEdinburgh 10:00AMDiscussion 10:30AMTheFutureofDynamicCompressionScience YogiGupta WashingtonStateUniversity 11:30AMDiscussion 12:00PMLunch WorkshopCo chairwillleaddiscussiononthemorningplenarytalks TesuquePavilion TesuqueA,B 1:00PMExperimentalNeedsforMaterialPhase,Strength,andDamage.NeilBourne AtomicWeaponsEstablishment JamesAsay SandiaNationalLaboratories 35